查看更多>>摘要：A macroscopic model based on a double-porosity approach is proposed to simulate the swelling caused by the subdivision of particles and aggregates that occurs when bentonites are hydrated under a high water content and low confinement. In the model, it is assumed that although the water that occupies this new porous structure can be considered mobile (associated with the macrostructure), its contribution to variations in the energy of the system is similar to that caused by the immobile water that occupies the microstructure. Assuming isothermal conditions, a functional relationship between the increase in the void ratio and the decrease in internal energy was defined from the Clausius-Duhem equation. From this functional relationship, a macroscopic constitutive model was derived to determine the macrostructural swelling as a function of the decrease in the microstructural effective stress. The model was applied to simulate both tests with a large void ratio (up to 50) and processes with a notable variation in salinity (from deionized water to 1 M solution), and satisfactory results were obtained in all cases. This study proposes a simple strategy to incorporate the model into the equations generally used to solve hydro-chemical-mechanical boundary problems at the engineering scale and is thus of direct practical interest.
查看更多>>摘要：The authors have realized that the affiliation for the first author Yao-Jia Cheng, was presented incorrectly. The only correct affiliation that should have been presented in this paper for the first author was the affiliation "School of Earth Sciences and Engineering, Nanjing University".
查看更多>>摘要：? 2022 Elsevier B.V.Volcanic edifices are composed of an assortment of materials with varying mechanical behaviours. The range in mechanical behaviours of these rock materials presents a critical unknown element to volcanic stability assessments. In this study, we explore the deformation behaviour (e.g. uniaxial, triaxial, and tensile deformation behaviour) of volcanic materials from seven geotechnical units associated with a small, shallow intrusion at Pinnacle Ridge, Ruapehu, New Zealand. First, we provide a complete characterisation of the rock masses using field (e.g. rock mass characterisation) and lab (compressive and tensile strength analyses) data for each geotechnical unit. The new data show a range of tensile and triaxial compressive strengths dependent largely on porosity, which is further modified by hydrothermal alteration. More altered rocks are generally weaker (with the exception of the brecciated lava margins) under triaxial conditions. Altered rocks generally transition from brittle to ductile behaviour at lower confining pressure, although this depends on the porosity. Using the stratigraphy and geomorphology of Pinnacle Ridge in conjunction with the rock property data we collect, we then use finite element modelling to depict the deformation behaviour of these units under different pore pressure and seismic conditions. The modelling shows that a relatively minor increase in pore pressure (e.g. < 3 MPa above hydrostatic conditions) is sufficient to change the slope failure type from deep-seated rotational sliding to extensional rupture. The presence of a low-permeability, low-rock mass strength material, even if very localised like a hydrothermal vein, can reduce slope stability by locally increasing pore pressure and providing a weakness plane that facilitates failure. The modelling also shows that a relatively minor increase in pore pressure (e.g. < 6 MPa above hydrostatic conditions) in a shallow hydrothermal system is sufficient to cause localised failure in the material, especially in the hydrothermal vein material. Additionally, the low-permeability hydrothermal vein material can cause pore pressure compartmentalisation, decreasing the strength factor in all materials in the compartment. While Pinnacle Ridge and its associated hydrothermal veins are >1 km from the currently active hydrothermal system, similar veins may be present near active parts of the hydrothermal system at Ruapehu and are an important consideration for future stability models at Ruapehu and other volcanoes.
查看更多>>摘要：? 2022 Elsevier B.V.Rockburst poses a great threat to the construction safety of deep tunnels under high geostress conditions. Recently, numerous deeply buried tunnels have been constructed in China, especially in the Sichuan–Tibet railway area. In this study, two rockburst experiments (strainbursts and impact-induced rockbursts) were conducted under different initial geostresses using the strainburst experimental apparatus and impact-induced rockburst experimental apparatus equipped with an acoustic emission (AE) monitoring system. A video acquisition system was used to capture the rockburst process. The results demonstrated that the rockburst process is similar under different initial geostresses, including grains ejection, rock plates spalling/buckling, and fragments ejecting violently. Based on the result of the AE characteristics, the large- amplitude AE signals were concentrated in the lower frequency band and the rockburst intensity was increased gradually with increase in the initial geostress. The b-value and βt-value fluctuated slightly at first, subsequently increased steadily, and then decreased abruptly when rockburst occurred. Furthermore, the displacement and divergence fields on the specimen surface were calculated using digital image correlation (DIC) technology. The result shows that the zone of large deformation and high divergence is consistent with the rockburst zone. Moreover, 80%σpeak is a critical stress state where rocks begin experiencing slight damage.
查看更多>>摘要：? 2022 Elsevier B.V.High-position rockslides on Tibetan Plateau are usually characterized by multiple in-situ events and multi-period movement. Better understanding on the evolution process of high-position rockslide deposits can help to predict its development trend in the future. In this paper, taking the Chada high-position rockslide-debris avalanche as an example, a series of technical methods, including field investigation, drilling, remote sensing, isotopic dating and engineering geological analogy, are adopted to study the formation and evolution of the Chada gully deposits, and analyze the potential instability range of the jointed rock mass on the slope top. In view of the possible secondary hazards that may be induced by further movement of the top rock masses, the DAN3D software is adopted to simulate the dynamic processes and study the effects on the planning and construction of a railway station near the slope toe. The results show that the formation and evolution of the gully deposits can be divided into 4 periods as follows: 1) At around 43.5 ka BP ago, it was in a period of glacial deposition characterized by moraine deposits. 2) At around 17.5 ka BP, an earthquake induced a rockslide-debris avalanche in the gully. 3) At about 1.0 ka BP, an ice-rock avalanche occurred and formed a layer of purple-reddish boulders with a small thickness. 4) In modern times, during which some small-scale rock collapses were triggered by far-field earthquakes. The results also show that, no matter whether the entrainment effect is considered, the predicted rockslide-debris avalanche deposits cannot fully reach the gully outlet. When the entrainment effect is considered, only a small amount of debris or boulders will roll down and reach the proposed railway station site. Based on the simulation results, some monitoring and protective measures are proposed accordingly.
查看更多>>摘要：? 2022 Elsevier B.V.Moraine soils are widely distributed in the Qinghai-Tibet Plateau. With increased global warming, moraine soil-related geohazards have become increasingly common, posing a serious threat to the infrastructure (e.g., the Sichuan–Tibet Railway) and inhabitants of this region. This paper aims to investigate the mechanical behavior of ice-rich moraine soil in the Tianmo Valley by conducting a series of triaxial constant strain rate (CSR) and coupled thermomechanical (CTM) tests on artificially moraine soil containing different ice forms (crushed ice and block ice). The results show that in general, compared to moraine soil containing crushed ice, moraine soil with block ice has a higher peak strength, a similar internal frictional angle and a considerably larger cohesive strength. The stress–strain curve of the soil containing crushed ice shows a strain-hardening form, while that of the soil containing block ice is represented by a strain-softening model similar to that of dense soil. In the CTM tests, it is revealed that the rising temperature could cause a sharp increase in strain and lead to sample failure, even when the axial load is far below the material's peak strength. A comparison between samples with different ice forms reveal that the soil containing crushed ice is more sensitive to temperature change. The tests demonstrate that the ice form has a significant influence on the mechanical behavior of moraine soil, and the temperature rise can result in a dramatic decrease in soil strength. Therefore, efforts should be made to detect the occurrence form of buried ice and the changes in the environmental temperature as well as the stress state of moraine soil slopes in situ.
查看更多>>摘要：? 2022 Elsevier B.V.This study investigates shear zone development in a coarse-grained soil slope beneath a railway embankment under seismic action. Clarifying the dynamic stress and residual strain responses under different seismic excitations reveals the slope instability mechanism. A typical coarse-grained soil slope under construction of the Sichuan-Tibet Railway Railway was selected for large-scale shaking table model testing. The evolution of slope response parameters (dynamic displacement, acceleration, dynamic strain and residual strain, and dynamic earth pressure) was monitored. The seismic damage modes and resulting deformations of the embankment and slope were analysed. The evolution characteristics of a shear zone were described; the relationship among acceleration, dynamic stress, and dynamic strain was clarified; and the critical state of earthquake-induced slope instability was defined. The main conclusions are as follows: under seismic excitation, the slope slip surface forms mostly near the interface between the sand and breccia layers, and a weakness zone exists between the subgrade and slope surface. Under high-energy seismic excitation (i.e., PGA ≥ 0.4 g), positive peak acceleration is more suitable for assessing the elevation amplification effect. Considering the cumulative strain distribution contour maps, the growth characteristics in the dynamic stress peak area can describe the development of a shear slip zone. Acceleration amplification factors can reflect slope responsiveness, but the energy contained in the seismic waves determines deformation. When the ratio of dynamic to shear stress exceeds 2, the dynamic strain in the slope slip zone increases considerably with shear zone extension and slope instability. With increasing dynamic stress, the growth characteristics of residual strain exhibit stability, transition and failure states.
查看更多>>摘要：? 2022 Elsevier B.V.Fault slip due to resource excavation activities is a potential cause of earthquakes and rockbursts; its fundamental cause is the redistribution of the near-fault stress field. Knowledge of the distribution and evolution of full-field stress around natural faults is crucial to revealing the mechanisms of fault slip. However, natural faults are rough and numerous asperities on their surfaces lead to stress heterogeneity, which makes quantifying the distribution and evolution of near-fault stress challenging. In this study, we explored the distribution and evolution of full-field stress in rough faults using photoelastic analyses of direct shear tests involving three-dimensional printed fault models. The near-fault shear stress and secondary principal stress difference (SPSD) in the printed fault models under various shear loads were quantified, the distribution and evolution characteristics of near-fault stresses were analyzed, and the influences of asperities on near-fault stress evolution were addressed. Our findings indicate that numerous stress concentrations form near the upslope segments of asperities during fault slip. Near-fault shear stress and SPSD present a high similarity in concentrated stress distribution and evolution. It is more effective to characterize the effect of surface asperities on the slip of rough faults using SPSD drops than using shear stress drops. The sequence of local SPSD drops is closely related to the area enveloped by uphill fault slope curves, which facilitates the prediction of earthquake nucleation. Our study provides a basis for characterizing the effects of near-fault stress and surface asperities on the slip of natural rough faults.
查看更多>>摘要：? 2022 Elsevier B.V.Identifying the source of tunnel inrush is essential for its prediction and mitigation. In this work, hydrological, hydrochemical, and isotopic methods were used to identify the source of water inrush into the deep Xiakou tunnel of south China. In addition, a rainfall-runoff model was calibrated to predict its anticipated runoff volume and temporal characteristics. These methods reveal that water inrush in the northern tunnel originates in the Permian-Triassic karst aquifer to the north, and that a groundwater divide exists between two major springs (Xianglong Spring and Xiakou Spring). The southern tunnel also discharges karst water during heavy rainfall conditions, but mainly drains Jurassic fissure water in the dry season. The peak flows, peak times, and recession processes of five inrush events were effectively simulated with our calibrated, rainfall-runoff model. A catchment area of 16.3 km2 was delineated based on the water inrush point identified by optimal model parameters. The catchment analysis shows that about 53% of rainfall recharges into the water inrush point. These methods presented in this study facilitate the estimation of recharge areas in mountainous karst areas and provide a basis for the design of hydraulic structures for the control and mitigation of tunnel inrush.
查看更多>>摘要：? 2022 Elsevier B.V.Most soil-water characteristic curve (SWCC) models contain more than three parameters, but these parameters typically do not have a distinct geometric or physical meaning, or the parameters used are inaccurate because of their high reliance on inverse parameter estimation methods. This phenomenon greatly limits the application of SWCC in the study of mechanical and hydraulic properties of unsaturated soils. To explore the nature of SWCC, this paper reexamines the role of the parameters in the two most commonly used SWCC models from the perspective of the relationship between capillary and adsorbed water. A new and flexible SWCC model (named the MVF model) with four parameters is proposed, which can separate the two different regions by physical constraints on the residual saturation Sr and residual suction ψr. Ten published experimental data sets are compiled to evaluate the performance of the MVF model by comparing it with both the existing models and the experimental data. The MVF model shows excellent performance in terms of goodness of fit, and the fitting parameters are provided with a clear geometric meaning, which helps to establish the connection between the basic properties of the soil and the SWCC. This study consolidates the application and reliable determination of SWCC in estimating the mechanical and hydraulic properties of unsaturated soils.
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