Study on Face Stability of Shield Tunnel in Sandy Cobble Stratum

Abstract:

When the shield tunnel passes through the sandy cobble stratum， it is easy for the tunnel face to lose stability and cause accidents due to the stratum characteristics and construction disturbance of sandy pebble. In order to study the minimum supporting force required for the stability of the shield tunnel face in sandy cobble stratum， in combination with the instability mode of the tunnel face in sandy cobble stratum， and based on the three-dimensional Murayama model， the sliding surface of the soil in front of the tunnel face is assumed to be a logarithmic spiral slip line. In combination with the failure mechanism of the upper loose area， the ellipsoid drawing theory is introduced to improve the traditional prism silo model， and the limit support of the tunnel face in sandy cobble stratum is further derived by using the limit equilibrium method. Finally， the formula is verified by discrete element numerical simulation， and the error between the two is 3.1 %. The results show that the formula can accurately solve the limit support force of the tunnel face in sandy cobble stratum. The research results are expected to provide new ideas for the calculation of limit supporting force of tunnel face in sandy cobble stratum.

Key words:shield tunnel;sandy cobble ground;tunnel face stability;theoretical analysis;limit equilibrium method