The results of the study of the interaction of the pit enclosure made of flexible retaining walls, arranged in the conditions of dense construction, with the soil foundation are presented.
 Calculations were carried out by the method of numerical modeling, using the Plaxis software complex. The modeling is performed in a three-dimensional space, which provides an opportunity for a comprehensive assessment of the stress-strain state (SSS) of the elements of the system "soil array - retaining walls - structures of existing buildings" when using complex configurations of retaining walls and taking into account the factor of their spatial stiffness.
 For the analysis of the results, 4 characteristic sections were chosen. Modeling was performed taking into account the following stages:
 1) the initialization stage (formation of the soil massif in its natural state);
 2) installation of a retaining wall;
 3) alternate development of the pit to the design mark;
 4) load from the building at the stage of operation.
 Based on the results of the calculations, the SSS analysis of the elements of the system "soil massif - retaining walls - structures of existing buildings" was performed, and the reinforcement of the retaining walls was selected, and the costs of the main materials were determined.
 It is shown that taking into account the spatial stiffness of the retaining wall of the pit enclosure makes it possible to more effectively estimate the SSS of the retaining wall structure, more correctly estimate the additional deformations of neighboring buildings, due to taking into account the change in the stiffness of the retaining wall of a complex configuration, and therefore, in the future, to more effectively design the constructions of retaining walls.
 According to the results of the calculations, it is shown that retaining walls made in 2 rows in a staggered order, with piles with a diameter of 420 mm, have greater rigidity than retaining walls made in 1 row with piles with a diameter of 620 mm. Therefore, in order to reduce additional subsidence of neighboring buildings and reduce horizontal movements of the retaining wall, the option of the retaining wall made by placing piles in a staggered order is a priority in conditions of dense construction.
 Armature costs for option 1 are 46% higher compared to option 2. These results indicate that the 2nd option of installing a retaining wall is a more economical solution, however, in conditions of dense construction, its use is limited, since the settlement of neighboring buildings in this case will be greater, due to the lower rigidity of the retaining wall.