Grain Size Analysis for San Jose Construction Sites

A common mistake in San Jose is assuming all valley soil behaves like uniform sand. That assumption leads to underestimated settlement or drainage failures. We see it often on sites near Coyote Creek where thin silt lenses get overlooked. A proper grain size analysis catches those layers before they become a problem. Our lab runs the full curve: mechanical sieves for the coarse fraction and a hydrometer for fines passing the No. 200 sieve. The result is a precise ASTM D2487 classification that feeds directly into foundation design, permeability estimates, and fill suitability. Many projects in the city also pair this with a CBR test for road subgrade when the grain size distribution suggests marginal material.

In the Santa Clara Valley, a missing silt layer on the grain size curve can delay a project by weeks.

Approach and scope

San Jose sits on the alluvial plain of the Santa Clara Valley, where soil can shift from clean sands to fat clays in less than 50 feet horizontally. This variability makes grain size analysis non-negotiable. We wash samples through a full stack of sieves per ASTM D422, then run the hydrometer on the minus 200 fraction. The combined curve tells you the coefficient of uniformity, coefficient of curvature, and the exact percentages of gravel, sand, silt, and clay. For projects near the Guadalupe River or in the Evergreen foothills, these numbers dictate whether you need imported fill, lime treatment, or a deeper excavation. We also cross-check results against Atterberg limits when plasticity is suspected in the fines.

Site-specific factors

Downtown San Jose and areas along North First Street sit on Holocene alluvium with interbedded clays, silts, and sands. Missing the silt content on a grain size curve can lead to overestimating the friction angle by several degrees. That error cascades into undersized footings or retaining walls. Seismic demands under ASCE 7-16 add another layer: loose silty sands with more than 15% fines can exhibit cyclic mobility during a Hayward Fault event. A complete particle size distribution tells you whether the soil meets the gradation band for engineered fill or if it needs stabilization. Without that data, compaction specs are just guesswork. The cost of a re-test is trivial compared to the cost of a foundation that settles unevenly two years after occupancy.

Technical parameters

Parameter	Typical value
Test method	ASTM D422 / ASTM D6913 (sieve), ASTM D7928 (hydrometer)
Sample mass required	500 g for sands, 1,500 g for gravelly soils
Sieve range	3 inch to No. 200 (75 mm to 75 µm)
Hydrometer range	75 µm down to 0.2 µm (clay fraction)
Reporting parameters	D10, D30, D60, Cu, Cc, % gravel, sand, fines
Classification standard	ASTM D2487 (Unified Soil Classification System)
Typical turnaround	3-5 business days, rush available

Complementary services

Sieve Analysis

Mechanical shaking through a stack of sieves from 3-inch down to No. 200. We report the mass retained on each sieve and the cumulative percent passing. Compliant with ASTM D6913 for coarse and fine aggregates.

Hydrometer Analysis

Sedimentation test for material passing the No. 200 sieve. We use a 152H hydrometer and record readings over 24 hours to capture the full silt and clay distribution per ASTM D7928.

Combined Curve & USCS Classification

We merge the sieve and hydrometer data into a single semi-log plot. The soil gets a USCS group symbol and group name per ASTM D2487, ready for your geotechnical report.

Fill Suitability Screening

We compare your grain size curve against Caltrans or local agency gradation bands for structural fill, pipe bedding, and drainage layers. You get a clear yes/no on material compliance.

Relevant standards

ASTM D2487 – Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), ASTM D422 – Standard Test Method for Particle-Size Analysis of Soils, ASTM D7928 – Standard Test Method for Particle-Size Distribution (Gradation) of Fine-Grained Soils Using the Sedimentation (Hydrometer) Analysis, IBC Chapter 18 – Soils and Foundations

Common questions

What does a grain size analysis cost in San Jose?

A combined sieve and hydrometer test typically runs between US$110 and US$210 per sample, depending on the number of sieves and whether the hydrometer is needed. Most San Jose projects require both for a complete USCS classification. We carry out a firm quote once we know the sample count and turnaround time.

How is the grain size analysis performed?

We oven-dry the sample, break it down with a rubber mallet, and run it through a stack of sieves on a mechanical shaker. The material passing the No. 200 sieve goes into a sedimentation cylinder with a dispersing agent. A hydrometer measures the density of the suspension at timed intervals. The two datasets are stitched together into one continuous curve.

What sample size do you need?

For sands and silts, 500 grams is usually enough. If the soil contains gravel up to 3/4 inch, we need about 1,500 grams. We can split larger samples in the lab. Just bring us a gallon-sized zip-lock bag of representative material from your excavation or boring.

How long does the test take?

A standard sieve analysis takes one business day. The hydrometer test requires a minimum 24-hour sedimentation period. Combined, expect results in 3 to 5 business days. We offer a 48-hour rush service for an additional fee.

Do you follow ASTM standards?

Yes. Our procedures follow ASTM D422 and D6913 for sieve analysis and ASTM D7928 for the hydrometer. The final classification is assigned per ASTM D2487, which is the standard referenced by the IBC and most San Jose building officials.