Friction Characteristics Of Root-soil Interface Of 4 Types Of Soil

Silty sand, low liquid silt, low liquid clay and feldspathic sandstone weathered soil are objects of the study. Through direct shearing test, friction characteristics of root-soil interface between Caragana korshinskii root and 4 types of soil is studied, the results are as follows:There is linear positive correlation between Root-soil interface shear stress and vertical load. Friction Characteristics of root-soil interface between Caragana root and 4 types of soil both obey the Mohr-coulomb theory, and the cohesive force and the friction coefficient of root-soil interface can be deducted from this theory.Soil types have marked effect on the cohesive force, the friction coefficient and resistance strength of root-soil interface. The order of the friction coefficient is as follows: low liquid clay (0.615±0.041)>low liquid silt (0.572±0.028)> silty sand (0.511± 0.034)> feldspathic sandstone weathered soil(0.444±0.031), the order of the cohesive force is as follows:low liquid clay (6.60±0.21 kPa)> low liquid silt (6.34±0.29 kPa)> feldspathic sandstone weathered soil (4.91±0.13 kPa)> silty sand(3.18±3.15 kPa).The resistance strength of the low limit clay is the largest in 4 types of soil, and the second is the low liquid silt. Under the vertical load of 25kPa, the lowest of root-soil interface friction strength is silty sand, and the lowest turn to feldspathic sandstone weathered soil under the vertical load of 50kPa.With the increase of dry density, the cohesive force, the friction coefficient and resistance strength of root-soil interface of 4 types soil both have a tendency to increase; The friction coefficient of root-soil interface of 4 types soil both have a tendency to decrease and the cohesive force have a trend of increasing first and then decreasing with the increase of soil moisture content; Root-soil interface resistance strength of low liquid clay have the tendency of increasing first and then decreasing, the sequence of silty sand, low liquid silt and feldspathic sandstone weathered soil are consistent with low liquid clay under the vertical load of 12.5kPa and 25kPa, but the resistance strength of the root-soil interface of these three types of soil is gradually decreasing under the vertical load of 50kPa and 100kPa.The resistance strength of root-soil interface between Caragana korshinskii root and 4 types of soil increased significantly with the increase of the vertical load.It fully illustrat that the deeper the root is, the greater the resistance strength of the root-soil interface is. With the increase of soil depth, the vertical load of the root-soil interface increases gradually, the contribution of the root-soil interface friction force gradually increases, and the contribution of the cohesive force decreases gradually.The friction coefficient, cohesion and resistance strength of root-soil interface of 4 types soil both showed a decreasing trend with the increase of shear rate. When the shear rate is 0.02mm/min, the friction coefficient, cohesive strength and resistance strength of the root-soil interface is the largest, and the friction coefficient, cohesion and resistance strength of the root-soil interface is the smallest when the shear rate is 2.4mm/min.