Study On Damage Mechanism Of Slope Anchorage Structure Under Freeze-Thaw Cycling Condition

Slopes are slopes formed under natural conditions or human activities and are the most common and basic geological environment and engineering forms in engineering construction.Slope instability will have serious consequences.In order to ensure the stability of the slope,various forms of support and reinforcement methods can be adopted,of which the most widely used is bolt(cable)support technology.The principle of the anchor(cable)technology is to work together by anchoring the anchors(cables)firmly and firmly in relatively stable formations through grouting materials to bind them together as a whole.This technology has been widely used in transportation,water conservancy and hydropower,underground engineering,and municipal construction.The distribution area of permafrost in China accounts for 22.3% of the country’s total land area,while the distribution area of seasonal frozen land accounts for about 53.5% of the total land area of the country.The special physical and mechanical properties of rock and soil in the frozen quarters are issues that we need to consider in the construction of the project.In the slope engineering in the frozen quarter,if the bolt(cable)technology is adopted,not only the conventional design and calculation,but also the influence of the freeze-thaw cycle on the anchorage structure need to be considered.Therefore,it is of great significance to study the damage mechanism of slope anchorage structure under freeze-thaw cycle conditions for the construction of slope engineering in seasonally frozen areas.In this paper,the main research results obtained by consulting literature,theoretical analysis,model test,data calculation and formula derivation are as follows:(1)Freeze-thaw cycles would reduce the anchoring force of the anchor(normal rebar and GFRP tendons)-the interface of mortar and anchorage-sandstone;The anchoring force of the ordinary screwed steel bars as the anchor is lower with the increase of the number of freeze-thaw cycles,while the anchoring force with the GFRP tendons decreases with the increase of the number of the freeze-thaw cycles;The anchoring strength of anchor-sandstone interface gradually decreases with the increase of the number of freeze-thaw cycles;(2)Under normal temperature conditions,when the specimen is loaded to about one third of the maximum anchorage force of the anchor-sandstone interface under a loading condition,the loading and unloading are stopped and the loading is repeated until the breaking force of the specimen is about one time loading of the 56%,although the anchoring force still exists but its value compared with a load force decreased significantly compared with the front end of the anchorage segment was broken;(3)Through 30 groups of center-reinforced specimens,pull-out test was carried out,and the conclusions were applied to the anchorage support project.This process should follow the principle of economical application,so that the anchor rod-mortar anchoring force achieves the best effect.Therefore,it is recommended that the diameter of the welded steel bar be slightly smaller than the diameter of the main bar,the length of the main bar is three times the diameter of the main bar,and the unilateral welding is used.;(4)The anchorage angle has little effect on the value of local compressive stress of concrete,but the influence of slope angle,rebar diameter and anchor spacing has a great influence on the compressive strain of concrete;Concrete spray may slip along the direction of anchor angle until it completely fit the slope surface and in static equilibrium,spray anchor system reached a steady state,along the anchor angle direction will not be damaged;(5)The maximum thickness of sprayed concrete sprayed layer is related to the anchoring angle,the spacing of anchor rod,the diameter of anchor rod and the type of rebar.The influence of anchoring angle is very weak.The use of steel with higher yield strength can increase the spray anchor.The maximum thickness of concrete spray layer in the structure,and the two factors of bolt spacing and bolt diameter have a great influence on the maximum thickness of concrete sprayed shotcrete.