Deformation Law of Pile-anchor Retaining Foundation Pit in Deep Backfill Soil Sand-mudstone Composite Stratum

Abstract

[Objective] At present, most research in engineering field regarding foundation pit is based on the experience of excavations in soft soil and rocky strata. Given that the geological conditions in Chongqing involve deep backfill soil sand-mudstone composite stratum, it is essential to conduct a study on the deformation law of foundation pit. [Method] Taking the foundation pit project of Lanhuahu Parking Lot on Chongqing Rail Transit Line 10 as background, field-monitored data is utilized to summarize the horizontal displacement of retaining structures and the change law of land subsidence behind retaining piles. Additionally, the correlation between retaining structure horizontal displacement and land subsidence behind piles is explored. [Result & Conclusion] The maximum lateral displacement δh of the retaining piles ranges from 0.048% to 0.103% of the excavation depth H, which is significantly smaller than the statistical results observed in soft soil regions. The maximum land subsidence δv ranges between 0.033% and 0.22% of H, lower than that observed in gravel and soft soil excavations, and closer to the results observed in Qingdao soil-rock composite foundation pit. The influence range of foundation pit excavation extends from 1 to 1.5 times the excavation depth H. The relationship between the foundation pit maximum land subsidence δv and the retaining structure maximum lateral displacement δh can be expressed as δv = 0.45δh~2.35δh, with a mean value of 1.31δh. The ratio of the enveloped area of land subsidence to the enveloped area of retaining structure lateral displacement (Sw/Sp) is approximately 1.67.

Keywords

• foundation pit engineering
• backfill soil
• sand-mudstone
• horizontal displacement
• land subsidence
• monitoring and measurement