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Fluctuant marine and reservoir water levels are the main failure-inducing factors for embankment slopes. The soft embankment rocks, e.g., red-bed mudstone, eroded by the reservoir water level in the Three Gorges Reservoir area greatly influence the stability of the embankment slopes. In this study, unified strength theory was innovatively applied for damage evaluation and combined with the Weibull distribution to obtain the strength statistics of micro units. Additionally, one damage constitutive model and one damage evolution model considering the initial damage, strain softening and damage weakening were proposed. Then, a series of tests, e.g., modified cyclic wetting and drying test, triaxial compression test and modified numerical simulation test for reservoir embankment red-bed mudstone, were conducted to verify the feasibility of the proposed models. In addition, grey system theory was originally used to evaluate the effects of the Weibull distribution parameters (m and w) and the confining stress on the peak stress. Finally, the proposed model was tentatively applied to the modification of the limit failure height model of the bedded rock slopes. The verification implies that the proposed model results are consistent with the testing results, especially in the simulation of compaction, elastic deformation and strain softening and in the prediction of peak strength. The results from grey system theory analysis indicate that the micro unit strength parameter (w) has the most obvious effect on the strength. Moreover, the modified method based on the damage evolution model for calculating the limit failure height of the bedded rock slopes is conservative. [ABSTRACT FROM AUTHOR]

The well-known slide-prone red-stratum mudstones in the Three Gorges reservoir (TGR) area are currently undergoing sharp changes in (i) water level driven by the impounding/discharging operation of the Three Gorges dam and (ii) the rain/water H+ concentration driven by recent rapid industrial/agricultural development, and these changes are expected to impact geohazards. This potential impact emphasizes the importance of understanding the role of pH in the drying-wetting disintegration of red-stratum mudstones. Although many investigations have focused on the role of pH in mudstone disintegration, the red-stratum mudstones in the TGR area differ from mudstones elsewhere, and the role of pH has seldom been studied in these rocks. This work adds to the limited body of research by (1) experimentally investigating the possible role of pH in red-stratum mudstone drying-wetting disintegration and (2) revealing the micromechanisms responsible for this role. In the experiment, six disintegration performance indexes and two mechanical indexes, i.e. particle size gradation, slake durability index, decay constant, surface energy, box dimension, fractal dimension, cohesion and friction angle, were monitored throughout the disintegration process. A tri-piecewise linear fractal model is proposed to better describe the particle size distribution. This research shows that the acid enhancements stimulate the disintegration of red-stratum mudstones and significantly affect shear strength. In comparison, alkaline environments inhibit the mudstone fragmentation and slightly degrade the shear strength. Two possible micromechanisms and three potential effects of acid or alkaline agents are presented to account for the role of pH. The findings provide insights into the potential geohazard impacts of sharp changes in the exposure environment (i.e., water level and H+ concentration) of the red-stratum mudstones in the TGR area. • Established a multiphysics database of pH versus disintegration performance indexes. • Revealed the role of pH in drying-wetting disintegration of red-stratum mudstones. • Clarified the micromechanisms of the pH role in red-stratum mudstone disintegration. • Proposed a tri-piecewise linear fractal model of particle size distribution. • Challenged the previous understanding of the pH role/mechanisms in disintegration. [ABSTRACT FROM AUTHOR]

Monitoring data show that many landslides in the Three Gorges region, China, undergo step-like displacements in response to the managed, quasi-sinusoidal annual variations in reservoir level. This behavior is consistent with motion initiating when the reservoir water level falls below a critical level that is intrinsic to each landslide, with the subsequent displacement rate of the landslide being proportional to the water depth below that critical level. Most motion terminates when the water level rises back above the critical level, so the annual step size is the time integral of the instantaneous displacement rate. These responses are incorporated into a differential equation that is easily calibrated with monitoring data, allowing prediction of landslide movement from actual or anticipated reservoir level changes. Model successes include (1) initiation and termination of the annual sliding steps at the critical reservoir level, producing a series of steps; (2) prediction of variable step size, year to year; and (3) approximate prediction of the shape and size of each annual step. Annual rainfall correlates poorly with step size, probably because its effect on groundwater levels is dwarfed by the 30 m annual variations in the level of the Three Gorges Reservoir. Viscous landslide behavior is suggested. [ABSTRACT FROM AUTHOR]

Slip zone soils play a crucial role in the evolution of landslides. In this paper, slip zone soils of the Huangtupo Landslide in the Three Gorges Reservoir area, which is an ancient landslide affected by water level fluctuation, are taken as an example to research the influence of wetting–drying cycles on soil properties. The mercury intrusion porosimetry test is used to study the soil's microstructure, while the triaxial test is used to measure the mechanical parameters. The experimental results indicate that the wetting–drying cycles can change the micropore structures and macro-mechanical properties of the soils. Meanwhile, it is demonstrated that there is a certain relationship between the macro- and micro-properties. From the microcosmic perspective, the fractal structure unit formed in the long-term geological environment is the key factor affecting the mechanical properties of the slip zone soils. Then, based on fractal theory, a weakening model of slip zone soils during wetting–drying cycles is proposed. The correctness and reliability of the model are verified by the mechanical parameters from triaxial tests. Finally, it is indicated that the weakening model can be used to forecast the weakening coefficient of slip zone soils under wetting–drying action, which results from the periodic fluctuations of the reservoir level. [ABSTRACT FROM AUTHOR]

Abstract Geological disasters have occurred frequently in the Three Gorges Reservoir area. Therefore, the stability and failure mode research on riverside landslides has become increasingly important. Taking the toe of Liangshuijing landslide as a case study and combining the geological conditions of the Three Gorges Reservoir area, a centrifuge slope model is constructed. In addition, the fluctuation of the water level is simulated in the centrifuge model test. Based on the digital photography, laser displacement sensors (LDS), pore pressure transducers (PPT) and earth pressure sensors (E), multi-physical data are obtained. Finally, numerical simulation is carried out to analyze the stability and deformation characteristics of the slope model. The results indicate that: (1) At the water level rise stage, the model is dominated by the vertical displacement. And the horizontal displacement is much larger than the vertical displacement at the drainage stage. (2) Cracks first appear at the toe of the slope and extend to the middle and rear of the model gradually. Then, deformation occurs in the middle platform of the slope. (3) At the water level rise stage, the factor of safety increases rapidly. When the reservoir water level remains stable, the stability of the slope decreases slowly. And at the drainage stage, the factor of safety decreases first and then increases. (4) There is a significant positive linear correlation between the decline rate of the safety factor and the drainage rate over a certain test range. And the stability of the landslides on the reservoir banks would become worse gradually during the long-term cyclic operation of the Three Gorges Reservoir. Highlights • The fluctuation of the water level is simulated in the centrifuge model test. • Qualitative and quantitative method are combined to analysis the evolution of the landslide. • The failure mode and the deformation mechanism of the slope are revealed by the centrifuge model test. [ABSTRACT FROM AUTHOR]