基于地下水生态平衡埋深的隧道排水量设计计算

为解决富水地区隧道开挖后地下水过量排放导致水位下降，进而破坏植被的正常生长和生态平衡的问题，提出基于地下水生态平衡埋深确定隧道排水量的有效方法。依托福州市某在建公路隧道，根据工程水文地质学，同时结合地下水生态平衡埋深的概念，提出隧道允许排水量的计算方法。首先，利用地下水动力学中的面井法，建立单洞隧道的地下水渗流模型，揭示地下水排放量与地下水位降深的关系。其次，根据所提出的地下水渗流模型，在植被存活的前提下，得出满足地下水生态平衡埋深要求的隧道排水时间，继而得出地下水排放疏干漏斗的影响范围。然后，通过降雨入渗系数法得到在影响范围内降雨补给量W与总地下水排放量Qt进行比较。通过调整隧道每延米平均涌水量q，使W等于Qt，q即为隧道的最大允许地下水排放量。研究结果表明： 1）地下水生态平衡埋深一定时，随着隧道单位排水量的增大，隧道影响范围逐渐减小，降水补给总量也逐渐减小，排放总量逐渐增加，因此存在一个单位排放量使排水总量等于降雨补给量； 2）未考虑水分胁迫时间效应得到的排水量较考虑水分胁迫时间得到的排水量偏于保守。最终，确定在建隧道的排水量q=0.4 m3/(m·d)。

Design and Calculation of Tunnel Drainage Based on Ecological Equilibrium Embedment Depth of Groundwater

The drop of water table induced by excess drainage after tunnel excavation in water rich area would cause damage to normal growth of vegetation and ecological balance. As a result, the methods to determine the tunnel drainage volume based on ecological groundwater table are proposed. By taking a highway tunnel under construction in Fuzhou for example, a calculating method for the limit drainage volume of tunnel is proposed based on hydrogeology and the concept of ecological equilibrium embedment depth of groundwater. First, the groundwater seepage model of tunnel is established based on area well method in groundwater dynamics, which reveals the relationship between the water inflow volume and groundwater table drawdown. Second, according to the proposed groundwater seepage model, the tunnel drainage time that meets the requirements of the ecological equilibrium embedment depth of groundwater is obtained on the premise of the survival of vegetation, and then the influence scope of the drainage funnel is derived. Third, the rainfall supplement volume W within the influence range is obtained by using the method of rainfall infiltration coefficient, and then the W is compared to the total groundwater discharge volume Qt. Finally, through adjusting unit groundwater drainage q to make W equal to Qt, q is the maximum allowable groundwater discharge in the tunnel site. Some conclusions are drawn as follows: (1) When the ecological equilibrium embedment depth of groundwater is constant, with the increase of q, the influence range of the tunnel decreases, W also decreases, and Qt increases gradually. Therefore, there is a unit drainage that makes the total groundwater discharge equal to rainfall supplement. (2) The limit tunnel drainage obtained without considering the time effect of water stress is more conservative than that obtained with water stress. The q of the tunnel under construction is 0.4 m3/(m·d).