Monroe County, Louisiana – Investigations to Address Lignite Beds Disruption During Mining Resulting from Excess Pore Pressure
I2M personnel were engaged to conduct a comprehensive groundwater flow-net analysis of the future mining blocks to determine areas of excess pore pressure causing lignite bed elevation movement as overburden was removed in advance of bucket-wheel mining of lignite.
This activity was conducted for the purpose of minimizing mining of underclay that would decrease lignite quality by increasing “ash” levels to the coal stream sent by conveyor to the mine-mouth power plant nearby.
250 groundwater monitoring wells were drilled and installed with designed screen lengths, and logged (both to record lithology and by geophysical logging of gamma, SP and resistivity).
Top of well casings were surveyed for elevations and “slab” section flow-net maps and surface elevation maps of anomalous areas were constructed and keyed to master mining maps for future reference by the operator.
Results identified mining areas of high-, medium-, and low-pore pressure that were directly related to permeability differences present within the underclay and its thickness.
Small-diameter pore-pressure relief wells were installed throughout the areas mapped as exhibiting high-pore pressure.
Within 6 months, the local monitoring of pore-pressure (water levels) in wells indicated a marked decrease in pore pressure.
Three years later, mine management indicated to I2M that the lignite bed movement after removal of overburden had be reduced to near horizontal, as planned, and that they were moving high-quality lignite to the plant by conveyor now after passing the anomalous areas of the mine.
