Evolution laws of hydraulic parameters of red clay covers and design of seepage prevention
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摘要: 以红黏土为对象，通过室内单元体并结合填埋场现场原位试验，从建设施工和建成后长期服役两个不同时间尺度对土质覆盖层水力参数开展了5 a的跟踪监测；分析对比了从实验室到现场、从建设施工到建成长期服役水力参数的劣化衰减规律。结果表明：①5 a长期服役中，无植被红黏土覆盖层入渗系数从10-7 cm/s增大到10-3 cm/s，增大4个数量级；有植被条件入渗系数从10-7 cm/s增大到10-6 cm/s，增大1个数量级。②自然气候长期服役覆盖层中大孔隙逐渐增多，降雨雨强过大（如暴雨）导致土质覆盖层防渗能力和储水能力下降。工程设计中应根据当地降雨参数进行适当放大调整。③自然气候下经历反复吸、脱湿滞回循环，土质覆盖层的储水能力与降雨前土层吸湿起点（或初始吸力）和吸湿路径有关。采用室内吸湿起点初始吸力-1500 kPa的主吸湿曲线设计偏于保守，结果相对安全。Abstract: Through the laboratory unit and in-situ tests in landfill site, the hydraulic parameters of red clay soil covers have been monitored for more than five years on two different time scales of construction and long-term service. The degradation laws of hydraulic parameters from laboratory to field as well as from construction to long-term service are analyzed and compared. The results show that: (1) During the five years of long-term service, the infiltration coefficient of red clay covers without vegetation changes from 10-7 cm/s to 10-3 cm/s, with the variation fluctuated by 5 orders of magnitude, and the infiltration coefficient with vegetation is 2 orders of magnitude from 10-7 cm/s to 10-6 cm/s. (2) The macropores in the covers gradually increase in the long-term service of natural climate, and the excessive rainfall (such as rainstorm) leads to the decrease of water storage capacity of soil overburden. In engineering design, it should be adjusted according to the local rainfall parameters. (3) With the repeated cycles of moisture absorption and desorption, the water storage capacity is related to the initial matrix suction and path of moisture absorption before rainfall. The design of the main moisture absorption curve with the starting point of laboratory moisture absorption (initial matric suction) of -1500 kPa is conservative, and the results are relatively safe.
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图 1 土质封场覆盖层水分存储-释放循环防渗机理物理模型
Figure 1. Model for seepage prevention mechanism of water storage-release cycle in soil cover
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图 2 现场#1、#2试验区张力计和TDR埋设
Figure 2. Embedment of tensiometer and TDR in test areas No. 1 and 2
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图 5 现场无植被2015—2020年服役期红黏土入渗曲线
Figure 5. Infiltration curves of red clay without vegetation from 2015 to 2020
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图 6 现场有植被2015—2020年服役期红黏土入渗曲线
Figure 6. Infiltration curves of red clay with vegetation from 2015 to 2020
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图 7 2015—2020年各年有植被与无植被条件渗透系数对比
Figure 7. Comparison of permeability coefficients with and without vegetation from 2015 to 2020
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图 8 自然气候下2015—2020年服役期红黏土土水特征曲线（脱湿过程）
Figure 8. Soil-water characteristic curve of red clay in natural climate from 2015 to 2020 (moisture desorption)
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图 9 自然气候下2015—2020年服役期红黏土土水特征曲线（吸湿过程）
Figure 9. Soil-water characteristic curves of red clay in natural climate from 2016 to 2020 (moisture absorption process)
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图 10 2015—2020年间各年土水特征曲线变化分布范围图
Figure 10. Envelope map of distribution range of soil-water characteristic curves from 2015 to 2020
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图 11 体积压力板仪测试吸湿土水特征曲线与大孔隙“瓶颈（或墨水瓶）效应”[16]
Figure 11. Soil-water characteristic curve of hygroscopic soil measured by volume pressure plate apparatus and "bottleneck effect" of macropores
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图 12 长期服役原状红黏土有效储水率θa
Figure 12. Effective water storage rate (θa) of undisturbed red clay in long-term service
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图 13 现场自然降雨气候下红黏土土水特征点（第一场雨）
Figure 13. Soil-water characteristic points of red clay in natural rainfall climate (the 1st rain)
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图 14 现场自然降雨气候下红黏土土水特征点（第二场雨）
Figure 14. Soil-water characteristic points of red clay under natural rainfall climate (the 2nd rain)
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图 15 土水特征曲线滞回圈内各曲线定义和示意图[17]
Figure 15. Definition and schematic diagram of each curve in hysteresis loop of soil-water characteristic curves
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图 16 现场红黏土在两场自然降雨气候条件下的土水特征响应
Figure 16. Soil-water characteristic responses of red clay in two natural rainfalls
表 1 现场长期监测试验工况设计
Table 1 Design of field long-term monitoring tests
测试区 位置 植被条件 有/无仪器埋设 埋设深度 #1 4级平台 无 张力计、水分TDR 15，45 cm（各2支） #2 5级平台 有 张力计、水分TDR 15，45 cm（各2支） #3 6级平台 有、无（约一半） 无 无 
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表 2 现场和室内（实验室）开展的测试项目与测试方法
Table 2 Items and methods of field and indoor (laboratory) tests
现场 仪器和方法 室内 仪器和方法 现场覆盖层红黏土体积含水率和基质吸力监测 TDR/张力计联合监测 重塑红黏土基本物理性质和参数 室内土工
常规测试现场覆盖层红黏土双套环原位入渗 下文详述 重塑土室内变水头饱和渗透系数 室内变水头渗透试验 现场降雨等气候条件 翻斗式雨量计和气象信息网 室内重塑土的土水特征曲线 体积压力板仪（0~-1500 kPa） 现场覆盖层红黏土裂缝观测 详见文献[8] 现场取回的覆盖层原状土土水特征曲线 体积压力板仪（0~-1500 kPa）
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表 3 红黏土基本物理力学参数
Table 3 Basic physical and mechanical parameters of red clay
天然含水率/% 天然密度/(g·cm-3) 相对质量密度 液限/% 塑限/% 最优含水率/% 最大干密度/(g·cm-3) 压缩系数a1-2/MPa-1 内摩擦角/(°) 黏聚力/kPa 孔隙比 31.5 1.67 2.71 70.65 40.32 23.8 1.61 0.21 14.5 18.7 1.13
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表 4 自然气候下2015—2020年服役期红黏土土水特征曲线V-G模型拟合参数（脱湿过程）
Table 4 Fitting parameters of V-G model of soil-water characteristic curves of red clay in natural climate from 2015 to 2020 (moisture desorption process)
服役时间 饱和含水率θs/% 残余含水率θr/% 与进气值有关的倒数a 脱水速率n 建造之初(2015年) 49.05 18.78 2.59 1.01 第1年
(2016年)50.27 20.12 6.31 1.16 第2年
(2017年)50.31 19.74 8.52 1.19 第3年
(2018年)52.41 22.09 13.33 1.58 第4年
(2019年)53.95 19.47 10.86 1.55 第5年
(2020年)51.67 20.97 11.07 1.60
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表 5 自然气候下2015—2020年服役期红黏土土水特征曲线V-G模型拟合参数（吸湿过程）
Table 5 Fitting parameters of V-G model of soil-water characteristic curves of red clay in natural climate from 2015 to 2020 (moisture absorption process)
服役时间 饱和含水率θs/% 残余含水率θr/% 与进气值有关的倒数a 脱水速率n 建造之初(2015年) 34.10 18.78 43.30 1.55 第1年
(2016年)37.10 20.12 27.16 1.51 第2年
(2017年)36.08 19.74 30.63 1.54 第3年
(2018年)32.94 19.74 32.15 1.75 第4年
(2019年)36.10 22.09 42.47 2.11 第5年
(2020年)32.10 20.97 28.98 1.90
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表 6 长期服役原状红黏土有效储水率θa
Table 6 Effective water storage rate (θa) of undisturbed red clay in long-term service
水力条件 时间/a 田间持水率θc/% 枯萎持水率θr/% 有效储水率θa/% 脱湿 0 36.08 18.78 17.30 1.07 37.15 20.12 17.03 2.03 37.85 19.74 18.11 3.0 39.05 22.09 16.96 4.1 38.35 19.47 18.88 5.0 37.65 20.97 16.68 吸湿 0 31.00 18.78 12.22 1.07 31.75 20.12 11.63 2.03 37.15 19.74 17.41 3.0 32.94 22.09 10.85 4.1 29.06 19.47 9.59 5.0 28.43 20.97 7.46 *考虑测试过程中天平称量最小精度、体积压力板仪滴定管肉眼读数最小精度和测试加压压力表精度等，有效储水率θa的误差率为1.2%。
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