Loess Secondary Lining Supporting Time-based Metro Tunnel Creep Theory

With the development of the national rail transit construction,as an integral part of metropolitan transportation,subway tunnels populous city in general is becoming increasingly popular,especially in recent years along with maturity driving tunnel methods.Since the tunnel excavation and creep deformation around the hole to make rock becomes complicated,and the secondary lining as a safety reserve of the tunnel is the primary guarantee of tunnel construction,operational safety and operating life,which is reasonable support timing is particularly important.Therefore,a reasonable secondary liner supporting time is imperative,but also an important reference value for similar tunnel construction.Taking Xi'an Metro Line engineering background,using the finite element software ABAQUS simulation of tunnel excavation,the factors affecting the timing of the appropriate support secondary lining summarize,and analyze the results under a variety of factors to determine the various secondary lining in case of reasonable supporting time.In this paper,supporting time tunnel secondary lining mainly for the following studies:(1)The current research methods and results will be listed at home and abroad are analyzed,and the mechanism of creep and creep theory loess described.(2)According to the creep characteristics of loess,select the extended DRUCKER-PRAGER coupled creep model,based on surrounding rock stress-strain curves of time to determine the creep parameters of loess.(3)In the background of Xi'an metro line,two-dimensional simulation of excavation of the tunnel,the tunnel lining thickness at the beginning of 200mm?250mm?300mm?350mm and under 400 mm,according to hole displacement,stress and time curve,based on " deformation rate" guidelines and " limit displacement " reasonable guidelines drawn secondary lining supporting time was 7d?8d?16d?17d and 19 d.Research results show that the effect of changes in the thickness of the lining of the beginning of the second liner supporting time is more significant,the greater the thickness of the lining more early support can delay the timing of the secondary lining.(4)Respectively,to explore the Tunnel Lining strength c15 ? c20 ? c25 ? c30 and c35 displacement hole week working conditions,stress and time constraints,each obtained secondary lining conditions were reasonable opportunity to support 7.5d?8.3d?8d?13d and 12 d.Study results indicate that the strength of c30 initial support at the secondary liner supporting time delay is large,then small changes.(5)Effect research tunnel depth and different hole spacing changes Cave weeks displacement,stress-time curve,conclude that these two factors on the supporting influence of the timing of the secondary lining.Research shows that when the tunnel depth shallower depth of the tunnel within a certain range the more shallow depth,the secondary lining of the facilities to do can be delayed,but the depth increases to a certain extent,the secondary lining support substantially the same time.Compared with the depth factor,hole spacing variation influence of the secondary liner supporting time is not very obvious.(6)Based on early lining thickness,initial support strength,depth and spacing of holes in each operating mode corresponding to the secondary liner supporting time,least squares method,the secondary liner supporting time and the beginning of lining thickness,initial The regression equation between the supporting strength,depth and hole spacing.(7)The establishment of a three-dimensional numerical models to study different footage of the excavation crown displacement versus time curve analysis reveals that a reasonable opportunity to support secondary lining.Research shows footage of the excavation secondary lining reasonable opportunity to support smaller impact can be ignored in the construction of its impact.