Numerical Study On The Stability Of Longtan Long Tunnel Under Problematic Geological Conditions

Longtan Highway Tunnel is located in Baishiping-Langping section of HurongNational Main Trunk Line from Yichang to Enshi Cityin Hubei Province and is oneof key control projects in this section. The principal geological problem to be solvedfor this tunnel is the instability of surrounding rock induced by underground water.Therefore, it is of great importance for the prosterous construction of Longtan Tunnelto study the effect of underground water on the stability of surrounding rock. Thescopeofthisthesisisasfollowing:Firstly, based upon the former research on stability of surrounding rock, thisthesis models and analyzes the stress distribution in surrounding rock due toexcavationandinstallationofsupportmeasuresrespectively.Moreover, theinfluentialfactors and criterions for surrounding rock stability are also analyzed. And some newresultsareobtained.Secondly,basedupon the comprehensive analysis of geological conditions ofthetunnel site,arepresentativesegment of LongtanTunnel is takenas object investigated.After the situ rock mass of the segment were generalized, the physical mechanicalparametersofrockmassforstabilityanalysisweredetermined.Finally,byemployingthethreedimensionalfinitedifferencecodeFLAC-3D,theeffects of groundwater on the stability of surrounding rocks are numerically studied.Conclusionsdrawnfromthenumericallyresearchcanbesummarizedasfollows:1) Comparison between numerical simulation results and field monitoringresults of the tunnel in lower-water season has shown that the physical mechanicalparameters of surrounding rocks are reasonable and the ultimate stable state of thetunnel surrounding rock in the lower-water season can be obtained under thesupportingmeasuresinoriginaldesign.2) Water level plays a critical role on stability of surrounding rocks. Instabilityof surrounding rocks under high water level conditions is caused by fast velocity ofwater under the tunnel floor induced by high osmotic pressure gradient, themanifestation of which is that both amount of floor heaving and area of plastic zoneare large. Under different water levels, stability of surrounding rocks is analyzed interms of convergence ratio and plastic zone aspects, and a conclusion is concludedthat when water lever is greater 160meters, the possible to be instable so the support...