Constant Resistance Shrinkage Design And Mechanical Properties Of U-shaped Steel Support In Circular Roadway

The U-shaped steel collapsible support is made of multiple sections of U-shaped steel overlapped in pairs and bound with cables.It is commonly used in coal mine roadway support.Its section shape can be selected according to the actual roadway section shape and support requirements,but the support often deforms and damages when it does not achieve the ideal support effect in the actual support.Taking the actual support of U-shaped steel support in circular roadway as an example,depending on the extent of deformation and damage,it falls into two types:global damage and local damage.It can be concluded that the causes of deformation and failure are:(1)the coupling degree of support filler surrounding rock is low,the stress of support is complex,and the support strength is reduced;(2)The unreasonable strength and structure of the cable clamping of the support connector will lead to the phenomenon of high resistance shrinkage and low resistance shrinkage of the support,which failure to develop normal support capability of support.Based on the above analysis,the structure of the existing connector cable clamp is optimized and improved,and a new cable clamp is proposed.The splint bolt cable clamp and the new cable clamp are used as connectors for the U-shaped steel support of circular roadway.The mathematical modeling analysis of the support is carried out.The plane shrinkage resistance of the lap section,the shrinkage discriminant of the lap section and the composition of the internal force of the support after shrinkage are theoretically deduced and analyzed respectively.It can be seen that the friction coefficient f is the crucial factor affecting the shrinkage stability.The stable shrinkage process can effectively improve the stability of the support Soft metal gasket is added between Ushaped steel and cable clamp to change the friction state and reduce the fluctuation of axial bearing capacity of overlapping section.Further verify the working performance of the new cable clamp and the influence of soft metal gasket on the shrinkage stability.Through indoor test and finite element simulation,the shrinkage analysis of the straight U-shaped steel lap section using splint bolt cable clamp and new cable clamp(adding soft metal gasket between U-shaped steel and cable clamp)is carried out respectively.The comparative analysis of the test results and simulation results shows that the shrinkage consistency between the cable clamp and U-shaped steel is strong when using the lap section of new cable clamp,The axial bearing capacity can reach 300 kN with small fluctuation.The addition of soft metal gasket can effectively improve the stability of shrinkage.The lap section has no obvious plastic deformation,the overall high strength and stability,and does not exceed the material yield limit.The performance of the new cable clamp is better than that of the splint bolt.The new cable clamp and soft metal gasket are used in the U-shaped steel support of circular roadway.The indoor test and finite element simulation of the support are carried out,and the bearing capacity,support strength and shrinkage of the support are obtained.It can be seen that when the shed distance is 0.5m,the support strength of the circular support using the new cable clamp can reach 0.233 MPa,and the maximum shrinkage displacement of the overlapping section is 1168 mm.The overall strength and stability of the support are high,which can effectively control the deformation of surrounding rock and maintain the stability of roadway.