What is the value of a geotechnical investigation? Yes, our reports will provide bearing capacities for the structural design, soil settlement information for maintenance, and slope stability details. Perhaps you need deep foundations, a soil-nail wall or pavement design. These pieces of information are useful, but without a deeper understanding of the subsurface the information is just that—pieces. The true value of a geotechnical investigation comes when we thoroughly understand conditions below ground, and use our understanding to give our clients the strategies they need.
Often, as geotechs, we hand over our report, not knowing if or when it may be used. When the report is used, we may no longer be involved with the project, and others will use our report, including the understandings of the subsurface, to make plans and decisions. I was recently reminded of how much impact our work can have, even long after it’s completed.
It started back in 2012. GeoEngineers completed a geotechnical investigation in support of the sanitary sewer system improvements in Baton Rouge, LA. During exploratory drilling, we didn’t encounter any ground water. Most of the subsurface was clay, although we encountered a layer of silt in one of the borings. Without experience and understanding of the subsurface, the significance of this silt might have been missed.
The site was located near enough to the Mississippi River to be influenced by the river’s water level, and we noted that an excavation to install sewer pipes below the ground surface could create artesian conditions (when pressurized underground water is forced to the surface). We knew that the silt layer could provide a path for the water to quickly reach the surface, exacerbating the potential for ground heave and unstable construction excavations. Our report provided information about the subsurface, the type of soils the contractor should expect to find during the construction, and ground water conditions. Because of our understanding of the site, we also included construction recommendations, specifically the need for dewatering and water pressure relief to maintain stable excavations. We submitted the report and our involvement with the project ceased.
Fast-forward to 2016, and the sewer project is under construction. As the excavations progressed, the contractor found it harder to control the water. One day, after attempting to sump pump the water out of the excavation without success, the contractor uttered the magic words “unexpected conditions” and “claim.” To the frustration of the owner, the contractor halted construction. The soil began to heave, destabilizing the excavation. It seemed as though the water would continue to rise, carrying along with it the tempers of the contractor and the owner. Finally, the construction team consulted the contract and specifications, and what was included as part of the specifications? Our geotechnical report. The same report that included cautions about, and solutions for, this very water condition.
Four years removed and in the hands of people uninvolved in the original investigation, our report rescued the site owner from a potentially expensive delay and contractor dispute. By following the report’s recommendations, the contractor dewatered the excavation, and work continued normally. Our understanding of the subsurface, and anticipation of possible issues during construction, helped save time, money, and sanity. Valuable, indeed.