CAN ARTESIAN CONDITIONS REALLY EFFECT THE STABILITY OF AN INTERSTATE BRIDGE?

The structural integrity of a multi-span, interstate bridge degraded over the past ten years. Structural engineering evaluations identified cracks and shear of the abutment beam seat backwall and tilted bridge piers. Geotechnical and geological observations identified numerous boils in the channel bottom immediately adjacent to the abutment and dozens of emergent ‘springs’ along the stream bed side slopes. Review of construction records showed that the original roadway exploration borings encountered artesian conditions around elevation 1000 M.S.L. and that “volcanoes” of fine sand and silt formed around the steel piles during installation. A literature search identified U.S. Bureau of Water publications from the 1940’s that discussed the results of an extensive report of the municipal and industrial water resources within Nimishillen Creek of Canton, OH. The study revealed that the bridge abutment was founded on a large, ‘buried valley’. The buried valley is one of the longest and deepest in northeast Ohio. In the vicinity of the bridge the valley is about 2000 feet wide and 300 feet deep. The groundwater flow within the valley, measured in production wells to exceed 2000 gallon per minute, is split into two confined aquifers with the uppermost aquifer immediately beneath the abutment footing.

Geotechnical drilling investigations and the installation of vibrating wire piezometers confirmed artesian pressures exceeding 15 feet of head exist at the bottom of footing elevation. Artesian conditions are relatively rare in NE Ohio, so many have overlooked the possible contribution of the artesian pressure on the movement and failure of the bridge abutment. This presentation will outline the effects of the artesian conditions on the analyses and remediation of the bridge.