Experimental Investigation Of Damage And Deterioration Of The System Of Expansive Soil And Umbrella-Shaped Anchor Under Dry-Wet Cycles

Expansive soils often cause geological disasters such as slope instability due to their properties of swelling and shrinkage,fissure and overconsolidation.The disasters are even more frequent in the areas with frequent rainfall which threatens people’s lives and property due to the intense dry-wet cycles.At present,anchoring technology has been widely used in expansive soil slope treatment because of its low cost.However,the resistance of anchoring system to the deterioration of dry-wet cycles still needs further study.In this paper,expansive soil slope engineering is used as the geological background,and the umbrella-shaped anchor is used for model test.Model test by using umbrella-shaped anchor and theoretical analysis methods are used,which is focus on the deterioration caused by dry-wet cycles,to research the mechanism of anchorage force loss under dry-wet cycles and the comparison of expansive soil slope deterioration under the conditions of reinforced and unreinforced by anchor.The main conclusions are as follows:(1)In the dry-wet cycles,the anchorage force of umbrella-shaped anchor of the system of expansive soil and umbrella-shaped anchor increases first and then has a tendency of decrease both in the wetting stage and drying stage.The changes of anchorage force can be divided into four stages: water absorption and swelling stage,water absorption and softening stage,dehydration and hardening stage,dehydration and contraction stage.In the case of the same wetting process,except for the initial adjustment stage of anchorage force,the peak value of anchorage force is related to the drying duration of the previous dry-wet cycle in the subsequent dry-wet cycles,and the longer the drying duration,the lower the peak value.The valley value of anchorage force is related to the drying duration of this dry-wet cycle,and the longer the drying duration,the lower the valley value of anchorage force.(2)During the dry-wet cycles,the temperature,soil pressure,pore water pressure and displacement of the expansive soil slope reinforced and unreinforced by umbrellashaped anchors change in the same way.The variation of soil temperature has a lag,and the overall trend is rising.The soil pressure,pore water pressure and vertical displacement of slope surface increase in the wetting process,but decrease in the drying process.Because the rainwater accumulates at the foot of the slope as it rains,and the water in other parts of the slope infiltrates to the foot of the slope under gravity,the soil pressure,pore water pressure and vertical displacement show an upward trend at the foot of the slope and a downward trend at the top of the slope.(3)During the first dry-wet cycle,the main fissures of the expansive soil slope were almost formed.In the subsequent dry-wet cycles,the formed fissures were inherited and developed.The density of fracture network is related to the free swelling rate of expansive soil.The higher the free swelling rate,the denser the fracture network,the lower the fracture depth and more fractured in the soil.In the first two dry-wet cycles,the deterioration of expansive soil slope is the most intense,and then the deterioration effect is weakened due to the release of swelling-shrinkage stress.With the continuous dry-wet cycles,the fissures paralleled to the slope surface begin to appear at the bottom of the soil blocks that cut by the main fissures of the slope,and continue to extend to the center,weakening the connection between the soil blocks and the underlying soil.Small fissures begin to appear inside the soil blocks,which further cut and break the soil blocks,further degrading the slope.(4)The umbrella-shaped anchor has a positive effect on soil resistance to the deterioration of dry-wet cycles under the bearing plate.Anchorage effect can inhibit the swelling and shrinkage of the soil perpendicular to the bearing plate,but it has no effect on the surrounding surface soil.The variation of the fissures in the surrounding soil is similar to that of the slope without anchoring.In this regard,the following treatment measures for expansive soil slopes are put forward: Increase the number of umbrellashaped anchors appropriately to control the fissures scale;Use geomembrane to cover the slope surface to reduce the potential of swelling and shrinkage of expansive soil and the deterioration effect of the dry-wet cycles on the slope.There are 78 figures,10 tables and 119 references in this paper.