Precision Grain Size Analysis for Fayetteville Arkansas Construction Sites

A recent mixed-use development off College Avenue in Fayetteville hit an unexpected layer of silty clay at just six feet below grade. The initial site investigation had assumed a uniform sandy silt profile, but the reality was far more complex. The structural engineer needed to know exactly how much clay was in that layer before finalizing the foundation drainage. That is where a rigorous grain size analysis becomes indispensable. By running the full stack of mechanical sieves followed by a hydrometer test, we mapped the particle distribution from coarse sand right down to the colloidal fraction. When you are building on the weathered shale and limestone residuum that blankets much of Washington County, understanding the fines content is not a paperwork detail. It directly controls permeability, frost susceptibility, and the long-term settlement behavior of the footing. For projects near the West Fork of the White River, we often pair grain size data with Atterberg limits to build a complete index profile of the cohesive strata.

A well-graded soil with 35% fines is not the same as a uniform sand with 5% fines, even if both classify as SM under USCS. The grain size curve tells the real story.

Scope of work in Fayetteville Arkansas

Fayetteville sits at roughly 1,400 feet elevation on the Springfield Plateau, where the residual soils can shift from gravelly lean clay to fat clay within a few hundred lateral feet. Our grain size analysis protocol follows ASTM D422 for the combined sieve and hydrometer procedure, giving you a continuous particle-size distribution curve from the 75 mm sieve down to 0.001 mm. The test quantifies the percentage of gravel, sand, silt, and clay in your sample, which then feeds directly into the USCS classification per ASTM D2487. A key output is the coefficient of uniformity and the coefficient of curvature; these numbers tell you whether the soil is well-graded or poorly-graded, which matters enormously for filter design behind retaining walls. In Fayetteville, where stormwater infiltration requirements are strict under the current Arkansas Stormwater Management Plan, we often see geotechnical engineers requesting hydrometer data specifically to verify that the fines fraction will not clog a permeable pavement sub-base. The lab also calculates the D10, D30, and D60 particle sizes, which are essential inputs when you are designing a filter blanket or selecting drain pipe slot sizes for a retaining wall drainage system.

Precision Grain Size Analysis for Fayetteville Arkansas Construction Sites

Parameter	Typical value
Standard method	ASTM D422 / AASHTO T 88
Sieve range	75 mm to 75 µm (No. 200)
Hydrometer range	75 µm to 0.001 mm
Classification system	USCS (ASTM D2487)
Minimum sample mass	500 g for sandy soils, 200 g for fine-grained
Reported parameters	D10, D30, D60, Cu, Cc, % gravel, sand, silt, clay
Dispersion agent	Sodium hexametaphosphate solution

Critical ground factors in Fayetteville Arkansas

A common mistake we observe on Fayetteville projects is the decision to skip the hydrometer portion of the analysis and rely solely on the wash No. 200 result. You get a total fines percentage, sure, but you lose the silt-versus-clay split. That distinction is critical because clay minerals drive shrink-swell behavior and control the soil's reaction to water. In the deep cuts along I-49 through the Boone Formation residuum, a misinterpretation of the fines fraction led to slope raveling and repeated maintenance issues within the first three years after construction. When the hydrometer test is omitted, the engineer is forced to guess the plasticity characteristics from visual classification alone, which is notoriously unreliable in the mixed residual soils of Northwest Arkansas. The grain size curve, when plotted alongside the Atterberg limits, provides a defensible basis for classifying the soil as either silt or clay, which then dictates the allowable bearing pressure and the required undercut depth beneath footings.

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Applicable standards: ASTM D422-63(2007): Standard Test Method for Particle-Size Analysis of Soils, ASTM D2487-17: Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), AASHTO T 88-19: Standard Method of Test for Particle Size Analysis of Soils, ASTM E11-20: Standard Specification for Woven Wire Test Sieve Cloth and Test Sieves

Our services

Our Fayetteville geotechnical laboratory handles the full chain from sample receipt to final data report, with services that extend the value of a grain size curve into practical design parameters.

Combined Sieve and Hydrometer Package

Complete ASTM D422 analysis including mechanical sieving of the coarse fraction and hydrometer sedimentation of the fines, with a detailed particle-size distribution plot and USCS classification.

Hydrometer-Only Analysis for Fines

For samples already processed through the sieve stack, we run the 152H hydrometer test to determine the silt and clay percentages, providing the D10 through D001 particle diameters.

Wash No. 200 and Sieve Analysis

A faster option for clean sands and gravels where the fines content is expected to be below 5%. Includes the wash loss determination and a full sieve stack report.

Frequently asked questions

What is the typical turnaround time for a grain size analysis report in Fayetteville?

Standard turnaround is three to four business days from sample drop-off. We can accommodate 24-hour rush requests when the project schedule demands it, provided we receive the sample before 10 a.m.

How much does a combined sieve and hydrometer test cost for a Fayetteville project?

For a standard combined analysis following ASTM D422, the fee ranges from US$90 to US$200 per sample depending on the quantity of samples submitted and whether the soil is predominantly granular or fine-grained.

How does the hydrometer test separate silt from clay particles?

The hydrometer test relies on Stokes' Law, which relates particle settling velocity to diameter. A dispersing agent deflocculates the clay particles, and hydrometer readings are taken at timed intervals to calculate the percentage of particles finer than 0.075 mm, distinguishing silt-sized from clay-sized fractions.