Geophysical Imaging
Provided the client with S-scan geophysical subsurface imaging
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The Challenge
- Continuous cracking on a concrete slab in the building
- Geotechnical drilling wasn’t possible within the building, so an alternative method was needed to determine the cause
The client reported continuous cracking on the concrete slab within the building. The available geotechnical investigation data collected outside the building weren’t sufficient to establish the cause for the slab cracking. Due to low access within the building interior, geotechnical drilling inside the building wasn’t possible. Thus, Geocomp developed an investigation plan to cover an inclusive investigation conducted inside the building.
The Solution
Geocomp performed S-scan surveys within the building with wireless, highly sensitive accelerometers to provide continuous subsurface imaging which could not have been achieved with traditional geotechnical drilling activities. At select locations, S-scan results were corroborated with boring data to support causation analysis. Geocomp evaluated the causation of cracking with:
- Floor elevation survey and geotechnical boring investigations. The elevation survey clearly showed substantial differentials at the west side of the building and close to the perimeter where the cracks were visible.
- S-scan survey within the building included multiple lines from the west and east sides. The dense spacing of S-scan nodes (approximately 2-ft) allowed for characterizing the upper 10-15 ft. of subgrade which was primarily contributing to the settlement, leading to continuous cracks.
After observing the clear difference in elevation, the S-scan survey results identified a progressively thicker layer of clay from east to west, contributing to more consolidation and creep at the west edge. Approximately 1,200 linear ft of geophysical survey lines were surveyed within the building’s interior in just one weekend.
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