Geotechnical and Geological Engineering

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Article
  • Juciela C. dos SantosJuciela C. dos Santos
  • Roberto Q. CoutinhoRoberto Q. Coutinho
The Barreiras Formation comprises approximately 75% of the urban area of Maceio-Alagoas, which has a vast number of steep densely occupied slopes, located in embedded valleys called “grotas” where erosive processes cause a high risk of landslides. Despite the homogeneity of the local geology, the Barreiras Formation still presents few studies that provide geological/geotechnical information, and it is under these perspectives that this article is developed, part of a research carried out by the Federal University of Pernambuco through the Geotechnical Engineering Group for Slopes, Plains and Disasters. The geological/geotechnical characterization was carried out through the construction of a database with 474 SPT boreholes, located in a subarea of study in the city of Maceio, where it was possible to carry out a geostatistical evaluation of the penetration resistance values (Nspt) using the ordinary kriging method and the establishment of engineering geological units. A geotechnical detail study was carried out on a slope (Grota da Moenda) inserted in the studied subarea, which involved field investigations by means of the execution of SPT borehole and collection of undisturbed samples, while laboratory investigations provided information regarding the physical and mechanics of the soil through permeability (Tri-flex) tests, suction, double oedometer, direct shear and triaxial CID tests. The geotechnical parameters obtained in this research together with the probabilistic maps are of great importance in learning about the behavior of the soils in the investigated place, presenting initial parameters that could help in several engineering projects.
 
Article
The term soil improvement is commonly referred to the modification of soil structure in order to obtain a material with better physical and mechanical properties such as strength, stiffness or permeability. With this purpose, one of the most commonly used applications, particularly in coarse-grained soils, is the low pressure injection of cementitious mixtures. In recent years, there has been a growing demand for solutions with limited environmental impact and limited CO2 emissions and, in this regard, the cement present in the injected grout is evidently the weak point of traditional solutions. In this work, the experimental study of geopolymer materials as a substitute of cement mixture for low-pressure injection for coarse-grained soils improvement is presented. The study started with a focus on the geopolymer fresh mixture properties (density, viscosity, …) and the evolution over the time of the mechanical properties (compression and tensile strength and stiffness) comparing three different mix designs at three different monitoring temperatures. The same evaluations were repeated on sand samples injected with the different types of mixtures previously analyzed. For a selected mix design, a permeation test was carried out under controlled conditions to test the pumpability and effectiveness of geopolymer injection. Finally, to deepen the chemical interaction between the injected mixture and interstitial water, an injection test was carried out using a scaled model of a real injection system. The experimental study carried out was aimed both at the analysis of the characteristics of the geopolymer material and at its physical interaction with coarse-grained soil, passing through the measurement of the mechanical characteristics of the geopolymer material and of the solid sand skeleton mixed with geopolymers. Finally, the possible chemical interaction of the mixtures with groundwater was also evaluated in order to highlight any environmental issues. The results shown provide a preliminary but sufficiently broad picture of the behavior of geopolymer mixtures for low-pressure injection for coarse-grained soil improvement purposes both from physical–mechanical and chemical points of view.
 
A-line plot of expansive soils
Composite plot of Dr versus clay content of expansive soils from Africa, Australia, India and Oman
Variation of normalized liquid limit with % clay of expansive soils from Africa, Australia, India, and Oman
Article
Disintegration and decomposition of sedimentary materials and igneous/metamorphic rocks in arid and semi-arid plateaus form expansive soils. The parent materials of expansive soils are 5.3 million years (basic igneous rocks) to > 570 million years (basement complex rocks) old. Developing an index property to estimate the fraction of primary minerals that decompose to clay is important as expansive clays drive their moisture-related volume changes. Data of 119 expansive soils from Nigeria, Tanzania, Ethiopia, Sudan, India, Australia, Oman, Chad Basin, Morocco, Kenya, and Zambia are analyzed to develop an index property termed decomposition ratio (Dr) to quantify the fraction of primary minerals that decompose into expansive clay. The sand+silt fractions represent the undecomposed primary mineral content, while the clay fraction represents the fraction of primary minerals that decomposed completely. Expansive soils from India, Sudan and Tanzania are characterized by median Dr values of 0.52–0.74; expansive soils from Ethiopia, Nigeria, Australia, Ghana, Chad Basin, Morocco, Zambia, and Kenya are characterized by median Dr values of 1.02–1.43. Dr values < unity imply that < 50% of primary minerals have decomposed into clay. Analysis of Dr data indicated that clay formation tends towards equilibrium when weathering of parent material depletes their primary mineral contents to 35%. Normalizing liquid limit with Dr regulates variations in liquid limit of expansive soils with similar clay content but formed under different conditions.
 
Article
  • Pengqiang ZhengPengqiang Zheng
  • Yanqing LiuYanqing Liu
The stress distribution and deformation of roadway surrounding rock at different pillar widths are investigated through theoretical calculation, numerical simulation and field monitoring, taking into account goaf compaction. The purpose is to determine the best width and the stress evolution of the reserved roadway protective coal pillar in fully mechanized working faces. The results show that when the gangue in the goaf is slowly compacted, its stress will recover and the gangue will take over part of the overburden load. This will result in a reduction in the bearing pressure inside the surrounding rock. The stress recovery of the fallen gangue in the goaf center will peak and diffuse to the goaf edge in a decreasing manner. As the pillar width increases, the concentrated stress of the pillar will change from unimodal to bimodal. The bearing capacity will gradually increase. The peak stress and plastic failure area of the roadway solid coal wall will gradually reduce. Taking into account pillar stability, resource recovery and the need to prevent gas in the goaf from coming into the mining roadway, we recommend setting the pillar width in coal 3#, the protective layer, to 10 m. The mine replaced the original bolt-cable roof support scheme with a full-cable plus local grouting technique. Field practice indicates a displacement of 39, 20, 32, and 23 mm for the roadway roof, floor, pillar wall, and solid coal wall. The overall roadway deformation is well controlled, validating our numerical simulation result.
 
Article
This study analyzed the value of the coefficient of the subgrade reaction in different soil layers to improve the convenience and accuracy of determining the coefficient of the subgrade reaction of typical rock and soil in the Shijiazhuang area. For this analysis, we relied on the actual project of the deep foundation pit drainage section of the Dongli Station of the Shijiazhuang Metro Line 3, organized and analyzed the monitoring data obtained in the actual construction process, and discussed the deformation law of the foundation pit. The learning and training samples of the back-propagation neural network were established using an orthogonal experimental design method and the FLAC3D numerical simulation software. An inverse analysis of the rock elastic modulus E and coefficient of the subgrade reaction K in this area was conducted. The results of the inversion analysis of the coefficient of the subgrade reaction of typical geotechnical strata in the Shijiazhuang area were in good agreement with the normative values and experimental reference values in the survey and design data. These results were for the loess-like silty clay and silty clay in the Shijiazhuang stratum. The representative soil layer was modified using the corresponding theoretical formula, and the corresponding theoretical calculation reference formula was obtained.
 
Article
Excavation-induced ground movements and the resulting damage to adjacent structures and facilities is a source of concern for excavation projects in urban areas. The concern will be even higher if the adjacent structure is old or has low strength parameters like a masonry building. Frame distortion and crack generation are predictors of building damage resulting from excavation-induced ground movements, which pose challenges to projects involving excavations. This study is aimed to investigate the relation between excavation-induced ground movements and damage probability of buildings in excavation affected distance. The main focus of this paper is on masonry buildings and excavations stabilized using the soil nail wall method. To achieve this purpose, 21 masonry buildings adjacent to 12 excavation projects were studied. Parametric studies were performed by developing 3D FE models of brick walls and excavations stabilized using soil nail walls. Finally, probability evaluations were conducted to analyze the outputs obtained from case studies. Based on the obtained results, simple charts were established to estimate the damage of masonry structures in excavation affected distance with two key parameters including ''Dis-placement Ratio'' and ''Normalized Distance''. The results also highlight the effects of building distance from the excavation wall on its damage probability.
 
Article
Rock anchors are used to stabilise large-scale infrastructure such as the foundations of high buildings or road cuts, and their failure could lead to severe economic and social consequences. A rock anchor can fail in one or more of the following four modes; breakage of the tendon steel, tendon-grout bond failure, grout-rock bond failure and rock mass failure. In current rock anchor design, the knowledge for the first two failure modes is satisfactorily known and is relatively easy to test. The scientific background for the last two failure modes still has a potential of improvement and further development of the design criteria is needed. To help fill this gap, a series of block model tests were conducted on a small-scale test apparatus to evaluate the load capacity of a blocky mass under a rock anchor load. Digital image correlation (DIC) was used to monitor the full-field displacements in the block models. The tests showed that load arches were formed in the block layers and the anchor load was transferred to the side frames of the apparatus through these arches. The load capacity of the mass increased with the number of the block layers and the confinement. The observed load arches and the effect of the confinement were also captured in a numerical model using UDEC software. The DIC monitoring showed that the displacements in the block model were identical along a vertical line. At a given depth, the displacements decrease with the distance to the centre line of the anchor.
 
Article
To study the effect of strain rate on mechanical response, energy mechanism, damage mode and AE characteristics of granite rock, the uniaxial compression tests under different loading strain rates were carried out. The results showed that the higher the loading strain rate was, the greater the threshold stress and threshold energy were. There exists a good logarithmic relationship between the threshold stress, threshold energy and the loading strain rate. When the strain rate was low, the shear failure occurred in the granite sample with a large number of cuttings were generated; under the condition of high strain rate, the granite specimen occurred tensile failure, and the specimen was completely destroyed. Besides, for the low loading strain rate, the damage of the granite sample was developed, the acoustic emission signal increased continuously, and the cumulated number of AE ringing counts was continuously increased; on the contrary, for the high loading strain rate, the number of AE ringing counts was small and firstly increased stepwise, and sharply increased to the maximum value.
 
Article
The mechanical behavior of a granular medium is closely related to its saturation state. One of the underlying phenomena controlling this dependence is particle breakage. In the presence of water, the strength of a particle is weakened through various physical–chemical processes, which lead to an increase in the intensity of particle crushing. The acceleration of the particles fracturing results in the distinctive mechanical response usually observed in unsaturated soils. A multiscale experimental study was conducted to establish a causal relationship between the change of saturation and the increased breakage rate. Oedometric tests were used to understand the effects of saturation on the mechanics of the granular packing, while crushing and wedge splitting tests help appreciate the micromechanical origins of this typical behavior.
 
Article
Water inrush due to rock mass progressive failure in karst tunnels is one of the disasters in tunnel construction. The practical measures to ensure the safety of tunnel construction are to clarify the mechanism of water inrush and reserve the safety thickness. In this paper, the geomechanical model test and numerical simulation were carried out based on the Xiema Tunnel in Chongqing, China. The results of the displacement and hydraulic pressure of the monitoring points in the physical and numerical models were analyzed. In view of the reserved safety thickness between the tunnel face and the water-filled karst cave, the orthogonal numerical simulation tests were designed considering the influence of the tunnel diameter, the cave diameter, the cave water pressure, and the surrounding rock grade. The influence laws and response sensitivity of each factor on the safety thickness were obtained. According to the numerical simulation results and the multiple linear regression method, the formula of safety thickness was derived. Finally, some measures and suggestions for preventing and controlling water inrush disasters were obtained.
 
Article
It is anticipated that after the design life of roads, the pavement materials should have extensively deteriorated necessitating reconstruction/rehabilitation. The extent to which these materials deteriorate in terms of their geotechnical properties has not been fully understood. This study evaluated the extent of deterioration of a typical marginal, mechanically stabilised lateritic crushed rock base in the Kumasi city roads after over 25 years’ in-service. As-constructed materials properties were compared with post-design life properties to determine the degree of alteration of geotechnical, chemical, and mineralogical properties. Results of the study indicate that: the in-situ mean moisture content reduced by about 16% over the service period. The grading changed significantly producing mean fines contents of over 200%. The mean liquid limit and plasticity index were 40% and 22%; equivalent to about 16% and 70% increase respectively. The in-situ-resilience moduli were between 574 and 603 MPa, indicating a significant reduction of about 81–82%. The base materials had similar chemical composition with dominant oxides being silica, alumina and iron oxides with mean concentrations of 52.4%, 28% and 6.5%, respectively. Quartz, kaolinite, albite, and rutile were the minerals identified with no swelling clays present. In conclusion, although the mechanically stabilised lateritic base material during construction did not meet the specification strictly, the pavement performed beyond the design life. In addition, despite the deterioration in material properties, the base layer generally still possesses adequate resilience moduli and mineralogical stability to enable continual use during rehabilitation, except for zones with resilience modulus less than 200 MPa, which require strengthening.
 
Two typical layered formations
Fracture geometries: a delamination; b kinked penetration; c jog formation; d bifurcation (Gu and Siebrits 2006)
Simulation results for 3D fracture network propagation (Settgast et al. 2017)
Pattern of complex HF network with the increase in reservoir depth (Tan et al. 2020)
Fracture height morphology: a schematic drawing; b–c real fracture geometries (Fisher and Warpinski 2011)
Article
The fracture vertical stretching distance and fracture morphologies have great impact on the stimulated reservoir volume and well production in layered formation reservoirs. However, the prediction of fracture height shows large biases with the actual height in field operation. Fracture vertical propagation behavior and multi-field coupling mechanism are still unclear. In this paper, the fracture geometry patterns in conventional and unconventional layered formation are discussed, and multiple factors on hydraulic fracture height propagation are analyzed. We summarized advantages and disadvantages for present studies on fracture height growth and gave prospects for further research.
 
Article
Strength and elastic properties of rocks have vital importance for the design of structures in several rock engineering projects. Additionally, these parameters are extensively used in numerical modelling to envisage the mechanical behavior of rock before failure and their relevance to geotechnical characteristics in slope stability. This study was intended to predict the geomechanical properties of three different metamorphic rocks using simple and multiple regression analysis. The predictive models and their correlation coefficients were established and well discussed for P-wave velocity and different physico-mechanical parameters. Initially, simple regression analysis was performed and then the authenticity of the result was also validated by student’s ‘t’ and ‘F’ test. Further, 13 different empirical models were developed to predict the strength and elastic properties of these rocks through multiple regression analysis. The predicted values estimated from these models show a deterministic and closely associated result with the observed values. Analysis of variance of these rock-mechanics data was also compared to check the confidence of multiple regression models. The coefficient of determination (R²), the root mean square error (RMSE), the mean absolute percentage error (MAPE), and the variance account for (VAF) of these empirical equations were estimated and compared to quantify the performance of the models. The comparative result of statistical indices (R², RMSE, MAPE, VAF) revealed negligible error in developed models with high prediction performance and may be accepted for empirical models to predict the mechanical properties.
 
Article
Rainfall leads to the deterioration of slope stability conditions, while intense rainfall has been commonly associated with landslides on natural or engineered slopes. Deep excavations, typically related to geo-resources exploitation, e.g., in the case of surface mining, are often affected by rainfall events that jeopardize their stability. In this work, rainfall infiltration is directly incorporated in the slope stability analysis; this investigation is currently missing from the literature as mainly empirical methods are used regarding deep excavations. The very deep slopes from lignite mines are employed as typical examples, often reaching 200 m and presenting smooth inclinations and fine-grained soils. A general numerical framework was used; the safety factor’s deterministic analysis was supplemented by a Monte Carlo investigation to determine the probability of failure. The importance of the involved parameters—slope geometry, rainfall intensity, and soil properties—was studied through a parametric analysis. Initially, a typical slip surface is presented, relatively deep and reaching from toe to crest. The critical mechanism was the development—after the rainfall—of a smaller and more local than the initial (before rainfall) slip surface. Although the final surface is smaller than the initial one, it can be more than 50 m high denoting a significant hazard. The most influential parameters are rainfall intensity, soil permeability, and slope height. This study can serve as a basis for similar preliminary analysis in practice. Stability and reliability analysis reveals the need to supplement conventional safety factors with the probability of failure for a broader and improved overview.
 
Article
Empirical approaches play a significant part in the prediction of squeezing conditions in tunnels or caverns. On analysis of collected squeezing data from published literature, no empirical squeezing equations have been found for tunnels with a depth of more than 850 m. In this paper, an attempt has been made to generate linear classifications using rock quality index Q, rock mass number N, overburden height and tunnel span through a comparative study. 234 tunnel sections, especially of the Himalayan region, with depth up to 1900 m have been considered for the analysis. In this method, a demarcation line has been proposed to classify squeezing and non-squeezing conditions and it also allows computing probabilities of squeezing in combination with rock mass quality and tunnel depth. Further, developed equations have been compared with the existing four empirical squeezing equations in the case of the Rohtang road tunnel. The enhanced equations show better results to predict squeezing conditions for tunnels with overburden depth up to 1900 m in comparison to predictive competencies of previously existing criteria. The developed linear classifications are for deep and shallow seated tunnels in complex geological conditions using overburden height, tunnel span, rock quality index Q, and rock mass number N. The developed equations are useful for tunnel designers during the planning and support analysis of underground structures where very less physico-mechanical information are available for squeezing probability. It also suggests that the influence of tunnel depth on squeezing occurrence is a non-linear function.
 
Article
The frost resistance characteristics and deterioration law of rock masses under freeze–thaw cycles in cold regions are important prerequisites for engineering design and stability analysis. In traditional experimental research, there exists the problem of sample selection bias caused by the heterogeneity and anisotropy of the original rock samples, which leads to a large dispersion of experimental results. To mitigate this problem, using red sandstone in Ezhou as the target object, this research first established a similarity criterion formula. Then, to obtain reliable experimental results, 3-factor and 5-level orthogonal experiments were designed with the water-cement ratio, weight ratio of quartz sand and cement, and silica fume content as control factors. Finally, a freeze–thaw cycle experiment was conducted. Based on the control indices of strength and porosity, preliminary screening of the proportion was subsequently carried out by comparing the parameters of the original sandstone, and 3 schemes stood out consequently, based on which the freeze–thaw cycle experiments were conducted. Eventually, according to the similarity criteria and sensitivity factors such as weight, wave velocity and strength, the optimal quasi-sandstone material proportion scheme was determined as follows: water and cement ratio (0.42), quartz sand and cement ratio (1.1), and silica fume content (0.1%). The experimental results further reveal the deterioration law of sandstone under freeze–thaw cycles, which indicates that with the increase in freeze–thaw cycles, the frost resistance parameters of sandstone show a downward trend, and the frost resistance gradually decreases. The descending order of the sensitivity of the frost resistance indices of sandstone to the effect of freeze–thaw cycles is the strength deterioration coefficient, wave velocity deterioration coefficient, and weight loss ratio.
 
Article
Frequent production blasting is an important factor affecting the slope stability in open-pit mines; thus, it is essential to monitor and analyze blasting vibrations in open-pit mines. In this study, blasting vibration on the slope of an open-pit gold mine in Manaoke was monitored. First, regression analysis was performed on the monitoring results using the Sadowski formula, and the attenuation law of the slope blasting vibration was established. Second, the damage depth of the retained rock mass was determined using ultrasonic velocimetry, and the relationship between the damage depth and peak particle vibration velocity was fitted. Third, the Midas numerical software was used to analyze the stability of the slope under blasting vibration conditions. The results showed that the fitted vibration attenuation formula was close for four consecutive days, and the slope blasting activity was within a safe range. Ultrasonic velocity measurements showed that the damage depth of the reserved rock mass after blasting was between 1.0 and 1.5 m. The damage depth had a good correlation with the peak particle vibration velocity, which can adequately predict future reserved rock mass damage. The final numerical calculation results showed that the slope was in a stable state, and the slope stability was not considerably affected under the daily blasting vibration conditions. Thus, the blasting activities were in a safe range.
 
Article
Landslides, which are predominantly caused by the rheological behavior of preexisting joints, occur frequently around the world and are among the most catastrophic disasters. However, most researchers have rarely considered the rheological characteristics of bolted rock joints. In this study, based on rock-like materials, rheological direct shear tests of joints with and without anchor bolts were carried out, and direct shear tests were conducted for comparison. The results showed that under direct shear conditions, with the presence of bolts, less spalling and failure of the rock mass occurs, and the shear strength of the joints was significantly enhanced. Under rheological direct shear conditions, joints with bolts have more total rheological shear displacement, but the effect of the bolt on the shear displacement of the steady creep stage was not obvious, and the shear stiffness of the rock mass was reduced by the coupling effect between the bolt and joint. Using the Mohr–Coulomb criterion for further analysis, we found that during the rheological process, the reinforcement of bolts mainly focuses on cohesion, while under direct shear conditions, the reinforcement of bolts is mainly reflected in the internal friction angle. This study is expected to provide theoretical guidance for landslide control and protection and to further reduce the occurrence frequency of geohazards. This research is expected to provide theoretical guidance for the prediction and prevention of geological disasters.
 
Article
Due to undesired mechanical characteristics, some forest soils cause problems in road construction. Several methods have been proposed for stabilizing these types of soils. In this paper, the impact of two polymer materials on unconfined compression strength of a forest soil is investigated. The unconfined compression strength (UCS) tests were carried out on the soil samples treated with two different polymer materials as well as the control sample. The results of UCS tests show an increase in the maximum dry unit weight by adding polymeric materials of RPP (Road Packer Plus) and CBR Plus (California Bearing Ratio Plus) to the soil. The results also show that polymeric materials improve the UCS of the soil that is dependent on the percentage of polymeric materials and curing time. According to the obtained results, treated samples indicate an increase in the strength with different percentages of RPP and CBR Plus as 32.143–91.30% and 55.84–168.56% for 0.019–0.1% and 0.0096–0.09% content of materials, respectively. The results show that the highest level of the stress and strain for RPP were 151.42 (kPa) and 4.6% (with addition of 0.1% RPP) and 167.13 kPa and 3.1% (with addition 0.09% CBR Plus), respectively.
 
Article
Soil erosion is one of the major environmental problems in the Middle East and North Africa (MENA) region. Favoured by the harmful effects of climate change, and intensified by heavy rainstorms, droughts, runoff, soil features, and land cover; the Meskiana catchment, NE Algeria suffers hugely from this hazard. The main purpose of the present study is to adapt the RUSLE model to map the spatial distribution of soil erosion susceptibility in dry climate watershed based on the geographic information system (GIS) and remote sensing (RS) technique. The model considers erosivity (R), topography (LS), erodibility (K), cover management (C), and support practice (P) as the main predisposing and triggering parameters of the phenomenon. For data processing, slopes, precipitations, lithofacies, Normalized Difference Vegetation Index (NDVI), drainage density, and land use were integrated. Some parameters of the model were estimated using RS data and the erosion susceptibility was mapped using GIS. The results showed that the annual soil loss is about 61 t/ha/year in the entire study area, and identified the most heavily eroded areas, requiring immediate action. The compilation of GIS-RS geospatial technologies with field survey made it possible to assess the spatial variation of soil erosion quantitatively and rapidly. It can assist managers in the implementation of land degradation mitigation program with low-costs and enhanced accuracies.
 
Article
The configuration and safety factor of rockfill dams design depend on materials used in construction of the dam. In some regions, the available materials for using as impermeable element of the dam body are dispersive and it is inevitable to consider the dispersivity of the material in the design and construction. Internal erosion through cracks or other openings in the embankment is the most concern of using the dispersive soils. The authors have designed an embankment dam by using dispersive soil in East Africa after finalizing the dispersivity of materials based on the required tests. The foundation of dam and borrow areas consisted of dispersive soil and the effective measures has been considered in the design to safely deal with dispersivity according to recommendation of the design codes. The selected solution was the combination of chimney filter, filter drain, and selective placement of materials in the dam body as the effective solution considering the specification of the project. More precautions in addition to general recommendation have been incorporated into the design criteria due to placing the project in high hazard category. The local instability in the contact zones was the concerns of designers and bilinear parameters has been considered in the stability analysis as the base case. A drainage layer was added into half of the length of filter blanket and the feature of the design was determined according to nonlinear static and dynamic analysis of the dam body. This paper presents the measures and precautions that were taken into account in dealing with dispersive soil in order to ensure the safety of design.
 
Article
Early surface and structural deterioration of new pavements are becoming increasingly perceptible in Cameroon. This raises serious concerns regarding the nature, spatiotemporal evolution, and quality of materials used. Therefore, this study uses geotechnical identifcation, X-ray difractometry, and statistical methods to optimize the durability of lateritic gravelled material (LGM) pavements. The CBR values within the study sites are dispersed and present low variability (coefcient of variation-CV<15%), to high variability (CV>35%). Three groups of LGM were distinguished at the Bamileke Plateau: frstly, LGM at the BAN site were characterized by CBR (31%). Secondly, LGM of Bamendjou 1 and Bamendjou 2 sites, characterized by CBR varying between 25 and 27%, CI between 1.3 and 1.5, gravel content among 62.7 to 64.7%, and MDD between 1.76 and 1.82 g/cm3 . Thirdly the Sekakouo and Chenye sites LGM are dominated by fnes with C80µm between 38 and 44%. Swelling clay minerals are absent in these materials. It results that, these materials are suitable for use as a subgrade layer for any type of trafc, and as a sub-base for low-volume trafc T1 to T3, except those at the Sekakouo and Chenye sites. Prospecting of LGM deposits should be directed towards thosewith high proportions of Gm, gravel content, MDD, CI, SG, and low proportions of Pm, C80µm, C400µm, Pp, ɛs and C2mm.
 
Article
In the construction of tunnels in environments with extreme temperatures, excessive temperature differences will lead to the early cracking of concrete lining after pouring, which subsequently affects the safety and durability of the tunnel lining structure. On the basis of the secondary development platform of ABAQUS, this study compiled a series of subroutines for the analysis of the hydration heat release, thermal mechanical coupling and temperature humidity coupling of early-age concrete. Combined with the extended finite element method, the temperature humidity stress multifactor coupling numerical analysis model is established. Subsequently, the early-age cracking mechanism and control measures of tunnel concrete under the high ground temperature of the surrounding rock environment were examined and verified by field-measured data. Studies have shown that 57.8 °C is a critical temperature in theory. When the surrounding rock temperature is lower than this value, the lining can be normally constructed without early cracking. Meanwhile, when the surrounding rock temperature exceeds this value, wall-mounted thermal insulation materials must be used to avoid surface cracking due to the large temperature gradient of lining concrete. The conclusions obtained in this research can provide reference for the design and construction of tunnels under high ground temperature.
 
Article
In order to explore the directional support method of jointed rock mass and ensure the stable operation of roadway, the support effect of jointed rock mass was analyzed by numerical simulation and on-site monitoring. The results showed that directional support could effectively reduce the deformation and ensured the stability of surrounding rock. In the process of directional reinforcement support construction, the plane formed by multiple bolts was guaranteed to be perpendicular to the structural plane, and the bolt hole extended along the normal plane of roadway, the control effect of this support mode was the best. The stress change law of surrounding rock of roadway was monitored by using borehole force meter. The results showed that the stress released occurs in surrounding rock of roadway after excavation, and the cumulative stress change value did not increase 5 to 7 days after excavation. The jointed rock mass remained in a stable state under the action of directional reinforcement support. The directional reinforcement of roadway surrounding rock had a good control effect on roadway stability.
 
Article
Ring foundations are commonly adopted to support tall and heavy cylindrical structures such as silos, chimneys, cooling towers, circular storage tanks, and windmills. The construction of these structures in the earthquake-prone region poses a high risk due to the limited knowledge about their behavior under the earthquake loading when supported on a ring type of foundation. The present study focuses on analyzing the response of ring foundations resting on cohesionless soil during the event of an earthquake. A three-dimensional finite element numerical analysis was carried out to study the behavior of the ring foundation-silo system during the event of an earthquake. The variation in ring geometry such that the ratio of inner to the outer radius (Ri/Ro) was 0.2, 0.4, 0.6, and 0.8, soil densification (γ) under loose and dense condition, the height of silo (h) of 15 m (squat silo) and 25 m (slender silo) and the different earthquake loadings were considered to study their effect on peak acceleration and horizontal displacement of ring foundation. The input motions from 1979 El Centro, 2001 Bhuj, and 1989 Loma Prieta earthquake were considered for the dynamic analysis. The results indicated a decrease in the horizontal displacement of the ring foundation with an increase in height of the structure and soil densification. The foundation displacement was irrespective of the ring geometry for squat silo but showed variation with ring geometry for slender silo. The peak acceleration at the base of the ring foundation was observed to be increased with a rise in height of the structure and soil densification.
 
Article
Water inrush accident into tunnel has become a bottleneck problem restricting the construction of deep-buried long tunnels, and the effect of intersecting faults on water inflow into tunnel is more complicated. Based on in-situ water pressure test data, the change law of the seepage characteristics in fault zone is analyzed, and an improved Darcy–Brinkman seepage model based on the theory of three-district zoning of faults is established. By assuming that the permeability coefficient conforms to the superposition principle, the underground seepage numerical model of intersecting faults that with perpendicular directions to tunnel is established. Then five calculation conditions are analyzed when the tunnel excavation axis is located at different relative height of the fault intersection center, so as to obtain the effect of the relative vertical location of the tunnel to the fault intersection center on the water pressure field, the seepage velocity field and the water inflow into tunnel. The results show that water inflow into tunnel crossing intersecting faults has litter relationship with the upper or lower position between the fault intersection center and the tunnel, but mainly depends on the relative height between them. The smaller the relative height, the smaller the water pressure, the greater the water inflow. Compared with the theoretical formula method and the stochastic mathematical method, the numerical simulation method can reflect the gradual process of water inrush while encountering intersecting faults in excavation and the change law of water inflow in different space and time under specific geological conditions, which is most consistent with the in-situ water inflow monitoring data.
 
Article
Artificial islands near Dubai were constructed with geomaterials of significant gravel content from other areas of the United Arab Emirates (UAE). The fills were dynamically compacted and their present geotechnical properties are unknown. Large development projects are being proposed on the islands that will require extensive field testing to characterize the fills because existing correlations developed for nearby natural soils are not representative. The main focus of this study is to develop correlations between Standard Penetration Test (SPT), Cone Penetration Tests (CPT), and shear wave velocity (Vs) measurements applicable to the compacted fills with high gravel content. More than fifty (50) SPT and similar number of CPT tests are performed on a large area of the island. A number of Multi-Channel Analysis of Surface Waves (MASW) and Downhole Seismic (DHS) tests are conducted to measure the distribution of Vs with depth and imaging. The data is analyzed to develop correlations between SPT and CPT and between SPT and Vs. The proposed correlation between SPT and CPT generally does not agree with existing correlations for coarse grained soils. This study predicts larger values of tip resistance (qc) with N60 values. The predicted Vs values as function of N60; however, are comparable with some prediction equations in the literature. The Vs values from MASW and DHS for the fill are comparable on average; however, reliability of DHS increases with depth. The results from all tests reveal the inadequacy of earlier dynamic compaction in achieving consistent and uniform densification.
 
Article
This manuscript pivots around the durability results at the laboratory scale for the rocks of the sub-Himalayas. The sedimentary origin rocks of sub-Himalayas comprising sandstone, siltstone, claystone, mudstone, and silt-shale induce weathering-based failures in the cut and natural slopes. The higher weathering/slaking rates of incompetent lithologies such as claystone and mudstone cause failures in overlying competent sandstone/siltstone/silt-shale, units. During the geotechnical investigations, defining the descriptive categories of the rocks with any classification is the initial step. Slake Durability Tests are commonly used to classify and characterize clay-bearing rocks. This research utilized three different durability-based systems, and rocks were characterized. These classification systems are based on the slake durability index, disintegration ratio, and relative slake durability index. The research concludes that the relative slake durability classification over-estimates the durability of the rocks. This manuscript also concludes that a durability-based classification and detailed investigations should also be initiated for the sub-Himalayan region.
 
Article
The stability of remnant coal pillars is of great significance for safe mining of coal resources around them. The remnant coal pillars are often soaked in mine water with a certain height. Different water levels (or depths) may affect the stability of remnant coal pillar differently. In this paper, uniaxial compression tests were carried out on coal specimens with different water soaked depths. Deformation and damage characteristics of coal specimens under loading were analyzed through acoustic emission (AE) and digital image correlation techniques. The results show that the AE energy curve of each partially soaked coal specimens presents double peak, while that of fully soaked coal specimen has only single peak. As the soaked depth increases, the AE b value gradually decreases, which indicates that the micro-fracture of coal specimens decrease with the increase of water soaked depth. During deformation and damage, partially soaked coal specimens have obvious localized strain, and the local strain concentration area is basically distributed in the dry–wet transition area. While the surface of the fully soaked coal specimen presents relatively uniform deformation. Partially distributed water within coal matrix increases the heterogeneity of the coal specimens. These results reveal the deformation and damage characteristics of coal with different water soaked depths, and provide a useful reference for reasonably evaluating the stability of coal pillars.
 
Article
The arch is the main stress structure of metro station in the construction of arch cover method. The preliminary geological survey has some limitations, and the arch structure design based on the survey results is usually too conservative, which increases the investment cost. Therefore, it is necessary to optimize the design parameters of arch structure. In this paper, based on particle swarm optimization (PSO) algorithm, the engineering cost is taken as the optimization objective, and the monitoring control values of displacement are taken as the constraint condition. The scheme optimization is carried out for the thickness of outer primary lining and inner primary lining and removal length of temporary support. The final optimization values of parameters obtained by PSO algorithm are that the removal length of temporary support is 18 m, the thickness of the outer primary lining is 22 cm, and the thickness of the inner primary lining is 26 cm. Compared with the original design scheme, the engineering cost of the optimized scheme is reduced by 8.79%. The optimized parameters can not only meet the safety requirements of the project, but also effectively reduce the project cost, which has guiding significance to the actual project construction.
 
Article
The fully bonded bolting method is widely applied in geotechnical engineering areas and is considered as an efficient approach due to its better loading capacity compared with end-anchored methods. However, the mechanical property of fully bonded bolt under various bond lengths is still unclear. This study comprises a mixed methodology of laboratorial experiments and theoretical analysis to discuss the mechanical law of fully bonded bolts under different bond lengths. Results show that the plastic debonding at the interface tends to expand as the bond length increases. Moreover, the undergoing time of the yield stage, which is between the initial and peak force stages, shows an increasing trend that is also applicable to the corresponding pull-out displacement. We have also identified that AE capturing indicated that intense energy events/values are easy to identify when the bond length increases, a phenomenon; that is closely related to the longer frictional process of the specimens with longer bond length. This study provides a reference for the design of fully bonded bolts, that is, the bond length should be carefully considered to avoid the premature failure of bolting systems due to progressive debonding.
 
Article
The improvement of salt affected lands is a major environmental challenge in arid and semi arid regions all over the world. Electrokinetic treatment is one of the environmentally friendly and cost-effective methods that can be used in reclamation of saline soils. In this study, the effect of electrokinetic remediation (EKR) on compressibility characteristics of fine-grained salt affected soils was investigated. The soil samples were subjected to the following applied voltage gradients of 1, 2 and 3 V/cm during 7 days, followed by oedometer tests to evaluate the soil consolidation parameters. The obtained results are presented and discussed regarding to the variation of applied potential on compressibility characteristics of the treated soil samples. Experimental results show that each of compressive index and swelling index decreases with increasing the voltage, whereas preconsolidation pressure increase. These variations were attributed to water flow between electrodes and migrations of salt cations toward the cathode. Moreover, EKR demonstrates changes in soil pH as a result of electrolyse soil reactions. This research reveals that the use of EKR using direct current improves compressibility characteristics of saline soils involving a short time period. This process proves that it can be successful to soil remediation for civil engineering use.
 
Article
Numerical modelling development for capillary barrier investigation considering unsaturated soil-geotextile interface has been studied and evaluated in recent years. Most engineering constructions involving geomaterials and geotextiles application, such as reinforced walls, slopes, embankments, and roads, require understanding the hydraulic performance of those systems for design purposes (capillary barrier, drainage, filtration, etc.). Considering that the hydraulic behavior of those materials is directly dependent on their saturated-unsaturated state over time, unsaturated principles should be applied for their long-term evaluation. This paper presents a 1D (one-dimensional) numerical analysis of an unsaturated system composed of soil and gravel layers separated by a geotextile in a column laterally impermeable (2.0 m). A non-woven geotextile was applied considering different soil types from the literature, such as silty sand, sandy, compacted residual silty, bimodal, and compacted residual sandy soils. A SEEP/W finite element numerical model was developed to perform transient analyses through the system to evaluate its hydraulic performance in terms of capillary barrier formation considering different geomaterials combinations in different hydraulic conditions. A significant influence of geotextile hydraulic conductivity and water flow rate were verified on the capillary barrier effect. Also noticed were the different height and duration of capillary barrier formation for different soil profiles. A design chart-table was proposed to evaluate soil-geotextile performance in terms of capillary barrier for new geotechnical designs. Finally, it could be inferred that fine-grained soils demonstrated to develop higher and longer water column (positive pore pressure) compared to coarse-grained soils, independently of their initial suction.
 
Article
The mechanism for coal and gas outbursts in normal blind fault areas is not yet clear. Coal and gas outbursts induced by normal blind faults exposed at the 22,703 working face in the Yanjiao Coal Mine were taken as examples to carry out numerical simulation, detection and inversion through radar computed tomography (CT) transmission. In combination with ground pressure monitoring data before/after outbursts, the mechanism driving outbursts induced by superposition of multiple stresses and subjected to the influence of blind faults was primarily investigated in the present study. The results indicated that due to a cutting action applied by a blind fault on rock masses, the intersection of the fault plane and coal seam always remains in a stress concentration state as the working face advances. In addition to the impact of mining-induced abutment pressure, the intersection of the fault plane and coal seam is also under the actions of tectonic stress. Once the 22,703 working face arrives at a position 15 m away from the fault plane, coal masses between the working face and the fault plane are entirely damaged due to joint actions of abutment pressure and tectonic stress. In this case, the coal mass loses its carrying capacity entirely; the overlying strata of the working face settle sharply, and the strata behaviour of the working face becomes intense. Consequently, coal and gas outbursts are induced. In addition, according to ground pressure data before/after an outburst event at the face, a significant rise in local ground pressure monitoring data suggests coal rock instability. Prior to such an outburst, the operating resistance of the hydraulic support in a local region may increase by 300% compared with its normal value, which is an early warning index for a potential area of outburst. Therefore, not only do regions where the ground pressure rises abnormally need to be further explored but also the gas stress of the coal mass should be synchronously checked. In this way, prevention and control measures can be made in advance.
 
Article
Due to the complex and invisible of hydrogeology in karst area, underground construction often encountered gushing water disaster in engineering process, which has a significant negative impact on engineering construction. In this paper, based on the theoretical analysis, slurry performance control, indoors model experiment, engineer application, a new kind of grouting materials for plugging gushing water in karst conduit are systematically analyzed and put forward, furthermore, the plugging pattern of water inrush in karst conduit is attempt to carry out. The results show that the physical performances of cement slurry could be regulated by the dosage of xanthan on the research foundation of cement-sodium silicate slurry. Furthermore, according to the evaluation index of slurry diffusion pattern and sealing efficiency in indoor model experiment, the plugging modes of cement slurry, C-S slurry and modified binary slurry are summarized as long distance fillings, timely sealing and trapezoidal sealing respectively and the modified binary slurry possessed promising engineer application properties. Finally, the research results are successfully applied to the project of the China Resources Cement (Pingnan) limestone mine, which to a certain extent accumulates engineering experience for similar projects and promotes the development of grouting materials for controlling the water inrush damage in karst areas.
 
Article
As the cutting stone is a wear process, performing this process with diamond pieces' aid can be considered the wear of stone particles bypassing diamond grains on its surface. To better understand this process as well as the conditions governing the cutting diamond grain, it is necessary to be familiar with the cutting mechanism along with affecting parameters. In this case, forecasting the quantity of bead consumption is crucial for calculating manufacturing costs and mapping out the locations of the construction stone mines. In order to calculate the consumption of diamond cutting wire beads, this article used data collected from carbonate and granite stones. To do so, two methods, namely support vector regression (SVR) and genetic algorithm + Multilayer perceptron (GA-MLP), were chosen using MATLAB software toolboxes to estimate the bead wear. In each of above algorithms, a low-pass smoothing filter called Savitzky-Golay was used on the data. For this purpose, three rock properties, including uniaxial compressive strength (UCS), Schmiazek abrasivity factor (SFa), and Young's modulus (YM), were employed as the model's input. Then, twelve models were constructed, and the bead wear was estimated as well. At last, the accuracy of above models was assessed using the coefficient of determination (R2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${R}^{2}$$\end{document}), mean square error (MSE), root mean square error (RMSE), mean absolute error (MAE), mean absolute percentage error (MAPE), and variance account for (VAF). According to obtained results, it can be concluded that SVR approach and the Savitzky-Golay filter with Polynomial Kernel could better estimate the wear rate of diamond cutting wire bead.
 
Article
Water inrush disaster is a huge challenge to geotechnical and mining engineering, and easy to induce group death and injury accident. Similar simulation test is the basic method to reproduce the process of water inrush and research mechanism of water inrush disaster. Fluid–solid coupling materials are the key to success of similar simulation test. However, at present there are no mature materials to be widely accepted by scholars. The paper based on similar traditional simulation materials, with previous mass experiments, new fluid–solid coupling materials of impermeable layer, water-bearing layer and fault zone, was developed by adding various additives. With rock mechanics experiments, fluid–solid coupling material properties of strength, water-absorbing quality, permeability and expansibility were tested and obtained. Finally, the feasibility and applicability of fluid–solid coupling materials were verified. The research results can provide reliable fluid–solid coupling materials to similar simulation test on water inrush and also important to reveal water inrush mechanism.
 
Article
The 2018 Situbondo earthquake occurred along an unidentified fault source in East Java, Indonesia. Historical records from 1821 to 2018 show that no earthquakes before 2018 were recorded in this region. In this study, we use Global Navigation Satellite System (GNSS) data to estimate the coseismic displacements of stations in the study region. Significant coseismic displacements were estimated for stations located south of the epicenter. Using focal mechanism as preliminary information for the fault geometry, we conduct coseismic slip inversion on two possible fault sources, i.e., a northward dipping fault and a southward dipping fault. The seismic moment of the southward dipping fault, which is 2.7 × 10¹⁸ N·m (equivalent to Mw 6.2), is identical to the seismic moment from the seismic analysis. Also, displacement model of the southward dipping fault model better fit data than the northward dipping fault. We also find that high slip is concentrated at depths greater than 9 km. Our assessment of the fault suggests that it could rupture every 700 to 1700 years. Since the dilatation rate to the west from the epicenter is much higher, our result emphasizes the urgent need for further investigation of the Kendeng thrust, which may affect the megacity of Surabaya.
 
Article
Chimney subsidence can cause surface subsidence (ground settlement) in the form of a pit or sag when there is a mine roof collapse in a mine entry. Surface subsidence occurs when the roof collapse propagates upward and does not choke itself off due to the associated volume expansion of the rubblized fallen materials and where no sufficiently competent rock is present to bridge the cavity. This paper contains a review and evaluation of reported case history data associated with occurrences of surface subsidence related to chimney subsidence. This analysis included investigating the chimney subsidence height potential including relative to the overburden rock conditions, extraction height, mine depth, the width of entry and the roof rock fall distance. Also, this paper provides a summary of the results of an assessment of the bridging capacity of various more common competent coal measures in the roof. This numerical analysis was performed considering linear arch conditions. Parameters which were investigated in this analysis included the competent roof rock strength, thickness, depth, and spanning distance.
 
Article
Sand drain wells or prefabricated drain boards are widely used in natural soft ground improvement. The soil surrounding a drain can be highly disturbed during the installation process, which can result in two impacts on the soil in the smear zone. (1) The soil structure is totally destroyed, and the permeability of the smeared zone is reduced. (2) An increase in excess pore water pressure (uex-i) is induced by the shear of the soil due to drain installation. However, research on consolidation behavior due to the dissipation of installation-induced uex-i has not yet been reported. In this study, first, a structured soil was made by a large-scale one-dimensional consolidation test to simulate natural soft ground, and the soil parameters were back-analyzed. Second, a drain installation test was performed, and the radial consolidation after drain installation was investigated. The effect of drain installation on the consolidation behavior was equivalent to an additional load. Finally, the effect of installation stress on the consolidation rate under surcharge preloading was studied theoretically. The results showed that the installation of drains can induce an increase in excess pore water pressure, resulting in a decrease in permeability and a delay in the consolidation time during the surcharge stage, which should be well considered in engineering design.
 
Article
Salt-affected soils cannot meet the needs of engineering projects due to their deficiency in providing desirable geotechnical properties. Cement stabilization is widely used to improve the engineering properties of salt-affected soils, but cement has many backward effects, especially on the environment, limiting its application as a binder. This study evaluates the potential effects of salt on protein-based biopolymer treated sand. The influence of salt content, biopolymer content, and curing time on the strength and stiffness development of salt-affected sand was explored with unconfined compressive strength (UCS) testing. The UCS results showed that an increase in casein biopolymer content led to an increase in the unconfined compressive strength and stiffness; however, the addition of salt had a reverse effect on UCS results. By adding 2% casein solution, the compressive strength reached 1021.34 kPa, which is significantly greater than that of untreated soil with a value close to zero. When the salt content rose from 0.5 to 10% (for 2% casein content), a substantial strength loss (more than 48%) was observed in the UCS value from 978 to 501 kPa. This might be due to the salt existence in soil which adversely affected the biopolymer connections by blocking the bonds and bridges with soil particles. This adverse effect was gradually mitigated by the biopolymer increment until adding 3.5% sodium caseinate, then a higher percentage of the biopolymer was involved in further enhancement of compressive strength. Microscopic observation revealed that sodium caseinate acted as a binding agent between soil particles, while salt disrupted the sodium caseinate performance. To evaluate the physical properties of the sandy soil, permeability and wind tunnel tests were conducted. The inclusion of sodium caseinate as a protein-based biopolymer resulted in lowering the hydraulic conductivity and increasing the erosion resistance of salt-affected sand. Curing time had positive effects on strength development, increasing the erosion resistance, and reducing the permeability. Overall, sodium caseinate could adequately improve the engineering properties of salt-affected sand.
 
Article
In this paper, a technology of ecological slope protection with polyvinyl chloride (PVC) pipe is introduced to improve the slopes’ erosion resistibility. Through establishing a large scale test model similar to the actual project, it is proved that PVC pipes could effectively reduce the soil erosion of slope by reducing rainfall erosion. The effect of PVC pipes is measured by the changes of soil erosion rate. As the experimental results show, the slope protected with PVC pipes are less damaged than the unprotected ones. For the protected slopes, the amount of soil erosion (q) increases over erosion time, and reaches a peak at 120 min, then it decreases and gradually becomes stable. Four hundred and eighty minutes later, the q of the bare slope, slope D75 (using PVC pipe with a diameter of 75 mm), slope D110 (using PVC pipe with a diameter of 110 mm), and slope D160 (using PVC pipe with a diameter of 160 mm) reduces by 25.2%, 85.9%, 78.9%, and 48.7% respectively, compared with the initial value. The q is significantly different with different diameter slope protection modes. There was a negative correlation between D (diameter) and q, and between T (time) and q. The cumulative erosion amounts (Q) of the four slopes, the same as q, increases over erosion time, and eventually become stable, which is a “S” shape shown in a statistic table. The Q is significantly different with different diameter slope protection modes. In addition, there was a negative correlation between D and Q. The time was positively correlated with Q. The average soil erosion reduction rates of the slopes (D160, D110, and D75) are 67.13%, 71.89%, and 79.96%, respectively, indicating PVC pipes' ability to cut down the infiltration of rainwater, the smaller the diameter, the more effective. The moisture content of the bare slope is the highest, followed by slope D160, then slope D110, and finally slope D75.
 
Article
Ground vibration is one of the destructive effects of rock blasting. The prediction and control of the blast-induced ground vibrations are very important in mining and construction projects. Therefore, the maximum possible efficiency of the operation should be determined by considering the safety range. In this paper, to estimate the effect of surface and underground blast-induced ground vibration on concrete structures in the area of Gotvand Olya Dam, 30 and 14 records of 21 surface and 4 underground blasting operations (totally 44 data), respectively, were recorded using PG-2002 seismographs. The ground vibrations from the blasting operations were estimated using two empirical relationships with the accuracy of 0.93 and 0.88 for the surface and underground operations, respectively. With the help of a Genetic Algorithm (GA), the correlation of these relationships has increased to 0.96 and 0.9, respectively. Considering the elapsed time of concrete and using the U. S. Army Corps of Engineers standard, the allowable charge weight per delay was calculated for both operations for a hypothetical distance of 50 m. Based on the results of this study, the surface and underground blasting operations can be operated using Cordtex and Nonel systems, while the empirical relationships allow only the Nonel system with limited delay times or a limited number of blast holes. It is also recommended that, if possible, no blasting operations be carried out in the first 24 h of concreting. In case of exigency, the operation is scheduled in the first 7 h of concreting.
 
Article
Sandy natural levee deposits have been pointed out to provide seepage paths under river levees, which are largely related to the underseepage problems. However, few attempts have been taken to quantitatively study the relationship between the natural levees and the leakages in river levees. To capture the features of real natural levees, statistical studies are performed on the geometry and hydraulic conductivity of the micro-topographies along the Kinu River in Japan. By setting cases based on the retrieved data, a parametric study on the geometric and hydraulic parameters is performed by finite element seepage analysis. As a result, the embankment sitting on the landside of the natural levees is identified to be susceptible to leakages. In addition, rainfall and flooding are distinguished as the two driving forces of leakages depending on the hydraulic conductivity of the embankment bodies and the underneath foundations. The sandy natural levee deposits, with relatively high hydraulic conductivity, providing seepage paths for the under seepage, may magnify the effects of the seepage driven by the flooding, and lead to the classical backward erosion piping. Discussion and comments are addressed for the existing engineering practice in Japan.
 
Article
This article examines the tunneling process for constructing subway shields in cities aiming at preventing the risk of water and mud inrush in fault fracture zones and with abundant groundwater. Here, we studied the influence law and the response sensitivity of shield cutter heads with different types and diameters on the critical safety distance. Likewise, we reveal the influence law and response sensitivity of the front fault fracture zone with different thicknesses and water pressure on the critical safety distance. This study simulates the propulsion process of shield tunnels and the moment of water inrush using COMSOL Multiphysics fluid–structure coupling method. Using a numerical simulation of a three-dimensional finite element model, we obtained a formula for a critical safe distance for the fault fracture zone in front of the shield tunnel. This research has particular relevance to the construction of metro shield excavations in cities with fault fracture zones and abundant underground water.
 
Article
To study the influence of changes in the coal seam mechanical characteristics at depth on the stress relief effect of a borehole, this paper established the relationships between the borehole spacing, elastic modulus, and Poisson’s ratio of the coal seam. It then analyzed the stress relief effect of different borehole spacings in different coal qualities in a deep coal seam, using the FLAC3D numerical simulation software. The results indicated that after boreholes with different spacings were drilled in the deep coal seam, the peak stress value of the roadway-surrounding rock was transferred to the deep coal body, and the original peak stress position was reduced to varying degrees. Under the premise of ensuring the stress relief effect and improving stress relief efficiency, the relationship between borehole spacing and the elastic modulus of the coal seam was a negative exponential function, whereas the spacing of boreholes and Poisson’s ratio of the coal seam had a logarithmic function relationship. The research conclusions were applied to the − 1000 West No. 1 mining area in the Tangkou coal mine, which achieved good stress relief results.
 
Article
In the block caving mining, the significant rock mass deformation and surface subsidence will be formed with the continuous extraction of ore. However, the internal crack evolution mechanisms in rock mass and associated subsidence characteristics present one of the key issues in rock mining engineering. Although block caving method has been used for many years, current knowledge of the crack evolution mechanisms, the subsidence characteristics under the influence of rock mass structure and subsidence prediction capabilities are limited. Based on the rock mechanics model provided by CEMI (Centre for Excellence in Mining Innovation), crack evolution mechanisms and subsidence characteristics effected by the rock mass structure in block caving are numerically investigated using RFPA 2D, a numerical code based on FEM (Finite Element Method). Crack formation, propagation and coalescence in the overlying strata and the stress-balancing arch evolution in the stress field are represented visually during the whole process of extraction. The numerically obtained crack evolution shows that the stress-balancing arch has a significant influence on the fracture development of rock mass, and directly determines the slump form and rate of the rock mass. After understanding of the crack evolution mechanism in rock mass, the characteristics of surface subsidence are analyzed. Numerical experiments emphasize the geometrical configuration of joints and faults about mechanisms of subsidence development, including joints orientation, faults location and inclination, which can provide significantly meaningful guides for investigation of subsidence mechanisms and implementation of remedial measures.
 
Article
The results of a set of coupled thermo-hydro-mechanical (THM) finite element (FE) simulations are presented to evaluate the effect of long-term periodic temperature variations within a range of 10 ℃ applied to energy piles in a piled raft located on saturated stiff clay on the soil-pile-raft interaction. At shallow depths of the active pile, where the variation range is more significant than in other areas, the presence of the raft in direct contact with the soil causes the maximum thermal compressive stress to exceed approximately three-fourths of the axial mechanical stress, as well as the generation of tensile stress. Additionally, the stabilized additional settlement of the foundation was approximately one-sixth of the mechanical settlement, demonstrating the importance of evaluating the serviceability of the superstructure while considering additional stresses. However, it was observed that the variations in excess pore water pressure were not significant for the corresponding values considered. Furthermore, parametric studies revealed that variability in the thermal expansion coefficient and thermal conductivity of solid soil particles had a similar qualitative effect on the system's response, despite some quantitative differences. This implied that the effectiveness mechanisms governing the soil's temperature variations and thermal deformation potential were nearly identical, despite their distinct ability to alter the stress state.
 
Top-cited authors
Danial Jahed Armaghani
  • University of Technology Sydney
Indra Prakash
  • Geological Survey of India
Umesh C. Sahoo
  • Indian Institute of Technology Bhubaneswar
Neeraj Sharma
  • Birla Institute of Technology, Mesra
Ahmed Salih Mohammed
  • The American University of Iraq, Sulaimani