Experimental study on the influence of cracks on tunnel vibration under subway train load

The impact of train vibration on the tunnel lining is a popular research topic. Under long-term train operation, the tunnel lining may incur damage, mainly longitudinal cracks, which will further increase the vibration caused by running trains, impacting the lining and the surrounding soil and eventually endangering the safety of train operation. To understand the influence of cracks on tunnel vibration under train load, we performed a model test of a shield tunnel with and without typical cracks based on a line of Hangzhou metro prototype to characterize its dynamic responses under train vibration loads. To simulate the tunnel lining material, the tunnel segment was lined up with polymer cast nylon with low creep rate and high strength. An inverted shaker simulated the train vibration load, and an accelerometer was used to measure the dynamic response of the tunnel structure and the surrounding soil. The results show that the dynamic response of the cracked section is significantly larger than that of the intact section, and due to the propagation characteristics of vibration, the expansion effect inside the tunnel is significantly greater than that of the surrounding soil. When the frequency spectrum results of the tunnel structure and the surrounding soil are compared, it is found that the vibration level of the surrounding soil due to cracks is mainly concentrated at around 100 Hz, while that of the tunnel structure at around 315 Hz, indicating that the cracks have a targeted effect on the expansion of the dynamic response. Meanwhile, the excessive vibration of intact segments is –2 or –1 dB, and the existing vibration reduction measures can meet the damping requirements. However, the excessive vibration caused by typical cracks can go up to 12 dB. Therefore, corresponding vibration reduction measures should be taken according to specifications. Finally, this paper proposes some vibration reduction suggestions and crack repair measures.