Better Science, Better Results

Problem: Initial Florida Department of Transportation roadway explorations identified sinkhole conditions. The FDOT consultant performed ground penetrating radar and standard penetration test borings in conjunction with FDOT cone penetrameter testing, totalling 26 exploration points, which identified deep relic sinkhole conditions. FDOT determined that deep geophysical imaging was needed to assess risk.

Results: MERIT identified the sinkhole throat at 170 feet with corresponding identification of subsurface geometry, including competent limestone, weathered limestone, raveling soils, and upper sand unit.  Also evident was the geometry of the sinkhole depression infilled by the upper sand unit.

Outcome: Based on the totality of the geotechnical testing and deep geophysical imaging, risk modeling was performed to determine the potential activity of the sinkhole was low. Thus, no additional ground modification would be required to support the proposed roadway.

Problem: A potential sinkhole was identified at a former gas station, prompting concerns about groundwater contamination.

Results: MERIT identified a potential relic sinkhole at approximate stations 75 to 95 feet and potential raveling zone from stations 120 to 140 feet, achieving significantly higher resolution at depth than what can be achieved with surface electrical resistivity. The survey provided geometry of the Stratum 1 layer, in particular an infilled depression area related to potential active sinkhole; an understanding of distribution of Stratum 2 soils deposited that filled in the relic sinkhole, and geometry/distribution of the Stratum 3 or pinnacle karst.

Outcome: MERIT results saved the client time and resources on exploration drilling and remediation.

Problem: Large amounts of differential settlement were observed at an industrial property constructed over a former landfill. Due to the presence of an on-going landfill gas removal system, there were concerns that drilling/soil testing would penetrate confining units of the landfill and possibly of release contaminates.

Results: The MERIT survey was superior to the surface methods, revealing the existence of deep depression along the profile of the east building. This feature is considerable in size (22.5 x 18.8m deep) and was unable to be imaged by ground penetrating radar or surface electrical resistivity.

Outcome: MERIT enabled the foundation design to be roughly 60% smaller as it would have been using standard geotechnical techniques.

Problem: In 2010 a sinkhole opens up at the Bordeaux Village condominiums shallowing a car, making national news. The sinkhole was infilled and foundation underpinning and grouting of the structure was performed.

Results: Concerns over the exact location of the sinkhole throat lead to MERIT geophysical survey. Installation was performed over the sinkhole location using direct push, allowing for installation without drilling fluids which may reactivate the sinkhole. The throat was clearly imaged at 13 meters.

Outcome: Clear identification of the sinkhole throat enabled precision foundation stabilization via grouting and underpinning. Additionally MERIT was able to confirm the sinkhole’s conduit system and identify the vehicle.

Problem: A sinkhole on a private property adjacent to the Florida Turnpike leads to slumping of two lanes and six inch differential movement of the sound barrier, threatening a 54″ pressurized water main.

Results: The MERIT survey identified two distinct geophysical anomalies located in the subsurface, suggesting a sinkhole development type called cover-collapse. Cover-collapse sinkhole formation occurs when the underlying limestone is covered by significant layer of clay. Dissolution of the limestone creates a void in the clay which will eventually collapse.

Outcome: An engineering proposal was put forward to create an above ground bridge spanning the affected subsurface area identified in the MERIT images. Without MERIT to elucidate the problem, the cost of engineering and ensuring the safety of the infrastructure would have tripled from $2 million to $6 million.

Problem: Aerial surveys identified a section of exposed pressurized gas main adjacent to a North Florida creek. Ground survey identified sinkhole swallets near the pipeline. Initial surface geophysical investigation identified an anomaly 80 feet in length near the exposed pipeline.

Results: MERIT was deployed to provide high resolution imaging of the originally identified anomaly, resulting in the precise identification of a 20 foot wide feature instead of the original 80 feet assessment.

Outcome: Florida gas was able to focus their engineering efforts on the area defined by MERIT, reducing time and cost to 25% of the original bid.