# A Comprehensive Review of Open Caisson Modeling Technology: Current Practices and Future Prospects
## 5 Challenges and Future Directions
### Challenges
#### 5.1.3 Soil Variability and Unpredictable Subsurface Conditions  
Another significant challenge in open caisson excavation is interactions with extremely variable subsurface conditions, ranging from cohesive clay layers to lose sands and silts. These subsurface variations may induce excessive friction along the caisson walls, differential settlement, and difficulties in maintaining verticality during sinking. During open caisson excavation, [PERSON] et al. [163] conducted the field study on the deformation and stress characteristics of large open caissons in deep marine soft clay. They analyzed the deviations of caisson geometric posture, cone tip resistance, and lateral soil pressure. The findings provide valuable technical guidance for accurate modeling to predict ground movement and stress redistribution. Open caisson encounters various heterogeneous soil layers during the process of sinking. The inherent uncertainty and construction complexity often results in accidents such as deflection, sudden sinking, and sand gushing [164]. In recent years, researchers have extensively investigated the stress characteristics of caisson during excavation [10]. [PERSON] et al. [165], through field experiments, studied the force of the blade foot during the sinking process. [PERSON] et al. [166] evaluated a laterally loaded bridge caisson foundation in gravel using an in situ lateral load test. [PERSON] and [PERSON] [128] documented a case history of a caisson with a 20 m diameter, which became wedged due to the development of excessive soil-structure frictional stresses during sinking. Additionally, more recently, researchers [167; 168; 169] have investigated the settlement and performance monitoring utilizing diaphragm walls associated with the construction of a deep shaft. During caisson construction in dry sand, [PERSON] and [PERSON] [64] investigated soil deformation mechanisms from a small-scale laboratory study by analyzing data from seven tests to recognize the impact of significant caisson geometric properties and the competence of exterior cofferdams in controlling soil displacement. Two key mechanisms were identified as a driving ground movement: a compressive bearing zone beneath the cutting face and frictional forces contributions above the cutting face. [PERSON] et al. [170] conducted structural stress analyses based on automated caisson monitoring data and revealed that at the bottom four corners of the caisson, the vertical earth pressure was significantly greater than the other positions, depicting that at the four corners there was an apparent stress concentration phenomenon. Furthermore, the measured horizontal earth pressure at the base of the monitoring section was lower compared to pressures recorded at the middle and bottom regions of the caisson. This observation indicated the existence of a stress displacement region in the vicinity of the cutting face. During the sudden sinking process of an open caisson, [PERSON] et al. [156] investigated the soil disturbance and damage behaviors through the numerical simulation method. They found that the unequal distribution of soil damage was found to adversely impact the open caisson attitude and cause open caisson tilting. Periodic monitoring of caisson deformation and stress characteristics is crucial to ensure construction safety and to optimize design [164]. Using machine learning (ML) algorithms and monitoring data from the Changtai Yangtze River Bridge Project, [PERSON] et al. [171] estimated open caisson inclination. Several machine learning methods were evaluated to determine the most precise and productive prediction models. The findings provide ideal approaches with great accuracy and a low computation time. In engineering applications, these outcomes can improve the safety, stability, and control of open caisson sinking processes. Due to uncertain subsurface conditions and soil property variability, the excavation of open caisson's presents key challenges, which can result in increased friction, differential settling, and verticality problems.