## 5 Field Test
### Structural Design Parameters  
The test is intended to be a three-ring steel corrugated plate-mold bag concrete support structure applied sequentially downwards from ground level. Each ring is 710 mm in height and is made up of twelve steel corrugated steel plate members of equal arc length. Each steel corrugated plate is designed with an external diameter of 6240 mm, an internal diameter of 6000 mm, a circular angle of 30\({}^{\circ}\), an internal arc length (L) of 1570 mm, and a wave shape of 200 \(\times\) 55 mm. The width of the end flange plate (B\({}_{1}\)) is 100 mm, with six  
Figure 13: Test site and stratigraphic distribution: (**a**) test site, (**b**) circular shaft plan design, and (**c**) stratigraphic distribution. bolt holes of 22 mm diameter reserved for the circumferential connection. The width of the side flange plate (B\({}_{2}\)) is 80 mm, and five bolt holes of 35 \(\times\) 22 mm are evenly arranged along the arc length for longitudinal connection, as shown in Figure 2. All parts of the corrugated plate are made of a 7 mm thick Q235 carbon steel plate. The steel corrugated panel is pre-drilled with a 53 mm diameter concrete pouring pipe (\(\Phi_{1}\)) at the center and a 25 mm diameter pressure control pipe (\(\Phi_{2}\)) at the top. The mold bag laid behind the steel corrugated panel is made of a rectangular geotextile with a width of 1657 mm and a length of 1780 mm, which is folded in half and sewn with two strip geotextiles at the ends (shown in Figure 3a). The strip geotextile is 833 mm long, 100 mm wide, and has a semicircle of 100 mm diameter at both ends (shown in Figure 3b). The theoretical volume of a single mold bag after forming is approximately 0.134 m\({}^{3}\). The thickness of a single mold bag of concrete is determined by the thickness of the aperture of the corrugated steel plate on the excavation surface. At the same position as the steel corrugated panel, the concrete pouring pipe and the pressure control pipe are reserved. In order to compare the application effects of different mold bags, the first and second rings use polyester filament woven geotextiles, and the third ring uses polyester filament spun-bond needle-punched non-woven geotextiles. In the case of actual field tests, the lateral stability of the support structure can be provided by both vertical and lateral bolts. Considering the complexity and diversity of the actual field construction, to ensure the lateral stability of the support structure, we can use longitudinal and radial reinforcement on the corrugated steel plate and the whole support structure. This will allow us to enlarge both the excavation radius and depth by increasing the stability of the support structure. The main technical indicators of each are shown in Table 2.  
The grouting material for this test was prepared using 42.5-grade cement according to the C30 concrete strength grade. The mix ratio of cement, sand, and fine stone was 1:2.7:3.3, the water-cement ratio was 0.45, and the slump was controlled at 20-22 cm. In order to ensure the continuity of the grouting process and to take into account the volume of each mold bag, a small high-pressure concrete delivery pump with an outlet pressure of up to 10 MPa and a pumping speed of approximately 5.6 m\({}^{3}\)/h was chosen for this test. The test took 38 days to complete. After the excavation face was formed, it took about 1 h to install each ring of steel corrugated plates, and it took about 0.5 h to pour the mold bag concrete, which realized the rapid support of the excavation face. During the concrete pouring process, water seeped out from the outside of the mold bag, while no cement slurry seeped out. This means that the mold bags used in the test are breathable and permeable but not permeable to the slurry, and they achieve the role of wrapping and forming the concrete. The construction process and the overall support effect are shown in Figure 14.