黄土丘陵沟壑区刺槐动态固坡效应

植被能够有效提升浅层坡体的稳定性和抗蚀性。为了初步定量评估浅层滑坡易发的黄土丘陵沟壑区植被固坡作用在自然条件下的动态变化结果,以黄土丘陵沟壑区主要造林树种刺槐为例,考虑植被固坡的根系机械作用和水文作用在2017年全年自然条件下的动态变化。通过挖掘根系剖面对根系截面积分布进行调查,单根抗拉试验测试根系抗拉强度,以利用Wu模型对刺槐根系的附加黏聚力进行计算;通过现场调查确定研究样地与植被水文作用相关的参数,室内入渗试验和土壤离心试验获取土壤的水力学参数,利用生态水文领域水分运移软件Hydrus-1D对刺槐植被坡体水分的运移进行瞬态分析;最终基于变饱和条件下的无限斜坡模型对坡体的稳定性进行分析,并分别计算刺槐根系机械作用和水文作用对坡体稳定性的动态贡献率。结果表明:(1)刺槐根系机械作用对20,40,60 cm深度处浅层坡体的稳定性提升196.56%±28.08%,106.74%±13.19%,20.61%±2.43%,同时机械作用的贡献率还具有一定波动性;(2)刺槐在生长期内,通过林冠截留拦截70.2 mm的降雨量,蒸腾耗水作用改变坡体土壤含水量和吸应力,有效地提升坡体稳定性;(3)根系机械作用的贡献全年均存在,且波动性较水文作用贡献率的波动性小,但水文作用的贡献主要发生在刺槐的生长期,且水文贡献率的部分峰值较机械作用的贡献率大。研究结果进一步揭示了黄土高原丘陵沟壑区刺槐植被坡体在自然条件下的动态变化过程。

Dynamic Effect of Stabilizing Slope of Robinia pseudoacacia in Loess Hilly and Gully Region

Vegetation can effectively improve the stability and erosion resistance of shallow slope. In order to make a preliminary quantitative assessment of dynamic changes of vegetation slope consolidation under natural conditions in the loess hilly and gully region where the shallow landslide prone to occur, taking Robinia pseudoacacia, the main afforestation tree species in the loess hilly and gully region as an example, the dynamic changes of roots mechanical and hydrological effects of vegetation slope consolidation under natural conditions in 2017 were studied. The roots cross-sectional area distribution was investigated by digging the root section, the roots tensile strength was tested by single root tensile test, and the roots additional cohesion of R. pseudoacacia was calculated by using the Wu model. Field surveys were conducted to collect the parameters related to the hydrological effects of vegetation and the research plot. Laboratory infiltration experiment and soil centrifugation experiments were conducted to obtain the soil hydraulic parameters. Then the water transport software Hydros-1D was applied to do the transient analysis of the water content of the R. pseudoacacia slope. Finally, the stability of the slope was analyzed based on the infinite slope model under variable saturation conditions, and the dynamic contribution rate of roots mechanical and hydrological effects of R. pseudoacacia to the slope stability were calculated. The results showed that: (1) The mechanical effect of R. pseudoacacia roots on the stability of shallow slope at the depths of 20, 40 and 60 cm increased by 196.56%±28.08%, 106.74%±13.19% and 20.61%±2.43%, respectively. At the same time, the contribution rate of root mechanical function also had some fluctuation. (2) During the growth period of R. pseudoacacia, R. pseudoacacia canopy intercepted 70.2 mm rainfall, transpiration changed the soil water content and suction stress of the slope, so the stability of shallow slope was effectively improved. (3) The contribution of the roots mechanical action existed throughout the year, and the volatility was less than that of hydrological contribution rate. However, the contribution of hydrological action mainly occurred during the growth period of R. pseudoacacia, and most parts of the peak values of hydrological contribution rate were larger than those of mechanical action. The results further revealed the dynamic changes of R. pseudoacacia slope stability in the hilly and gully region of the Loess Plateau under the natural conditions.