Experimental Justification of the Soil Base Model for the Calculation of the Combined Raft-Pile Foundation

Abstract

A new design of a combined raft-pile foundation, which is devoid of the shortcomings of similar existing design solutions and installation methods are proposed. This technical solution has been implemented at one of the construction sites in Kharkiv (Ukraine). The proposed design makes it possible to efficiently use the load-bearing capacity of the soil base by involving the raft part in the response to the loading in a controlled manner with transfer of up to 50% of the total load to this without going beyond the allowable strains of the soil base. The remaining 50% of the load are taken up by piles. The article considers the improved soil base model of the combined raft-pile foundation to consider the nonlinear behavior of the elements “before” and “after” the connection between the raft and the piles (structural nonlinearity) to calculate the stress-strain state using the finite element method in present-day calculation software. Using the improved model makes it possible to qualitatively simulate the behavior of the CRPF with the structural nonlinearity in the behavior of its elements. As a result, we obtain reliable results on the stress-strain state of the base-foundation-structure system. The article presents the modeling and numerical calculation of the "soil base - combined raft-pile foundation - structure" system of a real building object by program SOFISTIK using the proposed soil base model and the method of determining its parameters. The comparison and analysis of the results of the numerical calculation and the field experiment of the settlement of the raft part and the initial settlements of the piles of the foundation confirmed the adequacy of the application of the improved soil base model in the form of a combination of two known models: a limited distribution capacity and a Fuss-Winkler and method of determining it parameters on the basis of preliminary pile test. The analysis of the stress-strain state of the combined raft-pile foundation at different stages of the interaction with the proposed soil base model helps to confirm the physical significance of this structural nonlinearity of the behavior of the foundation elements. Keywords: Soil Base, Combined Raft-Pile Foundation, Model, Modeling, Field Investigation