Studies on ground settlement and pre-arching stress of pre-cutting tunnelling method

Abstract

According to Rabcewicz (1964, 1965), tunnels should be driven full face whenever possible. The pre-cutting method is a popular tunnelling method based on this idea. This method allows safe excavation even in poor ground conditions by creating continuous pre-arching around tunnel periphery in advance. Because of high costs and safety risk in field test, the previous studies on pre-cutting method are limited and qualitative, which mainly focused on its machine, construction procedure and applicable conditions. To further develop this method, systematic and quantitative studies on ground settlement and pre-arching stress caused by it are needed. In this study, a 1:10 geo-mechanical physical model test was performed to understand the mechanism of pre-cutting method by simulating its construction process. The ground settlement, earth pressure and pre-arching stress during tunnelling were investigated. Afterwards, three-dimensional numerical simulations were performed to simulate the process of physical model test so as to compare with experimental results. The effects of different pre-cutting parameters such as length, thickness, lap length and sequence of cutting slots, which can’t be sufficiently covered by the model test, were studied by numerical method. Comparative studies between pre-cutting and New Austrian Tunnelling Method (NATM) under the same geological conditions were also carried out. In general, the comparative analysis shows that the physical model test has achieved satisfactory results and the pre-cutting method has a great advantage in controlling ground deformation compared with NATM.