Study On Mechanical Behavior And Dynamic Response For Highway Bridge-tunnel Connection Section

With the construction of highway in the mountainous areas, the number of bridge and tunnel engineering increases day by day. The significant characteristic of the bridge-tunnel connection section is the mutual influence between the connecting bridge and tunnel. What’s more, the bridge, tunnel and rock are disturbed frequently and mechanical behavior is more complex. However, the research on bridge-tunnel connection section is quite limited. According to the disadvantage in the previous research, a simulation test was modeled using similarity theorem. The characteristic of strain and stress and the fatigue damage for bridge-tunnel connection section under repeated traffic loading is studied, especially the surrounding rock and the construction. And the dynamic response of bridge-tunnel connection section under vehicular load in1or2periods is analyzed by numerical simulation. Because of the differential settlement at the junction of bridge and tunnel, the vibration equation of heavy duty vehicles passing the bridge-tunnel connection section is derived. And the vibration response equation of tunnel rock is established, the vibration response of surrounding rock under vehicles is obtained. After studying the mechanical behavior and vibration response under vehicles load by similar simulation test, numerical simulation and theoretical analysis, in the presented study, the back analysis and the stability analysis of the slope and is studied and the mechanical behavior of the tunnel surrounding rock is analyzed. Finally, with the field test, the research result and the actual results is compared to prove the correctness of the theoretical calculation. The main research content is as following:(1) The static force calculated model of bridge-tunnel connection section is built by Finite difference method software FLAC3D, the surrounding rock stress, plastic zone, side wall displacements and surface displacement of bridge-tunnel connection section under different rock grade is calculated. And, the influence of construction method (steps method, CRD method and siding head method) to surrounding rock stability is studied. What’s more, with the spread foundation and pile foundation, the stress and strain of surrounding rock and foundation is researched for guidance to the construction and design.(2) Using the finite element software MIDAS-GTS, the3-D dynamic calculated model of bridge-tunnel connection section is built and the dynamic load is applied by the size and time-dependent deformation of vehicle load. With obtaining the surrounding rock, linking stress and displacement, the stability of bridge-tunnel connection section is researched by various vehicle and different construction type. Comparing the dynamic response of two type of foundation under dynamic load, the reasonable foundation is presented for the theory basis of the project design.(3) On the basis of the experiment material and program, the tunnel surrounding rock stress distribution, the stability of tunnel portal and side and face upward slope in construction progress under different construction condition are studied. What’s more, considering the vehicle load and dynamic load, the stress, deformation, displacement and settlement of the key position of the construction and tunnel portal soil is studied. The common disease mechanism is also researched.(4) For obtaining the physical and mechanical parameters heading slope, the displacement back analysis technology is applied. Aiming at layered and homogeneous slope, the back analysis method is proposed based on fuzzy mathematics and inclination curve features characteristic analysis, and the objective function is presented. With the practice engineering, the effectiveness of method is proved by calculated objective function sensibility. Using the intensive parameter, the slope stability is analyzed with multi slide surface technology with FLAC3D.(5) Settlement difference occurs at the joint between bridge and tunnel, making impact action to tunnel-bridge section when vehicle passes, has significant influence to comfortableness of vehicle driving and the whole tunnel construction. Considering the rotation and overturn in longitudinal direction, the process of vehicle passing tunnel-bridge section is regarded as the forced oscillation with certain initial condition, by which the calculate model of man-vehicle-road is built under D’Alembert principle and vibration equation is given. What’s more, by Laplace transform, the acceleration of driver and the impact force to road is solved. And these magnitudes variation with time can be obtained. Finally, the influence factor to the impact is studied, to provide the theory basis of reduce the damage by impact loading result from settlement difference. For studying the above impact loading dynamic effect to tunnel section, with Green function and Lamb integral formula, combining the tunnel section features, the vibration response of rectangle and circle tunnel under the damping dynamic loading is derived by analytical integral method. And the closed solutions of vibration displacement response under impact or harmonic loads acting on inside of saturated soil tunnel, the travel time history of elastic wave and the transient and ordinary modes of vibration were obtained when the loading is in any position at the bottom of tunnel.