Study On The Mechanism Of Crack Generation And Control Methods Of Seasonal Frozen Soil Tunnel Lining

Cracks are found in the lining of seasonal frozen soil tunnels, which seriously affect thestability, applicability, durability of linings. Besides, further development of cracks in thetunnel lining would also induce other diseases that affect the safety of the tunnel. Based onLiang JiaPing2#tunnel project, starting from the filed test, by using the large general finiteelement software ANSYS, the seasonal frozen soil tunnel’s temperature field and stress fieldare calculated and analyzed in this Master Thesis. The seasonal frozen soil tunnel liningcracking mechanism is studied and analyzed to provide a theoretical reference for preventingfrom diseases mentioned above. The main conclusions are shown as follows:(1) By indoor experiments we can drawn: Liang Jiaping2#tunnel’s surrounding rockwater content is about10.8%, the saturation water content of undisturbed soil sample is about12.3%,the saturation surrounding rock free frost heave rate is about1.41%, mudstone freeexpansion rate is15%, the sandstone free expansion rate is8%, according to relatedspecifications, the surrounding rock is non-expansive soil.(2) Based on the analysis of the reasons that possibily generated the cracks in tunnellining, factors like high in-situ stress, water pressure, pressure of expansive soil, surroundingrock pressure are excluded. Through the study of the data from field test and monitoring workof Liang Jiaping2#tunnel, we found the changing rule of longitudinal cracks in sidewallconforms to that of the lining cracking caused by frost heave in surrounding rock. Therefore,aconclusion that the main reason of cracks in tunnel lining is caused by seasonal frost heave insurrounding rock can be obtained by preliminary judgment.(3) Through statistical analysis of air temperatures and rainfalls, we found the summerrainfall is abundant, and the winter temperature is lower in recent years in tunnel region,specifically,the negative temperature duration for around four months, most of the averagetemperatures are about-10℃.(4) Numerical calculation results of tunnel temperature field show that the frozen depthof surrounding rock circle is104cm, which is nearly as same as the measurement data(100cm), and the maximum freezing depth time on January19.in next year.(5) The frost heaving force calculation results show that the interior force of the LiangJiaping2#tunnel lining caused by frost heave is greater than the ultimate tensile strength oflining gconcrete, which are inconformity with the actual disease. (6) By reinforcement design for tunnel lining based on different frozen circlesofsurrounding rock, we found reinforcement area of tunnel lining and surrounding rock circle offrozen depth have linear relationships. So frost heave fortification should be considered fortunnel building in the seasonal frozen soil.(7) By comparisons of three different schemes of reinforcement scheme designs, thescheme that taking grooving reinforcing cage, arranging three Φ25bolts in tension zone of thetunnel wall is recommend to resist seasonal frost heaving force and to restrain the tunnelwall’s extrusion, and furtherly prevent the lining cracks generated. At the same time, groutingbehind the tunnel lining is aslo indispensable (the grouting range from0.6m to0.8m), whichcan reduce the soil porosity, the water gap of surrounding rock, and the rate of frost heave ofsurrounding rock. By doing in this way, the frost heave area in the surrounding rock can bereduced effectively.