Grain Size Analysis (Sieve + Hydrometer) in Murfreesboro, TN

Murfreesboro’s growth didn’t stop at the square. Since the 1980s the city pushed into the karst lowlands along the West Fork Stones River, where soil profiles flip from stiff clay to silty sand in less than 40 vertical feet. That stratigraphic jump wrecks gradation assumptions fast. A complete grain size analysis—dry sieve plus hydrometer—gives us the particle distribution from coarse gravel down to the 2-micron clay fraction. Without that curve, you’re guessing at drainage, frost susceptibility, and compaction behavior. We run the full ASTM D422 and D6913 suite in our IBC-aligned lab. For deeper exploration where SPT refusal hits rock, we often pair the gradation data with a seismic refraction survey to map the rockhead before setting pier depth.

A 10% shift in fines content can move a soil from SM to SC—and that changes the allowable bearing pressure by 30% under IBC Table 1806.2.

Scope of work

ASTM D6913 governs the sieve stack, and ASTM D422 (or D7928) drives the hydrometer side. IBC Section 1803 requires soil classification per USCS, and in Rutherford County that means nailing the silt-versus-clay boundary. Our lab hydrometers are calibrated with sodium hexametaphosphate dispersion, read at 0.5, 1, 2, 5, 15, 30, 60, 240, and 1440 minutes. The sieve train runs 75 mm to No. 200, with wash-through on the 75-micron pan. Typical Murfreesboro samples plot as silty sand (SM) or lean clay with sand (CL), depending on whether the borrow came from the Stones River terrace or the limestone residuum. When the gradation curve flags gap-graded material, we cross-check with Proctor compaction to nail maximum dry density before any fill spec gets written.

Area-specific notes

At 619 feet elevation, Murfreesboro sits on Ordovician limestone that weathers into fat clay lenses. In 2010 the city recorded over 300 sinkhole-related insurance claims in a single year, per the Tennessee Department of Commerce and Insurance. A grain size analysis that skips the hydrometer misses the sub-75-micron fraction entirely, and that’s where the collapse-prone fines hide. We’ve pulled samples near Middle Tennessee Boulevard where the minus-200 fraction jumped from 12% at 5 feet to 48% at 12 feet—classic epikarst infill. USCS classification flips on that number, and so does the internal friction angle used in slope models. Getting the full gradation curve isn’t optional here; it’s the difference between a footing that drains and one that traps water until the limestone dissolves another void.

Technical parameters

Parameter	Typical value
Sieve range (dry)	75 mm to No. 200 (75 µm)
Hydrometer range	75 µm to approx. 1 µm
Hydrometer reading intervals	0.5, 1, 2, 5, 15, 30, 60, 240, 1440 min
Dispersant	Sodium hexametaphosphate (NaHMP)
Sample mass (sieve)	500 g for sand; 2 kg for gravelly soils
Soil classification system	USCS (ASTM D2487)
Report turnaround	3 business days, same-week for rush

Linked services

Full Sieve + Hydrometer Package

Dry sieve from 75 mm to No. 200 plus hydrometer sedimentation on the minus-75-micron fraction. Includes USCS classification, coefficient of uniformity (Cu), coefficient of curvature (Cc), and percent gravel, sand, silt, and clay. Delivered as a signed PDF report with semi-log gradation plot.

Wash-Through Sieve Only

For coarse-grained soils where the fines content is visibly below 5%. We run ASTM D6913 with wash-through on the No. 200 sieve, oven-dry the retained fraction, and report the full coarse gradation. Suitable for concrete aggregate and drainage blanket spec checks.

Q&A

How long does a grain size analysis take in your Murfreesboro lab?

Standard turnaround is 3 business days from sample delivery. The hydrometer side runs a minimum 24 hours of sedimentation readings. Rush processing can deliver results same-week if we receive the sample by Tuesday morning and you flag it at login.

What does a grain size analysis cost for a Rutherford County project?

A full sieve-plus-hydrometer package typically runs between US$100 and US$200 per sample, depending on gravel content and whether we need to split the sample. Wash-through sieve-only runs at the low end of that range. We’ll confirm before testing.

Do you accept disturbed bag samples from Murfreesboro drillers?

Yes. Most of our gradation samples arrive as disturbed bag material from SPT splits or hand-auger borings. We dry the sample at 110°C, weigh it, and run a full visual per ASTM D2488 before starting the mechanical analysis.

Can you classify the soil for IBC bearing pressure tables?

The grain size analysis plus Atterberg limits gives us the full USCS classification—SM, SC, CL, CH, GP-GM, etc. That classification maps directly to IBC Table 1806.2 presumptive bearing pressures. We include the USCS symbol and group name on every report.