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位于承压含水层以上土壤中的地下排水管,应该间隔布置,以排除向上的承压补给和由于灌溉或降雨形成的正常下渗补给。承压条件下所需要的排水管间距要比正常间距窄,适当的排水管间距取决于几个参数。承压含水层以上土壤的导水率(译注:即渗透系数,以下同),决定着水流流向排水管的畅通程度以及当测压管水头和土层厚度一定时向上的承压补给量。流向地下排水管的水流运动取决于导水率的水平分量和垂直分量,因而土壤的各向异性影响着排水管间距。对于大多数土壤结构来说,水平导水率大于垂直导水率(译注:黄土例外)。对位于不透水层以上的土层,忽略其各向异性可能导致排水系统设计安全系数不足,而对于承压条件下无下渗补给的土层,则可能导致排水系统设计安全系数过大。对于既有向上补给又有下渗补给的土壤,各向异性的影响取决于对此问题有影响的各补给参数的量值大小。
Underground drainage pipes located in the soil above confined aquifers should be spaced apart to rule out upward pressure replenishment and normal infiltration recharge due to irrigation or rainfall. The drain spacing required under pressure conditions is narrower than the normal spacing and the proper drain spacing depends on several parameters. The hydraulic conductivity of the soil above the confined aquifer determines the flow of water to the drain and the amount of pressure supplied upward when the piezometer head and soil thickness is constant. The flow of water to the underground drain depends on the horizontal component and the vertical component of the hydraulic conductivity, so the anisotropy of the soil affects the distance between the drainpipes. For most soil structures, the horizontal conductivity is greater than the vertical conductivity. Neglecting the anisotropy in the soil layer above the impermeable layer may result in insufficient design safety factor of the drainage system. However, for the soil without pressure supply under infiltration, the design safety factor of the drainage system may be too large. For soils that have both upward and downward recharges, the effect of anisotropy depends on the magnitude of each recharge parameter that has an effect on the problem.