Study On The Dynamic Response Of The Shield Tunnel And The Surrounding Soil

Vibration induced by the subway vibration loading may cause soil consolidation and deformation, and then affects the safety of the subway. It also leads to malfunctioning of sensitive equipment, discomfort to people and in extreme cases damage to buildings. Taking the dynamic response of the shield tunnel and the surrounding soil caused by subways as the background, this thesis integrates the theoretical analysis, the laboratory test and the numerical simulation, aiming to study the transient response of the tunnel and the surrounding soil under traffic loads. The main contents and research findings of this thesis are as follows.(1) The analysis of the simplified double-beam system indicates that the double-beam system has two cut-off frequencies and three critical velocities, among which the lower cut-off frequency is controlled by the slab whose bending stiffness is greater and the higher cut-off frequency is dominated by the rail which has a smaller bending stiffness. If the load velocity reaches or exceeds the first critical velocity, due to the Doppler Effect, the displacements fluctuate significantly and the waves before the vibration source are compressed, causing shorter wavelengths.(2) Integrating the Track model and the Lining-Soil model establishes the complete Tunnel model. Research on this Tunnel model shows that the axial displacements cannot be neglected in practical applications due to that the amplitude of the axial displacements is about half of that of the radial dispalcements. The calculated pore water pressure is small as well but also cannot be ignored. Middle and high frequencies have greater influence on the rail and the slab, while low frequencies cause large effects on the soil. Larger load frequencies correspond to smaller critical velocities. If the load velocity is relatively high, the displacements and the stresses decay with high fluctuations, exhibiting obvious Doppler Effect. Increase of the load velocity results in decrease of the cut-off frequencies.(3) The dynamic triaxial tests of the undisturbed silty clay of layer No. 5 in Shanghai are conducted to analyze the influence of confining pressures and vibration frequencies on the dynamic parameters of the soil. With the increase of the dynamic stress amplitude, the hysteresis loops are not closed any more. The higher vibration frequencies lead to the greater strain under the same experimental conditions. The analysis also shows that the higher confining pressures correspond to the smaller damping ratios. The quadratic function of Geq / Gmax can be adopted to fit the relationship between the dynamic shear modulus and the dynamic shear strain in a certain strain range.(4) The effects of the load velocity and the load frequency on the dynamic response of the shield tunnel are studied by the three-dimensional numerical models. The results show that the increase of the load velocity increases the response of the tunnel while the increase of the load frequency decreases the response of the tunnel. Load velocies can cause the hysteresis of the response at different positions, and with the increase of the load velocity, the latency gradually increases. Load frequencies only affect the amplitude of the dynamic response but they do not have influence on the response hysteresis at different positions.The research findings of this thesis have certain academic value for the research on soil dynamcis, especially for the research on the vibration propagation and vibration control during the subway operation.