Abstract: Numerical simulation (FLAC3D) and field experiments are used to study the shape effect of tunnel section. Stress of primary support and tunnel deformation under horseshoe-shaped section and large curvature wall, quasi circle-shaped section are analysed and compared. Numerical simulation and field measurement indicat that deformation and deformation rate of surrounding rock under quasi circle-shaped section could be effectively lessened, especially convergence of side wall, compared with that under horseshoe-shaped section. Ratio between lost displacement while measuring in-site and total displacement of surrounding rock is large, and the lost ratio of lower bench is largest. Field experiments of different support stiffnesses are conducted. It is measured and analysed that pressure of surrounding rock mass, axial force of anchor, stress of steel frame and stress of shotcrete under different primary support parameters. Also the contact pressure shared by secondary lining and the stress of mode concrete under different primary support stiffnesses are measured and analysed. Deformation of tunnel under different support stiffnesses are also measured. It is concluded that the contact pressure of secondary lining and pressure ratio shared by secondary lining increae with support stiffness increase. And suitable support form is synthetically determined. That would offer valuable practical experience to tunnelling in soft rock mass with high tectonic stress-field.

Key words: carbonaceous slate stratum, numerical simulation, quasi circle-shaped section, support parameter