Showing papers in "Bulletin of Engineering Geology and the Environment in 2021"
TL;DR: In this paper, a numerical model of an anaclinal slope using the 3DEC software has been built to simulate the failure process of the physical model, and the numerical results show that standard cables, i.e., Poisson's ratio (PR) cables, cannot control the large deformations of the slope, and finally fails.
Abstract: Occurrence of toppling failure has been prominent due to the increasing of infrastructure construction, such as road slopes, dams, and hydroelectric stations. Many scholars have done research on the toppling failure characteristics, but paid less attention to the comparison of numerical simulations and physical models in order to propose reasonable and effective stability control methods. Based on previous tests on physical model and field investigations, a numerical model of an anaclinal slope using the three-dimension distinct element code (3DEC) software has been built to simulate the failure process of the physical model. Based on the prominent mechanical properties of the engineering-scale and model-scale negative Poisson’s ratio (NPR) cables, a numerical simulation model of the NPR cable has been developed. The numerical model has been used to simulate the effects of different types of model-scale cables on controlling the deformation of the anaclinal slope. The numerical results show that standard cables, i.e., Poisson’s ratio (PR) cables, cannot control the large deformations of the slope, and the slope finally fails. On the opposite, NPR cables can absorb the deformation energy and maintain the stable constant resistance force during the tensile process. This thereby allows avoiding tensile breakage of cables under the effect of large deformations of the slope and driving the slope towards a new equilibrium state. Through the comparison between the numerical simulation results and the physical model test results, the accuracy and rationality of the numerical simulations have been proven. The numerical model developed in this study can be used for future research works on the failure mechanism of anaclinal slopes and the control effect of NPR cables. It thereby lays a foundation for applying the NPR cables to control the toppling deformations of similar anaclinal slopes.
58 citations
TL;DR: In this paper, the authors established that the main controlling factors of the support effect are prestress, anchor cable length, and anchor cable spacing, and provided a theoretical basis for applying the prestressed anchorage system to control the large deformation of tunnel soft rock.
Abstract: Prestressed anchorage systems have been gradually applied in the treatment of large deformation in soft rock tunneling. However, the research of support parameters on the mechanical behavior of large section cavern surrounding rocks with high joint density and deep buried high ground stress is not enough. In order to study the mechanical behavior of surrounding rocks under prestressed anchor support, a mechanical model is established. It is determined that the main controlling factors of the support effect are prestress, anchor cable length, and anchor cable spacing. Therefore, considering the distribution characteristics of surrounding rock joints, the discrete element simulation of different anchor cable lengths, circumferential spacing, and prestress is carried out. Similar simulation verification experiments further substantiated the accuracy of numerical simulation. The experimental results are applied to field engineering. The results indicate that the numerical simulation method of ubiquitous-joint and DFN (Discrete Fracture Network) can attain accurate results. The primary deformation and plastic zone of the tunnel is mainly located at the left shoulder of the inclined shaft, wherein the plastic zone is mainly tensile failure. The depth of the outer bearing arch, i.e., the length of the long anchor cable, is preferably 10 m. With the increase of circumferential spacing and prestress, the deformation and plastic zone of tunnel surrounding rock show a linear decrease. This paper can provide a theoretical basis for applying the prestressed anchorage system to control the large deformation of tunnel soft rock.
53 citations
TL;DR: In this paper, a multi-layer fully connected network (ML-FCN) was proposed to optimize the deep neural network (DNN) and adopted to train the prediction model based on the Vs and SPT dataset in this paper.
Abstract: Soil liquefaction has been accepted as one of the factors causing natural disasters and engineering failures in the seismic. The mathematic prediction model for soil liquefaction is widely accepted, and the standard penetration (SPT) and cone penetration test (CPT) prediction model using the machine learning method is also developed. But for the Vs, the prediction model based on the machine learning method is limited. So, considering the advantage of the deep learning method, a multi-layer fully connected network (ML-FCN) was proposed to optimize the deep neural network (DNN) and adopted to train the prediction model based on the Vs and SPT dataset in this paper. The history dataset was divided into a training set, a validation set, and a testing set by a ratio of 6:2:2 for better evaluation. The SPT dataset was extracted to train a corresponding DNN prediction model. According to the comparison results, the model trained by ML-FCN DNN could predict the liquefaction potential with higher accuracy than the model proposed by Hanna et al. (Soil Dyn Earthq Eng 27(6):521–40, 2007), which is enough to be applied to real engineering, the parameter of Vs is essential to improve the model performance as for the three sets.
46 citations
TL;DR: In this article, a vector sum numerical manifold method (VSNMM) is proposed to investigate the stability of slopes, and the stability analyses of two slopes including a homogeneous slope and an inhomogeneous slope with three different materials are conducted.
Abstract: The NMM (numerical manifold method) has shown its ability to solve continuum and discontinuum engineering problems in the same framework. In the present paper, the vector sum NMM (VSNMM) is proposed to investigate the stability of slopes. With the (vector sum numerical manifold method) VSNMM, the FOSs (factors of safety) of slopes are obtained using the real stress fields of the slopes. Compared with the limit equilibrium methods, the deformation and stress field of a slope can be obtained using the VSNMM. Besides, the computational cost of the VSNMM is much less than that of the strength reduction numerical manifold method (SRNMM), since only one elasto-plastic analysis is needed in the VSNMM, while a series of elasto-plastic analyses is needed in the SRNMM. Based on the VSNMM, the stability analyses of two slopes including a homogeneous slope and an inhomogeneous slope with three different materials are conducted. The numerical results based on the two slopes show that the VSNMM can accurately calculate the FOSs of the slopes.
46 citations
TL;DR: In this paper, the authors proposed a new method considering the inertial force of earthquakes to assess the stability of anti-dip bedding rock slopes (ABRSs) by using the limit equilibrium method and genetic algorithm.
Abstract: Earthquakes are one of the most significant external factors that induce the failure of anti-dip bedding rock slopes (ABRSs). The pseudo-static method is currently (and is likely to remain in the near future) the most effective and popular method used to evaluate the stability and design of such slopes under the action of earthquakes. In this work, based on the limit equilibrium method and genetic algorithm, a new method considering the inertial force of earthquakes is proposed to assess the stability of ABRSs. Results previously obtained from centrifuge tests and reported in the literature were used to investigate the veracity of the proposed method. A parametric study was then performed to investigate the effects of earthquakes and the mechanical properties of the rock layers on the failure mechanism of an ABRS. The results show that ABRSs are more likely to undergo a complex combination of shearing and flexural toppling failure under the combined action of gravity and earthquake. The direction of the earthquake-induced inertial force, tensile strength of the rock layers, and shear strength of the joints significantly affect the stability of ABRSs. On the other hand, these factors have little influence on the shape of the failure surface. The failure surface is stepped (with steps of different heights) rather than a plane. The failure surface and corresponding safety factor of an ABRS can be readily found using the proposed method, and the failure mode of each rock layer can be obtained. The method proposed in this work provides a convenient theoretical tool for the design of ABRSs in regions prone to seismic activity.
44 citations
TL;DR: In this paper, the authors used PFC2D to perform uniaxial compression tests on a rock mass containing ten different types of hole defects to analyze their failure behavior and mechanical properties.
Abstract: In a rock mass, holes of various sizes and geometries naturally occur, which in turn can affect the mechanical properties of the rock mass. These defects often cause engineering problems in subsurface construction. In this study, PFC2D was used to perform uniaxial compression tests on a rock mass containing ten different types of hole defects to analyze their failure behavior and mechanical properties. Four failure modes were determined, and crack propagation and stress field evolution were studied. The results show that the hole defect reduces the uniaxial compressive strength, peak strain, and elastic modulus of a rock mass. Also, these defects accelerate the generation of cracks and promote the destruction of the rock. The failure modes can be classified as Y-type, inverted Y-type, upper left to lower right type, and upper right to lower left type. Before cracks are generated, the compressive stress concentration area is located on the left and right sides of the hole and distributed as a butterfly shape, and the tensile stress concentration area is located in the upper and lower parts of the hole. A zone where stress is decreasing is located near the tip of the tensile stress triangular area. The magnitude and concentration area of compressive and tensile stresses are greatly affected by various hole geometries. Finally, the maximum principal compressive stress decreases instantly after a crack coalesces. Overall, the hole shape has a noticeable influence on the stress distribution surrounding the hole, and a hole defect reduces the degree of failure of a rock mass.
37 citations
TL;DR: In this article, a new quantitative method for determining the crack damage stress of rock materials was proposed based on acoustic emission (AE) signal detection, in which real-time AE signals and axial, lateral, and volumetric strain values were recorded.
Abstract: The quantitative determination of crack damage stress is of significant importance for investigating rock deformation and failure. In this study, a new quantitative method for determining the crack damage stress of rock materials was proposed based on acoustic emission (AE) signal detection. Ten rock materials were subjected to uniaxial compression testing, during which real-time AE signals and axial, lateral, and volumetric strain values were recorded. The AE cumulative count curves of the different rock materials were calculated based on the AE counts. These curves were divided into three stages as the axial stress increased: the slowly increasing stage, the steady stage, and the sharply increasing stage. The point where the sharply increasing stage began was defined as the PR point and could be accurately determined based on a fitting optimization method. Then, the damage stress was calculated by using the crack volumetric strain model. Finally, the relationship between the R stress (axial stress corresponding to the PR point) and the crack damage stress was investigated for the ten rock materials. The results showed that there was a good correspondence between the R stress and the crack damage stress. Hence, the R stress can be used to determine the crack damage stress and the starting point of the unstable crack growth stage in rock materials.
37 citations
TL;DR: In this article, a double-criteria damage-controlled testing method was proposed to capture the complete stress-strain response of porous limestone, especially the post-peak behavior, under systematic cyclic loading.
Abstract: Cyclic loading–induced hazards are severe instability problems concerning surface and underground geotechnical projects. Therefore, it is crucial to understand the rock failure mechanism under cyclic loading. An innovative double-criteria damage-controlled testing method was proposed in this study to capture the complete stress–strain response of porous limestone, especially the post-peak behaviour, under systematic cyclic loading. The proposed test method was successful in applying the pre-peak cyclic loading and then in controlling the self-sustaining failure of rock during the post-peak cyclic loading. The results showed that the strength of the rock specimens slightly increased with an increase in the fatigue life in the pre-peak region due to cyclic loading–induced hardening. Additionally, a combination of class I and class II behaviours was observed in the post-peak region during the cyclic loading tests; the class II behaviour was more dominant by the increase in fatigue life in the pre-peak region. Damage evolution was assessed based on several parameters, such as the elastic modulus, energy dissipation ratio, damage variable and crack damage threshold stress, both in the pre-peak and post-peak regions. It was found that when the cyclic loading stress is not close to the peak strength, due to a coupled mechanism of dilatant microcracking and grain crushing and pore filling, quasi-elastic behaviour dominates the cyclic loading history, causing more elastic strain energy to accumulate in the specimens.
36 citations
TL;DR: Wang et al. as mentioned in this paper determined the moisture contents of unsaturated clay embankments in southern China considering the stress state, and 6 frequency domain reflectometry sensors were installed in a widened embankment to monitor the moisture content.
Abstract: To determine the moisture contents of unsaturated clay embankments in southern China considering the stress state, 753 moisture data of three existing embankments for about 20 years were measured, and six frequency domain reflectometry sensors were installed in a widened embankment in southern China to monitor the moisture content. The soil water characteristic curve (SWCC) and stress-dependent soil water characteristic curves (SDSWCCs) were determined in the laboratory using a pressure plate apparatus and a stress-dependent parametric equation was established. The finite element model of a typical unsaturated clay embankment in southern China considering the SWCC and SDSWCCs was created. Then, the variation of the moisture contents of the clay embankment was simulated. The results show that the vertical stress has an obvious effect on the moisture distribution in embankments, especially the positions inside embankments where the vertical stress is large and cannot be neglected. The finite element model considering the SDSWCCs, therefore, should be selected when analyzing the moisture filed of embankments in southern China. For the existing clay embankments in southern China, their moisture contents gradually increase from the optimum moisture content to equilibrium values, which is close to the plastic limit and increases by 99% of the optimum moisture content. In addition, the resilient modulus values at different locations of the embankment and that of the whole embankment are reduced by 55 to 62%. And the safety factor of the slope obviously decreases, and its reduction is greater than 60%.
36 citations
TL;DR: In this paper, an anionic bacterial extracellular polysaccharide is used to modify the geotechnical properties of the soil, particularly its strength and hydraulic conductivity.
Abstract: Several soil stabilization techniques have been adopted to favorably modify the geotechnical properties like hydraulic conductivity, strength, and compressibility of soil. In this study, xanthan gum (XG), an anionic bacterial extracellular polysaccharide is used to modify the geotechnical properties of the soil, particularly its strength and hydraulic conductivity. The addition of xanthan gum to soil improves its strength and stiffness and also decreases its hydraulic conductivity. The addition of xanthan gum induces polymer cross-linking, forms interconnected network of hydrogels in the voids of the soil matrix and causes preferential adsorption of the biopolymer molecules and cations on the soil surface. These interactions between the soil and the biopolymer alter the geotechnical properties of the treated soil matrix favorably. The decrease in permeability is nearly 1000 times with a small addition of 0.25% xanthan gum to the soil. Xanthan gum tends to aggregate the particles at lower concentration and at higher concentrations forms more viscous hydrogels that fill the pore spaces and clogs the pores. Strength also shows a similar increase and hence xanthan gum can be recommended for soil stabilization.
34 citations
TL;DR: Wang et al. as discussed by the authors analyzed the activity characteristics of this disaster and further analyzed the long-term activity of debris flow in Wenchuan County based on the analysis results of the disaster.
Abstract: Debris flow activity increased after the Wenchuan earthquake, and many debris flows continue to occur. Recently, a catastrophic debris flow event was triggered by strong rainfall on 20 August 2019 in Wenchuan County, China. The main purposes of this article are to analyse the activity characteristics of this disaster and further to analyse the long-term activity of debris flow in Wenchuan County based on the analysis results of this disaster. According to a field survey and remote sensing image interpretation, this strong rainfall triggered 15 debris flows that occurred simultaneously in the large watershed in northern Wenchuan County, and they were characterised by strong channel erosion and a disaster chain effect. The activity and sediment supply capacity of landslides have decreased significantly, and the landslides that provided materials for this debris flow event are mainly distributed on both banks of tributaries. The amounts of triggering rainfall and antecedent accumulated rainfall for this debris flow event were 13.7 mm and 47.1 mm, respectively. In addition, the channel runoff formed by strong short-duration rainfall eroded the channel deposits, and temporary check dams failed due to slope failures; these are the main causes for debris flows in the next period. Analyses of the debris flow volume versus watershed area and the maximum erosion modulus prove that the debris flow activity in Wenchuan County is decreasing with time, but more than 5~10 years will be required to recover to the pre-earthquake level.
TL;DR: A novel hybrid block-based neural network model for the purpose of producing high-resolution landslide susceptibility map (LSM) demonstrated more consistent tool for future landslide susceptibility zonation, implying on capability of developed HBNN in producing higher resolution and more reliable LSM for urban and land-use planners.
Abstract: Landslide susceptibility map (LSM) provide useful tool for decision makers in hazard mitigation concerns. In the present paper, a novel hybrid block-based neural network model (HBNN) for the purpose of producing high-resolution LSM was developed. This hybrid approach was found through the mixture of expert modular structures and divide-and-conquer strategy incorporated with genetic algorithm (GA). The introduced HBNN then was applied on southern part of Guilan province (north of Iran) using 14 causative factors covering topographic and geomorphologic features, and geological and tectonical factors as well as hydrology, land data, and climate conditions. The landslide inventory map was provided using a synergy work from monitored events, interpretation of aerial photographs, and carried out geotechnical investigations in the area as well as field surveys. To insight, the predictability of proposed HBNN was compared with two developed models using multilayer perceptrons (MLPs) and generalized feed forward neural network (GFFN). The generated LSM was validated using receiver operating characteristic (ROC) curves, statistical error indices, and sensitivity and weight analyses as well as monitored landslides. Based on the compared metrics, HBNN with 86.52% and 90.15% in prediction and success rate as well as 89.36% for precision-recall curve demonstrated more consistent tool for future landslide susceptibility zonation. This implies on capability of developed HBNN in producing higher resolution and more reliable LSM for urban and land-use planners.
TL;DR: In this article, comparative in situ grouting tests for long-term settlement treatment of a cut-and-cover tunnel of Nanjing Metro Line 10 were conducted to identify the effects of the grouting sequence and grouting material on the tunnel settlement treatment.
Abstract: This paper presents three comparative in situ grouting tests for long-term settlement treatment of a cut-and-cover tunnel of Nanjing Metro Line 10. The characteristics of the tunnel settlement and induced structural damage are described in detail. Comparative grouting tests were conducted to identify the effects of the grouting sequence and grouting material on the tunnel settlement treatment. The test results show that the total amount of uplift of the tunnel associated with the bottom-up grouting sequence is greater than that associated with the top-down grouting sequence. When a mixture of cement and water glass was used as grout, the average cumulative deformation and average deformation rate of the tunnel 6 months after the completion of grouting were −11.2 mm (uplift) and 0.018 mm/day (settlement), respectively. These values satisfy the control requirements and are better than those obtained using a cement and bentonite mixture as grout. Hence, a bottom-up grouting sequence and a cement and water glass grout mixture are advised. The findings presented in this paper provide useful guidance for similar projects.
TL;DR: In this article, a case study in the Muzhailing tunnel was carried out to explore the failure mechanism and investigate the control technology of the tunnel, where the numerical simulation software UDEC was used to establish a model, the results of which were analyzed.
Abstract: Deep tunnels in soft rock with high in situ stresses always exhibit large deformations. A case study in the Muzhailing Tunnel was carried out to explore the failure mechanism and investigate the control technology of the tunnel. The numerical simulation software Universal Discrete Element Code (UDEC) was used to establish a model, the results of which were analyzed. Combined with the rock mass strength criteria of the Geological Strength Index (GSI), the parameters of the rock mass around the tunnel were evaluated, and the microparameters of the rock mass from the UDEC were calibrated. Considering the results of the original support scheme to those calculated without support, failure first occurred in the roof and floor surfaces and then developed deeper into the surrounding rock. In the end, the tunnel suffered from a large asymmetric deformation with roof subsidence, rib shrinkage, and steel arch frame bending and twisting, which could be clearly observed from the stress, displacement, and crack evolution. Considering the failure of the original support with insufficient strength and stiffness, a new support scheme with high constant resistance anchor cables was proposed to control the large deformation of the tunnel. The anchor cables have been proved to be effective with high constant resistance and large deformation by the laboratory test, numerical simulation and field test. The results showed that the new support could effectively control the deformation of the tunnel. The new support scheme transforms the large deformation and nonuniform stress distribution of the tunnel into a small deformation and uniform stress distribution, which could provide useful references for support design in deep underground engineering.
TL;DR: In this paper, the effect of minimum principal stress and unloading rate on the spalling and rockburst of marble specimens was investigated by using true triaxial equipment combined with a high-speed camera, acoustic emission instrumentation, and scanning electron microscope.
Abstract: Hard rock often performs as brittle failures, such as cracking, spalling, and rockburst, induced by excavation in deep underground engineering. To understand the effect of the minimum principal stress and unloading rate on the spalling and rockburst of marble, unloading experiments were carried out by using true triaxial equipment combined with a high-speed camera, acoustic emission instrumentation, and scanning electron microscope. The experimental results showed that the failure process of marble specimens was more stable and less inclined to exhibit dynamic ejection with a low strain energy release per unit time under a low unloading rate. At the same time, the initial minimum principal stress controlled the marble’s failure mode by changing its mode from predominantly shear failure to shear-tension failure as the minimum principal stress decreased, similar to the spalling behaviors of surrounding rock observed in the underground tunnel. What’s more, the dynamic rockburst of the marble specimen was simulated under the condition with a high unloading rate, high initial minimum principal, and free face on the specimen. Based on these experimental investigations, a flowchart was also presented to estimate the possible failure mode of marble specimens under different initial minimum principal stress and unloading rate conditions, which would be conducive to the disaster prevention of hard rock in deep underground engineering.
TL;DR: In this paper, a systematic study was performed on how the strength and failure characteristics of soil-rock mixture (S-RM) can be affected by the rock block content, the oversize rock block processing methods adopted, and the sample size in triaxial tests.
Abstract: The mechanical behaviors of soil-rock mixture (S-RM) are very complicated and significantly affected by its rock block content and gradation composition. A systematic study was performed on how the strength and failure characteristics of S-RM can be affected by the rock block content, the “oversize rock block” processing methods adopted, and the sample size in triaxial tests. Both the deviator stress ratio and friction strength of S-RM increase together with the rock block content, but the former tends to decrease as the confining pressure increases. In the case of S-RM samples with the same gradation, these two parameters tend to decrease as the sample scale becomes larger. The development of deviator stress over axial strain of samples prepared using the equal quantity substitution method is similar to that of the samples of the natural gradation. During the shearing process, some large rock blocks in S-RM will be broken. The breakage mode of the rock blocks can be primarily divided into four categories according to its mechanism, namely, disintegration, corner breakage, fracturing, and breakage along bedding faces. As a result of the breakage, the strength envelope curve of S-RM follows a power function.
TL;DR: In this article, the authors investigated the effect of fracture length and angle on the mechanical properties and failure modes of combined roof-coal strata and concluded that longer cracks and/or cracks with angle closer to 30° tend to have the following characteristics: the more gentle the stress-strain curve of the combined coal and rock tends to be, the larger the decrease range of its elastic modulus, peak strength and peak strain, and the smaller the strain interval corresponding to the elastic-plastic stage.
Abstract: The mechanical property of roof is critically important for underground coal mining activities. The existence of hard roof that cannot cave naturally after coal extraction results in an unconsolidated goaf with large voids, and the sudden failure of this type of roof in uncontrolled manner will cause server windblast or rockburst hazard. To address this hazard, pre-existing fractures are created in roof by hydraulic fracturing or blasting to weaken the hard roof and promote its natural caving. The effectiveness of these roof weakening techniques is highly dependent on the geometry of pre-conditioned fractures and its impact on the mechanical behaviour of combined roof-coal strata, which has not been well-explored yet. Therefore, 21 groups of uniaxial compression testing on combined rock-coal specimens with pre-existing cracks were carried out, and the effect of fracture length and angle on the mechanical properties and failure modes of combined rock-coal strata were investigated. It can be concluded that longer cracks and/or cracks with angle closer to 30° tend to have the following characteristics. (1) The more gentle the stress-strain curve of the combined coal and rock tends to be, the larger the decrease range of its elastic modulus, peak strength and peak strain, and the smaller the strain interval corresponding to the elastic-plastic stage. The results show that the artificial fracture weakens the mechanical properties of composite coal and accelerates the process from micro-crack to macro failure. (2) When the specimen enters the plastic stage, the acoustic emission jumps sharply; the cumulative number of micro-cracks and the cumulative energy released during the whole loading process gradually decrease, and the number of micro-cracks and the released energy at the moment of failure also decrease gradually. (3) The crack-initiating stress for combined coal-rock specimens gradually decreases via one of three typical modes: preferential crack initiation of coal, simultaneous crack initiation of combined coal-rock and preferential crack initiation of rock, which also matches with coal failure, rock-coal failure and rock failure in the combined specimens. Thus, to promote the continuous fracture of the roof under loading, the length and orientation of the pre-conditioned cracks must be controlled and optimised.
TL;DR: In this article, a landslide susceptibility map (LSM) of potential cycles correlated with expected rainfall and land use and land cover (LULC) data utilizing the binary logistic regression (BLR) models in the Upper Rangit River basin of eastern Himalayan region, India.
Abstract: Landslide susceptibility assessment (LSA) is a method used to reduce landslide vulnerability defined as landslide spatial prediction with the help of associative factors. The goal of the analysis is to forecast potential (2040, 2060, 2080, and 2100 AC) rainfall and land use and land cover (LULC) with the aid of the CSIRO-MK3.6.0 General circulation models (GCMs) climatic model and the dynamic conversion of land use and its effects (Dyna-CLUE) model. The purpose of this work is to produce landslide susceptibility map (LSM) of potential cycles correlated with expected rainfall and LULC data utilizing the binary logistic regression (BLR) models in the Upper Rangit River basin of eastern Himalayan region, India. Including rainfall and LULC total nineteen factors have been incorporated, these are mainly topographical, hydrological, geological, and environmental factors. A total 671 landslide locations have been mapped which divided randomly as training (70%) and validation (30%) datasets of LSM. Current (2018) LSM was validated by 30% of landslide inventory location and the result of area under curve of receiver operating characteristic (ROC) indicated that the LSM has 92.4% and 89.6% of the success and prediction rate respectively. To demonstrate the accuracy of the BLR landslide susceptibility (LS) model, this model was used to generated future LSMs based on projected of rainfall and LULC. The result of projected representative concentration pathway (RCP)-based rainfall depicted that the increasing trend of rainfall in the future period and the moderate to very high LS zones has also increased from 2040 to 2100. This study will be used to further study of landslide hazard (LH) studies with climatic approaches, and will also contribute to regional planning and development of current and future Upper Rangit River basin.
TL;DR: In this paper, the authors performed a regional geological survey in discontinuous permafrost (PF) area along the Bei'an to Heihe Expressway between September 2009 and October 2016 to investigate the state and change of PF in northeast China.
Abstract: We performed a regional geological survey in discontinuous permafrost (PF) area along the Bei’an to Heihe Expressway between September 2009 and October 2016 to investigate the state and change of PF in northeast China. Underground resistivity changes were periodically detected along the foot of the subgrade and soil temperatures were monitored under the road foundation. We combined local meteorological and average annual air temperature data to analyze changes in PF thickness. The climate data show that the average annual temperature has gradually increased in the study area since 1980, rising to 0 °C around 1990, and the frost number has decreased to less than 0.5 since 1988. The soil temperature results show that the PF temperature in this section is higher than − 1 °C and is in a high-temperature PF zone affected by changes in seasonal air temperature. The PF under the left foot of the subgrade (LPF) and under the road central separation zone of the road (CPF) both show a decreased PF table, increased PF base, and severe PF degradation. Owing to different cover thicknesses, as well as differences in heat transfer between frozen and unfrozen soil, the base of LPF degraded faster than its table, to CPF the opposite is true. Underground resistivity measurements to verify the accuracy of the PF degradation results. The ground temperature monitoring data and climate data show good consistency. Comprehensive analysis results show that PF in the study area is in a strong degradation stage and will soon disappear.
TL;DR: In this article, the authors proposed an upper limit method of plastic limit analysis for a slope with a locked section structure, where the rock mass is divided into several rock blocks along its joint distribution, and a virtual speed is assigned to the slope and the locked section.
Abstract: The locked section is a kind of geological structure that is commonly found in natural slopes. The instability criterion of the slope with a locked section structure is not yet studied. In accordance with the mechanical properties of this type of slope, the rock mass is divided into several rock blocks along its joint distribution, and the upper limit method of plastic limit analysis is introduced. By combining the principle of virtual work and the characteristics of the slope, a virtual speed is assigned to the slope and the locked section. In addition, the maximum elastic strain energy that can be accumulated in the locked section is calculated to derive its deformation rate and internal energy dissipation power. The virtual velocity, internal energy dissipation power, and gravity work power of the locked section and the rock slope are solved simultaneously in accordance with the Mohr–Coulomb correlation flow law. Finally, the formula for calculating the safety factor of this type of slope under shear failure mode is derived. A slope in Xikou, Sichuan, China, is taken as an example to verify the proposed model.
TL;DR: In this paper, the potential use of cold-bonded geopolymer stabilizer made from limestone dust and bottom ash for grouting and deep soil (clay) mixing was investigated.
Abstract: This paper aims to research the potential use of cold-bonded geopolymer stabilizer made from limestone dust and bottom ash for grouting and deep soil (clay) mixing. For this purpose, the rheology and strength performances of the cement (PC)-based grouts with the stabilizers of limestone dust (LD), bottom ash (BA), geopolymerized cold-bonded limestone dust (GLD), and geopolymerized cold-bonded bottom ash (GBA) were investigated. The rheometer tests were conducted for the rheological performances at a wide range of stabilizer replacement (0–100%) and water/binder (w/b) ratio (0.75–1.5). Using proper replacements from the grout rheology, the unconfined compressive strength (UCS) tests (7 days, 28 days) were performed for the grouting (w/b = 1) and deep mixing (w/b = 1–1.25). The effect of stabilizer on the failure patterns was also examined from specimens of UCS tests. From the experimental work, the rheology of grout mixtures indicated (i) the adequacy of low amount of stabilizer replacements (< 50%); (ii) the dilatant behavior similar to PC; (iii) a decreasing trend of the shear stress, apparent viscosity, yield stress, and plastic viscosity with the increased w/b; (iv) slight to moderate responses of PC mostly; and (v) a potentially favorable rheology of cold-bonded stabilizers (GLD, GBA) for grout flow and workability regarding the yield stress and plastic viscosity. From the strength tests of grout mixtures (0–40%), the GBA additions yielded higher UCS performances for the grouting. For the deep mixing, both the additions of GLD and GBA were found more successful for the strength. The failure planes of UCS specimens were observed independent from the stabilizer types and dosage rates that dominantly failed in axially or near-axial splitting. From the study, the contributions of GLD and GBA from the potential of cold bonding are relatively promising for grouting and deep mixing.
TL;DR: In this paper, the authors investigated the effect of water contents on the strength and deformation of clay-bearing sandstone and proposed a complete constitutive model to predict the stress-strain relationship of the red sandstone.
Abstract: The presence of water has a great influence on the strength and deformation of clay-bearing sandstone. Most of the natural rocks suffer water softening of different saturations. In this study, due to the importance of the clay-bearing rocks in geoengineering practice, red sandstone was chosen to investigate the effect of water contents on the UCS (uniaxial compressive strength), TCS (triaxial compressive strength), BTS (Brazilian tensile strength), PLS (point load strength), and DSS (direct shear strength). The UCS and TCS are linearly decreased as the water saturation increases. When the water saturation increases from 0 to 100%, the UCS and TCS have decreased by about 52.8% and 29.3%, respectively. The BTS, PLS, and DSS are exponentially decreased with increasing water saturation, which have a reduction of about 45.5%, 66.3%, and 49%, respectively. Four typical deformation stages are observed during compression for this red sandstone samples, including an obvious compaction stage. The water saturation does not have any effect on the ratio of the strain on the transition points of these stages to the peak strain, as well as the stress. Besides, a rapid increase of the AE count occurs at the plastic yield point although the cumulative AE count has an obvious decrease trend with increasing the water saturation. Then, considering the effect of water saturation, a complete constitutive model has been proposed to well predict the stress-strain relationship of the red sandstone. The water’s weakening effect on the clay-bearing red sandstone has also been deeply discussed and developed.
TL;DR: In this paper, the authors attempted to improve the shrinkage and swelling potentials of cement-stabilised dredged sediments by addition of fly ash (FA), which satisfied both strength and durability criteria for reuse as road material as set by the Thailand Department of Highways.
Abstract: Dredged river or lake sediments are ideal for repurposing in engineering applications. Unfortunately, the low strength of these materials makes it necessary to amend them with chemical stabilisers before utilisation. This research attempted to improve the shrinkage and swelling potentials of cement-stabilised dredged sediments by addition of fly ash (FA). Material mixtures were created from combinations of sedimentary soil from Phayao Lake in Northern Thailand, Ordinary Portland cement (OPC) type I, and FA. Mechanical tests determined that the unconfined compressive strength of cement-stabilised sediments with 7% and 10% OPC increased with the addition of 25% FA. Digital imaging technology and free swell tests determined that the 3D volumetric shrinkage and swelling of OPC-stabilised sediment reduced by 40% and 2.8%, respectively, when 20% FA was added. With this additional OPC and FA, the treated sediment satisfied both strength and durability criteria for reuse as road material as set by the Thailand Department of Highways.
TL;DR: In this paper, a stochastic framework with a random elasto-plastic finite element-based program coded in MATLAB was provided to evaluate the reliability indices of individual failure modes with considering the inherent uncertainty of real site soil properties and unsaturated state.
Abstract: The stability of excavation in unsaturated soil is closely related to the variation of soil properties and matric suction. Determination of different failure modes and identifying the contribution of each one in an unsaturated soldier-piled excavation are the vital aspects of system reliability analysis. To address these issues, this paper provided a stochastic framework with a random elasto-plastic finite element–based program coded in MATLAB to evaluate the reliability indices of individual failure modes with considering the inherent uncertainty of real site soil properties and unsaturated state. In the next step, the sequential compounding method (SCM) was utilized to obtain the system reliability index by compounding the reliability indices of individual failure modes. Numerical results of a case study showed that in all failure modes, considering unsaturated state not only increases the mean value of factor of safety (FS) but also decreases the related standard deviation, which can be counted as a goal of reliability analysis. Among the reliability indices of the components, the most critical one is attributed to the lateral displacement. Furthermore, the safety ratio concerning the shear force has the maximum reliability index compared to the others. Moreover, based on the coefficient of variation (COV) of the components, it was found that the uncertainty of the soil parameters has the most significant effect on the global safety factor of the excavation.
TL;DR: A 3D slope stability analysis finite element sliding surface stress method program is developed, and the radial basis function network (RBFN) intelligent response surface method is introduced, which has the characteristics of strong adaptability, high fault tolerance, greater flexibility, and strong nonlinearity.
Abstract: At present, there are two problems in 3D slope reliability analysis: (1) the slope stability analysis method; (2) how to effectively extend the reliability analysis method from 2D to 3D slopes. This paper combines the advantages of the finite element method and the limit equilibrium method, develops a 3D slope stability analysis finite element sliding surface stress method program, and introduces the radial basis function network (RBFN) intelligent response surface method, which has the characteristics of strong adaptability, high fault tolerance, greater flexibility, and strong nonlinearity. With the response surface function built for the general framework for an intelligent response surface methodology for the reliability analysis of a 3D slope system, the reliability analysis of a slope is extended from 2D to 3D. The process involves generating samples, creating an intelligent response surface, and calculating the failure probability of the 3D slope system. Through the reliability analysis of typical examples and a comparison with Monte Carlo simulation (MCS) method results, the accuracy, feasibility, and superiority of the proposed intelligent response surface methodology for application to the reliability analysis of a 3D slope system were verified. A comparison with the analysis results of the 3D slope shows that the 2D slope stability calculation is too conservative and seriously overestimates the probability of slope instability. Furthermore, 3D analysis can consider the true stress state of a slope and is able to specify a definite range for a sliding body, thereby providing a basis and reference for determining reinforcement regions.
TL;DR: In this paper, a landslide susceptibility map of Fahliyan sub-basin was provided employing adaptive neuro-fuzzy inference system (ANFIS) in ensemble with the ant colony optimization (ACOR) and differential evolution (DE) algorithms.
Abstract: In this research, landslide susceptibility map of the Fahliyan sub-basin was provided employing adaptive neuro-fuzzy inference system (ANFIS) in ensemble with the ant colony optimization (ACOR) and differential evolution (DE) algorithms. Forty-three out of 61 landslides (70%) were employed to provide landslide susceptibility map and 18 landslides (30%) to validate the models. Thirteen landslide controlling factors including altitude, plan curvature, slope angle, aspect, profile curvature, distance to roads, distance to rivers, distance to faults, rainfall, TWI, SPI, land use, and lithology were employed to provide the map of landslide susceptibility. Weights of every effective factor class and effective factors were calculated based on frequency ratio of landslides relative to the class area and entropy model. The landslide susceptibility maps were generated by the GIS-based algorithms, and the resultant was validated using the training (70%) and test (30%) data of landslide locations for success and prediction rates, respectively. According to the entropy model, distance to road, rainfall, and SPI are the most effective factors on landslide occurrence in the area. The area under the curve (AUC) of ROC for the ANFIS, ANFIS-ACOR, and ANFIS-DE algorithms ranges from 0.845 to 0.946 for success rate curves and 0.793 to 0.924 for prediction rate curves, respectively. Therefore, performances of the analyzed models of landslide susceptibility are good to excellent. The success rate curves suggest that the employed algorithms have high prediction performance, but the success rate curves indicate that the ANFIS-DE algorithm has the best estimation performance (0.946) with respect to the other models.
TL;DR: In this paper, a physical experiment and corresponding numerical model were established to study the trends of the pore water pressure in the rock mass in a seepage channel, and reasonable agreements that would provide a reference for the conditions of high water-pressure disasters in deep buried tunnel construction were obtained.
Abstract: Well-connected seepage channels are the key components of tunnel water inrush. To study the trends of the pore water pressure in the rock mass in a seepage channel, the physical experiment and corresponding numerical model were established. First, in the seepage experiment under excavation disturbance, the propagation rate of the high-pressure water source and the growth rate of the pore water pressure in the rock mass were analyzed by considering the different water pressures. Second, under the same model size, parameters, and working conditions, the finite element method was used to simulate the seepage process of water in the rock mass. From the microlevel, the evolution process of the pore water pressure isosurface was obtained. The results showed that the pressure water head is positively correlated with the pore water pressure in the rock mass, which displays multiple approximate relationships. Moreover, when the water pressure is high, excavation disturbance can significantly increase the pore water pressure in the rock mass. The disturbance caused by the first excavation is larger than the subsequent excavations. In addition, the research results were compared with previous results. Reasonable agreements that would provide a reference for the conditions of high water-pressure disasters in deep buried tunnel construction were obtained.
TL;DR: In this paper, the authors conducted conventional consolidated-drained triaxial shear tests on calcareous sand collected from the South China Sea under different effective confining pressures, and then, they performed multiple sets of repeated loading-unloading tests on the same sand with equivalent physical properties under different deviatoric stress levels.
Abstract: Understanding the mechanical behavior of calcareous sand under repeated loading-unloading is important to engineering design for island-reef underground caverns and pile foundation projects. In this study, we conducted conventional consolidated-drained triaxial shear tests on calcareous sand collected from the South China Sea under different effective confining pressures, and then, we performed multiple sets of triaxial repeated loading-unloading tests on calcareous sands with equivalent physical properties under different deviatoric stress levels and effective confining pressures. Based on the results, we conducted an in-depth investigation of the effects of the loading mode and effective confining pressure on the strain softening behavior and shear strength angle of calcareous sand. We studied the variation in the unloading rebound modulus as the effective confining pressure and deviatoric stress level changed, verified the applicability of the Dunkan-Chang model’s estimation equation for the unloading rebound modulus to calcareous sand, and established the relationship among the volume contraction during unloading, the effective confining pressure, and the deviatoric stress level. The results of this study provide an important basis for selecting appropriate parameters for island-reef construction engineering.
TL;DR: Wang et al. as discussed by the authors investigated the roof leak characteristics and corresponding control technology based on a coal mine in Guizhou province, China, and found that the roof usually collapses when exposed to repeated underground mining; this will potentially lead to the instability of coal wall and even cause serious mining disasters.
Abstract: The roof usually collapses when exposed to the repeated underground mining; this will potentially lead to the instability of coal wall and even cause serious mining disasters. Based on this specific mining hazard, this work investigates the roof leak characteristics and corresponding control technology based on a coal mine in Guizhou province, China. The theoretical analysis, numerical simulation, and physical testing were carried out. By establishing a physical model, the roof structure and roof “pressure” law under repeated mining are studied, and the instable conditions of face-end roof are analyzed, so as to determine the influencing factors of face-end roof instability. By analyzing different roof structures, the working resistance of hydraulic support with stable face-end roof under repeated mining is determined. The leakage of face-end roof under different support working resistance, tip-to-face distance, and surrounding rock strength is simulated, and different methods are proposed to control face-end roof leaks. The results show that in the process of 17# coal seam mining, the roof collapse is serious, the roof pressure is frequent, and the broken roof instability would form the “granular arch” structure. Through the analysis of the roof structure, the tip-to-face distance, the strength of granular arch structure, and the working resistance of the hydraulic support affect the stability of the face-end roof. Using UDEC simulation software, it is obtained that the higher the strength of roof and surrounding rock, the smaller the tip-to-face distance, the more stable the face-end roof is. The prevention measures such as strengthening the broken face-end roof under repeated mining, improving the support strength of the working face hydraulic support and controlling the reasonable tip-to-face distance are put forward. Through field application, the face-end roof leaks have been effectively controlled, which has played a good reference for the prevention and control of face-end roof leaks under repeated mining.
TL;DR: In this article, inversion analysis for the in situ stress field of a valley in the upper reaches of the Lancang River is carried out by using stepwise regression analysis and the FLAC3D numerical simulation, and the temporal and spatial distribution characteristics of the stress are obtained.
Abstract: The in situ stress field in valley areas is an important factor to consider in the construction of hydropower projects in southwest China. Due to intense tectonic movement, the action of gravity, and rapid river erosion, the resulting stress has a complex distribution and a large magnitude. The availability of stress measurements is insufficient to provide adequate understanding of the regional stress state. In this research, inversion analysis for the in situ stress field of a valley in the upper reaches of the Lancang River is carried out by using stepwise regression analysis and the FLAC3D numerical simulation, and the temporal and spatial distribution characteristics of the in situ stress are obtained. Based on those results, the influence of stress unloading effects on slope stability is discussed. The results show that the formation of the modern in situ stress field is the comprehensive result of interactions among gravity, tectonic movement, and river erosion. The reliability of the inverse result can be increased by improving the mesh density of the calculated model and considering multistep river erosion. Under the influence of the unloading effects, tensile fractures were formed and the rock mass loosened near the slope surface. With the presence of bedding dipping into the slope, toppling failure was triggered by the unloading rebound that mainly occurred in the stress relaxation zone.