# Study on the Earth Pressure during Sinking Stage of Super Large Caisson Foundation
## 4 Analysis of Monitoring Data
### Distribution Characteristics of End Resistance of Caisson Foundation  
If the sinking process of the caisson foundation is smooth during soil excavation, it can be considered as equilibrium condition under the actions of gravity, buoyancy, bottom resistance, and side friction resistance. At the first sinking stage, the side friction resistance is almost close to 0, and the force equilibrium condition of the caisson foundation can be expressed in Equation (1). From Equation (1), the total end resistance can be obtained under the condition of not considering the side friction resistance. \[G-N_{\rm w}=R_{\rm b}+R_{\rm f} \tag{1}\]  
where, \(G\) is the gravity of caisson foundation, \(N_{\rm w}\) is the buoyancy, \(R_{\rm f}\) is the side friction resistance, and \(R_{\rm b}\) is the end resistance. For the distribution of the end resistance \(R_{\rm b}\) in different area of the caisson foundation, it can be calculated as Equation (2) if the earth pressure at the foot blade was known. \[R_{\rm b}=\sum_{i=1}^{n}\left(p_{i}^{\rm u}A_{i}^{\rm t}+\lambda_{i}p_{i}^{\rm u }A_{i}^{\rm b}\right) \tag{2}\]  
Figure 18: Averages of the field measured soil pressure with soil excavation step. where, \(n\) is the total number of zones of caisson foundation, \(p_{i}^{\text{u}}\) is the earth pressure on the tread, \(A_{i}^{\text{t}}\) is the tread area of the foot blade, \(A_{i}^{\text{b}}\) is the projected area of the incline of the foot blade, and \(\lambda_{i}\) is the scale factor of earth pressure between the incline and the tread of the foot blade. Here, the scale factor can be considered as the constant variable, therefore, by combining Equations (1) and (2), the distribution of end resistance of the caisson foundation can be obtained. After the first stage of soil excavation, the elevation of the foot blade in the outer bulkhead area was \(-32.95\) m, and the foot blade was buried into the soil by \(2.95\) m, hence, the side friction resistance can be ignored during the first stage of soil excavation. The end resistance can be calculated using the total weight and buoyancy of caisson foundation, and then, the end resistance in each area of caisson foundation can be also obtained based on the earth pressure and shape of the foot blade (Equation (2)). Figure 19 showed the variation and distribution of end resistance in each area during soil excavation procedure. From Figure 19, with respect to outer bulkhead, outer partition wall, inner bulkhead and inner partition wall area of the caisson foundation, the end resistances were respectively 26.3 thousand tons, 8.8 thousand tons, 10.1 thousand tons and 18.1 thousand tons before soil excavation. After soil excavation in the inner compartment (step 1), the end resistance of the inner partition wall decreased by 6.6 thousand tons, it slightly increased in the outer partition wall and inner bulkhead area, while it increased by 4.78 thousand tons in the outer bulkhead area. Then, after soil excavation step 2, the end resistance of the inner partition wall decreased by 3.31 thousand tons, it decreased by 2.57 thousand tons in the inner bulkhead area. Due to the total end resistance keeps constant, the reduced end resistance in the inner areas has transferred to outer areas. In the outer partition wall and outer bulkhead, it gradually increased by 2.66 thousand tons and 3.22 thousand tons respectively. After soil excavation step3, the end resistance in the outer bulkhead significantly increased to 43.53 thousand tons, it decreased by 3.22 thousand tons in the outer partition area, and it fluctuated around 6.0 thousand tons in the inner bulkhead and inner partition area. After the first stage of soil excavation(Figure 20), the end resistance in the outer bulkhead is 42.17 thousand tons, and it was 9.8 thousand tons, 6.27 thousand tons and 4.97 thousand tons respectively in the outer partition wall, inner bulkhead, and inner partition area. It can be concluded that the end resistance mainly concentrated on the outer bulkhead area.