# A Comprehensive Review of Open Caisson Modeling Technology: Current Practices and Future Prospects
## 5 Challenges and Future Directions
### Challenges
#### 5.1.2 Earth Pressure During Sinking
However, [PERSON]'s method predicted a distinct distribution characterized by a rapid earth pressure increaement to a depth of 4.5 times of the shaft radius, followed by a reduction to zero at a depth of 8.5 times the shaft radius. Figure 14: Earth pressure distribution around a shaft with depth h, radius \(a\) in cohesionless soil without surcharge [142; 146; 151; 152; 153]. [PERSON] and [PERSON]'s solution provided both lower and upper bounds for lateral earth pressure, corresponding to \(\lambda=1\) and \(\lambda=\mathrm{K}_{0}\), respectively. Notably, for \(\lambda=1\), the earth pressure aligned well with [PERSON]'s predictions. For shallow shafts, where the height ranged between one and two times of the shaft radius, negligeable differences among the theoretical methods are revealed, as shown in Figure 14. Currently, due to the dependence of the sinking and soil excavation construction of caisson foundations on the engineering experience, earth pressure distribution is unclear during soil excavation, resulting in limited control of the sinking operation [154]. Based on prior studies, it can be summarized that, unlike under plane strain conditions, earth pressure on the cylindrical walls did not rise linearly with depth for axisymmetric excavations conducted under active conditions. The normalized pressure falls and eventually approaches a depth-independent constant as soil movement increases. However, since the lateral stress coefficient cannot be accurately determined, theoretical solutions reflect notable differences. [PERSON]'s model assumed that the distribution of earth pressure is triangular and s increases linearly with depth. Although this simplification works well in many real-world situations, it might not take into account the non-linear soil behavior or intricate soil-structure interactions. The theories [PERSON] (1940) [141] and [PERSON] (1943) [142] are based on Rankine-based plastic equilibrium along horizontal planes under presumptions to minimize stress singularities at elastic-plastic boundaries. Although the earth pressure calculations align well with other theoretical findings, one major shortcoming of the theory is its unrealistic prediction of the plastic zone form, which, according to [PERSON], expands with depth and asymptotically approaches a constant radius, revealing theoretical limitations [151]. The safety of the sinking caisson foundation structure and its reliability is significantly impacted by soil excavation that solely relies on engineering expertise; therefore, more research is required to fully understand the sinking process through soil excavation. The earth pressure at the foot blade is an essential factor in determining the sinking resistance of a caisson foundation, and it serves as a crucial foundation for developing a soil excavation plan. An estimated computation model of the ultimate soil resistance of a caisson foundation during sinking was constructed based on the slip line field theory by [155], and equations for calculating the ultimate load capacity for the plane strain problem and the axisymmetric conditions were derived. [PERSON] et al. [16] employed identical methods to figure out the annular caisson foundation's ground pressure distribution properties, which were confirmed by practical examples. Using the centrifugal model test, they investigated the earth pressure beneath the foot blade and discovered that the ratio of earth pressure remains nearly constant between the foot blade's horizontal and oblique positions. [PERSON] et al. [156] and [PERSON] et al. [157] investigated the process of the caisson foundation's abrupt sinking and discovered that the foot blade's earth pressure will drop noticeably prior to the caisson foundation's abrupt sinking. A couple of investigations have been conducted on the end resistance of medium-sized or super large caisson foundations, while the rarer of current research has been on small- and medium-sized caisson foundations. [PERSON] et al.