Study On The Stability Of The Slope And Excavation Technology Of The Permafrost Tunnel Portal In High Altitude And Cold Regions

Along with the advancement of western development, China’s tunnel constructionin permafrost regions will be more and more, but the research on permafrost tunnel isnot systematic and perfect, and research on high altitude permafrost regions of tunnelconstruction technology research is less. The success or failure of the construction attunnel entrance is the key to decide whether the tunnel will be smoothly excavated，difficulty in construction，technically demanding，once not well controlled, it willgreatly enhance the overall cost of the tunnel. In permafrost regions, therefore, tunnelexcavation, the stability of the hole section and its countermeasure research isnecessary.In this thesis, according to the characteristics of the high altitude permafrost, basedon G214line of ELA mountain tunnel engineering, we study the heat to melt regularityand its protection on the slope side of tunnel entrance, the influence of excavation onslope stability at tunnel entrance, and hole technology. The following are the mainaspects:First of all, upward slope failure mode and mechanism of non-permafrost tunneland permafrost tunnel are summarized, by comparing and analyzing we draw theconclusion: compared with non-permafrost tunnel, upward slope failure mode ofpermafrost tunnel is greatly affected by temperature, and it has obvious seasonalcharacteristics.Secondly, based on the basic principle of finite element method simulation,ANSYS finite element software, the thermal physical unit, and considering phasetransformation, We make simulated calculation of soil temperature at two conditions ofnon-applied insulation measures and applied insulation measures at the ELA mountaintunnel entrance slope after excavation. We conclude that the melting of frozen soil islargely reduced after using the double net and spraying5cm thick polyurethane foam onthe side slope, combined with the construction of slope at ELA mountain tunnelentrance, summarize construction technology applicable to construction of similartunnel slope heat protection.Thirdly, the excavation types and auxiliary construction of permafrost tunnelmeasures are introduced,and through the digital simulation analyze the effect of theresection of how much of the foot of the slope on the stability of the slope whenexcavating tunnel in warm season or cold season. We conclude that when the tunnelzero depth in cold season, the safety factor of slope is the highest. As a result of the existence of bias, the stress of right tunnel near the mountain peaks is greater than theleft one, at the same time, total displacement of the right tunnel is greater than the leftone, and the stress and displacement of portal section increases with the increase of theexcavation depth this is consistent with the site monitoring data. Finally the thesisintroduce the support engineering-excavating construction technology of ELAmountain tunnel, and use the site monitoring measurement data on analyzing thestability of the tunnel, which is a good guide to the future construction of similarprojects.