Experimental study and evaluation on influence of deep alluvium foundation suffusion on deformation of soil skeleton in foundation of Luding Hydropower Station
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摘要: 泸定水电站因坝基覆盖层深部①层潜蚀诱发涌水险情，潜蚀过程中大量细颗粒持续流失能否诱发明显土骨架变形关系到电站自身、下游梯级电站及泸定县城的安全。土体颗粒级配、应力状态及细颗粒流失比例等均有可能影响土骨架变形，但其影响机制尚不清楚。为全面评价①层潜蚀对土骨架变形的影响，自行研制了可以模拟现场①层土体原始级配特征和应力状态的高应力、大直径的土体渗透稳定试验装置，建立了土骨架发生明显变形的判据，即潜蚀过程中试样累计体积应变大于等于1%时，表明土骨架已发生明显变形，提出了细颗粒运移比作为衡量细颗粒流失比例的评价指标。针对①层土体，开展了一系列极端不利水力条件下的渗流应力耦合潜蚀试验研究，重点探讨了颗粒级配、应力状态及细颗粒运移比对土骨架变形的影响规律。研究表明：所有试样潜蚀全过程的累计体积应变介于0.1%~0.49%，均小于1%，即①层土体中细颗粒大量甚至全部流失也不会诱发明显骨架变形，①层潜蚀诱发防渗墙开裂、折断，甚至突然溃坝的风险不大。颗粒级配显著影响细颗粒运移比、潜蚀临界和破坏坡降，5 mm以下颗粒含量越少，细颗粒运移比越大，潜蚀临界和破坏坡降越小；上覆压力对细颗粒运移比影响不大，但对潜蚀临界和破坏坡降影响显著，上覆压力越大，潜蚀临界和破坏坡降越大。研究成果为科学评价泸定水电站深部渗透稳定提供了重要依据，同时，也为其他类似工程安全评价提供了重要借鉴。Abstract: Suffusion of stratum ① in deep alluvium foundation of Luding Hydropower Station induces water gushing incident. Continuous migration of fine particles may induce skeleton deformation, and then it may threat the safety of Luding Dam, downstream cascade hydropower stations and Luding County. Particle size distribution of soil, stress and loss of fine particles may affect the skeleton deformation, but the detailed influence mechanism is not clear. In order to evaluate the influences of stratum ① suffusion on the skeleton deformation, a new high stress and large diameter soil suffusion apparatus which can simulate the stress and the characteristics of stratum ① particle size distribution is designed, and a criterion distinguishing the obvious skeleton deformation is proposed. When the volumetric strain during suffusion is greater than or equal to 1%, it indicates that the obvious skeleton deformation occurs. A new evaluation index called migration ratio of fine particles is proposed to weigh the loss of fine particles. A list of hydro-mechanical coupling suffusion tests under the extreme adverse hydraulic conditions are performed on stratum ① soil to investigate the influences of particle size distributions, stresses and losses of fine particles on the skeleton deformation. The results indicate that the cumulative volumetric strains during suffusion of all specimens range from 0.1% to 0.49%, and are lower than 1%, indicating that significant losses of fine particles in stratum ① soil do not induce obvious skeleton deformation, and suffusion of stratum ① soil cannot induce the cracks and breaking off of concrete cutoff wall and sudden dam break. The particle size distributions significantly affect the migration ratio of fine particles, hydraulic gradients initiating suffusion and failure. The less the percentage of finer than 5 mm, the larger the migration ratio of fine particles, and the lower the hydraulic gradients initiating suffusion and failure. The overburden pressure has a slight influence on the migration ratio of fine particles, but it significantly affects the hydraulic gradients initiating suffusion and failure. The larger the pressure, the larger the hydraulic gradients. The results may provide an important basis for the evaluation of deep seepage stability of Luding Dam, and an important reference for other similar projects.
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图 1 泸定水电站防渗墙端部附近潜蚀
Figure 1. Suffusion at bottom of cutoff wall in deep alluvium foundation of Luding Hydropower Station
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图 3 ① 层土体原始级配与等量替代后颗粒级配对比
Figure 3. Comparison between original and equivalent substitution grain-size distributions of stratum ① soil
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图 4 高应力、大直径土体渗透稳定试验装置
Figure 4. High stress and large-diameter soil suffusion apparatus
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图 7 粒径5 mm以下颗粒含量与潜蚀特征坡降的关系
Figure 7. Relationship between percentage finer than 5 mm and suffusion hydraulic gradients
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图 8 ① 层土体所处应力状态与潜蚀特征坡降的关系
Figure 8. Relationship between overburden pressure and suffusion hydraulic gradient
表 1 试验土体内部稳定性评价
Table 1 Evaluation of internal instability of test soils
土体颗粒级配曲线 内部稳定性评价结果 Kenney等[2] Wan等[3] Li等[4] ①层上包-平均线 内部不稳定((H/F)min=0.64 < 1) 内部不稳定(P=99.7%) 内部不稳定(当F > 15%时, H =10.8% < 15%) ①层平均线 内部不稳定((H/F)min=0.51 < 1) 内部不稳定(P=98.9%) 内部不稳定(当F < 15%时, (H/F)min=0.91 < 1.0；当F > 15%时, H=10.1% < 15%) ①层下包-平均2线 内部不稳定((H/F)min=0.38 < 1) 内部不稳定(P=99%) 内部不稳定(当F < 15%时, (H/F)min=0.86 < 1.0；当F > 15%时, H=6% < 15%) ①层下包-平均1线 内部不稳定((H/F)min=0.41 < 1) 内部不稳定(P=96.6%) 内部不稳定(当F < 15%时, (H/F)min=0.69 < 1.0；当F > 15%时, H=8.2% < 15%) ①层下包线 内部不稳定((H/F)min=0.51 < 1) 内部不稳定(P=90.2%) 内部不稳定(当F < 15%时, (H/F)min=0.93 < 1.0；当F > 15%时, H=8% < 15%) 
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表 2 ① 层土体潜蚀试验组合
Table 2 Suffusion tests of stratum ① soil
试验编号 上覆压力/MPa ①层土体 级配曲线 ρd/(g·cm-3) Dr ①-1 2.0 ①层平均线 2.241 0.85 ①-2 ①层下包线 2.106 0.85 ①-3 ①层上包-平均线 2.308 0.85 ①-4 ①层下包-平均1线 2.204 0.85 ①-5 ①层下包-平均2线 2.268 0.85 ①-6 0.5 ①层平均线 2.241 0.85 ①-7 1.0 ①-8 1.5 ①-9 2.5
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表 3 部分相关文献潜蚀试验成果统计
Table 3 Suffusion test results in literatures
文献 试验土样编号 试验类型 颗粒流失诱发的体积应变/% 是否发生明显骨架变形 Li[26] FR8-25-D0 有侧限试验 2.6 是 FR8-25-D1 0.9 是 FR8-25-D2 1.6 是 FR8-50-D 0.7 是 FR8-100-D 4.7 是 FR8-200-D 3.9 是 FR7-25-D 3.4 是 FR7-50-D 0.98 是 FR7-100-D 1.6 是 FR7-150-D 0.6 是 FR7-150-U 3.0 是 HF03-25-U 0.23 否 HF03-50-U 0.14 否 Moffat等[27] T-0-25-D 有侧限试验 7.0 是 T-5-175-U 5.0 是 C-20-50-U 1.0 是 C-30-80-U 2.4 是 Ke等[18] 35E-50 无侧限试验 2.4(轴向应变)
3.9(体积应变)是 35E-50-R 3.8 是 35E-100 2.0(轴向应变)
3.2(体积应变)是 35E-100-R 3.6 是 35E-200 1.8(轴向应变)
2.8(体积应变)是 35E-200-R 2.8 是 25E-50 1.4 是 15E-50 0.05 否 Chang等[19] GS-C-6 无侧限试验 6.5(轴向应变)，未给出体积应变 是 GS-I-1 0.14(轴向应变)
0.26(体积应变)否 Sibille等[20] Test N1 有侧限试验 3.9 是 Test N2 4.9 是 Test N3 5.0 是 Test N4 7.7 是 Test N5 5.7 是 Test N6 4.8 是 Test N7 3.9 是 Test N8 1.7 是 Slangen等[21] 6.0GB35-100 无侧限试验 0.62(轴向应变)
1.54(体积应变)是 6.0GB35-100(R) 0.7(轴向应变)
2.19(体积应变)是 6.5GB35-50 0.14(轴向应变)
1.89(体积应变)是 6.5GB35-100 0.04(轴向应变)
1.68(体积应变)是 4.8GB20-50 0(轴向应变)
0.12(体积应变)否 4.8GB20-50(R) 0.01(轴向应变)
0.03(体积应变)否 Prasomsri等[22] WE_F32.5 无侧限试验 1.15 是 WE_F35 0.09(轴向应变)
0.74(体积应变)是 WE_F15 0.01 否 WE_F20 0.02 否 WE_F25 0.01 否 WE_F30 0.01 否 田大浪等[28] G-US-30 有侧限试验 0.83 否 G-US-35 0.57 否 G-US-40 1.47 是 G-CS-30 0.51 否 G-CS-35 0.32 否 G-CS-40 0.93 是 樊茹玉[29] B3-35 有侧限试验 0.04 否 C5-15 0.02 否 C7-20 0.01 否 C8-20 0.01 否 D9-30 0.1 否 D12-25 0.01 否 A1-15 0 否 B2-20 0 否 C4-15 0 否 C6-10 0.01 否 D10-5 0 否 D11-15 0 否
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表 4 ① 层土体潜蚀试验成果统计
Table 4 Suffusion test results of stratum ① soil
试验编号 土体名称 上覆压力/MPa icr if k/(cm·s-1) 细颗粒运移比/% εv/% ϵv潜蚀/% ϵv潜蚀ϵv/% 是否发生骨架变形 最大平均/局部坡降 ①-1 ①层上包-平均线 2.0 2.41 4.81 6.0×10-5 5.4 2.4 0.27 11.25 否 16.5/95.1 ①-2 ①层平均线 2.0 1.88 3.57 1.4×10-3 7.1 3.8 0.20 5.26 否 16.7/22.5 ①-3 ①层下包-平均2线 2.0 0.82 2.17 1.0×10-2 11.5 2.6 0.49 18.85 否 15.6/48.8 ①-4 ①层下包-平均1线 2.0 0.47 1.70 1.4×10-1 40.6 4.3 0.10 2.33 否 13.2/35.1 ①-5 ①层下包线 2.0 0.06 1.19 1.9 43.3 4.3 0.16 3.72 否 1.2/7.4 ①-6 ①层平均线 0.5 0.16 0.55 5.6×10-2 15.8 1.1 0.20 17.70 否 4.2/17.6 ①-7 ①层平均线 1.0 0.54 1.46 1.1×10-2 10.6 2.5 0.20 7.91 否 3.6/38.4 ①-8 ①层平均线 1.5 1.09 2.06 2.2×10-3 15.8 2.5 0.15 6.12 否 4.4/20.1 ①-9 ①层平均线 2.5 2.08 3.93 1.2×10-3 18.1 4.5 0.25 5.57 否 4.4/15.4
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