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Strengthening effects of alfalfa roots on soil shear resistance in loess region |
ZHOU Xia, WEI Yang, LI Dongrong, JIANG Jing, ZHANG Chaobo |
College of Water Resources Science and Engineering, Taiyuan University of Technology, 030024, Taiyuan, China |
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Abstract [Background] Surface erosion, slope instability and soil-water loss caused by soil erosion have become major ecological and environmental problems in China. Plant measures are commonly used ways in preventing soil erosion, and are also the most effective and fundamental methods for soil and water conservation. Shrub and grass have become priorities for solving the contradiction between water resources and ecological environment and preventing soil erosion.[Methods] Direct shear tests were conducted on loess soil samples with alfalfa roots, using the devices including direct shear box, frame, jack, hydraulic pump, displacement sensor, pressure sensor, recorder etc. The shear strength of alfalfa root-loess samples with various soil water contents and in different soil depth (10, 20, and 30 cm) were measured, the characteristics of shear failure of the soil samples and the distribution of the failure roots in shear plane were determined, and the relationship between shear strength and shear displacement of samples in different soil depth and with different soil water content were analyzed.[Results] 1) The alfalfa roots increased the shear strength of the soil by 43.10%-89.41%, and increased the shear displacement by around 13.16-56.95 mm. 2) The shear strength of both the alfalfa root-loess samples and rootless soil samples decreased with increasing soil water content, and the soil water content presented a negative effect on the shear strength of the soil. When the soil water content was 18.97%, the shear strength of the soil composite sample was 10.02 kPa and the shear displacement was 70.55 mm. The maximum shear strength increased by 89.41% and the shear displacement increased about 25 mm compared with the bare soil sample. 3) When the soil water content was about 30% in the shear depth of 30 cm, the soil reinforcement effect of the root system was very limited. 4) The enhancement effect of alfalfa roots on soil shear strength decreased with the increase of soil shear depth, and the root system had a more significant effect on the shear strength of shallow soil.[Conclusions] The results are of practical importance to the selection of dominant species, to the improvement of slope stability and the prevention of soil and water loss on the Loess Plateau. It can also provide theoretical basis of vegetation measures for slope consolidation and soil and water conservation.
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Received: 07 June 2018
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