| In the 21 st century, the highway, railroad and subway tunnel construction in China is flourishing with the vigorous development of the transportation industry. On one hand, China is a mountainous country. On the other hand, tunnel has unique technical features. Tunnel is playing an increasing significant role in the transportation field. In fact, lots of tunnels are built in adverse strata sections such as water rich strata, soft and weak surrounding rocks, karst and fault fracture zone. To avoid engineering accidents resulting from the excessive deformation of surrounding rocks after the tunnel excavation starts, the pre-reinforcement measures must be applied to surrounding rocks before the excavation. Because of its good supporting performance, the pipe roof support has gradually become an important construction technology when the tunnel is built through poor sections. However, the design and construction of this technology are mostly based on similar projects, and this cannot meet the needs of the current project. Therefore, it is necessary to do the research on the quantitative analysis of pipe roof supporting parameters during the process of tunnel excavation.This paper introduces the construction methods and the characteristics of tunnel advance support and describes the research situation at home and abroad on the pipe roof support in the construction and supporting mechanism. At the same time, the paper introduces the steps of establishing the model of numerical calculation with ABAQUS. By choosing the geological parameters of Dawang mountain in Shenzhen, this paper establishes a numerical model with the aid of finite element software ABAQUS and based on the Mohr- Coulomb strength yield criterion. Under the two-dimensional model, through comparing and analyzing the tunnel deformation when pipes are set up and not, the feet-lock bolts are with different angles, lengths, number of rows and positions as well as surrounding rocks are with different properties, the obtained conclusion is as follows: the tunnel deformation can be effectively constrained when pipes are set up; and the length and angle of feet-lock bolt can obviously prevent the tunnel deformation only within a certain range; the number of rows and position are related to the deformation convergence of the corresponding parts; the property of surrounding rocks has the most significant influence on the tunnel deformation. Under the three-dimensional model, through comparing and analyzing the displacement and stress of the steel pipe under the different pipe parameters, the radius of grouting, the excavation method, the excavation footage and different rock properties of tunnel. The conclusion is as follows: the pipe diameter and pipe spacing have little effect on the tunnel deformation, but a greater influence on the stress of steel pipes; the grouting radius has a greater effect on both the tunnel deformation and the stress of steel pipes. With the larger of the grouting radius, the plastic zone is smaller, the tunnel deformation and the stress of the steel pipe is smaller, the pre-reinforcement area can better play its bearing capacity. The displacement effect and plastic zone excavated by the method of double side excavation is more smaller than CRD method, the tensile stress area of surrounding rock is smaller, the deformation of tunnel and the stress of the steel pipe are smaller; The excavation footages have significant influence for the tunnel deformation, with the increase of excavating footages, the influence range of the displacement of surrounding rock and the strain value of the plastic zone gradually increased. The deformation and stress of the rock after excavated has obvious change under different rock properties. Therefore, in the soft rock tunnel construction, should according to different geological conditions, selecting reasonable structure parameters of pipe-roof, and select the reasonable excavation method, control the excavating footages, ensure the tunnel construction smoothly. |
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