An improved Green-Ampt model for rainfall infiltration in the inner dumping site of an open pit coal mine
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摘要:
矿山内排土场因其储量大、结构松散和强度低等特点，在降雨条件下极易产生侵蚀或整体失稳破坏，因此降雨入渗分析对预测内排土场稳定性至关重要。以元宝山露天煤矿内排土场为原型，按相似试验理论进行物理模型试验，研究降雨入渗特征，根据试验结果对经典Green-Ampt入渗模型进行改进。结果表明：雨水入渗过程中，随着浸润锋的向下运移，坡面侵蚀由溅蚀凹槽开始，逐渐过渡为径流侵蚀，最后呈现为溯源侵蚀破坏，整体呈现平行于坡表面的浅层滑坡特征；浸润锋之上非饱和浸润层的存在，导致经典Green-Ampt模型计算结果不准确；在考虑浸润层厚度和累积入渗量基础上，推导出改进的Green-Ampt模型；改进后的Green-Ampt模型为分段函数，能够反映降雨入渗使坡面由非饱和向饱和过渡的实际特征。验证结果显示，使用改进模型，浸润锋入渗深度和累积入渗量的预测精度显著提升，虽然冲蚀破坏和初始含水率的差异导致降雨入渗后期的预测精度有所下降，但相关结果对煤矿内排土场降雨初期稳定性分析具有重要意义。改进后的Green-Ampt模型的计算结果与实测数据更为接近，能为分析露天煤矿内排土场降雨入渗规律及边坡稳定性研究提供参考。
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关键词:
- 内排土场 /
- 降雨入渗 /
- 改进的Green-Ampt模型 /
- 非饱和浸润层 /
- 浸润锋
Abstract:Due to the characteristics of large reserves, loose structure and low strength, an inner dumping site in the open pit coal mine is prone to erosion or overall instability under the rainfall conditions. The analysis of rainfall infiltration is quite important to estimate the stability of a dump. The inner dump of the Yuanbaoshan open pit coal mine is taken as the prototype, the physical model test is carried out according to the similar theory to study the characteristics of rainfall infiltration, and the classic Green-Ampt infiltration model is improved. The results show that during the process of rainwater infiltration, with the downward migration of the wetting peak, the erosion of the slope surface starts from the splash groove, gradually transits to runoff erosion, and finally appears as traceable erosion damage, showing the characteristics of shallow landslide parallel to the slope surface. The existence of unsaturated wetting layer above the wetting peak leads to the inaccurate calculation results if the classical Green-Ampt model is used. Based on consideration of the thickness of the infiltration layer and cumulative infiltration amount, an improved Green-Ampt model is derived. The improved Green-Ampt model is a piecewise function, which can reflect the actual characteristics of the transition from unsaturated to saturated slope caused by rainfall infiltration. The validation results show that the prediction accuracy of infiltration depth and cumulative infiltration volume is significantly improved. Because of the erosion damage and the difference in the initial water content, the prediction accuracy of the improved model decreases for the later stage of the rainfall, but it is of great significance for the stability analysis of an open pit coal mine dump at the initial stage of rainfall. The calculation result of the improved model is closer to the measured data.The improved infiltration model can provide an important reference for the studies of rainfall infiltration and slope stability of open-pit coal mine inner dumping sites.
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表 1 土料的物理力学参数
Table 1. Physical and mechanical parameters of the waste dump
参数 天然干密度/（g·cm−1） 天然含水率/% 重度/（kN·m−3） 黏聚力/kPa 内摩擦角/（°） 饱和渗透系数/（cm·s−1） 取值 1.63 10.4 17 35.4 22.5 0.0023 
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表 2 van Genuchten 模型拟合参数
Table 2. Fitting parameters of the van Genuchten model
参数 饱和体积含水率/% 残余体积含水率/% α n 拟合度（R2） 取值 34 11 0.12 1.94 0.9956
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