Study On The Pull-out Mechanical Performances Of Defected Bolt Grouted System

Bolt anchoring technology,as an effective reinforcement method,has been widely used in practical engineering,which can improve the wholeness and stability of rock mass.However,in the construction process,the defects of rockbolt grouted system caused by human and natural factors will exert some hidden dangers for the safety of the rockbolt grouted system.In this paper,numerical simulation method was used to study the pull-out mechanical properties of defect rockbolt grouted system and the influence on engineering,which can provide theoretical support for the design maintenance and safety performance of engineering structure.(1)Through the rockbolt grouted system pull-out test is carried out.The bond-slip constitutive model based on three-wire between bolt and mortar was proposed.And the model is validated by comparing the test results with simulation.(2)The bond-slip constitutive model based on three-wire rockbolt grouted system was established to study the influence of the bond defect length,the bond defect position and bond defect distribution pattern on the load displacement curve of the rockbolt grouted system and the variation curve of the tensile stress and shear stress of rockbolt grouted system with bond defect under the action of pull-out test;in addition,the influence of the bolt diameter and mortar thickness as the parameter variables on the mechanical properties of rockbolt grouted system with bond defect was studied.The results showed that the bond defect length affected the variation of bearing capacity and stress distribution of rockbolt grouted system to a large extent,and due to the bond defect,the stress distribution was horizontal at the position of defect;the closer the position of the bond defect is to the load end,the longer the nonlinear phase would the load displacement curve undergo before reaching the peak load,and with the change of the defect position,the peak load was almost in the same horizontal line;the peak load was increased with the increase of the bond defect spacing;the larger bolt diameter might result the large difference between the peak loads of the rockbolt grouted system;the mortar thickness had little effect on the bearing capacity of the rockbolt grouted system with the same bond defect length.(3)The bond-slip constitutive model based on three-wire rockbolt grouted system was established to study the influence of the bolt damage length,the bolt damage position,bolt damage distribution pattern and the bolt damage thickness on the load displacement curve of rockbolt grouted system as well as the variation curve of the tensile stress and shear stress of rockbolt grouted system with bolt damage under the action of pull-out test;in addition,the influence of the variation of the bolt diameter on the bearing capacity of the rockbolt grouted system with bolt damage was studied.The results showed that with the increase of the bolt damage length,the ultimate bearing capacity decreased,and the axial displacement declined rapidly;due to the bolt damage,the stress distribution was horizontal at the position of damage;for the same damage length,the larger the value of l_x,the better the anchoring performance of the rockbolt grouted system was;the distribution pattern of the bolt damage,the damage thickness and the diameter of the bolt had different effects on the variation in the load displacement curve of the rockbolt grouted system.