Numerical Analysis For Longitudinal Seismic Response Of Tunnels In Saturated Soils

Due to the spatial variation of earthquake ground motion, there will be travelingwave effect along tunnels in soils. As a two phase material, the dynamic response ofsaturated soil is more complex than one phase material. Therefore, dynamic analysis oflongitudinal tunnel response is an important topic for the seismic performanceevaluation of a tunnel. In this thesis, numerical methods for the analysis of longitudinalresponse of tunnels in saturated soils under asynchronous seismic wave is extensivelystudied, including the clarification of the basic equations for wave propagation andcharacteristics in saturated porous media, development of transmitting boundary,3Dfinite element implementation for asynchronous seismic wave motion and numericalsimulation of seismic response of soil-tunnel system. The main research results are asfollows:1. Systematically clarification of the dynamic basic formulations and wavepropagation characteristics in saturated soils was carried out with special attention paidto the establishment of pore water motion equation. It is pointed out that in dynamicanalysis of saturated soils the interaction between soil skeleton and pore water consistsof two parts: seepage force and inertial-coupling-force. It is also revealed that due to theexistence of inertial-coupling-force, the speeds of two dilatational waves are not equalrespectively to those in single-phased solid skeleton and pore water, even if thepermeability approaches to infinity.2. A high-order accurate local time-domain transmitting boundary for simulatingthe transient scalar wave propagation in unbounded saturated porous media, based onthe u-p formulation with an assumption of zero permeability coefficient, is derived fromthe cylindrical elastic wave radiation problem. Good wave-absorbing capabilities of thishigh-order transmitting boundary are demonstrated by several types of numericalexamples. Despite the assumption made in the derivation of this transmitting boundary,results showed that it can provide sufficiently accurate results in case the u-pformulation is applicable. Although numerical results show that direct application of theproposed transmitting boundary to general two dimensional wave problems in infinitesaturated porous media is not so accurate, solutions of acceptable engineering accuracy may still be achieved by setting the transmitting boundary relatively far away from thescatter.3. By introducing the accurate artificial boundary condition, the1D time domainfinite element method used to calculate the in-plane free field wave motion in elasticlayered half space is improved. The results obtained through1D finite element methodare extended to3D. Based on the consistent mass finite element equilibrium equations,the formula for calculating the equivalent loads generated by the free filed is given,which is expressed by nodal displacements of the element at the boundary.Viscous-spring boundary is used to absorb the scattered wave, and the input of seismicwave motion is realized by applying equivalent loads on the artificial boundary.Through compiling FORTRAN program combined with finite element softwareANSYS,3D numerical simulation of elastic layered half space site response underoblique seismic incidence of in-plane wave is achieved, and its accuracy and validity areproved by numerical examples.4. Based on the research above, a soil-tunnel structure interaction model wasestablished and research is conducted on the numerical method for longitudinal seismicresponse analysis of tunnels in saturated soils. It is demonstrated that using theequivalent loads calculated from asynchronous seismic waves input method as the inputloads without extral treatment to the truncated boundaries on the tunnel sturcture,satisfactory accuracy can be achieved as long as the model is relatively long along thelongitudinal direction. Numerical examples are given to study the influence of theincident angle and tunnel stiffness on the longitudinal internal force. Analytical methodfor traveling wave effect on tunnels in layered soil foundation under earthquakes is alsobriefly discussed.5. Based on the background of HK-Zhuhai-Macau immersed tunnel project, theasynchronous seismic analysis of immersed tunnel is presented. Discussion is focusedon the internal force and deformation at the joints of immersed tunnels when differenttypes of joints are adoptted. Safety of the project under seismic load is evaluated.