AASHTO 93 governs flexible pavement design across Louisiana, but Shreveport’s subgrade introduces variables no textbook can fully capture. The Red River floodplain deposits highly plastic clays with CBR values that swing from 2% to 12% depending on the season. We run full resilient modulus testing and backcalculate layer coefficients using local traffic spectra. For projects near the Port of Caddo-Bossier, where truck loads exceed 80,000 lb, the design must account for fatigue cracking in the asphalt layer and rutting in the granular base. Our lab, accredited under ASTM D1559 and D1883, delivers structural numbers calibrated to real subgrade behavior rather than generic county assumptions.
A pavement design is only as good as the subgrade modulus it assumes. In Shreveport, that assumption changes with every rainstorm.
Process and scope
The asphalt layer is designed using Superpave performance grading adapted to Louisiana’s binder selection criteria. For parking lots in Youree Drive commercial zones, we combine the pavement structural design with a plate load test on the prepared subgrade to verify the modulus before the first lift goes down. When the project involves deep fill sections near Cross Lake, we also reference the sand cone density results to confirm compaction above 95% of modified Proctor before assigning the final structural number.
Site-specific factors
Shreveport’s climate splits between summer droughts and winter saturation — a pattern that pumps fine-grained subgrade soils into the aggregate base. Without a proper filter layer, the pavement loses 30% of its structural capacity within five years. We saw this in industrial park expansions off I-220 where initial designs skipped the geotextile.
The high plasticity index of local clays — often above 30 — drives volumetric swell during the wet season. That uplift cracks the asphalt longitudinally before traffic even loads the section. Our design approach treats the subgrade as an active layer: we either stabilize it with lime to a depth of 12 inches or replace it entirely with select fill when the PI exceeds 25. For projects within the Shreveport city limits, we coordinate with the Department of Engineering and Environmental works to match the city’s standard pavement details.
Standards used
ASTM D1883 – California Bearing Ratio (CBR) of Laboratory-Compacted Soils, ASTM D1559 – Marshall Test for Asphalt Mixtures (historical reference for local specs), AASHTO T 307 – Resilient Modulus of Subgrade Soils, ASTM D2487 – Unified Soil Classification System, IBC 2021 – Section 1803 Geotechnical Investigations
Complementary services
Subgrade Characterization & CBR Testing
We extract Shelby tube samples at grade elevation and run laboratory CBR and resilient modulus tests. The resulting design CBR value is corrected for seasonal variation using Thornthwaite moisture indices applied to northwest Louisiana. We deliver the effective roadbed soil modulus for direct input into AASHTOWare or DARWin.
Pavement Structural Analysis & Layer Optimization
We model the full pavement section — asphalt surface, base, subbase, and treated subgrade — computing structural number, layer coefficients, and fatigue life under the design ESAL spectrum. For heavy truck corridors near the Shreveport Regional Airport, we include a terminal serviceability index target of 2.5 and a rut depth limit of 0.4 inches.
Typical parameters
FAQ
What is the typical structural number required for a residential street in Shreveport?
For a low-volume residential street with less than 0.3 million ESALs and a design CBR of 4%, the structural number typically falls between 2.8 and 3.2. This assumes a 2-inch asphalt surface over 8 inches of crushed stone base. We adjust upward if the subgrade is untreated high-plasticity clay.
How much does a flexible pavement design package cost for a commercial lot in Shreveport?
For a standard commercial lot up to 2 acres, the geotechnical investigation and pavement design package ranges from US$1,780 to US$4,980. The final cost depends on the number of borings, depth of exploration, and whether resilient modulus testing is required beyond standard CBR.
Do you account for the high shrink-swell potential of Shreveport soils in the pavement design?
Yes. We measure the plasticity index on every subgrade sample. When the PI exceeds 25, we recommend either lime stabilization to a minimum depth of 12 inches or removal and replacement with select fill. The design section then uses an increased structural number to offset any residual swell pressure beneath the treated layer. More info.