Research On Dynamic Stability And Earthquake Resistance And Absorption Of Tunnels In Mount. Gaoligong

Several tunnels of Road Dujiangyan-Wenchuan near the epicenter were heavily destroied and Tunnel 109 of Baocheng Railway collapsed during the Wenchuan Earthquake on May 12th . The bad traffic caused by seismic damage of tunnels made disaster rescue more difficult. This makes earthquake resistance research of underground structures an upsurge. The topic of this thesis is"research on dynamic stability and earthquake resistance and absorption of tunnels in Mount. Gaoligong". Firstly, the numerical simulation study on damage features of tunnel earthquake; secondly, earthquake damage prediction on mountainous tunnel of Mount. Gaoligong in strong earthquake and measures for earthquake resistance and shock absorption. The content includes the following:(1) Analytical method- response displacement method is adopted to do the antiseismic calculation of underground structure. Matlab matrix calculation software is used to write the calculation program. The analysis shows that tunnel depth, lining rigidity, cross dimension, formation rock-soil mass parameter and earthquake size have great influence on stress and defromation of underground structure.(2) Combined with Media software, multi-degree-of-freedom system with damp vibration and model ( vabration) analysis are adopted to get the damping ratio z of tunnel surrounding rocks in Mount. Gaoligong. Local damping coefficient of site surrounding rocks is calculated through the empirical formula"a=3.14*D"which can be a reference of dynamic parameter of the following value in simulation program. This thesis will establish a systematic calculating process for the whole determination process of damping coefficient.(3) Professor Li Tianfu makes a whole conclusion of defromation and damage features of mountain range tunnels near the epicenter in Wenchuan Earthquake, they are tunnel slope collapse and slump, portal rhegma, lining and surrounding rocks collapse, lining cracking and dislacation, bedplate cracking and uplift, primary support deformation and cracking, etc. Based on this, the author believes that the controling factor to seismic damage is the quality of the geological conditions of surrongding rocks. Establishing value models of fault, bedrock-cover discontinuity of portal, joint, collapse mass, soft and weak interface, surrounding rocks and dynamic response of lining structures shows that the bad geological conditions of surrounding rocks in seismic effect make the lining supporting structure produce seismic damage such as ring-sheared damage and axial crack.(4) Value models of exit and entrance sections are established. Synthetic wave in tunnel site which is also the peak acceleration value 0.46g is adopted in dynamic analysis. The result shows that the acceleration speed and displacement of lining structure in exit and entrance increases with the increase of in-tunnel depth. The maximum acceleration speed of portal lining structure in entrance is 1.3g; a 2.8 Mpa stress concentration is produced in the first 20 meters into the cut; 0.3 Mpa tensile stress is produced in vault of lining structure of 20 meters in exit; 0.8Mpa tensile stress is produced in vault of lining structure of 20 meters in entrance; local plastic of portal slope is deformed and damaged. Earthquake resistance protection length of exit is suggested to be 30 meters into the cut and entrance 20 meters.(5) Fault value model of F 1-2 is established and Synthetic wave in tunnel site which is also the peak acceleration value 0.46g is adopted in dynamic analysis. Large stress nearly 9.8Mpa is produced in rigid lining structure in fault structure zone of Bangmai-Shaojiazhai Fault of Mount. Gaoligong; alternate displacement of 0.07 meter in gravity direction takes place in lining structure and surrounding rocks. The plastic damage range is large in fracture zone and fracture zone in lining structure. Suitable earthquake resistance and absorption measures shall be adopted in deeply buried fracture zone in Mount. Gaoligong.(6) This thesis discusses the shock absorption effect in the earthquake of the shock absorption layer of big damping material, grouting of surrounding rocks and supporting stiffness from the aspects of physical simulaiton, analytical method- response displacement method and numerical simulation. The research shows that shock absorption of big damping materials after the use of grouting of surrounding rocks and secondary lining can effectively decrease the dynamic stress, displacement and plastic damage zone of secondary lining structure and thus carry out the shock absorption effect. Earthquake resistance protection length of entrance is suggested to be 20 meters and exit 30 meters. Measures for earthquake resistance and absorption: slope- sparging and anchoring net; surrounding rocks- grouting; primary support- steel arch; portal layer- excavation. Measures for earthquake resistance and absorption of"grouting+bolt-mesh-spurting+secondary lining"are suggested to be adopted in fault fracture zone.