You can’t take anything for granted; even the ground under your feet. That’s why it is important to have Geotechnical testing done before construction begins on a project. But nothing is perfect, and even the best Geotech firms can’t always determine exactly what it is going on beneath the surface.

A Sinking Feeling

On one of our job sites, the crew arrived one morning to discover that the building slab had sunk about 5 feet, taking a nearby forklift down with it. It turns out there was a sinkhole below this area in the slab on grade. Plenty of pre-construction Geotechnical testing done, but none of the reports indicated the presence of this deep sinkhole.

On another project the geotech report indicated the water table had risen 20 feet in a six-month span. The engineer said this was because the region was coming out of a severe drought and that had significantly dropped the water table prior to the recent rains, but I was skeptical. After grading we discovered that there was surface material on the slope that had been acting as a dam. Once the material was removed, the water table dropped, no problems after all.

Infill Building Sites

We are increasingly working on infill sites inside metropolitan areas, which have been passed over for one reason or the other, often because of the challenge of that particular site. With these challenges, it’s easy for geotech testing to often overlook a potential problem until work actually begins. Geotech is important in those situations, but it’s not a perfect science.

Geotechnical testing is important, but it’s not a perfect science. If the reports are too good to be true, then it probably is. Practicality and common sense still have to factor into the equation, we have found.

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Merrill Stewart is Founder and President of the Stewart Perry Company, a commercial building contractor based in Birmingham, Ala. Contact him via email
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