Theoretical And Experimental Study On Bearing Capacity Of New Tension-compression Composite Anchor

Aiming at the problem that the traditional tension type and pressure type anchors have concentrated force,the bond strength between the anchor and the rock and soil interface is insufficient,and the pullout bearing capacity is low,a new type of tension and compression composite anchor is developed.Through the model test,on-site in-situ test research and simplified theoretical analysis of the bearing capacity of the tension-compression composite anchor,the ultimate uplift capacity and anchoring performance of different bolts are compared and studied.The calculation formula of the uplift bearing capacity of the anchor and its ratio to the pull-out bearing capacity of the tension-type anchor(bearing ratio).(1)Through the model test of traditional anchor and tension-compression composite anchor,the ultimate uplift capacity and anchoring performance of different anchors are compared.The results show that the ultimate uplift capacity of tensile-compression composite bolts is greatly improved compared with traditional bolts,and it has better displacement ductility and deformation resistance.The residual pull-up bearing capacity of tensile-compression composite anchors is significantly improved.The shear stress of the tensioned anchor bolt is approximately linearly decreasing,and is the largest at the end of the tensioned anchorage section;when the tension-compression composite bolt with a ratio of 2:1is about to be destroyed The combined anchorage capacity of the anchored anchorage section and the pressure-bearing anchorage section is stronger,the interface bond strength is fully utilized,and the ultimate pullout capacity of the bolt is higher.(2)On this basis,through the on-site destructive test,the bearing capacity,load-displacement curve and strain data of the tension-type anchor and the tension-compression composite anchor are analyzed.The results show that the average failure load of the tension-compression composite bolt is greatly improved compared with the tension-type anchor,and it has better resistance to deformation;the tensile loss of the tension-compression composite anchor mainly occurs on thebearing anchorage section;When the composite anchor is broken,the tensile load factor is close to the corresponding tensile length coefficient.The TC11-1 anchor is characterized by simultaneous compression of the bearing anchorage section and the tensioned anchorage section.The TC12-3 and TC21-1 anchors are It has been destroyed successively;the significant improvement of the anchoring performance of the composite bolt is mainly due to the load decomposition,the two-way transmission mechanism of the interface shear stress and the short anchor bearing effect.(3)It is assumed that the shear stress between the anchor and the rock and soil is triangular.By considering the deformation coordination of the bearing anchorage section and the tensioned anchorage section at the bearing plate and the equivalent interface shear stress,the curve analysis of the bearing ratio is carried out..The results show that the bearing ratio increases with the increase of the length of the anchoring section,and the bearing ratio is distributed symmetrically with the length coefficient of the bearing anchorage section,and increases first and then decreases with the increase of the length coefficient of the bearing anchorage section.Under the same length of the anchoring section,the tensile and compressive bearing capacity of the tension-compression composite anchor can reach 2.0 times of the tensile anchor.