| Lots of water-enriched and weakly cemented sand layer are widely distributed innorthwestern region of china where need to strongly develop the traffic engineering,it is verydifficult and in high security risks to build large section tunnel project in this typical soft rockstrata, which seriously restricts the development of traffic engineering in northwestChina.How to safely and efficiently build high-quality tunnel in such soft rock geologicalconditions is one of the important topic faced by the current tunnel engineering.The paper relies on the Taoshuping tunnel project of Lanzhou-Chongqing railway whichis being built, discusses the construction method of double side wall heading andauxiliary construction measures,and so on.And related stress for the process of tunnelconstruction project were monitored and analyzed.The tunnel construction process are alsosimulated by the finite element software, with which we analyses the deformation law ofsurrounding rock, supporting structure stress distribution characteristics,and evaluates thecurrent construction methods,the feasible support parameters and supporting structure ofthe safety comprehensively combining with the monitoring results.Based on theanalysis above,the main research results can be enumerated as follows:(1)When building tunnels and other underground projects in such a specialwater-enriched soft rock strata, the key construction technology is the precipitation, the mostimportant security measure is pre-grouting,large section divided into small sections (doublewall method),the organizing principles is fast digging, fast shoring, quickly closing. Only inthose steps, the deformation of surrounding rock can be effectively controlled;the tunnelconstruction can be safely and efficiently finished.(2)By monitoring and analyzing the surrounding rock pressure, the contact pressure, thetwo liner reinforce internal force, we can find that all these are in the characteristic ofirregular wave changes, which are greatly affected by division of the excavation,the removalof temporary support and fluctuated change for a long time. After3to5months,all changesgradually disappear,and all the data monitored are in a steady state.All dates are in theallowable range, supporting structure is in a safe condition.(3)By analyzing the numerical simulation of tunnel construction process, we find thatsurrounding rock is easy to be disturbed, and the disturbance range is very large, thedeformation is very quick and lasting.After finishing the tunnel construction, the tunnelvertical and horizontal displacement maximum values is23.6mm and11.2mm;because of theasymmetry of double side heading method construction,supports structure stress also showsasymmetry,the1st and3rd maximum principal stress of the initial supporting structure reach to1.4MPa and-21.7MPa, the force of supporting structure is in a normal state after finishingthe tunnel construction.(4) Removal of temporary support is a key procedure of double side heading methodconstruction, removing the temporary support have an important impact on the surroundingrock displacement and supporting structure,displacement of surrounding rock and supportingstructure stress will happen mutation and mutation is in a large data.The maximum mutationof supporting structure stress can reach to7.4MPa, accounting for37.7%of the maximumdata. So, the removal temporary should be carried in small sections,small-scale andlittle shook, to avoiding large disturbance to the surrounding rock,and also should strengthenthe monitoring of the rock section, take measures as soon as possible when found deformationis too large. |
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