Study On Anchorage Performance And Load-Transfer Mechanism Of Embedment Section Of Prestressed Rock Cable Bolt

With the implementation of the western development strategy, highway traffic is the first infrastructure problem to be solved. In the roads construction of west regions, the reinforcement of high or dangerous slopes and the treatment of environmental geological hazards have become the important parts in engineering construction, and in the geotechnical engineering field anchorage technology is considered as the most direct and effective measure to deal with such engineering problems. All kinds of ground supporting structures based on prestressed cable bolt have been widely used in these projects since they are highly efficient, economical and practical. The engineering practice has been ahead of the theoretical study, and therefore failure of the prestressed cable bolt unavoidably appears in the anchorage engineering under construction or operation. It has theoretical and practical values to research the anchorage performance and load-transfer mechanism of the embedment section, which is served as the load-undertaking and load-transferring member. In the thesis, supported by"National Science Fund for Distinguished Young Scholars"Project"Disaster Reduction for Geotechnical Engineering"(No.50625824)and Scientific Program for Western Construction of Ministry of Communications"Safety Analysis of Geotechnical Anchorage and Treatment Technology Research"(No.200431874010), the anchorage performance and load-transfer mechanism of the embedment section through field investigation, data collection, experimental study, theoretical analysis, numerical simulation are systematically studied. The major works are summarized as follows:(1) Based on field investigation, and indoor data collection and analysis, research objectives, which are an initial draft of some adjustable internal factors influencing the anchorage performance of the embedment section, are determined. The anchorage with 4Ф15.24mm and 6Ф15.24mm widely used in the geotechnical anchorage of highway slopes, the practical rock, grouting material and steel stranded wire are treated as the raw materials to carry out the scale test , each internal factor is researched. Under the condition of guaranteeing the strength class and workability of grouting material, the way, which enhance the anchorage performance of rock cable bolts by changing the mixing ratio, is proposed. Moreover, the dominant failure mode for conventional prestressed cable bolt is summarized.(2) The advantages and disadvantages of anchorage load- transfer mechanism at home and abroad are analyzed. On the basis of Mindlin solution and interfacial constitutive model, the elastic solution of stress distribution on the bond interface between the grouting material and rock and those between steel stranded wire and grouting material are derived. Moreover, the dominant failure mode of the conventional prestressed cable bolt analyzed by using the present elastic solution.(3) Great improvement to the bulb structure of the bulb cable in the structural engineering is made based on the load-transfer mechanism and the dominant failure mode of the conventional prestressed cable bolt, the load-transfer mechanism of the bulb cable is analyzed, the anchorage performance through pull-out test is studied, and the optimal study on its anchorage performance at different aspects is carried out by using the present method.(4) The influence of the rock & soil coating thickness,the cleanliness and roughness of the holes wall in the embedment section on the shear characteristic of the interface between grouting material and rock through direct shear test are researched. The results of roughness test is analyzed by using fractal theory, and the way is proposed to quantificationally express the interfacial roughness by combining the fractal dimension D and roughness coefficient JRC. Whereas the bond strength between grouting material and rock is one of the key parameters for embedment section length design of prestressed cable bolt, Comprehensive Factors Method is recommended to determine the bond strength between grouting material and rock based on the direct shear test.(5) The finite element calculation model for pull-out test of rock cable bolts is established by using ANSYS. The present model is verified by experimental measured data. The stress distribution of embedment section of conventional cable and bulb cable are calculated, respectively. The different load-transfer mechanisms is comparatively analyzed. The numerical simulation of the load displacement characteristic of conventional cable and bulb cable in different pull-out courses to verify the reliability of the results of pull-out test is carried out.In the above-mentioned study, the experimental results could be explained by the theoretical results, and the numerical simulation results is agreed with the experimental results. As a result, it is found that the experimental results in this thesis are accurate and reliable, the theoretical study is reasonable and credible, the establishment of numerical simulation is scientific and applicable. The thesis could also provide referrence for optimal design, construction and relative specifications revision of the subsequent prestressed anchorage engineering.