| For many years,we have been working to restore the damaged ecologicalenvironment through planting measures,because of the complex and diverse climatic conditions and geomorphological types in the central and western regions of Inner Mongolia,which have created sensitive and fragile ecological zones.Because of the intersection and entanglement of plant roots in the soil and their interaction with the soil,they form a similar "reinforcing" and "anchoring" effect on the soil,thus increasing the resistance of the soil to various external erosion forces,which is the main expression of the plant’s soil consolidation ability.The enhancement of soil mechanical properties by forest roots is the root consolidation,and the enhancement of soil shear resistance by roots is one of the main mechanical mechanisms of root consolidation.In this thesis,the non-growing season branches and root system of sea buckthorn(Hippophae rhamnoides Linn.),a native tree species in the semi-arid region of Inner Mongolia,were studied for tensile,bending and flexural forces of branches,and their variability was analyzed to reveal the types of external forces that make sea buckthorn non-growing season branches susceptible to damage.The ultimate tensile and flexural material mechanical properties of single roots;the shear test study of root-soil complex was conducted to analyze the effects of internal and external factors such as root diameter,number of buried roots,burial method and soil moisture,soil type and shear rate on the shear properties of sea buckthorn root-soil complex.This study was conducted to reveal the mechanical properties of the root system of buckthorn branches for wind and soil consolidation,and also to provide a biomechanical reference for the selection of excellent soil and water conservation plant species for ecological restoration and vegetation construction in semi-arid ecologically fragile areas of Inner Mongolia and its similar areas.The conclusions are as follows.The ultimate tensile force,bending force and bending force of non-growing seasonal branches of sea buckthorn showed an increasing trend with increasing diameter in the range of 0.5-2.5 mm of the tested branch diameter.The ultimate tensile force,flexural force and bending force of non-growing seasonal branches of sea buckthorn increased with the increase of diameter,and the diameter showed significant positive correlation with the ultimate tensile force,flexural force and bending force,but the incremental functions were different.The effect of branch length on ultimate tensile force and flexural force of non-growing season branches was not significant;flexural force increased with the increase of branch length.The ultimate tensile strength,flexural strength and bending strength of non-growing seasonal branches of sea buckthorn decreased with increasing diameter,and the diameter was significantly and negatively correlated with ultimate tensile strength,flexural strength and bending strength,but the decreasing functions were different.The effect of branch length factor on ultimate tensile strength and flexural strength of non-growing seasonal branches was not significant;flexural strength increased with the increase of non-growing seasonal branch length.The average ultimate tensile strength(90.66 N)was greater than the flexural strength(45.98 N),and the difference was 44.67 N.The ultimate tensile strength and flexural strength of single buckthorn roots did not change significantly with the increase of diameter;the average ultimate tensile strength of single buckthorn roots(19.97 MPa)was different from that of single buckthorn roots.The average ultimate tensile strength(19.97MPa)was greater than the flexural strength(8.07 MPa),and the difference between the ultimate tensile strength and flexural strength of single root was 11.9 MPa,indicating that the type of external force that is easily damaged by single root of sea buckthorn is radial bending force.The growth rate of root-soil composite at 12.5 k Pa was(35%)significantly greater than that of-12% at 25 k Pa.It shows that the sea buckthorn root system in its dense distribution layer of about 80 cm shallow soil,the effect of improving the shear strength of the soil is obvious,i.e.,it is more effective in consolidating the shallow soil.From the growth rate of shear strength index,the growth rate of cohesion c is 28% and the growth rate of internal friction angle φ is-14%.The factors influencing the shear characteristics of root-soil complex include: soil moisture content,root diameter,number of buried roots,shear rate,soil type,and root burial method.The specific results were.(1)The cohesive force of vegetative soil and root-soil complex increased and then decreased with the increase of soil water content.The cohesive force of vegetative soil was smaller than that of root-soil complex.The peak cohesion of root-soil complex is 13.79 k Pa at 16.5% water content,and the maximum cohesion is 9.87 k Pa at 12.5% water content.(2)Under the submerged soil pressure(12.5k Pa and 25 k Pa),the shear strength increased with the increase of root diameter,the cohesive force showed a single-peak curve type with the increase of root diameter,and the curve change of internal friction angle showed a trend of decreasing first and then increasing.(3)The peak values of shear strength of root-soil composite are 18.95 k Pa and24.46 k Pa when the number of roots is 4 in shallow soil(12.5k Pa and 25 k Pa),and the peak values increase with the increase of vertical load,and the cohesive force increases with the increase of root diameter in a single-peak curve,where the peak value of cohesive force corresponds to 10.65 k Pa when the number of roots is 4.The peak value of internal friction angle corresponds to 37.79° when the number of roots is 10,and the change of internal friction angle tends to increase and then decrease,that is,the change of internal cohesion is more obvious with the change of the number of buried roots.(4)At 12.5 k Pa and 50 k Pa,the shear strength at the shear rate of fast shear(0.8mm/min)was greater than that at its slow shear(0.1 mm/min).The root-soil composite cohesion is greater than that of plain soil,and the angle of internal friction is opposite.(5)At 12.5kpa and 25 kpa,the shear strengths of all the five root burial methods were greater than that of the plain soil,and the growth rates of shear strength were in the order of vertical cross root burial method(46.92%,18.82%)> vertical parallel root burial method(33.59%,10.69%)> vertical pentagonal root burial method(28.34%,9.79%)>three flat and two vertical root burial methods(19.67%,16.66%)> horizontal parallel rooting method(15.84%,8.05%);the cohesive force under all five rooting methods was greater than that of the vegetative soil,which was ranked as vertical cross rooting method(174.33%)> vertical parallel rooting method(142.44%)> vertical pentagonal rooting method(123.45%)> three flat and two vertical rooting methods(89.39%)> horizontal parallel root burial method(60.43%).The variation of internal friction angle was small compared with that of the plain soil,and there was no obvious pattern. |
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