Field Test And Numerical Simulation Of Reinforcement Effect On Pressure (Diffusion) Anchor Cable

Prestressing anchor cable technology is one of the most rapidly developed and widely used techniques in slope protection in recent years. Pressure (diffusion) anchor cable has gradually taken the place of traditional tensile anchor cable due to its novel structure, reasonable bearing load, easy construction, high reliability and good endurance. It has both great theoretic and practical significance to study on reinforcement effect of this new type of anchor cable system. In this paper, based on the project Yi-Shui expressway high-steep slope crag reinforcement, distribution of anchor force, strain and displacement of pressure (diffusion) anchor cable in Jurassic sandstone-muskeg stratum is studied and the range of characteristic value of anchor which is middle or little tonnage including valid anchor length, carrying capacity, space between groups of anchors, the loss of prestressing force and etc is made clear and reinforcement mechanism of soft crag reinforced by pressure (diffusion) anchor cable is revealed with the method of field test and numerical simulation. The schemes of loading and monitoring and the corresponding measures for quality and safety control are made out based on the analysis of field test condition in the first part of this paper. After that, multi-schemes comparison tests for pressure and tensile anchor cables in platform and slope and the prototype test for pressure diffusion anchor cable are carried out by means of repetition loading and unloading. Based on the calculation and analysis of the field test datum, the results are presented including strain distribution along anchor section of pressure anchor cable, displacement and anchor force variation in every type of test anchor cable, surface displacement distribution of anchor pier in platform, variation of anchor force along with time, carrying capacity and failure mode for pressure and tensile anchor cables and so on which provide practical evidence for study on reinforcement mechanism of pressure (diffusion) anchor cable and confirming the anchor characteristic parameters. Three-dimension finite element analysis to pressure anchor cables is carried out by using ANSYS and the results such as distribution of surface displacement and stress as well as strain and stress along anchor section are put forward and the calculation results are compared with test results. In addition, construction technology and quality test measure for pressure diffusion anchor cable are summarized and recommended construction technique are put forward. The results of field test and numerical simulation demonstrate that ①the test maximum elastic loads on 2m to 4m pressure anchor cables can reach 734kN to 1151kN (55% to 60% Afptk), which proves that pressure anchor cable can carry higher load than tensile anchor cable; ②strain distribution along the anchor section is divided by load board and pressure strain is on upper side while tensile strain is on the bottom. The attenuation of pressure strain along anchor section is rapid and test valid anchor length is less than 240cm and it is suitable for pressure diffusion anchor cable to control the distance between neighboring load boards within 240cm; ③The failure process of pressure anchor cable is gradual which makes it safer and more reliable than tensile anchor cable; ④it is suitable for the space between groups of anchor cables to be set in 400cm because the test deformation range of single anchor cable is 150cm to 200cm; ⑤the loss of prestressing force is only 2.5% of the anchor force in the time of hauling and locking.