Effect Of Dicranopteris Dichotoma Roots On Soil Shear Strength Of Collapsing Wall

The collapse of collapsing wall is a key process in the development of collapsing gully,which is closely related to the shear strength of collapsing wall soil,and the plant roots can effectively improve the soil shear strength.In order to explore the influence of the plant roots on the shear strength of collapsing wall soil,by taking the southern common plants Dicranopteris dichotoma as the research object,and by setting up the different water content percent(15%?30%)and root weight density(0?1.25 g/100cm~3)and by using the shear test,the shear strength response characteristics of the different collapsing wall soil layer on the water content and root weight density are analyzed,the action mechanism of the water content and roots on the collapsing wall soil body shear strength is explored.The results are as follows:(1)The roots of the Dicranopteris dichotoma are mainly distributed in the soil layer depth of 0?5cm.The root length density decreases linearly with the soil layer depth increasing,while all the root surface area density,root volume density and root biomass density decrease logarithmically with the soil layer depth increasing;The roots with the diameter level?1mm accounts for the main part.(2)The shear strength of the root-soil composite in the red soil layer increases at first and then decreases generally with the increase of the water content,while the shear strength of the root-soil composite in the sandy layer and detritus layer decreases gradually with the increase of the water content;all the cohesion of the root-soil composite in each soil layer increase at first and then decrease in the trend with the increase of the water content,and the optimal water content is obtained by fitting,the red soil layer(22%?23%)>the sandy soil layer(19%?20%)>the detritus layer(18%?19%)respectively;all the internal friction angle of the root-soil composite in each soil layer decrease significantly with the increase of the water content,and the relationship between them is the negative correlation generally and logarithmically,the effect of the water content on the reduction of the internal friction angle of root soil complex in the red soil layer is significantly greater than that in the other two soil layers.(3)With the increase of the root weight density,the shear strength increasing of the red soil layer is higher than that of the sandy soil and detritus layer;the cohesion of root-soil composite is greater than that of the plain soil,but the difference among the internal friction angle is not obvious;the cohesion of each soil layer increase at first and then decrease generally with the increase of the root weight density,the optimal root weight density corresponding to the red soil,sandy soil and debris layers is obtained by the fitting,which is 2.06 g/100cm3,0.68 g/100cm3 and0.72 g/100cm3 respectively,the containing capacity of the red soil layer to the roots is higher than that of the other two soil layers;the improvement of the roots to the soil cohesion in the red soil layer is generally higher than that of the sandy soil and debris layer,but the effect of action decreases gradually with the increase of the water content,and the cohesive force of the sandy soil and debris layer has a small change with the root density,and has no obvious relationship with the water content.(4)The soil cohesion of each soil layer is affected by both the water content and the root weight density,while the internal friction angle is mainly affected by the water content.The relationship equation between shear strength,water content and root weight density of each soil layers is obtained through the equation fitting,all the model validity coefficient(NSE)are more than 0.82,the actual measured value of the equation is close to the simulated value,and the simulation effect is better.In summary,the"reinforced"effect of the roots can increase the shear strength of the collapsing wall soil,but its strengthening effect is reduced under the condition of high water content.Therefore,the stability of the collapsing wall soil shall be increased by reducing the water injection.In addition,the shear strength of the red soil layer on the upper parts of collapsing wall is higher than that of the sandy soil and detritus layer,and its structure of top stable and bottom loose can easily lead to the collapse of the collapsed wall,so an attention shall be paid to the protection of the loose soil layer at the bottom of the collapsing wall.