Field Pullout Tests Of Basalt Fiber-reinforced Polymer Ground Anchor

Basalt fiber reinforced composite?BFRP?anchor is mainly composed of basalt fiber and resin?i.e.,epoxy resin,polyethylene resin,polyester resin and so on?.Compared with steel bar,it has the advantages of high specific strength,good corrosion resistance and good coordination deformability with surrounding rock.It is a new type of high performance fiber anchor,and the research in the field of geotechnical anchorage technology is just starting.First,the previous research achievements in geotechnical anchorage of FRP are reviewed.Then,the working mechanism of the soil FRP anchorage system is analyzed and discussed.Two interface states?elastic and plastic?and the deformation properties of the surrounding rock?the shear deformation can be neglected and cannot be ignored?are established.It is proposed that the anchorage interface undergo three stages:the elastic,plastic and bond slip failure.Based on this model,the bond slip process is analyzed theoretically.Finally,9 groups of BFRP bolts and 2 groups of steel anchors were carried out in the field drawing test of loess slope.Through the analysis of load displacement curve,axial force distribution and shear stress distribution,the bearing performance of anchorage system under different anchor diameter and anchorage length was systematically studied.The increase in the bolt diameter can significantly improve the ultimate pullout load of the anchor system under certain conditions.With the increase of the anchorage length,the ultimate pullout force does not always increase linearly,but the increasing trend decreases gradually,showing the existence of a critical value in the anchorage length.The average bond strength of the 1^st and2^nd interface decrease with the increase of the anchor length.And the recommended values for average bond strength in interfaces are also presented for the design in practical engineering.The axial force of the anchors gradually attenuates along the depth,and the distribution pattern is related to the size of the tensile load,the diameter of the bolt and the length of the anchorage.The shear stress distribution obeys the single peak shape which increases first and then decreases with the anchorage depth,and the peak value appears in the range of 0.5m at the front of the anchorage,which is also influenced by the length and diameter of the anchorage.The comparison with steel bar anchor indicates that the first interface bonding performance of reinforcement anchorage system is better than that of BFRP anchor rod.Through the field excavation analysis,the failure mode and the corresponding failure mechanism of the anchorage system are analyzed.It is pointed out that the anchors with 12mm and 16mm diameter tend to fail by shearing in the interface between bar and grout(the 1^st interface),and 25mm fail by shearing in the interface between grout and surrounding soil(the 2^nd interface).The interface failure of the anchorage system is remarkable and the failure mode is affected by the diameter of the rod and the strength of the bonding medium.