Research on Failure Mechanism of Floor Heave in Underlying Expansive Soil Railway Tunnel

Floor heave deformation of railway tunnel is a common disease in the operation stage of high-speed railway in recent years. Due to its complex deformation mechanism, there is no specific and reliable evaluation method at present. In order to investigate the deformation rule and failure mechanism of the invert arch of railway tunnel when subjected to the expansion force of the bottom swelling surrounding rock, the tunnel floor heave loading test system is designed independently. The working conditions of the tunnel invert under different expansion forces are simulated. The test results show that (1) The circumferential stress on the outside of the arch foot and the inside of the invert arch is tensile stress, and the inside of the arch foot and the outside of the invert is compressive stress, and its maximum value is at the arch foot. The arch foot and the invert are more sensitive to the expansion of the basement, and it is easy to destruction. (2) After the invert bottom is bulging, the inner side of the invert and the outer side of the arch foot are strained. For concrete lining, the tensile strength is far less than the compressive strength, that is, these parts are prone to tensile damage, so they are the weak positions of the entire lining. It is recommended to properly reinforce at this position in practical engineering. (3) Under the action of basement expansion of the tunnel, the surrounding rock at both sides of the tunnel and the position of the arch is easy to fail and weaken the bearing arch effect, thus aggravating the deformation and failure of the lining.