The pile-beam-arch construction method is widely used in subway station engineering. However, the mechanical response of underground is not clear during the construction of using this method, particularly in subway station with asymmetric pilot tunnels layout. Taking one of the stations of Beijing subway line 17 as an example, the construction process is simulated by 3D FEM to reveal the mechanical response of the strata. Comparing the FEM prediction with monitoring data, the underground deformations at different construction phases are analyzed. The study shows that three construction stages consisting excavating pilot tunnels, primary lining and second lining greatly disturbed the strata. Comparing with the subway station with symmetrical pilot tunnels arrangement, the curves of surface settlement and the surface horizontal displacement generate a certain offset. The region affected by surface deformation is changed, which is benefit to the arrangement for monitoring points of surface displacement.
The subway station features large excavation volume, shallow burial depth and large impact on the surrounding environment during construction. Generally, the pile-beam-arch (PBA) method is selected for subway construction for the sake of ensuring the normal operation of urban transportation (Han et al. 2015 and Li et al. 2017). The method based on traditional technology of concealed excavation construction employs the concept of above-ground building construction (Liu et al. 2016). It forms a longitudinal support system consisting of beams and columns in the underground without causing major disturbances to the formation by using small pilot tunnels and piles. PBA method features high safety, weak impact on the surrounding environment (Li et al. 2020, Qu et al. 2013, Wang et al. 2012, Zhang et al. 2017).
Numerical methods are usually used to simulate the construction process based on PBA method. For example, FLAC3D was employed by Liu et al (2018) to study the underground deformation, plastic zone distribution and structural forces, optimize the construction plan of pilot tunnels and predict the surface settlement caused by subsequent construction. Luo & Wang (2016) analyzed the surface deformation characters in Subway Line 6 in Beijing during the construction process, and concluded that the surface settlement during construction phase of the pilot tunnels accounted for a large proportion of the total. Huang et al. (2018) studied the construction phases when large surface settlement occurs, summarized the weight of each phase in the total settlement, and established a practical method to predict the surface settlement.
