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Geotechnical Engineering

 

Interstate Technical Group on Abandoned Underground Mines
Fourth Biennial Abandoned Underground Mine Workshop

Abstract: Pressure Grouting an Open Mine Shaft in Indianola, Iowa

Paper

Mike Bourland, P.E
AML Engineer, Iowa Division of Soil Conservation
Len Meier
OSM, Mid-Continent Regional Coordinating Center

A shaft from an abandoned mine in Indianola, Iowa, was discovered in the Spring of 2000 as an opening appeared in a street providing access to a church. The surface opening measured about 30 feet in diameter and 15 feet deep. Borings revealed that the shaft extended more than 80 feet deep and contained substantial voids separated by layers of unidentified fill materials.

Due to the risk of collapse of the upper supported materials, the shaft depth and the presence of multiple void and fill areas, pressure grouting with angle drilling was chosen to close the void. Additional drilling and grouting from the surface would be completed after the shaft was stabilized and the surface depression backfilled.

The Contractor used a large well-drilling rig to make the grout holes. The excessive force of the drill rig made it difficult to determine if voids or soft material was encountered. Drilling and grouting continued until low grout takes were obtained. A limited depth of continuous sampling with a smaller auger drill rig was used to verify closure. A total of 17 grout holes, 1261 linear feet of drilling injection holes, and 4,117 cubic feet of grout were used to seal the shaft.

Several lessons were learned about the investigative drilling program, the specific equipment used on the site, and appropriate contract requirements that will improve the efficacy and efficiency of future AML projects.

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Updated: 04/07/2011

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