A foundation in the northwest Rosedale area and one near the Kern River floodplain east of downtown Bakersfield encounter radically different materials. The Rosedale site might sit on clean alluvial sands, while the river-adjacent property often hits silty, high-plasticity layers that hold water. Without a full grain size curve—sieve analysis plus hydrometer—you are guessing at drainage behavior, frost susceptibility, and compaction potential. We run the full stack because a simple wash-sieve split misses the fines fraction that controls most geotechnical problems in the southern San Joaquin Valley. Our lab processes material from test pits and SPT drilling across Kern County, delivering a particle-size distribution that connects field observation to engineering numbers.
A grain size curve without the hydrometer tail is only half the story—the silt and clay fraction governs permeability, shrink-swell, and seismic response.
Methodology and scope
Local considerations
ASCE 7-22 and the California Building Code classify Bakersfield as a high-seismic area, and grain size is the first trigger for liquefaction screening per the NCEER simplified procedure. A soil with a coefficient of uniformity below 3 and a fines content under 15 percent—common in Kern River channel deposits—puts a site squarely in liquefiable territory. Misclassifying a silty sand as a clayey sand shifts the entire seismic design category and can lead to under-designed foundations. The 2019 Ridgecrest sequence reminded every geotechnical engineer in Kern County that distant earthquakes still produce damaging ground motion here. A complete hydrometer curve gives you the percent fines and the clay fraction needed for the Boulanger-Idriss triggering correlation, making grain size analysis a non-negotiable step before any major structure.
Applicable standards
AASHTO T-88: Standard Method for Particle Size Analysis of Soils, ASTM D7928: Standard Test Method for Particle-Size Distribution (Hydrometer), ASTM D2487: Standard Practice for Classification of Soils for Engineering Purposes (USCS), NCEER Liquefaction Screening (Youd-Idriss 2001)
Associated technical services
Full Sieve + Hydrometer Package
Combined AASHTO T-88 and ASTM D7928 testing on a single split sample, providing the complete particle-size distribution from 3 inches down to 0.001 mm. Includes D10, D30, D60, Cu, Cc, USCS classification, and a soil description per ASTM D2487.
Wash-Sieve Analysis for Coarse Soils
For clean sands and gravels from Bakersfield’s alluvial fans, we run an ASTM C117 wash through the #200 sieve followed by mechanical shaking. This method reports percent gravel, sand, and fines with a 2-hour turnaround when project schedules demand it.
Hydrometer-Only Fines Characterization
When the coarse fraction is already known or sampled separately, we perform a standalone ASTM D7928 hydrometer test to define the silt-clay ratio. This data feeds directly into Atterberg limits correlation and shrink-swell potential assessment for Kern County expansive soils.
Typical parameters
Frequently asked questions
How much does a grain size analysis cost in Bakersfield?
A full sieve-plus-hydrometer test on a single sample typically runs between US$90 and US$210, depending on sample condition, maximum particle size, and whether rush processing is requested. Bulk pricing applies for projects with more than ten samples.
What is the hydrometer test and why do I need it?
The hydrometer test, per ASTM D7928, measures particle sizes smaller than 0.075 mm—the silt and clay fraction—by timing the settling rate in a water-dispersant suspension. Without it, you cannot determine the clay percentage, which controls permeability, plasticity, and liquefaction susceptibility. In Bakersfield’s mixed alluvium, skipping the hydrometer often leads to a misclassified soil and an incorrect foundation design.
How long does a grain size test take?
A basic wash-sieve analysis can be completed in one to two working days. The full hydrometer curve requires a minimum of 48 hours because ASTM D7928 mandates readings at specific intervals over 24 hours, plus oven-drying and data reduction. We report preliminary sieve data early if the project needs fast classification for field decisions.