February 03, 2011
The Panama Canal Authority, in Panama known as the Autoridad del Canal de Panama (ACP), is conducting a geotechnical investigation along the footprint of a new bridge crossing the new and existing Panama Canal. The initial stage of the geotechnical investigation consists of a geophysical survey which was done in an area north of Gatun Locks (which previous served as the "bridge" across the old Panama Canal), known as the Atlantic Crossing.
The ACP selected a team composed of ATI Panamericana (www.ambienttech.com), Spotlight Geophysical Services (www.spotlightgeo.com) and GeoView (www.geoviewinc.com) to perform the initial geophysical investigation.
The geologic characteristics of the study area include the Gatun Formation which consists of clayey sandstones and siltstones with inter-layered tuff and conglomerates. The Chagres Formation also consists of clayey sandstones and siltstones, but no tuff and conglomerate. The Pleistocene and Holocene Atlantic Muck overlies these formations, consisting of unconsolidated clays, sandy silts, organic matter, and marine shells.
The technical approach incorporated two non-invasive geophysical methods: multi-channel analysis of surface waves (MASW) and seismic refraction. Seismic refraction data were acquired on land and marine portions of the survey lines, while MASW data were acquired on land only.
Project Site Conditions: ATI Panamericana, Spotlight and GeoView executed this survey during the rainy season and access presented significant challenges as shown in the adjacent photos. The local area is jungle, clearing caused ground instability. Work had to be performed manually without vehicular access. Our Panamanian employees, accustomed to local climate, were determined to complete the project along with our professional staff. The project was completed on budget and on time.
Conclusions: a total of 4.13 km of MASW, 3.82 km of land seismic refraction, and 1.45 km of marine seismic refraction data were acquired. Excellent data quality was obtained with each method to provide S-wave and P-wave velocity models to depths of 30 meters.
The interpreted stratigraphic layers include soft fill and sediments, stiff sediments, saturated sediments and weathered Gatun Formation and an un-weathered Gatun Formation.
Localized zones of lower-velocity material occur throughout the survey area and are attributed to pockets of thicker sediment in-filling weathered zones within the Gatun Formation west of the Canal and thicker pockets of soft fill material east of the Canal.
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