Field Studies of the Stressed State of the «soil base – combined pile raft foundation» System of the Multifunctional Complex in Kharkiv City

Abstract

In the projects of buildings and structures, in the last two to twenty-five years, in world practice, the so-called combined pile raft foundation (CPRF) is increasingly used, for which, in the design and calculations, it is assumed that the calculated load from the building is distributed between the piles and the raft, allowing up to 50% inclusion in the work (resistance) of the raft. As part of the scientific and technical support [1-8] of the construction object, instrumental automated monitoring of the stress state of the «soil foundation - combined pile raft foundation» system of the multifunctional complex on St. Pushkinska, 2 in Kharkiv (Ukraine) is carried out. The building has 7 floors and a mezzanine floor, including 2 floors of underground parking, 5 floors of shopping and entertainment area. There is a parking lot on the first 2 floors. The building system is a monolithic reinforced concrete frame with beamless floor slabs. The foundation of the building is a combined pile raft foundation with the centering of bored piles under the load-bearing elements of the frame. The soil base is represented by Quaternary alluvial-deluvial sediments – loams, sands and clays. As part of the implementation of the project, 23 sensors of two types were installed during the zero-cycle construction works: strain gauges (Geosense, England) to determine the stresses in the shafts of bored piles and in the upper and lower grids of the raft reinforcement and soil pressure sensors (Geokon, USA), which were placed under the sole of the raft. The results of the monitoring showed that the actual pressure under the raft does not exceed the pressure from its own weight of the raft (≈25kN/m2), which indicates the absence of inclusion in the work of the raft due to insignificant relative settlements of the combined pile raft foundation. Taking this fact into account when modeling the "base - foundation - structure" system and calculation in the SOFiSTiK showed a qualitative and quantitative convergence of effort values in reinforced concrete structures of a combined pile raft foundation.