The Performance Comparative Study Of Different Types Of Prestressed Anchor In A Cut Slope Of The Guangda Railway

With the rapid development of prestressed anchor rope technique, it has been more and more widely used in engineering. Currently, the main tension concentrated type of anchor rope, pressure concentrated type of anchor rope and pressure dispersion type of anchor rope, were the most widely used in the actual construction. However, there is short of adequate theoretical and data support to select proper type of anchor rope, moreover, most of the designers select it according to their experience or favor. Therefore, the comparative study of these three kinds of prestressed anchor rope has a high practical value and theoretical significance.In this paper, the field experiment as the main study method was deeply researched and validated by comparing with the results of model test and numerical simulation, which is based on a cut slope of railway line from Guangtong to Dali in Yaoanshan area. The loss of prestress after tension of these three kinds of prestressed ropes in the same engineering geological environment and the distribution of prestress in the grouting materials were emphatically discussed. The advantages and disadvantages of working performance of the three kinds of anchor ropes has been clear.Firstly, We formulated a long-term monitoring field test program including arrangement of measuring points, test content and test log in this paper. Then, prestress was exerted to these three kinds of ropes on a slope by graded cycle tension method. The results show that the axial distribution of the grouting materials of these three kinds of ropes according to the long-term monitoring of the strain and prestress loss of grouting materials and analyzed the regularity of prestress loss of different types of anchor ropes. On this basis, we analyzed that the relationship between the prestress loss and the stress distribution in the inner part of the grouting materials, and other factors that lead to the loss of prestress were analyzed. The advantages and disadvantages of the working performance of these three kinds of anchor ropes were clear, and we think that was mainly caused by the difference between the stress distribution of the grouting materials.Simultaneously, in order to further study the performance of the three types of prestressed anchor cable in the same conditions, archetype slope and anchor ropes were scaled down according to the similarity theory, and tested these three kinds of anchor ropes by model test indoors in this paper. The results show that the loss of prestress of these three kinds of anchor ropes was almost consistent with the field test, and validated the result effectively.Finally, the three-dimensional finite element analysis of three kinds of anchor ropes was carried out by finite element software flac3d. It was concluded that the stress distribution laws of the three kinds of anchor grouting materials was also basically consistent with the field test and validated the result effectively. The analysis further explained that the difference of the stress distribution between the three kinds of anchor ropes was an important reason for the performance of the anchor ropes.Analysis of field test, model test and numerical simulation results showed that:(1) The pressure dispersed anchor rope had minimum prestress loss rate, followed by pressure concentrated type, and prestress loss rate of concentrated tension anchor was the largest of three types of prestressed anchor ropes. (2) After tension, three stages appeared in all three kinds of anchor:a sharp decline in the prestress, steadily decline and stability of prestress. In all three kinds of anchor ropes, the pressure dispersed type had the shortest stabilizing time of prestress, and the tension concentrated type required longest time. (3) For all three kinds of anchor ropes, the stress concentration was found in the grouting materials under the action of load. On the one hand, the axial stress value in the area of stress concentration between tension concentrated type and pressure concentrated type had large difference (tension concentrated type was much larger than that of pressure concentrated type), which made the tension concentrated anchor segment grouting materials damaged more easily, causing greater loss of prestress. On the other hand, pressure dispersed type anchor rope made the load sharing in the block bearing plates, which made the bearing plates in the vicinity of the grouting materials produce less damage, resulting in the decrease of gradual variables of grouting. So the pressure dispersed anchor long-term prestress loss was less than the pressure concentrated type. (4) The load in tension concentrated anchor rope of grouting transmitted larger ranges than the other two types of anchor ropes, resulting in the increase of disturbance scope on the surrounding rock. So the creeping quantity of surrounding rock increased under long-term stress and this was the important reason why long-term prestress loss of tension concentrated type was greater than the other two types. (5) The effective transmission distance of single anchorage unit of pressure dispersed type anchor rope bearing the load in the grouting materials is 2.5 to 3m. So base on these, this paper suggest that the design of the distance of bearing plate with pressure dispersed type anchor should be not less than 3m in general.