# Bearing Capacities and Failure Behaviors of F-Type Socket Joint in Rectangular Pipe Jacking Tunnel
## 2 Full-Scale Experiments
### Test Overview Rectangle Pipe Jacking  
To consider the research objectives and test loading conditions, the rectangle pipe jacking test section size was set at 1500 mm \(\times\) 1625 mm \(\times\) 1075 mm (length \(\times\) width \(\times\) height). F-type socket joint construction, as shown in Figure 1, mainly contains the pipe body concrete, a steel ring, and a waterproof rubber ring; the section size and reinforcement of the pipe section are shown in Figure 2. The assembly process through the steel ring extrusion socket rubber ring was set to complete, so as to achieve the purpose of waterproofing and resistance to deformation of the joint; the rubber ring section is shown in Figure 3. The pipe joint was cast in C50 concrete, and the steel ring was made of 10 mm thick Q235 steel ring, which was buried at the socket end of the pipe joint in the course of casting. The mechanical property indexes of concrete materials, the mechanical property indexes of steel and the mechanical property indexes of haw  
Figure 1: Joint construction. (**a**) Detailed dimensions. (**b**) Joint socket segment. (**c**) Cross-sectional dimensions and reinforcement. (**d**) Header socket segment. (**e**) Olecranon rubber section size. The bending test of the rectangular pipe joint was divided into three groups of conditions, and each group of conditions was assembled from two pipe joints, with a total length of 3 m. The horizontal restraint device was arranged outside the side wall of the pipe joint to induce the pipe joint bending deformation during the loading process, and playing a lateral protection role [26]. The test load was applied through the jack at the upper end of the counterforce frame, the distribution beam was used to transfer to the pipe joint, and finally, the joint bending test loading was completed; the experimental loading process is shown in Figure 2.  
To simulate the vertical restraint effect of the stratum on the pipe joint in actual engineering, the vertical support of the stratum on the pipe joint was achieved by uniformly arranging the equivalent foundation springs at the bottom of the pipe joint. The restraint effect of different stratum conditions was achieved by changing the number of equivalent foundation springs. The correlation between the number of springs and the equivalent bed coefficient was based on the principle of equal foundation reaction force per unit displacement of the foundation, which is \(n\cdot k=K_{v}\cdot S\); the equivalent foundation stiffness can be calculated, where \(K_{v}\) is the number of equivalent foundation springs and S is the area of the pipe jacking base plate. The foundation springs were tested by loading tests and the single spring stiffness was obtained as \(k=1734\) kN/m. The foundation springs were arranged in three ways, with 9, 6 and 4 springs uniformly arranged, respectively, as shown in Figure 3. \begin{table}
\begin{tabular}{l c c c c c} \hline \hline
**Material** & **Elastic** & **Cube Compressive** & **Yield Strength** & **Extreme Strong** & **Shore A Hardness/\({}^{c}\)** & **Tensile Strength/MPa** \\  & **Modulus (MPa)** & **Strength/\({}_{cw}\)** & **MPa** & **\(f_{y}\)**/MPa** & **\(f_{w}\)**/MPa** & \\ \hline concrete & 34,500 & 53.1 & & & \\ Q235 & 19,600 & & 216 & 352 & & \\ HRB400 & 203,000 & & 385 & 527 & & \\ rubber & & & & 54 & 12.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mechanical properties of test materials. Figure 3: Spring support. Figure 2: Bending test of joint. Circumferential strain gauges were arranged in the concrete and steel ring at the joint area of the pipe joint to measure the force deformation characteristics at the top and bottom plates, side walls and chamfers of the pipe joint. In addition, to study the cross-sectional deformation of the pipe joint during the test loading process, three horizontal, vertical and oblique guyed displacement meters were arranged at the joint in the form shown in Figure 4.  
Joint shear test loading was displacement-controlled, and the loading system was divided into 14 levels.