Stability parameter analysis of a composite foundation of an oil storage tank in a loess area treated with compaction piles

The research takes the composite foundation of the Lintao oil depot belonging to the Gansu branch of PetroChina treated with compaction piles in the collapsible loess region as the research background. A large number of compaction piles dispersed in the composite foundation are simplified using the equivalent continuum method. Discrete piles arranged in a triangular shape are simplified in the model, where the annular piles and compacted soil are arranged alternately, which can provide new ideas for the three-dimensional calculation mode of composite foundation and greatly improve the convergence and computational efficiency of the finite element model. To more realistically reflect the actual situation, the soil-structure and fluid–structure interactions, the material and the contact nonlinearities are considered, and a large-scale three-dimensional calculation model, which includes the composite foundation, concrete foundation, tank and liquid, is established. A sensitivity analysis is used to analyze the sensitivity of the elastic modulus, internal friction angle and cohesion of the composite foundation. The sensitivity of a single factor is evaluated based on the absolute value of the slope of the result-parameter curve; the relative sensitivity of various parameters is discussed according to the dimensionless sensitivity. The results show that for composite foundation, an increase in the friction angle or the cohesion of the foundation will significantly increase the safety factor. The sensitivity of the friction angle is greater than that of cohesion, and the sensibility of the elasticity modulus on the stability is very small. The results suggest that the accuracy of the mechanical parameter selection should be considered in the research on the stability of composite foundations. Measures to increase the angle of internal friction should be preferentially taken and increasing the cohesion should be considered secondary to improve the stability and safety reserve of composite foundation.