In The Know – By Neil Waggoner

27 October 2020

Jessica Huff

A story about the need for investigating your soil before building.
Ole Clyde called me and wanted to develop a subdivision on the west side of Highway 45 Alternate near Artesia, Mississippi. He said he had gotten a good deal on some pastureland with catfish ponds. My first response to Ole Clyde was to get a Site Survey and Soil Borings. Being the hardheaded, stubborn man that he is Ole Clyde, declined my advice and went full steam ahead developing his new subdivision, and called it “Artesia Heights”.
About 6 months later Ole Clyde called me. He had filled in some of the catfish ponds, made a few roads, and was building houses. He did the layout himself and had one house sitting on top of an old pond levee, so half the house was sitting on part of a filled in pond. He asked me why his concrete slabs were cracking. My response was that he should have used a Licensed Geotechnical Engineer to investigate the soil under each house and given that information to a Structural Engineer to design the foundation and slab for each house.
I explained to him that a Geotechnical report would have told him what to do with the dirt under the house. Artesia, Crawford, and the areas west of the Tombigbee River form what we call “The Prairie”. These areas are known for Black Prairie Soil. In the Winter when it is wet, the topsoil is comparable to chewing gum. In the dry Summer, it gets hard as concrete. In the summer when the clay is hard, I have seen bricks heave up out of the ground.
Because our firm, JBHM Architects, works on buildings throughout Mississippi, we know that in this area over-excavation of existing soil is typically required. An excavation of 4 feet deep under the footprint of the building, plus 8 feet beyond the footprint is not unusual. After the bottom of the excavation is compacted, new Select Fill Soil is imported to the building site and installed in 8” lifts, compacted in each layer. This will provide a solid pad for the foundation to sit.
If Ole Clyde would have taken my advice and used a Professional to design the foundation and the slab, he most likely would have included a minimum 24” deep reinforced concrete footings, with #4 rebar and welded wire in the slab. The slab would have been installed on a vapor barrier, 4” of granular fill, and the soil I mentioned earlier under the granular fill should be compacted to minimum 95% of the standard dry density of the soil.
In the end, Ole Clyde said I was a smart fella, and that I “musta learned somethin over at Mis’sipi’ State”. He also said he would most likely listen to me next time and build the foundations of his new houses to last.

Neil Waggoner, AIA, NCARB
JBHM Architecture
Columbus Office