Methodology for taking into account the process of soil compaction when assessing the interaction of structures with the soil base using the finite element method

During the interaction of structures with the soil base, the process of soil compaction under the foundations predominates, when irreversible deformations associated with a decrease in the volume of pores in the soil begin to develop. Usually, zones of plastic deformations associated with shear deformations will also arise, but they will be local, not large in size and do not significantly affect the redistribution of stresses in the “Base-Foundation-Building” system. Based on this, the article proposes a methodology for assessing the interaction of structures with the soil base under conditions close to compression pressing, which is based on the use of a mathematical model that describes the process of soil compaction and compression test data. The presented approach allows using data from oedometer soil tests conducted at small pressure ranges (0.1-0.3 MPa) to assess the interaction of foundations with the base of most modern structures such as high-rise buildings, industrial facilities and others, under which the pressure in the base only starts from 0.3-0.4 MPa. To implement the method, the semi-logarithmic law of soil compaction of K. Tertsagi was chosen, which allows extending the compression curve obtained in laboratory conditions at small pressure values to the required pressure ranges with larger values and determining the deformation modulus in this wider pressure range. The method is implemented in the Simulia Abaqus environment using the user subroutine UMAT (user subroutine). It is shown that the results of numerical modeling are consistent with the data from laboratory tests. In addition, it was found that taking into account the process of soil compaction and the dependence of the deformation modulus on pressure allows you to practically eliminate the influence of boundary conditions on the stress-strain state of the "Base-Foundation-Superstructures" system, which is especially important when assessing the mutual influence of closely located structures with significantly different limits of the compressible layer. The advantage of the proposed approach is also that in addition to compression test data, other data on soil deformability obtained on more modern laboratory devices, such as a stabilometer, can also be used.