Experimental Study On Anchorage Characteristics Of Prestressed Anchor Cable Under Unloading Conditions

With the advantages of strong subjective mobility,small disturbance,light structure,material saving and construction safety,the problems of insufficient theoretical research and backward design methods of prestressing anchor cables have been exposed.Especially in advance pre-stressed anchorage and side-anchored excavation projects,the pre-stressed anchor cables are still designed according to the limit equilibrium principle and empirical method,without considering the influence of excavation unloading on the anchorage characteristics of tensioned anchor cables.In this paper,the effects of unloading on the anchorage characteristics of two kinds of prestressing anchor cables?tension-concentrated and pressure-concentrated?are studied by means of physical model test of simulated materials and the conclusions of numerical simulation calculation,which provides a reference for the design of parameters of prestressing anchor cables in the future.The main research contents and results are as follows:?1?Using physical simulation test method,the construction process of slope unloading after tension of anchor cable is simulated,the influence of unloading on anchorage characteristics of pre-stressed anchor cable is studied,and the distribution curve of shear stress on the surface of anchor cable body,the distribution of shear stress on the surface of grouting body and the change of development law of pre-stress after locking under unloading are given.The test results show that:Firstly,the effect of unloading on the surface shear stress of the cable body is mainly reflected in the increase of the shear stress near the starting point of the internal anchor section,and has no obvious influence on the distribution and scope of the surface shear stress of the cable body.Secondly,unloading has no obvious influence on the distribution of shear stress of grouting body of two kinds of anchor cables.The main influence is that the peak value of distribution curve increases and the curve moves right.The average increase of peak value of shear stress of tension-dispersed anchor cables is 3.44%,which is much less than that of Pressure-dispersed anchor cables,and the average right displacement of shear stress distribution curve of tension-dispersed anchor cables is larger than that of Pressure-dispersed anchor cables.Thirdly,he effect of unloading on the change of prestressing force of anchor cable is as follows:within 15 minutes after unloading,the prestressing force of anchor cable increases sharply,reaches its peak within 30 minutes,and finally decreases slowly until it is stable,which has no obvious influence on the overall development trend.However,unloading has a greater effect on the prestress of pressure-concentrated anchor cables than that of tension-concentrated anchor cables.?2?Using FLAC^3D to carry out numerical simulation analysis based on physical model test.The required parameters are calculated by using the data measured in physical model test.The obtained distribution law of shear stress on the surface of grouting body and physical model test can basically verify each other.On this basis,the influence of unloading on the anchorage characteristics of pre-stressed anchor cables is further studied in terms of the distribution characteristics of the axial stress field of surrounding rock.The simulation results show that the effect of unloading on the stress distribution along the axial direction of the anchor cable is mainly reflected in the compression and expansion of the tension zone in the pressure zone,accompanied by the increase of the tension stress value,but the effect of the tension-concentrated anchor cable is greater than that of the pressure-concentrated anchor cable.