查看更多>>摘要：? 2022 Elsevier B.V.Umbrella-shaped anchors, as new stabilizing structures, have been increasingly adopted in engineering practice due to their simple structure, ease of installation, and high load capacity. Reservoir operation, especially during rapid drawdown, affects the long-term stability of reservoir bank slopes as this process affects the stress, seepage and deformation characteristics of the water-level fluctuation (WLF) zone. Thus, the characteristics of the deformation and failure mode of WLF zones reinforced by umbrella-shaped anchors under rapid drawdown conditions are important for the design and construction of anchoring measures. Five slope-anchor scale models based on the Yingpan landslide were established as transparent soil models considering different slope angles and drawdown rates. Displacement, velocity and macroscopic deformation data were obtained using particle image velocimetry (PIV) technology. The results indicated that the deformation process of both reinforced and unreinforced slopes under rapid drawdown conditions could be divided into four phases: initial, shallow sliding, multisliding and stable phases. In the anchor-reinforced models, loss of soil particles occurred when the water level dropped to reach the anchor heads, causing the anchor plates to loosen and slope deformation to accelerate, especially near the lower row of cables. The anchor heads failed first, and progressive slope sliding ensued. Under rapid drawdown conditions, soil liquefaction and subsequent loosening and sliding occurred, generating a far larger zone of accumulation than the zone of collapse. This indicates that soil liquefaction is another important factor of the link between rapid water level drawdown and slope instability causing local collapses. Combining the experimental results and 47 sets of field monitoring data, it could be concluded that the slope stability decreases with increasing slope angle of the WLF zone. This occurs because a higher water level is needed for deformation initiation in the WLF zone in the case of a higher slope angle.
查看更多>>摘要：? 2022 The AuthorsRoad networks in low and lower-middle income countries (LIC/LMICs) are rapidly expanding to enhance social and economic growth. The construction of a new road often requires cuttings to be made, especially in hilly topography. In LIC/LMICs, many practitioners rely on guidelines to design roadside cuttings, however, some of these guidelines lack accuracy as they are not developed using rigorous stability analysis methods. Stability charts offer a more reliable alternative to some guidelines; however, these are difficult to use in the field. To overcome this gap, we present a new methodology to develop rigorous and user-friendly guidelines for the preliminary design of roadside cuttings. The guidelines are developed using failure criteria commonly employed by practitioners (i.e. Generalised-Hoek-Brown for rock and Mohr-Coulomb for soil) and a rigorous Limit Equilibrium Method, Morgenstern-Price, for stability analyses. In addition, we consider upslope geometric boundary conditions and slope seepage. The guidelines are designed to be user-friendly by including categories with accessible descriptions to characterise the slope material and geometry that can be selected by a practitioner in the field. Then the methodology is showcased by producing new guidelines for the design of road cuttings in Nepal and Ethiopia. We believe the systematic use of guidelines developed following the novel methodology here illustrated will reduce design error, and thus lead to road cuttings of increased life span.
查看更多>>摘要：? 2022 Elsevier B.V.Soil-rock-mixture (SRM) slopes widely exist, and their failure may cause serious damage to infrastructures and endanger human lives. Thus, it is important to study the mechanical behaviors of SRM slopes. Analyzing these behaviors is complicated and typically involves soil-rock-structure interactions. Fortunately, numerical methods can provide adequate descriptions of these behaviors. Discontinuous deformation analysis (DDA) is a powerful method that can be used to simulate the behavior of solid blocks, including rocks and structures. Smoothed particle hydrodynamics (SPH) can effectively simulate the behavior of fluid flows and soil materials. To take advantage of both methods, the coupling of DDA and SPH is investigated in this study, where the coupled DDA-SPH method is used to study the mechanical behaviors of SRM slopes. Two verification tests are investigated to demonstrate the accurate calculation of the interaction force and impact force using the coupled method. A series of simulations are then performed considering different shapes, sizes and contents of rocks and their distributions in SRM slopes. Results show that the deformation of the SRM slope is proportional to the roundness but inversely proportional to the sorting coefficient of the rock blocks. Additionally, the deformation of the SRM slope with rocks distributed along the potential sliding surface is much smaller than that with rocks distributed in the sliding body. In addition, the runout distance of an SRM landslide and the maximum impact force on nearby buildings increase with higher rock contents, which is more destructive to nearby structures and human lives.
查看更多>>摘要：? 2022 Elsevier B.V.Ancient landslides of unknown origin can be found in large numbers in mountainous regions; some represent valid markers of (pre-)historic natural regimes referring to either long-term evolution or short-term peak events of climatic and seismotectonic nature. An example is represented by the Balta rockslide in the Romanian Carpathian Mountains. Its location in the seismically active Vrancea-Buzau region, as well as its morphological features, deep-seated rupture surface and large debris volume, raise the question of its failure history with regard to a possible co-seismic triggering. A 3D volume based reconstruction of the slope morphology together with field measurements of elasto-plastic in-situ rock properties allow to estimate pre-failure conditions of the slope, with special regards to the geological, i.e. flysch bedrock of poor to fair rock quality, and structural settings, i.e. anti-dip slope bedding crossed by the main joint family. The reconstructed slope behaviour was tested under static and dynamic forces with the 3D distinct element code 3DEC, subsequently used to simulate a failure scenario with a 120 s long real earthquake record that leads to the realistic post-failure morphology of Balta. For the latter, we observe a principally joint-controlled failure combined with internal fracturing of the undamaged rock mass. After 230 s of simulated time, the landslide debris reaches the valley bottom with maximum displacements of 1350 m and is marked by a lateral expansion to a broader extent than the source zone width, as observed in the field. Extension of this work to other pre-historic slope failures in the valleys of Vrancea-Buzau yield valuable new information for future seismic hazard estimations of the region.
查看更多>>摘要：? 2022 Elsevier B.V.This paper presents an experimental investigation on eleven loess soils retrieved from NW China to explore the influence of grading and age on soil mechanics. There are overall consistent characteristics in stress-strain relationship and stress paths for the loess tested though detailed property depends on the combination of vi and p0'. The critical state parameters are quantitatively analyzed against the soil properties. The critic state line (CSL) in p' ? q plane is less variable. The M value of specimens tested varies from 1.15 to 1.41 and the corresponding φcs' is between 28.8° and 34.8°, which is not clearly related to the loess grading and plasticity index. In the volumetric plane, the intercept Γ of CSLs varies from 1.63 to 2.17 and the gradient λ of loess fall within a narrow range of λ = 0.08 ± 0.03. The λ linearly increases with the increasing plasticity index Ip. The intercept Γ and gradient λ against grading indices has an overall liner trend, i.e., decrease with the increase of D50 and increase with the increasing Cu and Cc values. The intact loess usually has a higher IB value, roughly between 0.5 and 0.9, indicating a relatively high liquefaction potential.
查看更多>>摘要：? 2022In this study, swelling pressures of MX80 bentonite were determined by different common methods, and the microstructures were investigated by performing mercury intrusion porosimetry (MIP) tests. The obtained results and in-depth analysis allowed the microstructure-based conceptual model to be proposed for the determination of expansive soil swelling pressure. This conceptual model implied that the comparable swelling pressures determined by the swell-under-load (SUL) method, the constant-volume (CV) method, the zero-swell (ZS) method, the pre-swell (PS) method and the Cui's method were attributed to the similar macro (or micro) void ratios (eM or em) generated during hydro-mechanical loadings. The higher swelling pressure with the swell-consolidation (SC) method corresponded to the “extra” pressure that was needed to compress the “extra” macro void ratio eM created during initial swelling under low pressure. However, the swelling pressures determined by the SC method and other methods were expected to be comparable in the case of swelling under high pressure because swelling generated similar eM (or em) in that case. This conceptual model also provided useful information for better understanding of the swelling mechanism involved at microstructure level for expansive soils.
查看更多>>摘要：? 2022 Elsevier B.V.The durability, which refers to the ability of earthen structures to ensure their functionality over time while maintaining their required mechanical performance, is a key issue in evaluating the effectiveness of lime treatment. In this study, the effect of wetting-drying cycles on the compressibility and the microstructure was investigated with lime-treated/untreated samples considering the wetting fluid and the maximum aggregate size (S0.4, Dmax = 0.4 mm; S5, Dmax = 5 mm) effects. Results showed that the wetting-drying cycles caused an increase of void ratio and changed the bi-modal porosity to tri-modal characteristics for the untreated samples, while it led to a reversible variation of void ratio and an unchanged bi-modal pore size distribution characteristics for lime-treated samples, indicating the soil improvement by lime treatment. Thereby, the wetting-drying cycles made the compression curve of untreated samples change from convex to linear shape, while their effect was visible but not significant for the lime-treated soil. Higher decrease of macro-pore void ratio with loading was obtained on the lime-treated samples under wetting-drying cycles compared to the as-compacted samples, indicating a slight softening of soil structure by the wetting-drying cycles. Regarding the effect of wetting fluid nature, synthetic seawater resulted in a higher compressibility than deionised water. This was attributed to the presence of higher quantity of macro-pores in the samples wetted by synthetic seawater induced by the shrinkage of clay fraction. The aggregate size had slight effect on the compressibility of as-compacted samples due to their similar production of cementitious compounds and matric suction. Nevertheless, after wetting-drying cycles, the lime-treated samples S5 had lower decrease of macro-pore void ratio than the lime-treated samples S0.4, due to the significant reduction of macro-pore population with wetting-drying cycles.
查看更多>>摘要：? 2022For the deformation and evaluation of reservoir accumulative landslide, it is of great significance to study the strength characteristics of slip zone soils under rainfall and reservoir operation. In this paper, slip zone soils from Tongjiaping landslide in the Three Gorges Reservoir area is taken as the research case, and the self-developed seepage device matching with the ring-shear test is designed and manufactured. Then, the shear strength of slip zone soils under different seepage-shear conditions is studied to reveal the strength evolution law of riverside landslide. Eventually, the creep characteristics of slip zone soils are described by the Burger model. The experimental results indicate that: (1) the weakening effect of slip zone soils will be induced by the increase of seepage cycles, change amount of seepage pressure, initial and constant seepage pressure, which decrease the residual strength of slip zone soils. (2) When the seepage cycles are <15, the weakening of residual strength of slip zone soils is not obvious. While when the cycles reach 20, the residual strength of soil samples decreases rapidly. (3) The Burger model, which connected the Maxwell model and Kelvin model in series can appropriately reflect the creep characteristics of slip zone soils of Tongjiaping landslide. The research results reveal the weakening law of mechanical strength of slip zone soils under seepage cycles, which provides a basis for the mechanism of accumulative landslide under the fluctuation of reservoir level.
查看更多>>摘要：? 2022Dewatering is mandatory for deep excavations above confined aquifers. Artificial recharge is then commonly used to alleviate the adverse impacts of dewatering. Together, these construction technologies complicate stratum responses including groundwater flow and stratum deformations. This study conducted a coupled hydro-mechanical numerical analysis on a case history of a deep excavation with dewatering and recharge construction measures. The numerical model and input parameters were validated by field data. Results of drawdown distributions, pore pressure variations, vertical effective stress and stratum deformations were analyzed in association with construction activities. It is found that the drawdown of the confined aquifer was closely correlated to dewatering and recharge activities. The excavation-induced settlement mainly occurred in soft soil layers, whereas the stratum deformation induced by dewatering and recharge occurred in the aquifer and adjacent aquitards. The distinct stratum responses could be attributed to different changes in pore pressure and effective stress induced by excavation, dewatering and recharge.
查看更多>>摘要：? 2022 Elsevier B.V.Coral reef limestone (CRL) is a type of biomass limestone formed by reef-building corals and other biological skeletons. Owing to its complex diagenesis environment, CRL consists of a different composition and structural characteristics compared to other homogeneous rocks. In this study, a series of triaxial compression experiments with real-time computerized tomography (CT) scanning revealed the evolution of fracture damage in CRL. The evolution of crack shape characteristics through three-dimensional reconstruction was visually displayed. Moreover, a calculation method for Poisson's ratio was derived using the CT value. Results indicate that the ratio of crack initiation stress to peak stress in CRL ranges from 60% to 75%, and the residual strength after destruction is high. According to the evolution curve of CT value, the triaxial test process was divided into the compression stage I, damage stage II, and destruction stage III. Under the external load, the compaction and damage law of specimens could be characterized using the characteristic parameters of pores as well as the damage variable D. In the CT value-based rock damage constitutive model, the initial damage factor of CRL ranges from 2.95 to 14.78, which is significantly higher than that of homogeneous rocks.
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