Research on the deformation response analysis of foundation pit retaining structure and adjacent highway subgrade under stratified dewatering and extreme rainfall conditions

Abstract

[Objective] To investigate the impact of stratified dewatering in a foundation pit under extreme rainfall conditions on the stability of the foundation pits retaining structures and the adjacent road embankment, [Methods]a three-dimensional finite element analysis model was constructed based on the deep foundation pit project of the Yancheng Railway Passenger Hub. The accuracy of the model was validated using field measurement data. By systematically analyzing the variation patterns of lateral displacement of the retaining structures, axial force of the concrete supports, and settlement of the adjacent road embankment during the stratified dewatering and excavation processes, the influence of stratified dewatering and extreme rainfall conditions on the lateral displacement of the retaining structures and the settlement of the adjacent road embankment was revealed. [Results] The results show that, under stratified dewatering conditions, the maximum lateral displacement of the retaining walls increased by approximately 7% to 45%, and the maximum bending moment increased by about 5% to 13% compared to the scenario without considering stratified dewatering. During the excavation process, the surface settlement of the road embankment without considering stratified dewatering was significantly smaller than that with stratified dewatering. When the rainfall condition increased from heavy rain(28.15 mm/d) to heavy downpour(100.80 mm/d), the lateral displacement of the retaining structures increased by about 40%. When the rainfall condition increased from heavy rain(50.00 mm/d) to heavy downpour(100.80 mm/d), the maximum horizontal displacements at the toe and shoulder of the road embankment slope increased by about 35% and 142%, respectively. Under extreme rainfall conditions(100.80 mm/d), as the embedment depth of the wall increased, the reduction in the maximum lateral displacement of the wall decreased from 13% to 6%, and the maximum horizontal displacements in various regions of the road embankment slope showed a gradually decreasing trend. As the horizontal distance of the internal supports decreased, the large lateral displacement of the wall reduced by about 9%, and the maximum displacement of the road embankment slope decreased by about 11%. [Conclusion] Stratified dewatering in foundation pits under extreme rainfall conditions has a significant impact on the stability of the retaining structures and the adjacent road embankment. It is recommended to appropriately increase the embedment depth of the retaining structures or reduce the horizontal spacing of the internal supports during deep foundation pit construction, especially during the rainy season, to achieve better control over the stability of the retaining structures and adjacent buildings.

Keywords

layered dewatering of foundation pit / foundation pit excavation / rainfall intensity / enclosure structure / adjacent highway