| The western region in China has the most unique and complex geological structure in theworld. The new tectonic movement and seismic activity have moved frequently and the activefault has developed since the Quaternary. Guanggan highway is located in the northern sectionof Longmen Shan fault zone which is one of the three active fracture in Sichuan Province,located in the transfer of the Qinghai-Xizang fault block and the South China fault block, Thehighway which has the very complicated geological conditions is difficult to built after the5.12Wenchuan earthquake. In the tunnel construction process, landslide disasters had beenoccurrenced frequently,especially caused by aftershocks role. The highway tunnel collapseincidents have been analyzed and the influence of aftershocks to the collapse after theearthquake have been researched which have great significance to the protection of tunnelconstruction safety.The article have taken the landslide disasters which occurred in the Guanggan highwaytunnel construction as example, summarized the type of characteristics and analyzed thelandslide collapse mechanism through the Geological Survey, the theoretical analysis; Theimpact of earthquakes on soft rock tunnel construction and the impact of tunnel collapsed in thesecond on two lining cracking in aftershocks role have been researched through a numericalsimulation.The following conclusions have been obtained through research:(1) The physical and mechanical properties of phyllite after earthquake on a trial basishave been analyzed, earthquake have maken the wall rocks which in the tectonic fault zonemore broken, poor interlayer and lower intensity, the overall nature of the variation in thegroundwater, the surrounding rock crusher have been an important cause of the tunnel collapse.(2) The impact of earthquakes on soft rock tunnel construction has been analyzed throughFLAC3D software, the results show that the soft rock tunnel produces large plasticdeformation,the free surface stress apperas relaxation phenomenon and the stress concentrationphenomenon of spandrel arch waist position is obvious after the earthquake, thus it has the adversely affect on the stability of surrounding rock of the tunnel,and thus prone to landslideinstability.(3) It has considerd that the main factors of the tunnel collapse is four aspects: the fracturezone, groundwater, earthquake impact and construction through the survey analysis of theGuanggan highway tunnel collapse case.It has summarized the type of tunnel collapse from thecontrol factors, aggravating factors, form factors, the mechanism factors four aspects of thecollapse combined with previous studies, and summarized that the tunnel collapse mechanismsare mainly four kinds: plastic extrusion, shear slip, fragmentation loose and vibration collapseand proposed response to treatment measures. Treatment Measures for fault fracture zone andcollapse caused by the groundwater combined with conventional treatment measures have beenproposed.(4) The reason of tunnel collapse which in the level and structural surface developmentlots has been analyzed by the the UDEC discrete element software,it is considered that theposition of spandrel and arch waist in tunnel, the spacing and location of structure surface andthe combination of different cutting between structure surface and level surface determinesdetermines the location and size of tunnel collapse, generally the smaller the spacing, thegreater the angle which the structure surface and the level surface cutting, the more likelycaused landslides.(5) The influence of the same location the initial collapse again to collapse underaftershocks on the two lining by FLAC3D software. The results show that the treatment ofcollapse which in the tunnel initial excavation is not complete, even if we do the secondarylining facilities,do in aftershocks role, it will make the initial landslide area whichcorresponding to the location occur collapse again after the earthquake, a greater response tothe second lining is produced and the cracking of secondary lining is generate. Studies haveshown that the destruction of seismic waves from the bottom at normal incidence for two liningdamage is greater than that in the seismic wave levels.(6) The crack width in different parts of the second lining is calculated to determine thesafety of the lining combined with the numerical results and using the reinforced concretedesign principles. It is considered that the treatment measures of secondary lining cracking byCarbon Fiber Reinforced is better combined with previous studies of traditional and newsecondary lining cracking and on-site treatment measures. |
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