Numerical simulation of the experiment on testing a group of piles using different models of soil base

Abstract

In the paper, the influence of the selected model of the soil environment on the stress-strain state (SSS) of the pile foundation is studied. The following issue sare considered: 1) analysis of the main models of the soil environment, widely used in modeling the interaction of foundations with soil foundations; 2) Numerical modeling of the stress-strain state of the "base – pile foundation" system was performed using foundation models in the form of: variable stiffness coefficients, volume tricelastic and elastic-plastic elements of the soil mass; 3) a comparison of the SSS of a pile foundation obtained by numerical modelingusing various foundation models and verification of the results by comparing with the data of a field experiment of testing a group of piles is given. This study is based on field experiments on testing full-scale piles, conducted by prof. Bartolomey A.A. and colleagues. In the experiment, a groupof 9 piles with a length of 5 m and a section of 30x30 cm was driven into the ground. The piles were combined with a reinforced concrete grillage. Numerical modeling of the stress-strain state of the system "base - pilefoundation" was carried out using the SP "Lira – SAPR 2019".

It was revealed that the calculated values of longitud in alforces in piles modeled by rod elements, and the interaction with the base of the base stiffness factors simulated by variables give good convergence with the data of experimental studies. The error for all experimental fields in a wide range of loads is up to 20%. When determining the value of the variable stiffness coefficients, it is necessary to refine the miteratively more than 3 times. The disadvantage of modeling the foundation with variable stiffness factors is the difficulty in obtaining the correct values of bending moments in piles. When using a soil foundation model in the form of volumetric elastic finite elements, the error in determining the longitudinal forces in piles is up to 45%, and the use of elastic-plastic volumetric soil elements increases the accuracy of the calculation. After comparing the calculated and actual values of piles ettlement, we observe an excellent correlation of the results in the variant of the numerical model using volumetric elastic-plastic finite soil elements with the Mohr-Coulomb strength criterion. The error is within 0.8 ... 2%. The use of the model of volumetric elastic elements of the soil massif leads to an under estimation of settlement in piles within the range of up to 8%. The model using variable foundation stiffness factors also under estimates settlement in piles by up to 15%.