Research On Optimization And Mechanism Of Full-length Bond Anchorage System For Earthen Sites

Earthen sites are important carriers of human history and culture.There are a very large number of earthen sites with very complete types in China.However,earthen sites in open-air environments have been affected by natural forces such as wind erosion,rain erosion,freeze–thaw,and earthquakes,and human activities over a long time period,and unstable blocks,cut directly from fissures or cracks,have developed widely at these sites.This has become the primary hazard affecting the long-term preservation of earthen sites.Therefore,increasing attention has been given to ideal reinforcement methods for unstable blocks at earthen sites.Anchorage technology has been widely used in the field of stability control of earthen sites due to weak disturbance,strong compatibility and excellent deformation control.Based on the research of conventional geotechnical anchorage engineering and earthen sites anchorage engineering,it is recognized that there are many deficiencies in anchorage technology and anchorage performance testing technology of earthen sites.The performance and force transmission mechanism of the full-length bond anchorage system for earthen sites are affected by a variety of anchorage parameters such as bolt type,slurry,and site soil properties,and different combinations of these parameters,but these effects are still unclear.This has become a key issue restricting the development of anchorage technology and theory for earthen sites.Therefore,the research on the optimization and mechanism of the full-length bond and anchorage system of earthen sites is carried out.The conventional anchorage technology and anchorage performance testing technology of earthen sites are optimized,and the relevant supporting equipments are innovated.Then,the experimental study on the influence of bolt type,geometric anchorage parameters and slurry-to-soil strength ratios on the performance of the full-length bond tensile anchorage system for earthen sites is carried out.Based on in-situ anchorage,pull-out test and interfacial strain monitoring,the failure mode,ultimate load,load-displacement characteristics,and the distribution and variation of interfacial strain of different anchorage systems are obtained.The performance of different anchorage systems is compared and analyzed,and the mechanism of the full-length bond tensile anchorage system for earthen sites is explained.After that,for the frequently occurring failure mode of the bolt-slurry interface,the two-line bond-slip model is used to conduct a theoretical analysis of the full-range behavior.Finally,based on these foundations,a wooden full-length bond tension-compression composite anchor bolt for earthen sites with a better mechanical mechanism is proposed,and its anchorage performance and working mechanism are explored.The main research results are as follows:(1)The anchorage technology and anchorage performance testing technology of the earthen sites were optimized,and corresponding equipment was innovated,including“controllable high-efficiency drilling equipment”,“special dust-proof device for drilling rig”,“complete set of hole cleaning device”,“equipment for penetration and reinforcement of anchor hole walls”,“grouting system”,“slurry-soil interface strain test method”,“device for laying slurry-soil interface strain gauge”,and “pull test constant force loading system”,as well as the usage method of each equipment.Most of these research and innovated resultshave been successfully applied in this research.(2)The performance of the full-length bond tensile anchorage system composed of the same slurry and wood bolts,glass-fibre-reinforced plastic(GFRP)bolts and steel bolts was compared;Then,based on the test of the influence of the geometrical anchorage parameters of each anchorage system on the performance of the anchorage system,the rules of bolt diameter,slurry thickness and bond length on the bond strength between bolt and slurry were quantitatively analyzed,and the distribution of bond stress with bond length was qualitatively analyzed;Finally,the anchorage mechanism of the full-length bond tensile anchorage system was analyzed from the aspects of the force mechanism,deformation and strength characteristics between the bolt and the slurry determined by the bolt type.The influence mechanism of the axial and radial anchorage parameters on the bond performance between the bolt and the slurry was explained,and the optimal values of the anchorage parameters of each type of bolt were given.(3)Based on the optimization of bolt type and geometric anchorage parameters,preliminary and final selection tests of the new type of anchorage slurry with different compositions were carried out,and then five slurry-to-soil strength ratios based on compressive strength were determined.The performance test of the full-length bond tensile anchorage system composed of five slurry-to-soil strength ratios and wood bolts and GFRP bolts was carried out.The failure mode,ultimate load,load-displacement curve characteristics and dual interface strain distribution curves of different anchorage system were obtained.The optimal threshold value of the slurry-to-soil strength ratios of the anchorage system of earthen sites was given,and the influence mechanism of slurry-to-soil strength ratios on anchorage performance was discussed.(4)Based on the field test results,the applicability of the dual-line bond-slip model to the bond-slip behavior of the bolt-slurry interface of full-length bond tensile anchorage system was verified.The full-range bond-slip behavior was divided into four stages: elastic stage,elastic-softening stage,elastic-softening-loosening stage and softening-loosening stage.The expressions of interface slip,interfacial shear stress distribution and axial strain distribution for each stage were derived,and the analytical solutions of a series of parameters,such as load-displacement relationship and effective anchorage length,were obtained.According to the pull-out test results,the parameters of the model were calibrated.By comparing the experimental values with the theoretical values,the applicability of the theoretical solution was verified,and the influence of anchorage parameters on the performance of the anchorage system was analyzed.(5)On the basis of the above experimental and theoretical studies,the wooden full-length bond tension-compression composite anchorage system with more reasonable mechanical mechanism was proposed and compared with the conventional wooden full-length bond tensile anchorage system.The physical and mechanical compatibility of the anchorage materials and the reliability of the tension-compression composite bolt structure were tested.The anchorage performance and failure mechanism of the tension-compression composite anchorage system and the tensile anchorage system were compared and analyzed.Accordingto the simplified mechanical model,two calculation methods of ultimate load were given.