Sometimes projects require creativity to collect data. GeoSonics/Vibra-Tech used their innovative skills to install marsh geophones to monitor vibration in a canal.
The Grove Park Canal Access project in Rehoboth Beach, Delaware provides canal access via a pier and dock large enough to accommodate two 30’ pontoon boats as well as kayaks and canoes. The construction included building a wooden boardwalk and attaching a floating aluminum dock. Before work could begin, piles needed to be driven into the canal to support the new structure. Project personnel were concerned that pile installation activity may produce vibrations that could cause damage to a 16-inch cast iron water pipe buried in the canal. The concern was not only that vibration may cause damage to the pipe but that vibration may also cause settlement of the pipe. Settlement can occur in certain soil conditions because vibration can cause an increase in pore pressure and shear strain.
GeoSonics/Vibra-Tech was retained to develop the vibration monitoring plan and develop the vibration monitoring specifications for the project. Our Engineers reviewed the site’s geotechnical report, the equipment that would be needed to complete the project, the water main properties and the existing inspection report of the pipe. The plan that was developed provided guidance on safe vibration levels and appropriate monitoring locations. Prior to the installation of the helical and timber piles adjacent to the cast iron water pipe, GeoSonics/Vibra-Tech needed to install marsh geophones that were capable of being submerged in water for an extended period. These geophones had to be housed in a waterproof vessel and submerged in the mud over the existing pipe. Installation of the vibration monitoring sensors had to take place during low tide for accuracy and ease of placement. Vibration data were collected during construction activity. An alert was set up to notify project personnel if vibration readings reached or exceeded the set criteria established for the project.