Model test on the deformation law of shield tunnel underpassing high speed railway roadbed

The purpose of this paper is to investigate the effect of shield underpass construction on the deformation of the U-shaped trough structure and stratum of the high speed railway roadbed. The proposed Shijiazhuang rail transit line No.4 underpassing the Beijing-Shijiazhuang high-speed railway roadbed is selected as the engineering background. The stratum and structural model test materials are formulated based on the geometric similarity ratio, and the test monitoring system is designed. A phi 1 200 mm small shield is employed to carry out 2 sets of laboratory model tests for different distances from the vault of the shield tunnel to the bottom of pile in the roadbed. The results show that: with the increase of the distance from the shield tunnel vault, the settlement of the strata decreases, the influence range of the shield construction on the strata is about 2 times of the diameter of the tunnel, and the significant influence range is one time of the diameter of the tunnel; with the increase of the burial depth, the settlement of the strata under the structure caused by the shield construction decreases, and the maximum difference of settlement is 10% at the distance of 0.5 and 1.0 times of the diameter of the tunnel respectively from the shield tunnel vault; a dehiscence occurs between the U-shaped trough and the adjacent strata, and the percentage of settlement of the strata occurring during the shield tail release phase is greater than 74%. It is recommended to use grout filling material with good water retention and certain early strength after the completion of segment assembly to control the settlement deformation. Meanwhile, deep hole grouting should be carried out to timely fill loose ground pores so as to increase the compactness.