| Along with the construction scale of the highway tunnel growing.In the soft rock tunnel project. As well as determining the stability of rock, determining the reasonableness of the initially supporting structure is the focus of the study and difficult of the engineering design in the course of construction. As the conditions of rock varied,rock instability accidents occur from time to time, bringing huges losses of people's lives and property. Therefore, in view of the characteristics of weak rock varied from time to time in the course of tunnel construction, the research on behavior of early supporting structure to tunnel rock have a certain production practical significance.Most of the rock yield criteria include Mohr-Coulomb yield criteria and Drucker-Prager yield criteria. And most of the problems in projects can be simplified as plane strain, plane stress or axisymmetric problems to solve. In this paper, using the Mohr-Coulomb yield criterion, at the same time,looking the early supporting structure and the rock as a whole structure using the plane strain element to solve nonlinear problems.This paper describes the methods and the steps of the ABAQUS/CAE module established finite element model, and then to elastic-plastic theory, creat the numerical model of supported tunnel and unsupported tunnel in Class III-Rock, at the same time the results are analyzed and compared. By the analysis of the results on finite element, after early supported , the supporting structure hindered the further deformation of the surrounding rock, reduced the stress of rock in the tunnel and greaterly eased the rock stress concentration problems, at the same time reduced the Rock plastic region, the overall stability and durability of the surrounding rock have a large degree of improving.On the basis evaluation of the tunnel surrounding rock stability in supported tunnel and unsupported tunnel, further as an example to the LaoLing V-Rock Tunnel, I analyed the tunnel rock deformation and failure characteristics, the initial support structure on the impact of the stability of the rock and the changes of the initial support parameters on the stability of the rock changes. At the same kind of rock, the deformation analysis in the different conditions of bolt spacing, different radiation of bolt and sprayed concrete under different parameters conditions were calculated, and with different kinds of rock-depth circumstances, Quantitative analysis on displacement changes of vault and floor in the same type of rock were analyed. Through the process of analysis, forecasting the deformtion of the state of the surrounding rock and supported structure as a whole in the construction of the tunnel. On evaluation of the surrounding rock stability, and at the same time contrast the conclusions of viscoelastic verified before and after tunnel support, the simulation results show the correctness of this paper. And use the method of bolt encryption based on them to optimize and improve the process for tunnel construction and give some advice on early support recommendations.This papers approved the following conclusions:1,The initial support structure play an important role for the stability of the tunnel, from the compared the stress and displacement of before and after Supporting rock tunnel, the result of Supporting reduce a large extent stress concentration region, as well as reduce the displacement of key points of the tunnel, the mothod of early flexible support and the rock as a whole struction in the analysis process theoretically give a good interpretation of the role of the support and the impact of mechanical behavior on the support to rock. 2,The development of tunnels plastic region have a great impact for the stability of the tunnel rock, the plastic region are much smaller in which excavate an Invert than which not. Therefore, for the soft rock should be excavated and closed the Invert as soon as possible;3,The tunnel rock stress and displacement change not only causal link with the time, Also with the depth of the tunnels, the bolt spacing, as well as the starting point of the anchor. For the scope of bolt strengthening region, the starting point of the anchor which is 0 degrees is the best supporting, but we must accord to the specific situation of the surrounding rock on the economic and practical. The impact of the density of bolt exist not only in different rock stype circumstances, at the same time for the same kind of rock which have different depths the impact should not be overlooked. For the same kind of rock, with the increase of the tunnel depths, the stress and displacement in the location of the vault,invert have varying degrees of increase.4,In the same kind of rock which are in different depths circumstances, the early supporte use the same Supporting measures will cause inconsistencies stress on the surrounding rock, as well as uncoordinated displacement(eg. The vault), in a certain period of time the rock which in the depth has reached the limits of rock displacement, and the changes of the displacement which in shallow depth of is smaller, this caused the partial destroying on surrounding rock, thereby affecting the stability and durability of the overall structure of the tunnel, Against such situation in the same kind of rock use different bolt density as early Support, This situation has considerably reduced the harm, rock displacement of the tunnel is ensured to be coordination and the overall stability and durability of the tunnel are enhanced, and the use of the tunnel life is increased. And increasing the density of bolt to the hours of work and economic demands is not too high, it can be served as an ideal methods to put into the course of construction.
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