Seismic Crosshole Study
Atlantic Bridge, Colon, Panama
GeoView, Inc. performed multiple seismic crosshole and downhole studies for the Atlantic Bridge Project in Colon, Panama. The project site was located at the crossing of new Atlantic Lock Complex of the Panama Canal. The purpose of the investigation was to provide information regarding the seismic shear wave and compression wave velocities of the overlying unconsolidated sediments and underlying rock. Based on previous surface based seismic work performed at the site by GeoView and Spotlight, it was suspected that this portion of the site could have unusually low shear wave velocities. If actually present, these low velocity zones presented a significant challenge for the planned design of future deep foundations.
The investigation was conducted in accordance with the requirements in ASTM D4428 (Standard Test Methods for Crosshole Seismic Testing) and ASTM D7400 (Standard Test Methods for Downhole Seismic Testing). Each crosshole test consisted of a set of three boreholes oriented in a linear fashion, spaced 2.5 meters apart. The boreholes were installed to a depth of approximately 25 meters. To ensure accuracy of the crosshole data, the verticality of the boreholes was checked using Mount Sopris borehole deviation logger. This provided the correct separation distances between the boreholes at each depth interval.
The data was collected with a 24 channel seismograph. A crosshole slide hammer was used as the seismic source. Two 28-Hz triaxial borehole geophones were used as the receivers. The resulting seismic data was of excellent quality. The calculated shear wave and compressional wave data was provided in both tabular format and as a waterfall plot. It clearly showed zones with shear wave velocities less than 100 meters/second. These zones of extremely slow material were verified by subsequent studies.
Data Samples Collected at the Project Site - Click to Enlarge
Collection of Deviation Data
Seismic Crosshole Waterfall Plot
Graphical Plot of Seismic Data
Mount Sopris Deviation Logger