Mechanism and Control of Large Deformations in Super-Deep Soft Rock Tunnels:A Case Study of Haba Snow Mountain Tunnel on Lijiang-Shangri-la Line of Yunnan-Xizang Railway
Super-deep soft rock tunnels are prone to extensive deformations owing to high in-situ stresses and the presence of soft surrounding rock,often necessitating frequent replacement of primary supports.The authors focus on the Haba Snow Mountain tunnel project on the Lijiang-Shangri-la line of the Yunnan-Xizang railway.Specifically,the characteristics,mechanisms,and control techniques of large deformations in deep soft rock tunnels are examined.The large deformation characteristics of the selected tunnel are analyzed,and the mechanisms underlying these deformations are elucidated.A control technique involving advance stress relief,a combination of long and short anchor bolts,intensive grouting,and multi-layered support is proposed.Large deformations in the Haba Snow Mountain tunnel primarily manifest in the form of tunnel face instability,a rapid rate of support deformation,large deformation amplitudes,and severe structural damage.Implementing the proposed control measures effectively controls these large deformation phenomena.Measurement results indicate the following:The extrusion deformation of the tunnel face drops by over 60%,the overall tunnel deformation declines by over 40%,structural stress is considerably reduced,and the surrounding rock and contact pressures are lower than the structural design load of 1.0 MPa.
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