A layered elastic analytical method for predicting peripheral surface deformation of deep foundation pits with multi-layer complex lithology

Excavation of deep foundation pits in open-pit mines with multi-layered complex lithology is prone to cause deformation of the surrounding surface, posing a threat to the safety of adjacent rigid structures. However, existing prediction methods rarely consider the layered differences in the effect of excavation unloading, resulting in insufficient accuracy. Current research on layered elasticity theory mainly focuses on pavement engineering and the field of single-layer soil foundations, lacking targeted applications in deep foundation pits with multi-layered complex lithology. This study takes a deep foundation pit of an open-pit coal mine in Xilingol League, Inner Mongolia as a research case, and constructs numerical simulation models with different excavation depths, aiming to clarify the deformation mechanism of the surrounding surface. By integrating the Fourier integral method and the differentiation of layered unloading effects, and considering the continuity conditions of interlayer interfaces, a layered elastic analytical method is proposed. The results show that the theoretical solution is consistent with the numerical simulation results, with an average relative error of less than 0.3%, thus verifying the reliability of the theoretical method. The study found that the deformation of the surrounding surface is related to the depth of the rock and soil mass, elastic modulus, and Poisson’s ratio, and the deformation increases significantly with the increase of excavation depth. When the settlement of the surrounding surface is close to the safety threshold, the optimal spatial geometric parameters of the foundation pit are determined as an excavation depth of 200 m and a slope angle of 30°. The distance from the slope top also has an impact on the deformation of the surrounding surface, showing a nearly significant negative correlation function relationship. In foundation pit excavation, as the slope height and slope angle increase, the deformation becomes more obvious. These research results provide safety guidance for the excavation design of deep foundation pit projects in open-pit mines with surrounding rigid buildings.