PDF(1016 KB)
PDF(1016 KB)
PDF(1016 KB)
大型引调水渠道经山前平原段衬砌失稳机理及对策
Mechanism and Countermeasures of Instability of Tunnel Lining in Foothill Plain Section of Large-scale Water Diversion Channel
高地下水位是危及大型长距离引调水挖方渠道衬砌安全的最主要因素之一,尤其是挖方渠道途经山前平原时,其衬砌安全极易受山前过渡带地下水变化的影响。为了揭示地下水变化对渠道衬砌板稳定影响规律,以南水北调中线某段典型挖方渠段为例,利用地下水监测资料及三维渗流模型分析,结合山前平原地层结构特点,首次阐明输水渠道与山前平原地下水互馈关系,并给出相应对策建议。结果表明:渠道切割山前平原表层透水层形成阻水效应;降雨及山前径流致使山前至渠道之间地带地下水位升高,是导致衬砌板隆起破坏的直接原因。研究成果可为类似山前平原区引调水渠道设计、运维及险情整治提供理论依据和技术支撑。
High groundwater level is a most essential factor that threatens the safety of linings in large-scale, long-distance water diversion channels. Particularly when such channels traverse foothill plains, the lining stability is highly influenced by groundwater fluctuations in the foothill transition zone. A typical excavation channel section from the middle route of the South-to-North Water Diversion Project was taken as a case study. By utilizing groundwater monitoring data and a three-dimensional seepage model, we examined how groundwater changes affect the stability of the channel lining in line with the geological characteristics of foothill plain. For the first time, we elucidated the feedback relationship between water supply channel and groundwater in foothill plain and proposed relevant countermeasures. Our findings reveal that the channel intersects the surface permeable layer of foothill plain, creating a water-blocking effect. Rainfall and runoff from the foothill elevate the groundwater level between the foothill and the channel, directly resulting in uplift and damage of lining plate. The results offer theoretical foundation and technical support for designing, operating, and maintaining water diversion channels in similar foothill plain regions and for managing associated risks.
引调水渠道 / 山前平原 / 高地下水 / 衬砌失稳 / 渗流分析
water diversion channels / foothill plain / high groundwater level / lining damage / seepage analysis
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Seepage field regulation is crucial for the stability of canal slope and liner plate along the middle route of the South-to-North Water Transfer Project, especially for stretches excavated in expensive soil area with high groundwater level. In this article, the seepage field of a typical section was simulated with 3-D finite element technology to investigate into the rationality and effectiveness of seepage regulation measures comprehensively. The distribution of seepage field was analyzed and the seepage control measures were compared. Results show that the uplift pressure on canal pavement would be reduced significantly by drainage cushion with drainage holes opening only when groundwater level is higher than the canal water level, by drainage cushion replaced by drainage board, and by drainage holes replaced with permeable joints of liner plate in addition. The differences in the three measures were compared, and their application conditions were discussed and corresponding suggestions were given.
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南水北调中线工程运行以来,发挥了巨大社会效益,沿途及京津冀地区对其调水需求日增,渠道停水检修将带来较大风险,因此面临输水状态下渠道衬砌板破坏抢修难题。部分挖方渠道衬砌板下有复杂的渗控措施,输水状态下采用围堰干地抢修渠底和较深部位的渠坡衬砌板时,需解决围堰基坑内外水位差可能带来的基坑内渠坡抗浮和渗透破坏问题。鉴于此,在渠道渗控设计及围堰布置基础上,根据“前堵后排”思想,提出一种围堰基坑“外、中、内”三防线渗控方案,即围堰基坑外围渠基透水管封堵,基坑周边安装水泵抽排。三维渗流场模拟结果表明,该方案可显著降低基坑周边衬砌板下砂垫层内水平渗透比降和基坑涌水量,能保证基坑渗流安全。研究成果可为南水北调中线输水状态下挖方渠道围堰干地抢修提供理论依据和技术支持。
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Having produced tremendous social benefits since its operation, the middle route project of the South-to-North Water Transfer has attracted increasing demands from areas along the route and in the Beijing-Tianjin-Hebei region. Maintenance of the channel with water cutoff would bring about risks; hence repairing the channel lining board and in the meantime maintaining water delivery poses a difficulty for engineers. Complicated seepage control measures were arranged under the lining board in some excavated channels with high-level groundwater. In emergency maintenance of the lining board at bottom or at deep by constructing cofferdam in the presence of water conveyance, engineers are faced with anti-floating problems and seepage failure possibly caused by the water level difference inside and outside the cofferdam foundation pit. In view of this, in line with the design of seepage control and cofferdam layout, we propose a seepage control plan for the cofferdam foundation pit: to block the permeable pipe of the canal foundation outside the cofferdam foundation pit, and to install water pump around the pit for drainage. Simulation results of the three-dimensional seepage field demonstrate that the horizontal permeability gradient and the water inflow of the foundation pit can be reduced remarkably by using the plan, hence ensuring the safety of foundation pit. The research finding offers theoretical basis and technical support for the emergency maintenance in the presence of water delivery.
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