Grain Size Analysis (Sieve + Hydrometer) for Eugene Oregon...

A recent mixed-use project in the Whiteaker neighborhood hit a lens of silty clay at 6 feet that nobody expected. The contractor had assumed clean alluvium based on a few shallow test pits. It took a full grain size analysis with hydrometer to confirm the fine fraction was above 40 percent, which changed the foundation drain design and the compaction spec. In Eugene, where the Willamette River has been rewriting the subsurface for millennia, soil gradation can shift dramatically within a single city block. Our team runs sieve stacks from 3-inch down to No. 200 and then hydrometer readings when fines exceed 12 percent, giving you a complete particle-size distribution curve that actually means something for your footings or pavement subgrade.

A gradation curve without hydrometer data below the No. 200 sieve is just half the story in Eugene's silty floodplain soils.

Our service areas

Scope of work

What we see repeatedly in Eugene is that soils mapped as 'sandy silt' on the USGS quadrangle turn out to be gap-graded, often missing the medium sand fraction entirely. That gap matters: it affects permeability, frost susceptibility, and how the material compacts under a vibratory roller. The combined ASTM D6913/D422 method we use separates coarse fraction by sieve and fine fraction by hydrometer using a sodium hexametaphosphate dispersant. We report D10, D30, D60, coefficient of uniformity, and coefficient of curvature on every job, not just when someone asks. For sites near the Amazon Creek floodplain, we often pair the gradation curve with Atterberg limits to nail down the USCS classification before the structural engineer locks in the bearing capacity assumptions. The lab runs a minimum of 500 grams for soils with visible fines, and we wash the No. 200 sieve with distilled water to avoid flocculation artifacts that inflate the silt percentage.

Grain Size Analysis (Sieve + Hydrometer) for Eugene Oregon Construction Sites — Technical reference — Eugene Oregon

Area-specific notes

Eugene sits on a complex stack of Pleistocene Lake Allison deposits, Missoula Flood slackwater silts, and Holocene Willamette River channel sands. The 44th parallel cuts right through town, and the valley floor here drops below 430 feet elevation, which means the water table can sit within 3 to 6 feet of the surface from November through April. When a grain size analysis skips the hydrometer on a silty sand from the Row River formation, the reported fines content can be off by 15 to 20 percentage points. That error cascades: the USCS classification flips from SM to ML, the seismic site class per ASCE 7-22 might shift from D to E, and the design loses its intended conservatism. For liquefaction assessments, the fines content from a full hydrometer test feeds directly into the SPT-based triggering correlations per Youd and Idriss (2001). A wrong number there is not academic: it is a foundation that sinks during a Cascadia event.

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Standards used

ASTM D6913-04(2009)e1 – Standard Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis, ASTM D422-63(2007)e2 – Standard Test Method for Particle-Size Analysis of Soils (Hydrometer), ASTM D2487-17e1 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), AASHTO T 88-22 – Standard Method of Test for Particle Size Analysis of Soils, IBC 2021 Section 1803 – Geotechnical Investigations (referencing ASCE 7-22 site classification requirements)

Reference parameters

Parameter	Typical value
Test Methods	ASTM D6913 (sieve), ASTM D422 (hydrometer)
Sieve Range	75 mm (3 in) to 75 µm (No. 200)
Hydrometer Range	75 µm to approximately 1 µm (clay fraction)
Minimum Sample Mass	500 g for soils with fines; 200 g for clean sands/gravels
Dispersant	Sodium hexametaphosphate (NaHMP) solution per ASTM D422
Reported Parameters	D10, D30, D60, Cu, Cc, percent gravel/sand/silt/clay
Sample Preparation	Oven-dried at 110 ± 5°C, washed over No. 200 sieve
QA/QC	Duplicate hydrometer readings at 1, 2, 5, 15, 30, 60, 250, 1440 min

Common questions

How much does a grain size analysis with sieve and hydrometer cost in Eugene?

For a combined ASTM D6913/D422 test on a single sample, budget between US$90 and US$190 depending on whether we are running just the coarse sieve or the full hydrometer curve. Most Eugene projects submit 3 to 5 samples per boring to capture vertical variability, so a typical report runs a few hundred dollars total.

Do I really need the hydrometer test, or is the sieve enough?

If the washed No. 200 fraction is above 5 to 12 percent, the hydrometer is necessary to quantify the silt and clay split. In Eugene's Willamette Valley silts, skipping it often misclassifies an ML as an SM, which changes the seismic site class under ASCE 7-22 and can lead to an unconservative liquefaction assessment.

What is the typical turnaround time for a gradation report?

A sieve-only report leaves the lab in 24 to 48 hours. A combined sieve and hydrometer test requires the full 24-hour sedimentation reading period, so final reports typically go out in 3 to 4 business days. We can expedite to 48 hours for an additional fee when a foundation pour is waiting on the classification.

Location and service area

We serve projects across Eugene Oregon and surrounding areas.

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