The Detection of the Boulders in Metro Tunneling in Granite Strata Using a Shield Tunneling Method and a New Method of Coping with Boulders

While tunneling metros in granite strata using a shield tunneling, cutter heads of shield machines frequently get stuck and are damaged by boulders. Currently, effective methods for solving this problem have not been found in the world. By studying the Shenzhen Metro Line 7 in China, this research proposed a new method for predicting and coping with boulders in metro tunneling using a shield tunneling by combining microtremor survey, supplementary precise geological prospecting and surface drilling blasting. Moreover, with the elaboration of the principle and implementing steps, this method was applied in the specific engineering example. To begin with, the characteristics of H/V curve shapes of boulders exposed in the excavated sections using the shield tunneling were obtained. On this basis, we interpreted and judged the distribution forms of boulders in the unexcavated sections ahead. Afterwards, supplementary precise geological prospecting was performed to the boulders in the predicted positions according to the interpretations so as to verify and revise the interpretations. After ascertaining the distribution location and size of boulders ahead shielding sections, surface drilling blasting or punching was carried out to blast boulders. Engineering application results showed that this method has favorable effects and can provide a scientific and reasonable guidance for the development of theories of microtremor survey and the detection of boulders.