Mechanical Analysis And Parameter Optimization Of Composite Support Of Anchor-reinforced Shotcrete Arch Rib

With the advantages of convenient construction and economic efficiency,the reinforced concrete arch rib composite support structure has been widely used in weak surrounding rock.At present,the research on the structure mainly focuses on the mechanical analysis of the mechanism of support and reinforcement and the bearing force of the structure under the surrounding rock load,and has not yet involved the synergy between the structure and the surrounding rock.The lack of analysis of the structure's bearing force from the angle of the combined load-bearing force of surrounding rock and composite support is not conducive to its wide application in China.This paper first considers the interaction between the surrounding rock and the composite support,expounds the mechanism of the reinforcement of the composite support and the joint load-bearing mechanism of the surrounding rock,establishes the mechanical model of the combined load-bearing body of the surrounding rock and composite support,and deduces the analytical formula of the force,deformation,and carrying capacity of the joint load-bearing carrier,respectively.The deformation,stress and bearing capacity of the combined carrier are obtained by numerical examples.The results are optimized according to the analytical formula.The main contents and conclusions are as follows:(1)By using the theory of composite curved beams,the analytical expressions of internal force and radial displacement of the composite curved beams of the surrounding rock and support structures under uniform load are derived.This expression can directly reflect the force state of the joint bearing carrier.In the structure of the surrounding rock and support composite curved beams,The bending moment,axial force,and shear force in the arch ribs of the curved rock beam and the reinforced jet-jet concrete increase from the vault to the arch foot,and the maximum value appears at the arch foot.Compared with the bending moments of the curved beams of the surrounding rock and the supporting structure,the surrounding rock will bear the main bending moment.Become the main load-bearing part.Under the condition of increasing the load,the change slope of the internal force increases,the internal force of the arch of the support structure becomes larger than the increase of the vault,and the stress at the arch foot is larger.(2)The analytical expression of the bearing capacity of the joint support carrier formed between the arch rib and the surrounding rock of the spout anchor-reinforced spout concrete is derived.The expression reveals that the bearing capacity of the joint bearing carrier is not only related to the parameters,but also related to the actual construction sequence and the supporting state.When the supporting parameters are certain,the bearing capacity of the joint bearing carrier will also be related to the deformation of the surrounding rock.The load-bearing capacity of the combined support carrier will be increased with the increase of the deformation of the surrounding rock.The variation of load-bearing capacity and load-bearing ratio with surrounding rock is as follows:when the load-bearing strength and anchor rod supporting parameters are raised,the load-bearing structure becomes the main load-bearing structure,and the load-bearing capacity of the surrounding rock can be greatly exerted,and the stress state of the supporting structure can be improved.If the parameters of reinforced reinforced concrete arch rib support are only blindly enhanced,the bearing capacity of the support will increase,and the main bearing structure will gradually change from the surrounding rock to the reinforced concrete arch rib,failing to make good use of the characteristics of the self-bearing capacity of the surrounding rock.There is great unreasonableness for the safety and economy of the project.(3)The radial displacement of surrounding rock in analytical form is taken as the index of orthogonal test results.The main influence parameters and secondary influence parameters of the composite support effect are sorted in order:reinforced arch rib thickness,surrounding rock strength,concrete strength,anchor length,anchor distance.At the same time,the parameters of concrete strength,length and spacing of Anchorage rods,and thickness parameters of reinforced injection concrete arch ribs were optimized for the bearing effect of joint support carrier support.The concrete label number was from C20 to C30,and the length of Anchorage was from 2m to 2.5 m.,The spacing of anchor rod is in the range of 0.8m?1.2 m,and the thickness of reinforced concrete arch rib is in the range of 0.2?0.4m.