| Rapid economic development and sci-technological progress demand a transportation moresecure, comfortable, fast and convenient, and hence a large number of highway construction.China is a mountainous country, more than 2/3 of whose territory is canyons, hills and mountains.With the implementation of develop-the-west strategy, expressway construction has been pushedfrom the plains to mountainous areas. Corresponding to this, the expressway tunnel constructionis also rapid growth.Tunnel construction is often the key project in expressway construction, the cycle and thequality of which will directly affect the whole process of expressway construction. In themountainous zones, it is inevitable for tunnels to penetrate rock layers of complex geologicalcondition, resulting in a large number of geological disasters. Among these disasters, the largedeformation of soft rock is a common one, the occurrence of which will seriously disturb thetunnelling.Effected by Liangyun Fracture (Yunxi- Yunxian Fracture), the rock structure of the studyingarea were developed, and the rock mass were weak, which brought difficulties for theconstruction. The paper classified the large deformation according to the tunnel largedeformation conditions along the line. The article mainly studied the deformation characteristicsof soft rock tunnel in Shiman Expressway, especially carries out the numerical simulation ofentrance partial stress section in Huocheling tunnel.The paper compared the common elastic-plastic and viscosity-elastic-plastic constitutivetheories, combined with the mechanics characteristic and displacement changes curve, chose theimproved Burgers Model for the weak rock tunnel. The paper simulated the large deformationand supporting structure stress through FLAC3D finite different software, and analyzed the rockmass parameters and interaction effect between the supporting structure and surrounding rock.Finally it optimized the supporting structure and construction procedure of soft tunnel andensured the safety construction.The main content and conclusion were as follows:(1)The engineering geology condition analyses of the studying area. The Liangyun fracture had so obvious effect for the mechanics character and surrounding rock strain along the line thatthe mechanics performance dropped rapidly after excavation and appeared large deformation.Combined with the large deformation examples of Shiman Expressway, the paper divided thelarge deformation of studying area into 3 classes: controlled by rock character, controlled by rockmass structure, and controlled by land form and the simulation model belong to the third type.(2) Because of the close relation of tunnel surrounding rock deformation and time, onlyapplying rheoligic mechanics viewpoint can fully illuminate the interacting relationship betweensurrounding rock deformation characteristic and supporting structure. Through the analysis ofexisting viscoplastic constitute theory and the combination with the surrounding rock mechanicscharacteristic and deformation monitor condition of studying area, the author had chosen theimproved Burgers creep model which connected Burgers Model and Coulomb-Mohr Model inseries and had the proper expression of rock properties for and after yielding.(3) Through the numerical simulation of large deformation of Huocheling Tunnel partialstress YK54 + 022 section by FLAC3D, the deformation properties was similar with the filedaccident, which sufficient declared the rationality of the simulation method and model andensued the simulation accuracy and analyzing reliability. The simulation realized the deformationprocess. With the analyses of the mechanics properties about preliminary supporting structure,the structure with large deformation section reached a rather large stress, which has exceeded thesupporting structure strength. The stress distribution along the hole was extremely uniform, andthe tensile stress was appeared in the arch crown deviation to the right. From the shear stress map,the local part of preliminary supporting structure had stress concentration phenomenon that hasaggravated the destroying degree of structure.(4) Through the simulation of core soil construction and different length conditions, theresult indicated that keeping core soil could effectively prevent working face from becomingdeformed and collapse. Under the premise not affecting construction, tried to reserve the coresoil same length with lower bench in order to protect the working face. Simulation resultdisplayed that without core soil, working face of upper bench reaches 40～50 cm deformationalong the axis which can be regarded as collapse in weak rock. After setting up core soil, thesurface of soil and lower bench get certain collapses phenomenon, but restrained working facedeformation and having the stability action.(5)The mechanics parameter selecting was critical fort simulation effect, and also was anindispensable step in simulation process. The paper used Coulomb-Mohr model to study thesensitiveness of E,μ, C,φ, and analyzed the changing state of cycle displacement, stress andplastic circle under keeping other value constant changing one parameter with 20%. The resultindicate that parameterμ,φsensitiveness was much obvious to surrounding rock mechanicsproperties. Therefore the selecting ofμ,φvalue need to pay attention to ensure the simulationreliability. (6)For the regular hard rock tunnel, need to make full use of the surrounding rockself-supporting capability, and the secondary lining can be carded out fall behind the preliminarysupporting structure. But for weak surrounding rock, need to carry out the preliminarysupporting structure as early as possible to ensure the couple of structure and surrounding rock,and the preliminary supporting structure got sealing prevention action before appearingacceleration creep deformation. According to the "Expressway Tunnel Design Standard",secondary lining construction should combine the monitor condition. In some practical project,the secondary lining could be exerted as early, beard the pressure with preliminary supportingstructure and guarantee the stability of tunnel rock..In conclusion, the paper analyzed the weak rock character and classified the largedeformation of Shiman Expressway. Through the simulation research of Huocheling tunnelpartial stress section with FLAC3D software, analyzed the deformation condition of surroundingrock and the stress state of supporting structure in the construction. It also use simulation methodto study the stress behavior of anchor and the interaction effect between supporting structure andsurrounding rock, and optimized the construction procedure and supporting structure for thetunnel excavation. The research result could be feedback to the practical, applied to the similarprojects and also had certain reference.
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