Shallow tunnelling method (STM) for subway station construction in soft ground

Abstract

This paper provides an in-depth illustration of the shallow tunnelling method (STM) used for tunnelling in shallowly buried soft ground. Limited arching effect and limited ground strength mobilization are the two mechanical characteristics of the STM. The stability of the cutting face and the dry tunnelling condition are the two preconditions that should be satisfied for the STM. Some “necessary” auxiliary methods mainly served to guarantee these two preconditions are highlighted. Five principles, namely proper auxiliary methods, sequential excavation with short advance length, rigid support with quick installation, short ring closure time and systematic deformation monitoring, which are required to follow when using the STM are summarized. The state-of-art of the STM is classified into five different construction approaches according to tunnelling sequences, which are adopted in the construction of the nine subway stations in Beijing. The tunnelling procedures, support measures and settlement characteristics associated with excavation are demonstrated. Statistical analyses of the settlement data of 342 ground surface monitoring points above these nine stations are performed to illustrate the ground deformation characteristics of the STM. Numerical simulations are also employed to study the ground deformation characteristics of different construction approaches under the same geological conditions. This paper systematically demonstrates the applicability of STM in theory and practice. It is helpful in updating the database of the world tunnel projects and serving as a practical reference for future similar projects.