This study investigates the effects of grass age on hydraulic properties of coarse-grained volcanic soil, namely: Komaoka soil. The soil-water characteristic curve (SWCC), unsaturated coefficient of permeability, outflow, runoff, and the variations in volumetric water content/matric suction under different rainfall intensities varying from 15, 30, 60, to 120 mm/h are measured by carrying out column tests. In addition, permeability tests are performed to determine the saturated coefficients of permeability of bare soil and grassed soils. In these tests, grassed soils with grass ages varying from 1 to 6 months are used to study the influence of root volume ratio on the hydraulic properties. The experimental results reveal that the grass age has an influence on the hydraulic properties of Komaoka soil. At the same volumetric water content, grassed soil with higher grass age has higher matric suction. Both saturated and unsaturated coefficient of permeability are significantly reduced with the increase in the grass age. Moreover, there is a decrease in the outflow and an increase in the runoff for grassed soil with higher grass age. Matric suction decreases later in grassed soil than that of bare soil under rainfall events. The higher the grass age, the longer time is taken to observe the change in matric suction. However, the matric suction of grassed soil is dramatically reduced while there is a gradual decrease in matric suction of bare soil. Furthermore, even though the matric suctions remain constant at somewhere in the vicinity of 2 kPa under long and intense rainfall events, higher volumetric water contents are recorded for grassed soil with higher age. The new model is proposed to estimate the unsaturated coefficient of permeability of coarse-grained soil due to the effects of grass roots. The good agreement between estimations and experimental results shows that the proposed model is useful to capture the decrease in unsaturated coefficient of permeability of grassed soil.

这项研究调查了草龄对火山岩粗粒土壤水力学特性的影响：毛冈土壤。在15、30、60至120mm / h的不同降雨强度下，通过测量土壤-水特征曲线（SWCC），非饱和渗透系数，流出，径流以及体积水含量/基质吸力的变化，变化范围为15、30、60至120 mm / h。列测试。另外，进行渗透性测试以确定裸土和草土的渗透性的饱和系数。在这些测试中，使用草龄在1至6个月之间的草皮土壤来研究根系体积比对水硬性的影响。实验结果表明，草龄对小冈土壤的水力特性有影响。在相同的体积水含量下，草龄较高的草土具有较高的基质吸力。随着草龄的增加，饱和和非饱和渗透系数均显着降低。此外，草龄较高的草皮土壤的流出量减少，径流增加。在降雨条件下，草土壤的吸力下降比裸土的吸力下降晚。草龄越高，观察基质吸力变化的时间就越长。然而，草土壤的基质吸力显着降低，而裸土的基质吸力逐渐降低。此外，即使在长期而强烈的降雨事件下，基质吸力在2 kPa附近的某处保持恒定，对于较高年龄的草皮土壤，仍记录有较高的体积水含量。提出了一种新模型来估计由于基层的影响而使粗粒土的渗透性的不饱和系数。估算值与实验结果之间的良好一致性表明，所提出的模型对于捕获草土的非饱和渗透系数的减小是有用的。