坡面水保措施下土壤水分特征及对坡体稳定性的作用

Variations of Soil Moisture under Soil and Water Conservation Measures and the Corresponding Effects on Slope Stability

为掌握不同水保措施下土壤含水率分布规律和土壤含水率对土壤抗剪强度影响程度的差异性,对上辛庄水保科技示范园的水平条和鱼鳞坑措施径流小区和裸土对照小区的不同土层深度的土壤含水率和土壤抗剪强度展开实验,结合当地的气候、地质、土壤和水文条件,研究了0~100 cm土壤深度下不同水保措施下的土壤质量含水率空间分布特征及其对土壤抗剪强度的影响。研究结果表明,坡面含水率总体上下坡大于上坡;对于不同坡面的相同坡位处,土壤含水率差异较小,水平条坡面】鱼鳞坑坡面】对照坡面。结合原状土和重塑土的抗剪强度实验可知,在土壤容重=1.04 g cm-3、含水率为7%~16%的范围内,抗剪强度随着含水率的增加先增加再减少。在此条件下,含水率对抗剪强度的影响主要是通过影响土壤的黏聚力来改变抗剪强度,对内摩擦角的影响较小。结果表明,采取水平条措施的坡面蓄水能力比鱼鳞坑坡面和对照坡面强,有较好的水保效益;在含水率低于16%的情况下,相对于采取水平条措施和鱼鳞坑措施的坡面,裸土坡面容易受破坏,坡体内部的潜在失稳风险较大。

To investigate the distribution of soil moisture and the corresponding effects on soil shear strength, tests were conducted on different slope soil layers under the Horizontal bar measure and the Fish-scale pit measure respectively, and the slope without vegetation was also tested to be the contrast group. All tests were carried out under the same conditions, such as climate, geology, soil type and hydrological conditions at Shangxinzhuang Soil and Water Conservation Demonstration Park, Yanqing, Beijing. Results indicated that under all conditions, soil moisture had a trend that raised up at first and then dropped with the deepening of the soil depth from 0 cm to 100 cm. About the soil moisture value of the same slope positions under different measures, we found a rule that the highest value was obtained for the slope under the Horizontal bar measure, followed by the slope under the Fish-scale pit measure and the bare slope. With regard to the correlation coefficient between soil moisture and the corresponding soil shear strength in different slope, the lowest value appeared at the bare slope, which was significantly higher than other two plots. Combined with the results of direct shear test, the soil shear strength increased first and then decreased with the increasing of soil moisture when soil bulk density was 1.04 g cm-3and soil moisture ranged from 7% to 16%. Under this condition, corresponding effects of moisture on the shear strength was mainly through soil cohesion that could change the shear strength rather than internal friction angle. Our results also showed that the water-holding capacity of the slope under Horizontal bar measure was relatively high, that was to say it had better water conservation benefits.Moreover, under the same condition, the bare slope might be more prone to be subjected to destruction and instability due to the low value of soil moisture and the weaker correlation with shear strength.