| As a complex geological type,Hard-Soft Heterogeneous strata are often encountered in the construction of underground tunnel,due to the different mechanical properties of soft and hard rock,tunnel excavation often shows different excavation characteristics,especially in deep buried tunnels,because the ground stress is relatively high,and the rock is non-uniform,if the supporting measures are improper and supporting time delays,engineering accidents like surrounding rock instability,support damage and collapse are likely to happen,resulting in time lag,economic losses and casualties.Therefore,study on the deformation and stress of surrounding rock and supporting structure in the process of tunnel excavation is very import.This paper take the hard-soft heterogeneous area of the Cong Keng tunnel in Nan San Long railway as the engineering background.With the help of MIDAS/GTS numerical analysis software,this paper analyzes the deformation of surrounding rock and the stress of primary support of the tunnel under the condition of hard-soft heterogeneous strata,and further studies the asymmetric supporting measures of the tunnel hard-soft heterogeneous strata.The main contents are as follows:(1)The safety risk of tunnel excavation under special hard-soft heterogeneous stratigraphic conditions and the present construction problems are kNown through the collection and analysis of the cases of hard-soft heterogeneous stratigraphic tunnel collapse.The current research situation of tunnel construction at home and abroad under this kind of special strata is kNown by reading research results of tunnel excavation characteristics at home and abroad under hard-soft heterogeneous strata.The theory of the mechanics characteristics of supporting structure and the surrounding rock in tunnel excavation are expounded in detail to provide theoretical basis for the follow-up research works.(2)The hard-soft heterogeneous strata in the project are divided according to twodimension and three-dimension.Different simulation schemes are made according to hard-soft heterogeneous stratigraphic types of tunnels under deep burial conditions to build the twodimensional and three-dimensional model of coexisting stratum of ? and V grades soft and hard surrounding rock.The two-dimensional model is used to dynamically analyze the construction of hard-soft heterogeneous stratigraphic tunnel from the aspect of same location with different angles and same angle with different locations in the boundary of the surrounding rock while the three-dimensional model is analyzed from the aspect of different angles between the boundary of surrounding rock and the horizontal plane and from the aspect of different angles between the boundary of surrounding rock and the plane of tunnel axis to study on the deformation of tunnel surrounding rock and deformation law of supporting structure are researched.(3)The numerical simulation results of three typical hard-soft heterogeneous sections of CongKeng Tunnel are selected to compare with the field measuring horizontal displacement of side walls and the vault settlement,which can verify the accuracy of numerical modeling process and material parameter selection and explain the reliability of using the finite element numerical simulation method to summarize the mechanics of hard-soft heterogeneous stratigraphic tunnel excavation.(4)Considering the present situation that full-scale symmetrical support cannot effectively control the deformation of surrounding rock in hard-soft heterogeneous strata,the unsymmetrical support measures modeling analysis of reducing the strength of the hard rock side support and strengthening the soft rock side support is carried out according to bilaterally symmetrical distributed hard-soft heterogeneous surrounding rock strata(90°boundary).The supporting effect is verified from the two aspects of the deformation of surrounding rock and the internal force of the supporting structure. |
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