The karst geologic setting of south-central Kentucky presents many challenges to engineers and construction firms. Karst areas are characterized by numerous sinkholes and subsurface drainage systems that can include caves, regolith arches, and highly irregular bedrock surfaces. The increased commercial and residential development in south central Kentucky, particularly Bowling Green which is in Warren County, has created an increased interest in the existence and location of these unmapped karst features, particularly regolith arches. Regolith arches arc formed by the downward movement affine-grained soils as a result of water infiltration from the ground surface into subsurface drainage systems. The reason for this interest in the location of unmapped karst features is the tendency for construction induced vibration and topographic changes to cause collapse of these regolith arches. It is well documented that construction and topographic changes can cause regolith arches to collapse. However, a lesser documented cause has become more common. This cause is the installation of underground utilities. The primary way underground utilities can lead to the dropout of regolith arches is by directing water into an active regolith arch. This occurs because utility lines are typically backfilled with highly permeable gravel. In the Warren County area, native soils are silts and clays which possess a very low permeability. The gravel backfilled utility creates a conduit that captures a significant amount of surface runoff. If a regolith arch is located near and underground utility line, there’s a dramatic increase in water volume entering the regolith arch than would have occurred had the utility line not been installed. This paper will document two case histories in Bowling Green, Kentucky, which is in Warren County, where dropouts have developed due to the combination of construction activity and underground utility construction
