During site development, much research is conducted to ensure there aren’t geologic surprises that could affect the placement or integrity of planned structures or construction costs. Fracture trace analysis (FTA) is a cost-effective first step. FTA is a non-invasive (usually desktop) review of existing/available topographic (preferably LiDAR), hydrologic (water bodies and well information), aerial photographic (current and historical), and remote sensing imagery (e.g., infrared, vegetative health index, RADAR) to identify lineations that might be faults, fractures, open bedding planes, contacts, dikes, or other hydrogeologically significant features that can affect depth-to-rock, soil properties, and the occurrence and/or movement of water beneath the site. After this step, other surveys can proceed with greater confidence that intrusive testing is being performed in the right place.
Uncovering Hidden Hazards: The Power of Fracture Trace Analysis
A housing complex was proposed for a 65-acre site in Maryland. RETTEW’s FTA established there would be no negligible hazard. Still, topography and terrain slope (calculated from LiDAR), historical stream maps, and aerial photographs from the 1930s through 1960s (see Figures 1-4) identified five distinct linear features crossing the site (see Figure 5). Based on their lengths and appearance in independent datasets, two were classified as major features,” and they intersected on the site.
The client received RETTEW’s FTA report with georeferenced geologic maps, topographic and terrain slope maps, historical aerial photographs, and interpretive feature traces before a geotechnical boring program. A few days later, the geotechnical engineer supervising the drilling reported drilling at the intersection of the two major features and encountering an anomalous thickness of very soft and wet (70% saturated) soils. In addition, borings along the trace of one of the features revealed similar conditions. His message concluded, “Definitely something going on down there…it is nice when the data lines up!”
Contact us in the early stages of your project, and we will tell you if (and where) something is “going on down there.”
Meet Chuck Rhine
Senior Geophysicist
Meet Chuck Rhine whose impressive 30-year career in geophysical surveys includes everything from marine investigations to exciting discoveries like an airplane in Lake Mead. Go “beneath the surface” and get to know Chuck!