Quantitative assessment of water richness in mining area of river basin by transient electromagnetic method
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Abstract:
In order to ascertain the scope and extent of the impact river infiltration on the exposed goaf and backfill area, we used the transient electromagnetic method to detect underground mining goaf and open-pit mining backfill near the Huhe Wusu Ditch and Ulan Moron in Ordos. According to the different distance from the river, the electrical response characteristics were analyzed from the unidimensional, planar, and three-dimensional perspectives. Combined with the results of drilling pumping test in the geophysical exploration area, the feasibility of quantitative detection of water richness by transient electromagnetic method was discussed. The results show that the transient electromagnetic method can accurately survey the water-rich range and intensity of geological anomalies at a shallow buried depth not exceeding 150 m in the river basin. The high-resistance characteristics of the non-aqueous (or weakly-water-bearing) goaf near the river are obvious while the low-resistance characteristics of the water-filled backfill near the river are also obvious. The nearby rivers had a great influence on the backfilling area, to the lateral distance up to 500 m. The backfilling area presented a clear water-rich "funnel". Both the lateral influence range and the water-rich intensity decreased with depth, which was basically consistent with the space scope of the open-air stripping backfill. And the nearby rivers had less impact on the goaf and the upper rock with the lateral distance less than 80 m, vertically mainly affecting the upper aquifer of the goaf, and the goaf was basically free of water, or weakly aquiferous. The relationship between the unit water inflow and the apparent resistivity of the drilling was established, and the use of transient electromagnetic method to quantitatively detect the unit water inflow and water-richness level was explored.
