TRENDS IN THE DEVELOPMENT OF PROCEDURES FOR THE INSTALLATION OF FOUNDATION-PIT ENCLOSURES IN A DENSE URBAN SETTING

摘要

The "wall in the ground" ― both monolithic, and also sectional with monolithizing of the joints in a trench with a bentonite grout ― is frequently used as an enclosing structure for large-scale and critical underground structures in Moscow. The advantages of this design are as follows: high strength and impermeability of the enclosure; the ability to work out an installation procedure; the possibility of including the enclosure as a component part of the foundation design, etc. At the same time, heavy material consumption (especially for a temporary enclosure), and also a possible change in the hydrogeologic regime of the area with intersection of accumulated paths of ground-water filtration should be classed as disadvantages of the procedure used to build the design. In the majority of cases, excavators with clamshell equipment on a pressure rod (the imported "Pok-lein" and "Casagrande" types of excavators, or domestic excavators, for example, the EO-5124) are used to open a trench for a clay grout (a basic element of the "wall-in-the ground" method. The width of the excavated trench is usually 600 mm, and the depth of the excavation will reach 20 m. Certain procedural difficulties resulting occasionally in risk of softening of the foundation beds of nearby buildings occur in a number of cases when soils with course inclusions are excavated with clamshells.