The practice of arranging a pit deeper than the level of the soles of the foundations of the surrounding buildings

Abstract

A rational constructive-technological decision to arrange a fence of a deeper pit for a new building than the depth of laying strip foundations of the surrounding buildings has been substantiated and tested in practice. The decision to arrange the fence was tested based on the results of complex experimental and theoretical studies under the conditions of a wet loess massif. At same time, regulatory restrictions on additional subsidence of these buildings foundations are provided. It has been proven that the additional subsidence of existing objects did not exceed the permissible values according to the norms. This happened due to the arrangement of the pit fence, the phasing of soil extraction in the initial stages under of the soil berm protection. The technology provided for the construction of a pit fence with sheet piling (I-beam No. 30) with a step of 1 m, with timber lagging between them. Then they installed the capping beam, struts, rakers and gradually raised the floor and outer wall of the parking lot of the new building.
 The results of long-term geodetic observations of the foundations deformations of buildings located in the zone of the pit influence of the new building at various construction stages of its enclosure are described.
 Sufficient convergence of the simulation results in the plane condition using the FEM and field studies was determined (the relative error did not exceed 20%). An elastic-plastic soil model of the "basement - foundations of an existing building - pit enclosure" system was used for modeling.
 The article describes examples of the results of FEM modeling of soil massif deformations at various stages of pit fence construction.
 It was determined that during construction the largest horizontal movements of the pit fence vary from 8 to 23 mm in the area of existing buildings.The maximum vertical movements of the bases foundations of these buildings amounted to 10 mm, which does not exceed the permissible values according to the norms.
 Prospects for further research on assessing the level of reliability of the pit enclosure by determining the variability parameters of the components of the system "foundation - foundation of the existing building - pit enclosure" have been determined.