Research On Prestress Loss Of Free Section Of Rock And Soil Prestressed Anchor Cable

There are more and more application of prestressed anchor cables in rock and soil anchoring,and the prestress loss of prestressed anchor cables is very important in engineering practice as an index to judge the effectiveness of prestressed anchor cables.Its loss in rock and soil is very important in engineering practice.The mechanism has also attracted more and more attention from people in the field of geotechnical engineering.Many researchers have done a lot of research on the influence of the creep of rock and soil,the relaxation of steel bars and the influence of geological conditions on the anchoring force.However,because the internal stress of the anchor cable is difficult to measure.With the advancement of technology,the non-contact force measuring device of the magnetic flux sensor allows us to study the internal stress of the anchor cable.At the same time,the development of numerical simulation software makes it possible to analyze the details of the anchor cable.This paper will select the prestress loss of the free section of the tension-concentrated prestressed anchor cable for research.The main research contents and results are as follows:(1)Derive the prestress loss formula of the free section of the rock-soil anchor cable through theoretical analysisBy reading a large number of documents and summarized the calculation methods of the prestress loss of the free section of the rock-soil anchor cable by other scholars in the existing research,and defined the pre-stress loss of the free section of the rock-soil anchor cable that its stress loss is friction loss.The influence factors of the prestress loss of the free section of the rock-soil anchor cable are analyzed,the force characteristics of the free section of the rocksoil anchor cable are summarized,and the friction loss formula of the free section of the rocksoil anchor cable is derived.(2)Design field test and analyze test resultsDesign three experimental programs,and select the most suitable experimental method by analyzing their advantages and disadvantages.In this paper,the magnetic flux sensor is used to investigate the influence of the length of the free section,the spatial position of the steel strand and the drilling method on the prestress loss of the free section in the anchor cable of the foundation pit.Through analysis,the friction loss of the free section is obtained,and the theoretical formula is proved to be applicable.The value ranges of the two coefficients for calculating the friction loss are given.A standard experimental method for detecting the friction loss of the free section is given.(3)Compare the influence of different free section length and anchoring stress on the friction loss of free sectionUsing FLAC3 D software and field test data to establish a three-dimensional numerical model,the parameters of the free section grouting body are obtained by inversion of the test parameters.Comparing different lengths of free-segment anchor cables,it can be obtained that the longer the free-segment,the more step length is needed to transmit force from the anchor opening to the inside,and the more pre-stress loss at the anchor opening under the same tensile stress.The longer the free section,the greater the friction loss.Comparing the influence of anchoring stress on the free section,it can be concluded that the greater the anchoring stress,the smaller the pre-stress loss at the anchor opening,and the smaller the proportion of the corresponding free section friction loss to the total stress,and the 70% anchoring stress condition It can meet the tensioning needs of the prestressed anchor cable,thus saving the time and cost of the project.Starting from theoretical analysis,field test,and numerical simulation,this paper studies the mechanism of the prestress loss of the free section of the tension-concentrated prestressed anchor cable,and compares the influence of different free section lengths and anchoring stress on the friction loss of the free section.It provides a useful reference for the design,construction and testing of prestressed anchor cables.