Controlling Rainfall Infiltration in Slopes Using an Unsaturated Barrier Layer under Coarse-Grained Layer Pressurization
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摘要: 传统土质边坡表面硬化防渗措施易因降雨入渗产生干缩开裂问题，威胁工程安全，采用非饱和阻隔层（capillary barrier layer，CBL）阻隔保护可提升工程的长期稳定性，但存在导水能力随长期降雨入渗而下降的现象.针对传统非饱和阻隔层中毛细阻滞能力随降雨入渗衰减的问题，本文从水-气耦合角度，提出了通过粗粒层增压以增强非饱和阻隔层阻隔降雨入渗的方法.采用系列物理模型试验，在气密封闭条件下，探讨不同降雨强度、CBL初始含水量和粗粒层增压值等条件对其阻隔降雨入渗的影响，主要取得以下认知：（1）当粗粒层注气增压（1~3 kPa）时，降雨全部从细粒层、过渡层与粗粒层界面排出，完全抑制降雨突破过渡层/粗粒层界面而进入粗粒层，显著提升非饱和阻隔层的阻隔效率.（2）二元结构最大导排能力随粗粒层增压值增加而增大，而随细粒层含水量增加而下降.（3）提出综合阻隔性能指数以量化注气条件下非饱和阻隔层对降雨入渗的阻隔效果.该研究成果开创性地利用土体气相作为阻隔层排水驱动力，可为边坡防护工程等领域提供科学依据.Abstract: Traditional surface hardening and impermeabilization measures for earthen slopes are prone to desiccation cracking due to rainfall infiltration, threatening engineering safety. The application of an capillary barrier layer (CBL) for protection can enhance the safety and stability of the project. However, its hydraulic conductivity decays with the long-term process of rainfall infiltration.To address the attenuation of capillary barrier strength in conventional unsaturated CBL during rainfall infiltration, this study proposes a method to enhance the infiltration resistance of the unsaturated barrier by pressurizing the coarse-grained layer from a coupled water-gas perspective. A series of physical model tests were conducted to investigate the effects of different rainfall intensities, initial CBL moisture contents, and coarse-grained layer pressurization levels on infiltration resistance. The main findings are as follows. (1) When the coarse-grained layer is pressurized (1-3 kPa), rainfall is entirely discharged along the interface between the fine-grained layer, the transition layer, and the coarse-grained layer, completely preventing rainfall breakthrough into the coarse-grained layer and significantly improving the barrier efficiency of the unsaturated CBL. (2) The steady-state lateral drainage rate of the binary structure increases with higher pressurization in the coarse-grained layer but decreases with increasing moisture content in the fine-grained layer. (3) A Comprehensive Barrier Efficacy Index (CBEI) is proposed to quantify the effectiveness of the unsaturated barrier under air injection conditions. This result innovatively establishes the soil gas phase as the drainage driving force in barrier layers, providing a scientific basis for slope protection engineering.
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Key words:
- coupled water-gas /
- rainfall infiltration /
- barrier effect /
- slope /
- engineering geology
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图 1 物理模型结构示意
1.供水系统；2.输水阀门；3.降雨模拟器；4.医用针头；5.供水支架；6.降雨支架；7.降雨运移路径；8.细粒层；9.混合层；10.粗粒层；11.双源稳压注气系统；12.注气通路；13.细粒层多孔排水板；14.细粒层/混合层排水搜集；15.粗粒层注气铜管网；16.粗粒层多孔排水板；17.增压气体运移路径；18.边坡层；19.粗粒层排水收集；20.边坡层排水收集；21.测压点
Fig. 1. Physical model of the CBL
图 3 注压与测压单元
a. 粗粒层注气铜管网; b. 细/粗粒层测压玻璃腔
Fig. 3. Pressure injection and pressure measuring unit
图 4 F0无粗粒层增压条件下二元结构降雨入渗示踪
Fig. 4. Tracking of rainfall infiltration in capillary barrier layer under F0 no pressurization condition in coarse-grained layer
图 5 F1粗粒层增压条件下二元结构降雨入渗示踪
Fig. 5. Tracking of rainfall infiltration in capillary barrier layer under F1 pressurization condition in coarse-grained layer
图 6 F1二元结构测压变化趋势
Fig. 6. Trend chart of pressure variation in capillary barrier layer for scheme F1
图 7 F3二元结构测压变化趋势
Fig. 7. Trend chart of pressure variation in capillary barrier layer for scheme F3
图 8 不同方案二元结构侧向排水速率趋势
Fig. 8. Lateral drainage rate trend chart of capillary barrier layer with different schemes
图 9 不同粗粒层注压条件下二元结构侧向排水速率
Fig. 9. Lateral drainage rate of capillary barrier layer under different coarse-grained layer injection pressure conditions
表 1 二元结构地层颗粒级配与主要物理参数
Table 1. Particle size distribution and physical parameters of the dual structure layer
土样 土壤类型 粒径分布(%) 干密度(g/cm3) 饱和渗透系数(cm/s) 混合比例 中砾 细砾 中砂 细砂 粉粒/黏粒 20~10 mm 10~5 mm 5~2 mm 0.50~0.25 mm 0.250~0.075 mm <0.075 mm 细粒层 粉砂 - - - 20 75 5 1.45 1.19×10-2 粗粒层 圆砾 30 20 50 - - - 1.7 1.05 UDL 圆砾 16.55 11.03 27.58 8.97 33.63 2.24 1.62 5.28×10-2 1∶1 边坡层 黏土 - - 1.6 2.8 95.6 1.6 5.3×10-6 
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表 2 试验方案
Table 2. Schemes of rainfall tests
方案名称 降雨强度
(10-4 cm/s)粗粒层增压值
(kPa)CBL初始含水量
(细粒层/混合层/粗粒层)降雨时间
(h)F0 3.64 0 低(7%/4.75%/2.5%) 10 F1 3.64 2~3 低(7%/4.75%/2.5%) 10 F2 3.64 2~3 高(F1完成后连续降雨试验) 10 F3 5.34 2~3 高(F2完成后连续降雨试验) 10 F4 3.64 1~2 高(F3完成后连续降雨试验) 10
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表 3 不同方案的细/粗粒层降雨排水特征参数
Table 3. Drainage paramters of different experimental schemes
方案 稳定增压强度(kPa) 细/粗粒层总排水体积(mL) 细/粗粒层稳定排水速率(mL/min) $ \mathrm{l}\mathrm{g}\frac{{K}_{c}}{{K}_{f}} $ $ {\eta }_{cb} $ F1 0.95 4 805.4/0 10.12/0 1.946 2.01 F2 0.81 5 526.8/0 9.56/0 1.97 F3 0.90 7 456.2/0 12.50/0 2.58 F4 0.72 5 526.5/0 9.38/0 1.76
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