Man-Made and Natural Mechanisms Leading to Catastrophic Collapse in the Karstic Epler Formation of Eastern Pennsylvania

This invited presentation will discuss massive sinkholes in Pennsylvania including characterization and engineered solutions.A complex interplay of man-made and natural mechanisms can lead to ground surface collapse in certain geologic settings. While similarities are sufficient to generalize the mechanisms, the complexity often renders it difficult to discern the relative importance and inter-relationships of specific factors. This presentation focuses on mechanisms potentially at play in an area of Ordovician limestones in the Lehigh Valley sequence of the northeast-trending Great Valley Section of the Appalachian Valley and Ridge Physiographic Province, located in eastern Pennsylvania. Sinkholes have historically been responsible for substantial damage to infrastructure in the regional area. The general mechanism involved is the downward movement of soil, usually by water, into the karstic carbonate bedrock voids and fissures. Substantial volumes of soil and water may be transported laterally and lead to catastrophic collapse where bedrock is dewatered, clay-filled features eroded, and the flows accessible to a discharge outlet. Three different micro-settings are recognized: 1.) sinkholes along public water and sewer mains constructed in the soil overburden not penetrating karst where cause and effect relationships are ambiguous; 2.) sinkholes and collapse associated with infrastructure such as abutments founded in a karstic creek bed where surface-groundwater interactions are important; and 3.) structural damage above and adjacent to creek banks in residential areas (culverts, underground utilities, houses, and pavement) characterized by soil disturbance and concentrated surface runoff.