The use of planar and three-dimensional calculation models for the numerical modeling of retaining walls in conditions of dense urban construction

In modern realities, the construction of multi-story buildings increasingly has to be carried out in the conditions of dense urban development. Since high-rise buildings are characterized by the presence of deep pits, there is a need to select the parameters of the enclosing structures (retaining walls) and take into account the influence of the pit arrangement and enclosing structures on the existing building. Numerical simulation of the stress-strain state (SSS) of the elements "soil base - existing structures - pit enclosure" was performed to assess the impact of choosing the dimensions of the calculation scheme when designing a deep pit and assessing its impact on existing buildings and selecting effective parameters of enclosing structures. with different dimension options (flat two-dimensional and spatial three-dimensional) calculation scheme. Modeling was performed using the finite element method using a nonlinear model of soil deformation in the Plaxis software package. Since the soil conditions within the construction site are complex (the presence of a significant layer of plastic and flowing clay soils and powerful aquifers), the level of groundwater within the construction site was taken into account in the modeling and the effect of water lowering during the development of the pit was modeled accordingly for a more correct assessment of the stress-strained state of pit enclosure elements and the impact on existing structures. Numerical calculations of retaining walls provide for taking into account the technological sequence of the construction of retaining walls and modeling of the step-by-step development of the pit. Studies have shown that the use of a spatial finite-element model of the system "soil base - existing structures - pit enclosure" provides an opportunity to more correctly and effectively assess the stress-deformed state of system elements due to taking into account the spatial rigidity of the elements of the pit enclosure and the foundations of existing structures. The values of the displacements of the retaining walls obtained by the calculation of the spatial finite element model (FEM) are 20% smaller than the values obtained using the plane FEM. The values of the bending moments obtained by the calculation of the spatial FEM are 10% smaller than the values obtained using the plane FEM.