Predicting additional settlements of the surrounding buildings during the construction of an underground parking lot using the wall-in-the-ground method in a densely built-up urban area, taking into account the gradual development of the foundation pit

Abstract

In the context of the intensive development of underground space in megacities, predicting additional settlements of the surrounding buildings during the construction of underground parking lots using the wall-in-the-ground technology is crucial for ensuring the preservation of historical buildings in a densely built-up urban environment. An analysis of the multifactorial interaction between the enclosing structures, the soil mass, and neighboring structures reveals the complex kinetics of deformation processes caused by the sequential excavation of the pit, the redistribution of stresses, changes in the hydrogeological regime, and the rigidity of the support system. Numerical modeling based on the Hardening Soil elastoplastic model, taking into account small deformations, allows for the step-by-step development of horizontal movements of the fence and vertical settlements of the day surface, demonstrating the characteristic shape of the settlement mound with a maximum at a distance from the wall, where the position of the extremum correlates with the depth of the excavation, the length of the filling, and the type of spacers. Comparison of different fastening schemes – anchor, spacer, and top-down – establishes that the use of technology with sequential device of overlaps provides a reduction in settlements by 2.0-2.3 times due to increasing the overall rigidity of the system and limiting the movements of the upper part of the structure. Quantitative patterns of accumulation of deformations at the stages of production of works indicate a nonlinear nature of the process, in which up to 18,7% of the final settlements are formed already at the stage of the wall device, and the maximum increment falls on the stage of the excavation of the second and third tiers. Verified calculations show that the nonlinear multi-stage approach reduces the prediction error to 9.9% compared to simplified empirical methods that overestimate values by 56-62% and linear models with a deviation of 30-35%. Stable correlations between the soil deformation modulus and the amount of settlement, the ratio of horizontal movement of the fence and vertical surface deformation (0.83 on average), as well as the exponential attenuation of settlements, which determines the influence zone within 1,4-2,7 depths of the pit, depending on the design solution, have been established. The identified effect of delayed stabilization of settlements for 18-42 days after excavation and the unevenness of foundation deformations emphasize the need for spatio-temporal analysis to justify monitoring programs and protective measures, including compensatory injection. The obtained dependencies and quantitative indicators contribute to the improvement of geotechnical forecasting methodology, optimization of design solutions, and minimization of risks in the development of underground space in historical city centers, providing specialists with tools for assessing the relevance of specific technological approaches in complex urban conditions.