When we mobilize our CME-75 track rig onto a site near the Red River, the first thing we check is whether the stiff clay crust is hiding something softer underneath. Shreveport sits on the Jackson Group formation, which means Eocene-age clay mixed with Pleistocene terrace deposits—a combination that can turn a straightforward building pad into a settlement headache. We run Standard Penetration Tests with the automatic hammer on that rig, pulling Shelby tubes from depths where the blow count drops below 6. Those undisturbed samples go straight to our lab for consolidation testing, because a raft/mat foundation design here lives or dies on the compression index of the fat clay layer. Most of our work involves commercial buildings along Youree Drive and industrial warehouses out by the Port of Caddo-Bossier, where the water table sits just 6 to 10 feet below grade and the clay swells every spring.
In Shreveport, a mat foundation isn't just a thick slab—it's a structural raft that bridges the Yazoo clay's seasonal volume changes and keeps a building level through drought and flood cycles.
Process and scope
Site-specific factors
A medical office building on Bert Kouns Industrial Loop taught us this lesson the hard way. The original geotech report called for spread footings at four feet, but the contractor hit gray, slick clay at seven feet that smelled like swamp gas. They poured anyway. Within three years, the slab had cracked at the expansion joints and the east wing settled two inches relative to the lobby. We got called in to design a retrofit mat foundation under the existing structure—jacking columns, drilling micro-piles for temporary support, and casting a 24-inch reinforced mat tied into the perimeter grade beams. The differential settlement vanished once the load was spread across the entire footprint. That project drove home what we already knew about Shreveport: when the plasticity index exceeds 30 and the seasonal moisture swings 15 percent, a raft/mat foundation design is not an upgrade; it’s the only option that keeps your framing square and your drywall intact. We now recommend a liquefaction screening on any site within half a mile of the Red River floodplain, because the loose silts at 20 feet can lose strength during a moderate earthquake on the Sabine uplift.
Standards used
IBC 2021 (with Louisiana amendments), ASCE 7-22 (Minimum Design Loads), ACI 318-19 (Building Code for Structural Concrete), ASTM D2435 (One-Dimensional Consolidation), ASTM D4546 (Swell/Collapse Testing)
Complementary services
Full-Service Mat Foundation Package
From SPT borings and Shelby tube sampling to one-dimensional consolidation and swell testing, we build the geotechnical model that drives the mat thickness, reinforcing layout, and settlement predictions. Deliverables include bearing capacity calculations, modulus of subgrade reaction contours, and construction observation during the mud-mat pour and rebar placement.
Forensic Mat Foundation Review
When an existing slab-on-grade or spread-footing building shows distress, we mobilize our rig for supplemental borings, install settlement plates, and run laboratory swell-consolidation tests on the offending clay layer. The resulting retrofit raft/mat foundation design addresses the root cause—not just the symptoms—and gets submitted with a stamped repair letter to the structural engineer.
Typical parameters
FAQ
What does a raft/mat foundation design cost for a commercial building in Shreveport?
For a typical commercial structure between 5,000 and 20,000 square feet, the complete geotechnical investigation plus the raft/mat foundation design package runs from US$1,060 to US$4,510, depending on the number of borings, lab tests required, and whether we need to run a swell-consolidation suite on the Yazoo clay. The fee includes the stamped design report, construction recommendations, and one site visit during the mud-mat pour.
When is a mat foundation better than deep piles in Shreveport?
We lean toward a mat when the bearing stratum is within 30 feet of grade and the structural loads are moderate—think three- to five-story buildings with column spacing under 25 feet. Mat foundations spread the load across the entire footprint, which works well on Shreveport’s stiff upper clay. Piles become necessary when we encounter very soft, normally consolidated clay below 25 feet or when the building has heavy concentrated loads that would punch through a mat.
How long does the design process take from investigation to stamped submittal?
The field investigation typically takes two to three days with our CME-75 rig. Lab consolidation and swell tests require about two weeks for full results. Once we have the soil parameters, the raft/mat foundation design and report preparation take another week. So you’re looking at roughly four weeks from mobilization to a stamped, permit-ready submittal for the City of Shreveport.