Evaluation of the Water Shielding Performance of a Capillary Barrier System through a Small-Scale Model Test
Abstract
:1. Introduction
2. Characteristic of the CB System
3. Soil Samples and Water Retention Characteristics
3.1. Soil Samples
3.2. Water Retention Characteristics
4. Laboratory SSCB Model Test under the Lateral No-Flow Condition
4.1. Apparatus and Conditions of the SSCB Model Test
4.2. Production of the SSCB Model
4.3. Preparation for the SSCB Model Test
4.4. Infiltration Behavior in the SSCB Model Test
4.4.1. Result for Case 1
4.4.2. Result for Case 2
4.4.3. Result for Case 3
4.4.4. Measurement Results of the Diversion Lengths in the SSCB Model Test
4.5. Diversion Length on the SSCB Model Test
5. Summaries and Conclusions
- The inside of the SSCB model proposed in this study was 45.5 cm long, 47.0 cm high, and 15.0 cm wide. Notably, the amount of drainage water under the lowest tested rainfall intensity (I = 20 mm/h) reached a steady state within 6 h. We can hence infer that the production work and the testing results of the SSCB model were better when the testing time was relatively short. Moreover, since this model was smaller than the large-scale models described in previous works, it was expected that its production work and testing would have a lower cost.
- The following rainfall intensities were achieved during the SSCB model tests: 20 mm/h (Case 1), 50 mm/h (Case 2), and 100 mm/h (Case 3). The time required by the sand layer to reach the saturation state in each of the above cases was 180 min, 85 min, and 45 min, respectively; moreover, breakthroughs occurred at 210 min, 85 min, and 45 min, respectively. Thus, the rainfall intensity was very closely related both to the time required by the sand layer to reach the saturation state and to the time of breakthrough occurrence in the CB system.
- The diversion lengths in the SSCB model test of this study were measured based on two criteria (i.e., LUD1: at the interface between the sand and the gravel layers, and LUD2: the occurrence point of the finger flow at the height of the soil moisture sensors (No. 3 and No. 4) installed in the gravel layer), because water infiltration occurred irregularly from the interface between the sand and the gravel layers. The LUD1 values obtained for Case 1, Case 2, and Case 3 were 13.5 cm, 11.7 cm, and 0 cm, respectively; meanwhile, the LUD2 values were 24.8 cm, 11.2 cm, and 0 cm, respectively. These results indicate that LUD1 and LUD2 were 13.3% and 54.8% lower, respectively, in Case 2 (I = 50 mm/h) than those in Case 1 (I = 20 mm/h). Finally, in Case 3, under the extreme rainfall intensity of 100 mm/h, our CB system collapsed.
- The diversion lengths (LD) under the lateral flow condition were estimated by the empirical equation of Steenhuis et al. [28] based on the hydraulic conductivity functions and soil-water characteristic curves of the sand and gravel. In Case 1, Case 2, and Case 3, they were 145.5 cm, 56.8 cm, and 27.7 cm, respectively. However, considering that the lengths of ΔL1 and ΔL2 would be reduced by the occurrence of breakthroughs in the SSCB model test, the effective diversion lengths (i.e., LED1 and LED2) for the real CB system were derived. The LED1 and LED2 values in Case 1, Case 2, and Case 3 were 114.2 and 125.5 cm, 23.7 and 23.1 cm, and −17.1 and −17.1 cm, respectively. Here, negative LED1 and LED2 values (i.e., −17.1 cm and −17.1 cm in Case 3) indicated that there is no water-shielding performance of the CB system under extreme rainfall (i.e., I = 100 mm/h).
- The diversion lengths in the CB system were compared: LD (estimated by the empirical equation) and LED1 and LED2 (estimated based on the SSCB model test). The results indicated that LED1 and LED2 were lower than the correspondent LD values, and that their reduction reflected the differences in rainfall intensity between one case and the other: the LED1 and LED2 values were 21.5% and 13.8% (Case 1), or 58.3% and 59.2% (Case 2) lower, respectively, than the correspondent LD values. Thus, when the effective diversion lengths based on the SSCB model test are applied to the real CB system design, it is expected that since the reduced water-shielding performance of the CB system is taken into account, and the stability of the CB slope will be further improved. In addition, since the LED1 and LED2 values have a slight difference, applying the average of the two values to the CB system design may be a reasonable suggestion.
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Conflicts of Interest
References
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Sample | Toyoura Sand | Silica Sand No. 1 |
---|---|---|
Soil particle density, ρs (g/cm3) | 2.64 | 2.65 |
Mean particle size, D50 (cm) | 1.69 | 4.65 |
Maximum dry density, ρd max (g/cm3) | 1.64 | 1.67 |
Minimum dry density, ρd min (g/cm3) | 1.37 | 1.45 |
Uniformity coefficient, Cu | 1.63 | 2.24 |
Curvature coefficient, Cc | 0.97 | 0.84 |
Relative density, Dr (%) in the CB model test | 53.8 | 87.9 |
Saturated hydraulic conductivity, ksat (m/s) | 1.45 × 10−4 | 2.44 × 10−3 |
Soil Sample | θs | AEV | EX | a | n | m |
---|---|---|---|---|---|---|
Toyoura sand | 0.432 | 2.45 | - | 2.80 | 10.02 | 0.75 |
Silica sand No. 1 | 0.389 | - | 0.05 | 0.39 | 0.015 | 0.07 |
Case No. | Case 1 | Case 2 | Case 3 | |
---|---|---|---|---|
Sand layer | Initial dry density, ρdi (g/cm3) | 1.50 | 1.50 | 1.50 |
Initial water content, wi (%) | 0.64 | 1.11 | 0.33 | |
Initial volumetric water content, θi | 0.01 | 0.02 | 0.01 | |
Gravel layer | Initial dry density, ρdi (g/cm3) | 1.64 | 1.64 | 1.64 |
Initial water content, wi (%) | 0.87 | 1.19 | 1.30 | |
Initial volumetric water content, θi | 0.01 | 0.02 | 0.02 | |
Drainage material: nonwoven fabric | Material (Fiber cross-section: ◎) | -Outside: polyethylene -Inside: polyester | ||
Thickness (mm) | 0.13 | |||
Hydraulic conductivity for vertical plane (m/s) | 1.30 × 10−3 | |||
Rainfall intensity, I (mm/h) | 20 | 50 | 100 | |
Slope angle, Φ (°) | 10 | 10 | 10 | |
Measurement time (h) | 6 | 6 | 6 |
No. | I (mm/h) | Time to Reach the Saturation State of the Sand Layer | Time of Breakthrough Occurrence |
---|---|---|---|
Case 1 | 20 | 180 min | 210 min |
Case 2 | 50 | 85 min | 85 min |
Case 3 | 100 | 45 min | 45 min |
Case No. | Case 1 | Case 2 | Case 3 | |
---|---|---|---|---|
Rainfall intensity, I (mm/h) | 20 | 50 | 100 | |
Lateral nonflow condition | Measured LUD1 (cm) | 13.5 | 11.7 | 0 |
Measured LUD2 (cm) | 24.8 | 11.2 | 0 | |
Lateral flow condition | Estimated LD (cm) by Equation (2) | 145.5 | 56.8 | 27.7 |
ΔL1 (cm) | 31.3 | 33.1 | 44.8 | |
ΔL2 (cm) | 20.0 | 33.6 | 44.8 | |
Effective diversion length, LED1 (cm) | 114.2 | 23.7 | −17.1 | |
Effective diversion length, LED2 (cm) | 125.5 | 23.1 | −17.1 |
qv (mm/h) | ksat (cm/s) | κ | b | Φ (°) | hae (cm) | haex (cm) | LD (cm) |
---|---|---|---|---|---|---|---|
20 | 1.45 × 10−2 | 0.038 | 0.13 | 10 | 24.5 | 0.5 | 145.5 |
50 | 0.096 | 56.8 | |||||
100 | 0.192 | 27.7 |
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Kim, B.-S. Evaluation of the Water Shielding Performance of a Capillary Barrier System through a Small-Scale Model Test. Appl. Sci. 2021, 11, 5231. https://doi.org/10.3390/app11115231
Kim B-S. Evaluation of the Water Shielding Performance of a Capillary Barrier System through a Small-Scale Model Test. Applied Sciences. 2021; 11(11):5231. https://doi.org/10.3390/app11115231
Chicago/Turabian StyleKim, Byeong-Su. 2021. "Evaluation of the Water Shielding Performance of a Capillary Barrier System through a Small-Scale Model Test" Applied Sciences 11, no. 11: 5231. https://doi.org/10.3390/app11115231