Experimental Study On Shear Strength Of Root-soil Composites

In 2018,the Party Central Committee decided to build a free trade pilot zone on the entire island of Hainan,among them,the National Ecological Civilization Experimental Zone is also one of the main targets of this construction,therefore,the slope protection form of vegetation slope protection has gradually become a new trend in Hainan Province.Starting from the slope protection of vegetation,this paper selects the most widely distributed soil in Hainan Province--red clay as the base soil,and selects the common plant species in Hainan Province--the root of the tree as a composite material.The root-soil composite combining the two was used as the research object,and the soil mechanics tests such as direct shearing,oblique shearing and triaxial transformation were carried out,exploring the factors related to the shear strength of the soil-soil composite soil in the vegetation slope protection,the purpose is to expand the research on the influence of tree roots on the shear strength of slopes.Therefore,it is more reasonable and effective to control the slope through the form of vegetation slope protection,and to facilitate more accurate evaluation of the stability of vegetation slope protection.In order to break through the ordinary experimental instruments,it is too small to simulate the stress of the root-soil complex of medium and large plants,also in order to make the experimental results more in line with the actual situation,my team deliberately developed and produced large indoor straight shears and large indoor oblique shears,which are mainly used to measure the strength change of the composite when the relative position of the roots changes in the soil.During the test,various physical experiments were carried out on the soil and roots,the soil mechanical parameters such as specific gravity,internal friction angle,water content,porosity,liquid limit and plastic limit of the soil were measured,physical parameters such as diameter,density,shear modulus and elastic modulus of the root are measured,too.After that,the large-scale direct shear and oblique shears developed by the team were used as the main experimental equipment,change the water content of the soil,the relative inclination angle of the roots,the relative position of the roots and the soil,the root-soil complexes of these different cases were subjected to direct shear,oblique shear and triaxial experiments,The experiment measured shear strength and the shape of the cracks,the deformation of the roots,the relative displacement of the roots and the stress changes of the roots during the shearing process under different conditions.The test data show that the shear strength of the root-soil composite decreases with the increase of water content after the water content is greater than the plastic limit of the soil,the peak value and average shear strength of the shear strength measured when the parallel double roots are at different angles to the shear plane are decreasing,among them,the shear strength decays faster,and the closer the water content is to the liquid limit,the closer the shear strength peak to the average shear strength;the vertical arrangement of the root system does not allow the shear strength of the root-soil composite to be maximized,under the experimental conditions of this paper,the shear strength of the root-soil composite peaks when the direction of the single-slope landslide is at a certain angle;the more vertical the projection of the root in the vertical plane,the higher the shear strength of the root-soil composite.According to the survey results of local slope protection in Hainan,the local slope generally has shallow instability,which can determine the block that may fall.When the root system is above the slip surface,considering the force transmitted by the external wind load through the branches to the horizontal direction in the root system,the stability of the slope may be adversely affected at this time;but when the root system is below the slip surface,it will have a good slope effect.Due to the strong roots of the trees,the roots are usually below the slip surface under normal conditions.At this point,the root system will hinder the sliding of the slope.If shallow instability occurs,either the roots are removed from the deep soil or the roots are pulled off.That is,the slope effect of the root system passing through the slope of the slip surface is significantly greater than that of the plant roots not passing through and the plain soil.It also shows that the anti-slip effect of the root system in the shallow landslide is very significant.