Report of Subsurface Exploration Intl Bridge PSI (2).pdf

This document is a detailed geotechnical report of subsurface exploration and evaluation conducted by Professional Service Industries, Inc. (PSI) for the Cameron County International Bridge project located in Brownsville, Texas. The report focuses on Pier No. 5, which is the first bent south of the north abutment on the downstream span, and was designed to bear at elevation -26.24 feet. The investigation involved two soil test borings drilled to approximately 70 feet deep, with comprehensive testing including penetration tests, split-barrel sampling, soil classification, and laboratory analyses of soil samples.

Key findings reveal significant geotechnical challenges, including a large layer of very soft clay just above the estimated pier bearing level and groundwater encountered at depths of 46-48 feet. The evaluation indicates the pier has experienced base failure with periodic side shear failure, and its frictional capacity is nearly exceeded under transitory live loads. As a result, the report recommends installing a new foundation support using driven or augercast pile foundations, specifically targeting the very stiff to hard silty clays below elevation -33 feet. The recommended pile types include pre-cast concrete, concrete-filled steel shell, and concrete-filled steel pipe, with estimated design capacities of 40 to 60 tons when driven or augered to about elevation -35 feet.