Geotechnical monitoring during the installation of cast-in-place piles

Abstract

An example is cited for the geotechnical monitoring of production operations involving the installation of cast-in-place piles under complex geologic-engineering conditions in a dense urban setting.According to domestic and international regulatory requirements [I, 2], reconstruction and new construction under conditions complicated by urban development should be carried out with continuous geotechnical monitoring of the preservation of neighboring buildings. As a minimum, monitoring should include the following: observations of the deformations of surrounding buildings from geodesic marks placed on the foundations, and beacons installed in the cracks of building structures; monitoring of the vibration parameters of foundations of adjacent buildings and bed soils; and, recording of changes in the groundwater table when excavating below the natural table. In the most complex cases, the monitoring program is supplemented by measurements of pore pressure and layer-by-layer strains and stresses in the beds of neighboring buildings. Accumulated monitoring experience suggests that none of the existing foundation technologies can be acknowledged a priori as safe for surrounding buildings. Every technology associated with the excavation of soil or tunneling in the ground exerts dynamic effects on neighboring buildings.Control of vibration parameters in structures of adjacent development, which may be excited during work production involving site development and substructure installation, is one of the most critical monitoring components. Dynamic monitoring is an early-warning tool that announces deviations from lenient production regimes, which has yet to result in settlement of the entity being preserved. In many cases, this effect can be reduced to values safe for neighboring buildings. The adjustment of lenient production regimes is most effective in those cases where it is carried out during the installation of a test site.In reconstructing the tenement building at No. 23 Malyi Morskyi St. in Saint Petersburg, the need to perform technological investigations of the installation of cast-in-place piles 620 mm in diameter, which had been proposed for use as foundations beneath frame columns, arose in connection with the decrepit state of the surrounding buildings.The geologic-engineering conditions at the site are characterized by the following stratification. A layer of silty sand, which is interrupted at a depth of 4 to 5 m by a 1 m lens of silty sandy loam of fluid consistency, resides from the surface to a depth of 6.8 m beneath a backfill soil 1.5-m thick. Underlying this to a depth of 23.5 m are marine and lacustrine-glacial silty-clayey soils of fluid consistency, which can change their properties from those characteristic of a solidlike body to those inherent to a liquid-like medium under effects encountered in construction. They are underlain by interbedded slightly and highly plastic glacial clayey soils. The total thickness of the latter amounts to 6.7 m; slightly plastic glacial clayey soils interbedded with...