About the author:

1. Hunan Zhongda Design Institute Co.,Ltd., Changsha, Hunan 410075, China;2. School of Civil Engineering, Central South University, Changsha, Hunan 410075,China

Abstract:

To address the deformation control challenge in the shallow-buried underwater tunnel withsmall clearances in soft rock excavated by roadheader, uniaxial creep tests were performed to examine thecreep behavior of mudstone siltstone under varying moisture conditions. Based on the experimentalresults, the Cvisc creep constitutive model was adopted to fit the stress-strain relationship, and theconstitutive parameters were calibrated accordingly. A numerical simulation model with rock mass creepwas developed to investigate the stress and deformation characteristics of the tunnel. Using this model,the excavation sequence distance and timing of secondary lining installation were optimized. The resultswere then validated by comparison with field monitoring data. The research results show that undersaturated conditions, the strength of mudstone siltstone decreases, making it more susceptible to creepdeformation. The Cvisc model provides better agreement with the mechanical behavior of the surroundingrock and ensures higher construction safety. Under different excavation sequence distance and secondarylining delay distance, the strength of the initial support concrete meets the safety requirements, and thevault settlement patterns are generally similar. The tunnel vault settlement exhibits the highest sensitivityto excavation sequence distance and secondary lining delay distance, followed by the settlements at theshoulder,waist, invert and foot of the tunnel. Increasing the excavation sequence distance and reducingthe secondary lining delay distance effectively enhance tunnel stability and control vault settlement. Theoptimal excavation sequence distance and secondary lining delay distance are determined to be 39m and 9m, respectively. The vault settlement simulated using the Cvisc model shows minimal deviation from themonitored values,with consistent trends, indicating that the surrounding rock deformation eventuallyconverges.