查看更多>>摘要：? 2022 Elsevier B.V.Heifangtai terrace is famous in China for its irrigation-induced loess landslides. The frequently recurring loess flowslides initiated along the platform margin of the irrigated Heifangtai terrace have caused 42 fatalities and significant economic losses due to their long-runout and high-speed mobility. Yet it is still unclear if the recurring loess flowslides almost always initiate in the same places, and their initiated conditions and subsequent mobility behaviors have not been fully evaluated. To better understand such under-researched questions, we selected three typically recurring loess flowslides on the Heifangtai irrigated area. We performed multiple geophysical surveys using electrical resistivity tomography (ERT) and multichannel analysis of surface waves (MASW). We tested water content, density, and strength of loess using in-situ profile sampling. In addition, we examined the steady-state shear behaviors of saturated loess utilizing a ring shear apparatus under undrained conditions. The geophysical signatures and in-situ loess property profiles showed that hydrogeological conditions are crucial to initiating the recurring loess flowslides. The results also demonstrated that the shear liquefaction behavior of saturated loess controls the mobility after the failure of the loess flowslides. Liquefaction potential was assessed based on a chart showing the liquidity and plasticity index, pore pressure ratio, and steady-state line, which were developed as new criteria of liquefaction susceptibility assessment. The novel criteria essentially contain general information about fine-grained soil's nature, state, and behavior. These findings provide a better understanding of the dynamic mechanisms of the loess flowslides and their implications for landslide hazard mitigation.
查看更多>>摘要：? 2022 Elsevier B.V.The Authors have presented an interesting paper (Hrubesova et al., 2020), which aims (in part) to validate the Moharjerani (1999) calibration approach for establishing the 80 g/30° fall-cone penetration depth equating to the liquid limit by the Casagrande percussion-cup approach, determined according to the British Standard. In this paper, the Discussers present some clarifications on, and state various observations regarding, the approaches adopted in the Hrubesova et al. (2020) investigation, as well as the Moharjerani (1999) calibration approach employed therein. The Discussers also present a description of some relevant literature not covered in the Authors' paper (Hrubesova et al. 2020) aimed at making further clarifications on this important area of geotechnical practice.
查看更多>>摘要：? 2022 The Author(s)In the context of two-dimensional models for complex geophysical surface flows such as debris flows, muddy slurries, oil spills over land, hyperconcentrated floods, lava flows, etc, depth-averaged rheological models relate the shear stress state within the fluid column to the depth-averaged local flow features. Despite it is the most influencing term on the mobility of complex shallow flows, the numerical treatment of the resistance contribution to the flow momentum is still a challenging topic, especially when dealing with 2D large-scale applications. In this work, two novel strategies for the explicit upwind discretization of generalized non-Newtonian resistance terms in two-dimensional numerical models are proposed, called integral and differential approaches. These new strategies are applicable to generalized rheological formulations in any type of mesh topology. Results from benchmark tests running in orthogonal, triangle structured and triangle unstructured meshes demonstrate that both approaches represent an improvement for the explicit upwind integration of the 2D resistance force compared with previous procedures. It is shown that the alignment of the flow with the mesh main-axis, which has been previously attributed to faults of 2D FV numerical methods and insufficient mesh refinements, is directly related to the loss of the rotational invariance of the integrated resistance force. This is caused by the erroneous procedure for including the 2D resistance term into the local flux balance at the cell edges. Furthermore, a novel implicit centered method for the integration of the 2D resistance force has also been derived for the quadratic frictional non-linear resistance formulation. Despite the implicit procedure fails to converge to steady uniform flow states, the differential explicit upwind and the implicit centered methods show similar level of accuracy, robustness and computational efficiency for transient 2D frictional visco-plastic flows.
查看更多>>摘要：? 2021Temperature-dependent basic friction angles of granite fractures were investigated through three-core tilt tests with different heating temperatures, cooling treatment methods, specimen sizes, and tilting rates. Specimens were first heated to a predetermined temperature, then rapidly cooled to room temperature using two different cooling treatments (i.e., water and liquid nitrogen). The results indicated that the basic friction angles of thermally treated granite fractures increased linearly with the rise in heating temperature which could be mainly attributed to surface conditions altered by thermal stresses. The microcracks of the specimens subjected to thermal treatments were characterized using P-wave velocities and scanning electron microscope images. The basic friction angles increased as specimen sizes increased when the heating temperature was 400 or 800 °C. The tilting rate also had a significant impact on the basic friction angle of granite fractures subjected to the thermal treatments. The overall trends of the testing results with the two types of thermal treatment methods were similar when the heating temperature was 400 °C, while different evolutions were observed under the heating temperature of 800 °C. This study can provide some referential value for the stability analysis of jointed rock masses subjected to high temperature (e.g., geothermal exploration and nuclear waste disposal), and also the protection of stone cultural relics suffered from fire.
查看更多>>摘要：? 2022 Elsevier B.V.Due to their geological history, highly overconsolidated stiff clays often contain fissures which can induce strength degradation and structural anisotropy. The aim of this paper is to deepen our knowledge on the monotonic and cyclic behavior of this type of clay. For this purpose, a series of laboratory tests on overconsolidated Merville clay samples were carried out to analyze the influence of the fissure orientation and amplitude on its behavior. Clay samples were scanned by X-ray tomography (CT) and scanning electron microscope (SEM) to obtain a representation of the structure at the micro scale completed by observations of fissure networks within intact specimens. Specimens tested at the same effective confining pressure had different shear strengths due to the influence of the amount and orientation of pre-existing fissures. The value of the shear strength of horizontally drilled specimens was found higher than that of vertically drilled specimens. This anisotropic behavior was mainly the result of preferential orientation of the fissures within the clayey material. The results of one-way and two-way cyclic tests demonstrated also the strong influence of pre-existing fissures on the cyclic behavior. As for the monotonic shear strength, the cyclic resistance of a fissured clay is mainly governed by the intensity and the orientation of pre-existing fissures within the specimens.
查看更多>>摘要：? 2022 Elsevier B.V.Excavation is one of the common triggers for slope failures. Loss of support at the toe of a slope due to mining excavation can cause unloading of geomaterials close to the excavated area and stress redistribution. The deformation behaviour of arching-type slopes is different from the deformation behaviour of common dip slopes. Therefore, it is necessary to study the deformation and failure mechanism of slopes under excavation conditions. In this study, a series of physical model tests was conducted on arching-type slopes with different slope angles and relative densities. The physical models were monitored by various instrumentation, such as a digital camera, a high-speed camera, earth pressure gauges, and a multi-smartphone measurement system. The deformation characteristics during excavation were analysed by using particle image velocimetry (PIV). The results show that the yielding area, including the arch-shaped large deformation area and upper small deformation area, and two sides of unyielding areas were clearly observed and considered features of arching-type slope deformation related to the arching effect. In arching failures, slopes with higher relative densities can generate larger initial kinetic energy. Toe failure, sliding failures, tension cracks, and bulking failure subsequently occur in the final failure. The equations for the maximum excavation width and the curve of the stable arch of arching-type slopes are verified.
查看更多>>摘要：? 2022This paper presents a procedure for tracking rockfall trajectories and extracting kinematic parameters from both the impacts and the resultant fragments. A set of full scale rockfall experiments was performed in a quarry located in Vallirana, Barcelona (Spain). The study site was chosen due to the presence of a rigid discontinuity surface, inclined at 42° in the middle of the slope, whose configuration was expected to favor the breakage of the blocks. The trajectories of the blocks released and of the resultant fragments were recorded with three video cameras. A C++ program was specifically developed to track the 3D trajectory of blocks and fragments, and measure velocities before and after the impact. Two different modules were implemented, one for the blocks that break and one for those that do not. The trajectory of a non-fragmented block is obtained by comparing it to its 3D model. In this way, both the center of mass position and the orientation of the block are tracked. For fragmented blocks, the local coordinates of the fragments determined from the images are converted to terrain coordinates using the program we developed. A total of 16 blocks and 36 rock fragments after impact were tracked. The parameters obtained were georeferenced and linked to a common system of 3D terrestrial coordinates. The captured parameters allow obtaining the velocity distribution of fragments, the coefficient of restitution, and energy balance for the blocks that break. To our knowledge, this is the first attempt to capture kinematic parameters of rock fragments that result from the impact and breakage of rock blocks in full-scale tests. Although the analysis of the rockfall fragmentation phenomenon is beyond of this work, we have compared the performance of the fragmented and unbroken blocks. To this purpose, we have built 3D models of the rock fragments generated using images captured with a drone. The results indicate that blocks that fragment show higher rebound velocities and coefficients of restitution than the blocks that do not although there exists a certain overlap between the two groups. Despite the experiment is carried out on the same discontinuity surface and with small variations in the impact velocities, impact kinetic energies and impact angles, the coefficients of restitution obtained present a wide range of values, both for the blocks that break and for those who do not. The number of tested blocks is too small to draw generalizable conclusions, but they highlight the stochastic nature of the rebound process and the necessity to consider additional parameters for its understanding. Finally, the results confirm the relation between the dissipated energy and, especially the impact energy and the new area created by fragmentation. Furthermore, the blocks that hit the ground with the face are those that generate the most new area while those that hit the vertex generate less.
查看更多>>摘要：? 2022 Elsevier B.V.Loess–mudstone landslides occur easily because of earthquakes or rainfall; they account for a large number of landslides in the loess area of China. The Buzi landslide was one of the two largest landslides triggered by the 2013 Minxian–Zhangxian Ms. 6.6 earthquake and resulted in two deaths. Field investigations showed that it was a loess–mudstone landslide with a short sliding distance (approximately 20 m). By simplifying the original site conditions of the landslide, a model slope was built to perform a large-scale shaking table test. The dynamic response of the model was investigated in the time–frequency–energy space using the Hilbert–Huang transform method, and the failure mechanism was clarified from an energy perspective. The Hilbert spectrum indicates that the distribution characteristics of the instantaneous frequency energy are completely different between the loess layer and mudstone layer. Under 0.06 g, large energy is mainly concentrated in a frequency range 10–40 Hz in the loess layer, whereas the energy is mainly concentrated in the 5–10 Hz range in the mudstone layer. This implies that complex reflection and refraction waves occurred in the loess layer. With the increase in intensity, the energy in the loess layer gradually concentrates in the 5–10 Hz range, suggesting that the absorption capacity of the loess layer for high-frequency energy from the relative movement of soil particles increased. The marginal spectra changed from single peak to multipeak with increase in elevation under 0.06 g and changed from multipeak to single peak (with a predominant frequency of approximately 5.6 Hz) with increase in intensity, demonstrating that elevation (>1/2H) can amplify the high-frequency cumulative energy under 0.06 g, showing that input seismic energy gradually takes dominance. Large cumulative energy (10–40 Hz) and instantaneous energy are mainly distributed at the slope shoulder and loess layer. This causes the formation of cracks and a sliding surface in the loess layer. The failure phenomenon of the model slope is close to that of the Buzi landslide, in which sliding occurred at the middle–upper part of the slope within the loess layer.
查看更多>>摘要：? 2022 Elsevier B.V.The shear strength characteristics of compacted bentonite preferred as feasible buffer/backfill component is essential to the mechanical stability of the multi-barrier system in the context of nuclear waste disposal. This paper presents an investigation on the potential aging-induced changes in shear strength and microstructure of compacted GMZ bentonite at a dry density of 1.68 Mg/m3 and various water contents. For this purpose, direct shear and Mercury Intrusion Porosimetry (MIP) tests were correspondingly performed, as well as the soil-water retention tests. Statically compacted bentonite specimens were kept at constant volume and water content conditions for different periods of aging time up to 90 days, prior to experimental investigations. Results showed that the shear strength decreased with aging time, with a more noticeable trend during the first 30 days. Aging effect on shear strength was less pronounced for specimens at water content of 24%. Significant changes in microstructure after aging were observed, characterized by an increase in tiny pores (< 6 nm) and a decrease in inter-aggregate pores. The former phenomenon is related to the interlayer hydration as water redistribution is expected to occur, while the latter one is attributed to the exfoliation of clay particles that fill and reduce the inter-aggregate pores, which accounts for the dry density effect on soil-water retention curves (SWRC). Aging-induced changes in microstructure are governed by the water uptake from the non-interlayer space acting as reservoir into the interlayer pores, thereby promoting a further clay layer hydration and an arrangement of clay fabric. As such, both the effective degree of saturation (mainly considering the capillary water) and total suction decreased with aging, as well as the Bishop-type effective stress, thereby resulting in a decrease in the shear strength of compacted GMZ bentonite.
查看更多>>摘要：? 2022The mechanical characteristics and gas tightness of salt rock play a decisive role in the safety evaluation of salt caverns. Triaxial compression coupled permeability tests were performed on Chinese impure salt rocks under thermal-hydro-mechanical (THM) coupling condition. The results revealed that the peak strength decreased with the decrease of confining pressure and the increase of temperature. The permeability of salt rock decreased with the increase of confining pressure, while the increase of temperature led to an increase in permeability under lower effective confining pressure, and a decrease in permeability under higher effective confining pressure. Moreover, there is a critical effective confining pressure, which controls the evolution trend of salt rock permeability with temperature. The dilatancy boundary and failure strength envelope of impure salt rock at different temperatures were given, which can be expressed by exponential and hyperbolic functions respectively. An empirical formula for the evolution of the final permeability of the salt rock with the effective confining pressure at different temperatures was established. Considering the effects of effective confining pressure and inelastic volume strain, a new model was proposed to predict the permeability evolution of salt rock under THM coupling condition at different temperatures. The results of this paper can help understand the mechanical characteristics and permeability evolution of salt rock under THM coupling condition, and provide the necessary basis for the safety evaluation of salt caverns.
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