Assessment and prediction of the impact of new construction on subsoils and foundations of existing buildings under complex engineering-geological conditions of megacities

Abstract

The article is devoted to the assessment and prediction of additional deformations of subsoils and foundations of existing buildings during new construction in conditions of dense development in megacities with a complex engineering-geological profile, including weak clay strata, thixotropic water-saturated soils, and technogenic deposits. It examines the multifactor nature of changes in the stress-strain state of the soil mass during the excavation of deep pits, construction of new foundations, and transformation of the hydrogeological regime, as well as the role of loading history and technological impacts (vibrations, dynamics of construction equipment, liquefaction, ground volume losses). Results are summarized from comparing instrumental monitoring and three-dimensional numerical modeling by the finite element method for 32 objects with pit depths of 8,5-18,4 m and distances to existing development of 2-25 m, including observations for 148 buildings; nonlinear soil models Hardening Soil and Hardening Soil with Small-Strain Stiffness were applied with parameter calibration by back-analysis based on early construction stages. It is shown that there is a systematic underestimation of stiffness from standard laboratory tests compared to effective parameters obtained from back-analysis, which is critical for the correct description of small-deformation zones. A typical structure of prediction errors is identified: in the near zone up to 10-12 m, settlements are often underestimated due to hard to-formalize technological factors, while in the far zone overestimation is frequently observed, associated with incorrect description of deformation attenuation and neglect of the stiffness contribution from the existing development itself. The kinematic relationship between the maximum horizontal deflection of the retaining structure and surface settlement (ratio of 0,68-0,75) is quantitatively confirmed, with nonlinear reduction of absolute deformations as flexural stiffness of the structure increases and the effect of diminishing efficiency. A probabilistic assessment of damageability is provided, demonstrating a sharp increase in risk for buildings in poor technical condition already at additional settlements of about 10–12 mm and the increased importance of unevenness and deformation rate. The material enables identification of relevant parameters for adaptive design, justification of protective measures, and extension of monitoring with account for long-term consolidation and secondary settlements.