| Along with the developing of highway conduction and the increasing of highway grade, the construction scale and quantity of the vehicular tunnel have also increasing. Then the stability problem of vehicular tunnel excavation is coming. The stability of the surrounding rock and support of the vehicular tunnel is the mainly aspect of directly influence the tunneling cost. If we can't prevent the collapse of surrounding rock, the direct economic expense of a medium type collapse accident could reach about 2 million to 3 million RMB. In addition, the collapse of the surrounding rock collapse often goes with conduction equipment loss and personnel casualty, and also severely delays the project time. The economic loss and society influence which it results in also can't undervalue. So, how to guarantee the surrounding rock stability in conduction and long-term working time is the key technical problem which should be urgently settled when the vehicular tunnel is conducted. The finite element numerical simulative method overcomes the waste of time which is spent on test situ supervised,the waste of fund and manpower. To analyze the stress distribution and deformation of the surrounding rock systemically and intuitionistically after the tunnel excavation in different condition could direct the project.The rock mass is a kind of complex material that has the mechanics characteristic of non-linearity, elastic-plastic nature, non-homogeneity, anisotropism and rheology. The elastic-plastic deformation nature is one of the earth important natures. The elastic-plastic theory of rock mass mainly includes yield hypothesis and constitutive model. For rock mass material, the most common yield criterion or damage condition is Mohr-Coulomb yield criterion andDrucker-Prager yield criterion. This paper adopts Mohr-Coulomb elastic-plastic yield criterion. The constitutive relationship is the mathematical expression that reflects mechanics performance of material. The constitutive relationship model of soil mainly includes the elastic model, the elastic-plastic model, viscoelastic and plastic model and so on. This paper adopts the elastic-plastic model.After the tunnel excavation, the surrounding rock is lack of the support of primary rock and it destroys the primary balance state and the rock swell into the cavity interspace. As a result, it changes the relatively balance state of border particle and bring the adjustment of stress, strain and energy to obtain a new balance and form a new stress state. This is called the surrounding rock's secondary state of stress. The rock's savageness state of stress is called the primary state of stress. The surrounding rock deformation will destroy the stability of the underground chamber. So, we should support the surrounding rock. The support would change the stress distribution and deformation of the surrounding rock again and form a new state of stress field which called the tertiary state of stress of rock mass.This paper briefly introduces the function and strong points of the finite element procedure ABAQUS. And particularly expounds the means and approach of using the ABAQUS/CAE module to set up the finite element model. Then take the four-lane and grade V surrounding rock, and the excavation method is benching tunneling construction method for example to simulate the practical excavation. Analyze and compare the calculate results. Through the analysis of the finite element calculate results, find out that after every time excavation, the stress of the surrounding rock would redistribution and bring some deformation. After supporting the surrounding rock, the support would block the surrounding rock deformation and reduce the stress and then to great degree mitigate the stressconcentration problem. To use the simulation method of finite element to substitute the practical excavation process can save the time of experiment, manpower and money in the range that precision and credibility allow. It can also expand the range and fine of the parameter studied and offer an effective means for the research of the surrounding rock stability of the highway tunnel excavation by using the simulation method.On the basis of the highway tunnel excavation finite element that has been set up, the influence to surrounding rock stability such as the grade of surrounding rock, excavation method and sequence, tunnel span and rock mass parameter and so on was researched by the method of numerical simulation and do the project design. Then analyze and compare the stress field and displacement field variety discipline of surrounding rock in every project. And sum up the following series of conclusion.(1) The deformation discipline of different lithology surrounding rock is basically the same in the same excavation method, but the quantity is very different. The better the lithology is, the smaller the deformation of the surrounding is and the greater interior stress is, then the stronger the ability of resisting deformation is. For the worse lithology surrounding rock, after the excavation we should support in time to restrict the deformation of the surrounding rock and prevent the collapse to guarantee the stability of the tunnel.(2) The position of the greater deformation in construction, the more concentrated stress and easier to destroy is: the side of the tunnel, the arch crown and the springing. These positions should be pay greater attention to. And these positions should also supervise to feedback the construction.(3) The different excavation method is different to the disturbance of surrounding rock. So we should on the basis of the surrounding rock grade tochoose reasonable excavation method. Although the method of excavation by step could control the stress and deformation of the surrounding rock in time, the disturbance is greater and the construction is not convenience. So, this method only is adopted in soft rock.(4) For different tunnel size, the bigger the span and the larger the excavation space is, the larger the load release. So the secondary stress increase accordingly and the deformation is more remarkable, the influence range of excavation is greater too. For large-span tunnel, the stress concentrated phenomena is more distinct compared with small-span tunnel.(5) For the different rock parameter, the surrounding rock in elastic area, the stress is mainly determined by Poisson's ratio and the deformation is codetermined by elastic module and Poisson's ratio. The internal friction angel, swelling angle and cohesion has small influence to the displacement and stress of the rock around the cavity. But for the rock mass which has come into the plastic area, the stress and displacement is codetermined by elastic module, Poisson's ratio the internal friction angel, swelling angle and cohesionIn conclusions, the model this article sets up, the analyze method and the variation discipline of the stress and displacement could offer reference for the tunnel structure design and construction in different surrounding rock. |
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