# A Comprehensive Review of Open Caisson Modeling Technology: Current Practices and Future Prospects
## 1 Introduction  
In subsurface excavations in urban areas, shafts are currently gaining renewed significance as the growing demand for an upgraded transportation infrastructure and environmental pressures continue to increase. For the traditional retaining structure for deep excavation in soft soil distribution area, confined water induces serious problems. During the dewatering process, serious risks and emergency measures can result in uncertainty in construction; this process can also face serious environmental influences. To solve these problems, press-in open caisson modeling and continuous combinations to form large-scale deep excavation methods have been proposed and promoted in the Shanghai Subway of China. The development of potential continuous combined open caisson requires systematic modeling methods to simulate and understand the working conditions under extreme conditions. However, there is a distinct gap in the literature regarding large-diameter open caisson shafts. In the existing literature, there seems to be a scarcity of well-documented case studies examining the performance of open caissons. This scarcity was not unexpected while considering the difficulties and costs associated with monitoring construction sites. Potential issues like sinking difficulties, excessive inclination, or instability of the cutting surface are expected to occur during the construction of a deep open caisson [1; 2; 3]. In urban areas, shafts are generally built by caisson sinking or underpinning. [PERSON] and [PERSON] [4] described underpinning as a construction technique which involves incremental excavations and the installations of a pre-cast concrete segmental ring, which includes watertight gaskets. This process occurs when the grouting behind the annulus is completed, as shown in Figure 1a. In this traditional open caisson construction technique, during excavation, a concrete surface collar is cast to support the shaft. Advancement of the excavation is carried out in stages, with structural floors and stepping or benching installed as the caisson descends. Grout is used to prevent seepage and stabilize the base, while the permanent roof slab and surface treatments ensure the structural integrity of the completed shaft. This method is well-suited for shallow shafts and soil conditions that remain stable without extensive lateral support. Figure 1: (**a**,**b**) Construction technique of underpinning and press in caisson sinking modified after [4]. Figure 1b shows another approach using the press-in method, which is particularly advantageous in soft or unstable soil conditions. A surface collar and jacking arms are utilized to press the caisson segments into the ground, reducing reliance on traditional excavation methods. Bentonite slurry fills the annulus, providing lateral support and minimizing the risk of soil collapse during the sinking process. The base of the caisson is stabilized using a concrete tremie plug and single-size stone. This method enhances construction safety and precision in densely populated urban areas where minimal ground disturbance is essential. Essentially, caisson-sinking as described by [5], involving progressively lowering the shaft structure either by self-weight or with the assistance of jacks in a controlled manner from the surface level, as shown in Figure 1b. A cutting edge is connected to the first caisson ring to aid the sinking operation in this technique. Regardless of the method employed, any underground construction project induces ground movements that can damage existing structures. Current practices in geotechnical engineering strive to minimize these movements, emphasizing the significance of accurate assessments for successful project outcomes. For the Heathrow express trial tunnel constructed in London clay, [PERSON] et al. [6] investigated the ground movements during shaft construction. The study validated ground movement prediction methods using monitored data.