Effect of Angle and Lithology on Infiltrating to Fine/Coarse Dual-Structure Slope under Rainfall Condition
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摘要: 土质边坡在降雨条件下易形成滑坡灾害，采用表面硬化等传统方法防止降雨入渗边坡时，存在运行过程中表面开裂导致其防护功能失效的问题.从生态优先与长期有效性角度，采用上细/下粗的非饱和二元结构地层阻隔降雨入渗防护边坡.利用系列物理模型试验，研究降雨条件下不同边坡角度（10°、20°、30°和40°）与不同地层岩性特征（亚砂土/粗砂、亚砂土/砂砾、亚砂土/圆砾和亚砂土/角砾）对其阻隔降雨入渗的影响，并提出了细/粗二元结构地层抑制降雨入渗的综合阻隔能力的评估方法.结果表明：（1）采用亮蓝示踪剂可直接观测非饱和二元结构地层对降雨入渗边坡的阻隔过程.（2）二元结构的综合阻隔能力随粗粒层粒径和不均匀系数的增加而增强.（3）无降雨条件下，增加边坡角度能促进二元结构地层排水；在降雨条件下，亚砂土/砾砂二元结构粗粒层稳定排水强度和降雨入渗综合阻隔能力均随边坡角度呈先增加后减少的规律，建议最优边坡角度范围为25°~27°.研究成果对边坡稳定治理具有重要参考价值.Abstract: The occurrence of landslide is mainly caused by rainfall. Traditional treatment methods, such as spraying concrete on the surface of landslide to inhibit the penetration of rainfall on soil slopes, will fail during long-term operation resulted from failures, leading to landslides. Therefore, considering the ecological function and the long-term effectiveness of the reclamation method, this paper adopts the dual-structure of unsaturated capillary barrier layer (CBL) with fine/coarse lithology to prevent rainfall from infiltrating into the soil slope. The effects of slope (10°, 20°, 30°, 40°) and lithological characteristics (sandy loam/coarse sand, sandy loam/gravel sand, sandy loam/pebble and sandy loam/breccia) on the infiltration of rainfall into the soil slope were investigated through a series of physical model tests. Furthermore, a new method is defined to evaluate the total capacity of the capillary barrier (CCB) of the fine/coarse bilayer. The research results show that: (1) The process of preventing rainfall from infiltrating the soil slope with brilliant blue FCF (C.I.42090) dye tracer can be observed visually. (2) CCBS increases with the increase of coarse particle diameter, which is also related to the shape of pores and coarse particles, that is, the drainage efficiency of breccia with the same particle composition is higher than that of boulders. (3) The larger the slope angle of the four types of CBLS soil, the higher the drainage speed of CBL after rainfall, and the stable drainage strength and the total barrier capacity of loam/gravel sand CBL with rainfall intensity of 4.73×10-4 cm/s, could increase firstly and then decrease with the increased slope angles. It is suggested that the design slope of CBLS is 25°-27°, in order to achieve the optimal total barrier capacity. The results of this study have a certain reference value for future landslide control.
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Key words:
- slope /
- dual-structure /
- unsaturated seepage /
- rainfall /
- infiltrated control /
- disaster geology
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图 1 非饱和边坡阻隔层物理模型试验结构
1.边坡体；2.粗粒层；3.细粒层；4.降雨支架；5.降雨器水位控制阀；6.针头；7.降雨模拟器腔体；8.供水系统；9.供水系统支架；10.碎石层防护层；11.排水侧多孔板；12.细粒层排水收集；13.粗粒层排水收集；14.边坡底部排水收集
Fig. 1. Physical model of the CBL
图 3 亚砂土/角砾二元结构阻隔降雨入渗示踪
Fig. 3. Tracing of rainfall infiltration for the dual-structure of sub-sandy soil/angular sand
图 4 不同岩性的二元结构地层排水速率（边坡角度30°）
Fig. 4. Coarse-grained drainage rate of the four dual-structure layers with the angle of 30°
图 5 CBL综合阻隔能力与粗粒层不均匀系数的关系（30°）
Fig. 5. Relationship curve between CBL comprehensive barrier capacity and coarse-grained layer non-uniformity coefficient (30°)
图 6 无降雨条件下边坡角度增加（20°增至30°）对CBL持续排水的影响
a.亚砂土/粗砂；b.亚砂土/砂砾；c.亚砂土/角砾；d.亚砂土/圆砾
Fig. 6. Coarse-grained drainage of the four CBLs due to the increased angle of the slope from 20° to 30°
图 7 不同边坡角度的亚砂土/砂砾粗粒层排水效果
Fig. 7. Coarse-grained drainage of sub-sandy soil/gravel layers with different slope angles
图 8 亚砂土/砂砾粗粒层排水占降雨百分比与边坡角度关系
Fig. 8. The relationship of drainage percentage of coarse grain layer for sub-sandy soil/gravel structure vs. the slope angle
表 1 二元结构土层颗粒级配及主要物理参数
Table 1. Particle size distribution and physical parameters of the dual-structure layer
土样 土壤类型 粒径分布（%） d50 Cu 干密度 饱和导水系数 粗砾 中砾 细砾 粗砂 中砂 细砂 粉粒/黏粒 40~20 mm 20~5 mm 5~2 mm 2~0.5 mm 0.5~0.25mm 0.25~0.75mm < 0.075 mm (mm) (d60/d10) (g/cm3) (cm/s) 细粒土 亚砂土 - - - 15 20 45 20 0.095 1.7 1.45 7.65×10-3 粗粒土1 粗砂 - - - 60 25 15 - 0.57 5.0 1.70 1.96×10-2 粗粒土2 砾砂 - 20 20 50 10 - - 1.4 10.2 1.70 0.102 粗粒土3 圆砾 15 25 50 10 - - - 3.7 13.5 1.70 0.638 粗粒土4 角砾 15 25 50 10 - - - 24 22.9 1.70 1.60 边坡土 黏土 - - - - 1.6 2.8 95.6 0.005 4.3 1.60 2.53×10-6 注：d50、d60和d10为在土的粒径累计曲线上过筛重量分别占50%、60%和10%的粒径；Cu为不均匀性系数. 
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表 2 试验方案
Table 2. Schemes of rainfall tests
方案 阻隔层地层岩性 降雨强度(10-4 cm/s) 降雨持续时间(min) 边坡倾角 染色示踪 F1-1 亚砂土/粗砂 4.73 480 20° - F1-2 660 30° - F2-1 亚砂土/砾砂 4.73 480 10° - F2-2 480 20° - F2-3 660 30° 是 F2-4 660 40° - F3-1 亚砂土/圆砾 4.73 510 20° - F3-2 660 30° - F4-1 亚砂土/角砾 4.73 510 20° - F4-2 660 30° 是
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表 3 边坡角度为30°时不同岩性二元结构的综合阻隔能力
Table 3. Barrier capacity of different dual-structure layers with the angle of 30°
方案 阻隔层地层岩性 降雨持续时间(min) 粗粒层累积排水量(cm3) $ \mathrm{l}\mathrm{o}\mathrm{g}\frac{{K}_{\mathrm{C}}}{{K}_{\mathrm{p}}} $ $ \eta $ F1-2 亚砂土/粗砂 660 27 401 3.89 3.82 F2-3 亚砂土/砾砂 660 30 420 4.60 4.60 F3-2 亚砂土/圆砾 660 30 029 5.40 5.33 F4-2 亚砂土/角砾 660 32 284 6.80 6.75
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表 4 边坡角度为20°时不同岩性二元结构的综合阻隔能力
Table 4. Barrier capacity of different dual-structure layers with the angle of 20°
方案 阻隔层地层岩性 降雨持续时间(min) 粗粒层累积排水量(cm3) $ \mathrm{l}\mathrm{o}\mathrm{g}\frac{{K}_{\mathrm{C}}}{{K}_{\mathrm{p}}} $ $ \eta $ F1-1 亚砂土/粗砂 480 20 544 3.89 3.73 F2-2 亚砂土/砾砂 480 22 053 4.60 4.49 F3-1 亚砂土/圆砾 510 23 291 5.40 5.31 F4-1 亚砂土/角砾 510 23 351 6.80 6.70
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表 5 不同边坡角度亚砂土/砂砾二元结构的综合阻隔能力
Table 5. Barrier capacity of sub-sandy soil/gravel structure with different angles
方案 边坡角度 降雨持续时间(min) 粗粒层累积排水量（cm3） $ \mathrm{l}\mathrm{o}\mathrm{g}\frac{{K}_{\mathrm{C}}}{{K}_{\mathrm{p}}} $ 二元结构综合阻隔能力 F2-1 10° 480 20 386 4.60 3.82 F2-2 20° 480 22 053 4.60 4.14 F2-3 30° 540 30 420 4.60 4.15 F2-4 40° 660 18 266 4.60 3.72
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