Model tests and discrete element simulations on the cracking characteristics of layered soft rock tunnel under different bedding features

Abstract

The angle and direction of bedding have a significant influence on the cracking and damage observed in tunnels excavated through layered soft rock. To investigate the cracking characteristics of tunnel lining structures under varying bedding conditions, this study initially conducted layered soft rock tunnel cracking tests. By analyzing the acoustic emission signals, lining deformation, and evolution of mechanical behavior during the loading process, the spatial distribution of lining cracking locations was determined for different bedding characteristics. Based on this, the cracking characteristics and crack patterns of the lining and surrounding rock were revealed using discrete element simulation. The study results indicated that bedding planes in their normal orientation represented a high-risk area for lining cracking due to stress concentration and inward compression of the lining, which resulted in the rupture of contact force chains and the initiation of cracks. Besides, the bedding characteristics exerted a significant impact on the crack pattern of the tunnel lining. Among these, the crack pattern of the lining evolved from tension/compression to shear, and then back to tension/compression, with deformation and internal forces showing an increasing and then decreasing trend, reaching a peak at an angle of 45°. As the bedding direction increased, cracks transitioned from a dispersed distribution to longitudinal penetration, while shear failure became more pronounced. The deformation and internal forces continued to increase, and the tunnel’s bearing capacity was weakest at a direction of 90°. This study systematically uncovers the failure mechanisms of layered soft rock tunnels, offering direct support for optimizing tunnel support parameters and a theoretical basis for maintaining existing tunnels.