| Soft rocks tunnels are prone to large-scale deformation of the surrounding rock and even collapse during the construction process.collapse often cause delays in the construction period,resulting in loss of life and property,and affect tunnel operations.Supporting design and construction during the construction of highway tunnels are the major problems that must be solved by majority of scientific and technical staff,especially the support problems of soft rocks tunnels.For this series of problems,this paper makes a study on the engineering characteristics and supporting types of soft rocks,and systematically studies the configuration of similar materials in the geomechanical model tests,which is different from the representative of the tension and anchor supporting structure.Supporting conditions In the progressive destruction test,the failure mode,stress and strain of the surrounding rock,and the force characteristics of the support members were systematically studied.The main research contents and results are as follows:(1)Using barite powder as fine aggregate,quartz sand as coarse aggregate,building material gypsum as adjusting material and rosin-alcohol solution as raw material of cementing agent,similar materials of grade Ⅳ surrounding rock can be configured,through direct shear test,without The physical and mechanical parameters measured by the lateral compressive strength test can meet the scope of the model test requirements.This class has the advantages of easy molding,low price,wide source,rapid drying,non-toxicity,etc.It is a good surrounding rock.similar materials.(2)Self-designed and processed a set of model test device,which can perform multi-function underground structure model test.The test device has the characteristics of detachable,full-field monitoring and good economic applicability.(3)Through the model test,the regular pattern of deformation and failure of surrounding rock was obtained:① There are two stages of tunnel failure.One is the settlement of the vault but no landslide and accompanied by the phenomenon of side wall intrusion.In the second stage,the vault collapsed on a large area and developed toward the form of a collapsed arch.② Tunnel deformation failure is caused by the shear damage of the arches and is transferred to the dome with the overlying load to the vault.③When the overburden load is at the same level,the displacement of the cave tunnel is the largest,followed by the bolting tunnel and the bolted tunnel,indicating that the bolting and anchoring support structure can play a role in limiting the deformation of the surrounding rock.And the restraining effect of the tension and anchor support structure on the deformation of the surrounding rock is more obvious.④ The final form of tunnel failure is arched landslide and a complete collapsed arch is formed;the collapse form of bolted tunnels and tensioned and anchored tunnels is partially collapsed and no obvious collapsed arches are formed.(4)Through the model test,the law of stress change of surrounding rock is obtained:①The surrounding rock pressure is greater than the horizontal pressure,and the vertical pressure change value is also greater than the horizontal pressure change value.② The test results verified that the surrounding rock was in the loose state circle→pressure arch→original rock stress from the tunnel contour line.③ The loose circle of the Maodong tunnel is larger than that of the bolt support and the pull bolt supporting tunnel.The loosening circle range of the bolted tunnel and the bolted tunnel is similar,indicating that the bolt and the pull anchor structure strengthen the surrounding rock and improve the surrounding area.The rock bearing capacity has narrowed the looseness of the surrounding rock.(5)Through the model test,the change law of the force characteristics of supporting members is obtained:① In the structure of the tension and anchor support,the maximum axial force of the bolt is near the end of the bolt;under the bolt support conditions,the maximum axial force of the bolt is located in the middle of the bolt.② The maximum axial force increment of the anchor rod under the tension and anchor support structure is greater than that under the bolt support conditioa③ The axial force of the anchor bolt under the condition of bolt support is greater than the axial force of the top anchor bolt,and the axial force of the anchor bolt under the condition of the anchor bolt support is equal. |
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