A large water line break occurred beneath the first floor of a 10-story office building in San Diego . Flooding occurred over a large portion of the first floor of the building. To support an ongoing geotechnical evaluation of the property, we were called upon to provide geophysical services in marking the surface trace of the water line, and utilizing ground penetrating radar (GPR) to search for voids under the concrete slab.
The survey area had many obstacles (desks, chairs, file cabinets, printers, and copy machines) and therefore, a standard survey grid was not acquired, rather a systematic traversing and continuous monitoring of the GPR was conducted over the search area. GPR traversing was performed in all accessible areas of the office in an attempt to locate voids beneath the concrete slab. One approximately 10 foot diameter void (.5 to 1.5 inches thick) was found just below the surface of the concrete above the water line approximately 40 feet from the location of the leak. Following the delineation of voids, concrete cores were collected at several locations and were successful in validating the GPR results.