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Historical shear deformation of rock fractures derived from digital outcrop models and its implications on the development of fracture systems
... The fracture/fault slip data are derived from digital outcrops using method proposed by Wang et al. (2019). Basically, this method analyzes the anisotropy of the fracture surface morphology caused by slip displacement on fracture surfaces that are automatically extracted from the digital outcrop and then ...
... The relative amount of slip indicators may also serve as a good measure of the quality of the fracture/fault slip data, which according to Hippolyte et al. (2012) has a primary influence on the quality of the stress inversion results. For a more rigorous and detailed description of this method, please see Wang et al. (2019); here, we mainly discuss its quality assessment. Usually, thousands of fracture surfaces, hence fracture/fault slip data, can be extracted from just one single outcrop, and much more detailed information about the strain of the outcrop can be provided by this large amounts of data than traditional paleostress inversion methods whose data are manually collected in the field. ...
... The detailed information about the strain of the outcrop also shows that some of the assumptions of the traditional paleostress inversion methods are problematic as will be discussed later in the application examples. Wang et al. (2019) defined the terms "quasi striations" and "quasi steps" to refer to slip indicators that are causing similar anisotropy of the fracture surface morphology as the traditional fault striations and fault steps do, whether they can be obviously seen on the fracture surface or not. A parameter θ * max =C that describes the contribution of fracture surface morphology on the shear strength was proposed by Grasselli et al. (2002). ...
The knowledge of the strain/stress field evolution in time is fundamental to the understanding of the dynamic system. Based on the principle that past tectonic stress should have left traces in the rocks, geologists have been trying to determine the paleostress history from evidence found in rocks for decades. Recent development of techniques for automatic extraction of fracture surfaces from digital outcrop models and estimation of historical shear deformation on rock fractures provide an efficient way of quantitatively acquiring large amounts of high‐quality fracture/fault slip data from outcrops. Unlike traditional paleostress inversion methods whose data are manually collected in the field, the new techniques provide much more detailed information about the strain of the outcrop and a good opportunity to develop quantitative methods for deciphering more realistic paleostrains. In this study, instead of fitting the slip data from several fractures to calculate the overall strain tensor, the local strain tensor is calculated for slip on each fracture from the outcrop. Then, the local strain tensors are grouped into populations corresponding to different strain events using a clustering analysis technique. Theoretical advantages of this new method over the traditional ones are discussed. The applications on outcrops in the eastern Tian Shan area give a clear picture of the late Cenozoic paleostrain variation over space and time and also throw light on the cause for the change in the strain regime in time, the fracture development patterns, and the distribution of shear displacements in fracture networks.
... The fracture/fault slip data is derived from digital outcrops using method proposed by Wang et al. (2019). Basically, this method analyzes the anisotropy of the fracture surface morphology caused by slip displacement on fracture surfaces that are automatically extracted from the digital outcrop, and then estimate the slip direction, as well as the relative amount of slip indicators (fault striations and steps). ...
... The relative amount of slip indicators may also serve as a good measure of the quality of the fracture/fault slip data, which according to Hippolyte et al. (2012), has a primary influence on the quality of the stress inversion results. For a more rigorous and detailed description of this method please see Wang et al. (2019), here we mainly discuss its quality assessment. Usually thousands of fracture surfaces, hence fracture/fault slip data, can be extracted from just one single outcrop, and much more detailed information about the strain of the outcrop can be provided by this large amounts of data than traditional paleostress inversion methods whose data is manually collected in the field. ...
... Wang et al. (2019) defined the terms "quasi striations" and "quasi steps" to refer to slip indicators that are causing similar anisotropy of the fracture surface morphology as the traditional fault striations and fault steps do, whether they can be obviously seen on the fracture surface or not. A parameter * / that describes the contribution of fracture surface morphology on the shear strength was proposed byGrasselli et al. (2002). ...
The knowledge of the strain/stress field evolution in time is important to seismic hazard assessment and risk mitigation, and is fundamental to the understanding of the earth dynamic system. Based on the principle that past tectonic stress should have left traces in the rocks, geologists have been trying to determine the paleostress history from evidence found in rocks for decades. Recent development of techniques for automatic extraction of fracture surfaces from digital outcrop models and estimation of historical shear deformation on rock fractures provide an efficient way of quantitatively acquiring large amount of high quality fracture/fault slip data (direction and sense of slip occurs on the fault plane) from outcrops. So unlike traditional paleostress inversion methods whose data is manually collected in the field, this high quality fracture/fault slip data provide an opportunity to develop fully automatic and quantitative methods for deciphering paleostrain. In this study, for slip on each fracture, the corresponding local strain tensor is calculated, then the local strain tensors are grouped into populations corresponding to far-field strain events and local strain events using a clustering analysis technique. The applications on outcrops in the eastern Tian Shan area give a clear picture of the paleostrain variation over space and time, and also throw light on the relationship between paleostrain, fracture development and the distribution of shear displacements in a thrusting environment.
... As shearing strictly depends on threedimensional contact area location and distribution (Gentier et al., 2000), Grasselli et al. (2002) proposed a method for the quantitative three-dimensional description of a rough fracture surface, and based on this description, Grasselli and Egger (2003) proposed a constitutive criterion to model the shear strength of fractures. Wang et al. (2019) defined the terms "quasi steps" and "quasi striations" to refer to morphological structures that are created during the creation of new crack surfaces and the friction on the frictional interface. The same morphological structures are also causing anisotropy of the fracture surface morphology, hence the anisotropy of the surface morphology's contribution on its shear strength. ...
... The parameter θ * max /C was proposed by Grasselli et al. (2002) to describe the contribution of fracture surface morphology on the shear strength. Wang et al. (2019) proposed a theoretical model that describes the contribution of quasi steps and quasi striations on the shear strength. ...
The macroscopic energy budget provides good constrains on the physics of earthquake rupture dynamics. However, energy estimations from seismological data or geological analyses face problems of model dependency, insufficient estimation, and scale dependency. The earthquake rupture is a mixed process between the frictional slip failure and the shear fracture of intact rock. The frictional slip rupture propagation is described by, essentially, the same framework of the shear fracture of intact rock. Since the fault surface morphology is the direct result of the microscopic rupture processes near the crack tip or on the frictional interface, we therefore in this study quantitatively link the fault surface morphological structures to the macroscopic fracture energy and frictional energy. The link between the fault surface morphological structures and the macroscopic energy partitioning is verified by the direct shear experiment. The energy budget and the rupture arrest are investigated using fault surface morphology data obtained in the field. For the frictional slip failure, the fracture energy slowly occupying more of the energy budget may be the rupture arrest mechanism. For the shear fracture of intact rock, the rapid increase of the frictional energy and the fast growing of the frictional energy's proportion in the energy budget may be the rupture arrest mechanism. The mechanism of rupture arrest and the energy dissipation sources can be determined with the fault surface morphological structures, the rupture arrest can then be deterministic when the loading energy sources are also taken into consideration.
... The methodologies for extracting information from this data range from manual characterizations [62][63], to semiautomatic and automatic techniques [21,[64][65][66][67][68][69][70]. These techniques have applications in various branches of geology, where applications to geological engineering stand out with the classification and characterization of rocky massifs [71][72][73], geothreats with the determination of susceptibility to mass movements [50,74], cartography with the identification of lithological limits [75], structural geology with the use of data for analysis and structural modeling [48,[76][77][78], sedimentology [79][80], stratigraphy and reservoir characterization [81][82][83], and in geoeducation [84]. The cutting edge of the technique is oriented toward the field of planetary geology [85], the implementation of virtual reality [84] and the use of artificial intelligence algorithms to get more out of it of the data acquired with these techniques [70] and the implementation of more sophisticated sensors in UAVs such as multispectral cameras, and sensors for conventional geophysical surveys. ...
This paper aims to present a methodological approach for capturing information and characterizing difficult-to-access geological outcrops using unmanned aerial vehicle-based digital photogrammetric data, which has been growing in importance as a three-dimensional modeling method along with the use of 3D geomodelling, geological, stratigraphic and structural software packages, and specialized programmed algorithms in complex geological cases. In this way, it is possible to document rock outcrops, geological structures, stratification or foliation plans, geometry of outcropping lithologies, underground and surface mining works, karst systems, etc. The data obtained will then serve as a basis for the geomodelling of the geological structure of mineral deposits and oil and gas. Traditionally, the photogrammetry technique in Geosciences has been limited to simplifying and improving the work of surface mapping, topography, cartography, interferometry patterns, surface geomorphology and spectral analysis of high-resolution satellite images. However, currently, the evaluation of the discontinuities of a rock massif can be carried out, the structural domains with high precision, in a short time and in a complete way remotely, taking the information gathered in outcrops to other scenarios so that the work be interactive.
... Because of difficulties of manual sampling and complicity of data acquisition, various methods such as computer approaches have been applied to show three dimensional discontinuity orientation from two dimensional discontinuity trace information gathered from digital image analysis of exposed rock face. [14][15][16][17][18][19][20][21][22][23][24][25] There have been significant advances in the technologies for the characterization of rock faces both above and underground to display the geometry of discontinuities [14][15][16][17][18][19][20][21][26][27][28][29][30] Remote sensors can capture high resolution and accurate 3D information of object surface from a considerable distance. 31,32 It has become a well-established technique in rock mass characterization to extract geometrical and geotechnical information about discontinuities and rock mass surface to replace traditional methods. ...
The mean discontinuity spacing can significantly varies with varying the scanline direction. To clarify the assessment of mean discontinuity spacing using measurement and relevant conventional equations, several artificial cubic models having three different discontinuity sets with various spacings and orientations were made by foam. The grand mean measured discontinuity spacing (X GMM) of various scanline directions on different profile planes had a linear correlation with the block size (X BS) of the typical artificial models (X GMM = 0.725X BS). Then, a new method using image analysis of in-situ rock mass was applied to assess mean rock mass block size as an alternative solution to represent the mean discontinuity spacing. The scaled images were prepared from ninety-four cases of twenty zones of in-situ rock masses in several mines, and the discontinuity spacing was also measured in six scanline directions for each case, as measurement was carried out in 564 scanlines. The images of in-situ rock masses were analyzed by Split-Desktop software and rock block size distribution , X 20 , X 50 (mean size) and X 80 were determined. The rock block size obtained by the images analysis (X 50-image analysis) had a good linear correlation with the grand mean measured discontinuity spacing of six scanline directions of each case (X GM-measured) for various rock mass conditions (X GM-measured = 0.70X 50-image analysis). The obtained relation can be a reliable solution to specify the mean value of discontinuity spacing using image analysis of rock mass.
... Because of difficulties of manual sampling and complexity of data acquisition, various methods such as computer approaches have been applied to assess three dimensional discontinuity orientation from two dimensional discontinuity trace information gathered from digital image analysis of exposed rock face (Kemeny and Post 2003;Kemeny et al. 2006;Strouth et al. 2006;Slob et al. 2007;Haneberg 2008;Sturzenegger and Stead 2009;Lato et al. 2010;Mah et al. 2011;Sturzenegger et al. 2011;Mohebbi et al. 2017;Liu et al 2019b). There have been significant advances in the technologies for the characterization of rock faces both above and underground to display the geometry of discontinuities (Kemeny et al. 2006;Tonon and Kottenstette 2007;Strouth et al. 2006;Slob et al. 2007;Torres 2008;Haneberg 2008;Sturzenegger and Stead 2009;Lato et al. 2010;Mah et al. 2011;Sturzenegger et al. 2011, Cacirari andFutai 2016;Buyer and Schubert 2017;Wang et al. 2019). Remote sensors can capture high resolution and accurate 3D information of object surface from a considerable distance (Lato and Vöge 2012;Riquelme et al. 2014). ...
Several in-situ rock mass properties and blasthole parameters can affect the rock fragmentation. Because of the complexity of the variables affecting the fragmentation results of blasted rocks, to predict a proper value of the median fragment size has long been a difficult task. The blastability index (BI) represents the effect of five parameters of rock mass description (RMD), joint plane spacing (JPS), joint plane orientation, specific gravity and uniaxial compressive strength on the rock fragmentation. The median discontinuity spacing significantly varies with varying the scanline direction and an acceptable value of the median discontinuity spacing will not be expected in practice. The JPS rating also has a constant value of 20 for a wide range of joint spacing values between 0.1 and 1 m, whereas joint spacing can be in this range for most cases. A new method using image analysis of the in-situ rock mass was applied to represent JPS and RMD (belonging to one of the cases: friable, blocky and massive) as an alternative solution. The images contain the details of all individual discontinuities and interlocked in-situ small and large rock blocks. BI, rock strength factor, blasthole parameters, powder factor, fragment size distribution of blasted rock and in-situ block size distribution using image analysis technique were assessed in 15 zones of Sungun open pit copper mine, Angouran lead and zinc open pit mine, Bonab silica mine, Soufian limestone mine and Rashakan limestone mine. The results for rock mass properties and blasthole patterns cover a wide range using different mines. The fragment size distribution was assessed by Split Desktop program with proper delineating images using the Pixler software and blasting was carried out with electric delay detonators. The relations between fragment size and parameters such as in-situ block size (F50), σc, rating of joint plane orientation, powder factor (q), ϕh, Q and Lc were analyzed. The relations with high correlations were achieved by applying the new approach for the defined conditions. Not only the problem of assessing discontinuity spacing has been improved using this method but also the lower number of parameters that properly represent the factors affecting the rock fragmentation have been used. The results were also analyzed by the Sanchidrián and Ouchterlony model and modified Kuz–Ram models. The fragment size obtained by the new method in this study, Sanchidrián and Ouchterlony model and extended modified Kuz–Ram model by Cunningham (in: Proceedings of 3rd world conference on explosives and blasting, Brighton, 2005) after using correction factor [c(A)] significantly better fitted to the results than the modified Kuz–Ram models by Cunningham (in: Fourney, Dick (eds) Proceedings of 2nd international symposium on rock fragmentation by blasting, Keystone, 1987) and Gheibie et al. (Int J Rock Mech Min 46(6):967–973, 2009).
... Characterization or description of cracks is the prerequisite of the study of the relationships between mechanics, fluid transport and the geometry of cracks. [1][2][3][4] Characterization of individual cracks in a three-dimensional (3D) space is a very difficult task and the key elements are identifying and segregating individual cracks when they are intersected. This study provides an effective approach to address these challenges. ...
Cracks and fractures commonly exist in rocks and other brittle media and can significantly impact material deformation and fluid migration. Adequate characterization of cracks is essential to address relevant mechanical and fluid dynamic problems. A key challenge in characterizing cracks in three-dimensional space lies in the effective identification and separation of individual cracks from their intersected networks. We present a method for identifying, segregating and characterizing cracks in 3D space directly from a volumetric image acquired from microtomography as follows: 1) pre-processing digital images and segmentation; 2) analysing basic information of the binary images statistically; 3) filtering and/or removing non-crack related structures in the images; 4) smoothing and mending images; 5) thinning the void structures to reduce thickness in preparation for the separating step; 6) separating intersections in a crack network; 7) labelling cracks across intersections by the same identifier and restoring cracks to their original thickness. The characterization of cracks in three dimensions can be achieved after the above-described processing steps. Once the detailed characteristics of individual cracks in a 3D system are documented, statistical variables such as fractal dimensions can be extracted and thus the scaling law of the cracks can be defined. Potential application of our method and procedure includes predicting the characteristics of fractures at large scale and the relationships among the geometry of cracks, permeability, and stress states.
... There is also the possibility to infer historical shear deformations of fractures, as proposed in Wang et al. (2019). This method involves extracting fracture surfaces from the point cloud and combing the results with a theoretical model that fits shear strength from fault striations and steps. ...
The study of outcrop analogues of petroleum reservoirs is well established in the petroleum industry through the use of digital outcrop models (DOMs). These models, which are also known as virtual outcrop models (VOMs) or 3D outcrops, are of great importance for understanding the behavior of actual reservoirs. This topic has been reviewed by many authors, and the studies vary in detail according to the technologies involved. The present study applies systematic review methodology traversing a number of articles to find the trends in studies utilizing DOMs. The articles included in this review indicate that the technologies used to generate DOMs are still predominantly classified as Light Detection and Ranging (LiDAR) and digital photogrammetry, with the first being present in most of the works, and the latter attracting attention owing to the popularity of unmanned aerial vehicles (UAVs). These studies have attracted a significant amount of attention to outcrop analysis, and the information acquired can be used to better fit reservoir simulations. Furthermore, a trend is identified with a focus on outcrop geometry and structural data. This work also discusses some of the available opportunities related to the generation of DOMs as well as emerging technologies that can improve the quality of the outcrop models in order to provide better reservoir simulations. Finally, this work discusses the findings and highlights of the articles answering the initially raised research questions.
... One is LiDAR (Light Detection and Ranging), which is extensively used in the field of geosciences via Terrestrial Laser Scanners (TLS) or via aerial vehicles, through Airborne Laser Scanners (ALS) [9]. It utilizes a laser scanner to generate point clouds that can be triangulated and textured with digital photos [3], [10]- [14]. Despite the high precision of those equipment to digitally represent the geometry of an outcrop [15], some disadvantages of TLS and ALS are related to its heavy weight, purchase cost and operational complexity [16], [17]. ...
This paper proposes a technique named Printgrammetry, a structured workflow that allows the extraction of 3D models from Google Earth platform through the combination of image captures from the screen monitor with Structure from Motion algorithms. This technique was develop to help geologists and other geoscientists in acquiring 3D photo-realistic models of outcrops and natural landscapes of big proportions without the need of field mapping and expensive equipment. The methodology is detailed aiming to permit easy reproducibility and focused on achieving the highest resolution possible by working with the best images that the platform can provide. The results have shown that it is possible to obtain visually high quality models from natural landscapes from Google Earth by acquiring images at high Level of Detail regions of the software, using a 4K monitor, multi-directional screenshots and by marking homogeneously spaced targets for georeferencing and scaling. The geometric quality assessment performed using Light Detection and Ranging ground truth data as comparison shows that the Printgrammetry dense point clouds have reached 98.1\% of the total covered area under 5 meters of distance for the Half Dome case study and 96.7\% for the Raplee Ridge case study. The generated 3D models were then visualized and interacted through an immersive virtual reality software that allowed geologists to manipulate this virtual field environment in different scales. This technique is considered by the authors to have a promising potential for research, industrial and educational projects that doesn't requires highly precision models.
Rock materials naturally contain cracks and fractures, which may produce rock fragments or grains under geological and engineering conditions. Identification and characterization of the spatial extent of discontinuity traces and size distribution of fragments/grains are prerequisites for accurate geomechanical assessments of the stability of rocks containing natural or artificial discontinuities. This study introduces an advanced image processing methodology that leverages color gradient analysis and multi-threshold criteria to effectively detect and delineate fracture traces or boundary outlines. Furthermore, this approach facilitates the acquisition of precise fragment or grain size distribution statistics. To comprehensively characterize these discontinuity traces, the methodology employs the calculation of fractal dimensions alongside the use of an equivalent diameter conversion technique. These tools enable the quantification of the complexity and size distribution of the fragments or grains. The efficacy of this approach has been demonstrated through a series of case studies, encompassing a wide range of applications including digital images from numerical simulations, experimental tests, field observations, and micrographic analyses of rock structures. In these studies, the method proved capable of satisfactorily calculating the fractal dimensions of fractures, cracks, and contacts. Simultaneously, it accurately and efficiently determined the size distribution, as evidenced by frequency histograms and cumulative distribution curves obtained from the images. In essence, the proposed approach provides an automatic quantitative methodology to identify and characterize macroscopic and microscopic rock structures containing discontinuity traces or comprised of fragments/grains. This advancement holds significant potential for enhancing the precision and efficiency of geological and geomechanical assessments.
The combination of lidar and digital photography provides a new technology for creating a high-resolution 3D digital outcrop model. The digital outcrop model can accurately and conveniently depict the surface 3D properties of an outcrop profile, making up for the shortcomings of traditional outcrop research techniques. However, the advent of digital outcrop poses additional challenges to the 3D spatial analysis of virtual outcrop models, particularly in the interpretation of geological characteristics. In this study, the detailed workflow of automated interpretation of geological characteristics of fractures and cavities on a 3D digital outcrop texture model is described. Firstly, advanced automatic image analysis technology is used to detect the 2D contour of the fractures and cavities in the picture. Then, to obtain an accurate representation of the 3D structure of the fractures and cavities on the digital outcrop model, a projection method for converting 2D coordinates to 3D space based on geometric transformations such as affine transformation and linear interpolation is proposed. Quantitative data on the size, shape, and distribution of geological features are calculated using this information. Finally, a novel and comprehensive automated 3D quantitative characterization technique for fractures and cavities on the 3D digital outcrop texture model is developed. The proposed technology has been applied to the 3D mapping and quantitative characterization of fractures and cavities on the outcrop profile for the Dengying Formation (second member), providing a foundation for profile reservoir appraisal in the research region. Furthermore, this approach may be extended to the 3D characterization and analysis of any point, line, and surface objects derived from outcrop photos, hence increasing the application value of the 3D digital outcrop model.
The coupled Thermo – Hydro – Mechanical behavior of a radioactive waste disposal facility during its re-saturation is affected by water vapor generated by the heating of pore water. In this study, a Thermo – Hydro – Mechanical coupled analysis of a confirmation test being conducted at the Horonobe Underground Research Center was performed, and how the increase in pore pressure caused by the generation of the water vapor affects the engineering barrier performance was discussed. As a result, by considering the water vapor in the analysis, the evaporation of the moisture content around the heater led to the increase in porosity by about 10% and the decrease in saturation by about 15% as the air pressure in the voids increased. Therefore, it was necessary to consider the effect of the water vapor generation due to the temperature rise near the heater in order to simulate re-saturation behavior in the long-term behavior evaluation of the buffer materials.
Stresses in the Earth's crust are affected by tectonic loading processes; while crustal stresses are also the immediate driving forces of tectonic deformations. The brittle tectonic deformations, to a large extent, are in the form of developing fracture/fault systems in the upper crust. Regional studies of the development of fracture/fault systems and their corresponding spatial and temporal variation of crustal tectonic strain can therefore provide insight into the complex interactions between fracture/fault systems, tectonic paleo-strian and crustal stresses.
Previous studies of fractures at laboratory rock sample scale examined the relationships between many factors and the development of fractures, and established constitutive models based on statistical or physical processes. However, it's difficult to generalize them in fracture-strain problems at larger scale with complex geological background. On the other hand, many enlightening results have been obtained from the study of fractures at outcrop scale by reasoning based on observations, geological background and geological knowledge. However, compared with the complex geological background, the data used for analysis may be relatively limited to be statistically representative or too qualitative, which may leads to the weak foundation of the reasoning results.
In order to overcome the above drawbacks, this dissertation presents innovative methods for fracture system and tectonic strain research based on high-precision and high-resolution outcrop laser scanning data. The methods can be sequentially divided into the following three topics.
The primary problem of doing fracture system research on outcrop point cloud data is to build the digital fracture model, i.e., the automatic extraction of fracture surfaces from the point cloud data. In this dissertation, we propose an algorithm using a region-growing approach for the automatic extraction of the full extent of individual fractures from outcrop terrestrial laser scanning data. Compared with manually acquired field survey data, our method obtained substantially greater amount of and better-quality fracture data.
In the digital fracture model, the shear deformations on each rock fracture surface is the key part of understanding the development of fracture systems. In this dissertation, we propose a quantitative method to derive historical shear deformations of rock fractures from fracture surface data based on the analysis of effects of indicating structures (quasi fault striations and quasi fault steps) on the shear strength parameter of the fracture surface. The validity of the proposed method was proved by testing it on a constructed fracture surface with striations and an outcrop fracture surface with clear fault steps. The application of this method on an example outcrop shows an intuitive idea of how the rock mass was deformed and that the distribution, occurrence and mode of new fractures are strictly controlled by preexisting fractures, i.e., the historical slip data on fracture surfaces obtained by this method has broad prospects of applications.
Finally, we propose a clustering analysis based method that utilizes large population of fracture historical slip data to do the tectonic strain analysis. Firstly, the Lagrangian strain tensors corresponding to historical shear slip on each fracture surface are calculated, and then the principal shortening directions of these strain tensors are clustered to obtain the tectonic shortening directions experienced by the outcrop. The results of the applications of the method on 21 outcrops in the study area of this dissertation show two main tectonic shortening events. From this, the development pattern of fracture systems in these two tectonic shortening events can be analyzed, and the spatial variation of the degree of shear deformations on fracture surfaces in shortening events provides an important basis for the reconstruction of tectonic paleo strain.
Conventional manual surveys of rock mass fractures usually require large amounts of time and labor; yet, they provide a relatively small set of data that cannot be considered representative of the study region. Terrestrial laser scanners are increasingly used for fracture surveys because they can efficiently acquire large area, high-resolution, three-dimensional (3D) point clouds from outcrops. However, extracting fractures and other planar surfaces from 3D outcrop point clouds is still a challenging task. No method has been reported that can be used to automatically extract the full extent of every individual fracture from a 3D outcrop point cloud. In this study, we propose a method using a region-growing approach to address this problem; the method also estimates the orientation of each fracture. In this method, criteria based on the local surface normal and curvature of the point cloud are used to initiate and control the growth of the fracture region. In tests using outcrop point cloud data, the proposed method identified and extracted the full extent of individual fractures with high accuracy. Compared with manually acquired field survey data, our method obtained better-quality fracture data, thereby demonstrating the high potential utility of the proposed method.
Rock mass characterization requires a deep geometric understanding of the discontinuity sets affecting rock exposures. Recent advances in Light Detection and Ranging (LiDAR) instrumentation currently allow quick and accurate 3D data acquisition, yielding on the development of new methodologies for the automatic characterization of rock mass discontinuities. This paper presents a methodology for the identification and analysis of flat surfaces outcropping in a rocky slope using the 3D data obtained with LiDAR. This method identifies and defines the algebraic equations of the different planes of the rock slope surface by applying an analysis based on a neighbouring points coplanarity test, finding principal orientations by Kernel Density Estimation and identifying clusters by the Density-Based Scan Algorithm with Noise . Different sources of information —synthetic and 3D scanned data— were employed, performing a complete sensitivity analysis of the parameters in order to identify the optimal value of the variables of the proposed method. In addition, raw source files and obtained results are freely provided in order to allow to a more straightforward method comparison aiming to a more reproducible research.
From the actually available experimental evidence, it can be concluded that the proposed strength simulation model reflects properly the relative contributions of various relevant parameters to the overall shearing strength of irregular rock surfaces. The model can, therefore, serve as a useful tool for interpreting the results of large-scale direct shear tests performed in situ. It has also a potential application as a method for predicting the strength of the rock mass from the strength of its components.
Determination of fracture orientation can be an important aspect of structural analysis in reservoir characterization. The availability of ground-based laser scanner systems opens up new possibilities for the determination of fracture surface orientation in rock outcrops. Scanners are available in low-sample-density, low-accuracy, and fast, high-sample-density, high-accuracy models. These automatic laser scanner systems produce enormous volumes or "clouds" of point data at an instrumentdependent accuracy and resolution, which can be at the millimeter level. This huge volume of data calls for an automated and objective method of analysis. We have developed a surface classification algorithm based on a multipass partitioning of the point cloud. The method makes use of both spatial proximity and the orientation of an initial coarse-grained model of the point cloud. Unsupervised classification of surface sets is demonstrated herein using the new algorithm. Both previously mentioned types of scanners have been used to map the Jackfork sandstone outcrop at Big Rock Quarry in Little Rock, Arkansas. We apply the surface classification algorithm to these data to extract fracture surface orientations from the point cloud. The effectiveness of these new technologies when applied to fracture analysis is clearly demonstrated in this example. It is also shown that the low-density, low-resolution type of scanner is adequate to define general geomorphology but is inadequate for fracture definition. The surface classification algorithm can be used to reliably extract fracture and bedding strike and dip angles from the three-dimensional point locations acquired using centimeter-accurate, highdensity laser scanner systems.
Laser ranging is extremely accurate and efficient. Terres- trial scanning lidar (light detection and ranging) applied to outcrop stratigraphic mapping enables researchers to capture laser range data at a rate of thousands of individual X, Y, Z and laser-intensity points per second. These data, in conjunction with complementary remotely and directly sampled data, are used to conduct high-precision facies characterization and to construct 3D geological computer models. Out- crop data are presented here to explain our workflow and to discuss the construction of rock-based 3D Digital Outcrop Models (DOMs). Reproducibility and quantification are the drivers of this methodology. High-resolution terrestrial lidar acquisition, processing, interpretation, and visualization are discussed and applied to mapping of geological surfaces in three dimensions. Laser-generated models offer scientists an unprecedented visualization medium in a quantitative 3D arena. Applications of this technology include constructing and visualizing complex 3D Earth models from outcrops for improved reservoir mod- eling, flow simulation in hydrocarbon and aquifer systems, and prop- erty modeling to constrain forward seismic modeling.
The stability of a rock slope depends on the rock mass geo-structure and its discontinuities. Discontinuities show up at the rock surface as smooth and often plane surfaces. From their location and orientation the main families of fractures can be inferred and a stability analysis performed. To gather information on their distribution, surveys are typically carried out with geological compass and tape along scan lines, with obvious limitations and drawbacks. Here an highly automated image-based approach is presented to compute the required rock parameters: an accurate high resolution Digital Surface Model of the area of interest is generated from an image sequence and segmented in plane surfaces within a multi resolution RANSAC search, which returns location and orientation of each plane. To avoid measuring ground control points, the camera may be interfaced to a GPS receiver. Multiple overlapping and convergent images are captured to achieve good accuracy over the whole network, minimize occlusions and avoid poor object-camera relative geometry. The method is applied to the rock face of Corma di Machaby (Italy): the results are compared to those of a traditional survey with compass and to those of a laser scanner survey.
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.
Brittle and ductile structures adjacent to fault terminations and echelon fault steps of left-lateral strike-slip faults in the Lake Edison Granodiorite of the central Sierra Nevada, California are related to stress perturbations caused by fault slip. The structures associated with fault terminations change from dilatant splay fractures only, to splay fractures and ductile fabrics on opposing sides of the fault, to ductile fabrics ahead of the fault with decreasing distance from a younger neighboring pluton and, presumably, with increased temperatures. The distributions of deformation mechanisms correlate with the inferred local magnitudes and spatial distributions of the maximum tensile stress, the mean stress, and the maximum shear stress. Displacements along the faults are transferred across echelon stepovers by mineralized dilatant fractures in extensional steps. To accommodate slip transfer across contractional steps, rock apparently was squeezed vertically out of the step by ductile flow; concentrations of mobile and immobile elements indicate that diffusive mass transfer was not significant. Increased mean stress in contractional steps apparently enhanced crystal-plastic flow of quartz. A flow law that includes a pressure effect through correlation with pressure-dependent solidus temperatures is more successful than other experimentally derived flow laws in predicting the observed distribution of ductile fabrics.
Three-dimensional (3D) laser scanning data can be used to characterize discontinuous rock masses in an unbiased, rapid, and accurate manner. With 3D laser scanning, it is now possible to measure rock faces whose access is restricted or rock slopes along highways or railway lines where working conditions are hazardous. The proposed method is less expensive than traditional manual survey and analysis methods. Laser scanning is a relatively new surveying technique that yields a so-called point cloud set of data; every single point represents a point in 3D space of the scanned rock surface. Because the density of the point cloud can be high (on the order of 5 mm to 1 em), it allows for an accurate reconstruction of the original rock surface in the form of a 3D interpolated and meshed surface using different interpolation techniques. Through geometric analysis of this 3D mesh and plotting of the facet orientations in a polar plot, it is possible to observe clusters that represent different rock mass discontinuity sets. With fuzzy k-means clustering algorithms, individual discontinuity sets can be outlined automatically, and the mean orientations of these identified sets can be computed. Assuming a Fisher's distribution, the facet outliers can be removed subsequently. Finally, discontinuity set spacings can be calculated as well.
The study of the mechanical behaviour of fractured rock masses should always be based on accurate rock surveys of the geological structure. Traditionally surveys are performed manually by using compass and directly accessing to the rock mass: this is often dangerous or unpractical while the samples size is small, i.e. not optimal to characterize the rock mass completely. In this paper, alternative techniques will be discussed. Using photogrammetry or a laser scanner, an accurate 3D digital model (DSM) of the rock surface is generated. Discontinuity orientation and position on the rock face are derived from the DSM in order to perform a deterministic reconstruction of the rock mass and the determination of the rock blocks lying on the slope. Different levels of automation in discontinuity planes detection were implemented: interactive identification of single planes and interactive selection of macro-areas with automatic segmentation of planes. Segmentation results are organized in order to be directly used for the deterministic reconstructions of the rock masses and the study of the rock mass stability conditions with the key block method and the Distinct Element Method in a 3 dimensional field. These alternative methodologies have been validated trough the comparison with traditional surveys in two different pilot sites (Arnad, North West Italy and Le Trappistes, Swiss).
In this paper a Matlab tool called DiAna (Discontinuity Analysis), for the 2D and 3D geo-structural analysis of rock mass discontinuities on high resolution laser scanning data is presented.The proposed approach is able to semi-automatically retrieve some relevant rock mass parameters, namely orientation, number of sets, spacing/frequency (and derived RQD), persistence, block size and scale dependent roughness, by analyzing high resolution point clouds acquired from terrestrial or aerial laser scanners.In addition, with a specific DiAna option called filterveg, we are able to remove vegetation or other disturbing objects from the point cloud, which is one of the main problems in LIDAR data processing.Some examples of the proposed method have demonstrated its ability to investigate rock masses characterized by irregular block shapes, and suggest applications in the field of engineering geology and emergency management, when it is often advisable to minimize survey time in dangerous environments and, in the same time, it is necessary to gather all the required information as fast as possible.
Simple strike-slip fault zones mark the third stage of faulting in granitic plutons in the Mount Abbot quadrangle of the Sierra Nevada of California. Deformation began with the opening of nearly vertical subparallel joints. These joints were filled mostly with epidote and chlorite, are up to a few tens of meters long, and typically are less than 1 cm wide. Next, some of these joints slipped left-laterally and became small faults. Small faults accommodated up to ∼2 m of displacement and are characterized by mylonitic fabrics and ductilely deformed quartz. Oblique fractures commonly developed near the ends of small faults and in many cases linked faults end-to-end. Simple fault zones developed as abundant oblique fractures linked small faults side-to-side. These fractures opened and were filled with chlorite, epidote, and quartz. Such fractures are scarce outside the two faults that mark the boundaries of a zone. Simple fault zones typically are 0.5-3 m wide, hundreds of meters long, and laterally displace dikes up to ∼10 m. Displacement is concentrated along the boundary faults, which are characterized by cataclastic textures and brittlely deformed quartz. The fault zones consist of noncoplanar segments a few tens of meters long that join at steps or bends. The segmentation reflects the initial joint pattern and indicates that fault zones grew in length as noncoplanar faults linked end-to-end. Away from bends, the most prominent internal fractures have straight traces and strike 20°-60° counterclockwise from the boundaries, whereas near bends they have gentle S-shaped traces and are nearly perpendicular to the boundaries.
We suggest that as some faults linked to form longer structures, a "shear stress shadow" was cast over adjacent smaller faults, causing slip on them essentially to cease. In this manner, displacement progressively became localized on the longer faults and fault zones. If the regional shear strain rate remained constant during this process, then the shear strain rate across the still active faults must have increased. This may have caused cataclastic textures to develop in the boundary faults.
A single steeply dipping joint set in the Mount Givens Granodiorite, central Sierra Nevada, was studied to clarify the mechanics of fracture and joint formation in granitic rocks. The joints were filled with fluid during, or immediately following, formation; these fluids deposited epidote and chlorite within the joints. Examination of lithologic markers in outcrop and thin section demonstrates that relative displacements are normal to the joint surfaces. A method is developed for estimating the tensile stress responsible for initiating joint growth. The stress and fracture toughness estimates are compatible with existing data from laboratory fracture experiments.-from Authors
Three-dimensional (3D) laser scanning data can be used to characterize discontinuous rock masses in an unbiased, rapid, and accurate manner. With 3D laser scanning, it is now possible to measure rock faces whose
access is restricted or rock slopes along highways or railway lines where working conditions are hazardous. The proposed method is less expensive than traditional manual survey and analysis methods. Laser scanning is
a relatively new surveying technique that yields a so-called point cloud set of data; every single point represents a point in 3D space of the scanned rock surface. Because the density of the point cloud can be high (on the
order of 5 mm to 1 em), it allows for an accurate reconstruction of the original rock surface in the form of a 3D interpolated and meshed surface using different interpolation techniques. Through geometric analysis of
this 3D mesh and plotting of the facet orientations in a polar plot, it is possible to observe clusters that represent different rock mass discontinuity sets. With fuzzy k-means clustering algorithms, individual discontinuity
sets can be outlined automatically, and the mean orientations of these identified sets can be computed. Assuming a Fisher's distribution, the facet outliers can be removed subsequently. Finally, discontinuity set
spacings can be calculated as well.
Fractures within granodiorite of the central Sierra Nevada, California, were studied to elucidate the mechanics of faulting in crystalline rocks, with emphasis on the nucleation of new fault surfaces and their subsequent propagation and growth. Within the study area the fractures form a single, subparallel array which strikes N50°-70°E and dips steeply to the south. Some of these fractures are identified as joints because displacement across the fracture surfaces exhibit dilation but no slip. The joints are filled with undeformed minerals, including epidote and chlorite. Other fractures are identified as small faults because they display left-lateral strike slip separations of up to 2 m. Slickensides, developed on fault surfaces, plunge 0°-20° to the east. The faults occur parallel to, and in the same outcrop with, the joints. The faults are filled with epidote, chlorite, and quartz, which exhibit textural evidence of shear deformation. These observations indicate that the strike slip faults nucleated on earlier formed, mineral-filled joints. Secondary, dilational fractures propagated from near the ends of some small faults contemporaneously with the left-lateral slip on the faults. These fractures trend 25°+/-10° from the fault planes, parallel to the direction of inferred local maximum compressive stress. The faults did not propagate into intact rock in their own planes as shear fractures. Rather, adjacent faults were linked together by secondary, dilational fractures. Extensive secondary fracturing between faults produced larger fault zones that accommodate 10-100 m of left-lateral slip. As deformation progressed, faulting evolved from relatively short, closely spaced faults to longer, more widely spaced fault zones.
A physically motivated constitutive law for the behaviour of geologic discontinuities with dilatancy and contact surface degradation (damage) is presented. In the formulation of the law, the paper distinguishes between macroscopic and microscopic features of the contact surface. Through macroscope considerations. an incremental constitutive law is derived which is applicable to a large class of contact-friction problems. By idealizing the microstructure to consist of interlocking asperity surfaces, the constitutive equations are specialized for the description of rock joints including effects such as dilatancy, asperity surface degradation and bulking. Several examples are considered demonstrating the law's behaviour and agreement with experimental data. The incremental form of the equations that are derived are amenable to implementation in numerical procedures such as finite element and discrete element (rigid block) computer programs.
A model is presented to determine the effect of boundary conditions on the shear behaviour of a dilatant rock joint. The model is given in both graphical and mathematical forms. It relates the normal load-deformation response of a joint to its shear load-deformation and dilatant behaviour. The proposed model predicts the increase in normal deformability of an initially mated joint as it traverses a range of unmated conditions. It provides a tangent formulation for the deformability of a rock joint that fully accounts for the coupling between joint normal and shear response due to dilatancy. Finally, the applicability of the proposed model to predict the behaviour of a rock joint under applied constant normal stiffness boundary conditions is verified using existing experimental results.
Assessing the shear behavior of intact rock and rock fractures is an important issue in the design of a potential nuclear
waste repository at Yucca Mountain, Nevada. Cyclic direct shear experiments were conducted on replicas of three natural fractures
and a laboratory-developed tensile fracture of welded tuff. The tests were carried out under constant normal loads or constant
normal stiffnesses with different initial normal load levels. Each test consisted of five cycles of forward and reverse shear
motion. In this paper, the results of the constant normal load shear experiments are analyzed using several constitutive models
proposed in the rock mechanics literature for joint shear strength, dilatancy, and joint surface damage. It is shown that
some of the existing models have limitations. New constitutive models are proposed and are included in a mathematical analysis
tool that can be used to predict joint behavior under various boundary conditions. © Rapid Science Ltd. 1998
The location and orientation of rock discontinuities, which are traditionally obtained from geological surveys with obvious
drawbacks (safety, rock face accessibility, etc.), may also be derived from a detailed and accurate photogrammetric or laser
scanning survey. Selecting from the point cloud determined on the rock face a set of points distributed on a particular discontinuity,
location, dip, and dip direction can be computed from the least-squares estimate of the plane interpolating the set of points.
Likewise, the normal vector to the surface may be computed from an interpolation or approximation of the surface by appropriate
functions. To become a real alternative (both in terms of productivity as well as accuracy) to a traditional survey, interactive
or automated software tools are necessary, to allow the efficient selection of the point sets on the discontinuities or the
interpretation of the normal vector pattern. After introducing the two best technologies available today for data acquisition
and their performance, the paper presents an approach, based on the random sample consensus (RANSAC) procedure, to the segmentation
of the point cloud into subsets, each made of points measured on a discontinuity plane of the rock face. For each subset,
the plane’s equations coefficients are first determined by robust estimation and then refined by least-squares estimation
after outlier removal. The segmentation algorithm has been implemented in RockScan, a software tool developed to facilitate
the interaction with the point cloud in the identification of the discontinuities; rather than using the three-dimensional
(3D) data, selection of regions of interest is performed on oriented images of the rock face. Finally, application of RockScan
to four different test sites is discussed and results presented. The sites differ in size (from tens to hundreds of meters),
rock surface characteristics, and the technology used to produce the point cloud (in three cases photogrammetry, in the fourth
laser scanning), giving the opportunity to test the methodology in different contexts. In the first and in the fourth site
an extensive traditional survey has been performed, providing reference data to validate the RockScan results.
Laboratory research during the past 10 years has explained many critical links between the geometrical characteristics of fractures and their hydraulic and mechanical behavior. One of the remaining research challenges is to directly link fracture geometry with shear behavior, including behavior in response to changes in normal stress and shear direction. This paper describes results from a series of shear tests performed on identical copies (replicas) of a natural granite fracture. Based on these tests, we developed a method using image processing techniques to identify and quantify damage that occurs during shearing. We find that there is a strong relationship between the fracture’s geometry and its mechanical behavior under shear stress and the resulting damage. Using a three-dimensional geostatistical model of the fracture surfaces, we analyze the dependence of the size and location of damage zones on the local geometry and propose an algorithm for predicting areas that are most likely to be damaged during shearing in a given direction.
A new constitutive criterion, relating stress and displacements, is proposed to model the shear resistance of joints under constant normal load conditions. It is based on an empirical description of the surface, and on the results from more than 50 constant-normal-load direct-shear tests performed on replicas of tensile joints and on induced tensile fractures for seven rock types. This constitutive model is able to describe experimental shear tests conducted in the laboratory. Moreover, the parameters required in the model can be easily measured through standard laboratory tests. The proposed criterion was also used to estimate the joint roughness coefficient (JRC) value. The predicting values were successfully correlated with JRC values obtained by back analysis of shear tests.
In this paper we present a method for fast surface reconstruction from large noisy datasets. Given an unorganized 3D point cloud, our algorithm recreates the underlying surface's geometrical properties using data resampling and a robust triangulation algorithm in near realtime. For resulting smooth surfaces, the data is resampled with variable densities according to previously estimated surface curvatures. Incremental scans are easily incorporated into an existing surface mesh, by deter- mining the respective overlapping area and reconstructing only the updated part of the surface mesh. The proposed framework is flexible enough to be integrated with additional point label information, where groups of points sharing the same label are clustered together and can be reconstructed separately, thus allowing fast updates via triangular mesh decoupling. To validate our approach, we present results obtained from laser scans acquired in both indoor and outdoor environments. I. INTRODUCTION
The choice of a general criterion to determine the shear strength of rough rock joints is a topic that has been investigated for many years. The major problem is how to measure and then to express the roughness with a number (e.g., joint roughness coefficient) or a mathematical expression in order to introduce the morphology of the joint into a shear strength criterion. In the present research a large number of surfaces have been digitised and reconstructed using a triangulation algorithm. This approach results in a discretisation of the joint surface into a finite number of triangles, whose geometric orientations have been calculated. Furthermore, during shear tests it was observed that the common characteristic among all the contact areas is that they are located in the steepest zones facing the shear direction. Based on this observations and using the triangulated surface data, it is possible to describe the variation of the potential contact area versus the apparent dip angle with the expression Aθ*=A0[(θmax*−θ*)/θmax*]C, where A0 is the maximum possible contact area, θmax* is the maximum apparent dip angle in the shear direction, and C is a “roughness” parameter, calculated using a best-fit regression function, which characterises the distribution of the apparent dip angles over the surface. The close agreement between analytical curves and measured data therefore suggests the possibility of defining the influence of roughness on shear strength by the simple knowledge of A0, C and θmax*. Based on the samples studied here, the values of these parameters capture the evolution of the surface during shearing. Moreover, they tend to be characteristic for specific rock types, indicating that it might be possible to determine ranges for each rock type based on laboratory measurements on representative samples.
Suggested ISRM. methods for the quantitative description of discontinuities in rock masses
Suggested ISRM. methods for the quantitative description of discontinuities in rock
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