Assessment of changes in hydrogeological conditions and their impact on the deformation behavior of building foundations during new construction in dense urban environments

Abstract

In the context of intensified urban development in megacities, significant transformations of the hydrogeological regime of territories caused by the barrage effect of underground structures, water-retention systems, leaks from utilities, and changes in infiltration nutrition lead to complex changes in the stress-strain state of the soil foundations of existing buildings. An analysis of long-term monitoring of groundwater levels and foundation deformations in the central areas of a major Russian city demonstrates that the maximum fluctuations in piezometric levels occur not during active excavation, but with a delay of 3-7 months after the start of operation of the buried parts of new structures, which is due to the inertia of filtration processes in multi-layered aquifers. The established correlation between the depth of the pits and the amplitude of changes in the groundwater level, characterized by a determination coefficient of 0.847, indicates a nonlinear nature of the hydrogeological impact that significantly exceeds the predictions obtained from simplified analytical models. Comparison of the predicted and actual additional settlements of buildings located in the area affected by new construction reveals a systematic excess of the observed values over the calculated values by a factor of 1.3-1.7, while the contribution of the redistribution of effective stresses due to changes in pore pressure is 41-56% of the total settlement. The identified stages of the deformation process – primary elastic, secondary consolidation, and tertiary creep – demonstrate the duration of the secondary stage up to 14 months, which significantly differs from traditional concepts. The influence of the anisotropy of the filtration properties of soils (the ratio of horizontal and vertical permeability from 2.4 to 7.8) and the seasonal component of the hydrogeological regime, which leads to an increase in the amplitude of level fluctuations by 1.8-2.3 times in the barrage effect zone, is particularly significant. The use of calibrated numerical models that implement a coupled formulation of the joint filtration and deformation problem using nonlinear soil models reduces the discrepancy between predictions and field data to 8-12%, confirming the crucial role of hydrogeomechanical processes in the formation of uneven deformations, slopes, and relative differences in the settlements of historical buildings. The results obtained highlight the need to improve the regulatory framework and design practice in the direction of mandatory consideration of related hydro-mechanical effects when assessing the impact of new construction on existing buildings in dense urban environments, especially in historical centers, where the protection of architectural monuments requires increased accuracy in predicting geotechnical risks and the implementation of continuous automated monitoring systems.