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In order to clarify the suction characteristics of unsaturated clay under different conditions of water and salt, taking soil in western Jilin province, China as the research object, the suctions (matrix suction and osmotic suction) of samples with different water content, salt type, and salt content were determined by filter paper method. The results indicate that salt type and content have insignificant influence on the matrix suction. With the increase of water content, the matrix suction decreases at different rates in different suction regimes. When water content is constant, the osmotic suction increases with the increase of salt content, and under the condition of a constant salt content, the osmotic suction first increases and then decreases with the increase of ion concentration of the pore water, and can reach tens of MPa. The concept of suction equilibrium water content is proposed. When water content of sample is higher than this value, the magnitude of osmotic suction will always be greater than that of matrix suction. This indicates the necessity to consider osmotic suction in the presence or change of salt in soil. The applicability of the traditional models of matrix suction and osmotic suction in the full suction range of clay is discussed, and it is found that the traditional models cannot make a full explanation to the variation in suction. Based on the experimental data, an improved van Genuchten matrix suction model and an osmotic suction model, transformed by the Planck blackbody radiation formula, are proposed. [ABSTRACT FROM AUTHOR]

At present, the international evaluation method of loess collapsibility only evaluates loess once collapses, but some scholars have found that loess is characterized with the phenomenon of repeated collapsibility under certain conditions. To explore the characteristics of repeated collapsibility of loess and to find a simple and feasible method for evaluating repeated collapsibility of loess, this paper selects soil samples with different water content for repeated compression tests. Loess is a typical structural soil, and its structure is significantly weakened by water and pressure. This paper combines three main parameters influencing the structure of loess to define a comprehensive physical index and explores the relationship between the comprehensive physical index and the structural yield strength of loess under repeated collapsibility. Using the structural yield strength of loess to normalize the compression curve during repeated collapse, a method for evaluating repeated collapsing of loess has been proposed. This method combines the compression index of loess with the basic physical parameters of loess, which is more suitable for evaluating the repeated collapsibility of loess. By comparing the calculation results with the measured results, it was determined that this method has high accuracy. This method was used to calculate the coefficient of collapsibility of Guyuan loess, and the results show that loess with a moisture content of < 17% can collapse twice. [ABSTRACT FROM AUTHOR]

The underground mining roadways are composed of different strata in southern China mining areas. In the rock-coal composite roadways (RCCRs), surrounding rock comprises coal seam and other strata, such as sandstone, mudstone and siltstone. In this paper, a systematic laboratory experimental study was carried out in which uniaxial compressive strength test was used to investigate the reinforcement of fabricated rock-coal composite (RCC) specimens possessing different anchoring (bolting) setups: no bolt, one horizontal bolt in the coal, two horizontal bolts in the coal and one horizontal bolt in the coal together with an inclined bolt crossing the coal-rock interface. The results show that the failure of RCC specimens with no bolts initially occurs in the coal. Bolting improves the mechanical behaviour of the RCC specimens and the level of improvement is related to the number and orientation of the bolts. Using one horizontal bolt in the coal together with a 30° inclined bolt crossing the coal-rock interface results in the highest strength and the most effective reduction of differential deformation of the RCC specimens. Based on the experimental laboratory results, a field study was carried out to demonstrate further the effectiveness of the inclined bolting and anchoring crossing the coal-rock interface in the stress compression zone for restraining the uneven deformation of the RCCR. [ABSTRACT FROM AUTHOR]

This study addresses the challenge of deformation and failure on loess slopes, predominantly triggered by rainfall, by evaluating the efficacy of various slope protective measures. Recognizing the escalating preference for ecological protection techniques, this paper focuses on identifying optimal strategies that align with local rainfall patterns. A comprehensive analysis of loess slopes under diverse rainfall conditions was conducted, encompassing scenarios with prime soil, stabilized soil, and no protection. Utilizing the finite element software ABAQUS, a sophisticated rainfall infiltration slope model was developed and validated against experimental data. The investigation reveals that under low rainfall intensities, the choice of protective material—whether stabilized or prime soil—exerts limited influence on slope pore pressure. In contrast, at higher rainfall intensities, the impact of these protective materials on slope stability becomes significantly more pronounced. [ABSTRACT FROM AUTHOR]

Acid rain has important influences on the physical and mechanical properties of rock as a result of mineral conversion and dissolution of cement. There are clear spatial correlations between the occurrence of slope failure and rainfall pH value in acid-rain areas. Although some fatal landslides have been ascribed to acid rain, those landslides all consisted of sedimentary rocks that generally contained carbonate minerals, which are particularly susceptible to dissolution in acidic conditions. This paper describes the mechanical deterioration of the structural plane based on acid-rain simulation experiments on a slope cut in hard rock along Sichuan provincial highway S211, China. In the experiments, the cohesion and internal friction angle of the structural plane fell to 35.4% and 6.8% of their original values, respectively, and the strength deterioration exhibited a power-law relationship with the exposed area of the rock bridges. Mineralogical and hydrochemical analyses including polarising microscopy, X-ray diffraction, scanning electron microscopy, and inductively coupled plasma optical emission spectrometry were employed to describe the micromechanisms of weakening. Mechanical weakening of the structural plane is attributed to deterioration of both the composition and the structure. Transformation from hard essential minerals to clay minerals through pyroxene chloritisation, plagioclase illitisation, illite smectitisation, and chlorite dissolution reduced the strength properties of rock bridges. In addition, abundant secondary micro-cracks were formed by propagation of worm-like dissolution pits, thus disintegrating rock bridges and further reducing the strength of the structural plane. This paper provides a better understanding of slope failure mechanisms in areas affected by acid rain. [ABSTRACT FROM AUTHOR]

The superelevation phenomenon is common in the movement of debris flows around curves. This paper presents a new method to calculate the superelevation of debris flow when it encounters obstacles in the flow process. The calculation method is based on the Bingham Model for debris flow determination. In this paper, physically significant internal and external roughness coefficients are determined by analysing the internal characteristics and external channel boundary conditions of viscous debris flows in Xiedi gully, China. According to the situation of debris flow passing through the bend, when the debris flow moves to the sidewall of the gully with velocity, the movement state is divided into two parts: radial and normal. One part of the mud rock fluid continues to move in the tangential direction and generates superelevation, and the other part moves in the radial direction and generates upward climbing along the sidewall. Thus, the formula for calculating the superelevation of debris flow bend is derived. Based on the debris flow physical and dynamic parameters, such as density and weight of the debris flow, cohesion, internal friction angle, yield stress and dynamic viscosity of liquid-phase slurry, the reliability of the formula is verified, which provides a theoretical basis for future studies of debris flow disaster prevention and control in similar areas. [ABSTRACT FROM AUTHOR]

The occurrence of rockburst is related to the surrounding rock stress and geological rock mass strength. Rockburst occurs frequently during the construction at a deep tunnel in southwest China (a tunnel with a depth of approximately 2080 m, and a length of 13 km), leading to casualties, damage to construction equipment, and schedule delays. The application of the rockburst criteria based on the stress-strength/strength-stress ratio shows that they are not suitable for the construction stage. This paper suggests a simple and feasible rockburst intensity criterion based on the Geological Strength Index (GSI) for the construction stage. In this criterion, the strength of the rock mass exposed during excavation is estimated by the Hoek-Brown criterion and is used to reflect the geological conditions of the surrounding rock, considering the influences of the joint conditions and engineering disturbance. The maximum principal stress along the tunnel is obtained by the in situ stress inversion. The ratio of the rock mass strength to the maximum principal stress (σcm/σ1) is taken as the evaluation index. The criterion is as follows: σcm/σ1 > 1.2, none rockburst; 0.75 < σcm/σ1 ≤ 1.2, slight rockburst; 0.4 < σcm/σ1 ≤ 0.75, moderate rockburst; and σcm/σ1 ≤ 0.4, intense rockburst. The engineering applications show the reliability of this rockburst intensity criterion. The results of this paper provide a reference for rockburst intensity evaluation during the construction stage of deep tunnels. [ABSTRACT FROM AUTHOR]

The failure of waste slag is a disaster that impacting both environment and lives. In China, there are many waste slags after the engineering projects such as the construction of railway and road. Although the treatment of the waste slags obeys the regulations that the government have established, some accidents still happened. In order to ascertain the reason for the unexpected failure, the inverse analysis is needed to check the initial stability status and the level of potential damage of slag sites. The conventional failure probability of waste slag site is analyzed based on relevant factors that have considerable uncertainty and are difficult to quantify. Therefore, assuming that the failure of slag sites will occur under extreme scenarios, a methodological procedure of risk post-assessment and management under extreme scenarios is proposed in the paper, which indicates that risk management is necessary during the procedure of design, operation, and maintenance of the slag site. In this method, the Tsunami-Squares method was used to simulate the movement process of tailings sand due to the dam failure and generate hazard mapping with the intensity parameters (flow path and thickness). The integrated risk of economic loss, fatalities, and contamination to children and adults was considered in the paper. Following the As Low As Reasonably Possible principle, the F–N diagram was divided into five domains to represent four different risk acceptable conditions, and accordingly, the risk treatment measures were proposed respectively for waste slag sites. A risk management mode of "risk-sharing community" was presented that sparkplugged the representatives of multi-stakeholder to participate in the risk management. The proposed methodological procedure of risk analysis and management could provide effective supports to the decision-making of the design factors and the implementation of stabilization and monitoring of waste slag sites. [ABSTRACT FROM AUTHOR]

The collection of relevant information about the vulnerability of infrastructure damaged by landslides is not an easy task due to the existence of several compounding factors and uncertainties. This makes it difficult to quantitatively estimate their vulnerability to slow-moving landslides. This paper presents a new vulnerability assessment model for masonry buildings on slow-moving landslides based on physical models and field observations. A masonry building model is made of brick and concrete at a scale of 1:10 to physically simulate the damage in structures caused by ground tension cracks commonly developed on slow-moving landslides. The tension crack opening process is simulated through a load-controlled table with an aperture on which the building model is constructed. The strain on the wall and its foundation were measured, and the damage of the model (crack formation and evolution for each loading step) was collected, described, and analyzed. These data were used to develop failure criteria for masonry buildings in rural areas in China in terms of a quantitative vulnerability curve. The quantitative model of vulnerability for masonry structures was established based on fuzzy mathematics and the Weibull function applied on the test data and observations. The vulnerability curve is verified with field cases of masonry buildings damaged by ground tension cracks associated with slow-moving landslides in the Three Gorges Reservoir area. The results support further testing and use of vulnerability curve proposed. [ABSTRACT FROM AUTHOR]

Tunnel excavation in mountainous areas can sometimes reactivate or trigger landslides. The problem of tunneling-induced landslides may be influenced by not only the tunnel location and slope geological conditions but also construction deficiency without timely treatment. This paper presents a case study of Jimei landslide in Sichuan Province, China. This dormant landslide was largely induced by the excavation of a twin tunnel in the landslide body. Field investigation, slope movement monitoring, and numerical simulations show that the formation mechanism of the Jimei landslide triggered by tunneling can be summarized as follows: (1) The adverse geological conditions of stratified sliding mass consists of multilayer sliding surfaces and cracked sliding blocks. (2) The rock surrounding the tunnel underwent large and continuous deformation because of construction deficiency without timely treatment. (3) There was a reduction in the shear strength and increase in the bulk density of the sliding mass because of rainfall infiltration during the rainy season. [ABSTRACT FROM AUTHOR]

Rapid assessment of the distribution of earthquake-triggered landslides is an important component of effective disaster mitigation. The effort should be based on both seismic landslide susceptibility and the ground shaking intensity, which is usually measured by peak ground acceleration (PGA). In this paper, we address this issue by analyzing data from the Mw6.1 2014 Ludian, China earthquake. The Newmark method of rigid-block modeling was applied to calculate the critical acceleration of slopes in the study area, which serve as measurement of slope stability under seismic load. The assessment of earthquake-triggered landslide hazard was conducted by comparing these critical accelerations with the distribution of known PGA values. The study area was classified into zones of five levels of landslide hazard: high, moderate high, moderate, light, and very light. Comparison shows that the resulting landslide hazard zones agree with the actual distribution of earthquake-triggered landslides. Nearly 70% of landslides are located in areas of high and moderately high hazard, which occupy only 17% of the study region. This paper demonstrates that using PGA, combined with the analysis of seismic landslide susceptibility, allows a reliable assessment of earthquake-triggered landslides hazards. This easy-operation mapping method is expected to be helpful in emergency preparedness planning, as well as in seismic landslide hazard zoning. [ABSTRACT FROM AUTHOR]

This paper presents a technique for estimating the geometrical representative elementary volume (REV) of a fractured rock mass based on fracture connectivity. A three-dimensional fracture network model, of dimensions 78 m × 50 m × 50 m, was generated and validated for a granite rock mass using joint data collected from an exploration tunnel at the Songta dam site in southwest China. Two hundred and forty cubic specimens with edge lengths ranging from 1 to 20 m were sampled from the model, and connectivity parameters of each specimen, including the number of intersections per unit volume (C1) and the intersection length per unit volume (L1), were calculated. The REV was determined using the connectivity parameters and a series of statistical tests. The results demonstrate that both the C1- and L1-based REVs are equal to 11 m × 11 m × 11 m. In this work, the volumetric fracture intensity (P32) was also used to calculate the REV for comparison. The REV obtained by P32 is 9 m × 9 m × 9 m, which is smaller than that calculated by C1 and L1. Finally, the geometrical REV for the rock mass by integrating C1, L1, and P32 is 11 m × 11 m × 11 m. [ABSTRACT FROM AUTHOR]

Tamusu mudstone, located in Inner Mongolia, is being recognized to be the potential host formation in deep HLW disposal across China. This paper describes diverse laboratory experiments performed using the fractured Tamusu mudstone, with concern to the study of the combined mechanical and thermal effects on its hydraulic properties, as well as its self-sealing effect. A single rough fracture is generated down the sample diameter direction before the sample's installation. Considering a heating-cooling cycle, the evolution of the samples' hydraulic properties under different stress conditions has been monitored. The hydraulic conductivity is proved to be not only related to the temperature-induced water viscosity and density variation but also the change of stress state. At the same thermal conditions, the increase of confining pressure (or deviatoric stress) may weaken the flow capacity of the fractures and thus reduce the permeability. The non-coincidence for the curve of permeability versus temperature at the heating and cooling stage indicates that the permeability alterations in the fractures are irreversible. Fracture zone changes were observed by X-ray computer tomography (CT) before and after the tests. The self-sealing behavior, which may be beneficial from high confining pressure, was detected for fractured Tamusu mudstone. Morphologies of fracture surfaces were detected by the 3D scanning technique, which shows that the fracture surface roughness, due to the alteration of asperity contacts and void spaces under high stress, may take an important part of the responsibility to the change of permeability. [ABSTRACT FROM AUTHOR]

The high-content salt rock stratum is a highly water-soluble, corrosive, and expansive stratum, and it is extremely difficult to construct tunnels in the stratum. The China-Laos cross-border railway friendship tunnel, which traverses the high-content salt rock stratum, sustained extremely serious damage during the construction. Therefore, studying the mechanisms by which the salt rock stratum tunnels are damaged is the key to ensuring the long-term service of the tunnel. In this paper, a comprehensive method system was used, such as on-site exploration, laboratory tests, and theoretical analysis, to identify the mechanisms by which the tunnels are damaged in the high-content salt rock stratum. Research has indicated that the main component of the rocks that surround the tunnel in the salt rock stratum is rock salt (NaCl and Na2SO4). Excavation in the salt rock stratum is prone to various catastrophes, such as the precipitation of salt crystals on the lining surface, the formation of a cavity at the bottom of the tunnel, cracking of the concrete lining, bulging and cracking of the inverted arch, and serious corrosion of the steel structure. Tunnels in salt rock stratum will undergo physical erosion and physicochemical erosion of the concrete lining in a water environment, and the precipitation of salt crystals and expansion will eventually damage the lining of the structure. Also, due to the accelerated corrosion effect of water and salt on the structure of the lining, cavities occur in the lining in a short time, and this results in a decrease of the bearing capacity. [ABSTRACT FROM AUTHOR]

Landslides are common occurrences along Chinese rail routes. Accordingly, the accurate determination of sliding-surface locations and the underlying causes become critical from the landslide-disaster-management and loss-mitigation viewpoints. In this study, the landslide in the K66 section of the Jiheng Railway (installed in Jinggangshan City, Jiangxi, China) was investigated. The causative factors and characteristics of the landslide were analyzed using geophysical methods as well as drilling and monitoring techniques. The results reveal that a combination of the transient electromagnetic method and electrical resistivity tomography can be used to identify the location of water-rich landslide-prone regions. When combined with the drilling information, these results reveal the tendency of landslide occurrence in regions comprising strongly weathered carbonaceous shale. Moreover, an uneven slope deformation is observed along the railway line. The seepage of surface water into the slope is revealed as the primary cause of landslides. This is because the reduced strength of the strongly weathered carbonaceous shale facilitates the formation of sliding surfaces. This paper presents a comprehensive survey plan for landslides occurring along railway routes. Furthermore, an assessment of the risk of future landslide occurrences in the investigation area is presented, thereby providing an appropriate reference for landslide prevention and loss mitigation. [ABSTRACT FROM AUTHOR]

To overcome the problems existing in the application of the traditional stability control method of the surrounding rock of deep shafts, in this paper, a stability control method for the surrounding rock of deep shafts is presented based on the New Austrian Tunnelling Method (NATM) and the Norwegian Method of Tunnelling (NMT), and a support design method of deep shafts is also proposed. In addition, taking a deep shaft construction project as an example, the support design process of a deep shaft is presented: the engineering geology and in situ stress of the deep shaft are collected and processed to evaluate the rock mass quality with the Q-system, rock mass rating (RMR), and geological strength index (GSI). The strength and deformation parameters of the intact rock are obtained via laboratory tests, and the rock mass mechanical parameters are calculated using the generalized Hoek–Brown method. Then, a variety of support design methods based on rock mass classification systems are applied to determine the primary and permanent support, and the support time is obtained on the basis of a convergence-confinement analysis and engineering experience. A two-dimensional plane-strain model is constructed to analyze and evaluate the safety of the proposed support system, incorporating the major geological discontinuities and non-hydrostatic in situ stress state prior to excavation. [ABSTRACT FROM AUTHOR]

Accurately determining geomechanical parameters and rock mass deformation are key components of slope stability assessment as well as structural design and safe construction. Numerical models are therefore commonly applied to these issues as a component of back analysis, which provides a practical tool for determining geomechanical parameters in rock engineering. Although once quantified, rock mass deformation can also be calculated using an appropriate numerical model, the traditional approaches tend to be time-consuming and cannot be used to accurately determine deformation uncertainty in practical rock engineering. A relevance vector machine (RVM) was adopted in this study to build the complex mapping relationship between geomechanical parameters and slope deformation, while an artificial bee colony (ABC) was also utilized to search for optimal parameters based on the RVM model and displacement monitored in the field. On this basis, both deformation and associated uncertainty can be predicted using this model via the input of determined geomechanical parameters. The method advocated in this paper was then applied to a rock slope at the Longtan hydropower station, China; results demonstrate that the RVM model accurately describes the relationship between geomechanical parameters and displacement increments and can thus be used to predict both deformation and associated uncertainty. [ABSTRACT FROM AUTHOR]

Landslide failure time prediction is considered a challenging issue in landslide research. A significant goal of landslide research is to provide scientific and accurate prediction methods. In this paper, the short-term forecasting of landslides (STFL) model is proposed by analyzing landslide deformation characteristics in a known evolution process. The landslides on the southern slope of the West open pit mine (SSWOPM) in Liaoning province, northeast China, and Huangci in Gansu province, northwest China, were selected as the study cases. After pre-processing, which include eliminating abnormal data (t test), adding missing data (cubic spline interpolation), and smoothing noisy data (Savitzky–Golay filters), the displacement data are assembled to serve as the model's input parameters. The parameters of STFL can be obtained through the Levenberg–Marquardt (LM) algorithm. Using the forecasting criterion, the time of failure of landslides can be predicted and determined. Forecasting results provide evidence that the STFL model can achieve an accurate prediction of landslide displacement (correlation coefficient R2 > 0.99). The forecasting results of the SSWOPM and Huangci landslides indicate that the forecasting failure time of the STFL model is March 10, 2014 and January 31, 1995, respectively, which are near the actual failure time compared with those obtained using the Verhulst model. This finding indicates that the new method has excellent reliability and accuracy in landslide prediction and a robust description of the landslide movement. [ABSTRACT FROM AUTHOR]

The understanding of the initial ground stress field in a deep and long tunnel can help to optimize the support structure design and reduce the occurrence of collapse and other failures in tunnel construction and operation periods. Daxiangling Tunnel is a deep and long tunnel under multiple faults condition, many collapses, rock bursts, and large deformations occurring during construction. This paper presents a study of initial ground stress field regression analysis in Daxiangling Tunnel. A three-dimensional geomechanical model with faults is established first, which satisfies the deformation compatibility equation at the fault location. Then, according to the superposition principle, the distribution of regional stress field under the fault condition is obtained by the method of partition inversion. The results show that the distribution of the ground stress field in the Daxiangling Tunnel areas is mainly tectonic stress. The horizontal stress in the area is greater than the vertical stress, and the extreme value appears at the maximum excavation depth. Owing to fault extrusion shear, the stress relaxation exists in the stratum near the fault. The regression analysis results are generally consistent with the measured results, and the relative error is controlled within 10%. However, owing to the boundary effect of the finite element model, the regression stress values near the tunnel entrance and exit are distorted. This can be corrected by applying a mathematical statistical method to obtain the initial stress field of the Daxiangling tunnels with higher applicability. [ABSTRACT FROM AUTHOR]

The severity and harmfulness of a rockburst event are significantly correlated with the scale of rock mass ejection, especially when the rock mass are not supported. This paper presents a microseismicity-based method for the early estimation of rockburst occurrence and its potential scale, which is graded according to the volume of the rockburst pit (Rv). The establishment of the estimation method involves a rockburst database, a grading scheme of the rockburst scale, selection and clustering analysis of rockburst samples, training of an artificial neural network (ANN) model, and dynamic updating. Firstly, a rockburst database is established from cases that were collected from the tunnels at depths of 1900–2525 m in the Jinping II hydropower station, located in southwest China. A grading scheme regarding the rockburst scale is preliminarily proposed on the basis of statistical analysis. Next, seventy-four rockburst cases, collected in tunnels with microseismic (MS) monitoring from October 2010 to March 2011, are selected as typical rockburst samples by using cluster analysis, and the relationships between the microseismicity and rockburst scale are deeply revealed. Then, three MS parameters, namely, the cumulative number of events, the cumulative energy, and the cumulative apparent volume, are determined and used together as input indicators for the identification of the rockburst scale. The estimation model is trained and cross-validated by the ANN optimized through genetic algorithm (GA). Finally, the performance of this microseismicity-based method has been validated by thirty-one cases that occurred in the tunnels with a cumulative length of 1.85 km, excavated from April 2011 to November 2011. The result indicates that approximately 83.9% of the rockburst cases could be reliably estimated. This study provides a new and feasible method for rockburst scale estimation, which can be used separately or applied as a complementary approach to current prediction methods for risk assessment and management of rockbursts in drill-and-blast tunneling. [ABSTRACT FROM AUTHOR]

The Loess Plateau can be considered as a landslide-prone area in northwest China. The genera consensus about the interaction between landslide deposit and terrace sediments is not well studied; this paper summarised 40 loess landslides in the South Jingyang Platform, Shaanxi Province, China to help understand of this issue. Four of the loess landslides with high mobility have been analysed in detail. Three trenches T1, T2 and T3 dug after the loess landslides LD37, LD11 and LD38 highlighted the landslide-induced changes in geomorphology and internal geometry of geology, respectively. Furthermore, observation of upwards seepage flow on the profile of trench T3 is believed to be the trigger of the high speed, and long runout flowslides in the study area. A newly developed sandbox apparatus is used to reproduce the landslide kinematics due to a mass travelling over an inclined plane. The sandbox experiments show that the sediments are sheared and pushed upwards after the collision with the deposits. The deposits are then wrapped in a space between sediments, which tends to form the 'sandwich' structure. The distal sediments are thrust when the loess deposits' kinetic energy consistently dissipates, developing the accumulated folded strata. These results reveal the deposits' interactions with the sediments in the study area and provide key guideposts regarding prevention and mitigation of loess landslide hazards. [ABSTRACT FROM AUTHOR]

On August 20, 2019, many catastrophic debris flows broke out in meizoseismal area of Wenchuan M s 8.0 earthquake in China under the influence of continuous heavy rainfall. This paper takes the Chutou gully debris flow event occurred on August 20, 2019 as an example. The 3-D numerical simulation software, RAMMS, is used to back calculate the event and predict the future hazard. Coulomb and viscous turbulent friction, μ and ξ are calibrated in RAMMS. Numerical simulation reveals the movement process of Chutou gully from the aspects of flow depth, velocity, discharge, and run-out solid materials volume. The simulation results show that more than two-thirds of the solid materials are still deposited in the main channel, which could provide material basis for the re-occurrence of high hazard debris flow. In addition, based on the intensity and probability of debris flow, the hazard of debris flow is divided into high, middle, and low degrees. According to the simulation results and hazard assessment model, the hazard map of Chutou gully debris flow in various rainstorm return periods (20, 50, 100, and 200 years) is established, which can provide guidance for the future land-use planning and debris flow prevention works. [ABSTRACT FROM AUTHOR]

Tunnels are commonly constructed in loess with a high water content or saturation degree, which can lead to large ground deformation, structural cracking, and even tunnel collapse during construction, in addition to tunnel leaks, sidewall settlement, and frost damage. A complete understanding of the distribution, source, and effects of groundwater in loess is therefore of critical importance, particularly to comprehensively consider loess landforms and material properties and tunnel design and construction practices. This paper presents a review and analysis of previous studies and 27 typical loess tunnels in China, which indicates three different types of water-rich loess surrounding rocks: natural water-rich loess (type I); excavation disturbance-induced water-rich loess (type II); and surface rainfall infiltration water-rich loess (type III). The formation mechanism, seepage field characteristics, and consequent stress and deformation characteristics of the surrounding rock are explained in detail. Key problems, strategies, solutions, and countermeasures are proposed as a helpful reference for theoretical research, design, construction, and maintenance of tunnel engineering in loess. [ABSTRACT FROM AUTHOR]

This paper reports that the geometrical representative elementary volume (REV) of fractured rock masses is anisotropic, and the geometric shape of an REV is of a complex, irregular geometry. A 3D fracture network model of 98 m × 80 m × 80 m was created using the field information collected from tunnel PD254 at the Maji dam site in China. One hundred random cubes of various sizes with the same sampling direction were selected to assess the volumetric fracture intensity (P32). Changing the sampling direction along the dip direction and dip angle at a 10° increment, the REV size of each sampling direction was inferred using the Wald–Wolfowitz runs test and P32 values. The REV sizes of entire rock masses and each fracture set were calculated, and the results indicated that the REV sizes varied with the different sampling directions. The anisotropy ratio and standard deviation were employed to quantify the degree of the anisotropy of REVs. Based on the results, the anisotropy of REVs for fracture set 2 is the most significant, and that of fracture set 3 is the worst. The relationship between the anisotropy of REVs and fracture sets was discussed; one fracture set, two fracture sets, and three fracture sets were selected randomly from these simulated rock masses to evaluate the characteristics of the anisotropy of REVs. The mean value and the anisotropy of REVs increased with the number of fracture sets. The maximum REV size with a sampling direction was selected as an REV for each fracture set. Four cubes with different directions and different sizes were assembled into an irregular geometry. This geometry can represent the geometric shape of the REV of entire rock masses. [ABSTRACT FROM AUTHOR]

Identifying deep-seated toppling failure presents unique challenges for the study of natural slope deformation in mountainous regions. In the absence of an effective quantitative approach, this study aims to provide a comprehensive grading system in order to establish a slope engineering geological model that can evaluate the deformation of a deep-seated metamorphic toppling slope. The toppling slope used in this study, located in Zhala, southwest China, affects a large area with a deformed rock mass of over 2.5 million m3. In order to objectively reflect the intensity of rock mass toppling, the deformation phenomena of this deep-seated toppling slope are first described in detail. Then, a grading index system is proposed to evaluate the degree of toppling deformation. This comprehensive index system includes the dip angle change of the rock strata, tensile cracks, rock mass structure, weathering grade, and longitudinal wave velocity. The toppling slope is divided into four toppling intensity zones: a completely toppled zone, a highly toppled zone, a moderately toppled zone, and an un-toppled zone. The detailed description and subdivision of the degree of deep-seated toppling deformation is the basis of establishing a fine engineering geological model. Different from the previous when the bottom boundary of toppling was considered as the only potential control boundary, this paper reveals that there may be multiple potential control slip zones in the deep-seated toppling slope, and different deformation degree zones correspond to different stability. As an engineering slope, engineering treatment measures can be formulated according to the degree of toppling deformation. [ABSTRACT FROM AUTHOR]

The 1718 great Tongwei earthquake in northwest China caused more than 300 large-scale landslides near the epicenter resulting in more than 70,000 deaths. Although previous studies agree that the earthquake-induced landslides in the area are loess-landslides, which slid along ancient terrain surfaces, there is a dearth of evidence to unravel the actual failure mechanisms of these widely-documented events. To clarify their characteristics and mechanisms, the landslides in Pan'an Town, located in Gansu Province, China were rigorously investigated. The field surveys revealed that the landslides occurred in an area comprising loess deposits of several tens of meters underlain by a basal mudstone layer. It was also revealed that instability in the area is strongly influenced by a river valley with large erosion bank slopes, as well as steep mudstone slopes, which are well developed. The majority of the landslides triggered by the Tongwei earthquake were loess-mudstone composite landslides, with the sliding surface in the deep mudstone. Three huge landslides on the northern mountain located at the river bend of Pan'an Town with a total volume of about 6.06 × 10 m are the main mass movements during the 1718 catastrophe. In addition, by taking the typical landslide named the Weijiawan landslide as a case study, the internal structure of the earthquake-triggered landslides and their stability were studied. The new findings not only aided the unraveling of the failure mechanisms but also provided insights and knowledge on early recognition of earthquake-triggered landslides in northwest China towns, especially in the surrounding valley, which shares similar geological conditions with landslides studied in this paper. [ABSTRACT FROM AUTHOR]

High-intensity coal mining activities in China's western mining area are damaging fragile ecological environments. The key to coordinating ecological protection and coal mining is to understand the law of overlying strata migration in high-intensity mining. However, it is difficult for conventional monitoring methods to efficiently monitor overburden movement in high-intensity mining areas in real time. In this paper, a space-sky-surface (3S) integrated system is proposed to conquer this challenge. This monitoring system consists of three parts: a space monitoring component (a combination of a global navigation satellite system (GNSS) and interferometric synthetic aperture radar (InSAR)), a sky observation component (an unmanned aerial vehicle (UAV) equipped with a measuring camera (MC)), and a surface exploration component (ground-penetrating radar (GPR) and high-density electricity method (HDEM)). This system was successfully applied to the 12,401 longwall face in the Shangwan coal mine (the maximum mining height is 8.8 m). The deformation cloud map of the entire mining area was obtained through InSAR monitoring technology accompanying the 3D laser scanning to improve the accuracy in the local region of 12,401 longwall face. The distribution characteristics and dynamic evolution of surface fractures were obtained using UAV and MC (visible light camera + infrared camera). Using the HDEM and GPR technologies, the fracture development was well detected. Based on the strata movement theory, combined with the monitoring results, a three-dimensional model of overburden rock fracture after 12,401 longwall face mining was constructed. Monitoring results and the fracture model provide a basis for controlling air leakage in the goaf and remediation of surface fracture. [ABSTRACT FROM AUTHOR]

This paper presents an in-depth analysis of the deformation characteristics and reactivation mechanisms of a giant ancient translational landslide in the Three Gorges Reservoir (TGR) based on more than 6 years of monitoring data with the assistance of in situ surveys. The Outang landslide, divided into three active parts, has a total volume of approximately 90 million m3 and slides along weak interlayers (WIs). Since the impoundment, the landslide has been experiencing persistent deformations with some distinct movement signs. The temporal displacements are marked by seasonal cycles of fast displacements in the summer followed by almost imperceptible movements for the remainder of each hydrologic year. The spatial displacement rates gradually increased with the increase in altitude. The primary triggering factors for slope movement could transition from the drawdown of the reservoir water to the periodic rainfall. The affected areas by the former and latter are mainly concentrated in the front part and the upper part of the slope, respectively. The landslide exhibited a composite push-retrogression-type failure evolution with the fluctuating reservoir levels destabilizing rock masses at the front part of the landslide and the precipitation mainly mobilizing materials in the upper part of the slope. Currently, the landslide is in a state of continuous movement. The toe area and upper part of the landslide should receive high priority for the development of preventative measures. [ABSTRACT FROM AUTHOR]

A μ(I) rheology–based avalanche flow model whose governing equations are established in a rectangular Cartesian coordinate system is proposed in this paper. The motivation is updating the term related to gradients of the depth-averaged pressure and extending the application of μ(I) rheology to natural avalanche simulation. The main advantage of the proposed method is that it captures the constitutive properties of the avalanche by introducing the μ(I) rheology. The main novelty of the present model that distinguishes other μ(I) rheology–based approaches is that the in-plane shear is not considered in our model (consistent with the traditional Savage–Hutter theory); thus, the μ(I) rheology only plays a part in describing the normal transverse stresses. Experimental example shows that the proposed model can predict the moving process of granular flow satisfactorily. Simulation of a natural case (the Ermanshan avalanche in China) demonstrates that the simulation can approximately reproduce real avalanches tolerably well. [ABSTRACT FROM AUTHOR]

Most landslides induced by reservoir impoundment and rainfall in the Three Gorges Reservoir area of China are usually characterized by bedding-plane shear zones. This paper presents an experimental study of the interaction between water and shear-zone materials. A series of tests, including wetting-drying cycles and soaking tests, were carried out. The results show that the fluid-solid interaction not only reduces the shear strength of shear-zone soil but also accelerates the disintegration process of clastic rock from shear zone. After the fluid-solid interaction at different pH values, the clastic rock samples produce the most clay minerals in acidic solution. Similarly, the clay minerals of shear-zone soil samples increase dramatically after 45 days of soaking in acidic environment. According to the tests, it is found that the shear-zone soil in eluvium may originate from the weathered clastic rock near the shear zones under long-term fluid-solid interaction. [ABSTRACT FROM AUTHOR]

As a natural foundation and fill material for construction in loess areas, there exists a significant impact on the stability of the engineering construction due to the permeation characteristics of the eolic sediment Malan loess. In this study, a series of air permeability tests were conducted for intact loess and remolded loess by using an improved air permeameter. We determined the influence of the water content, wetting and drying, dry density on the air permeability ka, and the use of microstructure models, scanning electron microscope (SEM) micrographs, and 3D super depth of field microscope micrographs to elucidate the microscopic mechanism of the air permeation. The results show that the air permeability ka of the remolded loess increased with the initial water content of remolding loess at dry density of ρd ≦ 1.6 g/cm3 increase, which is because of the formation of aggregates, and menisci water effect in loess; however, at dry density of ρd > 1.6 g/cm3, the air permeability started to decrease. The ka reduced remarkably as the water content of the intact and remolded loess increased during wetting process, and the air permeability during the drying process was always higher than the air permeability in the wetting process at the same water content. With the increase in the dry density, the air permeability of the remolded loess decreased; from a microstructural perspective, large and round pores tend to be small and elongated and irregular pores at high dry density. This paper will contribute to elucidating air permeability characteristics of loess and reducing the permeation risk in stability of the engineering construction in the Loess Plateau. [ABSTRACT FROM AUTHOR]

The advantages of outstanding economic efficiency and green environmental protection have positioned microbially induced technologies among the most promising reinforcement methods for structural planes. In this work, the enhanced mechanical properties of a weak structural plane at Baihetan Hydropower Station in China are investigated after microbially induced calcium carbonate precipitation. Sporosarcina pasteurii is actively cultured, and a standard curve relating bacteria concentration and optical density is developed. The curves of bacterial growth and urease activity are then investigated. Microbial reinforcement of weak structural plane specimens is conducted. The mechanical properties of weak structural planes are tested after reinforcement, and effects of bacteria concentration on the uniaxial compressive, shear, and triaxial compressive strengths are discussed. Based on XRD, EDS, and SEM analyses, the product of the microbially induced process is found to be calcium carbonate crystals, which measure approximately 5~10 μm. It is observed that the crystals are well grown and distributed around particles in the weak interlayers. These particles are gradually encapsulated by induced crystals and finally cemented with interfaces of the tuff. The results also reveal that maximum increments of 148, 130, 192, and 114% of the uniaxial compressive strength, triaxial compressive strength, cohesion, and friction angle of the rock mass, respectively, can be obtained by adopting the microbially induced reinforcement method. It is expected that this paper can provide theoretical support for the reinforcement of structural planes of rock masses via ecologically green methods that save energy and reduce emissions. [ABSTRACT FROM AUTHOR]

One task facing by the geotechnical engineers is to protect the workspace in an underground construction/excavation site from various forms of geological disasters, such as the water inrush, rock burst, and collapse of the surrounding rock/soil. In this paper, a combined controlling measure was proposed based on underground mining and water environment: the method of strip mining has been initially proposed as an effective measure against underground workspace floor failure when mining above confined aquifer in the Bucun coal mine, China, and however, its ability to avoid floor water inrush has yet to be demonstrated; in the next step, field trials using caving zone backfill technology to prevent underground workspace floor failure and excavate retained strip coal pillars were implemented based on the theoretical calculation and numerical simulation results. Engineering practice showed that the failure depth of the underlying strata of the workspace had no growth without the possibility of water inrush, and the safety of the underground space was achieved. Thus, this study represents a successful attempt to develop the combined strip mining and caving zone backfilling technique to ensure the safety of the underground workspace and control surface subsidence when excavating the retained strip coal pillars above confined aquifer. The proposed combined technique can also be used in other underground excavation activities with similar problems. [ABSTRACT FROM AUTHOR]

When using a Terrestrial 3D laser scanning (TLS) to monitor the mining subsidence in a mining area, the conventional methods are to set up the public target manually, or to set up the ground control network in advance. However, these have the disadvantages of high labor intensity and low efficiency. In order to overcome the shortcomings of the conventional methods, this paper presents the subsidence monitoring method using TLS without a target in the mining area. Feature points are used to splice the multi-station point clouds in the same phase, and a few station coordinates are used to uniformly transform the multiphase data into a geodetic coordinate system. Afterwards, the surface digital elevation model (DEM) is established by using the point clouds after coordinate transformation, and the dynamic subsidence value and subsidence basin during the period of observation are obtained by DEM subtraction. Compared to traditional methods, this method simplifies the field measurement process, reduces the labor intensity, and transfers the main work to the internal industry. It is suitable for surface subsidence monitoring with a harsh external environment and complicated topographic conditions. Surface deformation values are important basic data for mining area subsidence parameters acquisition, mining area environmental assessment, land reclamation, and ecological restoration. As a consequence, it is of great value to popularize and apply in mining area for subsidence monitoring. [ABSTRACT FROM AUTHOR]

Mining extremely thick coal seams under layer of loose unconsolidated Cenozoic alluvium is common in north China. However, this may cause serious consequences including breaking down workface, submerging equipment, even serious flooding accident and casualties, because there is an alluvium aquifer composed of sand, clay, and gravels directly overlying above coal seams. Formulating preventive and control measures in advance is extremely important to a mine. In this paper, case study of water and sand inrush prevention is taken in Xiexin coal mine. A 15.5-m thick coal seam is threatened by unconsolidated Cenozoic alluvium water hazard during mining. By the research and exploitation of hydrological characteristics and strata lithology of unconsolidated Cenozoic alluvium, the lowermost layer in some areas is the layer of clay with good water resistance, and part of areas is permeable water-bearing sand mixed with gravel belonging to weak aquifer, which provide an advantageous condition to possibly set and optimally design sand-proof and caved-proof pillars. Considering its geological and hydrogeological characteristics, slice long-wall mining technology which extracts thick coal seams from top to bottom by dividing it into two slices is employed. Based on observations carried out in the field and physical model testing in the lab, strata failures induced by slice long-wall mining were investigated. The study indicated that the maximum height of the caved zone for upper slice was about 5.62 times of the upper slice mining height and the comprehensive height of the caved zone for two slices was about 4.71 times of the total mining height of two slices. The height of caved zone derived from physical model testing was consistent with the height obtained from field measurements. According to the hydrogeology of alluvium, overlying strata lithology, and mining conditions, the optimal design of sand-proof pillar at areas with weak water rich aquifer, and caved-proof pillar at areas with the lowermost layer of clay for workface 1702, workface 1704, and workface 1706 were given for safe production. The optimal design and technique measures, such as slice mining and reducing the thickness of extractions within the upper or lower slice, were successfully practiced. Overall, the conclusions are of engineering significance for coal mines suffering from water and sand inrush of unconsolidated Cenozoic alluvium. [ABSTRACT FROM AUTHOR]

To mitigate potential damage from debris flows, numerous check dams have been constructed in thousands of debris flow gullies all over the world. However, the efficiencies of these check dams are largely unknown because they are normally designed based on empirical methods. This paper presents an assessment of the impeding effect of check dams constructed in the Hongchun debris flow gully in Sichuan Province, China by using an improved finite difference model. Compared with other models, the improved model can consider both the impeding effect of check dams and bed entrainment. We analyzed the impeding effect of these check dams on different initial scales of debris flows. The results show that these check dams perform quite well in constraining bed entrainment downstream of the gully. The average velocity, peak discharge, and final scale of a debris flow in the gully can be substantially reduced by constructed check dams. The impeding effect is sufficient when the initial volume of the debris flow is less than 1.5 times that of the catastrophic debris flow event that occurred in this gully on 14 August 2010. This study improves our understanding of the influence of check dams on the dynamic and bed entrainment processes of debris flows. The model adopted in this study can be a robust tool to quantify the efficiencies of existing check dams and provide reasonable guidance in the design of check dams in debris flow gullies. [ABSTRACT FROM AUTHOR]

The Geological Strength Index (GSI) is an important parameter for estimating rock mass properties and can be estimated either through direct observations or by using a quantitative GSI chart or equations. This study aims to discuss the applicability of the RMR89 method and the latest version of GSI|2013 by applying them to a case study and to the data published in the earlier papers. The relevant rock mass properties, including blockiness and discontinuity conditions, of the walls of 15 exploratory adits with a total length longer than 1100 m in a hydropower project in China have been assessed to provide data for the analysis. In addition, a repeat analysis of the earlier published data has been conducted to validate the results derived from the case study. The results show that the GSI values calculated with the RMR89 are generally larger than those obtained from the qualitative GSI chart, with an average magnitude of about five. The GSI values predicted from the values of JCond89 and RQD are consistent with those derived through the qualitative observational method for a medium-quality rock mass but are relatively smaller or larger for a poor-quality (i.e., GSI<45) or a high-quality (i.e. GSI>65) rock mass, respectively. By comparing the results of the RMR89 method and the qualitative GSI chart method and analyzing the classification factors considered by the two methods, two new equations based on the RMR89 system have been developed for estimating the GSI. Their application to the case study and the published data prove that these two equations have higher predictive accuracy than the original RMR89 method and the latest version of GSI|2013. It is expected that the acquisition of more engineering examples will enable the two formulas to be further verified and improved. [ABSTRACT FROM AUTHOR]

Quantitative estimation of rill erosion research plays a significant role in the understanding of rill formation and their development mechanisms, which is lacking presently. In this paper, rill erosion is quantified to analyze and evaluate the spatial and temporal distribution in typical gully heads of the Loess Plateau of China. Although several studies have carried rill erosion quantification, the variability analysis of rill erosion rates at different slope position is limited primarily because of the unavailability of high resolution elevation models. Using the low-altitude photography with Unmanned Aerial Vehicles (UAVs), digital surface models (DSMs) with centimeter accuracy were generated, and then geometrical parameters of a total of 1,129 rills at tableland-slope (T-S), hillslope (S), and slopes affected by artificial vegetation (SV) in the study were counted. Then, spatial and temporal development as well as erosion rates of the rills at the three sites were compared. Although many studies revealed the erosion law at the S position, few studies have linked the development of rills at the T-S position, and artificial afforestation at the SV position exacerbates the rill erosion. Furthermore, based on the centimeter-resolution DSMs obtained by the two-stage UAV photography, we found that the slope gradient which was the most susceptible to rill erosion were 5-10°, 35-50°, and 65-80° at T-S, S and SV sites, respectively. At the SV, rill incision was the most sensitive to slope changes, and rill incision potential proved to be the greatest. Generally, the higher the rill erosion depth, the smaller the frequency of occurrence, but this trend was mitigated at the SV position. Therefore, urgent action is needed to control rill erosion caused by artificial afforestation on hillslopes to alleviate and eliminate the adverse effects of vegetation planting on rill erosion on the Loess Plateau of China. [ABSTRACT FROM AUTHOR]

A loess dam is not fully compacted, so there may be a high permeability area in a loess dam. The seepage channel appears inside the dam body, and osmosis damage occurs; these events cause the dam body to be unstable and destroyed. In this paper, the loess dam in the Ansai Area, Yan'an, Shaanxi Province, China, is used as an example monitoring target, and the whole life cycle of the dam is monitored by measuring cracks, liquid level and pore pressure. The timeline regarding multiple instances of damage during the period is used as the basis for subdividing the whole life cycle, and dam damage types are distinguished according to the internal factors and external conditions. By analysing the on-site monitoring data, the dam experienced three obvious types of damage from the onset of monitoring until the dam broke. The triggering factors of the three damage types differ. One factor type is the difference in liquid levels on the two sides of the dam and the seepage channel that is then formed inside the dam. The fine-grained soil in the dam is removed from the seepage channel under the action of hydrodynamic force, the soil at the foot of the dam slope tends to be saturated under the action of osmotic water and the shear strength of the dam slope is reduced. When the soil weight of the upper soil is greater than the shear strength of the soil at the foot of the dam, the first damage type occurs; therefore, it is called "internal erosion damage". The second type of damage is attributed to the softening of the dam feet under immersion by rainwater, resulting in the dam collapse; it is called "slumping damage". The third type of damage is due to the infiltration of rainwater through a crack at the top of the dam. The soil at the top of the dam slides along the rainwater intrusion surface, and the width of the dam top is continuously decreased until it completely disappears; therefore, it is called "slippery damage". On that basis, the loess dam failure modes are proposed due to the difference in hydrodynamic forces on the two sides of the dam and formation of a seepage channel. The fine-grained soil is removed from the seepage channel under the action of hydrodynamic force. The seepage channel is continuously expanded, the soil at the foot of the dam is saturated under the action of seepage water, the soil shear strength is reduced, the dam body becomes unstable and the width of the dam crest is decreased. Under the joint action of infiltration and rainfall, the dam begins the next round of infiltration and erosion and the width of the dam roof continues to decrease. The cycle continues as the width of the dam roof is continuously reduced until overtopping occurs. [ABSTRACT FROM AUTHOR]

Uncertainty in the locations where rockbursts may occur with respect to a tunnel cross-section greatly increases the difficulty in monitoring and providing warnings of rockbursts and mitigating their effects. In this paper, we analyze the characteristics of 40 rockbursts that occurred in a railway tunnel in China. The rockbursts are divided into three cases depending on their position with respect to the tunnel cross-section and the prevailing geological conditions. An in situ microseismic (MS) monitoring system was established to determine the likely position of rockbursts with respect to tunnel cross-sections. The spatiotemporal evolution of the MS events that occurred during the development of rockbursts belonging to the three cases was subsequently obtained. The mechanism responsible for the changing positions of rockbursts with respect to tunnel cross-sections was further elucidated by analyzing the fracture type of the MS events and conducting numerical simulations using three-dimensional distinct element code (3DEC). Finally, support schemes, based on the monitoring and simulation results, are suggested. [ABSTRACT FROM AUTHOR]

Pipeline laying optimization should consider not only the construction cost but also the maintenance cost. However, how to consider the maintenance cost in the early stage of pipeline laying is not fully clear and lacks in-depth research. In this paper, a classification system for pipelaying methods was proposed in terms of the spatial relations between pipeline and its site geomorphology as well as construction methods. A detailed statistic for both development and distribution of geohazards and pipelaying method of the Zhongxian-Wuhan gas pipeline was conducted on the basis of field investigations. With the statistics results, the correlations of pipeline laying methods, geohazard development was studied, and the results showed the geohazard development and distribution vary with different pipeline laying methods. In addition, the construction costs and maintenance costs of various pipelaying methods were estimated. Significant differences in the construction and maintenance cost were observed for different pipeline laying methods. From the perspective of engineering practice, the construction cost and long-term maintenance cost must be synthetically considered in the early stage of pipeline laying in the high geohazard risk areas. [ABSTRACT FROM AUTHOR]

Double-row stabilizing piles are widely used to stabilize large-scale landslides. The construction process of double-row stabilizing piles is often accompanied by constructional time delay (CTD), which is defined as the time interval between the installation of front-row and rear-row stabilizing piles. The CTD is often selected based on the designer's experience and the construction arrangement due to the lack of design guidelines for double-row stabilizing piles. In this paper, the CTD is considered as a design parameter and optimized based on the robust design concept. The signal-to-noise ratio, which is a function of the mean and standard deviation of factors of safety (FOS) of the stabilizing piles, is used as a measure of the design robustness. The FOS of the double-row stabilizing piles are computed using an analytical model that considers the CTD. A framework based on the concept of robust design is proposed for determining the most preferred CTD considering multiple objectives, including safety, cost, and design robustness. This framework is illustrated with a case study, the Hongyan landslide project, Taizhou, Zhejiang, China. Based on the outcome of this study, the most preferred CTD is obtained. [ABSTRACT FROM AUTHOR]

The pentagonal prism is the dominant structural shape in the columnar jointed rock mass (CJRM) structure, and its anisotropic mechanical properties are crucial for engineering safety. In this paper, we propose an anisotropic constitutive model to accurately describe the anisotropic behavior of the CJRM. First, a generalized model of a pentagonal prism column with variable angle θ was established according to the basic structural features of the CJRM. Based on this model, the constitutive relationship space was derived in three dimensions and then improved through analysis of the influence of the inner disturbed belt and coordinate deflection. Subsequently, considering the CJRM at the Baihetan Hydropower Station in China, we determined the optimal value of θ using one set of in situ test results, thereby obtaining the constitutive relationship for this structure. Finally, the optimal constitutive model of the pentagonal prism was verified by the remaining test results, and its anisotropic characteristics were compared with the existing quadrangular and hexagonal prism constitutive models. The results revealed that the calculated elastic parameters of the pentagonal prism model are in good agreement with the test results and that the curve of the horizontal elastic modulus is approximately circular, which reflects the quasi-transverse isotropy of the proposed model. We found that the calculated results of the three models exhibit different deviations from the test results, owing to the different structural characteristics, and that the deviation in the pentagonal prism model is the smallest. [ABSTRACT FROM AUTHOR]

Landslides are one of the most common geological hazards in many parts of the world, which have brought catastrophic consequences to mankind. Seismic shaking can be an important trigger factor generally resulting in large-scale landslides. For some paleolandslides triggered by earthquakes, despite the lack of historical records, certain paleoseismic parameters can be back-analyzed. In this paper, the discrete element method (DEM) was applied to back-analyze the peak ground acceleration (PGA) triggering the Tahman landslide, a paleolandslide located in eastern Pamir, northwest China. Firstly, detailed field geological and geomorphological investigation was conducted to reveal the natural and seismic characteristics of the landslide. Subsequently, discrete element modeling was carried out. Simulation results suggested that the Tahman rock slope was stable under natural conditions. Owing to arid climate and water shortage of the study area, the influence of water was ignored. Additionally, from the perspective of the occurrence time of the landslide and geomorphologic feature of the deposits, the landslide was not caused by glacier activity and freeze–thaw events, and thus, must have been triggered by an earthquake. A peak ground acceleration (PGA) of 0.55 g was found to be a critical value for triggering landslides, and a PGA of 0.76 g could best simulate the kinematic process of a landslide when the simulation results were calibrated against the current geomorphological features of the landslide deposits. It can be concluded from the present study that: (1) PGA amplification in the rock slope was related to the topography during earthquake excitation; (2) the effective duration of the seismic wave had a considerable impact on the back-analyzed PGA, which decreased with increasing effective duration; and (3) the long runout of the Tahman landslide was due to its large volume and the interaction of the slide mass with moraines. [ABSTRACT FROM AUTHOR]

This paper evaluates the weathering behavior and weathering degree of basalt from the Wudalianchi UNESCO Global Geopark in the north-east of China. The geopark possesses the most typical and perfect geoheritage examples of a modern volcanic eruption activities in China. Laboratory experiments were conducted on basalt samples to simulate basalt's weathering process under different environmental conditions. The basalt samples were subjected to either 10 rain cycles or 375 heat-cool cycles. After different numbers of cycles, the weight loss, ultrasonic velocity, and 3D surface morphology were quantitatively evaluated. All the treatments led to sample weight loss. However, the different factors (i.e., water and temperature) result in different degrees and patterns of basalt weathering. In the rain cycles, the sample surfaces became smoother, but new pores were detected. The coupled effects of the mechanical erosion by rain and the tensile stress generated by water invasion and air escape are considered the primary mechanism of grain detachment from the sample surface. In the heat-cool cycles, the sample surfaces became rougher, and the sample's mechanical properties display a decreasing trend with an increase in heat-cool cycles. Thermally-induced stress led to grain detachment in the sample surface and internal particle dislocation, which initiates internal cracks. The experimental results have direct significance for the protection of basalt in the Wudalianchi UNESCO Global Geopark. [ABSTRACT FROM AUTHOR]

Loess tunnel erosion is a distinctive soil erosion pattern that commonly occurs in collapsible loess areas. The resulting soil erosion is a serious and complex problem. At present, most of the research methods on loess tunnel erosion are based on field investigation, and the knowledge obtained is, therefore, mostly qualitative. Erosion characteristics and erosion rates of loess tunnels are rarely revealed quantitatively by laboratory physical modeling or field investigation. In this paper, we report the results of a small model test based on three types of archetypal geological structures that are recognized by field investigation, i.e., vertical fractures, horizontal fractures, and round holes, These results reveal the effect of different initial flow cross sections on the erosion characteristics of loess tunnels. We found that, where water crosses an area of loess, waterfalls dominate initial erosion. We also studied the mud erosion rate to quantitatively reveal tunnel-erosion rates and their variation with time and found that tunnel erosion occurs in three stages: a rapid-erosion stage, an erosion slow-down stage, and a slow uniform-erosion stage. Using a model test to undertake quantitative studies into the relationship between the erosion rate of a loess tunnel and both initial dry density and initial water content, we demonstrated a significant linear negative correlation between these parameters. Through physical simulations combined with field investigation and analysis of survey results, we found that the erosion of loess tunnels occurs with a certain periodicity and that the tunnel-erosion base level plays a decisive role in the erosional features and final morphology of loess tunnels. By increasing our understanding of the internal mechanisms of loess tunnel erosion, our work will contribute to the prevention of cave erosion and reduction in the risks of associated disasters in the Loess Plateau of the Yellow River in China and in other loess-containing areas around the world. Our studies also provide a theoretical basis for carrying out soil and water conservation work in similar areas. [ABSTRACT FROM AUTHOR]

Large squeezing deformation has always been a critical concern in the construction of deep-buried tunnels in soft-weak rock masses. This paper describes a case study on the large deformation mechanism and supporting method of the Maoxian tunnel in Sichuan Province, China, which is located in the core area influenced by the 2008 Wenchuan earthquake and suffered severe large deformation in broken phyllite under high geo-stress. Through a survey on the geological features, the deformation mechanism of surrounding rock and the failure characteristics of supporting structures of the Maoxian tunnel in F1 fault zone were studied. It was found that the occurrence of large deformation was due to the combined action of the high geo-stress and poor self-stability of carbonaceous phyllite. In order to control the squeezing deformation, single and double primary support methods were adopted in succession. A comparative field test was conducted to study their supporting mechanism and mechanical behavior in terms of surrounding rock pressure, internal stress of the steel arch, and axial force and bending moment of the secondary lining. The results revealed that the single primary support method cannot ensure the long-term safety of the tunnel, since many cracks in concrete occurred after about 180 days. The double primary support method, however, was able to control the large deformation and rheological effects of broken phyllite under high geo-stress effectively. [ABSTRACT FROM AUTHOR]

The influence of mining activities on groundwater quality is a growing concern due to highly toxic metals in the tailings. Carbonate rocks are common in the surrounding rocks of ore deposits. But such mining districts generally do not have the conditions to construct traditional tailings impoundments due to the different degrees of karstification. This paper utilises field investigations, chemical analyses, and permeability tests, etc. to study the effect of tailings impoundments on the underlying karst water systems in the Gejiu world-class Sn-polymetallic mine located in a typical karst region in southern China, with samples collected from both karst springs deriving from the mining area and tailings porewater. Because of the abundance of sulphide minerals in the ores, acid mine drainage is expected to pose a high risk. However, the results indicate that the tailings porewater is moderately neutral and is characterized by the SO4–Ca–Mg hydrochemical type. This can be attributed to the substantial buffering capacity of carbonate minerals. Pollution elements in the tailings porewater mainly include SO42− and toxic metals including As, Cd, Mn, Pb, and Hg. The type of pollution factors and the degree of contamination are not consistent in the different tailings impoundments. The hydrochemical classification of four karst springs distributed in the south of the mining area is HCO3–Ca–Mg. The concentrations of SO42− and the toxic constituents in the springs are far below the national standards for drinking water. The spring water not being contaminated may be attributed to the operation mode of the tailings impoundments (peripheral discharge and reuse of ponded water), the residual clay between the tailings impoundments and the carbonate bedrocks and the sufficient buffering capacity of the underlying karst systems. The tailings disposal at the Gejiu tin mine within the natural karst depressions is able to provide a reference for the operation of karst mines in China and elsewhere. [ABSTRACT FROM AUTHOR]

The structural, physical and morphological characteristics of loess will change as a result of the dissolution of mineral components, mainly carbonate, when it is exposed to acid rain, industrial acid leakage or other acidic environments. This study investigates the physical and structural characteristics of the Malan loess, Xi'an area, China, after carbonate dissolution. The presence of carbonate is determined by scanning electron microscopy (SEM)/energy-dispersive X-ray (EDX) and X-ray diffraction (XRD) analysis. The loess was soaked with 0.2 mol/L acetic acid. The degree of degradation of the loess, carbonate and other minerals was determined by the abundances of elements in the solution. Microstructural analysis combined with the loess characteristics of adsorption, water stability, compressive yield stress and shear strength are used to explain the changes in the soil structure after carbonate dissolution. The results show that bonds in the cementation are irreversibly lost during the remoulding process, and additional bonds are destroyed with the removal of large amounts of carbonate, causing the skeletal particle surface area, specific surface area, adsorption capacity and water stability to decrease. The compressive yield stress and cohesion of the soil are considerably more sensitive at higher water contents. Calcium carbonate is the main carbonate component in the loess, and the secondary calcium carbonate connects the skeletal particles by coating and bridging; the strong cementation stops the particles from dispersing in water. The change in strength and deformation of the soil change its microstructure, which indicates that the secondary calcium carbonate affects the soil structure and stability by reducing the aggregate wettability and changing the mechanical strength of the soil aggregate. This paper will contribute to elucidating the formation and destruction of loess. [ABSTRACT FROM AUTHOR]

Based on the rock mass quality classification, this paper proposes a new prediction formula for the attenuation parameters of blasting vibration velocity in jointed rock masses. A parametric sensitivity study is also conducted while considering a variety of influence factors, including joint angle, joint spacing, and joint stiffness. Compared to the existing blast-related standard in China, in which the attenuation parameters are merely derived from rock hardness, without considering the joint characteristics of rock masses, the proposed prediction formula is proved to be a more promising approach to carry out accurate blasting design and blasting safety assessment. [ABSTRACT FROM AUTHOR]