基于NSMC方法的某核工程场地裂隙地下水数值模拟不确定分析

Uncertainty analysis for groundwater modeling in fracture rocks for the nuclear facility site based on null space Monte Carlo method

裂隙介质渗透结构表现为高度的非均质性与各项异性。为了科学有效地预测某核工程场地裂隙地下水的流动规律,揭示裂隙岩体地下水的渗流特性,笔者等采用Pilot Point调参方法与null space Monte Carlo方法(NSMC),开展了裂隙岩体渗透结构的不确定性分析研究,构建了符合实际水文地质条件的多个渗流数值模型集合。结果表明:该方法获得的各个实现地下水位模拟结果能够与实际观测数据较好吻合,可反映工程场地裂隙地下水动力特征与流动趋势;各个实现的参数化渗透结构在空间上存在一定的差异性,但整体变化趋势是保持一致的,渗透参数的不确定性表现为在实测数据分布区域相对较低,钻孔空白区域相对较高;该方法可以弥补单一、确定性模拟结果在表征裂隙介质渗透结构方面的局限性,有效地降低模型参数的不确定性与随机性。此方法对进一步提升裂隙岩体渗流模拟精度与预测能力,深化裂隙地下水迁移规律的认识具有重要的意义。

Objectives:The permeability in a fractured rock has obviously heterogeneous and anisotropic properties.To scientifically predict the groundwater flow characteristics of the fractured medium for a nuclear facility site,we put an emphasis on the uncertainty analysis of the hydraulic field in this paper.Methods:Based on the hydraulic test data,Pilot point calibration technique and null space Monte Carlo method were employed to establish the groundwater flow model.The corresponding uncertainties analysis was conducted to obtain a series of realizations that meet the hydrogeological conditions in support of the safety assessment.Results:The simulated hydraulic heads of different realizations were in a good agreement with the measured data.The numerical results could well reflect the actual hydrogeological conditions of the site.Besides,the hydraulic conductivity fields of different realizations exist some differences in the space domain.However,the overall change trends are similar.The variance of hydraulic conductivity filed around the boreholes is relatively low and is high in no borehole areas.Conclusions:NSMC method could well make up for the limitations of single and deterministic numerical model in characterizing the hydraulic conductivity filed in fractured medium,and effectively reduce the uncertainty and randomness of model parameters.It is positive to further improve the groundwater flow prediction ability.The simulations results could deepen the understanding of groundwater migration behavior in fractured rocks.