When we set up a full sieve stack with a hydrometer sedimentation cylinder for a project here in Richmond, it’s not just about shaking sieves—it’s about reading the geology right. The city sits across the Fall Line, so a single site can transition from Piedmont residual silts and weathered rock near the James River to Coastal Plain sands and marine clays within a few hundred feet. That split geology means particle sizes change fast, and getting the full gradation curve—coarse fraction through ASTM E11 sieves plus the fines fraction via hydrometer following Stokes’ law—is what lets us nail the USCS classification without guessing. For any cut-and-cover work in Church Hill or deep foundation design in the river alluvium near Mayo Island, a combined sieve and hydrometer analysis gives the hard numbers on percent gravel, sand, silt, and clay that control drainage, frost susceptibility, and liquefaction screening before you pour a yard of concrete.
On the Richmond Fall Line, the difference between a well-graded sand and a gap-graded silty sand changes everything—drainage, compaction, and liquefaction susceptibility all pivot on one gradation curve.
Technical details of the service in Richmond Virginia
Critical ground factors in Richmond Virginia
One thing we see repeatedly in Richmond is contractors running a simple wash-200 on site and assuming they have the full gradation, then getting surprised when a hydrometer curve from the lab reveals 35% clay in what looked like a clean sand. On the Coastal Plain side of town—think areas east of I-95 toward the airport—those clay fractions can carry moderate to high plasticity, and if you’re designing a stormwater retention basin or compacted fill pad, the fines content directly affects permeability, shrink-swell behavior, and frost heave susceptibility under Virginia’s freeze-thaw cycles. Skipping the hydrometer portion on a fine-grained soil is risky: you miss the clay-size fraction that governs undrained shear strength and consolidation rate. The IBC and the Virginia Uniform Statewide Building Code both point to site-specific gradation data when classifying soils for foundation design, and an incomplete grain size distribution leaves you guessing on the very parameters that determine whether your footing drains freely or traps water against the stem wall for a decade.
Our services
The grain size distribution is rarely the only data point a Richmond project needs. These are the core tests we run alongside the sieve and hydrometer suite to build a complete geotechnical index profile.
Atterberg Limits (Liquid & Plastic Limit)
Run on the minus-40 fraction of the same sample used for hydrometer analysis. Gives you the plasticity index and the A-line classification to nail the USCS symbol—critical for Richmond’s Coastal Plain clays and Piedmont silts where the gradation alone doesn’t tell you how the soil will behave with moisture.
In-Situ Density (Sand Cone or Nuclear Gauge)
Once the lab gradation confirms the soil type and the Proctor curve is established, we verify field compaction with sand cone testing per ASTM D1556. For Richmond projects on the alluvial terraces, hitting 95% of modified Proctor on a well-graded sand with silt (SW-SM) requires knowing exactly where you sit on the gradation curve—too much fines and the density won’t come up without moisture adjustment.
Common questions
What does a combined sieve and hydrometer grain size analysis cost in Richmond?
For a typical combined analysis—coarse fraction by sieves down to No. 200 plus hydrometer sedimentation on the fines—budget between US$100 and US$190 per sample, depending on whether we’re running the full ASTM D6913/D7928 protocol with wash sieving and multiple hydrometer readings, and whether you need the classification report with the gradation curve plotted and USCS symbol assigned per ASTM D2487.
How long does the hydrometer portion take compared to just a sieve analysis?
The sieve portion can be completed in a day if the sample is oven-dried and we’re just doing a mechanical shake. The hydrometer sedimentation analysis adds at least 24 to 48 hours because the readings are time-dependent—you need the full series from 15 seconds through 24 hours to build the Stokes’ law curve for the silt and clay fractions. We typically report the combined result in 3 to 4 business days from sample receipt.
Why can’t I just run a wash-200 and skip the hydrometer for a Richmond site on the Fall Line?
A wash-200 gives you total percent passing the No. 200 sieve but doesn’t split silt from clay. On Richmond’s Fall Line, where you can have Piedmont residual silts mixed with Coastal Plain marine clays in the same boring, knowing the clay fraction specifically matters for drainage design, frost heave susceptibility, and the USCS classification—an ML (silt) and a CL (lean clay) behave very differently under load even if both pass the No. 200 at 85%. The hydrometer is the only way to get that split reliably.