Ductility Performance Of Inflatable Expansion Control Anchor Rod Experimental Research

Inflatable expansion control type anchor rod is a new type of friction anchor rod,which can provide anchoring force immediately after the completion of the construction of the anchor rod.There is no need to wait for the grouting to condense like the grouting anchor rod,which can greatly shorten the construction period;after the completion of the foundation pit project operation,Can be completely recycled,providing convenient conditions for the subsequent development of the surrounding underground space,and has broad application prospects in the field of geotechnical engineering.With the development of geotechnical engineering,not only the bolt support system is required to have sufficient bearing capacity,but also the diversification of geotechnical engineering requires higher and higher ductility performance of the bolt support system.The inflatable expansion control type anchor rod achieves the anchoring effect by squeezing the soil on the outer surface of the anchoring section of the steel pipe sheet to generate the anchoring force.After the support project is completed,the pressure is relieved through the air pressure control device,so that the anchor rod can be recycled and reused.Its structure is mainly divided into: steel pipe piece soil squeezing device,rubber air bag expansion device,steel bar force transmission structure,air pressure control device,and inflation pipeline device.In this paper,by changing the variables such as the inflation pressure,the thickness of the squeezing pipe piece,the outer surface roughness of the squeezing pipe piece,etc.,5 sets of inflatable expansion control anchor rods are made for pull-out tests,the load-displacement curve and the axial strain aging curve are drawn,and the displacement is calculated.The ductility coefficient,observation of the internal deformation of the squeezed soil segment and the anchor hole,objective and direct research on the ductility performance of the inflatable expansion control anchor rod by comparing the ordinary grouting anchor rod,the main content and results are as follows:The pull-out test process of the inflatable expansion-controlled anchor rod is mainly divided into: the elastic phase,the yield phase,and the local deformation phase.As the inflation pressure increases,the yield displacement of the anchor rod when it reaches the ultimate bearing capacity also increases.After reaching the ultimate bearing capacity,the pull-out resistance of the anchor rod slowly decreases and finally stabilizes at a certain fixed value,showing a good Ductile characteristics.Calculating the displacement ductility coefficient and residual strength analysis,the displacement ductility coefficient of the inflatable expansion control anchor rod with the extruding segment thickness of 3mm is the highest,and the displacement ductility coefficient of the inflatable expansion control anchor rod with the extruding segment thickness of 10 mm is the lowest.As the thickness of the soil squeezing pipe increases,the displacement ductility coefficient of the inflatable expansion control anchor rod will decrease,and the residual strength of the anchor rod will increase.With the increase of the roughness of the outer surface of the soil squeezing pipe,the residual strength of the anchor rod increases.During the pull-out test of the inflatable expansion control type anchor rod,the anchor section of the extruded segment is subjected to pressure,the middle anchor section of the extruded segment is subjected to tension,and the force state of the anchor segment at the bottom of the extruded segment varies with the inflation pressure and The increase of the drawing load changes from compression to tension.From the comparison of displacement ductility coefficient,residual strength and load-displacement curve,it can be seen that the inflatable expansion control anchor rods all show good ductility characteristics and have better ductility performance than ordinary grouting anchor rods.Based on the spherical hole expansion theory,the stress state of the soil around the anchor hole during the test of the inflatable expansion-controlled anchor is analyzed,and the calculation formula of the bearing capacity of the inflatable expansion-controlled anchor is deduced,and the theoretical calculated bearing capacity is compared with the experimental value,Which provides a basis for engineering applications.