Development of methods for predicting and preventing the uplift of underground structures at high groundwater levels taking into account long-term consolidation and creep of soils

Abstract

Ensuring the stability of underground structures under high groundwater level conditions requires consideration of long-term rheological processes that determine the evolution of the stress-strain state in the contact zone between the structure and the base. The interaction of embedded objects with a water-saturated soil mass is characterized by a decrease in effective stresses during groundwater level rise, which leads to a reduction in frictional forces along the lateral surface and weakening of the anchoring effect of the overlying soils. An additional influence is exerted by the creep of the soil skeleton, accompanied by the time-dependent relaxation of shear stresses and leading to progressive degradation of retaining forces even under a stable hydrogeological regime. Numerical modeling by the finite element method using the soft soil creep model made it possible to quantitatively evaluate the change in the factor of safety against uplift for various soil types over 50 years of operation. For peaty deposits, the reduction in the factor reached 31,1%, with the critical value of 1.0 being exceeded already in the 5-10th year, whereas for medium-density loams the loss amounts to only 9,2%. Rheological parameters, including the secondary consolidation coefficient and modified compression indices, demonstrate significant variability: the Ca/Cc ratio exceeds the threshold value of 0.04 for organic soils, indicating the need for explicit accounting of viscoplastic behavior. Cyclic fluctuations in groundwater levels with amplitudes from 0,3 to 2,5 m cause nonlinear accumulation of upward vertical displacements of the structure, reaching 93,8 mm in soft clays under frequent cycles over 30 years. Comparative analysis of structural measures revealed the limited long-term effectiveness of soil anchors due to relaxation of prestressing, amounting to a loss of up to 62% of the force by the 50th year, while the combination of drainage and a surcharge slab provides a stability factor of 1.58 at moderate costs. Multiple regression analysis established the determining role of the secondary consolidation coefficient and specific cohesion in the prediction of long-term stability, with a multiple correlation coefficient of 0.96. Model verification based on geotechnical monitoring data from real objects confirmed that the deviation of calculated displacements from observed values remains within 4,8-9,8%. The obtained regularities emphasize the necessity of a differentiated approach to assigning safety factors depending on the genetic soil type and the inclusion of rheological characteristics in normative methods for calculating underground structures under complex hydrogeological conditions.