Research on the Collaborative Load-Bearing Performance of Bolts and Rock Mass During Tunnel Excavation

ABSTRACT

Rock bolts are widely used as initial tunnel support, yet the collaborative load-bearing mechanism between bolts and surrounding rock remains unclear. This study investigates this behavior through geomechanical physical model experiments based on a tunnel project in southwest China. Key parameters, including stress and displacement evolution, damage zone distribution, and bolt axial force, were examined at various excavation stages. Results show that: (1) the surrounding rock bears over 98 % of the total load, while bolts carry only a minor portion; (2) bolting significantly enhances rock mass performance, increasing ultrasonic wave velocity by 2.2 %–15.4 % and reducing damaged zone thickness by 3.7 %–28.5 %; (3) stress release is more pronounced at the crown and invert, leading to larger deformations and higher bolt axial forces, whereas the shoulder and sidewall experience lower forces. These findings offer practical guidance for tunnel construction and support optimization.