GeoSonics/Vibra-Tech has the monitoring technology to help you stand tall, with confidence and stability, allowing your project to tower above the competition.
Holder Construction, based in Atlanta, Georgia and Flintco Construction of Tulsa, Oklahoma were awarded a joint venture to construct a new 54 story, 1.5 million square foot building to house corporate headquarters in Oklahoma City, Oklahoma for Devon Energy, the largest U.S. based independent oil and natural gas producer.
In order to construct the tower, two existing parking decks had to be demolished that were in close proximity to other buildings, including the historic Colcord Hotel. The project also required drilling and installation of caissons around the perimeter of the excavation site to support a deep building footprint. Another concern was that the neighboring structures needed to withstand pile driving and other heavy construction activity necessary to build the foundation and support system.
GeoSonics/Vibra-Tech was retained by the project development manager to conduct preconstruction surveys for structures surrounding the site. This service also included installing Re:mote vibration monitoring systems to provide measurements of ground settlement near three adjacent structures and monitoring static ground water levels near the site.
Re:mote seismographs were placed around the perimeter both outside and inside surrounding structures to provide vibration monitoring data and vibration alarm notification to construction personnel. Potential ground settlement and static ground water level adjacent to the construction of the tower was monitored using three Multiple Point Borehole Extensometers (MPBX) and one piezometer. All Re:mote systems were programmed to take measurements every 30 minutes and plot readings on a graph updated and posted to a website every four hours.
Each MPBX wire transducer detected settlement at three depths; ground surface, 10 feet, and 25 feet below the ground surface. For measuring surface settlement, a fiberglass rod with a hydraulic anchor was secured in a borehole at a depth of approximately 55 feet (elevation 1142 feet) to serve as a reference point. Additional fiberglass rods were anchored in boreholes at elevations of 1172 feet and 1187 feet corresponding to depths of approximately 25 feet and 10 feet from the surface. After allowing two days for the equipment to settle, all measurement transducers were zeroed to provide a starting baseline for all subsequent data.
The piezometer, installed at the Colcord Hotel, is a vibrating wire pressure transducer with a 50 psi range. The piezometer borehole was drilled to 47 feet (elevation 1152 feet) and back filled to 45 feet (elevation 1154 feet) with coarse silica sand. One inch PVC riser pipe was then installed, with the deepest 10 foot section slotted. The borehole was again backfilled with coarse silica sand to 33 feet (elevation 1166 feet). The remaining depth of the borehole was filled with Bentonite grout. The riser pipe was cut off flush with the pavement surface. A day after completing the drilling and casing process, a water level meter was used to determine the initial height of the water to be at 27 feet below the pavement surface (elevation 1169 feet). Using the difference between the initial pressure reading and pressure measured with the sensor in the casing, and taking into account the elevation of the sensor relative to the surface elevation, the elevation of the static ground water level throughout the project was measured and compared.