ABSTRACT
Over the years, shield construction in soft-hard heterogeneous strata has posed significant challenges to engineers. It is these challenges that have demonstrably led to much concern on frequent project failures and accidents. In this paper, the authors present China’s experience in shield construction in such challenging strata and comprehensively overview its development trajectory. First, they establish the definitions for soft-hard heterogeneous strata and highlight the issues encountered during shield tunnelling in these heterogeneous conditions. Then, they give a profound explanation for the mechanisms that these conditions trigger ground collapse near the workface. Finally, they explore the evolution of China’s shield tunnelling technology in soft-hard heterogeneous strata and also elaborate the secondary damage to shield equipment and environmental impact caused by the deep-hole presplitting scheme during construction. In light of the aforementioned challenges, they propose a set of technological guidelines to be followed during shield tunnelling in soft-hard heterogeneous strata: 1) With technical advancements of shield machines, it is strongly recommended to excavate tunnels directly in soft-hard heterogeneous strata instead of pre-processing; 2) Presplitting hard rock strata is discouraged due to potential risks associated with secondary damage to shield equipment and environmental impact; 3) Shield tunnelling parameters must be within reasonable limits; 4) In these technological guidelines, it is essential to inspect wear and tear of cutter tools in real time, monitor shield postures and also take prompt and appropriate responding actions.
