# Model Test on the Behaviors of Deep Excavation with Lateral Confined Water
## 1 Introduction  
With the rapid development of coastal urban modernization, the utilization of underground space for urban rail transit, municipal facilities, and high-rise building basements has become increasingly frequent. This trend necessitates excavations that often contend with confined water conditions. Different from common confined water foundation pit projects, these excavations may encounter aquifers hydraulically connected to oceans or rivers. Additionally, factors such as artificial dewatering and recharge [1], typhoons, and heavy rainfall cause confined water levels to exhibit dynamic fluctuations, adding complexity to the surrounding environment. When a deep excavation is located withinconfined aquifer strata, the presence of confined water can partially alleviate the differential settlement in nearby structures caused by excavation-induced dewatering. However, it also poses challenges to the overall stability of the excavation structure. The inadequate consideration of confined water effects may lead to severe engineering accidents, as reported in coastal cities such as Shanghai, Hangzhou, Nanjing, and Zhanjiang, China [2; 3; 4; 5]. Therefore, it is imperative to conduct an in-depth investigation into the influence of confined water on excavation behaviors, so as to ensure the safety of excavation projects and to support the sustainable development of urban underground spaces. Soil disturbance during excavation significantly influences the response of strut structures in deep foundation pits [6]. Additionally, the distribution and fluctuating water levels of confined water induce extra complexity in the analysis of forces and deformations, necessitating that engineers thoroughly consider the mechanisms and extent of confined water pressure effects. Confined groundwater affects foundation pit stability primarily at the sidewalls and the pit bottom. Laterally, confined water pressure acts perpendicularly to the sidewalls, which can lead to the deformation of retaining structures and potential sidewall seepage. Vertically, confined water pressure at the pit bottom may cause sand boiling, bottom heave, or even intrusions. Previous scholars have studied the response of lateral confined water to foundation pit excavation. [PERSON] et al. [7] explored the influence of lateral confined water on the deformation characteristics of a foundation pit through numerical analysis, and the results show that diaphragm wall deformation in deep excavations is related to the earth pressure distribution on the sidewall, and lowering the confined water level can reduce external loads on the diaphragm wall, thereby reducing wall deformation. Similarly, [PERSON] et al. [8] used a finite element model to study the mechanism of diaphragm wall deformation caused by dewatering prior to excavation, identifying soil-wall interaction and redistribution of earth pressures as key factors. [PERSON] et al. [9] reported a case wherein seepage occurred in a foundation pit influenced by lateral confined water layers due to defects in tri-axial mixing piles and weaknesses around abandoned piles, which allowed confined water to seep through abandoned pile holes into the pit. This disturbance caused noticeable ground settlement and roadway cracking. For vertical confined water pressure at the pit bottom, issues like intrushing can occur when the weight of the impermeable layer above the confined aquifer is less than the confined water pressure [10]. [PERSON] [11] studied excavation failures using a centrifuge model, finding that piping occurred when confined water pressures reached 1.05-1.18 times that of the earth pressure above the confined aquifer, while bottom heave occurred at 1.11-1.30 times, and sand boiling at 1.28-1.32 times. [PERSON] et al. [12] developed a numerical model for excavations in soft clay overlying confined aquifers, examining failure mechanisms and stability as confined water pressure rises. [PERSON] et al.