General recommendations are presented for geotechnicai monitoring, and an example of monitoring during construction of a transportation-commercial complex in the center of Saint Petersburg is given.Geotechnical monitoring is one of the most important components of the geotechnical accompaniment of urban reconstruction [1]. Monitoring attaches special urgency under conditions where weak clayey soils prevail, and is conducted to ensure the reliability of structures being raised, and preservation of the surrounding setting and utilities. It is a tool for the on-going correction of work production during site development and substructure installation.The existence of a well-founded structural solution and a flexible procedure for performing work is a necessary, but insufficient condition for successful construction. A multitude of additional factors affect the production process: the qualification of personnel, the condition of the equipment, observance of rules, etc., as well as noncorrespondence between the computational schemes employed for geotechnical substantiation of the contractor design and plan for work production, and the actual geotechnical situation.The geological and hydrogeological media, capital development, and critical utilities located in the zone of risk associated with the construction or reconstruction of an entity should fall within the sphere of monitoring, in addition to the construction site.Monitoring consists of two stages -preparatory and operating. The following work is performed during the preparatory stage: 9 analysis of initial information on results of inspection of the surrounding setting; 9 examination of the technical status of the surrounding setting in the zone where monitoring is being conducted, and recording of defects. 9 determination of background parameters of the oscillation of building structures due to on-going influences (transport, work in progress nearby, etc.); 9 the installation of crack-opening beacons and sensors; 9 determination of the tilt of building walls, and the nonuniformity of settlements; 9 the installation of inspection wells for monitoring the ground-water table, and the installation of geodesic marks; and, 9 more precise definition of design criteria with respect to permissible effects.
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...
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