Investigations into ground surface settlement characteristics of excavation under dewatering and excavating conditions using the response surface experimental design method

The soil surrounding an excavation experiences continuous ground settlement due to the combined effects of dewatering and excavation, which significantly impacts both the stability of the excavation and its surrounding environment. Objective To elucidate the key factors governing ground settlement during the dewatering and excavation process, as well as to establish an empirical model based on these findings, this study systematically investigated a deep metro station excavation in Hangzhou, situated on a typical river terrace with a dual-layered geological structure. Methods Firstly, a numerical analysis method for settlement in braced excavations was proposed by incorporating a hybrid Mohr-Coulomb (MC)-Modified Cambridge (MMC) constitutive model, derived from the deformation mechanism of excavation soil and a comparison with actual monitoring data. Subsequently, the response surface method (RSM) was employed, to establish an empirical model for ground settlement caused by dewatering and excavation under dual-layer geological structure conditions in the study area, accounting for various operational factors and their interactions, and to analyze the zoning characteristics of ground settlement. Results The findings suggest that the drawdown of the groundwater table, Hd, exerts the most significant influence on the surface settlement, followed by the depth of the underground diaphragm wall, Hw, and excavation width, B. Additionally, there is a notable interaction between B and Hd. The regression model developed based on these factors demonstrates high accuracy in predicting maximum surface settlement, Hm. Conclusion This study not only presents an empirical model for excavation engineering under similar geological conditions but also provides a practical framework for excavation design, construction, and monitoring. These contributions are crucial for effectively managing settlement deformation in excavations and their surrounding environments.