航道疏浚对水体水质影响的模拟研究

发布时间：2018-06-03 08:38

本文选题：疏浚 + 悬浮物　；参考：《重庆交通大学》2014年硕士论文

【摘要】：为了维护航道的通航标准及改善泥沙淤积状况，一般需要定期对航道进行疏浚作业，然而在施工过程中容易因泥沙搅动、外泄而产生悬浮泥沙，并在水流作用下扩散到周边区域，导致以施工区为中心的附近水域混浊度增加，同时，泥沙中携带的有毒、有害物质也会使水体的使用质量下降。基于此，在疏浚环境影响评价过程中，针对不同的水域及水质污染的特点，选择相应的底泥水质模型对疏浚导致的悬浮污染物的影响范围作出预测及评估，从而选择正确的清淤处理方案，是非常必要的，同时对水环境的保护以及环保疏浚的开展具有十分重要的指导意义。本文基于FLUENT软件，模拟工程区域泥沙悬浮扩散状况；并以数值模拟的预测结果为依据，分析比对两种疏浚方式（绞吸式和抓斗式）在不同疏浚期下（枯水期和雨水期）悬浮泥沙的浓度分布及扩散范围，确定最佳施工方案。通过对绞吸式溢流沉淀池中泥沙沉降过程的模拟，比对分析不同进水口流速下对泥沙的沉降效果及出水水质的影响，揭示泥沙颗粒的沉降规律。研究结果表明：通过两种疏浚形式（绞吸式和抓斗式）分别在汛期和旱期施工时悬浮扩散对施工区域的影响对比表明，沿三维方向所选大部分监测断面在旱期施工时所产生的泥沙浓度值是低于汛期的。以一个疏浚点所产生的悬浮扩散为基点，通过折算出超水质标准的扩散面积对比分析表明，汛期均大于旱期，即利用两种疏浚形式分别进行疏浚作业时，在汛期施工所产生的泥沙悬浮扩散对施工区周边水域的影响比旱期更大，即确定旱期为最佳疏浚期。根据两种疏浚形式下在最佳施工期内各个监测断面最大泥沙浓度和区域平均浓度的对比分析表明，在所选监测断面z=10、20、30、40、50，抓斗式疏浚方式无论从泥沙浓度最大值还是区域浓度平均值均高于绞吸式疏浚方式，在断面y=-9、-7、-5、-3、-1及x=14、13、12、11上，由于绞吸式释放源强比抓斗式更大，除靠近疏浚源附近断面y=-9及x=14处采用抓斗式挖泥船疏浚时泥沙浓度最大值相比于绞吸式较小外，其余监测断面无论从泥沙浓度最大值还是区域浓度平均值均大于绞吸式疏浚方式，即确定绞吸式疏浚为最佳疏浚形式。基于FLUENT软件对绞吸式疏浚方式下泥水处理构筑物溢流沉淀池中泥沙沉降过程进行模拟，并选取四个备选流速，对不用进水口流速下泥沙沉降效果及出水泥沙浓度进行比对分析，，结果表明：随着进口水水流流速的减小，沉淀池内的异重流、短流现象较严重，导致泥沙颗粒沉降效果受到影响，出水水质较差；随着进水口水流流速的增加，沉淀池进水口处异重流的强度得到改善，但沉淀池内水力停留时间缩短，沉淀效果也会受到影响。所以在进水口流速的选取上应综合考虑上述两方面的因素，既要从流态上减轻异重流的影响，还需从理论上考虑泥沙颗粒在池内的水力停留时间，才能从本质上改善泥沙颗粒的沉降效果。本研究针对性较强，为长江航道疏浚工程的开展提供了理论支持，并为三峡航道绿色施工技术研究提供了技术保障，研究具有重要的使用价值和现实意义。
[Abstract]:In order to maintain the navigation standard of the channel and improve the silt condition, it is generally necessary to dredge the channel regularly. However, in the process of construction, the suspended sediment is easily caused by the agitation of sediment, and it is diffused to the surrounding area under the action of water, which leads to the increase of turbidity in the surrounding waters of the construction area and the sediment in the sediment. In the process of environmental impact assessment of dredging, according to the characteristics of different water and water pollution, the corresponding sediment water quality model is selected to predict and evaluate the influence range of the suspended pollutants caused by dredging, so as to select the correct clearing treatment side. The case is very necessary, and is of great guiding significance for the protection of water environment and the development of environmental dredging.
Based on the FLUENT software, this paper simulated the sediment suspension diffusion in the engineering area, and based on the prediction results of the numerical simulation, analyzed the concentration distribution and spread range of the suspended sediment in the two dredging modes (winch and grab) during the different dredging period (the dry period and the rainwater period), and determined the best construction scheme. The simulation of sediment settling process in a flow sedimentation tank is compared to analyze the effect of sediment settlement and water quality at different inlet flow velocity, and the settlement law of sediment particles is revealed.
The results show that the influence of the suspension diffusion on the construction area during the construction of two types of dredging (winch and grab) during the construction of the flood season and the drought period, respectively, shows that the concentration of most of the monitoring sections along the three dimensional direction is lower than the flood season. For the base point, the contrast analysis of the diffusion area of the converted water quality standard shows that the flood season is greater than the drought period, that is, when the dredging operation is carried out by two kinds of dredging, the influence of the suspended sediment diffusion on the surrounding waters of the construction area is greater than that in the drought period, that is to determine that the period of the drought is the best dredging period. According to the two dredging period, the dredging period is determined as the best dredging period. The comparison and analysis of the maximum sediment concentration and regional average concentration of each monitoring section in the best construction period shows that in the selected monitoring section z=10,20,30,40,50, the method of grab dredging is higher than the method of dredging from the maximum value of the sediment concentration or the regional concentration, and in the section y=-9, -7, -5, -3, -1 and x=14,13,12,11 As the suction type release source is stronger than the grab type, the maximum value of the sediment concentration is smaller than that of the winch in the dredging of the grab dredger near the section y=-9 and x=14 near the dredging source, and the maximum value of the sediment concentration or the average value of the regional concentration is greater than that of the stranded suction dredging, that is to determine the suction suction. Type dredging is the best form of dredging.
Based on the FLUENT software, the sediment deposition process in the overflow sedimentation tank of the mud water treatment structure under the suction dredging is simulated, and four alternative flow velocities are selected to compare the sediment settlement effect and the cement sand concentration at the flow velocity without the inlet. The results show that with the decrease of the flow velocity of the imported water flow, the difference in the sedimentation tank is different. Heavy flow and short flow phenomenon are serious, which results in the effect of sedimentation of sediment particles, and the water quality is poor. With the increase of flow velocity of the inlet, the strength of the gravity flow at the inlet of the sedimentation tank is improved, but the hydraulic retention time in the sedimentation tank is shortened and the precipitation effect will be affected. Therefore, the selection of the flow velocity of the intake should be integrated. Considering the above two factors, we should not only reduce the influence of the flow in the flow state, but also consider the hydraulic retention time of the sediment particles in the pool theoretically, in order to improve the sedimentation effect of the sediment particles in essence.
This study is more pertinent and provides theoretical support for the development of the dredging project of the Yangtze River channel, and provides technical support for the green construction technology research of the Three Gorges waterway. The research is of great use value and practical significance.
【学位授予单位】：重庆交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：X82;U616

【参考文献】