Study On The Effect Of Cyclic Loading On The Mechanical Properties Of Amorpha Fruticosa Root Systems

Amorpha fruticosa,a common soil fixing plant in coal mining subsidence area of Shenfu Dongsheng coalfield,was taken as the researching object in this thesis.The TY8000 servo controlled testing machine was used to study the effects of cyclic loading on the mechanical properties of tensile and tensile shear combination of taproots and root segments with lateral root branches In the range of 1-5mm root diameter,as well as the deformation characteristics in the stress process.This study can enrich the mechanism of root soil consolidation,and provide a theoretical basis for vegetation construction in Shendong mining area.The main results are as follows:(1)Cyclic loading did not change the correlation between the mechanical properties and root diameter of taproots and root segments with lateral root branches of Amorpha fruticosa.In the range of 1-5mm root diameter,the ultimate tensile force and ultimate combined tensile and shear force of taproots and root segments with lateral root branches under axial and radial single loading,cyclic low loading,cyclic high loading and alternating loading were positively correlated with root diameter by power function,and the ultimate tensile strength and ultimate combined tensile and shear strength were negatively correlated with root diameter by power function.(2)Both axial and radial cyclic high loading and alternating loading could significantly improve the strength of taproots and root segments with lateral root branches of Amorpha fruticosa(P < 0.05).In the range of 1-5mm root diameter,the tensile strength of taproot segments under axial cyclic high loading and alternating loading was 1.23 times and 1.2 times of single loading,and the tensile strength of root segments with lateral root branches was 1.49 times and 1.23 times of the single loading respectively.The combined tensile and shear strength of taproot segments under radial cyclic high loading and alternating loading was 1.31 times and 1.36 times of the single loading,and the combined tensile and shear strength of root segments with lateral root branches was 1.52 times and 1.46 times of the single loading respectively.In addition,the radial low loading cycle can also significantly improve the combined tensile and shear strength of root segments with lateral root branches(P < 0.05),and the averagely combined tensile and shear strength is1.43 times of the single loading.(3)In the range of 1-5mm root diameter,there was no significant difference in the tensile force and combined tensile and shear force(P > 0.05)between taproots and root segments with lateral root branches of Amorpha fruticosa under axial and radial single loading,cyclic low loading,cyclic high loading and alternating loading and there was also no significant difference in the tensile strength and combined tensile and shear strength(P > 0.05).The results indicated that taproots and root segments with lateral root branches had no significant difference between tensile strength and combined tensile and shear strength under different loading modes.(4)Under different loading types,the constitutive curves of taproots and root segments with lateral root branches of Amorpha fruticosa showed different characteristics.The constitutive curves of taproots and root segments with lateral root branches under axial single loading,cyclic low loading,cyclic high loading and alternating loading all showed the characteristics of convex curves,while the constitutive curves of taproots and root segments with lateral root branches under radial loading all showed the characteristics of concave curves.The increase of root stress under axial loading decreased with the increase of root strain,while it under radial loading increased with the increase of root strain.The results showed that the tensile properties of the root under axial loading at the initial stage were greater than those at the later stage,while the tensile shear combination characteristics of the root under radial loading at the later stage are greater than those at the initial stage.(5)The F-S images of taproots and root segments with lateral root branches of Amorpha fruticosa showed similar elastic-plastic characteristics during axial cyclic loading.There was an obvious inflection point in the loading curve.Root segments occurred elastic deformation before the inflection point and elastic-plastic deformation after the inflection point.The distribution of the curves was gradually intensive with the increase of loading times,that is,the deformation of root segments gradually tended to be stable.In the process of 50 times of axial cyclic loading on taproot segments,the strain at the last time of low loading cycle was 54.2% of the first time,and the last time of high load cycle was 39.63% of the first time.Taproots and root segments with lateral root branches of Amorpha fruticosa under cyclic radial loading in the process of its F-S elastoplastic characteristics of images also showed a similar elastic-plastic characteristic.With the increase of loading frequency,the curve was also gradually concentrated.The strain of the last loading produced 34% of the first in the process of the low loading cycle and the strain of the last loading produce25.13% of the first in the process of the high loading cycle.