Research of the deformation patterns of existing structures near excavations using the finite element method
DOI:
https://doi.org/10.32347/2410-2547.2025.115.192-203Keywords:
finite element method, material model of soil, existing building, retaining wall, excavation pit, interface, finite element modelAbstract
The article discusses a number of common issues related to modelling the system «base - pit enclosure - existing building» using the finite element method (FEM) and investigates the impact of the pit dimensions on the deformation of the existing building. The first part of the article is focused on the aspects related to the determinations of the finite element model (FEM), its discretisation, as well as the contact interaction of structures with the soil massif and their impact on the accuracy of calculations.
The investigation of the effect on the stress-strain state of the foundation and structures of the existing building revealed the sensitivity of the Mohr–Coulombmodel to the vertical dimensions of the model, with an error of up to 47% in additional displacements when its dimensions in depth change by 2.5 times. Using of a model with hardening soil, which allows for the change in stiffness with depth, showed a reduction in error of up to 4%, but determining the input parameters for these models is a non-trivial task and requires not only compression and triaxial tests, but also the competence of a geotechnical engineer. It is emphasized that the introduction of contact elements is mandatory in the modelling of deep structures, and the weakening of the contact between the structure and clay soil with a strength coefficient to Rinter=0.6, according to the results of calculations, showed an increase in displacements by a quarter and a quantitative change in bending moments in the retaining wall.
In solving the experimental tasks, it was found that additional settlements of theexisting building foundation depend on the local stiffness of the pit enclosure, and the non-uniformity of deformations develops along the wall near the pit, which must be taken into account during monitoring. The investigation has shown that the location of the pit at a distance greater than its depth in dispersed soils significantly reduces the settlement of the building due to the exclusion of additional pressure within the collapse prism. Additional stresses of up to 250 kPa under the footings of the foundations of an existing building, in the conditions of excavation of a 6 m deep pit, cause the soil to work mainly within the limits of elastic deformations, but when this value is exceeded, a nonlinear increase in additional settlements is observed due to the development of plastic deformations.
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