Research On Anchorage Mechanism Of Polymer Microbolt To Pisha-Sandstone Block

In Inner Mongolia,Shaanxi,Shanxi and other provinces of China,there is a special silt rock called Pisha-sandstone.Because of its low degree of lithogenic formation,high content of montmorillonite and poor cementation among particles,the rock structure is easily destroyed due to water expansion,mud disintegration.Under the influence of special lithology,there is a compound erosion pattern of wind power,water power and gravity in the Pisha-sandstone sandstone area,resulting in serious water and soil loss.Gravity erosion in gully area is the main erosion type in Pishasandstone sandstone area,accounting for more than 30%of the total erosion.Gravity erosion is mainly manifested in the forms of erosion,collapse and slump,among which collapse is the main form of mass gravity erosion phenomenon is very prominent,resulting in a large amount of erosion and destruction,which is the main source of soil erosion and sediment yield in the middle reaches of the Yellow River.It is of great significance to control water and soil loss and reduce sediment inflow into the Yellow River to effectively control the bulk gravity erosion in the Pisha-sandstone sandstone block.The main principle leading to block gravity erosion of Pisha-sandstone sandstone is that there are a large number of vertical cracks in the white sandstone layer with relatively high strength,which makes the sandstone blocks on the slope separated from the parent body,resulting in the tendency of falling and overturning.When reaching a certain limit state,the lump-like gravity erosion occurs suddenly.Anchorage is one of the important ways to control mass gravity erosion such as collapse.However,the traditional anchoring methods mostly use cement mortar as the anchoring material.Because of the water content of cement mortar,the structure of Pisha-sandstone sandstone will be damaged,and the anchoring effect will be seriously weakened or even completely lost.In order to solve this problem,this paper introduces the concept of anarchic grouting,introduces the non-aqueous reactive polymer grouting material into the treatment of gravity erosion of Pisha-sandstone blocks,combines the polymer grouting technology with rock and soil anchoring technology,and uses the polymer micro-bolt to reinforce the separated sandstone blocks with overturning tendency on the slope surface.It is of great significance to master the anchoring mechanism of polymer micro-bolt to Pisha-sandstone sandstone for the design and construction of anchoring.In this paper,the anchoring mechanism of polymer micro-bolt on Pisha-sandstone sandstone block was studied by means of field pull-out test,numerical simulation analysis and theoretical analysis.The main work is as follows:(1)Through the polymer micro bolt anchorage system for the site drawing test,for different types of rod body(galvanized pipe,light round bar,bamboo),different anchor solid density(0.6 g/cm3 and 1.2 g/cm3),different anchor solid diameter(12 mm,16 mm,25 mm),different length(0.3 m to 0.7 m)anchoring body combination of anchorage system under the condition of failure modes and ultimate pull-out force.For galvanized pipe,when the length of anchor solid is short,the bonding failure occurs between the anchor solid and Pisha-sandstone sandstone,and when the length of anchor is long,the galvanized pipe is broken.For the smooth steel bar,the failure mode is the slip failure of the interface between the smooth steel bar and the polymer.For bamboo bars,there are two failure modes,one is slippage of the interface between the bamboo bars and the polymer,the other is that the bamboo bars are broken.(2)According to the experimental results,the distribution of axial force and shear stress along the length direction of galvanized pipe and circular steel rod with different materials under the action of drawing force and the evolution process of stress distribution with the increase of load are analyzed,and the anchoring mechanism of polymer mini-bolt to exposed Pisha-sandstone sandstone block is revealed.Under different working conditions,the distribution of axial force and shear stress of polymer micro-bolt is basically the same.The axial force of the bolt is not uniformly distributed in the whole anchorage section,and is the largest at the loading end,and gradually decreases along the axial direction of the bolt from the loading end,but the axial force at the bottom of the anchorage section is not 0.With the continuous increase of pulling force,the axial force of each part of the bolt body also increases.And the closer to the bottom of the bar,the smaller the increase of axial force at each load increment.The shear stress is 0 at the loading end,then increases and then decreases along the anchorage depth,and its peak value appears near the load end.The greater the drawing force,the greater the peak shear stress.(3)The distribution law of axial force and shear stress in galvanized pipe with different anchorage length along rod body is simulated by using finite element analysis software.Based on the Mindlin position displacement solution,the formulas for calculating the axial force and shear stress of the micro-bolt were obtained,and the distribution law of the axial force and shear stress along the rod body of the polymer micro-bolt was proved.