2.4.2. Thrust Loading System

The thrust loading system was mainly composed of reaction wall, screw jack, and pressure sensor. The basic principle is that the trapezoidal load is applied by three jacks and reacting on the reaction wall and transferred to the test pile through the pressure sensor, as shown in Figure 5. The jacks were all screw jacks with a maximum lifting capacity of 10 t produced by Shanghai Baoshan Hugong Group, and were arranged at 9.8 cm, 35 cm, and 60.2 cm of the loaded section, as illustrated in Figure 7. The pressure sensor only played the role of load transfer in the thrust loading system, and its parameters are introduced in the following data acquisition system.

**Figure 7.** Layout diagram of screw jacks and steel strain gauges.

The monotonic and graded method was applied in the loading process of the trapezoidal load, and the single-stage loading process mainly includes the loading stage and the holding stage. The loading magnitude (*Fl*), the loading step length (Δ*F*), the loading rate (*Vl*), the loading time (*tl*) and the holding time (*th*) should be controlled during the loading process. He et al. [18], Zhou et al. [19] and Chen et al. [20] adopted the same loading method in the loading test of test pile, which kept Δ*F*, *Vl*, *tl* and *th* constant in the whole loading process. This method is only applicable to a type of test where the test pile does not produce cracks during the whole loading process. Therefore, the bearing characteristics experiments of the test pile were carried out according to Chinese specification (GB/T 50152-2012) [21].
