查看更多>>摘要：? 2022 Elsevier B.V.Discovering groundwater resources in a fault-controlled aquifer system appears to be a viable solution to water scarcity in the mountainous areas of Taiwan. Regoliths, fractured bedrock, and faults commonly exist in such aquifer systems. To investigate the groundwater behavior in the three subsurface media, a 3-D hybrid model (equivalent porous media/discrete fracture network) involving various in situ investigation techniques (borehole drilling, outcrop investigation, borehole televiewer logging, sonic logging, and downhole hydraulic tests) was proposed to assess the hydraulic properties and groundwater storage of the Dili fault zone of Central Taiwan and its surrounding formations. Subsequently, the model was verified through a case study of a simple fracture network. Based on the validated model, flow path analysis was successfully performed to reveal the hydrogeological role of the fault zone, which acts as a conduit for groundwater flow. To ensure the simulated result regarding the hydraulic properties of the fault zone, this study proposes three additional cross-checking techniques, namely stable water isotopes, derivative plots of pumping test data, and identification of hydraulic gradients. The results of the investigation show that the hydraulic properties of the fault zone obtained by the three approaches are consistent with those determined by the numerical method, and the use of the three cross-checking techniques has been confirmed to be suitable for effectively exploring the hydraulic properties of a fault because the site characterization data are insufficient. Finally, the developed hybrid model was used to calculate the groundwater storage of each geological zone, indicating its great potential for the development of groundwater resources in the study area. Therefore, this study integrates in situ investigation techniques, numerical models, and three evaluation approaches of fault zone hydrogeology to construct a systematic, feasible, and applicable exploration methodology that can be employed for groundwater resource exploration in a fault-dominated aquifer system.
查看更多>>摘要：? 2022 Elsevier B.V.Deep rock tunneling exhibits a significant three-dimensional (3D) space effect. The complex stress path and extrusion deformation during excavation are the most significant and decisive factors in the stability and construction safety of a deep tunnel. 3D and forward numerical analyses based on generalized Zhang–Zhu (GZZ) strength criterion are performed to investigate the principal stress rotation behavior and active control mechanism during deep tunneling. The surrounding rock element experiences significant stress rotations because of the sharply increased shear stress (τry) near the tunnel face. A dimensionless stress index (τry/I1) is proposed to quantitatively evaluate the principal stress rotation during excavation. τry/I1 increases with increasing buried depth, and the deep tunnel presents significant principal stress rotation that reaches a large τry/I1 value. The mechanical behavior of the advanced core rock is primarily affected by the strengthening parameter, geological strength index (GSI). Strengthening of the core rock can greatly improve the stress conditions and mechanical behavior, increase the strength of the rock mass, and reduce the stress rotation. The pre-extrusion deformation of the core rock and pre-convergence of the surrounding rock are discovered to follow a consistency law, which suggests that the pre-convergence deformation and surrounding rock stability near the tunnel face depend on the extrusion deformation of the tunnel face. The GZZ strength-based 3D forward analysis and stress control method proposed in this study can enhance the design and construction of deep and ultra-deep tunnels by weakening the 3D space effect (e.g., tunnel face extrusion and stress rotation) and exerting the strength potential (self-bearing capacity) of a rock mass.
查看更多>>摘要：? 2022 Elsevier B.V.In the mountainous areas passed by the Sichuan–Tibet Railway, rockfall is one of the important geological hazards with characteristics of unpredictable and sudden occurrences. For high and steep slopes, this study employs nap-of-the-object photogrammetry with the characteristic of close flight distance to reconstruct a 3D geological model, which is clear and qualified for discontinuity identification. For the rockfall investigation of areas where unstable blocks are widely distributed, this study proposes a new methodology for 3D rockfall risk statistical analysis to conduct well-directed rockfall simulations and perform a rockfall analysis on a tunnel portal. This methodology first narrows down the rockfall source regions through a field investigation and by slope aspect. Then, the critical source areas that threaten the tunnel portal are determined by preliminary simulation results. Finally, unstable blocks within the critical source areas are interpreted, and well-directed simulations are performed. The rockfall risk analysis on the tunnel portal is conducted on the basis of trajectory distributions and kinematic parameters. This methodology greatly simplifies the rockfall simulation process and reduces the workload of unstable block identification and interpretation. As a consequence, in the Kangyuqu area, several unstable blocks are identified for simulations. Results indicate that rockfalls reaching the tunnel portal have a kinetic energy range of 300–20,000 kJ, a velocity range of 8–30 m/s, and a maximum jump height of 25 m.
查看更多>>摘要：? 2022 Elsevier B.V.We propose a method for evaluating the risks of slope failure induced by heavy rain over a wide area by combining infiltration analysis, surface flow analysis, and slope stability analysis based on three-dimensional limit equilibrium method. The influence of the resolution of terrain data is also examined. To determine rainfall-induced water transportation, we employ an infiltration analysis, using the Green-Ampt model, and a surface flow analysis, using the diffusion wave model. For the slope stability analysis, a three-dimensional arc-slip calculation applying the Hovland method is used. The infiltration depth is obtained from the results of the infiltration analysis, whereas the simulated data are used as input data for the slope stability analysis. A region in Kamaishi City, Iwate Prefecture, Japan, where slope failures were observed during typhoon Hagibis on October 12 and 13, 2019, is selected in this study as the target area and a series of analyses are performed. The topographical survey data by an Unmanned Aerial Vehicle (UAV) observed before and after the typhoon are used to identify the actual collapse locations and compare them with the results of the slope stability analysis. In addition, high-resolution topographic data of the target area using UAV data is created and differences in the factor of safety distribution with and without the UAV data for terrain data are compared and discussed. The obtained results revealed that the proposed method can roughly represent the actual slope failure, which is useful for evaluating rainfall-induced slope failure hazards. The results derived from utilizing detailed terrain data by UAV show the importance of using a high-resolution terrain model for evaluating the stability of microtopography, such as forest roads.
查看更多>>摘要：? 2022 Elsevier B.V.Coal rock water immersion softening is common in coal geology, and it is of great significance to effectively control and utilize the process of water immersion softening and fracturing of coal. In this paper, the progressive failure and softening characteristics of coal samples under localized or full water immersion conditions were determined based on the stress-strain and acoustic emission (AE) response under uniaxial compression, and the obtained characteristics were compared to the properties of the as-received coal as a control. The uniaxial compressive strength, axial stiffness, and softening coefficient of the water-immersed coal samples were reduced compared to those of the control, and the softening degree increased with increasing degree of water immersion. Further, the stress threshold values for crack initiation and crack damage and their ratios to the peak stress decreased with increasing softening degree. The crack damage (CD) point marked the beginning of the unstable propagation of visible fractures and the intense evolution of tensile/shear cracks, accompanied by a rapid increase in the AE counts, regardless of whether the coal had been water-immersed or not. For quantitative characterization and identification of softening characteristics, a new comprehensive index and its softening coefficient are proposed considering the stress threshold and volumetric strain at the CD point, and it is applied to the step-by-step fracturing mechanism of softened coal by hydraulic fracturing. The effective utilization of coal softening and fracturing can avoid the harsh conditions imposed by high-pressure water injection in hydraulic fracturing, which alleviate the dynamic disaster of coal and rock to a certain extent.
查看更多>>摘要：? 2022 Elsevier B.V.This study presents a methodology to integrate two simulation codes, i.e., cohesive element-based numerical manifold method (Co-NMM) and unified pipe network method (UPM), for 2D coupled two-phase seepage-stress analysis of waterflooding processes in fractured rock masses. The Co-NMM is an extension of the numerical manifold method (NMM) and designed for efficiently addressing continuity-discontinuity problems of rock especially complex multiple-fracture propagation, while the UPM is a relatively novel approach for underground seepage analysis with single?/multiphase fluid flow in both fractured and fractured porous reservoirs. To link the Co-NMM and UPM properly, a two-phase seepage-stress coupling model is proposed for considering interactions between the fractured rock mass and two-phase fluids. The mechanical behaviour of the fractured rock mass responds to the variation in skeletal effective stress induced by the average two-phase fluid pressure in both the rock matrix and fractures, including deformation of the rock matrix, change in fracture aperture and the initiation and propagation of fractures. Accordingly, the induced changes in hydraulic behaviours such as the porosity, permeability and capillary pressure are captured by nonlinear stress-dependent coupling functions. Furthermore, an implicit sequential solution is adopted to execute the two solvers, consisting of two iteration loops, i.e., the two-phase flow solving loop and seepage-stress coupling solving loop. The relative performance of the developed 2D hybrid NMM-UPM method is illustrated for four cases related to the waterflooding process in porous and fractured porous mediums.
查看更多>>摘要：? 2022 Elsevier B.V.A full understanding of the interaction mechanisms among flow-like landslides and impacted protection structures is still an open issue. Although several approaches, from experimental to numerical, have been used so far, a thoroughly assessment of the hydromechanical behaviour of the landslide body is achievable only through a multiphase and large deformation approach. This paper firstly proposes a conceptual model for a specific type of protection structure, namely a Deformable Geosynthetics-Reinforced Barrier (DGRB), i.e., an embankment made of coarse-grained soil layers reinforced by geogrids. In such a case, the sliding of the barrier along its base, under the impulsive action of a flow-type landslide, is an important landslide energy dissipation mechanism, and a key issue for the design. Then, two different approaches are proposed: i) an advanced hydro-mechanical numerical model based on Material Point Method is tested in simulating the whole complex landslide-structure interaction mechanisms, ii) an analytical model is set up to deal with the landslide energy dissipation and the kinematics of both the landslide and barrier. The calibration of the proposed analytical model is pursued based on the numerical results. Finally, the analytical model is successfully validated to interpret a large dataset of landslide impact field evidence, for whose interpretation also five empirical methods available in the literature are tested.
查看更多>>摘要：? 2022 Elsevier B.V.It is essential and important for engineering design and maintenance to systematically investigate the physical–mechanical properties of frozen soils. At present, a series of tests have been carried out on frozen silty clay based on improved testing techniques. The results indicate that brittle and plastic failures occur for frozen silty clay under low and high confining pressures, respectively, and strengthening and weakening effects from the water content and confining pressure on the frozen strength are also observed. With the increase in confining pressure or water content, the compressive strength first increases to a maximum and then begins to decrease, and at the same time, the pressure fracturing of pore ice is gradually aggravated. Under the combination of confining pressure and water content, the microstructure evolution of frozen silty clay includes the soil particles or cementing soil crushed and reclotted, the initial soil skeleton destroyed, the pore ice fractured and melted, and the growth of microcracks, which mainly depends on the amount of water content and axial and radial loads. The tearing of cementing soil or sliding of soil particles causes drum-shaped deformation of the sample.
查看更多>>摘要：? 2022 Elsevier B.V.Soil moisture is strongly spatially variable and scale dependent, but there is a lack of research focusing on factors that link soil actual evaporation to the spatial distribution of topsoil moisture at the slope scale. External factors (e.g., meteorological) have similar effects across entire slopes; hence, this paper instead explores the internal factors controlling differential soil actual evaporation. We consider the effects of historical rainfall on soil erosion, and adopt a combined approach encompassing slope investigations, a slope rainfall simulation experiment, slope erosion analyzed by 3D laser terrain scanning, and evaporation experiments. Along the runoff direction, we show that the relative topsoil clay content increases, but slope surface deformation and failure lead to a decrease in the relative content of clay in deposits located on the lower of slope. The original thickness of slope surface decreases in the upper part of the slope, due to particle migration, while the slope surface relatively far away from the upper part of the slope tends to be thicker, due to the accumulation of slope deposits. The actual evaporation of the topsoil relatively far from the upper part of the slope is significantly weaker (63%–72% probability), which may be related to the high clay content, dense soil structure, and high content of clay minerals. The topsoil evaporation also tends to weaken as overburden thickness increases. Here, we suggest that marked differences in the original thickness of the slope surface and in the properties of the topsoil caused by the migration and deposition of soil particles under successive years of rainfall erosion, are important factors controlling differences in topsoil actual evaporation in different parts of the slope. This understanding lays the foundation for the analysis of hydrological processes in different parts of a slope, which is crucial for the study of shallow slope mechanical behavior.
查看更多>>摘要：? 2022 Elsevier B.V.The residual strength of sliding basal soils plays a pivotal role not only in the movement of bedding landslides controlled by clay-rich interlayers but also in remobilized granular deposits. Many studies have focused on better understanding the residual shear behaviors of clayey and granular soils under relatively low shear rates. However, the residual strength varies with various clay fractions for clayey soils and fine-size fractions for granular soils, as well as shear rates (especially in fast ranges) need further examined. In the present research, results of a low- to high-rate continuous ring shear test on a clayey soil and three granular soils at the shear rates ranging from 0.5 to 50.0 mm/s were reported. The clayey soil was remolded from the shear zone soil of a bedding landslide controlled by a clay-rich interlayer with main minerals of illite-smectite, and the granular soils included two silica sands and one mixture of silica sand with fine granite residual soil particles. The results show that saturated clayey soil has an obvious positive shear rate effect on its residual strength after a certain shear rate; the mechanism is the transformation of shear mode, i.e., from sliding shearing to turbulent shearing with the increasing of shear rate. The high clay fraction may promote this transformation of shear mode. In addition, the critical shear rate of the clayey soil that has a positive shear rate dependency of the residual strength (i.e., rate-strengthening) is related to the clay fraction, i.e., a smaller critical shear rate appears in the clayey soil with higher clay fraction. The residual strength of saturated granular soils with different fine-size fractions do not show any shear rate-dependent, while the fine-size fraction affects the residual strength both in drained and undrained conditions; that is, the higher the fine-size fraction is, the lower the residual strength is. Moreover, the neutral shear rate effect of granular soils in this study may be related to the low normal stress and low shear rate range. The authors believe that, results such as those obtained in this work, may be useful for developing a more suitable constitutive model to better understand the postfailure motion (or reactivation kinematics) of bedding landslides controlled by clay-rich interlayers, as well as rock avalanche deposits remobilized by heavy rainfall.
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