Tectonic movement, heavy rainfall and other environmental factors are important factors causing the slope instability of accumulation body. Aiming at jiangdingya H1 landslide in Bailong River Basin, Zhouqu County, Gansu Province, the deformation law and stability of accumulation landslide under the coupling condition of earthquake and rainfall were systematically analyzed by means of laboratory physical model test, numerical simulation and theoretical derivation. The results show that: 1) The crack development law of landslide model test under the coupling effect of earthquake and rainfall is analyzed, and the stability characteristics of landslide deformation and failure in three stages are obtained. 2) According to the model test and numerical simulation results, it is found that the coupling effect has the greatest influence on the stability of the slope toe of the accumulation landslide, and the failure mode of the accumulation landslide changes from “pull-shear” failure to “compression-shear” failure, and the failure of the accumulation landslide occurs in a local location. 3) Based on the unbalanced thrust method and GA model, a landslide stability calculation model of loose accumulation body under the coupling effect of earthquake and rainfall was improved by comprehensively considering the effects of complex factors such as seismic inertia force and seepage force. The research results can provide reference for landslide prevention, monitoring and early warning in Zhouqu area of Gansu Province.

It is very necessary to research the bearing characteristics of composite pile group foundations with long and short piles under lateral load in loess areas, because these foundations are used widely. But few people researched this problem in loess areas up to now worldwide. In this paper, firstly, an indoor test model of a composite pile foundation with long and short piles is designed and then employed to explore the vertical load bearing characteristics and load transfer mechanisms of a single pile, a four-pile group, and a nine-pile group under different lateral loads. Secondly, ANSYS software is employed to analyze the load-bearing characteristics of the test model, and for comparison with the experimental results. The results demonstrate the following. (1) The lateral force versus pile head displacement curves of the pile foundation exhibit an obvious steep drop in section, which is a typical feature of piercing damage. A horizontal displacement limit of the pile foundation is 10 mm and 6mm for the ones sensitive to horizontal displacement. (2) The axial force along a pile and frictional resistance do not coincide, due to significant variations and discontinuities in the collapsibility of loess; a pile body exhibits multiple neutral points. Therefore, composite pile groups including both long and short piles could potentially maximize the bearing capacity and reduce pile settlement. (3) The distribution of stress and strain along the pile length is mainly concentrated from the pile head to a depth of about 1/3 of the pile length. If the lateral load is too large, short piles undergo rotation about their longitudinal axis and long piles undergo flexural deformation. Therefore, the lateral bearing capacity mainly relies on the strength of the soil at the interface with the pile or the horizontal displacement of the pile head.

The water sensitivity and structural characteristics of collapsible loess are two typical factors that significantly influence its mechanical behaviors. This paper presents a simple and practical elastic-plastic model based on the modified Cam-Clay model to well capture the essential behavior of unsaturated intact loess. The model employs deviator stress and spheric stress as the stress variables, with the water content serving as the moisture variable. The critical state surface of the model can be determined by utilizing the shear strength parameters of unsaturated soil under axisymmetric stress conditions. An initial yield surface equation is established by incorporating structural strength into the elliptical yield surface equation, which is used to determine the starting point for elastic-plastic deformation calculations under different humidity and stress combinations. The model comprises several parameters, each of which has a clear physical interpretation and can be conveniently obtained through conventional triaxial tests. The validity of the model for unsaturated intact loess is confirmed through a comparison with the stress–strain relationship of unsaturated intact loess in the axisymmetric stress state. This work has the potential to significantly enhance our ability to predict and mitigate potential geotechnical disasters, such as foundation deformation under axisymmetric conditions and slope stability problems under non-axisymmetric conditions. Ultimately, the application of this model could contribute to the safety and stability of infrastructure and construction projects in loess regions.