Red mud is the tailings generated from the production process of aluminum industry and is mainly stacked in open‐air at present, so how to ensure the stability of red mud stockpile is very important. Regarding mud stockpile of Guizhou Aluminum Factory as the research object, this paper studies the physical and mechanical properties of Bayer red mud from wetting process, Bayer red mud from drying process, and sintering red mud through laboratory test and finally analyzes its stability under extreme rainfall condition in this region by the Geo‐Studio software. The research results show that the red muds in different processes have big difference in physical and mechanical properties. The strength of sintering red mud is about 4.2 times of that of Bayer red mud from wetting process on average, and the strength of Bayer red mud from drying process is about 1.5 times of that of Bayer red mud from wetting process on average. So, the sintering red mud can be used as the subdam of red mud stockpile, to reduce the risk of collapse and dam break. The stability coefficients of the mixed stocking method under three rainfall conditions are 2.611, 2.597, and 2.631, respectively, all of which are above 1.0. It reveals that the dilatation scheme of using the sintering red mud with good engineering properties to stockpile the Bayer red mud is feasible. It can not only guarantee the safety and stability of red mud stockpiles, but also reduce the risk of red mud dam break and the capital investment of red mud yard.

Triaxial unloading creep tests of layered rock specimen of Jinping II hydropower station were carried out using the rock creep testing machine; thus the creep deformation curves under different confining pressures were acquired. The test results showed that, in addition to the obvious unloading creep characteristics of rock specimen, the nonlinear accelerating creep deformation emerged under the last stage confining stress condition, and the whole creep curves presented the typical rock creep three stages. On the other hand, the Burgers creep model constitutive equations under the three-dimensional stress state were also deduced. Based on the creep test data, through identifying the creep parameters using the optimized algorithm, the corresponding parameters of triaxial creep constitutive model were obtained. By comparative analysis of creep parameters, it can be concluded that creep parameters nonlinearly degraded with the decrease of confining pressure gradually. Moreover, when the load is below the long-term strength of rock, the creep parameters are only related to the unloading ratio, while in the case that the load is larger than the long-term strength of rock, the unloading creep parameters are related to both unloading ratio and creep time. According to the creep parameters under the first-stage stress level, and through introducing unloading ratio damage factor to describe the degrading rule of creep parameters on other stress levels, the method of uniformity determining the creep parameters was proposed. It was assumed that the damage degree in rock interior was relative to both unloading ratio and creep time; a nonlinear creep damage model of rock under unloading was proposed, which could better reflect the nonlinear characteristics of rock creep. The results showed that rock nonlinear creep damage model achieved perfectly consistent results with the creep test.

The pipe umbrella is one of the most commonly used prereinforcement techniques in tunnel construction. Current theoretical analyses of the pipe umbrella support mechanism are primarily based on the elastic foundation beam principle, whereby only a single pipe is concerned, and the interactions among pipes are ignored. In this study, a double-parameter elastic foundation beam theory-based model was established with consideration of the arching effect between two pipes. The model can simulate the support mechanism of the pipe umbrella system in shallow-buried tunnels. The support mechanisms of a pipe umbrella system installed in a rectangular tunnel and an arched tunnel were investigated. In the two cases, the arching effect and a single pipe were considered. The results indicate that the arching effect leads to larger pipe deflection and internal forces than considering a single pipe. The influences of the diameter of a single pipe, the distance between two pipes and the shear parameters of the surrounding rock on the pipe deflection and the arching effect are discussed. In addition, the proposed model was validated by the in situ monitoring results.

Given the wide distribution of carbonate pillars in the Three Gorges reservoir area, there is a need to investigate the possible structural damage they experience from long-term water-level fluctuations. This study analysed the coupled effects of an improved time-dependent crack propagation pattern and failure modes of structural rock masses under stress-seepage using the Jianchuandong pillar hazardous rock mass (JCD) as a case study. A new crack simulation method based on FLAC ^3D is proposed in which the interface element is immediately set on the surface of the yielding zone during the calculation step when a zone yields under tensile or shear stress. The two zones are directly separated during the tension or shearing of the bond at the contact surface. The JCD simulations illustrated that fractures and failure zones within the rock mass would propagate along the existing vertical cracks and extend to the base toe. The base rock mass would experience fracturing, finally leading to failure of the entire rock mass. The presented model provides sufficiently accurate predictions and is a suitable method for analysing time-dependent failure of pillar hazardous rock masses subject to water-level fluctuations. Thematic collection: This article is part of the Role of water in destabilizing slopes collection available at: https://www.lyellcollection.org/cc/Role-of-water-in-destabilizing-slopes

Many Chinese aluminum enterprises now choose to mix sintering process red mud and Bayer process red mud in the proportion of 1:1 to form mixed red mud and then stockpile the mixed red mud in the open air. In this study, the strength characteristics and the mechanism behind cementation hardening of the mixed red mud were investigated from the aspects of microstructure and macromechanical properties under different dewatering times. It was found that many hydraulic cement minerals and active ingredients in the red mud undergo a series of hydration reactions and carbonization reactions during dewatering, forming cementing minerals, which finally results in a large increase in the cohesion. These reactions mainly complete in the first 70 days of dewatering. In addition, the influence of acid on the strength characteristics of mixed red mud was also studied. It was found that even though the mixed red mud is soaked in a high-concentration acid solution (2 mol/L) for a long period (60 day), its strength only decreases slightly. These findings can provide important references for the open-air storage of red mud and the analysis of stability of the stockpile.