Dynamic responses and long-term damage evolution of tunnels in expansive strata under dynamic loads from high-speed trains

The combined effects of dynamic loads from high-speed trains and surrounding soil expansion pressure often lead to structure failure in tunnels during their service period. This study conducts a series of expansion pressure, expansion rate, and shear strength tests on expansive soil to analyze the impact of the initial moisture content and dry density on expansion behaviors. The results indicate that the expansion pressure is negatively (positively) correlated with the initial moisture content (dry density). The expansion rate decreases with increasing vertical pressure and initial moisture content. The expansive soil’s shear strength, internal friction angle, and cohesion are approximately linearly negatively correlated with initial moisture content. A three-dimensional dynamic computational model combining the train dynamic load, surrounding soil, and lining structure is established to study the tunnel’s dynamic responses and long-term damage evolution. The simulation results indicate that the combined effects of high-speed train dynamic loads and expansion pressure cause the tunnel’s maximum vertical acceleration and vertical displacement response to occur at the center of the invert. In contrast, the maximum peak of the minimum principal stress response occurs near the invert beneath the track. The minimum responses of the acceleration, vertical displacement, and peak of the minimum principal stress occur at the roof, hance, and wall, respectively. The tunnel’s vertical acceleration, vertical displacement, and peak minimum principal stress are positively correlated with expansion pressure (or train speed). When the train speed is below 300 km/h, changes in the expansion pressure (or train speed) do not alter the shape of the response envelope diagram or the relative intensity of the response at each measuring point. The upper structure of the tunnel (above the wall) experiences little damage, which is concentrated primarily in the invert and both side feet of the tunnel. Tensile damage is greater than compression damage, and the expansion pressure significantly affects the rate of damage development in tunnels during the first 15 years of service.