Old Post Office Foundation Failure Investigation

The purpose of this paper is to describe the cause of distress to the foundation and slab of an old post office building, and to discuss several remedial options. The subsurface investigation program revealed a relatively unique soil condition. The subsurface conditions generally indicated an in-place uncontrolled fill layer consisting of highly plastic soils with variable amounts of gravel, debris, brick, glass fragments, clam shell pieces, scrap metal, and coal ashes. The fill layer was followed by clayey sandy gravel, sandy silt, and sandy clay overlying limestone conglomerate bedrock. Layers of very loose sand-silt-rock mixture were noted below the soil/rock interface. The highly fractured rock appeared to have voids (cavities) filled with silt-sand mixtures. These voids may have been formed as a result of solution activities (sinkholes) in limestone conglomerate formation. Two categories of remedial approaches, namely deep and shallow remediation, are discussed with regard to their economical and potential risk implications.