Use of 2D and 3D modeling to assess the stress-strain state of retaining walls of complex configurations

A comparison of the calculation results of the foundation pit enclosure made of flexible retaining walls is presented. Calculations were performed by the method of numerical modeling using Plaxis PC software, which is based on the finite element method. This task was implemented in three-dimensional (3D) and flat (2D) formulations of the problem, which provides more opportunities for a comprehensive assessment of the stress-strain state (SSS) of the elements of the "soil massif - anti-landslide structures" system when using complex configurations retaining walls. 
Calculations were performed within three calculation sections for different stages of construction: 1st stage – the initial faze (formation of the soil massif in its natural state), 2nd stage – excavation of the first layer of the pit, 3rd stage – excavation of the second layer of the pit. Based on the results of the calculations, the SSS analysis of the elements of the "soil massif - anti-landslide structures" system was carried out and the reinforcement of the retaining walls was selected. An assessment of the slope stability was also performed at the stage of full excavation of the foundation pit. 
It is shown that the advantage of using a plane FEM to assess the stress-strain state in the anti-slide structures is a much smaller amount of time spent on calculations and ease of understanding, but the disadvantage of this method is the lack of the possibility of taking into account the spatial stiffness of structures. It has been demonstrated that the use of spatial FEM allows taking into account the spatial stiffness of structures, which in the future makes it possible to more effectively design the retaining walls structures, however, modeling using this method is quite labor-intensive and requires significant resources of computer equipment for making calculations. 
According to the results of the calculations, the displacements obtained in the calculation using 2D modeling are on 6-43% more than using 3D modeling, the bending moments are on 12-33% more.