Monitoring moisture dynamics in multi-layer covers for mine tailings remediation using autonomous and remote time-lapse electrical resistivity tomography

The dynamics of moisture content in engineered multi-layer covers constructed on mining wastes were monitored at pilot-scale using 2D autonomous, remote and non-invasive time-lapse electrical resistivity tomography. This innovative monitoring approach was combined with conventional point sensors to assess the hydrogeological behavior of 280 m-long experimental covers under real meteorological conditions at an active mining site. The covers with capillary barrier effects (CCBE) were designed to act as oxygen barriers whereas the covers with low saturated hydraulic conductivity layers (LSHCC) aimed at limiting the water infiltration rate through the covers. A methodology was proposed to process the daily hydrogeophysical datasets from four 23 m-long instrumented sections and estimate the 2D distributions of moisture content daily. Hydrogeophysical monitoring suggested that the CCBE was able to maintain high degrees of saturation (above 85%) in the moisture-retaining layer throughout the 1-year monitoring period and was not significantly affected by the slopes of inclined sections, which would make it an efficient oxygen barrier. Larger spatio-temporal changes in moisture content were identified from hydrogeophysical data in the LSHCC. Most of the low hydraulic conductivity layers remained below 85% of saturation and the estimated moisture content was at the lowest level during August 2022, which was attributed to the combined effect of low precipitation, rapid vegetation development and potential water percolation through the cover. Overall, the methodology proposed in this study allowed to monitor the hydrogeological behavior of the covers, which was helpful to investigate the performance of the covers. This study provided the first "proof-of-concept" at pilot-scale and under real conditions that the geoelectrical method can be used as a complementary monitoring technique to extend spatially the monitoring of moisture dynamics in mining wastes, which might be useful for geochemical and geotechnical monitoring programs in large-scale mining waste storage facilities.

本研究采用2D自主、远程和非侵入式的时序电导率层析成像技术，在矿山废料上构建的工程多层覆盖物的水分含量动态变化进行了现场规模监测。这一创新的监测方法与传统的点式传感器相结合，以评估280米长的实验覆盖物在真实气象条件下的水文地质行为。具有毛细障碍效应（CCBE）的覆盖物被设计为氧气屏障，而具有低饱和水力传导率层（LSHCC）的覆盖物旨在限制水分通过覆盖物的渗透速率。提出了一种方法，用于处理来自四个23米长仪器段的每日水文地质数据集，并估算每日水分含量的二维分布。水文地质监测表明，CCBE在整个1年的监测期间能够维持水分保持层的高饱和度（超过85%），且不受倾斜段坡度的影响，使其成为高效的氧气屏障。LSHCC中的水分含量在时空尺度上发生了较大的变化。大多数低水力传导率层的水分饱和度保持在85%以下，且在2022年8月估算的水分含量处于最低水平，这归因于降水量低、植被快速生长和覆盖物下可能的水分渗透。总体而言，本研究提出的方法能够监测覆盖物的水文地质行为，有助于研究覆盖物的性能。本研究首次在试点规模和真实条件下提供了“概念验证”，即地球物理方法可以作为补充监测技术，用于扩展矿山废料中水分动态变化的监测范围，这可能对大规模矿山废料储存设施中的地球化学和岩土工程监测计划具有实际意义。