###### Abstract  
Pressure balance control between steel sleeve fillings and stratum is the key to ensuring project safety in the receiving construction of subway shield tunnels. Here, to realize the active regulation of the filing pressure in the steel sleeve, this study first improves the fixed cover of a conventional steel sleeve to a piston cover that can slide freely along the longitudinal direction of the sleeve and puts forward the corresponding methods for hydraulic pressure regulation and mechanical pressure regulation. The pressure-holding sealing performance of a new steel sleeve structure was tested, and a hydraulic pressure regulation method and a mechanical pressure regulation method were proposed. Finally, an effective path to proactive filler pressure regulation in the steel sleeve was explored. By improving the structure scheme of the steel sleeve, A steel sleeve model was designed at a 1:5 proportion, following the shield receiving steel sleeve structures and their sizes in practical tunneling. The model test was performed for several processes of active control of filler pressure, including pressurization by injection, decompression by discharge, machinal pressurization in low pressure, machinal pressurization in high pressure, and machinal decompression. The laws of filler pressure variation with hydraulic pressure and machinal thrust, the reactive force of hydraulic jack, and stress of steel sleeve were researched. The results revealed that the maximum stress of the new steel sleeve structure was 14.5 MPa under an elastic stress state, and the circumferential stress was always eight times the longitudinal stress. The new steel sleeve structure shows controllable pressure-holding sealing performance. The hydraulic pressure decrease appears as a slow linear trend of about 0.1% of the initial pressure per min after 1 min of pressure holding. The variation in the filler pressure at the central position of the steel sleeve is 16-24% greater than that at the periphery. Both hydraulic pressure regulation and mechanical pressure regulation could achieve controllable proactive regulation effects on a steel sleeve's filler pressure. The proposed new shield-receiving steel sleeve structure and the study results about its sealing performance and filler pressure regulation will promote the shield-receiving technology to be more controllable and safer. shield tunnel; shield receiving; steel sleeve; pressure regulation +
Footnote †: journal: Applied Sciences  
and chemically improved soil layers method, a novel material shield-cuttable tunnel-wall system construction method, an underwater receiving construction method, a steel sleeve receiving construction method, a concrete sealed cabin receiving construction method, a piston sealing steel ring receiving method and a receiving method in foamed concrete [15; 16; 17; 18; 19; 20; 21]. Steel sleeve receiving construction is a new method featuring space savings, safety, reliability and a minor influence on the environment. This method has been widely used in metro shield tunneling projects, including Guangzhou rail transit's Line 2, Line 8, and the Nanyan Line; the TA08 Fuqiao Station-Daxinggong Station section of Nanjing Metro Line 3; and the Nangang Station-Yonglu Station section of Guangzhou Metro Line 13 [22; 23; 24]. As a result, the steel sleeve-receiving construction method is useful for inhibiting surrounding ground settlement and building deformation, minimizing water leakage and sand inrush risks, accelerating construction speed and saving construction costs. The conventional shield-receiving steel sleeve device is a circular bucket-like structure that is open at one end and sealed at the other (Figure 1). The open end connects the tunnel portal to form a closed container. Before the shield-receiving construction, the steel sleeve is filled with a mixture of sand and water; then, it is sealed after a certain pressure is reached and sustained [25]. The shield machine drives into the steel sleeve after tunnel excavation.