Houston’s geology is dominated by the Beaumont Formation—Pleistocene-age clays and silts that dictate how water moves and how foundations perform. The expansive clays in this unit have a plasticity index often exceeding 25, making particle-size distribution a critical parameter before any structural load is applied. A complete grain size analysis, combining mechanical sieving with the hydrometer method per ASTM D422, resolves the full gradation curve from coarse sand down to colloidal clay. This data feeds directly into USCS classification and helps engineers anticipate shrink-swell behavior that costs Harris County property owners millions in foundation repairs annually. For projects near the Buffalo Bayou, where alluvial soils interlayer with older deposits, we often pair the test with a CPT investigation to correlate stratigraphy with laboratory-measured fines content.
In Houston’s Beaumont clays, the difference between a poorly graded sand and an elastic silt is often less than 10% passing the No. 200 sieve—the hydrometer resolves that margin.
