Bulletin of Engineering Geology and the Environment最新文献

Geothermal heating and cooling is a new type of building energy-saving technology that utilizes surface geothermal energy, which causes temperature changes in the surrounding geotechnical bodies when it works, and affects the strength characteristics of loess when it is applied in loess areas. To investigate the change in the strength of intact loess under the effect of temperature, this study uses loess in the Xi'an area of China as the main research object and conducts consolidated undrained triaxial shear tests on intact loess at four different temperatures (5 ℃, 20 ℃, 50 ℃ and 70 ℃) to analyze the change law of shear strength of intact loess specimens under varying temperatures. The results show that the stress‒strain curves of loess specimens show strain softening under the effect of different temperatures, while the stress‒strain curves of remodeled loess show strain hardening, and the strength of loess gradually decreases with increasing temperature under the same confining pressure. Based on the binary medium modeling of a geotechnical body, the shear sharing ratio is modified by considering the effect of temperature and confining pressure. The variation in the shear sharing ratio with temperature (T), confining pressure (sigma), parameter m, and structural yield strength (sigma_{s}) is investigated. The strength criterion of intact loess is modified to establish a strength criterion applicable to intact loess under high temperatures, and the strength criterion is verified by indoor test data, which show that the strength criterion has good applicability to intact loess under high-temperature conditions.

Landslide susceptibility evaluation is pivotal for mitigating landslide risk and enhancing early warning systems. Current practices in developing Landslide Susceptibility Mapping (LSM) often overlook the diverse mechanisms of landslides, and traditional machine learning (ML) models lack the capability for autonomous feature learning in landslide contexts. This study proposes a methodology that precedes the application of deep learning algorithms for LSM by classifying landslides and selecting relevant factors based on their deformation mechanisms. In the Zigui-Badong section of the Three Gorges Reservoir area (TGRA), landslides are classified into rock landslides (RL) and soil landslides (SL) based on the geological conditions and historical landslide inventory. A comprehensive evaluation index system, comprising thirteen factors is established. To identify the most pertinent factors for each type of landslide, these factors are ranked according to their contribution to landslide occurrence. For susceptibility assessment, this study introduces a Convolutional Neural Network (CNN) model and benchmarks its performance to traditional ML models including Classification and Regression Trees (CART) and Multilayer Perceptrons (MLP). The efficacy of these models is evaluated using the Receiver Operating Characteristic (ROC) curve and various statistical analysis methods. The findings indicate that LSMs that consider different types of landslides yield more accurate and realistic outcomes. The CNN model outperformes its counterparts, with MLP being the second most effective and CART the least effective. Overall, this study demonstrates the superiority of an LSM approach that accounts for landslide diversity over traditional, monolithic methods.

Bentonite is utilized as a barrier material in high-level nuclear waste repositories due to its superior low permeability and swelling properties. However, its engineering properties are influenced by the chemical composition of the infiltrating pore water during operation. Understanding the effect of salt solution on the mechanical properties of bentonite is crucial for evaluating the performance of buffer and backfill barriers in deep geological repositories for nuclear waste. In this study, various concentrations and types of salt solutions were used to treat Na-bentonite samples, which were then subjected to free swell test, no loading swelling ratio test, Atterberg limits test, compaction test, and analysis of the content of exchangeable cations. The results showed that the content of counterbalance cations changed significantly after the addition of salt solution, and the decrease in free swelling rate increased gradually with the increase of solution concentration. The effect of different types of salt solutions on swelling was primarily determined by the type of cation that governs charge level and hydration capacity. The inhibition of the free swelling rate was stronger for high-concentration low-valence salt solution than that for low-concentration high-valence one. Bentonites undergoing cation exchange exhibited a decreased plasticity index, a decreased maximum dry density, and an increased optimum water content. This was mainly due to the cation exchange that occurred between bentonite layers under the action of the salt solution, which affected the crystal layer structure, double electric layer structure, and intergranular stress. Finally, the van’t Hoff equation was used to quantitatively characterize the differences in swelling in the test results.

Shield tunneling can cause deformation of the interlayer soil. Traditional static methods do not consider the shield dynamic load and the construction influence on the dynamic performance of interlayer soil, resulting in inaccurate results. Therefore, this paper proposes a dynamic analysis method to assess soil deformation. Firstly, the composition and stress state of interlayer soil were monitored on site. Secondly, the dynamic triaxial tests were conducted based on the monitoring results to analyze the soil dynamic characteristics. Then, a dynamic constitutive model of the interlayer soil was constructed, which considers the change of the dynamic performance. Finally, the dynamic effect of shield on soil is simulated based on viscoelastic mechanics, and the dynamic analysis of interlayer soil deformation is realized by three-dimensional finite element method. The results indicate that the interlayer soil near the excavation face is more significantly affected during the crossing stage. Shield construction increases the dynamic strength and dynamic modulus of the interlayer soil, while reducing the damping ratio. The Hardin-Drnevich model and the logarithmic-linear model can well describe the evolution laws of dynamic modulus and dynamic strength. The dynamic analysis method is closer to real construction and has higher prediction accuracy.

A quantitative assessment of the seismic stability of anchored anti-dip slopes is of great importance for the safety of residents and infrastructure in seismically active regions. However, the subject has received relatively little scientific attention globally. This study aims to analyze the dynamic stability of an anchored anti-dip slope during the Ludian earthquake in Yunnan Province, China, a region characterized by active faults and frequent strong earthquakes. The Manhekuan slope located near the Lancang River fault, an active fault in Yunnan Province, was chosen as a case study to propose a method that integrates engineering geological investigations with the discrete element method (DEM). To validate its effectiveness, the proposed method is compared with the pseudo-static method and subsequently applied to optimize the anchorage parameters of the Manhekuan slope. The results indicate that the stability factor achieved by the proposed method is slightly higher than that of the pseudo-static method, showing a 3.6% increase. The proposed method effectively describes the shear evolution characteristics of the anchor cable and its influence on the seismic dynamic stability of the anchored anti-dip slope. The dynamic stability of the Manhekuan slope under the Ludian earthquake is reasonably analyzed using three indices: stability factor, geological body displacement, and anchorage force. This analysis leads to the determination of optimal anchorage parameters for the Manhekuan slope. The findings provide a valuable reference for evaluating the seismic stability of anchored slope engineering in seismically active regions, including the Himalayas.

Assessing the stability and the determining the critical slip surfaces (CSS) represent two significant endeavors concerning 3D seismic landslides. The minimum potential energy method is applied to evaluate the stability, with specific improvements proposed. Specially, the mobilized shear stress on slip surface is derived through the static equilibrium condition on x-axis direction of the sliding mass. The movement trajectory of a landslide (moving direction) is jointly determined by the forces acting on the sliding mass and is equivalent to the vector sum of these forces. Seismic acceleration is characterized using the pseudo-dynamic method, capturing the temporal and spatial variations in seismic forces. By considering the total potential energy of landslide as the objective function, a novel insight for identifying CSS of seismic-induced landslides is developed. A comparison and analysis show that the relative errors between the safety factor(SF) obtained using the proposed method and limit equilibrium method are less than 3%. Results also indicate that the proposed model can effectively determine the location and shape of CSS against 3D seismic landslides. A real case study shows that the proposed method not only accurately evaluates the stability and location of the slip surface of an actual slope but also yields spatial characteristic parameters of the sliding mass that are close to the measured values. Finally, a sensitivity analysis is conducted on several parameters affecting the stability of seismic-induced landslide.

Landslides resulting in complete river blockage have frequently occurred in the Three River Region (TRR) during the geomorphological evolution of the Tibetan Plateau. River-damming landslides occurring in low-relief regions of the TRR have received less attention compared to those in deeply-incised valleys. The 2.5 Mm³ Cuoduoqin rockslide originated from the south-facing hillslope of a southeast-east-trending ridge, leading to complete blockage of the Quzhaqu River. The original failure mainly involves blocky metamorphic limestone and phyllite. The Quzha Lake Fault providing rear rupture and two other groups of joints facilitating sidewise and toe releases are considered predisposing factors contributing to slope instability. Ongoing tectonic uplift and cyclic glaciations are considered preparatory factors, shifting the slope from stable to marginally unstable. A prehistoric earthquake, likely corresponding to an ancient rupture event on the active Nujiang Fault Zone (NJFZ), is deemed as the most probable trigger for this large rock slope failure. The 2D discrete element method (DEM) software UDEC is utilized to analyze the static slope stability and to reproduce the kinematic process of the rockslide. The static analysis indicates that the original rock slope was in equilibrium under natural conditions. The kinematic process can be divided into three phases: initial detachment within seconds after applying seismic load, downslope acceleration after crossing the slope knickpoint, and accumulation after traveling into the valley bottom. This case study, focusing on the development and kinematics of the Cuoduoqin rockslide, can help enhance the understanding of effective risk assessments of landslides in high-altitude and low-relief regions.

The present study aimed to understand the debris flow characteristics in view of frequent extreme rainfall events, expansion of road networks, tourist influx, and population pressure in the NW & Central Himalaya. Notably, majority of the human settlements, roads, bridges, buildings, and even protection measures in the NW & Central Himalaya do not take into consideration such debris flow impact scenario despite a history of debris flow disasters. The Voellmy-Salm rheology dependent dynamic runout simulation method was used to determine the debris flow pressure and velocity regime in 9 debris flow locations belonging to different litho-tectonic conditions. Results revealed that the debris flow pressure and velocity in these 9 studied debris flows might reach up to 3000 kPa and 20 m/s, respectively. The debris flow pressure and velocity of these orders have the potential to damage the protection measures and infrastructures, which have also been observed in other hilly terrains. The sensitivity analysis was carried out at a range of input parameters by considering 729 possible simulations and debris flow pressure and velocity are found to follow relatively better corelation until ~ 250 kPa flow pressure and ~ 15 m/s velocity thresholds. The influence of slope topography on the debris flow characteristics is also observed in the form of amplification of flow pressure and velocity at concave portions. The rapid development of road network in the NW & Central Himalayan region and its subjectivity to potential debris flow risk is also discussed.

Rocks often have a rate effect on mechanical behaviors and exhibit a negative Poisson’s ratio (NPR) effect after being thermally damaged. However, to date, their combined role in mechanical behaviors has not been clarified. This study micromechanically explores the rate and NPR effects on the compressive behaviors of thermal-damaged rocks using the compression-hardening grain-based model (CHGBM) implemented by the Universal Discrete Element Code (UDEC). The original, moderately, and highly thermal-damaged Suizhou granite samples were subjected to unconfined compression tests for calibrating UDEC-CHGBM. With developing thermal damage from the original state, the rock sample decreases in the peak stress and modulus, exhibiting a transition of pre-peak stress-stain relation from the approximately linear to nonlinear, and a transition of Poisson’s ratio from the positive (lateral extension) to negative (lateral contraction). Our UDEC-CHGBM reproduced these experimental phenomena with reasonable accuracy. With increasing strain rates, the peak stress and modulus increase in a power law manner. The dynamic increase factors of the peak stress and modulus also increase with enhancing thermal-damaged degrees. Due to the thermal damage, the grain contact increased in the maximum allowable closure, thus enhancing compression-hardening capacity and nonlinear characteristics, resulting in a promotion of the rate effect. Lateral contraction deformation can reduce the proportion and magnitude of the tensile stress within the sample, and inhibit intergranular microcracking. The NPR effect depends on both the degree of thermal damage and strain rate. We shed light on the synergistic effects of the rate and NPR on macro- to micromechanical behaviors of thermal-damaged rocks.