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Geometrical heterogeneity of the joint roughness coefficient revealed by 3D laser scanning
... When using profiles to infer the roughness of rock joints, some geometric features (within the interval between profiles) may be neglected (Tatone and Grasselli 2010). Researchers attempted to improve the accuracy of roughness estimation by reducing the sampling interval of profiles (Babanouri et al. 2020;Bao et al. 2020). The sampling interval of profiles typically utilized in previous studies ranges from 0.1 mm to 15 mm (Babanouri et al. 2020;Diaz et al. 2017;Indraratna et al. 2015;Ram and Basu 2019;Singh and Basu 2016). ...
... Although these studies have verified the influence of the sampling interval of profiles on roughness estimation, some studies have drawn inconsistent results on the appropriate sampling intervals of profiles. For example, Bao et al. (2020) found that when the sampling interval of the profiles was less than 4 mm, the average roughness of the profiles remained unchanged regardless of the roughness of rock joints. In contrast, Ge et al. (2021) found that the specimen scale and the roughness degree significantly impacted the appropriate sampling interval for accurately estimating roughness. ...
... The works conducted above are based on the profile slices with a width of 0.5 mm. Generally, the interval of profiles significantly impacts the accuracy of the estimated rock joint roughness (Bao et al. 2020). Herein, five profile slice widths (i.e., 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm) were adopted to investigate the influence of the width of profile slices on the 3D roughness estimation. ...
Rock joint roughness is one of the crucial parameters impacting the mechanical and hydraulic properties of discontinuities. It can be conveniently estimated from two-dimensional (2D) profiles in engineering practices. However, since the morphological features of rock joints are three-dimensional (3D), 2D profiles can lead to incomplete and biased roughness estimates. The limitations of 3D roughness estimation using profiles were first investigated. It showed that the average roughness of profiles underestimated the 3D roughness. The estimation error was related to the scale and roughness of rock joints. Moreover, the 3D roughness values estimated by conventional methods using profiles were inconsistent. After confirming that the local 3D morphological features can be characterized by profile slices composed of adjacent profiles, we proposed a method based on profile slices to estimate the 3D roughness. The required minimum number of profile slices and the appropriate profile slice width for acquiring the adequate accuracy of 3D roughness were determined by a data-driven approach. The data-driven approach can overcome the practical problem of unavailable reliable prior statistical information on rock joint roughness. The effectiveness of the proposed method was validated with experimental results and other methods, where relative errors for the 3D JRC and θ* max/(C + 1) estimated by the proposed method were –10.9% to 9.1% and –4.6% to 4.1%, respectively, for rock joints ranging from 100 to 2900 mm. Additionally, the proposed method is sensitive to the measurement direction. This new method can further facilitate the practicability of profiles in estimating the 3D rock joint roughness as follows:
HighlightsThe limitations of 3D roughness estimation using 2D profiles are investigated
The profile slices composed of adjacent profiles are adopted to estimate 3D roughness
A data-driven approach is derived to dynamically determine the required minimum number (RMN) of profile slices during the measurement process
The influences of joint scale, roughness variation coefficient, and measurement direction on the RMN of profile slices are investigated
The relative errors of 3D roughness estimated by the proposed method are less than 10%
... Later, Yong et al. (2019) concluded that statistical analysis of the JRC might increase the precision and dependability of the roughness estimation results. Bao et al. (2020) studied roughness anisotropy based on 31 natural joint samples. A 3D laser scanning approach was used for digitizing the joint morphology, and the JRC values in different orientations were obtained, considering the influences of the sampling interval (SI) on the JRC calculation process. ...
... Nevertheless, the SI values for studying the roughness of field-scale joints (!1 m 2 ) are generally too large (Fig. 30). Bao et al. (2020) found that as the SI increases, there is a distinct threshold beyond which the JRC value changes from constant to variable. According to their study, the JRC value keeps constant if the profile line SI is smaller than 4 mm, which is independent of the joint roughness. ...
Abstract: The joint roughness coefficient (JRC), introduced in Barton (1973) represented a new method in rock mechanics and rock engineering to deal with problems related to joint roughness and shear strength estimation. It has the advantages of its simple form, easy estimation, and explicit consideration of scale effects, which make it the most widely accepted parameter for roughness quantification since it was proposed. As a result, JRC has attracted the attention of many scholars who have developed JRC-related methods in many areas, such as geological engineering, multidisciplinary geosciences, mining mineral processing, civil engineering, environmental engineering, and water resources. Because of such a developing trend, an overview of JRC is presented here to provide a clear perspective on the concepts, methods, applications, and trends related to its extensions. This review mainly introduces the origin and connotation of JRC, JRC-related roughness measurement, JRC estimation methods, JRC-based roughness characteristics investigation, JRC-based rock joint property description, JRC's influence on rock mass properties, and JRC based rock engineering applications. Moreover, the representativeness of the joint samples and the determination of sampling interval for rock joint roughness measurements are discussed. In the future, the existing JRC-related methods will likely be further improved and extended in
rock engineering
... Q-system was specifically developed for tunnels and uses six parameters which include rock quality designation (RQD), degree of joint alteration and clay filling, number of joint sets, joint roughness, water inflow and stress reduction factor. There are only limited studies which have used laser scanning to estimate the Q value [137,138]. Laser-scanning studies in underground mines have primarily used RMR or GSI for rock mass characterisation [112,127] while there are limited studies on the estimation of Q-values using laser scanning [137]. The RMR index uses six parameters: the uniaxial compressive strength (UCS) of rocks, rock quality designation (RQD) value, joint and bedding spacing (JS), joint condition, groundwater condition and orientation of discontinuities with respect to the opening axis [139]. ...
... The joint surface condition, meanwhile, another important parameter in GSI, is obtained partially using laser scanning. Mah et al. [146] and Bao et al. [138], for instance, showed how the joint roughness can be estimated accurately using a 3D point cloud obtained from laser scanning. However, besides this, infilling and weathering of the rock mass have to be manually assessed in the field to obtain an accurate GSI value. ...
Laser scanning can provide timely assessments of mine sites despite adverse challenges in the operational environment. Although there are several published articles on laser scanning, there is a need to review them in the context of underground mining applications. To this end, a holistic review of laser scanning is presented including progress in 3D scanning systems, data capture/processing techniques and primary applications in underground mines. Laser scanning technology has advanced significantly in terms of mobility and mapping, but there are constraints in coherent and consistent data collection at certain mines due to feature deficiency, dynamics, and environmental influences such as dust and water. Studies suggest that laser scanning has matured over the years for change detection, clearance measurements and structure mapping applications. However, there is scope for improvements in lithology identification, surface parameter measurements, logistic tracking and autonomous navigation. Laser scanning has the potential to provide real-time solutions but the lack of infrastructure in underground mines for data transfer, geodetic networking and processing capacity remain limiting factors. Nevertheless, laser scanners are becoming an integral part of mine automation thanks to their affordability, accuracy and mobility, which should support their widespread usage in years to come.
... Qsystem was specifically developed for tunnels and uses six parameters which include RQD, degree of joint alteration and clay filling, number of joint sets, joint roughness, water inflow and stress reduction factor. There are only limited studies which have used laser scanning to estimate the Q value [137,138]. Laser-scanning studies in underground mines have primarily used RMR or GSI for rock mass characterisation [113,127] while there are limited studies on the estimation of Q-values using laser scanning [137]. The RMR index uses six parameters: the uniaxial compressive strength (UCS) of rocks, rock quality designation (RQD) value, joint and bedding spacing (JS), joint condition, groundwater condition and orientation of discontinuities with respect to the opening axis [139]. ...
... The joint surface condition, meanwhile, another important parameter in GSI, is obtained partially using laser scanning. Mah et al. [146] and Bao et al. [138], for instance, showed how the joint roughness can be estimated accurately using a 3D point cloud obtained from laser scanning. However, besides this, infilling and weathering of the rock mass have to be manually assessed in the field to obtain an accurate GSI value. ...
Laser scanning can provide timely assessments of mine sites despite adverse challenges in the operational environment. Although there are several published articles on laser scanning, there is a need to review them in the context of underground mining applications. To this end, a holistic review of laser scanning is presented including progress in 3D scanning systems, data capture/processing techniques and primary applications in underground mines. Laser scanning technology has advanced significantly in terms of mobility and mapping, but there are constraints in coherent and consistent data collection at certain mines due to feature deficiency, dynamics, and environmental influences such as dust and water. Studies suggest that laser scanning has matured over the years for change detection, clearance measurements and structure mapping applications. However, there is scope for improvements in lithology identification, surface parameter measurements, logistic tracking and autonomous navigation. Laser scanning has the potential to provide real-time solutions but the lack of infrastructure in underground mines for data transfer, geodetic networking and processing capacity remain limiting factors. Nevertheless, laser scanners are becoming an integral part of mine automation thanks to their affordability, accuracy and mobility, which should support their widespread usage in years to come.
... Li et al. [35] digitized 112 joint profiles retrieved from the literature at sampling intervals ranging from 0.1 mm to 3.2 mm, and two sets of empirical equations of JRC were proposed. The roughness parameters value may vary with the sampling interval [32,[36][37][38]. However, there are still many knowledge gaps regarding the response of roughness parameters to sampling interval, where understanding the dependency of roughness parameters on sampling interval is important. ...
... The JRC calculated based on its relationship with statistical roughness parameters may vary with the sampling interval as argued by Tatone and Grasselli [24], Bao et al. [38] and Huang et al. [54]. The present study examined the relationship between the statistical roughness parameters and the sampling interval using artificial rock joints. ...
Accurate determination of the surface roughness is of significant importance in estimating the mechanical and hydraulic behaviors of rock joints. The correlation between joint roughness coefficient (JRC) and various statistical roughness parameters calculated from digitized Barton’s roughness profiles was explored with Pearson’s correlation coefficient method. The results show the strongest correlation between the standard deviation of the roughness angle and JRC following an excellent linear relationship. In addition, the correlation in the JRC with textural parameters is better than its correlation with amplitude parameters. Twenty-nine rock joint surfaces from fine sandstone, coarse sandstone and granite joint samples with a wide range of surface morphology were digitized using a high-resolution 3D scanner instrument. Further, the statistical roughness parameter values were calculated for each joint profile at eight different sampling intervals for sensitivity analysis of these statistical roughness parameters with regard to the sampling interval. The result indicated that textural parameters generally have a certain degree of dependency on sampling interval, following a power-law relationship. Specifically, when the sampling interval increases, the structure function value increases whereas it decreases for other textural parameters. In contrast, the dependence of the amplitude parameters on the sampling interval is not significant.
... The measurement rate of the scanner is 18,000 measurements/s; the m ment accuracy reaches a 0.05 measurement level; the volume accuracy is 0.02 m mm/m; and the resolution is 0.1 mm. The measurement accuracy of the equipmen the requirements for calculating the roughness of a structural surface [16,17]. The working temperature of the laser scanner is 0~40 °C; therefore, it was necessary to Due to the randomness of the morphological characteristics of the structural planes of the rock samples after splitting, in order to study the influence of roughness on the physical and mechanical properties of the structural planes, and the law of shear slip, the randomly generated structural plane roughness should first be quantitatively calculated. ...
... The measurement rate of the scanner is 18,000 measurements/s; the measurement accuracy reaches a 0.05 measurement level; the volume accuracy is 0.02 mm ± 0.2 mm/m; and the resolution is 0.1 mm. The measurement accuracy of the equipment meets the requirements for calculating the roughness of a structural surface [16,17]. The suitable working temperature of the laser scanner is 0~40 • C; therefore, it was necessary to prevent excessive temperatures affecting the measurement task during use. ...
The surface morphology of a structural plane is an important factor affecting the shear mechanical behavior of a structural plane. A direct shear test of a rough structural plane is carried out, and the shear mechanical behavior and slip weakening characteristics of a structural plane under different levels of roughness and normal stress conditions are studied; the normal stress conditions ranged from 2 MPa to 14 MPa. The results show that the shear strength and shear stress drop of a rough structure increase as the normal stress and roughness levels also increase. The higher the roughness level, or the greater the normal stress level, the more elastic energy the structural plane accumulates before shear failure. Once the shear stress is great enough and shear failure occurs, the shear slip of the rough structural plane shows obvious stick slip characteristics, and it releases more energy. Under high normal stress conditions, the convex body of the structural plane is damaged earlier in the process of direct shear, and the duration of convex body damage and failure is longer. After direct shear, the roughness of the structural plane decreases exponentially as normal stress levels increase. The shear slip of the structural plane, which has a significant degree of roughness under high normal stress conditions, shows a significant number of slip weakening characteristics, which is the main reason that the stick slip of the structural plane releases a lot of energy.
... Azinfar et al. [18] studied the influences of scale effect on 3D roughness parameters such as the fractal parameter (D), amplitude parameter (A), roughness parameter (R s ) and (2A 0 θ* max /(C + 1)). It is noted that the sampling interval has a negative exponential relationship with the JRC value [19]. While the roughness of the joint surface AHD proposed by Ban et al. [20] has a positive size effect, there was a negative size effect and no size effect in a certain direction. ...
... There are many contradictions in the existing research results regarding the size effect. Most scholars believe that there is a negative correlation between the sampling interval and JRC [19], while the roughness characterization method proposed by Ban et al. [20] shows a positive size effect, a negative size effect and no size effect in a certain direction. The size effect of roughness is linked to the characteristics of the joint surface itself and the shear direction. ...
Roughness is an important factor affecting the engineering stability of jointed rock masses. The existing roughness evaluation methods are all based on a uniform sampling interval, which changes the geometrical morphology of the original profile and inevitably ignores the influence of secondary fluctuations on the roughness. Based on the point cloud data obtained by 3D laser scanning, a non-equal interval sampling method and an equation for determining the sampling frequency on the roughness profile are proposed. The results show that the non-equal interval sampling method can successfully maintain the morphological characteristics of the original profile and reduce the data processing cost. Additionally, direct shear tests under constant normal load (CNL) conditions are carried out to study the influence of roughness anisotropy on the shear failure mechanism of joint surfaces. It is found that with the increase in shear displacement, the variations in the shear stress are related to the failure mechanisms of dilatancy and shear fracture of the joint. Finally, the distributions of shear stress, dilatancy and fracture areas on the rough joint in different shear directions are calculated theoretically. Results show that the anisotropy and failure mechanism of rough joint can be well characterized by the modified root mean square parameter Z2′.
... Accurately evaluating the mechanical properties of rock masses, such as unconfined compressive strength, tensile strength, and shear strength, is crucial for ensuring the economic viability and safety of rock engineering (Liu et al. 2024;Lan et al. 2003Lan et al. , 2010Lan et al. , 2019Lan et al. , 2022aBao et al. 2020;Liu et al. 2022Liu et al. , 2023Zhao et al. 2022aZhao et al. , b, 2023. Among these properties, the unconfined compressive strength is most commonly employed due to the simple operation. ...
Due to the size effect, it is essential to first determine the mechanical parameters of experimental-scale rocks and then select appropriate models to extrapolate to the engineering scale for engineering design. Although extensive research have been conducted on the size effect of rocks, the mechanism for the observed strength reverse size effect of crystalline rock is still unclear. In this study, a series of unconfined compressive tests were conducted on the granite samples with different diameters and same slenderness ratio. Then, a grain-scale model containing joints and micro fissures was established specifically for the granite samples to capture the progressive failure behavior that contributes to the observed reverse size effect. It was verified that the numerical model can well-reproduce the observed reverse size effect, which first increases and then decreases with the increasing size. Based on the grain-scale simulation, the size effect was primarily controlled by crack propagation paths, crystal fracture strength, and the influence of pre-existing joints and micro fissures. Specifically, the ascending stage of the strength size effect was governed by the shorter crack path after crack initiation along weak planes (such as pre-existing micro fissures and weak boundaries). The occurrence of the inflection point in the strength size effect was attributed to the increased contribution of intergranular shear strength, resulting in widespread failure. After exceeding the inflection point, the strength decreased due to the localized failure along pre-existing joints.
... The laser scanner technique can also be extended to field surveys and could allow for the measurement of roughness profiles as the direction of kinematically admissible sliding varies, thus providing valuable information for the assessment of the Joint Roughness Coefficient (JRC) on a larger scale. According to Bao et al. [48], the sampling intervals of profile lines and digital points both affect the calculated JRC values. The laser scanning technique can overcome these limitations, allowing the evaluation of the anisotropy of roughness. ...
When evaluating the shear strength of rock mass discontinuities, certain challenges arise due to the difficulty in quantifying the roughness characteristics of surfaces and the strength of asperities. Recent research has focused on enhancing techniques for assessing these characteristics and exploring the application of laser scanning to aid in evaluating discontinuity features. The analysis of reflectivity values (I) obtained through a laser scanner survey presents an efficient method for assessing mechanical characteristics, such as joint compressive strength (JCS). Reflectivity measurements demonstrate correlations with Schmidt hammer rebound values (r). The laser scanner technique would enable the measurement of JCS without the direct application of the Schmidt hammer on rocks in areas where rebound values (r) measurements are unavailable. The use of a laser scanner allows for the acquisition of high-precision geometrical information concerning the 3D roughness and anisotropy of rock surfaces. In this study, an innovative technique was introduced that utilizes laser scanner data from six previous experimental surveys conducted on rock formations in Southern Italy. This technique facilitates the evaluation of roughness profiles, considering potential variations along kinematically admissible sliding directions, allowing for the estimation of the Joint Roughness Coefficient (JRC). This new methodology aids in evaluating the parameters of Barton’s equation to determine the strength characteristics of rock mass discontinuities.
... Engineering examples have demonstrated that the slope instability often manifests along joint surfaces in the form of shear sliding Shariati and Fereidooni 2021). The shear mechanical behavior of joints is closely related to their geometric characteristics, and the morphology is a key factor influencing the shear response of joint surfaces (Bao et al. 2020b). However, it is challenging to accurately describe the roughness of joint surface and determine representative strength parameters under actual field conditions. ...
The instability of slope blocks occurred frequently along traffic corridor in Southeastern Tibet (TCST), which was primarily controlled by the rock mass structures. A rapid method evaluating the control effects of rock mass structures was proposed through field statistics of the slopes and rock mass structures along TCST, which combined the stereographic projection method, modified M-JCS model, and limit equilibrium theory. The instabilities of slope blocks along TCST were then evaluated rapidly, and the different control factors of instability were analyzed. Results showed that the probabilities of toppling (5.31%), planar (16.15%), and wedge (35.37%) failure of slope blocks along TCST increased sequentially. These instability modes were respectively controlled by the anti-dip joint, the joint parallel to slope surface with a dip angle smaller than the slope angle (single-joint), and two groups of joints inclined out of the slope (double-joints). Regarding the control effects on slope block instability, the stabilization ability of double-joints (72.7%), anti-dip joint (67.4%), and single-joint (57.6%) decreased sequentially, resulting in different probabilities of slope block instability. Additionally, nearby regional faults significantly influenced the joints, leading to spatial heterogeneity and segmental clustering in the stabilization ability provided by joints to the slope blocks. Consequently, the stability of slope blocks gradually weakened as they approached the fault zones. This paper can provide guidance and assistance for investigating the development characteristics of rock mass structures and the stability of slope blocks.
... Regarding 3D fracture surfaces, the distribution of morphological features is significantly different along each perspective direction (Bao et al. 2020b). Among the above 2D and 3D indicators, θ P+ , θ * max /(C + 1) 2D , Z′ 2 , WPA and θ * max /C all consider the directional distribution in their definitions. ...
The roughness feature of a natural rock fracture surface is an important factor affecting the shear and poromechanical behavior of rock. The scale effect and spatial distribution characteristics of the fracture surface roughness are notable challenges at rock engineering sites. In this article, morphological data of a large-scale field rock fracture surface were collected using a 3D scanner. Then, the original surface was divided into several small fracture surfaces. With the use of a 2D roughness statistical index, the 2D roughness (JRC2D) of the fracture profile was evaluated. The 3D roughness (JRC3D) of the fracture surface along different directions was obtained via the weighted averaging method. Based on four oblique analysis schemes, the elevation statistical trend and roughness scale effect of fracture surfaces with different widths were examined. With increasing fracture size, the average elevation () and the standard deviation of elevation () showed different typical change patterns. The impact of size variation on the fracture surface roughness includes four types and exhibits significant anisotropy. Based on small fissure surfaces without mutual coverage, the spatial distribution characteristics of the fracture roughness were analyzed and were proven to exhibit high dispersion and anisotropy. With increasing width of the analyzed small fracture, the roughest position on the fracture surface basically remained the same, but there was a significant change in roughness anisotropy.
... The map was rasterized at a 30 m grid spacing for the following calculation after the parameter assignment. Studies have shown that JRC 0 and JCS 0 strongly depend on lithology [49][50][51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66]. The values of JRC 0 and JCS 0 assigned to each rock type were estimated based on test data from the references listed in Table 1. ...
Coseismic landslides pose a significant threat to the sustainability of both the natural environment and the socioeconomic fabric of society. This escalation in earthquake frequency has driven a growing interest in regional-scale assessment techniques for these landslides. The widely adopted infinite slope model, introduced by Newmark, is commonly utilized to assess coseismic landslide hazards. However, this conventional model falls short of capturing the influence of rock mass structure on slope stability. A novel methodology was previously introduced, considering the roughness of potential slide surfaces on the inner slope, offering a fresh perspective on coseismic landslide hazard mapping. In this paper, the proposed method is recalibrated using new datasets from the 2013 Lushan earthquake. The datasets encompass geological units, peak ground acceleration (PGA), and a high-resolution digital elevation model (DEM), rasterized at a grid spacing of 30 m. They are integrated within an infinite slope model, employing Newmark’s permanent deformation analysis. This integration enables the estimation of coseismic displacement in each grid area resulting from the 2013 Lushan earthquake. To validate the model, the simulated displacements are compared with the inventory of landslides triggered by the Lushan earthquake, allowing the derivation of a confidence level function that correlates predicted displacement with the spatial variation of coseismic landslides. Ultimately, a hazard map of coseismic landslides is generated based on the values of the certainty factor. The analysis of the area under the curve is utilized to illustrate the improved effectiveness of the proposed method. Comparative studies with the 2014 Ludian earthquake reveal that the coseismic landslides triggered by the 2013 Lushan earthquake predominantly manifest as shallow rock falls and slides. Brittle coseismic fractures are often associated with reverse seismogenic faults, while complaint coseismic fractures are more prevalent in strike–slip seismogenic faults. The mapping procedure stands as a valuable tool for predicting seismic hazard zones, providing essential insights for decision-making in infrastructure development and post-earthquake construction endeavors.
... Furthermore, it will also undoubtedly have an impact on the correlation between crack geometric parameters and rock mechanics properties. Some researchers have shown that when the sampling interval of a crack surface meets a certain condition, the calculation results of the morphology parameters are very stable, and much research has been carried out to explore a reasonable sampling interval (Bao et al. 2020;Ge et al. 2021). However, there have been few reports about the effect of the sampling threshold on the correlation between crack geometric parameters and rock mechanics properties, which limits mechanical experimental investigations on complex crack rocks to a certain extent. ...
Soft rocks, such as coal, are affected by sedimentary effects, and the surrounding rock mass of underground coal mines is generally soft and rich in joints and cracks. A clear and deep understanding of the relationship between crack geometric parameters and rock mechanics properties in cracked rock is greatly important to the design of engineering rock mass structures. In this study, computed tomography (CT) scanning was used to extract the internal crack network of coal specimens. Based on the crack size and dominant crack number, the parameters of crack area, volume, length, width, and angle were statistically analyzed by different sampling thresholds. In addition, the Pearson correlation coefficients between the crack parameters and uniaxial compression rock mechanics properties (uniaxial compressive strength UCS, elasticity modulus E ) were calculated to quantitatively analyze the impact of each parameter. Furthermore, a method based on Pearson coefficients was used to grade the correlation between crack geometric parameters and rock mechanical properties to determine threshold values. The results indicated that the UCS and E of the specimens changed with the varied internal crack structures of the specimens, the crack parameters of area, volume, length and width all showed negative correlations with UCS and E , and the dominant crack played an important role both in weakening strength and stiffness. The crack parameters of the angle are all positively correlated with the UCS and E . More crack statistics can significantly improve the correlation between the parameters of the crack angle and the rock mechanics properties, and the statistics of the geometric parameters of at least 16 cracks or the area larger than 5 mm ² are suggested for the analysis of complex cracked rock masses or physical reproduction using 3D printing. The results are validated and further analyzed with triaxial tests. The findings of this study have important reference value for future research regarding the accurate and efficient selection of a few cracks with a significant influence on the rock mechanical properties of surrounding rock mass structures in coal engineering.
... The conjugate prior distribution theory was used to choose the prior distribution, but it required the complete likelihood function (Han et al., 2022). Bao et al. (2020) considered that JRC 2D of the selected discontinuity in different directions all conformed to the lognormal distribution. However, it lacked of validation for more discontinuity samples. ...
Three-dimensional (3D) roughness of discontinuity affects the quality of the rock mass, but 3D roughness is hard to be measured due to that the discontinuity is invisible in the engineering. Two-dimensional (2D) roughness can be calculated from the visible traces, but it is difficult to obtain enough quantity of the traces to directly derive 3D roughness during the tunnel excavation. In this study, a new method using Bayesian theory is proposed to derive 3D roughness from the low quantity of 2D roughness samples. For more accurately calculating 3D roughness, a new regression formula of 2D roughness is established firstly based on wavelet analysis. The new JRC3D prediction model based on Bayesian theory is then developed, and Markov chain Monte Carlo (MCMC) sampling is adopted to process JRC3D prediction model. The discontinuity sample collected from the literature is used to verify the proposed method. Twenty groups with the sampling size of 2, 3, 4, and 5 of each group are randomly sampled from JRC2D values of 170 profiles of the discontinuity, respectively. The research results indicate that 100%, 90%, 85%, and 60% predicting JRC3D of the sample groups corresponding to the sampling size of 5, 4, 3, and 2 fall into the tolerance interval [JRCtrue–1, JRCtrue+1]. It is validated that the sampling size of 5 is enough for predicting JRC3D. The sensitivities of sampling results are then analyzed on the influencing factors, which are the correlation function, the prior distribution, and the prior information. The discontinuity across the excavation face at ZK78+67.5 of Daxiagu tunnel is taken as the tunnel engineering application, and the results further verify that the predicting JRC3D with the sampling size of 5 is generally in good agreement with JRC3D true values.
... Many existing studies [41][42][43][44] have noted that the distribution of JRC values approximates the normal distribution or left-biased normal distribution after statistical analysis of the JRC values of large-scale sample data. Therefore, in this study, we regard the distribution of the JRC values related to the limited sample data as the normal distribution. ...
The JRC data collected from a rock mass joint surface difficultly obtain enough large-scale JRC sample data, but small-scale JRC sample data, which usually contain indeterminate and incomplete information due to the limitation of the measurement environment, measurement technology, and other factors. In this case, the existing representation and analysis methods of the JRC sample data almost all lack the measures of confidence levels in the sample data analysis. In this paper, we propose the concept and expression method of confidence neutrosophic number cubic values (CNNCVs), and then establish CNNCVs of joint roughness coefficient (JRC) (JRC-CNNCVs) from the limited/small-scale JRC sample data subject to the normal distribution and confidence level of the JRC sample data to analyze the scale effect and anisotropy of JRC values. In the analysis process, the JRC-CNNCVs are first conversed from the JRC sample data (multi-valued sets) in view of their distribution characteristics and confidence level. Next, JRC-CNNCVs are applied to analyze the scale effect and anisotropy of the JRC values by an actual case, and then the effectiveness and rationality of the proposed expression and analysis method using JRC-CNNCVs are proved by the actual case in a JRC multi-valued environment. From a perspective of probabilistic estimation, the established expression and analysis method makes the JRC expression and analysis more reasonable and reliable under the condition of small-scale sample data.
... After the data were collected by GOM software, they were imported into Surfer software, and the profile line parallel to the shear direction was extracted. The roughness of the shear surface is expressed by Z 2 (the root-mean-square of the relative height fluctuation) (Bao et al. 2020) (Fig. 6). ...
Most of the major rivers in the eastern margin of the Tibetan Plateau are distributed along the tectonic suture zone, where many giant landslides are present. The catastrophic Baige landslide that occurred in 2018 developed in the Jinsha River tectonic suture zone. What is the geo-structure prone to sliding in the Jinsha River tectonic suture zone? How does it control landslide evolution? A special soft rock/soil, altered clay, is found in the Jinsha River tectonic suture zone, and this altered clay may play an important role in giant landslide initiation. To understand the mechanism of the strength weakening of the altered clay and its effect on the formation of giant landslides, taking the Baige landslide as a typical case study, detailed field surveys and laboratory experiments were performed, and the process and mechanism of the transformation of altered clay into sliding zone soil were analyzed. The results indicate that (1) the altered clay is rich in platy layer clay minerals, so it has strong water sensitivity and expansibility. Furthermore, it has significant strain-softening behavior and extremely low residual strength due to the directional arrangement of clay minerals. (2) The evolution process of the Baige landslide was controlled by altered clay and rock mass discontinuities. Altered clay developed along ophiolite discontinuities and formed the weak interlayer of the slope. Due to long-term gravity creep, intermittent rainfall, and earthquakes, the strength of the altered clay was continuously weakened, and the sliding zone gradually penetrated, which finally led to the failure of the Baige landslide. The results of this manuscript are helpful for understanding the evolution mechanism of giant landslides in tectonic suture zones around the world.
... Therefore, 3D laser scanning technology has achieved technical innovation from single-point measurement to surface measurement. The 3D laser scanning technology has been used widely in scanning the geometric parameters of rock mass discontinuity in open slopes and tunnels (Bao et al., 2020a). Feng et al. (2003) attempted to use a 3D laser scanning system to measure the parameters of discontinuity of rock mass for the first time. ...
... The fracture surface morphology reflects the trace of crack development, so studying fracture surface morphology can directly explore how crack propagates. 3D optical scanning (Bae et al. 2011;Bao et al. 2020;Jiang et al. 2016;Song et al. 2022) and scanning electron microscopy (SEM) (Liu et al. 2022b) were often used to obtain the morphological characteristics and microscopic fracture characteristics. Many scholars studied rock fracture surfaces using these two methods (Hallbauer et al. 1973;Kranz. ...
After excavation, the rock mass often fails in the state of triaxial extension. To explore the fracture mechanism of sandstone under triaxial extension at different loading rates, the triaxial extension tests under confining pressure of 10 MPa and 30 MPa with different loading rates (range from 1 × 10–4 to 1 mm/s) were carried out on sandstone. Scanning electron microscopy and 3D optical scanning were used to obtain fracture characteristics. The results show that failure strength and elastic modulus increase with the increasing loading rate. Based on the analysis of asperity height, slope angle, aspect direction, fractal dimension, and fracture pattern, the fracture mechanism of sandstone at different loading rates was obtained: at a lower loading rate, microcracks propagate along weak structures. Microcracks grow into tensile cracks under lower confining pressure; grow into shear cracks under higher confining pressure. At a higher loading rate, more grains are damaged. Microcracks grow into tensile cracks under lower confining pressure; microcracks grow into tensile–shear cracks under higher confining pressure.
... In the previous laboratory experiments carried out on jointed rock specimens, the specimens were prepared mainly in three ways: (a) collecting specimens containing primary fissures from the site for testing; (b) cutting a certain regularity of joint surfaces on rock specimens with the help of tools (diamond wire saw, high-pressure water gun, hacksaw, etc.); (c) preparing jointed rock-like materials through preembedded resin and steel sheets. However, the joints and fissures in underground rock mass usually exhibit a certain irregularity and roughness that is quite different from the smooth flaws produced by conventional methods such as high-pressure water-jet and pre-embedded resin sheets, and the primary flawed specimens are not conducive to the quantitative studies of roughness Bao et al. 2020). In latest years, the growth of 3D printing together with 3D sculpting has made it easier to prepare irregular and rough jointed rock specimens and better match the real shape of natural joint surfaces. ...
Flaws including joints and fissures in the surrounding rock of deep caverns are usually characterized by irregularity and roughness, and are also vulnerable to dynamic loads in addition to the static loads of in-situ stress. In this study, rock specimens with a filling rough joint were prepared by the 3D printing technology and rock-like materials. In addition, dynamic impact tests were conducted on the jointed rock masses with the split Hopkinson pressure bar (SHPB) system. The influence of the impact strain rate and joint roughness coefficient (JRC) against the failure process and dynamic mechanical properties of the specimens were investigated through the digital image correlation (DIC) method together with high-speed camera. The findings indicate that the dynamic mechanical parameters for joint rock masses are of high sensitivity to impact strain rate and JRC. The failure strain, dynamic compressive strength, failure energy and dynamic elastic modulus all increase with increasing JRC and strain rate, and are generally linearly related to the strain rate. Under dynamic loading, microcracks first appear near the tip of the rough joint and continue to develop along the joint direction, ultimately creating the main fracture surface. The vertical strain band first appears near the rough joint and finally follows the joint direction throughout the entire specimen, while the horizontal strain occurs near the rough joint surface, mainly caused by the shear slip on both sides of the joint surface. With the growth of strain rate, the propagation rate of the strain band also grows, and the failure degree of the rock mass progressively intensifies.
Article highlights
Rock mass specimens containing rough joint were prepared through rock-like material and 3D printing technology.
The influence of the joint roughness coefficient (JRC) and impact strain rate on the dynamic mechanical properties of the jointed rock masses was investigated.
The evolution of the strain field of rough jointed rock mass under impact load was explored through DIC.
... Subsequently, Z θ 2 for different shear directions are calculated, which is presented in Fig. 12. Accordingly, the relationship between Z θ 2 and shear strength in the corresponding shear direction is summarized in Fig. 13. For a better understanding of the effect of different directions in the values of shear strength, the values of JRC in each direction can be referred from Bao et al. (2020c), in which, the values of JRC in each direction are presented for the same joint surface. ...
The anisotropic shear strength of rough joints is examined from both experiments and numerical simulations in this paper. The rough joints in the experiment are prepared by combining 3D laser scanning and 3D printing technology. The direct shear tests are conducted in eight shear directions under constant normal load condition (CNL) with the normal stress of 0.2, 0.5, and 1.0 MPa. The dramatic variation of shear strength in different shear directions is observed from experimental results. Meanwhile, the numerical simulation based on the three-dimensional discrete-element method (DEM) is conducted, in which, the method to generate the identical rough joint by connecting triangular walls is proposed. With the calibrated microparameters from the unconfined compression test and direct shear test, the anisotropic shear strength is also observed in the numerical simulation, which is consistent with the experimental result. Accordingly, the topography anisotropy of the rough surface is analyzed, and the statistical parameter, Z θ 2 , is found closely related to the anisotropic shear strength of rough joints. Based on this, the Barton model is modified to estimate the shear strength of artificial joints with an anisotropic effect involved.
... Macrostructures are important factors affecting the deformation and stability of a rock mass, which can be analyzed by statistic method [41,42]. Therefore, it is necessary to conduct quantitative statistical analysis of the rock mass macrostructures to analyze their effects on the large deformation of the Guanshan tunnel. ...
The large deformation is a common engineering problem during tunnel excavation. For brittle rock tunnels, the large deformation is closely related to the rock mass structure. In this study, taking the Guanshan tunnel as an example, large deformation of a deep-buried brittle rock tunnel in a strong tectonic active area was analyzed. The large deformation was explained in terms of the surrounding rock (diorite) mechanical properties and the development and evolution of macro and microcracks. The results showed that the diorite in the Guanshan mountain is characterized by high strength and brittleness. However, numerous microcracks are developed in the diorite, which can easily induce a cataclastic brittle failure of the surrounding rock by the transformation of the stress field. In terms of the spatial distribution, the macro and microcracks in the surrounding rock have a good unified relationship, whose development mechanism is related to strong tectonic activity. The stress environment of the surrounding rock changed during the tunnel excavation. A borehole camera revealed that the large deformation of the Guanshan tunnel is synthetically influenced by the macro and microcracks in the surrounding rock. The deformation includes the relaxation of the original macrocracks, fracture of the microcracks, and rock dilatation caused by the opening of the microcracks, among which the fracture of microcracks is the dominance. This study provides a new concept for analyzing large deformation in brittle rock tunnels, indicating that the negative effects on the stability of the surrounding rock induced by the development and evolution of microcracks should be fully considered in strong tectonic active areas.
... Scale of discontinuities Discontinuities within a rock slope can include faults, bedding planes, joints, and cleavage at the macroscale and microscale (Palmström 2001;Bao et al. 2019Bao et al. , 2020 (Fig. 2). A size-based classification of discontinuities is presented in Fig. 3. Their characteristics can be altered by various processes, including changes in the stress regime (e.g., unloading in response to river or glacial erosion and loading in response to earthquakes) and weathering (e.g., freeze-thaw cycling). ...
Rock avalanche is one of the most spectacular and catastrophic type of natural hazard phenomena. Those events typically start with a giant rock block or multiple blocks becoming detached from the rock slope, progressively fragmenting and transforming into rapidly moving cohesionless rock debris. Discontinuities are widely distributed in rock masses. Although research on rock avalanche phenomena is extensive, the role of discontinuities in different phases of rock avalanches, including the susceptibility, development, and runout phases, has not been systematically and comprehensively addressed, which has aroused a long-standing controversial issue. In this paper, the effects of discontinuities on the three phases of rock avalanches are systematically reviewed and discussed. The preexisting discontinuities influence not only the detachment of rock masses in the failure process but also their disintegration and propagation during runout. As a precursory factor, discontinuities control the kinematic feasibility of rock slope failure and the rock mass strength and thus control the susceptibility of the rock slope to failure as well as the size and spatial distribution of potential rock slope failure areas. During the development phase, the existing discontinuities will propagate and coalesce, increasing the slope fragmentation and decreasing the resistance to failure, and the kinematics of detachment evolve. It is worth noting that the evolution and failure phase would not happen, or just in moments in an earthquake-triggered events(s) or similar events. During runout, the control of discontinuities on rock avalanches is primarily reflected by shear and progressive fragmentation accompanied by heterogeneous distributions of stress and grain size, efficient energy transfer, and characteristic deposits. Nevertheless, dynamics of rock avalanches is complex, and controversial disputes remain; there is no straightforward conclusion. The inherent geology might play a dominant role in determining their strengthening or weakening effect in the various stages of rock avalanches. Several perspectives on future research are discussed, and approaches for focusing on the challenging research required to better our understanding of the role of discontinuities are suggested.
... To explore a reasonable sampling interval, a lot of research has been carried out. For example, a negative exponential function relationship between the JRC and the threshold sampling interval value has been discovered Bao et al., 2020b); the threshold sampling interval can be determined by the curvature of the relationship curve between the morphology parameter and the sampling interval (Ge et al., 2021). ...
The description accuracy of the rock-joint morphology is closely related to the sampling interval and the sampling window size. In this study, a diorite joint was taken as the research object. By selecting five morphology parameters (D, Z2, Rp, θ*max/(C+1)2D and M), according to the principle of the progressive coverage method, characteristics of the five morphology parameters were analyzed under the condition of five sampling intervals and five sampling window sizes. The results show that in general, the large sampling window is more conducive to obtaining stable values of the morphology parameter, while Rp, θ*max/(C+1)2D and M are more sensitive to the sampling spacing effect under the condition of small sampling interval; the differential sensitivities of the sampling interval effect and the sampling size effect of these morphology parameters were comprehensively compared, and the interaction between the sampling interval effect and the sampling size effect was discussed. The influence of the sampling window size on the sampling interval effect (and the influence of the sampling interval on the sampling size effect) can be ranked as: M > D > Rp > θ*max/(C+1)2D > Z2; the normalized standard deviations were calculated based on the normalized morphology parameters, and it is found that there is correlation between the joint roughness and the sensitivity of the morphology parameters to the sampling interval-size combined effect, which can be used to judge the applicable roughness conditions of different morphology parameters. The research results are not only conducive to improving the understanding of the high-precision quantitative description of rock-joint morphology, but also can provide references for future research on the relationship between rock-joint morphology and shear mechanical behavior of rock joint.
... By scanning the joint surface before and after shearing, the dense point cloud with three-dimensional spatial coordinate information of the joint surface can be obtained quickly and non-destructively with high precision Yang et al. 2016;Zhang et al. 2016). The reconstruction technique can then be used to digitize the joint surface and import it into a computer for processing and evaluating the roughness degradation or damage state of the joint surface (Bao et al. 2020;Fathi et al. 2015;Gui et al. 2017Gui et al. , 2018Indraratna et al. 2014;Wang et al. 2019). The 3D roughness parameters can be obtained to characterize the joint surfaces (Chen et al. 2015;Fathi et al. 2015;Ge et al. 2014;Grasselli et al. 2002;Zhang et al. 2017). ...
A series of direct shear tests on specimens with artificial joints were performed to investigate the rate-dependent characteristics of damage and roughness degradation of three-dimensional joint surfaces under different normal stresses and shear velocities. A novel method was proposed to identify and extract the damaged area of joint surfaces based on the combination of the three-dimensional scanning technology and the color image segmentation method. Based on the proposed method, two main failure modes were identified on the joint surface, including asperity wear and debris backfilling. By controlling different shear displacements and shear velocities, the rate-dependent damage evolution of the joint surface during shearing was revealed. Four damage states are defined to better understand the local damage mechanism of joints. The statistical results indicate that the damage area ratio increases with increasing normal stress and shear velocity. The damage develops more rapidly at a higher shear velocity during progressive shearing. Furthermore, the three-dimensional roughness parameter is measured in 36 analysis directions on the sheared joint surfaces to quantitatively describe the asperity degradation. It is observed that the average roughness parameter increases with increasing shear velocity under the same normal stress but decreases with increasing shear displacement. The results in the present study may provide some references for revealing the mechanical behavior and damage state of joints subjected to dynamic loads.
... Regarding research on heterogeneous methods, in recent years, numerical simulation, as an advanced technique, has provided a new way to study rock heterogeneity [13][14][15][16][17][18]. On the one hand, numerical simulation has the advantage of controllability. ...
With the increasing depth of coal mining and expanding mining scale, the rocks surrounding deep roadways are in a complex mechanical condition of frequent dynamic disturbance. The heterogeneity has an important influence on rock mass failure under dynamic loads. Therefore, it is necessary to study the deformation and failure of heterogeneous roadway under dynamic load. In this paper, the effect of heterogeneity on stability of roadway under static and different dynamic loads is studied. According to the results, the effect of rock mass heterogeneity on the deformation and failure of surrounding rock varies with different degrees of heterogeneity. Under static loading conditions, the stability of roadway is negatively correlated with the degree of heterogeneity of the rock mass. Under dynamic loading conditions, the change of heterogeneity degree has significant influence on the stability of surrounding rock. With the increase in dynamic load strength, the change in variation difference in the average value of roof sag, stress distribution, and plastic zone caused by variations in heterogeneity will increase. This study contributes to understanding the deformation and failure characteristics of heterogeneous roadways under dynamic loads and can be used to analyze heterogeneous roadways under dynamic loads.
... (3), (4), (12), the initial aperture of each fracture was determined from the measured transmissivity and DI, the coefficient b described above, and the JRC 0 . As the value of JRC 0 for each fracture was not available, I assigned JRC 0 a wide range of values of 3, 6, 9, 12, and 15, which represent the common range of previously reported JRC 0 values (Asadollahi and Tonon, 2010;Bao et al., 2020;Barton and Choubey, 1977;Wang et al., 2017) and agree with the results of measuring JRC 0 values in Horonobe (Appendix A). For the calculation of E 0 , when the mechanical aperture derived from Eq. (4) is smaller than the hydraulic aperture, the mechanical aperture was assumed to be the same as the hydraulic aperture, following Barton et al. (1985). ...
The transmissivity of a fracture can be related to fracture roughness (JRC0), initial aperture (E0), effective normal stress (σ'n), and tensile strength (σt) of the intact rock, based on the Barton–Bandis model and their data, and the transmissivity (or E0) can increase by shear-induced dilation. Previous studies revealed that the transmissivities of fractures in fault zones, detected as flow anomalies (highly transmissive zones) during borehole investigations at six sites, decrease uniformly with an increasing effective mean stress normalized to σt. If this uniform change in transmissivity is explained by σ'n-dependent fracture-normal displacement following the Barton–Bandis model, those transmissivities represent the upper limit of transmissivities of fractures in fault zones that can increase by shear-induced dilation. To verify this possibility, the E0 of fractures was estimated using those transmissivities, σt, and possible JRC0 and σ'n. Then, using this estimated E0, the changes in transmissivity were simulated, varying σ'n. The results reproduced very well the observed uniform change in transmissivity. The estimated values of E0 are tens of micrometers to a few millimeters, which can occur by slight shear displacements (e.g., 0.05–2.00 mm) during shear-induced dilation, easily achievable in fault zones. Thus, the requirements for the highest transmissivities are slight shear displacements and no/limited fracture-sealing rather than large shear displacements. Transmissivities in fault zone fractures that have already reached the highest transmissivities do not change significantly by shear displacement, while the transmissivities of fractures sealed by mineral filling can increase by orders of magnitude, as confirmed by recent fault-stimulation-experiments.
... Examples of such are remote sensing (e.g., infrared thermal imaging (Teza et al., 2015), X-ray computer tomography (Klobes et al., 1997;Re and Scavia, 1999), laser scanning (Lee and Cho, 2002;Ge et al., 2014;Liu et al., 2017a), and numerical simulation (Park and Song, 2013); among which the laser scanning is regarded as a powerful tool to collect a dense point cloud from the joint surface. The shear failure areas can be derived from the point cloud (Liu et al., 2017b;Bao et al., 2020), due to the technique's inherent high resolution and efficiency. ...
Two artificial intelligence models-backpropagation neural network (BPNN) and support vector machines (SVM)-were created to investigate the effects of mesostructure characteristics on the shear mechanical behaviors of rock joints. This was achieved through learning training samples for the evaluation of the five basic geometrical parameters sensitivity (i.e., slope angle, horizontal orientation, elevation difference, curvature, and aperture distribution), and for determination of the shear failure regions when rock joints were subjected to low-normal and shear loads. First, the digital elevation models (DEMs) of rock joints were produced through point clouds collected using a laser scanning system. Five geometrical parameters were specified as the inputs for the artificial intelligence models, and an approach was developed to calculate the 3D aperture distribution using a point cloud registration algorithm. Shear failure regions were considered as the outputs, which were extracted from images taken after direct shear testing via the global threshold algorithm. Secondly, BPNN and SVM models were employed in order to establish relationships between the geometrical parameters and shear failure areas by machine learning on training samples. Thirdly, the information value (IV) algorithm was used to verify the two trained models. Results showed that the BPNN and SVM models made acceptable determinations of the shear failure areas, which corresponded to the real situation. The predictions from the BPNN and SVM models were more accurate than those from the IV algorithm. Furthermore, shear failure regions depended primarily on the aperture distribution of rock joints during the shearing process, followed by horizontal orientation, elevation difference, and then the slope angle. The effect of parameter curvature on shear failure was less than the other four parameters.
As crucial connecting components in steel bridge structures, high-strength bolts are susceptible to corrosion from environmental factors such as corrosive agents in the air and rain during long-term service. This corrosion can reduce their load-bearing capacity, thereby threatening the safety of the entire structure. Most studies assess the degree of corrosion through mass loss, but lack a comprehensive quantitative analysis of its impact on mechanical performance. This study investigates the axial tensile performance degradation of corroded bolts based on fractal characteristics of the corroded surface and tensile mechanical performance experiments. By analyzing the fractal dimensions of corroded surfaces, which ranged between 2.026 and 2.053 for more severely damaged threads, a strong correlation was established between surface corrosion and tensile performance degradation. Bolts were classified into three categories based on fractal dimension, which quantitatively reflected the degradation of bolt tensile performance. finding that the ultimate tensile strength and load-bearing capacity decreased by 2.5–6.8 % and 1.25–5.5 %, respectively. Notably, the load at 75 % displacement dropped from 390 kN to 340 kN, a reduction of over 15 %.Finite Element Method (FEM) was used to simulate the bolt tensile process, and experimental data were used to fit damage-plastic constitutive models for bolts with different corrosion levels. The Void Growth Model (VGM) fracture criterion was employed to simulate bolt tensile fracture, predicting the axial tensile performance degradation of bolts with varying corrosion levels, and established a correction formula to quantify the impact of fractal dimension on the ultimate tensile strength of corroded bolts.This study provides a new approach for assessing corrosion impact and predicting the axial tensile performance of bolts in service.
Morphology and shear strength assessment is vital for jointed rock mass geomechanics. The measurement point interval (ΔIp) significantly impacts joint precision in shear tests. A study on 45 joints using six statistical parameters over 500 intervals classified three morphological stages: steady decline (I), sharp drop (II), and fluctuations (III). Smaller ΔIp increases data volume but not accuracy, impairing efficiency. Thus, a model was created for Stage I stability. Insights guided the selection of an optimal ΔIp, maintaining details and facilitating processing. A link between common 2D parameters and the Joint Roughness Coefficient (JRC), incorporating the optimal ΔIp range, was established. The correlation between joint size and interval choice was examined. Results displayed diverse size effects (positive, negative, or neutral) depending on ΔIp and metrics. Though interval influence patterns remained constant, Stage I showed that larger joints can tolerate wider intervals without precision loss, suggesting larger ΔIps for large joint evaluations.
2D profile lines play a critical role in cost-effectively evaluating rock joint properties and shear strength. However, the interval (ΔIL) between these lines significantly impacts roughness and shear strength assessments. A detailed study of 45 joint samples using four statistical measures across 500 different ΔIL values identified a clear line interval effect with two stages: stable and fluctuation-discrete. Further statistical analysis showed a linear relationship between the error bounds of four parameters, shear strength evaluation, and their corresponding maximum ΔIL values, where the gradient k of this linear relationship was influenced by the basic friction angle and normal stress. Accounting for these factors, lower-limit linear models were employed to determine the optimal ΔIL values that met error tolerances (1%–10%) for all metrics and shear strength. The study also explored the consistent size effect on joints regardless of ΔIL changes, revealing three types of size effects based on morphological heterogeneity. Notably, larger joints required generally higher ΔIL to maintain the predefined error limits, suggesting an increased interval for large joint analyses. Consequently, this research provides a basis for determining the optimal ΔIL, improving accuracy in 2D profile line assessments of joint characteristics.
The mechanical and hydraulic behaviors of rock fractures are strongly dependent on the properties of the surface morphology. In this study, a sandstone fracture surface is taken as the research object. The morphological properties of the fracture surface characterized by parameters Z2s, Z2, and SRv are analyzed under the different sampling windows and profile lines. The results show that the large sampling window is more conducive to obtaining stable values of the morphology parameter Z2s. The coefficient of variation (CV) and the percentage of variation (PV) are proposed to determine the stable values of the morphology parameter Z2s, which is defined as a representative elementary surface (RES). It is confirmed that there is a RES with a size of 220 mm in the study region. The large sampling window generates a long correlation length of the morphology parameter Z2s. The differential sensitivities of the morphology parameters Z2 and SRv are compared under the different profile lines. It is found that the parameter Z2 can better describe the random variation properties of the surface morphology, while the parameter SRv is more suitable for describing the spatial structural variation properties of the surface morphology. The findings of this work are of great significance for investigating the size effect and anisotropy of rock fracture permeability.
Joint roughness coefficient (JRC) is an important criterion to determine the shear strength of rock, for example, as one of the inputs for the Barton–Bandis model. Conventionally, the Barton comb profilometer is widely used in the field but it is labour-intensive, has limited accessibility and involves potential hazard. This study aims to evaluate the structure from motion photogrammetry technique in producing reliable JRC measurements. To achieve this, a sample from a rock slope is used to determine the JRC readings. A drone is used to take a high-quality image of the rock slope using unmanned aerial vehicle photogrammetry method. Image processing consists of four quality ratings: low, medium, high and ultra-high. Digitalisation of the JRC of the rock slope takes place to create a 3D model using photogrammetry. The JRC measurement results are compared with the manual Barton comb profilometer method to verify the photogrammetry technique. As a result, the JRC of the rock slope can be produced by using the image analysis technique. The ultrahigh quality has the most accurate measurement as actual length with 0% error compared to actual measurements using Barton comb. For low, medium and high quality, the errors were 10.26%, 7.69% and 2.56%, respectively, to the actual length of the selected lines. However, the medium quality is the most efficient way because it can produce the reliable JRC measurement within a short period and can be used in fieldwork.
The morphological characteristics of the fracture surface play a crucial role in determining its shear strength and deformation. Additionally, the fracture surface undergoes varying degrees of damage at different positions during the experimental process. This study aims to investigate the local damage mechanism of the fracture surface post-experiment, as it is essential for understanding the size effect and anisotropy of mechanical properties in rock masses. To achieve this, 3D scanning and 3D printing technologies were employed to create molds of rough fracture surfaces, and rock-like material mortar was used to cast samples of these rough fractures. The direct shear tests were successfully conducted on two rough rock fracture surfaces under varying normal pressures and shear directions. The analysis of the fracture surface’s shear stress law indicates the presence of apparent anisotropy and varying damage modes in response to changes in normal pressure. Following the experiment, it was observed that the damage is localized on specific areas of the fracture surface, and its distribution characteristics are significantly influenced by the shear direction and normal pressure. Using 3D scanning technology, the JRC2D of various profiles and JRC3D of fracture surfaces are determined through the utilization of the geometric index WPA. Both local and overall roughness of the fracture surface were weakened after the shearing. Notably, the degree of local damage was found to be significantly related to the roughness feature at the corresponding position.
The physical and mechanical properties of coarse-grained slip zone soil are notably different from those of fine-grained slip zone soil, which is mainly composed of clay particles. Many scholars have been interested in the meso-level mechanical properties of coarse-grained slip zone soil. However, no regularity in results has been observed thus far. In this study, a series of medium-scale shear tests are conducted on slip zone soil specimens with different coarse grain contents based on a medium-scale shear apparatus. This apparatus was independently revamped and capable of real-time monitoring. The digital images of the sheared soil specimens were recorded in real time by a high-resolution camera and combined with particle image velocimetry (PIV) technology. A discrete element model involving numerical samples was established to analyze the meso- and macro-level mechanical properties. The results show that the coarse grain content (CGC) has a considerable influence on the shear deformation of slip zone soils and on the meso- and macro-level mechanical properties of the slip zone soil. Moreover, the precise thickness of the main shear band of the slip zone soil under the testing conditions was derived. The numerical sample with high CGC showed obvious dilatancy. The contact force chain network of particles is thick and complex, and the distribution range of the displacement field and the normal contact force are large. This indicates that the slip zone with a high CGC will have more significant uplift when a landslide failure occurs. This study innovatively integrated a variety of research methods, such as visual shear instrument, PIV, and discrete element numerical simulation, and provided important guidance and reference to reveal the influence of CGC on the macro-mesoscopic mechanical properties of slip zone soil and the evolution trends of landslide deformation with high CGC.
Rock shear strength can be estimated using the Barton–Bandis model, which relies on the joint roughness coefficient (JRC). The Barton comb profilometer is widely used in the field. However, it requires much labor. It is also difficult to access and potentially dangerous. As far as we know, no comprehensive work is dedicated to determining the JRC of the rock block sample using the image analysis technique. The JRC measurement results are compared with the manual Barton comb profilometer results to determine the reliability of the close-range photogrammetry (CRP) technique. This photogrammetry technique is applied to measure the JRC of the rock slope in the study area. Using the CRP method, a drone (DJI Phantom 4 Pro) captures a high-resolution image of the rock slope. The JRC of the rock slope is digitized through image processing to create a three-dimensional model comprising four quality ratings: low, medium, high, and ultrahigh. The ultrahigh quality has the most accurate measurement among all the quality ratings. It has a 0% error compared with the actual measurement using the Barton comb, whereas low, medium, and high qualities have 15.54%, 9.46%, and 2.7% errors, respectively. However, the medium quality is the most efficient because it can produce a reliable JRC measurement within a short period and can be used for fieldwork.
Disturbance induced by stress relief has a significant effect on the laboratory properties of rocks in high in situ stress regions. A better understanding of its mechanism can help evaluate rock properties in regions such as the Tibetan Plateau. In this study, the progressive failure process of gneiss with high disturbance in the eastern Himalayas was explored using triaxial tests, acoustic emission minoring, X-ray computerised tomography (CT), and three-dimensional reconstruction. We established a grading standard to evaluate the impact of disturbances on the mechanical properties of Eastern Himalayas gneiss. With an increase in the degree of disturbance, the compressive strength c and φ decreased. The disturbance exerted a greater influence on the frictional strength than cohesion. In addition, the frictional strength cannot be fully mobilised in gneiss with a high disturbance, which is supported by the unchanged normalised crack initiation stress and the reduction of shear cracks. The internal fracture network reconstructed by CT scanning indicates that the fracture modes of gneiss are determined by the disturbance. With the advancement of disturbance, the main failure mode of gneiss is transformed from shear sliding failure controlled by foliation into splitting failure controlled by microcracks.
Rammed earth ruins can be regarded as a special soil mass made by humans. Generally, the stability of rammed earth ruins is largely controlled by the morphological characteristics of rammed layer interfaces (RLIs), which have not been well studied yet. In this paper, the Yongchang Section of the Ming Great Wall, a representative of rammed earth ruins in northwestern China, was selected as the study area, and morphological data from three typical RLIs were collected uisng a handheld 3D scanner. For each typical RLI, within three concentric analysis domains with different sizes, the spatial characteristics of microslopes were explored by ArcGIS, and the 3D roughness values along eight analysis directions were calculated. Ultimately, this study indicates that the most notable characteristic of RLIs is the morphological regularity provided by the rammed pits. Thus, within the analysis domains employed here, the spatial characteristics of microslopes and 3D roughness values are size-independent overall. Moreover, the distributions of 3D roughness are basically more isotropic than anisotropic. Additionally, minor bumps on the RLIs were formed by construction, fracturing, and weathering, and they contribute to the limited heterogeneity of the RLI morphology. Thereinto, the weathering-induced can further be divided into minor bumps caused by wind erosion and rainfall erosion. On the whole, RLIs that have undergone wind erosion have significantly higher surface hardness values (60–90 HA) than rainfall-eroded RLIs (< 50 HA).
Rock mass stability is closely related to the shear strength of rock joints. Measuring the joint surface morphology is of vital importance for evaluating the shear strength of rock joints. Although non-contact measurement methods such as laser scanning are advantageous in high precision, the characteristics of high purchase cost or rental fees and being susceptible to the operating environment have weakened their practicability for in-situ batch measurement of the three-dimensional (3D) morphology of joints. To facilitate the possibility of utilizing cost-effective contact-based devices to replace the non-contact ones, we proposed a methodology to reconstruct the 3D morphology of rock joints using two-dimensional (2D) joint profiles measured by contact measurement methods (e.g., a profilograph). First, through a comprehensive comparison of commonly used spatial interpolation methods, the V4 method from the Griddata function is determined as the optimal one for the proposed methodology. Then, based on the optimal spatial interpolation method, the appropriate profile interval is determined through a referential band derived in this study. Finally, the performance of the proposed methodology was validated from experimental and theoretical perspectives. Results show that the relative errors of the test cases are within the engineering permissible error range, and more than 92% of the test cases are associated with an error less than 5%. In addition, the influences of the joint mechanical parameters, joint roughness level, and joint size on the appropriate profile interval are investigated. This methodology offers a cost-effective alternative for in-situ batch measurement of joint 3D morphology in the field survey of rock joints.
The hydro-fluctuation belt is the most sensitive part of the reservoir bank slope. The rock mass in the hydro-fluctuation belt has been affected by the cyclic dry–wet process. The water infiltrates into the rock mass through its pores and cracks. Through time, the cyclic dry–wet process is posing a significant impact on the evolution and seepage characteristics of jointed sandstone. In this paper, a series of tests such as seepage test, scanning test of the joint surface morphology, and measurement test of ion concentration were conducted to investigate the impact of the cyclic dry–wet condition on a single-jointed sandstone. The following conclusions were made based on the experimental results: (1) There is a positive correlation between the hydraulic conductivity (kf) and the number of dry–wet cycles (n). Initially, the trend was steep. Gradually, it reached a plateau. (2) The fractal dimension D was slightly decreasing when the number of dry–wet cycles increased. A considerable drop in the fractal dimension was observed within the first eighth dry–wet cycles. (3) A negative correlation between the hydraulic conductivity and the fractal dimension was established by the logistic model with four parameters. (4) On the one hand, calcareous cement was dissolved and disintegrated by the water. On the other hand, feldspar minerals underwent physical and chemical reactions. In the meantime, the water–rock interaction altered the ion concentrations, microstructures, and the permeability of sandstone. The findings of this paper provide a theoretical basis for the stabilization of the reservoir bank slope
In this paper, the fluid flow through rough fractures was investigated via numerical simulation based on the lattice Boltzmann method (LBM). The accuracy of LBM was validated through the numerical simulation of the parallel plate model and the verification of the mass conservation of fluid flow through rough fracture. After that, the effect of roughness on fluid flow was numerically conducted, in which, the geometry of fractures was characterized by the joint roughness coefficient (JRC), fractal dimension (D) and standard deviation (σ). It was found that the JRC cannot reflect the realistic influence of roughness on the permeability of single fracture, in which, an increase in permeability with increasing JRC has been observed at the range of 8~12 and 14~16. The reason behind this was revealed through the calculation of the root mean square of the first derivative of profile (Z2), and an equation has been proposed to estimate the permeability based on the aperture and Z2 of the fracture. The numerical simulations were further conducted on fluid flow though synthetic fractures with a wide range of D and σ. In order to unify the parameter that characterizes the roughness, Z2 was obtained for each synthetic fracture, and the corresponding relationship between permeability, aperture and Z2 was analyzed. Meanwhile, it was found that the fluid flow behaves differently with different ranges of Z2 and the critical point was found to be Z2 = 0.5. Based on extensive study, it was concluded that Z2 is a generic parameter characterizing the roughness, and the proposed equation could be used to predict the permeability for fluid flow in fracture.
Strength criteria for intact rock are essential for the safe design of many engineering structures. These criteria have been derived mainly from tests in the compressive stress region. Very few results have been published for confined, direct tensile tests on intact rock. No appropriate criteria are available for addressing the issue on tensile strength of intact rock at current stage. We present the results of direct triaxial tensile tests on Longmaxi Shales under varying confining stresses. These and the results from previous tests in marble and sandstone prove that the phenomenon of "tension cut-off" at low confining stress and the positive correlations between confining stress and tensile strength above the confining stress threshold for brittle rocks occur also in more ductile rocks like shales. Such findings are consistent with the concept that tensile failure processes for intact rock are universal. Our results demonstrate that friction processes still have a significant role on intact rock strength in the tensile region which is leading to confined tensile failure and transitioning to a purely tensile mode. Further, strength criteria are presented which consider the frictional processes leading to failure under confined, direct tension tests and validated against published tensile strength data.
When translating digital roughness profiles of a closed rock joint along the shear direction, the overlapping translational areas can reasonably represent the main potential contact areas in shear tests. By translating Barton’s ten typical roughness profiles, a series of statistical parameters, including the overlapping areas (S*), overlapping number (N*), cumulative overlapping projection length (), and the weighted cumulative overlapping projection length (), were utilized to quantify the 2D joint roughness. Based on the dimensional analysis, these parameters were combined to estimate the joint roughness coefficient. The correlation coefficient results show that the parameter combinations of and or allow good estimation of the joint roughness coefficient of Barton’s 2D roughness profiles. A conceptual joint model was used to extend the 2D translational overlapping statistical parameters to a 3D condition, revealing the suitability of the 3D translational overlapping volume parameter and the hourglass parameter to estimate the joint roughness coefficient of common rock joints. However, the overlapping number parameter N*−1 becomes unreliable and lacks practical significance for common rock joints because there are so many meaningless weak links among the overlapping volumes. Shear tests were conducted on 25 sandstone joints to verify the applicability of and to estimate the joint roughness coefficient. The results indicated that these two parameters show good agreement with the experimentally back-calculated values, allowing the establishment of a new joint roughness coefficient fitting formula.
Empirical estimation is a common method for getting mode I fracture toughness KIC of rock. By collecting data from tests in this study and literature, 204 sets of KIC and tensile strength σt test data are obtained for new empirical KIC‐σt relations regression. The empirical relations make the estimation of KIC values from σt conveniently, but test procedures and lithology will influence its reasonability and reliability. Results indicate that the empirical KIC‐σt relations obtained from the four different suggested KIC test methods are all in good but obviously different linear relationship. The analyses show that cracked chevron notch Brazilian disc specimen (CCNBD) test‐based empirical relation is more accurate for estimating KIC than the other three test‐based empirical relations. As to different lithology, isotropic rocks such as sandstone and carbonatite may be more appropriate for the application of empirical estimation method. However, for coarse grained or anisotropic rocks such as granite and marble, estimation method should be applied carefully because of possibly weak KIC‐σt relations.
Research on monitoring and forecasting technology for slope stability is important for ensuring railway operation. This paper presents field investigation of force and displacement within a strata slope using a real-time remote monitoring system. Based on the interactions of the landslide body, the landslide bed and the monitoring anchor of slope, the mechanical principle of relative movement between the landslide body and the landslide bed can be found. This paper puts forward stress data obtained from a monitoring anchor as the main criterion for landslide stability. The stress will change continually inside the slope mass before the occurrence of a landslide. When the sliding force is larger than the anti-sliding force, deformation and landslides will occur; thus, the change in stress occurs before the change in displacement. In this study, the internal stress, deep displacement and surface strain of a railway slope were measured by a real-time remote-monitoring system, and a vibration metre was installed on the surface of the railway slope to study the influence of the train vibration load on the stability of the slope. The monitoring results are synthetically analysed temporally and spatially, then a railway slope forecasting model is proposed. According to the railway slope field application, the forecasting model makes successful predictions.
In rock mechanics, the study of shear strength on the structural surface is crucial to evaluating the stability of engineering rock mass. In order to determine the shear strength, a key parameter is the joint roughness coefficient (JRC). To express and analyze JRC values, Ye et al. have proposed JRC neutrosophic numbers (JRC-NNs) and fitting functions of JRC-NNs, which are obtained by the classical statistics and curve fitting in the current method. Although the JRC-NNs and JRC-NN functions contain much more information (partial determinate and partial indeterminate information) than the crisp JRC values and functions in classical methods, the JRC functions and the JRC-NN functions may also lose some useful information in the fitting process and result in the function distortion of JRC values. Sometimes, some complex fitting functions may also result in the difficulty of their expressions and analyses in actual applications. To solve these issues, we can combine the neutrosophic numbers with neutrosophic statistics to realize the neutrosophic statistical analysis of JRC-NNs for easily analyzing the characteristics (scale effect and anisotropy) of JRC values. In this study, by means of the neutrosophic average values and standard deviations of JRC-NNs, rather than fitting functions, we directly analyze the scale effect and anisotropy characteristics of JRC values based on an actual case. The analysis results of the case demonstrate the feasibility and effectiveness of the proposed neutrosophic statistical analysis of JRC-NNs and can overcome the insufficiencies of the classical statistics and fitting functions. The main advantages of this study are that the proposed neutrosophic statistical analysis method not only avoids information loss but also shows its simplicity and effectiveness in the characteristic analysis of JRC.
To better understand the interaction of parallel joints and its effect on the mechanical behavior of jointed rock mass models, the results of a physical experiment program undertaken in the laboratory were present in this manuscript. The joint spacing and joint overlap are varied to alter the relative positions of parallel joints in geometry. Accordingly, four basic failure modes identified from the testing results are tensile failure across the joint plane, shear failure along the joint plane, tensile failure along the joint plane, and intact material failure. The wing cracks from tensile failure across the joint plane mode represent the interaction between parallel joints which depends on the joint dip angle, joint spacing and joint overlap. With the increment of parallel joint interaction, the corresponding normalized strength and maximum displacement at peak stress of jointed rock mass models reduced generally except at α=0°.
The knowledge of fluid flow through rock fractures is directly related to hydrocarbon migration, waste disposal, and carbon dioxide sequestration. The hydraulic nature and response of the fractures are directly controlled by the roughness of the fracture surfaces. However, this parameter is hard to understand because it can behave differently under different ambient conditions. The prevalent controlling parameters are the fracture inflow pressure, aperture of the fracture, and shearing displacement during flow. To understand the influence of these parameters, a systematic study was carried out numerically on different fracture geometries. In this paper, two-dimensional fractures with different surface roughness were simulated in a finite-element modeling (FEM) program, and the fluid-flow parameters were evaluated. The Navier-Stokes (NS) equation was used to model the fluid flow through the roughness profiles generated using Barton's joint roughness coefficient. By simulating the laminar fluid flow through the NS equation and predicting the particle transport using a streamline particle-tracking method, the flow-velocity profiles, outlet-pressure distribution, Reynolds number, shear rates, and particle transmissivity were measured. The parameters at different locations along the length of the fractures were compared to identify changes in the fluid flow. The models show that local undulations have considerable effect on the fluid flow. The velocity and shear-rate evolution, pore-pressure distribution, and Reynolds number of the flow indicate the presence of a strong wall effect on the fluid flow. The aperture and shearing displacements of the fracture walls also have significant control over the wall effect.
The mechanical and hydraulic anisotropy of rock joints are strongly dependent on the surface roughness and aperture. To date, accurate quantification of the anisotropic characteristics of joint surfaces remains a key issue. For this purpose, the digital image processing (DIP) technique was used to retrieve the joint surface topography, and a variogram function was used to characterize the anisotropy of the joint surface roughness and estimate the joint aperture. A new index, SRV
, related to both the sill and the range of the variogram is proposed to describe the anisotropy of the joint surface roughness, and a new aperture index, b, is derived to quantify the joint aperture. These newly proposed indexes, SRV
and b, were validated by characterizing three artificial triangular joint surfaces, then the values of both SRV
and b were calculated along 42 directions on an artificial joint surface. The range of SRV
was between 0.058622 and 0.331283, while that of b was from 0.270433 to 0.397715 mm. The results show that the newly proposed indexes SRV
and b are effective for quantifying the anisotropic roughness and aperture of joint surfaces, respectively. In addition, based on the hypothesis that there exists a smooth upper wall for the artificial joint, a relationship between the indexes SRV
and b was obtained based on the data analysis. It indicates that the trends of the indexes SRV
and b tend to coincide, although some of their individual values differ. In this respect, the hydraulic aperture of rock joints is related to not only surface roughness but also the distribution of asperities on the surface. In addition, this method can also be used to characterize the roughness of real rock joints when the joint surface is treated by dying with ink before taking digital photos. This study provides a new method for properly quantifying the directional variability of joint surface roughness and estimating the mechanical and hydraulic properties of rock joints based on the DIP technique.
Numerous empirical equations have been proposed to estimate the joint roughness coefficient (JRC) of a rock fracture based on its fractal dimension (D). A detailed review is made on these various methods, along with a discussion about their usability and limitations. It is found that great variation exists among the previously proposed equations. This is partially because of the limited number of data points used to derive these equations, and partially because of the inconsistency in the methods for determining D. The 10 standard profiles on which most previous equations are based are probably too few for deriving a reliable correlation. Different methods may give different values of D for a given profile. The h–L method is updated in this study to avoid subjectivity involved in identifying the high-order asperities. The compass-walking, box-counting and the updated h–L method are employed to examine a larger population of 112 rock joint profiles. Based on these results, a new set of empirical equations are proposed, which indicate that the fractal dimension estimated from compass-walking and the updated h–L method closely relate to JRC, whereas the values estimated from box-counting do not relate as closely.
This study used precisely digitized standard roughness profiles to determine roughness parameters such as statistical and 2D discontinuity roughness, and fractal dimensions. Our methods were based on the relationship between the joint roughness coefficient (JRC) values and roughness parameters calculated using power law equations. Statistical and 2D roughness parameters, and fractal dimensions correlated well with JRC values, and had correlation coefficients of over 0.96. However, all of these relationships have a 4th profile (JRC 6-8) that deviates by more than +/- 5 % from the JRC values given in the standard roughness profiles. This indicates that this profile is statistically different than the others. We suggest that fractal dimensions should be measured within the entire range of the divider, instead of merely measuring values within a suitable range. Normalized intercept values also correlated with the JRC values, similarly to the fractal dimension values discussed above. The root mean square first derivative values, roughness profile indexes, 2D roughness parameter, and fractal dimension values decreased as the sampling interval increased. However, the structure function values increased very rapidly with increasing sampling intervals. This indicates that the roughness parameters are not independent of the sampling interval, and that the different relationships between the JRC values and these roughness parameters are dependent on the sampling interval.
1] A grain-based Universal Distinct Element Code model was developed to generate a deformable polygonal grain-like structure to simulate the microstructure of brittle rock. It takes into account grain-scale heterogeneity including microgeometric heterogeneity, grain-scale elastic heterogeneity, and microcontact heterogeneity. The microgeometric heterogeneity can be used to match the grain size distribution of the rock. The discrete element approach is able to simulate the microheterogeneity caused by elastic variation and contact stiffness anisotropy. The modeling approach was evaluated using Lac du Bonnet granite and spö Diorite. The microheterogeneity played an important role in controlling both the micromechanical behavior and the macroscopic response when subjected to uniaxial compression loading. The crack-initiation stress was found to be controlled primarily by the microscale geometric heterogeneity, while the microcontact heterogeneity controlled the strength characteristics. The effect of heterogeneity on the distribution and evolution of tensile stresses and associated extension cracks was also examined.
The Shear Strength of Rock Joints in Theory and Practice The paper describes an empirical law of friction for rock joints which can be used both for extrapolating and predicting shear strength data. The equation is based on three index parameters; the joint roughness coefficientJRC, the joint wall compressive strengthJCS, and the residual friction angleφ r . All these index values can be measured in the laboratory. They can also be measured in the field. Index tests and subsequent shear box tests on more than 100 joint samples have demonstrated thatφ r can be estimated to within ± 1° for any one of the eight rock types investigated. The mean value of the peak shear strength angle (arctanτ/σ n ) for the same 100 joints was estimated to within 1/2°. The exceptionally close prediction of peak strength is made possible by performing self-weight (low stress) sliding tests on blocks with throughgoing joints. The total friction angle (arctanτ/σ n ) at which sliding occurs provides an estimate of the joint roughness coefficientJRC. The latter is constant over a range of effective normal stress of at least four orders of magnitude. However, it is found that bothJRC andJCS reduce with increasing joint length. Increasing the length of joint therefore reduces not only the peak shear strength, but also the peak dilation angle and the peak shear stiffness. These important scale effects can be predicted at a fraction of the cost of performing large scale in situ direct shear tests.
The paper presents the results of different methods of determining the roughness of joints in quartzites, metagreywackes and
phyllites obtained from road cuts in central Portugal. The evaluation of the joint roughness coefficient (JRC) was carried
out using graphical and analytical procedures. Differences were found between the JRC graphic and the JRC calculated, depending
on the method used. The JRC calculated values obtained by the tilt tests and the Schmidt rebound hammer tests were compared
to the JRC calculated values established from the rock joint shear tests. It is concluded that if JRC is to be used, it is
essential to specify how it was established.
Cet article présente les résultats de différentes méthodes de déterminer la rugosité des discontinuités trouvées dans des
quartzites, métagrauwackes et schistes obtenus dans des talus des routes au centre de Portugal. L’évaluation du Coefficient
de Rugosité du Joint Joint Roughness Coefficient (JRC) a été réalisée à travers des procédures analytiques et graphiques.
Des différences entre le JRC graphique et le JRC calculé sont trouvées selon les méthodes employées. Les valeurs du JRC obtenues
par les essais d’inclinaison (tilt tests) et les essais de dureté par marteau de Schmidt ont été comparées aux valeurs du
JRC calculées à partir des essais de cisaillement des discontinuités. On conclu qu’il est fondamental d’indiquer comment le
JRC a été établit.
A new method of fractal measurement, the projective covering method (PCM), is proposed in this Letter. Based on the measurements by means of a laser profilometer, the fractal dimension D ∈ [2,3) of a fracture surface is directly estimated. The projective covering probability function is introduced to systematically analyze the multifractal behavior of the fracture surfaces.
The effects of joint roughness on the peak shear strength of fractured rock mass has been extensively investigated. Among these investigations, Barton's JRC-JCS model has been well recognized for its capability to characterize surface geometry. However, shear strength estimation is still a major challenge because of the difficulties involved in accurately calculating the joint roughness coefficient (JRC). Thus, alternative methods such as statistic methods based on fractal theory have been proposed to evaluate the impact of surface morphology on rock joints. Extensive evidences show that, the application of the fractal dimension alone cannot produce a satisfactory estimation of either the JRC or the peak shear strength. Therefore, this paper aims to investigate the peak shear strength of rock joints by adopting the fractal theory and via a numerical simulation. Gosford sandstone taken from Sydney Basin is adopted as the rock materials for both numerical validation and shear strength investigation. Along with numerical simulations on shear strength, a linear function has been proposed to describe the correlations among the root-mean-square of the first derivative of fracture profile (Z2), fractal dimension and the standard deviation. The peak shear strength is then accurately interpreted as a function of joint roughness indices: fractal dimension (D), standard deviation (SD) and Z2. Predictions by the proposed equation are compared with both the numerical simulation results and that reproduced by Barton's equation. Good agreement has been achieved even when the joint roughness coefficients (JRC) is varied which proves that the proposed equation is highly accurate and can be reused in other related applications.
Vegetation coverage has been effectively increased across the Chinese Loess Plateau (CLP) mainly because of the implementation of large-scale revegetation programs. Understanding the entire CLP's ecosystem carbon-water relationship and its response to the vegetation coverage increase and climate change is essential for the water resources management in this semi-humid to arid region. Water-use efficiency (WUE), defined as the ratio of gross primary productivity (GPP) over evapotranspiration (ET), is an important indicator linking carbon and water cycles at the ecosystem scale. In this study, the spatial and temporal variations in the ecosystem WUE were analyzed to investigate the responses of WUE variation to regional climate and vegetation coverage changes in the CLP using MODerate Resolution Imaging Spectroradiometer (MODIS) datasets of GPP and ET from 2000 to 2014. Results indicate that the spatial pattern of annual WUE was different from that of WUE over active growing season (AGS), generally with higher annual WUE but lower AGS-WUE for the semi-humid southeastern CLP areas. Significant increases were observed in annual and autumn WUE during the study period at both the per-pixel and spatial-average levels, while AGS-WUE, spring WUE, and summer WUE remained quite stable. Correlations between WUE trends and interannual variability of vegetation coverage (expressed as Normalized Difference Vegetation Index or NDVI), precipitation (P), and air temperature (T a) showed that WUE trends were positively correlated with NDVI variation due to faster increases in GPP as compared to ET caused by enhanced NDVI. Precipitation variation was generally negatively correlated to WUE variation by contributing to faster increases in ET than GPP especially at different seasons. The positive correlations between interannual variability of WUE and T a were subject to negative feedbacks between ET and T a. Similar results were also found using net primary productivity (NPP) to calculate ecosystem annual WUE (i.e., NPP/ET). Our findings suggest that revegetation-induced vegetation coverage change rather than P and T a changes is the primary cause for the increasing ecosystem annual WUE in the CLP. This study contributes to our enhanced understanding of the coupled carbon-water dynamics over regional terrestrial ecosystem under climate and vegetation coverage changes.
The stability of large underground caverns in steeply dipping layered rock masses is not only affected by the engineering geological characteristics of surrounding rock masses, but also by the excavation sequences and reinforcement measures. Certain places around the periphery of underground openings, such as the high sidewalls, would exhibit significant displacement increases and various failure patterns if the excavation and support were not properly designed. These issues can, according to the basic principles of structurally-controlled concept, be largely attributed to the mechanical properties of bedding planes and other discontinuities. In order to clarify the possible mechanisms behind these failures and to realize the dynamic adjustment of construction, a thorough investigation was conducted to the underground caverns of the Wudongde hydropower station throughout the excavation process. The geological conditions and mechanical properties of the rock masses in the study area were first introduced in detail. Four examples were then presented following the overall logic from geological background to failure mechanism and finally to reinforcement practice. The first example focused on the local wedge-type instability analyses, including the collection of necessary information, the identification of potential blocks, as well as the determination strategies for the factors of safety. The second example illustrated typical tensile failure mode of steeply inclined strata induced by large-scale excavation. The sudden normal unloading of bedding planes led to observable fractures along these weaknesses and considerable increases in sidewall displacements. Large quantities of extra reinforcements had to be installed to control further development of fractured range of the upstream sidewall. The third example highlighted the long-range influence of excavations on the stability of downstream roof, where multistage displacement increase and shotcrete cracking took place as a result of stress concentration and strata buckling, possibly also of the local unfavorable discontinuities. The last example was related to the failure mode of combined discontinuities on the surfaces of piers between two pits. Lessons learned from these examples mainly involve what the mechanical behaviors of the steeply dipping layered rock masses in different places after excavation will be like, and to what extent these behaviors could be predicted or anticipated, which then put emphasis on the importance of geological investigations, and how the optimization of excavation sequence and bench height as well as the timely installation of regular supports could effectively reduce the risks of instability.
In this paper, the rock mass stability around the tunnels in an underground mine is investigated using the distinct element method. A three-dimensional model was developed based on the available geological, geotechnical, and mine construction information. It incorporates the inclined lithologies including a weak interlayer, the persistent and non-persistent faults, and a complex tunnel system. The strain softening constitutive model was prescribed for the rock masses in the numerical model. The continuously yielding joint model was used to describe the non-linear behavior of the faults. To account for the deformations occurred between the excavations and rock supporting, the delayed installation of supports was implemented by using the stress relaxation method. Numerical analyses were performed to study the effects of the post-failure constitutive parameters of the rock masses, the mechanical properties of faults and the delayed supporting on tunnel stability. The following results are presented: (a) the rock mass deformations and failure zones around the excavations, (b) the joint shear displacements of the major fault, and (c) the failure conditions of the applied supports. Satisfactory comparisons are obtained between the predictions based on numerical modeling and the field deformation measurements. The analysis procedures presented in this study are applicable for stability assessment of various underground rock excavation projects located in different parts of the world having different geological settings and complex engineering situations.
Recently, the advent of optical systems has made possible the fast and accurate measurement of roughness discontinuity in three dimensions. In this study, a number of 3D roughness parameters such as fractal parameter (D), amplitude parameter (A), roughness parameter Rs and Grasselli’s roughness parameter (2A0θ*max/(C + 1)) have been presented to quantify the geometry of the fracture surfaces. However, all these roughness parameters are scale dependent and their values change with scale. In this paper, the variations in theses parameters have been investigated with regard to scale. For this purpose, initially, three natural fracture surfaces with the dimensions 500 × 500 mm² were selected and then, the four mentioned roughness parameters were calculated for these three surfaces in the range from 50 × 50 mm² to 500 × 500 mm². Finally, to evaluate the accuracy of roughness estimation by these roughness parameters, several joint replicas from the surfaces were constructed and the direct shear tests were carried out on them. Based on the experimental results, the Grasselli’s roughness parameter gives more accurate estimation of the variations in surface roughness in regard to scale. Also the effect of small-scale evenness on surface roughness has been investigated.
In this study, an anisotropic shear behavior of joint replicas is investigated under constant normal load condition (CNL). A new anisotropic peak shear strength model is proposed incorporating actual peak dilation angle and shear component of asperities. In this model, peak dilation angle is modified with mean plane to find out actual dilation angle and shear component is back calculated from experimental results. The results show that as the ratio of normal stress to compressive strength increases, peak dilation angle decreases exponentially whereas shear component increases in power function form. Further, an empirical model for estimation of peak shear displacement is proposed based on maximum asperity angle and friction angle. Afterwords, shear stiffness is calculated as a ratio of predicted shear strength and peak shear displacement. To conduct this study, three different natural joint roughness is transferred to silicon rubber molds and these molds are used to make joint replicas of mated joint of 90 mm diameter and 50 mm height by mixture of cement, sand, and water in the ratio of 1:1.5:0.45 by weight. The surface cloud of joint surface are generated using 3D non-contact type profiler. In this study, total 144 direct shear tests are conducted on prepared joint replicas using four normal stresses (0.25, 0.5, 1, and 1.5 MPa).
https://authors.elsevier.com/a/1U4QK4sPjBUZw~
Rock joint roughness coefficient (JRC) is an important parameter to determine the shear strength of unfilled hard rock joints. It is of great significance to acquire a representative value of JRC. For irregular undulated joints, the JRC has a strong directivity and surface inclination can reflect the roughness difference under the condition of cyclic shear. Considering Barton's standard joint roughness profiles as an example, the secant angles and tangent angles of surfaces dipping opposite to shear direction were calculated and then the mathematical relationships with JRC were investigated. Based on the results of the study, it can be said that all mathematical relationships of surface inclination of surfaces dipping opposite to shear direction with JRC satisfy the power law equations. The average value of entire secant angles of all surfaces dipping opposite to shear direction (β100%) has a higher sensitivity to evaluate JRC comparing with other parameters. It (β100%) is recommended as a new index to describe JRC considering the directivity. Under cyclic shear, it shows that the JRC of forward positive shear process (JRCfp) is basically larger than that of backward positive shear process (JRCbp) except the first and the fifth standard profile. Moreover, the JRCbp value of the seventh standard profile is smaller than that of the fifth and sixth one. With the digitized sampling interval increasing, the correlation coefficient of the relationships between β100% and α100% (average value of entire tangent angles of surfaces dipping opposite to shear direction) and JRC of Barton standard profiles both present a trend of decreasing and the former is a little larger than the latter under the condition of equal sampling interval.
Using measured data of over 100,000 discontinuities in 35 hydropower projects, this study conducts in-depth analyses on the statistical characteristics of geometric parameters of rock discontinuities and makes an improvement of Monte Carlo network simulation of discontinuities. A new method of determining the discontinuity persistent ratio is developed. The persistent ratio is defined as the percentage of discontinuity planes along the failure surface when the rock mass sheared in a defined direction. This definition overcomes the inadequacies of the traditional geometric projection method, and reduces the determination of the persistent ratio to the identification of the combined failure surface formed by discontinuity planes and rock bridges only. Lajtai (1969) strength theory for rock bridges is used in combination with the conventional failure mechanism of a joint. Dynamic programming is used to resolve the difficulties of identifying failure path in complicated discontinuity network. Finally, the joint persistent ratio can be determined and the methods have been widely applied in engineering practices.
