Research and application of a tunnel active–passive cooperative control mechanism

Existing tunnel support design generally takes the New Austrian Tunnelling Method as the core concept, and the widely adopted “anchor net spray + arch” structure as the support. The load-bearing relationship between the components of the support system is determined by the stiffness of the components. In the face of complex working conditions, the load distribution method is relatively singular, and the cooperative load-bearing of the support structure is prone to imbalance due to complex forces. To solve the above problems, the author's team proposed a tunnel active–passive cooperative control method based on excavation compensation theory and developed new materials for high prestress compensation. Taking the large-section soft rock tunnel in Eastern China as the engineering background, numerical comparative experiments were conducted on the tunnel excavation support under various influencing factors to study the high prestress compensation effect and the tunnel active–passive cooperative control mechanism. The results indicate that prestress can compensate for the radial stress loss caused by excavation, mobilize the load-bearing capacity of the surrounding rock, actively regulate the load-bearing relationship of the supporting structure, and effectively improve the deformation control effect of the surrounding rock. Based on a numerical-experimental investigation, field comparative tests under different prestress conditions were carried out. The monitoring results indicate that after applying high prestress to the bolt, the load-bearing rates of the active and passive support structures are 47.9 % and 52.1 %, respectively. The vault settlement is 28.5 mm, and the strength utilization rates of the bolt, arch, and spray layer are 48.1 %, 53.1 %, and 46.7 %, respectively. The active–passive cooperative control method effectively regulates the load-bearing relationship of the support structure, coordinates the stress of the support structure, and improves the control effect of the surrounding rock.