Research On Anchorage Mechanism And Design Method Of GFRP/CFRP Mixed Fiber Anchor

With the rapid development of China’s economy,the demand for urban buildings and underground space soars,and the safety awareness of foundation pit engineering cannot be ignored.The most commonly used traditional anchors in pile anchor support are mostly made of steel bars,which are prone to corrosion and pollution under the action of oxygen in groundwater and soil.The glass/carbon mixed fiber reinforced polymer anchor can not only eliminate the environmental pollution caused by the corrosion of traditional reinforced anchor,but also enhance the bearing capacity of anchor,which can ensure the safety of engineering personnel and prevent the loss caused by foundation pit accidents.On the basis of previous studies,this paper proposes a kind of end pressure-type GFRP/CFRP mixed fiber reinforced ground anchor.The anchoring mechanism and design method of GFRP/CFRP mixed fiber reinforced ground anchor are studied by systematic experimental research,theoretical analysis and finite element simulation.The main work and results are as follows.(1)An improved GFRP/CFRP mixed fiber reinforced composite external anchorage was designed,and the effects of surface form of reinforcement,structural form of anchorage and fiber hybrid ratio of GFRP/CFRP mixed fiber reinforced composite external anchorage were studied on the anchorage performance of GFRP/CFRP mixed fiber reinforced composite external anchorage.The results showed that compared with plain round reinforcement,ground GFRP/CFRP mixed fiber reinforcement has little influence on the anchorage effect;the longitudinal pressure produced by the interaction between the nut of the improved anchorage and the thread on the metal cylinder can effectively prevent the wedge clip from slipping off in the working process;when the volume fraction of CFRP is 4%,it can give full play to the high strength characteristics of CFRP material in the reinforcement and the low cost of GFRP material.(2)The finite element software ABAQUS is used to simulate and analyze the improved GFRP/CFRP mixed fiber reinforced composite external anchorage.The results showed that ABAQUS has good feasibility in simulating the external anchorage,which can be used to simulate the mechanical properties of the improved GFRP/CFRP mixed fiber reinforcement anchorage system;the radial stress of sleeve caused by wedge clip and cohesive is an important index to reflect the anchorage performance;the optimal parameter combination for designing the improved GFRP/CFRP mixed fiber reinforcement anchorage system is P=10kN～20kN,&=2mm～4mm,h=280mm.(3)The working principle of GFRP/CFRP mixed fiber reinforced ground anchor is introduced.Based on the stress mechanism,anchoring mechanism and failure mechanism,the axial stress of grouting body in anchoring section and the distribution law of bonding stress between grouting body and rock and soil mass in anchoring section are studied.The results show that: the peak value of the axial stress of the grouting body in the anchorage section is located at the bearing body,and the axial stress gradually decreases with the increase of the length of the grouting body in the anchorage section;the overall curve of the cohesive stress of the grouting body in the anchorage section first increases and then decreases.(4)A case study about a foundation pit retaining structures using GFRP/CFRP mixed fiber reinforced ground anchor and traditional reinforced steel anchor was presented using the finite element software ABAQUS.The results showed that during the whole excavation simulation process,the maximum horizontal relative displacement is located near the third anchor and row piles,and the unearthed part of the bottom of the foundation pit is almost not affected.The maximum vertical displacement is located on the right side of the row pile.The reason is that the gravity center of the soil on the right side of the row pile moves downward due to the effect of the pile anchor retaining structure.The maximum horizontal displacement and the maximum vertical displacement are within the range of 8m from the top of the foundation pit to the pile.Through the comprehensive comparison of results of displacement(deformation),stress and construction process,it can be concluded that the GFRP/CFRP mixed fiber anchor is better than the transfer fiber anchor It is more suitable for practical engineering.