| Civil Engineering, Transportation Engineering |
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| Centrifuge test modeling of impact of sediment consolidation on contaminant transportation |
| ZHENG Jian1,2,LI Yu chao1,2,CHEN Yun min1,2 |
| 1. MOE Key Laboratory of Soft Soils and Geoenvironmental Engineering, Zhejiang University, Hangzhou 310058, China; 2. Institute of Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China |
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Abstract The impact of sediment consolidation induced by capping on velocity of contaminant migration and outflow amount was analyzed in order to study the process of consolidation of sediment and the pore water release accelerate contaminant transport through the cover via advection in sediment capping technology. The special and temporal scaling effects of centrifuge tests were used, and the tests were simulated using numerical method. 1) The relationship between chloride mass concentration in the overlying water and time had a good correlation with that between sediment settlement induced by consolidation and time. The pore water squeezed by sediment consolidation remarkably accelerated the contaminant migration towards the overlying water.The design of contaminated sediment capping is unconservative if only contaminant diffusion is considered. 2) Tests for caps with varied thicknesses showed that the capping layer retained the migration of contaminant. The chloride concentration in the overlying water of 1 cm capping layer was 857% higher than 3 cm capping layer, and a thicker capping layer can significantly reduce the amount of contaminant moving into the overlying water. 3) The sediment settlements calculated by the layer wise summation method simulations are close to the experimental measurements with an average difference of 87%. The sediment consolidation time of centrifuge test was between the time calculated by two different drainage paths (the sediment height before and after consolidation was completed for capping). Sediment consolidation induced by capping can be simulated by centrifuge tests. 4) The numerical results of the sediment settlement under different thickness capping layer were higher than experimental measurements with an average difference of 109%, while those of the chloride mass concentration in the overlying water were lower than experimental measurement with an average difference of 166%. 5) The numerical results show that the breakthrough time can be shortened by 407 times if sediment consolidation is considered compared to diffusion.
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Published: 31 March 2016
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| Fund: 郑健（1990-），男，硕士生，从事环境岩土工程的研究.ORCID: 0000 0002 1119 3261. E-mail：21212033@zju.edu.cn |
底泥固结对污染物运移影响的超重力离心试验模拟
为了研究污染底泥覆盖技术中添加覆盖层造成底泥固结排水、以对流方式加速污染物击穿覆盖层的过程,利用超重力离心模型试验的缩尺缩时效应,研究添加覆盖层后底泥固结对污染物运移速度及出流量的影响,采用数值方法对试验进行模拟.结果表明：1）添加覆盖层后上覆水体中氯离子质量浓度随时间的变化过程,与底泥固结沉降量随时间的变化过程具有较好的相关性.底泥固结排出的孔隙水以对流方式显著加快污染物向上覆水体运移,仅考虑污染物以扩散方式运移的底泥覆盖设计方法偏不安全.2）覆盖层对底泥污染物运移有一定的延滞作用,1 cm厚度覆盖层的上覆水层中氯离子质量浓度比3 cm厚度情况高85.7%,增加覆盖层厚度可以显著地减少底泥污染物运移到上覆水体的量.3）采用分层总和法计算得到的底泥沉降与实测值接近,平均相差为8.7%；试验底泥固结时间介于以2种排水路径（添加覆盖层固结前、后底泥高度）计算得到的时间之间,通过超重力离心模型试验模拟底泥固结过程是可行的.4）覆盖层引起的底泥沉降的数值计算值较实测值偏大（平均相差10.9%）,上覆水体污染物质量浓度的数值计算值较实测值偏小（平均相差16.6%）.5）数值分析表明,与纯扩散相比,底泥固结造成污染物击穿覆盖层时间缩短40.7倍.
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