Evaluation method of diversion length of capillary barrier composing of 3 layers ground in considering the thickness of the upper soil layer

Capillary barrier (CB) refers to a soil layer structure composing of a sand layer over a gravel layer used as a rainwater infiltration control technique for preventing seepage. An important parameter for the design of CB is diversion length. Currently, the approximate equation of diversion length consistent highly with the experimental results are applied. However, this approximate equation is intended for the two-layer CB ground, also the influence of the thickness of the upper soil layers are not considered. In this paper, in order to establish a design approach that will contribute to the practical use of the three-layer CB ground with a soil top cover, the effect on rainwater infiltration control function by the thickness of the upper soil layer was quantitatively evaluated, and was clarified the mothod of applying the approximate equation of diversion length for the three-layer CB ground.