Subsurface Investigation and Monitoring of Vessel Impact Testing at St. George Island Bridge, Florida (05-2547)
Paul J Bullock, University of Florida
Scott J Wasman, University of Florida
Michael C. McVay, University of Florida

The paper reports on the subsurface investigation, as well as the soil and foundation monitoring of a bridge pier subject to a barge impact in Apalachicola, Florida. The soils investigation included SPT, CPT, DMT, and pressurementer testing in the vicinity of the pier. The site stratigraphy consisted of loose layers of silt, sand, and soft clay overlying medium dense sand. The piles, HP 14x73, were located beneath the existing mud line and could not be instrumented directly. Consequently, a composite pile made from a steel pipe and inner cast reinforced concrete was drilled through the pile cap and driven through the underlying soil. The composite pile was instrumented with strain gages along its length as well as an accelerator string to measure lateral displacement. The soil in both the front and rear of the pile cap was instrumented with push-in lateral stress and pore pressure cells. The combined stress cells (6), capable of dynamically measuring both total stresses and pore water pressure during the vessel collision were placed at various depths in the silt/sand and clay soils. A barge traveling at 3.8 mph struck the pier generating over 1200 kips of peak dynamic lateral load. The coarse grained soil (sand) exhibited little if any pore pressure change, but the silt size soil did. Both the lateral stress cells, and the instrumented pile gave excellent dynamic response from which the cyclic P-Y resistance of soil may be determined.