|
With high corrosion and fatigue resistance, high tensile strength, light weight, electromagnetic neutrality, Fiber Reinforced Plastics (FRP) has received considerable attention as alternatives to steel and aluminum as new-type geotechnical materials in construction.The history review and current state of geotechnical anchorages, to begin with, are presented. The brief tasks and the future challenges in the field of ground anchors are described emphatically.And, so far as the new-type FRP helical anchor is concerned in this paper, it is as follows, the properties of FRP tendons, the back ground of anchor, the assembly of anchor, the workmanship of anchor, the design philosophy of anchor, the anchor pullout test, the acceptance test of ground anchor, and the long-term monitoring of anchor.(1) The FRP tendons have a lot of attractive properties, and the performance of ground anchor is briefly effected by FRP materials properties, such as corrosion-resistance, tensile strength, shear stresses, long-term behavior of FRP.(2)The design philosophy of FRP anchor is different from the one of steel anchor because of the mostly linear relationship of strain to stress, high corrosion-resistance, low value of elastic module, low shear stress, large variation coefficient of strength, and creep property of FRP. And, the design of grouted helix anchor can adopt the partial material safety factors method.(3)The ultimate pullout capacity of the grouted helix anchor can be evaluated as follows, R= π · η· D · L · q k. The non-grouted helix anchors have different ultimate pullout capacities, with different anchor installed depths. 1) In shallow or transition depths, R=Gravity of anchorage failure zone+ Total friction of rupture surface. 2)In deep depths, R= π· B_c· (D~2-d2) · C_u/4.(4)The properties of soil in the anchor pullout tests are as follows,the density is 1.84g/cm2, the water content is 26.3%, the liquid limit is 51.0%, the plastic limit is 20.6%, the cohesive force is 43.7 kPa, the internal friction angle is 6°.(5)The results from the anchor preliminary improve tests with different constructive factors can be concluded as follows:1) The key problem facing the application of FRP tendons in post-tensioning is how to anchor them. The performances of four anchorage systems are bad in the in-site test.2) The failure in soil is observed in six deep anchors, and the pullout capacity is 8.33kN meanly. This value is close to the theoretic one (10.37 kN).3) And, the installation ability of anchor is limited, the grouted workmanship is bad, the joints between drill bars should be changed, and the performance of instrument for anchor pullout tests should be improved.(6) According to the linear dependent relationship between the installation torque and the pullout forces, the acceptable test method of helical anchor is presented, which can prove the work anchor quickly, precisivly, economically, and reliably. And, owing to the sensing properties of CFRP, a new-type instrument for long-term monitoring FRP anchor is presented.Overall, the new-type FRP helical anchor has a great prospect, when the corrosion resistance, shear strength, and long-term behavior of FRP are improved.
|