Research of surface settlement for a single arch long-span subway station using the Pipe-roof Pre-construction Method

During the construction process of the Pipe-roof Pre-construction Method (PPM), the main excavation is executed under the protection of a previously created and reliable structure, which ensures safety in construction. Moreover, PPM does not affect the road traffic, generally does not require the moving of underground pipelines, and does not cause excessive surface settlement. The Xinleyizhi Station of the Shenyang subway system is a single arch long-span structure in poor geological conditions and with a complex surrounding environment and strict requirements for construction period. After considering the problems and potential solutions, PPM was used to build this station. In order to ensure safety in construction, the whole construction process was closely monitored. The surface settlement monitoring results are studied in this paper, and the causes of settlement are analyzed. According to the field measurement, the most serious settlement occurred in the layer 1-7 pipe jacking. Because of repeated disturbance and 'shielding effect' in pipe jacking, soil displacement mode changes, and traditional Peck formula is no longer applicable. Modified Peck formula is proposed to predict settlement caused by pipe jacking, and the specific method of taking parameters values in modified Peck formula is given. Compared to the measured transverse surface settlement curve in monitoring, it is shown that the prediction results are in good agreement with the measured results.