地下水位监测频率和时长对滑体渗透系数反演结果的影响

滑体渗透系数是决定滑坡对降水入渗或库水位波动响应的关键参数。当滑坡区有较丰富的地下水位监测数据时，基于监测数据反演滑体渗透系数是公认的最有效途径之一。然而，反演参数的准确性受制于监测数据的采集频率和时长。确定反演滑体渗透系数的相对最优监测频率和监测时长是获取准确反演结果的前提。本文以三峡库区典型的碎石土滑坡——李家坡滑坡为例，通过渗流场反演模拟和反演结果与监测数据拟合途径，以反演结果的稳定性和离散性为评价指标，分析地下水位监测频率和监测时长对滑体渗透系数反演结果的影响，进而提出水库环境中反演碎石土滑坡滑体渗透系数的相对最佳监测频率和监测时长。研究发现:（1）监测时长不大于810 d、监测频率高于15 d/次时，可以获得水位误差相对最小、且基本稳定的反演结果；（2）监测频率1 d/次和5 d/次、监测时长同为270 d时，或监测频率10 d/次、监测时长540 d时，反演所得渗透系数的稳定性较好、离散性较小；（3） 监测频率15 d/次和30 d/次时，即使监测时长长达1 170 d，反演所得渗透系数的稳定性、离散性依然较差。综合反演水位误差大小、反演渗透系数的稳定性和离散性以及监测成本，认为监测频率5 d/次、监测时长270 d为三峡库区碎石土滑坡相对最佳的监测频率和监测时长。

Effects of frequency and interval of groundwater monitoring on the inversion coefficients of permeability of materials of a landslide

Coefficient of permeability of materials of a landslide is one of the key parameters that control its response to rainfall infiltration and reservoir water level fluctuation. It has been well recognized to be one of the most effective and reliable approaches that the coefficient of permeability of materials of a landslide is obtained with methods of inversion based on groundwater monitoring data when the data are available and abundant. However, the accuracy of the inversion results largely depends on the sampling frequency and interval of the monitoring data. Therefore, it is necessary to determine an optimal monitoring frequency and interval to get a reliable and accurate inversion coefficient of permeability of materials of a landslid. In this paper, coefficient of permeability of the Lijiapo landslide, one of the representative colluvium landslides in the Three Gorges Reservoir area, was obtained with the approach of inverse simulation of seepage field and fitting of the inversion and monitoring data. Effects of frequency and interval of groundwater monitoring on the inversion results were evaluated based on their stability and discreteness, and the optimal monitoring frequency and interval were proposed. The results show that (1) the error of the inversion groundwater level is getting much less when monitoring frequency and interval are higher than 15 day/per time and longer than 810 days respectively; (2) when the monitoring frequency is each day or 5 day/ per time and the interval is 270 days, or the monitoring frequency is 10 day/per time and the interval is 540 days, the inversion coefficient of permeability is the most stable with the least discreteness; (3) when the monitoring frequency is twice a month or once a month and the interval is 1 170 days, the results are not stable and with much greater discreteness. Practically, it is suggested that 5 day/per time and 270 days could be the optimal frequency and interval of groundwater monitoring for the inversion coefficient of permeability of a colluvium landslide in the reservoir area, considering the error of the inversion groundwater level, the stability and discreteness of coefficient of permeability as well as the costs.