Foundation performance in New Orleans starts with particle distribution, and our grain size analysis follows ASTM D422 with full hydrometer extension for the city's fine-grained alluvials. The Mississippi River delta has deposited interbedded silts, organic clays, and loose sands across the metro area—materials that change volume, drain poorly, and shift under load. A sieve-only curve misrepresents these soils. We run the complete stack from No. 4 to No. 200, then continue with hydrometer readings down to the 2-micron range, generating a continuous gradation that feeds directly into USCS classification per ASTM D2487.
For sites near the Industrial Canal or out in Metairie, we often pair this data with CPT testing to correlate tip resistance with fines content, and with Atterberg limits to confirm plasticity characteristics of the clay fraction before the structural engineer locks in bearing assumptions.
A combined sieve-and-hydrometer curve is non-negotiable in New Orleans—gap-graded levee sands and plastic deltaic clays behave radically differently, and the gradation tells you which one you are dealing with before the footing goes in.
Methodology applied in New Orleans
For deep foundation design in the CBD where piles socket into Pleistocene terrace deposits, we integrate gradation results with SPT drilling data to refine shaft friction estimates in coarse-grained strata. The hydrometer curve also flags the transition between silt and clay dominance, which controls consolidation settlement predictions in the compressible Holocene clays underlying most of the city.
Typical technical challenges in New Orleans
New Orleans grew by draining swamps that had been accumulating fine Mississippi River sediment for 7,000 years, and the resulting subsidence has left much of the city below sea level. This history matters for grain size analysis because the soils that remain—soft organic silts and clays with occasional sand lenses—are among the most settlement-prone in North America. When gradation testing skips the hydrometer, engineers miss the high silt content that explains why a levee section consolidates unevenly or why a sheet pile wall in the Ninth Ward starts seeping within weeks.
USACE design manuals for the Hurricane Protection System explicitly require full particle-size distribution curves for seepage and piping analyses. A poorly graded sand with a uniformity coefficient below 3, common in point bar deposits along the river, poses a different risk: it can fluidize rapidly under seismic or hydraulic loading. We quantify both extremes in a single test report, giving the design team the Cu, Cc, and percent fines they need to specify filter compatibility, estimate permeability via Hazen or Kozeny-Carman correlations, and apply the correct ASCE 7 site class for seismic design in a city where soft soil amplification is a documented hazard.
Our services
Our grain size analysis supports multiple geotechnical workflows across the New Orleans metro area. The two primary service configurations are:
Full Gradation Package (Sieve + Hydrometer)
Combined mechanical sieve analysis on the coarse fraction and hydrometer sedimentation on the minus-200 material. Includes oven-dry moisture content, preparation per ASTM D421, and a continuous particle-size distribution curve from 4.75 mm down to 2 μm. Delivered with D10, D30, D60, uniformity coefficient, coefficient of curvature, and USCS group symbol per ASTM D2487. Required for foundation bearing capacity calculations, seepage analysis, and liquefaction screening in Orleans and Jefferson Parishes.
Material Compliance Screening
Sieve-only analysis for aggregate base course, concrete sand, and fill material verification. Covers No. 4 to No. 200 with optional hydrometer add-on if fines exceed 5 percent. Used by contractors placing select fill under slabs in Lakeview or backfilling behind floodwalls to confirm gradation meets project specifications and USACE EM 1110 criteria for engineered fill.
Questions and answers
How much does a grain size analysis cost in New Orleans?
A standard combined sieve and hydrometer analysis typically ranges from US$110 to US$210 per sample, depending on whether the project requires single-point or multi-point testing and the number of samples submitted. Volume discounts apply for larger exploration programs, and we provide firm quotes after reviewing the soil types and project specifications.
How long does the hydrometer portion take?
The hydrometer sedimentation test requires a minimum of 24 hours of controlled-temperature readings, and often up to 72 hours for high-plasticity clays common in the New Orleans area. Combined with sieve drying, shaking, and data reduction, a full gradation report is typically ready within 3 to 5 business days from sample receipt. Expedited turnaround is available for active construction schedules.
Why is the hydrometer necessary for New Orleans soils?
New Orleans soils contain a significant proportion of silts and clays deposited by the Mississippi River—often 60 to 90 percent passing the No. 200 sieve. A sieve-only analysis stops at 75 microns and cannot distinguish between silt and clay, which have fundamentally different shear strength, compressibility, and drainage characteristics. The hydrometer quantifies the clay fraction needed for USCS classification, consolidation settlement estimates, and defensible liquefaction assessments under the IBC.
Do you provide the USCS classification from the grain size data?
Yes. Every grain size report includes the full USCS group symbol and group name per ASTM D2487, using the percent gravel, sand, and fines from the gradation curve combined with Atterberg limits data if available. For fine-grained soils classified as CL, CH, ML, or MH, we strongly recommend pairing the grain size analysis with liquid limit and plastic limit testing to confirm the plasticity-based classification, since the hydrometer alone cannot distinguish between a lean clay and an elastic silt.