基于土-水特征曲线的植物边坡抗剪强度研究

土-水特征曲线通常用于估计非饱和土壤的抗剪强度,但是由于植物根系的吸水作用和加筋效应,使得植物边坡的抗剪强度不能直接利用基于基质吸力的非饱和土抗剪强度计算公式进行计算。以裸露边坡和植被边坡为研究对象,采用张力计现场测试和室内剪切试验相结合的方法,拟合水土特征曲线关系。结果表明:(1)植物根系的植入有效地提高了边坡土体的进气值,较素土进气吸力值增幅41.10%。在同等含水率条件下,植物边坡基质吸力明显大于素土边坡,提高了边坡土体的持水能力。(2)边坡红黏土基质吸力与含水率的关系符合V-G模型,利用最小二乘法得到模型参数。(3)随着体积含水率的增大,带根土与素土的抗剪强度参数值变化趋势大致相同,均呈现先增大后减小的趋势,但带根土的变化参数大,当含水率21.29%时,带根土黏聚力相较于素土增加了4.86 kPa,增幅18.55%,而内摩擦角对根系存在的敏感程度不如黏聚力。(4)随着土壤基质吸力不断增大,植被边坡与素土边坡的抗剪强度力学参数变化趋势大体相同,当土基质吸力为60～90 kPa土体的黏聚力提高最为明显,但植被边坡由于植物根系的存在,土体内基质吸力对边坡土体的抗剪强度提高幅度更大,黏聚力与内摩擦角最大增长幅度分别为37.34%和40.30%。通过建立土-水特征曲线参数与植物边坡抗剪强度的关系,可计算不同含水率或基质吸力条件下植物边坡的抗剪强度,为进一步分析工程实际中植物边坡的稳定性提供理论依据。

Study on Shear Strength of Plant Slope Based on Soil-water Characteristic Curve

Soil-water characteristic curve is usually used to estimate the shear strength of unsaturated soil. In consideration of the water absorption and reinforcement effect of plant roots, the shear strength of plant slope can not be directly calculated by the formula of unsaturated soil shear strength based on matrix suction.In this paper, the bare slope and vegetation slope are taken as the research objects, and the soil and water characteristic curve of the test soil is obtained by combining the tensiometer field test and indoor shear test. The results show that the plant root implantation can effectively improve the air intake value of slope soil, which is 41.10% higher than that of plain soil. Under the same water content, the matric suction of plant slope is significantly higher than that of plain soil slope, which improves the water holding capacity of slope soil.The Van Genuchten model can be used perfectly to fit the datum from the soil water characteristic curve. With the increase of water content, the shear strength parameters of the soil with root and plain soil are similar, which are both increasing first and then decreasing. But the change parameters of the soil with root are large. When the water content is 21.29%, the cohesion of the soil with root increases by 4.86 kPa, and the increase is 18.55%, while the sensitivity of the internal friction angle to the root system is not as good as the cohesion.With the increase of soil matric suction, the change trend of mechanical parameters of shear strength of vegetation slope and plain soil slope is basically the same, and the cohesion of soil increases most obviously in the range of matric suction of 60~90 kPa. However, the matric suction of vegetation slope increases the shear strength of slope soil more greatly due to the existence of plant roots, The maximum increases of cohesion and internal friction angle are 37.34% and 40.30% respectively.By establishing the relationship between the parameters of soil water characteristic curve and the shear strength of plant slope, the shear strength of plant slope under different water content or matric suction can be calculated, which provides a theoretical basis for further analysis of the stability of plant slope in engineering practice.