Study On The Effect Of Plant Root Distribution And Tensile Properties On Soil Shear Strength

Compared with traditional engineering,vegetation is not only green and environmental protection,but also low investment and easy maintenance in slope reinforcement and soil erosion control.Therefore,vegetation measures are widely used in the prevention and control of slope geological disasters.In order to further reveal the mechanical action of plant root system soil consolidation,two common trees,Cryptomeria fortunei and Cunninghamia lanceolata,were selected as the research objects.In this study,the spatial distribution and tensile properties of roots and their contribution to the shear strength of soil were obtained through the excavation and measurement of roots in the field,indoor tensile test of single root and triaxial test of root soil complex.Considering the friction between the root soil interface,the mechanical model of the root system on the shear strength of the soil under the flexible state is established.Finally,the mechanical model of root soil interaction is verified by laboratory test,and the mechanical model is applied to calculate the contribution value of plant roots to the shear strength of soil,which provides a theoretical basis for the quantitative evaluation of shallow reinforcement of vegetation slope protection.The main results and conclusions of this study are as follows:1)The spatial distribution of roots of Cryptomeria fortunei and Cunninghamia lanceolata has three significant characteristics: The roots of both plants belong to shallow roots,and the roots are mainly distributed in the range of 0-30 cm depth of the soil layer,and the content of roots in the soil layer below 30 cm is less.The roots of both plants are mainly fine roots,more than 80% of the roots of Cunninghamia lanceolata are less than 1cm in diameter,and more than 87% of the roots of Cryptomeria fortunei are less than 0.8cm.The root biomass and root area ratio of Cryptomeria fortunei are generally higher than that of Cunninghamia fortunei in the same soil depth and at the same horizontal distance.2)Root tensile properties: the roots of Cunninghamia lanceolata and Cryptomeria fortunei show strong tensile strength in different diameter range,and the maximum tensile strength of the roots of the two kinds of plants is positively related to the root diameter,while the tensile strength of the roots of the two kinds of plants is negatively related to the root diameter,and the decreasing slope gradually decreases with the root diameter.3)The influence of plant root characteristics on the shear strength of root soil composite:the strength of root soil composite and plain soil sample increases with the increase of confining pressure,and the relationship curve between the axial strain and the main stress difference shows certain strain hardening characteristics;the reinforcement effect of root on soil is obvious only when the axial strain is large;the cohesion of root soil composite is significantly higher than that of soil composite The cohesion of plain soil and root soil composite samples is 6.5-24.3kpa higher than that of plain soil samples,but the change of internal friction angle is not obvious,which shows that the root system can improve the shear strength of soil mainly by improving the cohesion of soil;the strength of soil under each root distribution pattern increases with the increase of confining pressure,and the contribution to the growth of soil strength is horizontal-vertical > vertical > horizontal.4)Establish the mechanical model of root soil interaction: on the basis of Yan model,considering the friction between the root soil interface,establish the mechanical model of increasing the minimum value of shear strength of soil under the condition of flexible root system.Based on the Wu Waldron model,the mechanical model of the maximum increase of the root system on the shear strength of the soil under the rigid state is established to quantitatively evaluate the influence of the root system on the shear strength of the soil.5)Verify the mechanical model and expand its application: verify the established mechanical model of root soil interaction.By calculating and comparing the shear strength of the root soil composite in the indoor triaxial test and direct shear test,it is found that the theoretical model can effectively calculate the range of the increase of the shear strength of the root soil,and then expand the model to the quantitative analysis of the shear strength of the root soil of Cunninghamia lanceolata The range of improvement.Compared with the traditional engineering measures,vegetation is not only green and environmental protection,but also low investment and easy maintenance in slope reinforcement,slope and soil erosion control.Therefore,vegetation measures are widely used in the prevention and control of slope geological disasters.In order to further reveal the mechanical effect of root soil consolidation and slope protection,this study selected the common trees in southwest mountainous area,Cryptomeria fortunei and Cunninghamia lanceolata,as the research object,through field investigation and Research on root distribution,indoor test to explore the mechanical characteristics of root system and shear strength of root soil complex,establish mechanical model,verify and apply the mechanical model,and draw the following conclusions:...