A lot of the soil we see under Wilmington's surface tells a mixed story. You might hit clean sand in one borehole and stiff gray clay just twenty feet over. That's the legacy of the Fall Line and the Delaware River deposits. In our experience, guessing the gradation leads to bad numbers. We run the full ASTM D2487 suite—mechanical sieve for the coarse fraction and hydrometer on the fines—so you get a reliable particle-size curve. For projects near the Christina River or along the I-95 corridor, this data feeds directly into drainage design and bearing capacity estimates. When we see more than 12% passing the No. 200 sieve, we often recommend pairing the analysis with Atterberg limits to pin down the plasticity before finalizing the foundation type.
We've learned that a missing hydrometer on Wilmington silts can overestimate permeability by a factor of ten—and that changes the entire dewatering plan.
Technical details of the service in Wilmington Delaware
Demonstration video
Typical technical challenges in Wilmington Delaware
We reviewed a warehouse project off Governor Printz Boulevard where the geotech skipped the hydrometer on a silty sand. The material was classified as SP, drainage was designed for clean sand, and within two years the slab had differential settlement. Turned out the fines content was 22%—enough to hold water and soften the subgrade. On the other side of town, a retention basin on Lancaster Pike had a liner specified for a poorly graded gravel that didn't exist. The actual material was gap-graded, and the liner punctured after the first heavy rain. When we run the full sieve and hydrometer analysis, we catch these mismatches. The D15 and D85 from the grain size curve are what we use to check filter compatibility with the surrounding soil. Skip that, and you're gambling on a number that could cost you a rebuild.
Our services
Our Wilmington lab handles everything from sample prep to reporting. Depending on your project needs, we can focus on the coarse fraction or run the complete combined analysis.
Mechanical Sieve Analysis (Coarse Fraction)
We wash and dry the sample, then shake it through a full stack of ASTM E11 sieves. This gives you the gravel and sand distribution for drainage and compaction control on projects like road base under rigid or flexible pavement sections.
Hydrometer Analysis (Fine Fraction)
For material passing the No. 200, we run a sedimentation test with temperature-corrected readings at 0.5, 1, 2, 5, 15, 30, 60, 240, and 1440 minutes. This defines the silt and clay fractions that control compressibility and frost susceptibility in the I-95 corridor.
Questions and answers
What's the typical turnaround time for a grain size analysis in Wilmington?
Most projects get results in 3 to 5 business days after we receive the sample. If you're on a tight timeline—say a contractor waiting to pour—we can run it in 24 hours for a small rush fee. The hydrometer takes the longest because of the settling time, but we start it early in the day to keep things moving.
How much does a combined sieve and hydrometer test cost?
A full combined analysis (sieve plus hydrometer) typically runs between US$100 and US$200 per sample, depending on the number of sieves required and whether we need to do a wash first. We'll give you a firm number once we see the material.
Do you need a full bucket of soil for this test?
Not usually. For sands and gravels we need about 500 grams of dry material. For silts and clays, 200 grams is enough—but we prefer you send a one-gallon bag so we have extra for a re-test if something looks off. The key is that the sample is representative of the layer you're classifying.
Can you classify my soil from just a sieve analysis, without the hydrometer?
You can if it's obviously granular and clean, but in Wilmington we rarely skip the hydrometer. The silty deposits along the Delaware River often have enough fines to push the classification from sand to silty sand, which changes the engineering properties. We'd rather run the full test than give you a USCS symbol that's wrong.