Data from: Numerical simulation of the free surface and water inflow of a slope, considering the nonlinear flow properties of gravel layers: a case study

Groundwater is an important factor of slope stability, and ninety percent of slope failures are related to the influence of groundwater. In the past, free surface calculations and the prediction of water inflow were based on Darcy’s law. However, Darcy’s law for steady fluid flow is a special case of non-Darcy flow, and many types of non-Darcy flows occur in practical engineering applications. In this paper, based on the experimental results of laboratory water seepage tests, the seepage state of each soil layer in the open-pit slope of the Yanshan Iron Mine, China, were determined, and the seepage parameters were obtained. The seepage behaviour in the silt layer, fine sand layer, silty clay layer, and gravelly clay layer followed the traditional Darcy law, while the gravel layers showed clear nonlinear characteristics. The relation among the permeability, the porosity and the non-Darcy coefficient is investigated. A coupled mathematical model is established for two flow fields, on the basis of Darcy flow in the low-permeability layers and Forchheimer flow in the high-permeability layers. In addition, we considered the effect of the seepage in the slope on the transition from Darcy flow to Forchheimer flow. Then, a numerical simulation was conducted by using finite element software (LELAC 2.2). The results indicate that the free surface calculated by the Darcy-Forchheimer model is in good agreement with the in situ measurements; however, there is an evident deviation of the simulation results from the measured data when the Darcy model is used. Through a parameter sensitivity analysis of the gravel layers, we found that the height of the overflow point and the water inflow calculated by the Darcy-Forchheimer model are consistently less than those of the Darcy model, and the discrepancy between these two models increase as the permeability increases. The necessity of adopting the Darcy-Forchheimer model was explained.地下水是影响边坡稳定性的关键因素，九成边坡失稳均与地下水作用密切相关。以往边坡渗流自由面计算与涌水量预测多基于达西（Darcy）定律。然而，恒定流条件下的达西定律仅是非达西流的一种特殊情形，实际工程中存在大量非达西流动现象。本文以实验室渗流试验结果为依据，确定了中国燕山大铁矿露天边坡各土层的渗流状态，并获取了对应的渗流参数。粉土层、细砂层、粉质黏土层及砾质黏土层的渗流规律符合传统达西定律，而砾石层则表现出显著的非线性渗流特征。本文研究了渗透系数、孔隙率与非达西系数三者间的关联关系。基于低渗透层达西流与高渗透层福希海默（Forchheimer）流的控制方程，构建了双流场耦合数学模型。此外，本文还考虑了边坡渗流对达西流向福希海默流转变过程的影响。随后，采用有限元软件LELAC 2.2开展了数值模拟工作。结果表明，达西-福希海默模型计算得到的渗流自由面与现场实测数据吻合良好；而仅采用达西模型时，模拟结果与实测数据存在明显偏差。通过对砾石层开展参数敏感性分析，本文发现达西-福希海默模型计算得到的溢水口高度与涌水量均低于达西模型的计算结果，且二者的偏差随渗透系数增大而进一步扩大。本文阐明了采用达西-福希海默耦合模型的必要性。