Study On The Mechanical Properties And Slope Protection Effect Of Root-Soil Composite Under Freeze-Thaw Action

As a green flexible protection technology,plant slope protection is widely used in slope reinforcement due to its unique mechanical,hydrological and ecological effects.However,in the protection of slopes in cold areas,the influence mechanism and reinforcement effect of plant roots on soil mechanical properties under freeze-thaw conditions are not yet clear.Therefore,based on the soil slope of a mining area in Xilingol league,this article conducted mechanical experimental research on the Alfalfa root-soil composite and plain soil under different freeze-thaw cycles,and analyzed the influence of plant roots on the stability of shallow surface soil on slope.The main contents and conclusions are as follows:(1)The triaxial compression tests were conducted on samples with 0,1,3,5,7,10 and 14 freeze-thaw cycles and a moisture content of 12%,15% and 18% under different confining pressures,and the deformation characteristics of root-soil composite and plain soil were compared.The results indicate that: under 100 k Pa confining pressure,the stress-strain characteristics of plain soil with a moisture content of 12% and 15% exhibit a softening type,while the characteristic of root-soil composite only occurrs at a moisture content of 12%,and the failure strain of soil increased after plant roots were incorporated.Based on the damage deterioration law of elastic modulus,the deterioration state of the stiffness characteristics of soil during freezethaw is revealed.(2)Based on the results of triaxial tests,the strength characteristics of root-soil composite and plain soil were compared.It was found that the strength of two types of soils exhibited a trend of overall decrease and local increase,and continuous decrease with the number of freeze-thaw cycles and moisture content,respectively.The enhancement of the failure strength of root-soil composites under the conditions of12%,15%,and 18% moisture content compared to plain soil occurred within 1 and 10freeze-thaw cycles,within 7 and 1 cycles,respectively.And the growth rates are 7%-25%,2%-28%,and 3%-22%,respectively.The cohesion,internal friction angle,and elastic modulus of the two types of soil decrease with the increase of moisture content and freeze-thaw cycles,and there was a significant decrease in the early freeze-thaw period(within 3 cycles).In addition,the deterioration of the two types of soil was characterized by the damage of the failure strength and shear strength indexes,and the damage law of the soil during freeze-thaw was obtained.(3)According to the critical state theory of soil,the frictional reinforcement effect of plant roots after incorporation of soil was revealed.The results indicate that: with the increase of the number of freeze-thaw cycles and the moisture content,the critical state stress ratio of the two types of soils decreased.The incorporation of plant roots in seven freeze-thaw cycles increased the critical state stress ratio of soil,and the growth rate was 4.51%-43.53%.And under the condition of moisture content of 18%,the growth rate is the largest,which is about 4 times of the moisture content of 12%.The internal friction angle of root-soil composite and plain soil in the critical state is greater than the peak internal friction angle.(4)Based on experimental data,a numerical model for plant root reinforcement of soil slopes was established,and calculated the displacement and stress of shallow soil on slope under different freeze-thaw cycles.The results indicate that: The maximum displacement of both vegetation slope and bare soil slope occurs at the foot of the slope.The displacement and stress show a decreasing-increasing-decreasing trend with the changes along the toe of slope,slope middle,slope shoulder,and top of slope.And the displacement increases most severely at 1 freeze-thaw cycle and after 7freeze-thaw cycles.After 0-14 freeze-thaw cycles,the incorporation of plant roots reduces the soil slip at the top of slope,slope shoulder,slope middle,and toe of the slope by more than 16%,42%,15%,and 12%,respectively,and the stress increases by more than 21%,36%,2%,and 4%,respectively.The protection effect of plant roots on the shallow surface of slopes is significant.The results of this article can provide theoretical reference for revealing the mechanical reinforcement mechanism of soil slope in cold regions and the implementation of plant slope protection measures.