Study on the deformation mechanism and large deformation control method of a strongly weathered carbonaceous slate tunnel in western China

Abstract

In response to the significant soft rock deformation challenges encountered during the construction of the Minxian Tunnel along the Lanzhou-Haikou Expressway (G75), this study conducted a comprehensive analysis of soft rock types and the underlying mechanical mechanisms governing the deformation of the surrounding rock. It presented tailored mechanical transformation strategies to address diverse mechanical mechanisms. Also, it introduced the application of anchor cable with high pre-tightening force, constant resistance and large deformation, a proven solution widely employed in mining and rock engineering. Furthermore, the research proposed a high-prestress and active and passive combined support technique, encompassing pre-reinforced retaining structure, optimally arranged active retaining structure with long and short NPR anchor cables, steel arches, and permanent retaining structure of shotcrete. By implementing numerical simulations and on-site monitoring, the results demonstrated a remarkable reduction in the maximum deformation of the surrounding rock in the test section to only 73 mm, and the pre-tightening forces applied to the anchor cable with constant resistance and large deformation ranged from 280 to 300 kN, underscoring the effectiveness of the optimized retaining technique in controlling surrounding rock deformation. This research highlights the pivotal role of retaining structure with constant resistance and yielding support, which significantly improves deformation control.

Keywords

• tunnel engineering
• carbonaceous slate
• combined retaining structure
• numerical simulation
• on-site monitoring