Foundation Engineering

Pyrite oxidation and expansion in the New Albany black shale have caused serious foundation problems in numerous buildings and structures constructed in the black shale soil horizons in various parts of Kentucky. Pyrite oxidizes, causing various secondary sulfates to form when excavated shale or shale fill is exposed to the atmosphere, water, and humidity; these shales can therefore cause serious problems when used in foundations. These secondary sulfates are sensitive to water and humidity and can form when only minor amounts of water are present in foundation materials. In addition to heaving, these sulfate minerals can also create a mild sulfuric acid in foundation soils. These sulfates form by crystal growth and expansion by volume change, which cause subsequent soil expansion and heaving of any foundation materials when confined. Several structures—schools, hospitals, commercial buildings, water plants, and factories—have had expensive remediation to repair damaged sidewalks, floors, walls, utility conduits, and foundations. One home was condemned and others have severe damage. Repairing these conditions is sometimes more expensive that the original cost of building.

Even high-pressure natural gas pipelines have had catastrophic failures attributed to sulfate formation and ground heaving. In 1985, a catastrophic explosion of a natural gas pipeline in Metcalfe County was attributed to sulfate formation, sulfuric acid, and heaving of black shale soil horizons (http://www.ntsb.gov/doclib/reports). Zones of high concentrations of pyrite occur in the New Albany Shale in parts of the state and can be the cause of foundation failures.

More information can be obtained from

Foundation problems and pyrite oxidation in the Chattanooga Shale, Estill County, Kentucky

Published 2008

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Implications of Pyrite Oxidation for Engineering Works

 

Authors:
Hawkins, A. Brian

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Foundation Failures in Black Shale Soil Horizons

Condemned home in Berea, Ky., and expansive sulfate minerals in black shale.


Black shale outcrops and pyrite-heaving sulfates, Madison and Estill Counties


Estill County Middle School classroom flooring (left) had to be replaced and the Carhartt factory floor (right) was damaged by the pyrite oxidation and sulfate formation, which caused heaving in black shale foundation regolith in Estill County.


This home in Berea was condemned by county officials because of foundation failure, heaving, and broken utility lines related to pyrite oxidation and sulfate formation.


Clay City Water Treatment Plant

The water treatment plant sustained foundation heaving caused by pyrite oxidation and sulfate formation, threatening the viability of water lines, electric power, and functionality of the plant.


Black Shale Fires

Black shale can combust spontaneously when excavated, as evidenced by this burning black shale in Marion County, Kentucky. Black shale fires are thermochemical fires and are exceedingly difficult to put out since water usually accelerates the problems. Some black shale fires have started when citizens burned trash on a black shale outcrop.

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