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Abstract. Selecting a reasonable pile type and the pile foundation bearing stratum is important to design and construction in the karst area. It is needed to analyze the stress of pile foundation according to different types of karst caves. By numerical simulation, it is found that under the influence of the settlement of the karst cave filling, negative side friction appears in the area of the karst cave. The more the number of karst cave, the more increase the axial force of the pile. The larger the cave width, or the smaller the cave spacing, the smaller the positive side friction in the cave area. The larger the cave width, the more slowly the axial force decline. With the decrease of the cave spacing, the axial force of the pile under the same depth has an increasing trend.

Fissured strong expansive soil swelling behavior is complicated. In this paper, considering the typical filling fissures of strong expansive soils, fissure rate K r was given as a fissure content quantitative indicator. A prediction model was developed for the prediction of swelling effect on a fissured strong expansive soil using BP neural network approach, the gradient descent and the conjugate gradient algorithm methods were adopted. The actual test and predicted results of the two algorithms network showed high degree of similarity. The BP neural network model described by fissure rate, dry density, initial moisture content and overlying load can meet the precision requirements. The conjugate gradient method when compared with the gradient descent method, has a significantly improved calculation efficiency, the convergence rate is about 30 times lesser than the latter, therefore, conjugate gradient algorithm BP network prediction model for swelling in the actual engineering calculation has obvious advantages.

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Finite element method was used in the research and analysis about the earth pressure problem. However, in classical earth pressure theory, the soil deformation is not considered, and most studies are based on some assumptions of the contact surface, the study of earth pressure has been limited to a certain extent. In this paper, finite element method is used based on the different displacement modes of the retaining wall, to analyze the relationship between the active earth pressure and the displacement of the retaining wall, to provide the theoretical support to the design method and construction technology of the foundation pit deformation control.