Research On Mechinecal Properties Of Roots Regarding Soil Reinforcement Performance In Rocky Mountain Area Of Shanxi

The root system is the basic unit of soil reinforcement by plants, and the research on the tensile mechanical properties of root system lays the foundation of studies about soil reinforcing effects of plant roots. In slope protection engineering which employs plants, the root system improves the stability of the slope through its shear resistance and tensile resistance. Researches have shown evidence that the role which tensile strength of root system plays is one of the most important roles in enhancing slope stability. Root distribution of four plants found in Taiyuan City, Shanxi Province, namely Heteropappus altaicus(Willd.)Novopokr., Poa sphondylodes Trin., Festuca arundinacea, Plantago major L.,was studied to work out the root area ratios at different soil depths. Also,laboratory tensile tests were conducted to analyze tensile resistance properties of the roots of these four plants. Factors including root diameter, gauge length,water content were studied to determine their impacts on tensile resistance and tensile strength of the roots, with the view to reveal the basic mechanics regarding soil reinforcement of the roots. At the same time, the Wu’s model was adopted to evaluate the soil reinforcing performances of these plants. Root area ration and tensile strength were used to calculate the cohesive force of roots,which evaluates the potential of roots in soil reinforcement and slope protection.The results can serve as the foundation toward selecting suitable plants for soil reinforcement and slope protection, as well as further studying the mechanics of soil-reinforcement by plants.Main results of this research are as follows:(1) With the same gauge length and water content, root diameter of these four plants had a power function relationship with and was significantly positively related to their respective maximum tensile resistance. Meanwhile,root diameter also had a power function relationship with the maximum tensile strength, but they were significantly negatively related.(2) By conducting tensile tests on Poa sphondylodes Trin. roots with four different water contents, the author found that gauge length had the most significant impact on the maximum tensile resistance and the maximum tensile strength of the roots. To be specific, as the gauge length increased, both the maximum tensile resistance and the maximum tensile strength decreased. As for the roots of Heteropappus altaicus(Willd.) Novopokr. and Festuca arundinacea,in the two tests conducted with relatively high water contents, the gauge length had a significant impact on the maximum tensile resistance and the maximum tensile strength of the roots: as the gauge length increased, both the maximum tensile resistance and the maximum tensile strength decreased. However, in the another two tests conducted when water contents were low(after placing the roots outdoors for 6 hours and 12 hours, respectively), the gauge length’s impacton the maximum tensile resistance and the maximum tensile strength was not significant.(3) Water content had a significant impact on the maximum tensile resistance and the maximum tensile strength of roots of these four plants. To be specific, the water content was negatively related to the maximum tensile resistance and the maximum tensile strength of the roots.(4) When the depth of soil was the same for these four plants, Festuca arundinacea had the biggest root area ratio. In addition, within the depth where roots could reach, the root area ratios of these four plants showed the same trend of change, namely, as roots grew deeper, the root area ratios gradually decreased.As the soil depth increased, the speed of decrease in the root area ratio of these four plants became faster, and eventually the root area ratio was close to 0.Besides, as the soil depth increased, the differences between the root area ratio of the plants gradually narrowed.(5) All four plants experienced the biggest increase in their root cohesive forces when the soil depth was 0~5 cm. Among them, Poa sphondylodes Trin.had the biggest increased cohesive force, followed by Festuca arundinacea and Plantago major L., while Heteropappus altaicus(Willd.) Novopokr. ranked fourth. The same sequence was repeated when the soil depth was 5~10 cm. After that, as the soil depth increased, the increases in the root cohesive forces of the four plants experienced sharp decrease.A conclusion can be drawn by using the Wu’s model that Poa sphondylodes Trin. is best at reinforcing soil, whileFestuca arundinacea, Plantago major L. take the second and third places respectively, and Heteropappus altaicus(Willd.) Novopokr. shows the worst performance.