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For geotechnical stability analysis involving non-associated plasticity, the Davis approach with internal friction angle and dilatancy angle updated during the strength reduction process can lead to an improvement over the Davis approach without updating the two angles, according to recent studies. However, the Davis approach with internal friction angle and dilatancy angle updated may be overly conservative, especially for those geotechnical stability analyses involving large friction and small dilation, which provides the motivation to modify the Davis formula. In this work, a modified Davis approach is proposed by enhancing the original Davis formula. Based on the enhancing approach, two modified Davis formulas – a theoretically modified Davis formula derived from the geometric relation and an empirically modified Davis formula by multiplying the original Davis formula by an enhancement function – are investigated. The appropriate values of the parameters in two modified Davis formulas for practical use are studied. Numerical investigations disclose that the modified Davis formulas in conjunction with the appropriate parameters can lead to improved estimations of the geotechnical stability.

Cracks are the visual manifestation of soil failure. Exploring the propagation process of soil cracks is of great significance to the safety of geotechnical engineering. However, this part...

Water inrush disasters are the main cause of karst collapse. In this study, a physical model test was conducted to investigate the mechanism of karst collapse. The formation, expansion, and...

A comprehensive study is presented of the characteristics of calcareous concretions in the Connecticut Valley varved clay (CVVC), a glacial lake sediment, probed by an array of investigations, including compositional analyses via X-ray powder diffraction and energy-dispersive X-ray spectroscopy, mechanical property mapping by nanoindentation, selective dissolution, microstructure examination by optical and electron microscopy, and stable isotope analyses, with an objective to resolve some long-standing questions on their origin and growth mechanisms. Results show that these concretions are of a biogenic origin and consist of ~40 wt% primary host sediments and ~ 60 wt% secondary calcite post-depositionally precipitated as pore infills and inter-particle cement. The highly consistent layering and dry density between the carbonate-free host sediments in the concretions and in-situ varved sediments manifest that the precipitated calcite causes no disturbance to the original stratification and structure of the varved sediments. Moreover, both the mechanical properties (i.e., Young's modulus and hardness) and calcite concentration in concretions exhibit a radially decreasing pattern slightly disturbed by the sediments' layered textures. Further supported by the radial distribution patterns of stable carbon and oxygen isotopes, the CVVC concretions grow in a concentric pattern. A conceptual ion transport model is proposed to further interpret the growth mechanisms. These concretions grow radially in a nearly closed sediment system with diffusion-controlled transport of HCO3− from decaying organic matter and Ca2+ from porewater at direction-dependent rates dominated by the pore characteristics of the local host sediments. The diverse concretion morphologies are attributed to the different growth rates in different directions affected by the heterogeneous layering and pore sizes of the host sediments.

Soil-rock mixture(S-RM)is a widely distributed geotechnical medium composed of “soil” and “rock block” different both in size and strength. Internal rock blocks form special and variable meso-structural characteristics of S-RM. The objective of this work was to study the control mechanism of meso-structural characteristics on mechanical properties of S-RM. For S-RM containing randomly generated polygonal rock blocks, a series of biaxial tests based on DEM were conducted. On the basis of research on the effects of rock blocks’ breakability and sample lateral boundary type (rigid, flexible) on macroscopic mechanical behavior of S-RM, an expanded Mohr-Coulomb criterion in power function form was proposed to represent the strength envelop. At the mesoscopic level, the variations of meso-structure such as rotation of rock block, and the formation mechanism and evolution process of the shear band during tests were investigated. The results show that for S-RM with a high content of rock block, translation, rotating and breakage of rock blocks have crucial effects on mechanical behavior of S-RM. The formation and location of the shear band inside S-RM sample are also controlled by breakability and arrangement of rock blocks.

Triaxial tests on three types of soil–rock mixture (S-RM) samples with the same rock block content, but different grain size distributions, were performed in this study. To better understand the meso-mechanical behavior of soil–rock mixtures, one set of samples containing “oversized rock blocks” was designed. The oversized rock blocks in the other two sets were handled using the equivalent weight replacement method and the similar translation method. On this basis, the effect of the grain size distribution on the mechanical properties of the soil–rock mixtures was explored. The interlocking and the breakage of the large rock blocks were found to be two of the controlling factors of the mechanical properties of soil–rock mixtures. The deviator stress and the volumetric strain correlated well with the uniformity coefficient of the particle size distribution curve and performed differently under different confining pressure levels. Based on X-ray computed tomography (CT) slices of samples taken during the triaxial tests, the interaction of the internal rock blocks and the evolution of the sample meso-structure in the loading process were observed and analyzed; the present analysis provides explanations for the macroscopic mechanical behavior of soil–rock mixtures.

The parameters of the constitutive model, the creep model, and the wetting model of materials of the Nuozhadu high earth-rockfill dam were back-analyzed together based on field monitoring displacement data by employing an intelligent back-analysis method. In this method, an artificial neural network is used as a substitute for time-consuming finite element analysis, and an evolutionary algorithm is applied for both network training and parameter optimization. To avoid simultaneous back-analysis of many parameters, the model parameters of the three main dam materials are decoupled and back-analyzed separately in a particular order. Displacement back-analyses were performed at different stages of the construction period, with and without considering the creep and wetting deformations. Good agreement between the numerical results and the monitoring data was obtained for most observation points, which implies that the back-analysis method and decoupling method are effective for solving complex problems with multiple models and parameters. The comparison of calculation results based on different sets of back-analyzed model parameters indicates the necessity of taking the effects of creep and wetting into consideration in the numerical analyses of high earth-rockfill dams. With the resulting model parameters, the stress and deformation distributions at completion are predicted and analyzed.

Six non-expandable, hydrous 2:1 phyllosilicate minerals with different layer charges, including pyrophyllite and talc from the pyrophyllite-talc group and biotite, two muscovites, and margarite from the mica group, were nanoindented to probe their nanoscale deformation behavior and hardness. Remarkably different deformation responses were obtained, which are highly dependent upon the type and strength of interlayer interactions controlled by Coulomb or van der Waals forces. Concave load–displacement curves were observed on the micas with stronger Coulomb forces as interlayer interaction, while convex curves on the other group with weaker van der Waals attractions as interlayer interaction. The hardness increases with layer charge both within each group and between the two groups, ranging from 3.86 GPa for talc to 16.34 GPa for margarite, with the highest being four times greater than the lowest. Owing to their layered structure that favors kink band formation and layer delamination, pop-ins of varied extensions occur randomly in the load–displacement curves. An observed apparent indentation size effect is attributed to the pop-in events. The dependence of hardness on interlayer interactions between 2:1 layers instead of the atomic bonds within the 2:1 layer suggests that the interlayer interactions can be used as a hardness or plastic signature for phyllosilicate minerals.

The variation of stress–strain state induces changes in the permeability of clayey soil and then affects the properties of seepage and consolidation. In previous studies, variations of the permeability of soil in shear process were mainly neglected, and there were no reasonable descriptions of the permeability in such a condition. To study the variation of the hydraulic conductivity of clayey soil in shear process, new triaxial seepage equipment was designed by changing the conventional triaxial apparatus. Based on a series of tests under different confining pressures carried out by this equipment, the influences of the stress–strain state of clayey soil on hydraulic conductivity were investigated. Furthermore, a mathematical model for the hydraulic conductivity of clayey soil under the condition of large shear deformation was proposed. The comparison between the seepage test results and the calculated values of the proposed model indicates that the mathematical model can calibrate the effects of ...

A consolidation analysis method for an earth-rockfill dam based on the coupling of physical state, stress deformation, and seepage was established. In this method, a permeability coefficient model considering physical state and shear stress level was introduced, and it was integrated with Biot’s consolidation theory to simulate the coupling relationship. Taking the Nuozhadu high earth-rockfill dam as an example, a parameter back-analysis method using a neural network and evolutionary algorithm was applied to back-analyze the permeability coefficient model parameters of the core material based on observation data of pore water pressure in the dam. Then, consolidation numerical analyses were performed by using the back-analyzed parameters and the constant permeability measured in situ, respectively. The spatial and temporal distribution of pore water pressure calculated by the back-analyzed parameters coincided quite well with the monitoring data during construction and operation. However, the numer...

Based on a force analysis, an expression is derived to describe the critical Shields number for incipient motion of uniform cohesionless sediment particles on a riverbank slope in terms of flow parameters, outflow seepage, and physical and mechanical properties of sediments. Parametric studies were conducted to investigate quantitatively the effects of hydraulic gradient of seepage, slope angle, and flow direction on the critical Shields number. The results show that the critical Shields number decreases with an increase in the hydraulic gradient. Where bank collapse is concerned, the most dangerous direction of hydraulic gradient of outflow seepage is at an angle equal to the effective internal angle of friction of the sediment mass with respect to slope surface. At a certain value of hydraulic gradient, the critical Shields number decreases with increasing slope angle. Open flow becomes more erosive when the current direction changes from horizontally parallel with the riverbank line to turning downward.

A series of parametric studies were performed to investigate the three-dimensional (3D) effect on the stability of an earth–rockfill dam, with respect to some major factors, such as geometrical characteristics of the dam and topography of the canyon. The length–height ratio of the earth–rockfill dam clearly influences the 3D safety factor. A power function suitably expresses the relationship between the increment ratio for the safety factor and the length–height ratio. The canyon shape, gradient of dam slope and height of the dam significantly influence the 3D effect. The results may be used as a blueprint by combining the two-dimensional (2D) safety factor in common use, and the relationship between 2D and 3D safety factors established in this study.

泥水掘削溝壁の安定性を評価する方法は, 1960年代以降数多く提案されてきたが, 問題の複雑さゆえに十分に信頼できる方法は未だ開発されていない. 本論文では, 既往の方法の問題点を整理した上で, 従来考慮されなかったすべり土塊に作用する側方拘束力の重要性を指摘し, 簡易 Janbu 法の考えにもとづく新たな三次元極限平衡法を提案した. 本方法を砂地盤に構築された泥水掘削溝壁の遠心模型実験結果に適用し, 三次元弾塑性FEMの計算結果と比較することにより, 提案法の妥当性を検討した.

Static and dynamic numerical calculations were performed to study the dynamic response of a high core rockfill dam. 3-dimensional static analyses of an ideal high core rockfill dam were conducted using Duncan-Chang’s E-B model. Then based on the initial static stress filed, dynamic analyses of the dam subjected to earthquakes were conducted with the program EB3D in traditional way of visco-elastic model and Equivalent Linear Method. The dynamic response of the high core rockfill dam in the whole process of earthquake was analyzed with program FEMEPDYN, which is based on elasto-plastic model and Nonlinear Method. The dynamic behavior of the high core rockfill dam during the earthquake was analyzed, and the seismic characteristics of response were investigated. Compared with traditional Equivalent Linear Method, it is shown that the Nonlinear Method is more reasonable in describing the dynamic response of high core rockfill dam subjected to the earthquake motion.

In order to investigate the variation of the seismic response spectrum of slope reinforced with piles under the liquefaction of saturated subgrade, some acceleration sensors are used to record the seismic acceleration response of slope reinforced with stabilizing piles under the waterless condition and the saturated subgrade in the dynamic centrifuge modeling test, respectively. Then the different characteristics of the acceleration spectrum of seismic response are analyzed through the comparisons. The results prove that seismic response amplifies from bottom to top of the slope under the waterless condition, showing that seismic response is larger at the top of slope than that at the bottom of slope; however, seismic response of slope is restrained to a certain extent due to the liquefaction of saturated subgrade, so that seismic acceleration response of the soil mass of slope shall decrease at first with the increasing of elevation and then increase slightly. Moreover, due to the liquefaction, the low and intermediate frequency components of seismic response are reinforced to some extent, which reflects the reduction of global rigidity of the reinforced slope caused by liquefaction.