Abstract
Capillary barrier (CB) systems consisting of a fine-grained soil layer placed over a coarse-grained soil layer can generally provide a water-shielding effect, increasing the slope stability of soil structures during rainfall. In order to improve the water-shielding performance of CB systems, laboratory model tests have been previously conducted under various conditions; notably, large-scale model tests are especially required. The inefficiency in increasing the production time of CB models until now explains their high cost. In this paper, we propose a laboratory small-scale CB (SSCB) model test for a quick and efficient evaluation of the function of a CB system. In this model test, differently from previous studies, a side drainage flow in the direction of the inclined sand layer was set as the no-flow condition; moreover, the laboratory SSCB model tests were performed by considering three rainfall intensities (i.e., 20, 50, and 100 mm/h) under the lateral no-flow condition. The results showed that the larger the rainfall intensity, the shorter the diversion length was of the CB system. To evaluate the effectiveness of the SSCB model test proposed in this study, the diversion length was estimated by an empirical equation under the lateral flow condition based on hydraulic conductivity functions and the soil water characteristic curves of sand and gravel and then compared to the results of the SSCB model tests. It was hence demonstrated that the water-shielding performance of the CB system can be efficiently evaluated through SSCB model tests under the lateral no-flow condition, rather than through large-scale model tests.
Highlights
The results showed that the larger the rainfall intensity, the shorter the diversion length was of the Capillary barrier (CB) system
To evaluate the effectiveness of the small-scale CB (SSCB) model test proposed in this study, the diversion length was estimated by an empirical equation under the lateral flow condition based on hydraulic conductivity functions and the soil water characteristic curves of sand and gravel and compared to the results of the SSCB model tests
The results of the SSCB model tests for Case 1, Case 2, and Case 3 under I = 20, 50, and 100 mm/h, suggest that the rainfall intensity was very closely related to the time needed for reaching the saturation of the sand layer, as well as to the time of breakthrough occurring in the CB system
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Matsumoto et al [23] considered the use of a three-layer barrier for improving the water-shielding performance of the CB system They performed a series of laboratory CB model tests using a large-scale model box (3.0 m long, 1.5 m high, and 1.0 m wide). In the laboratory CB model tests of those mentioned above, a large-scale model with a lateral length ≥ 2.0 m was used: in this case, the water infiltration from the upper sand layer to the lower gravel layer occurred randomly This large-scale model test requires a lot of time for its functioning; its fabrication is expensive, and the corresponding testing time is high, making it difficult to perform many CB model tests under different conditions. Comparing the results of the SSCB model test with the values estimated by the empirical equation, we discussed the significance and validity of the laboratory SSCB model test under the lateral no-flow condition
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