Report of Subsurface Exploration Intl Bridge PSI.pdf

This document is a detailed geotechnical report of subsurface exploration and evaluation for the Cameron County International Bridge in Brownsville, Texas, prepared by Professional Service Industries, Inc. (PSI) on March 7, 1984. The investigation focused on Pier No. 5, which is located partway up the north slope of the bridge, and involved two soil test borings drilled to approximately 70 feet deep using hollow stem auger techniques.

The report reveals complex subsurface conditions, including layers of silty clay, sandy silt, and varying soil consistencies. Key findings include a large layer of very soft clay just above the estimated pier bearing level, groundwater encountered at depths of 46-48 feet, and evidence of pier settlement with the southeast corner several inches below design grade. The engineers recommend replacing the existing pier foundation with a driven or augercast pile foundation, targeting very stiff to hard silty clays below elevation -33 feet, with estimated pile design capacities of 40 to 60 tons and installation using specific geotechnical procedures to mitigate potential excavation and settlement risks.