| In this thesis,the root system of Astragalus adsurgens,a typical native plant species for sand control and soil conservation in the arid and semi-arid regions of Inner Mongolia,was used as the research object.By combining in situ field tests and indoor simulations,we investigated the mechanical properties of the root system of Astragalus adsurgens after being damaged by tension and shear,the ultimate tensile properties of single root,the shear properties of root-soil complex and the frictional resistance of root-soil interface,and analyzed the effects of root diameter on the tensile properties of single root;the effects of vertical load,soil moisture content,root diameter and number of buried roots on the shear properties of root-soil complex;the effects of soil moisture content,root diameter and number of buried roots on the shear properties of root-soil complex.The effects of soil water content,root diameter,loading speed and soil type on the frictional characteristics of the root-soil interface;reveal the change pattern of the mechanical strength indexes of soil consolidation resistance of Sartorius root system and its influencing factors,and provide basic mechanical data for the selection of excellent soil and water conservation species in the revegetation and reconstruction of the region.The main research findings are as follows:(1)The study on the morphological and quantitative distribution characteristics of the root system of standard plants showed that the representative root diameter classes of Sattawan were 0-0.5mm,0.5-1mm and 1-1.5mm,which were mainly distributed in the small diameter range and existed in the form of fine roots.(2)Field single-root in-situ ultimate tensile tests showed that the single-root ultimate tensile strength was positively correlated as a polynomial function with increasing root diameter,ultimate tensile strength and modulus of elasticity were negatively correlated as a power function with increasing root diameter,and the single-root ultimate strain was polynomially correlated as a function of increasing and then decreasing with increasing root diameter in the range of 0-4 mm of the tested root diameter.(3)The indoor root-soil composite direct shear test study showed that the growth rate of shear strength was 60%,cohesion was 73%,and internal friction angle was 5% for the Sartorius root-soil composite compared with the plain soil at a natural moisture content of9.6% and a soil dry density of 1.53 g/cm3.It showed that the presence of root system significantly increased the soil shear strength.With the increase of soil water content,the shear strength and cohesion showed a change pattern of increasing and then decreasing,while the internal friction angle had no obvious change pattern,indicating that cohesion played an important role in improving the shear strength of the root-soil complex.The study on the influencing factors of root-soil composite shows that the number of roots is 4and the effectiveness of shear strength is best in the range of root diameter 1～1.5mm under the vertical load of 12.5KPa and soil moisture content of 16.5%.(4)The indoor root-soil composite direct shear friction test study showed that the internal friction angle was 35.6°,friction coefficient was 0.7159,and friction coefficient ratio was 1.3414 at natural water content of 9.6% and dry density of 1.53g/cm3 in Sartorius root-soil composite.The values of internal friction angle and friction coefficient both showed a gradual decrease.The indoor single-root pulling friction test showed that the single-root pulling resistance tensile strength showed a linear positive correlation with the increase of root diameter and the single-root pulling resistance shear strength showed a power function negative correlation with the increase of root diameter in the test diameter range of 0-4 mm.The single-root pullout shear strength showed a pattern of increasing and then decreasing with the increase of soil moisture content,and the peak value was 95.5Kpa when the soil moisture content was 8.50%.The single-root pullout shear strength showed a pattern of decreasing and then increasing with the increase of loading speed.The single-root pullout shear strength in loess and sandy soil both show the variation rule of increasing and then decreasing with the increase of soil moisture content.(5)The self-repair of damaged healing wounds in the field with single roots subjected to 70% ultimate tensile in situ showed that the survival rate of the healing wounds after self-repair was significantly different from that of the parallel control in the range of 0-4mm root diameter.Significant differences in activity values were observed between the healing wound self-repair and the parallel control.Self-repair tests of in situ shear damage to root-soil complexes in the wild showed that the more severe the damage,the lower the survival rate of the root system,but it still had the ability to resist shear.With the increase of healing time,the shear strength and residual shear strength of the self-repaired root-soil complex gradually recovered. |
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