Classification of Soft-rock Tunnels and the Corresponding Large-section Construction Methods

摘要

This study is concerned with the classification of soft-rock tunnels which could instruct the tunnel construction more efficiently and effectively. It is difficult for NATM which is based on the geological classification to adapt to soft-rock tunnel construction. Through comparative study of the numerical models with different surrounding rock and different cross-sectional dimensions, the deformation characteristics of the soft-rock tunnel is put forward. Soft-rock tunnel is divided into four classes: A, B_1, B_2 and C. The classification is based on the proportion of the advanced displacement in the total radial displacement and the value of tunnel face extrusion. According to the different characteristics of these four classes of soft-rock tunnel, a high-speed construction with reinforcements of the surrounding rock in front of the face is put forward. The characteristics of the four classes of soft-rock tunnels are: In the general initial support conditions, the proportion of the advanced displacement in the total radial displacement of Class-A tunnels is low, which enables them to achieve self-stabilization. The corresponding proportions of Class-B_1 and Class-B_2 tunnels are beyond the limit, which can only enable them to achieve short-term stability. The extrusion of Class-B_2 tunnel's face is larger but it does not break the limit. The extrusion of Class-C tunnels breaks the limit which cannot maintain stability if without face reinforcements.