Deformation And Failure Mechanism Of Slope-ductile Anchorage Structure System Under Rainfall

Landslide is one of the most common natural disasters in mountainous areas.Its strong destructive power poses a great threat to life and property.Heavy rainfall is often one of the main factors that cause landslide.Anchor bolt/cable is one of the most economical and effective methods to solve geotechnical engineering problems that cannot be replaced.However,the commonly used anchor bolt and cable have some shortcomings such as limited anti-large deformation ability and insufficient anti-bending ability.Therefore,it is of great significance to develop the ductile anchor structure with anti-large shear deformation.This thesis proposes a ductile anchorage structure which can adapt to large deformation and damage of slope.The structure includes anchor head,sleeve in free section,shaped bar body,bolt and steel ball,etc.The anchorage section,D-shaped cable connecting the anchorage section and free section,and the working principle is that the support resistance of slope deformation is provided by contact,friction,cutting and deformation between sleeve,steel ball and shaped bar body.Taking the slope of Nongfengchang Bridge in Nilek County as the engineering background,model tests of slope-anchorage structure were carried out under different conditions,and parameters such as anchor shaft force,inner slope stress,pore water pressure,loading pressure and displacement were monitored to reveal the co-evolution mechanism of rainfall type slope-new anchorage structure.The main achievements were as follows.(1)The undisturbed soil samples of the silty soil layer of the slope in the field were taken to study the changes of the rock and soil mass in the slope under the action of rainfall and lateral load.With rainfall duration and rainfall intensity as variables,8groups of triaxial osmotic cyclic loading tests were carried out,and the test results showed that: The longer the rainfall duration is,the greater the intensity is,and the stronger the weakening effect on the sample strength is.The permeability coefficient at each stage of each sample is calculated.It shows that in the long-term periodic rainfall-axial loading process,the permeability coefficient decreases continuously when the rainfall intensity is small.The particle gradation analysis of the specimens recovered after the test was carried out with laser particle size analyzer,which showed that there was a certain degree of fine particle migration under the current intensity and rainfall duration in the test,and more tests and further studies were needed.(2)The ductile anchorage structure is mainly composed of anchor head,sleeve,shaped rod body,steel ball and anchoring section.Using the methods of theoretical mechanics and contact mechanics,the tensile working stage is divided into elastic working stage in front of the inclined plane of the clamp platform,plastic stage on the inclined plane of the platform,plastic stage of the flat slide rod body,and energy release stage on the inclined plane of the platform.Several static tensile tests were carried out by changing the number and diameter of steel balls.The test results show that the displacement-load curve of the specimen approximately changes periodically.The more the number of steel balls,the larger the diameter,the greater the maximum constant resistance provided by the steel balls,which verifies the correctness of the theory.(3)Model tests of unreinforced and reinforced slopes are carried out.After the test,the slip range of the slope model test is estimated to be 800-900 mm away from the loading place,and the slip range of the slop-anchorage structure model test is estimated to be 600 mm away from the loading place.The support of the new anchorage structure reduces the average displacement of the supporting area by25%-33%,and the tensile displacement of about 50 mm is also generated in the free section,which is not obvious at the anchorage head subsidence,reflecting the good adaptive deformation performance in the large deformation environment of the slope.According to the displacement change and the evolution process of bolt axial force,the co-evolution process of slope and anchorage structure can be divided into three stages: elasto-elastic support stage,local slip-plastic deformation stage,and large area slip-elastic-plastic cyclic deformation stage.(4)The model test of slope-new anchorage structure under rainfall condition was carried out,and the monitoring results showed that the loading force increased by20% after reinforcement,and the lateral stress of monitoring points in the slope generally increased.According to the lateral stress curve,it can be concluded that the distance between the slope and the loading place is more stable than 800 mm,the seepage flow in the slope is rising steadily or fluctuating.The first row of bolt assumes most of the supporting tasks while the third row hardly achieves the supporting effect,and the loading pressure is generally fluctuating and rising.The co-evolution process of slope and anchorage structure under rainfall conditions can be roughly divided into elastic-elastic support stage,deformation-elastic support stage and accelerated deformation-elastic-plastic cycle deformation stage.The supporting effect of the bolt model decreases under the condition of rainfall,which is reflected in that the slope surface displacement increases by 9-25% compared with that without rainfall,and it is easier to produce subsidence.There are 61 figures,12 tables and 92 references in this thesis.