Influences of construction defects of concrete cutoff walls on evolution laws of their leakage dissolution
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摘要: 渗流作用下防渗墙施工缺陷对其渗透溶蚀演化进程影响较显著，为探究防渗墙相邻槽段搭接不良和墙底分叉对其渗透溶蚀的影响机制，结合流体和化学动力学相关理论，建立含施工缺陷的混凝土防渗墙渗透溶蚀耦合分析模型。结合某土工膜防渗砂砾石坝，研究两种缺陷形式下防渗墙中钙离子浓度、孔隙率及渗流特性变化规律。防渗墙钙离子浓度随服役年份增长不断降低，且缺陷越严重，浓度越低；孔隙率随服役年份呈指数型增长，服役100 a后孔隙率增大约1.83倍；防渗性能随服役年份、接缝宽度和分叉高度的增长而减弱，相比防渗墙完好工况，当接缝宽度3.0 cm或分叉高度为3 m时，服役100 a后防渗墙等效渗透系数分别增大了8.20倍，40.38倍，大坝总渗流量分别增大了4.49倍，5.81倍。研究成果可为土石坝工程长效服役性能评估提供理论支撑。Abstract: Under the action of seepage, the construction defects of cutoff walls have a significant impact on the evolution process of their leakage dissolution. In order to investigate the influence mechanism of poor overlapping of the adjacent groove sections and the bottom bifurcation of the cutoff walls, based on the relevant theories of fluid dynamics and chemical dynamics, a coupling analysis model for leakage dissolution of concrete cutoff walls with construction defects is proposed. Based on a sand gravel dam project with geomembrane anti-seepage measure, the variation laws of calcium ion concentration, porosity and seepage characteristics of the concrete cutoff walls under two types of defects are revealed. The calcium ion concentration of the cutoff walls decreases with the increase of service year, and the more serious the defects are, the lower the concentration of calcium ion is. The porosity increases exponentially with the service year, and the maximum porosity increases by about 1.83 times after 100 service years. The anti-seepage performance of the cutoff walls decreases with the increase of the service year, joint width and bifurcation height of the construction defects. Compared with the intact condition of the cutoff walls, when the joint width is 3.0 cm or the bifurcation height is 3 m, the equivalent permeability coefficient of the cutoff walls increases by 8.20 times and 40.38 times respectively after 100 service years, and the total seepage flow of the dam body and dam foundation increases by 4.49 times and 5.81 times, respectively. The research results can provide theoretical support for evaluating the long-term service performance of earth-rock dams.
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Keywords:
- concrete cutoff wall /
- construction defect /
- leakage dissolution /
- porosity /
- seepage characteristic
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图 1 某重力坝整体计算模型示意图
Figure 1. Schematic diagram of computational model for a gravity dam
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图 2 典型服役年份下重力坝基底扬压力演化曲线
Figure 2. Evolution curves of base uplift pressure of gravity dam for typical service years
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图 3 典型服役年份下坝基渗流量演化曲线
Figure 3. Evolution curves of seepage flow of dam foundation for typical service years
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图 5 防渗墙施工缺陷模拟示意图
Figure 5. Schematic diagram of simulating construction defects of cutoff wall
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图 7 防渗墙中平均钙离子浓度变化曲线
Figure 7. Variation curves of average calcium ion concentration of cutoff wall
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图 8 典型工况下防渗墙孔隙率分布
Figure 8. Distribution of porosity of cutoff wall under typical working conditions
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图 9 各工况下防渗墙平均孔隙率变化曲线
Figure 9. Variation curves of average porosity of cutoff wall under various conditions
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图 10 防渗墙等效平均渗透系数变化曲线
Figure 10. Variation curves of average permeability coefficient of cutoff wall
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图 11 初始时刻坝体和坝基水位等值线分布
Figure 11. Distribution of water level contour of dam body and foundation at initial time
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图 12 各工况下大坝渗流量变化曲线
Figure 12. Variation curves of seepage flow through dam under various conditions
表 1 各材料分区计算参数
Table 1 Parameters for different material zones
材料 θ0 k0/(m·s-1) D0/(m2·s-1) 化学反应动力学参数 A/(mol/(L·s)) n Ksp 常规混凝土 0.08 5.20×10-9 1.00×10-9 1.00×10-8 4.50 5.50×10-6 二级配混凝土 0.08 2.00×10-8 1.00×10-9 1.00×10-8 4.50 5.50×10-6 三级配混凝土 0.08 5.00×10-10 1.00×10-9 1.00×10-8 4.50 5.50×10-6 防渗帷幕 0.08 1.50×10-8 1.00×10-9 1.00×10-8 4.50 5.50×10-6 基岩 0.10 8.00×10-5 1.00×10-9 — — — 坝体排水孔 0.50 2.50×10-3 1.00×10-9 — — — 坝基排水孔 0.50 2.50×10-3 1.00×10-9 — — — 
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表 2 计算模型渗透溶蚀参数
Table 2 Leakage dissolution parameters of model
材料 k0/(m·s-1) θ0 D0/(m2·s-1) 化学反应动力学参数 A/((mol/(L·s)) n Ksp 防渗墙 1.00×10-9 0.12 1.00×10-9 1.00×10-8 4.50 5.50×10-6 砂砾石填筑料 2.40×10-5 0.30 1.00×10-9 — — — 截流戗堤 1.00×10-6 0.25 1.00×10-9 — — — 上游闭气料 3.00×10-7 0.20 1.00×10-9 — — — 复合土工膜 3.50×10-13 — — — — — 排水棱体 2.00×10-3 0.50 1.00×10-9 — — — 砂卵砾石层 4.60×10-4 0.40 1.00×10-9 — — — 粉砂质泥岩 1.10×10-6 0.20 1.50×10-9 — — —
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表 3 计算工况表
Table 3 Design of calculation conditions
工况 服役年份/a 接缝宽度/cm 分叉高度/m 水位/m D-1 0~100 — — 上游：1880.50下游：1862.31 D-2 0~100 1.0 — D -3 0~100 2.0 — D -4 0~100 3.0 — D -5 0~100 — 1.0 D-6 0~100 — 2.0 D -7 0~100 — 3.0
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