# Force Analysis of Circular Diaphragm Wall Based on Circular Cylindrical Shell Theory
## 2 Project Profile  
The G3 Tongling Yangtze River Highway and Railway Bridge is a project under construction instead of the existing Tongling Yangtze River Highway Bridge, which connects the downtown area of Tongling on the south bank of the Yangtze River with the suburban area and the Zongyang County of Tongling on the north bank of the Yangtze River. The bridge is constructed according to the standard of \"4-line railway + 6-laneexpressway\". The four-line railway include two lines of prepared intercity railways and two lines of universal speed railways, from the south of Tongling to the Port in the north of the Yangtze River. The six-lane expressway is the six-lane G3 Beijing-Taipei Expressway with emergency parking belts on both sides. Combined, the railway and expressway of the bridge is 2682.2 m long. The main bridge is 1505 m long, and the main span is 988 m long. The approach bridge--the combination of the railway and expressway on the north of the Yangtze River--is 686.7 m long, and the approach bridge combining the railway and expressway on the south of the Yangtze River is 490.5 m long. The bridge adopts the joint type of cable-stayed bridge and suspension bridge and is designed as a cable-stayed suspension composite bridge. The north anchorage on the Zongyang Bank and the south anchorage on the Tongling Bank are the main components that bear the oblique tension. In this study, only the force and deformation of the circular diaphragm wall of the north anchorage foundation pit will be discussed in the construction process. The design size of the north anchorage is shown in Figures 1 and 2. The diaphragm wall of the foundation pit is a circular structure that is 1.5 m thick, and its outer diameter is 60 m long. Its bottom elevation is \(-\)50.500 m, its top elevation is +5.000 m, and its height is 55.5 m (excluding the cap beam). The circular diaphragm wall is divided into 40 slots, and there are 20 slots in the first-stage project, with a center-line arc length of 6.885 m, and 20 slots in the second-stage project, with a center-line arc length of 2.8 m. The cap beam is connected with the top of the circular diaphragm wall, with a total width of 4.5 m and a total height of 2 m, and the boundaries of the cap beam exceed both the inner and outer sides of circular diaphragm wall by 1.5 m. The excavation depth of the foundation pit is 47 m from the top of the cap beam to the bottom of the foundation. In order to meet the safety requirements of the circular diaphragm wall during the excavation stage of the foundation pit, the lining is set on the inner side of the circular diaphragm wall with a total height of 45 m. The thickness of the upper part (from 0 m to 15 m) of the lining is 1.5 m, that of the middle part (from 15 m to 30 m) is 2.0 m, and that of the lower part (from 30 m to 45 m) is 2.5 m. The circular diaphragm wall, cap beam and lining are all made of the same reinforced concrete. The strength grade of the concrete is C35 and it has an elastic modulus of 31.5 GPa, a Poisson's ratio of 0.2 and a bulk density of 25 kN/m\({}^{3}\). The foundation pit was excavated in layers using a top-down method, and one layer of lining (each layer is 3 m in height) was constructed after one layer of soil had been excavated, with a total of 15 layers. The specific construction situation is shown in Figure 2 and Table 1.