Evolution of hydraulic parameters of red clay cover with service time
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摘要: 红黏土具有高液（塑）限、低渗透、中—低压缩性和较高的力学强度,在西南喀斯特地区广泛用于路基、土石坝、各类尾矿和垃圾填埋封顶覆盖等防渗工程。对红黏土开展了实验室和现场水力参数对比测试；在填埋场建设了红黏土覆盖层试验区并开展了自然气候条件下的长期服役水力参数监测；分析对比了有、无植被红黏土水力参数的不同变化。结果表明：①红黏土饱和渗透系数在10-7 cm/s量级,渗透性低,防渗性能好；有效储水率约18.8%,与粉土—粉质黏土相当,储水能力好。②现场大体量大范围施工而实验室精细制样导致两者土样结构有显著差异。干密度相近时,现场土饱和入渗系数比室内重塑土大36.62%,防渗设计中应充分考虑实验室到现场间压实土防渗性能的“打折”现象。③在2.0年的长期服役中,无植被红黏土覆盖层在日照、降雨循环作用下因土层开裂导致渗透系数较建设之初最大增加2.9×104倍；有植被时渗透系数较建设之初或减小或增加,最大增加10倍,且与植被生长状态有关。有、无植被红黏土入渗系数和开裂情况对比表明：植被对土质覆盖层细粒土因日照-降雨气候作用导致防渗性能的劣化有明显的抑制作用。Abstract: Red clay is characterized by high liquid (plastic) limit, low permeability, medium-low compressibility and highmechanical strength. It is widely used in anti-seepage projects such as roadbed, earth dam, tailings and landfill cover in karst areas of southwest China. The hydraulic parameters of the red clay are tested in laboratory and field. The test area of red clay cover is built in landfill site, and the long-term service hydraulic characteristic parameters are monitored in natural climate. The hydraulic parameters of the red clay cover with and without vegetation are analyzed. The results show that: (1) The saturated permeability coefficient of the red clay is 10-7 cm/s with low permeability and good anti-seepage performance. The effective water storage rate is about 18.8%, which is equivalent to that of silt and silty clay, and the water storage capacity is acceptable. (2) The large-scale construction in the field and the fine sample preparation in the laboratory lead to significant differences in the structure of the two soil samples. With similar dry density, the saturated permeability coefficient of field red clay is 36.62% higher than that of laboratory remold red clay. The "discount" phenomenon of anti-permeability of compacted soil from laboratory to site should be fully considered. (3) In long-term service of 2.0 years, the permeability of the red clay cover without vegetation increases by the maximum increase of 5×103 times that at the beginning of construction due to soil cracking under the sun-rainfall cycle. With vegetation, the permeability increases or decreases compared with that at the beginning of construction (the maximum increase of 10 times) and is related to the vegetation growth state. It is shown that the vegetation has an obvious inhibitory effect on the permeability deterioration of fine-grained soil due to sun-rainfall cycles.
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Keywords:
- landfill /
- cover /
- clay /
- long-term service /
- hydraulic parameter /
- evolution law /
- vegetation root system
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图 5 不同压实度（干密度）重塑红黏土土水特征曲线
Figure 5. Soil water characteristic curves of remolded red clay soil with different degrees of compaction (dry densities)
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图 7 近似干密度室内重塑和现场红黏土土水特征曲线对比
Figure 7. Comparison of soil-water characteristic curves in laboratory remoulding and field red clay with approximate dry density
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图 9 不同测试方法和环境红黏土土水特征点对比
Figure 9. Comparison of soil-water characteristic points of red clay under different environments by different test methods
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图 10 现场红黏土自然降雨气候下的土水特征点
Figure 10. Soil-water characteristic points of red clay under natural rainfall climate
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图 11 自然气候条件下红黏土不同服役时间土水特征曲线
Figure 11. Soil-water characteristic curves of red clay in different service time under natural climate
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图 12 自然气候条件下不同服役时间红黏土的土水特征曲线
Figure 12. Soil-water characteristic curves of red clay in different service time under natural climate (dehydration process)
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图 13 自然气候条件下不同服役时间红黏土的土水特征曲线（吸湿过程）
Figure 13. Soil-water characteristic curves of red clay in different service time under natural climate (adding moisture process)
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图 14 自然气候长期服役有植被条件下覆盖层红黏土结构
Figure 14. Structure of red clay cover with vegetation in long-term service in natural climate
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图 15 现场试验区建造之初双套环入渗系数曲线
Figure 15. Infiltration curves of double rings at beginning of construction of field test area
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图 16 现场无植被条件不同服役时间红黏土入渗曲线
Figure 16. Infiltration curves of double rings of red clay in different service time without vegetation on site
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图 17 长期服役过程中现场探洞观测无植被条件红黏土裂缝
Figure 17. Observation of cracks in red clay without vegetation by on-site exploration during long-term service
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图 18 现场有植被条件不同服役时间红黏土入渗曲线
Figure 18. Infiltration curves of double rings of red clay in different service time with vegetation on site
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图 19 长期服役过程中现场探洞观测有植被条件红黏土裂缝
Figure 19. Observation of cracks in red clay with vegetation by on-site exploration during long-term service
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表 1 现场和室内开展的试验测试项目
Table 1 Items of field and laboratory tests
室内试验 现场试验 重塑红黏土的基本物理性质和参数 现场覆盖层红黏土体积含水率和基质吸力长期监测 室内重塑土变水头饱和渗透系数 现场覆盖层双套环原位入渗试验 室内重塑土的土水特征曲线 现场降雨量等气候条件和植被参数 从现场取回的覆盖层原状土土水特征曲线 现场覆盖层红黏土裂缝观测 
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表 2 国内外类似研究覆盖层细粒土土水特征值
Table 2 Characteristic values of fine soil of cover in similar studies
文献中土类名称 土类划分 饱和含水率θs/% 田间持水率θc/% 残余含水率θm/% 有效储水率θa/% silty sand（Khire[22]） 粉质黏土 42.0 28.3 10.4 17.9 Fine soil（Morris[23]） 粉质黏土 40.0 30.2 8.0 22.0 Silt loam（Scanlon[24]） 粉质黏土 47.0 27.4 8.0 19.5 钱塘江粉土（邓林恒[20]） 粉土 44.8 32.0 8.0 24.0 细粒土（Ng C W W[20]） 粉土 43.1 30.0 8.0 22.0 C类黏性黄土（焦卫国等[5]） 粉质黏土 47.1 34.6 12.1 22.5 本文红黏土 黏土 49.41 39.85 21.09 18.8 注： *上述土储水能力指标因干密度不同而略有差异,“土类划分”为根据中国GB50007—2011标准进行的分类。
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表 3 自然气候条件下不同服役时间红黏土的土水特征曲线V-G模型拟合参数和有效储水率（脱湿过程）
Table 3 Fitting parameters of V-G model and effective water storage rates of SWCCs of red clay in different service time under natural climate (dehydration process)
时间 θs θr a n θa 现场初始 49.05 18.78 2.59 1.01 16.30 现场第一年 50.27 20.12 6.31 1.16 17.03 现场第二年 50.31 19.74 8.52 1.19 18.11
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表 4 自然气候条件下不同服役时间红黏土的土水特征曲线V-G模型拟合参数和有效储水率（吸湿过程）
Table 4 Fitting parameters of V-G model and effective water storage rates of SWCCs of red clay in different service time under natural climate (adding moisture process)
时间 θs θr a n θa 现场初始 34.1 18.78 43.30 1.55 12.22 现场第一年 37.1 20.12 27.16 1.51 11.81 现场第二年 36.08 19.74 30.63 1.54 12.01
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表 5 现场无植被红黏土不同服役时间稳定入渗系数
Table 5 Infiltration coefficients of red clay without vegetation in long-term service
时间 干密度/(g·cm-3) 稳定入渗系数kf/(cm·s-1) 建造之初（0.0 a） 1.37 1.94×10-7 半年（0.51 a） 1.37 2.38×10-6 1年（1.07 a） 1.37 5.65×10-3 2年（2.03 a） 1.37 8.11×10-5 注： 测试方法现场双套环。
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表 6 现场有植被红黏土稳定入渗系数随服役时间变化规律
Table 6 Infiltration coefficients of red clay with vegetation in long-term service
时间 干密度/(g·cm-3) 稳定入渗系数kf/(cm·s-1) 建造之初（0.0 a） 1.37 1.94×10-7 半年（0.51 a） 1.37 1.78×10-7 1年（1.07 a） 1.37 7.49×10-7 2年（2.03 a） 1.37 1.03×10-6 注： 测试方法现场双套环。
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