## 6 Engineering Application  
Following design optimization based on the aforementioned test results, the construction parameters for the dual-steel-plate-confined high-performance concrete shaft lining structure for the intake shaft in the west zone of Zhangji coal mine were determined: the thickness of the shaft lining at the vertical depth range of 378-435 m was 800 mm, the thickness of the inner steel plate was 20 mm, the thickness of the outer steel plate was 16 mm, and the concrete strength grade was C65. The shaft lining in the control layer was no thicker than 800 mm, thereby ensuring that the shaft could be constructed using the drilling method. According to the drill shaft lining design theory, the shaft lining could withstand 4.815 MPa of pressure from water and soil at the bottom of the alluvial strata at a depth of 401.22 m. The test results in Figure 14 show that the hoop stress on the inner side of the concrete in the dual-steel-plate-confined high-performance composite concrete shaft lining structure was only approximately 28 MPa (only 1/4 of the ultimate stress for the concrete) under a load of 4.815 MPa. This finding indicates that the  
Figure 13: Failure form of the shaft lining model: (**a**) inner surface (**b**) outer surface. concrete in the dual-steel-plate-confined high-performance composite concrete shaft lining structure has a considerably higher compressive strength and is in an elastic state under normal working loads; consequently, the shaft lining structure is safe and reliable. Based on the engineering geological conditions and construction drawing, an AS-9/500 drilling rig equipped with a gantry crane with a hoisting capacity of 2000 kN was selected to hoist the drilling equipment and prefabricated shaft lining. During construction, a four-stage reaming and drilling scheme was adopted to produce a drilling diameter of 10.8 m. Subsequently, the shaft lining was sunk by flotation, and then the gap between the lining and the surrounding soil was filled. The project was completed without incident. The constructed shaft had a tilt ratio of only 0.252%, was not immersed in water, and was of excellent quality. This shaft (net diameter: 8.3 m) set a record for the largest-diameter shaft ever constructed using mine shaft drilling in China or elsewhere. The design parameters of the shaft lining were optimized based on the test results. To understand its deformation in the control layer under stress in real time and evaluate its safety during operation, the deformation of the shaft lining structure was monitored under stress. Field measurements were conducted using vibrating-wire sensors. A test site was set at the 20 th section of the shaft lining (corresponding to the layer at a depth of 398.0 m). When fabricating this section of the shaft lining, concrete strain gauges were embedded, and the busbars of all the measuring components were placed in a recessed junction box, which was connected to a 35 mm\({}^{2}\) core armored signal-shielding control cable when sinking the shaft lining by flotation. Real-time monitoring was performed on the ground. Large amounts of field data were obtained from long-term monitoring. Figure 14 shows the measurements of the hoop strain of the concrete in the shaft lining. Measurements began when the slurry submerged the layer where the measuring components were located after the 20 th section of the shaft lining was sunk. Water (as needed) was added as a counterweight in real time when sinking the shaft lining. The sinking of the shaft lining was completed on the 20 th day. At this time, the water in the shaft was 144 m from the opening. Starting on the 25 th day, the gap between the shaft and the surrounding soil began to be filled to cement the shaft. This process was completed on the 38 th day. Draining started on the 112 th day and was completed on the 195 th day. Subsequently, long-term observations were conducted.