Evaluation of heave prevention methods for floors founded on shale in the Ottawa Region

Heaving of floors founded on black shale in the Ottawa region is due to the oxidation of pyrite in it and the subsequent formation of jarosite and gypsum which crystallize between the layers of the thinly laminated fissile shale causing it to expand. Air must gain access to the shale for the oxidation reaction to occur. Work done in Ottawa indicates that air may be prevented from entering the shale by coating the freshly excavated surface with a layer of concrete before construction commences. This has been successful in preventing heave for at least seven years. Additional precautions which are needed to prevent entry of air to the shale after construction of the building are also discussed.