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。

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.