Abstract: The effect of quasirectangular shield tunneling on an existing tunnel is investigated, and the vertical deformation law of the existing tunnel is determined by estimating the vertical displacement of soil caused by soil loss. This calculation is based on the random medium theory combined with the cumulative probability curve, and the vertical displacement of the tunnel is calculated using the cooperative deformation model of rotation and abutment dislocation. Furthermore, an indoor model test is conducted for the newlybuilt quasirectangular shield tunnel underpassing the existing tunnel. The soil loss is monitored, as it is the only factor causing the settlement of the existing tunnel and displacement of the crown during the entire construction process. Moreover, to validate the reliability of the theoretical calculation method, the measured values are compared with the calculated values. The results reveal the following: (1) The theoretically calculated results concur with the measured values, thereby confirming the reliability of the method. (2) The settlement law of the existing tunnel caused by the quasirectangular shield tunnel is consistent with that of a circular tunnel. (3) Due to soil loss, the underpass of the new tunnel leads to the settlement of the existing tunnel. Furthermore, the crown deformation of the existing tunnel is largest at the intersection with the new tunnel. (4) The crown settlement deformation of the existing tunnel increases gradually with the excavation of the tunneling face. Additionally, a stage of rapid deformation is observed.

Key words:  quasirectangular shield tunnel, underpass existing tunnel, soil loss, vertical displacement; model test