Research On Anchorage Mechanism And Design Method Of Recyclable CFRP Anchor

The development of Chinese urban construction industry and underground space has gradually entered a rapid speed stage,and the support of foundation pit engineering is becoming more and more important.The traditional pile and anchor supporting system with the anchor(cable)left in the underground space after the project completion will not only easily cause the environmental pollution,but also invade the underground space of the adjacent building and become a construction obstacle for subsequent projects.Recyclable anchors(cables)made of Carbon Fiber Reinforced Polymer(CFRP)can well solve the above problem.On one hand,it can solve the corrosion and durability problems of traditional steel.On the other,it can greatly improve the bearing capacity of the anchor(cable)and provide better support for the sustainable development of urban underground space.Based on the existing studies,this paper presents a recyclable CFRP anchor in the form of a grouted reaming(i.e.,enlarged head),which is a type of anchor under compressive force.From the perspectives of anchoring mechanism and design method,the feasibility and working performance of CFRP anchors are studied in terms of theoretical analysis,experimental research and finite element simulation.The main research contents and conclusions are summarized below:(1)The structural form of recyclable CFRP anchors is systematically introduced with respects to external anchors,connectors and recyclable ends.A connector of CFRP anchor is developed based on existing studies and related national utility model patent was applied and issued.(2)Based on the three aspects of anchoring mechanism,failure mechanism and force mechanism,the working principle of recyclable CFRP anchors was introduced.Based on the related theories of elastic mechanics and Mindlin displacement solution,the bond stress between the grouting body and the rock or soil in the reaming anchorage section and the axial force distribution of the grouting body in the anchoring section are studied.The results show that the bond stress of the reaming grouting increases rapidly to the peak and then gradually decreases.The axial force is gradually attenuated from the peak.However,when the distance from the carrier(i.e.,the end of the anchoring section)exceeds 2 m,the influence of the bonding stress is small and thereafter the increase of the anchoring force of the grouting body is negligible.(3)A modified CFRP composite external anchor is designed and the effects of bonding material,the length of metal cylinder and the surface form on the anchoring performance of a single CFRP anchor with a diameter of 10 mm are studied.The results show that the longitudinal fastening force provided by the modified composite anchor nut can effectively prevent the slippery slip without applying preload.The surface form has a great influence on the anchorage performance of the anchors,the anchorage efficiency of the surface ribbed CFRP is 14.3% higher than that of the smooth one.The bonding materials have a certain influence on the stability of the modified composite anchors during the anchoring process.However,it has less effect on the final anchoring effect.(4)Relevant requirements about the design method of recyclable CFRP anchor on the basis of national standards was made,such as the design of recyclable CFRP anchor and related materials,safety factor,rod design,anchorage section design and construction.To meet the requirements of the specification,basic tests and final inspection and recycling are required before construction.(5)Finite element method(FEM)is applied using ABAQUS software to simulate a foundation pit excavation and support project.The results show that the maximum point of horizontal displacement is located at the top of the pile,and the minimum point of horizontal displacement is located at the leftmost side of the excavation of the soil at the bottom of the pit.Compared with the horizontal principal stress,vertical principal stress is negligible;the maximum stress at the contact between the second layer of anchor and the pile is 123 kN during the whole excavation process.The top of the pit starts to rise from 10 m from the pile body,which has less impact on the building.The results suggest that pile and enlarged head anchor supporting system has good efficacy.