Stability Analysis of Middle Rock Pillar and Cross-Section Optimization for Ultra-Small Spacing Tunnels.

The ultra-small spacing tunnel is a new tunnel type under the urban engineering environment, which not only has high requirements for deformation and settlement control, but also has great difficulty in construction technology. Since the middle rock pillar is the key part in the design and construction of ultra-small spacing tunnels, to explore the stability of the middle rock pillar in the ultra-small spacing (0-200 mm) subway tunnels, this study examined the Gangding-Shipaiqiao ultra-small spacing tunnels on Guangzhou Metro Line 3 in China by using ABAQUS and theoretical analysis, which mainly involved the plastic zone of the surrounding rock, the stress distribution and skew displacement effect of the middle rock pillar by defining the skew coefficient. The tunnel cross-sections of three different types were optimized, and a simplified calculation method was proposed with the load and ultimate bearing capacity of the middle rock pillar. Results show that the theoretical analysis of the bearing capacity of the middle rock pillar is essentially consistent with the results of numerical calculation. The conclusions obtained in the study are of important theoretical value to provide on-site engineering construction guidance. [ABSTRACT FROM AUTHOR]