Abstract
Addressing the technical challenge of high-precision attitude control during the launch phase of small-radius shield tunnels, this paper, based on a specific case study, innovatively integrates quantitative analysis and mechanical mechanisms to systematically summarize seven deviation correction strategies encompassing the collaborative application of active articulation and overcutting cutters. The following conclusions are drawn: 1) Controlling the pressure difference of thrust cylinders is the most direct means of shield attitude control; when the thrust differential threshold ΔP>100bar (taking an excavation diameter of 6280mm as an example) still fails to achieve correction effects, other auxiliary deviation correction measures should be employed; 2) Fully leveraging the advantages of active articulation, the articulation stroke difference is gradually increased in three steps, corresponding to 40%, 60%, and 80% of the design value; 3) When attitude remains uncontrolled, the overcutting cutter is activated employing a semi-circumferential overcutting mode with an overcutting length of 40mm, resulting in significant improvement of the shield head attitude and achieving an overcutting correction efficiency of 82%; 4) Rationally selecting segment erection positions, strictly fitting the tunnel axis according to segment taper, while appropriately retracting thrust cylinders to adjust the contact surface between cylinder shoe plates and segments, thereby eliminating lateral stress on the segments; 5) Promptly conducting secondary grouting on the outer arc side of segments that have just exited the shield tail, with the grout initial setting time controlled at approximately 6h, to prevent segments from shifting overall toward the tunnel exterior under lateral component forces during the correction process, thereby avoiding segment damage, step faults, and other issues. Engineering applications demonstrate that this technical system successfully corrected the maximum attitude deviation exceeding the limit from 203mm to within 50mm in the launch section; the shield attitude improved significantly from launch to Ring 14, and was restored to within allowable limits by Ring 27, substantially enhancing the safety, efficiency, and precision of small-radius shield tunnel launches, and holds significant value for broader application.
Full Text
Preamble
A Technical Summary of Correction Strategies for Small-Radius Secant Launch of Shield Machines
Qiu Tian
(Guangzhou Metro Engineering Consulting Co., Ltd., Guangzhou 510000, China)
Abstract
This paper addresses the technical challenge of achieving high-precision attitude control during the launch phase of small-radius shield tunnels. Through a specific case study, we innovatively integrate quantitative analysis with mechanical mechanisms to systematically summarize seven correction strategies, including the collaborative application of active articulation and overcutting knives. The following conclusions are drawn: (1) Controlling the thrust pressure differential of hydraulic cylinders represents the most direct means of shield attitude control; when the thrust differential threshold ΔP>100bar (for an excavation diameter of 6280mm) still fails to achieve the desired correction effect, auxiliary measures should be implemented. (2) The advantages of active articulation should be fully leveraged by progressively increasing the articulation stroke differential in three stages at 40%, 60%, and 80% of the design value. (3) If attitude remains uncontrolled, the overcutting knife should be activated using a semi-circumferential overcutting pattern with a 40mm overcut length, which yields significant improvement in shield head attitude with a correction efficiency of 82%. (4) Segment assembly positions should be selected rationally to strictly fit the tunnel axis according to segment taper, while simultaneously retracting thrust cylinders appropriately to adjust the contact surface between cylinder shoes and segments, thereby eliminating lateral stress on segments. (5) Secondary grouting should be promptly applied to the outer arc side of segments that have just exited the tail shield, with the grout initial setting time controlled at approximately 6h to prevent overall offset of segments toward the tunnel exterior under lateral force components during correction, which could lead to segment damage and misalignment. Engineering application demonstrates that this technical system successfully corrected the maximum attitude deviation in the launch section from 203mm to within 50mm. Shield attitude improved significantly from launch through ring 14, and returned to the allowable range by ring 27, substantially enhancing the safety, efficiency, and precision of small-radius shield launches and offering significant value for broader application.
Keywords: Shield machine; Secant launch; Small radius; Correction