Sand Cone Test: Procedure, Calculations and Example

The sand cone test is the old, reliable way to measure how dense a compacted layer really is. A technician digs a small hole in the finished lift, saves all the soil, and refills the hole with a calibrated sand so the hole's volume can be worked out. Weight divided by volume gives density, and that density, compared with a lab maximum, tells the crew whether the lift passes. This guide covers when the test is used, the equipment, the two calibrations, the field steps and the math, with a made-up example.

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The short version

Standards: ASTM D1556 and AASHTO T 191.
Measures: in-place wet density; dry density after a moisture test.
Used on: embankments, road fill, structural backfill, subgrade and base under pavement and slabs.
Result: usually reported as percent compaction against a Proctor maximum dry density.

The equipment

A jar (about a gallon) holding the test sand, with a detachable valve and a metal cone. ASTM D1556 describes a valve opening of about 1/2 inch and cone walls at roughly 60 degrees to the base so the sand fills evenly.
A flat metal base plate with a flanged center hole that the cone seats into.
Test sand that is clean, dry, uniform and free-flowing. ASTM calls for a uniformity coefficient under 2.0, all of it finer than the No. 10 sieve (2.0 mm), and under 3 percent passing the No. 60 sieve.
A container of known volume for calibrating the sand, a scale, digging tools, and a sealed can or bag for the soil.

Two calibrations come first

1. Cone correction. Some sand always ends up in the cone and the base plate rather than the hole. To measure it, fill the jar, set the plate on a flat surface, invert the apparatus on the plate, open the valve until flow stops, close it and weigh what is left. The difference is the cone correction. ASTM's annex has you repeat this at least three times and keep each result within 1 percent of the average. The jar, cone and plate are kept together as a matched set.

2. Sand bulk density. Pour the sand the same way into the calibration container of known volume. Sand weight divided by container volume is the bulk density. Humidity changes it, so ASTM sets a maximum interval between checks, and Indiana's DOT manual has technicians do it daily and with each new bag. Do not jar or vibrate anything while sand is flowing; that packs it tighter and throws off the density.

Field steps

These steps are a simplified walk-through; the standard itself governs real testing.

Weigh the full jar.
Prepare a spot. Pick a representative location, scrape off loose material and make a flat surface for the plate. Pin the plate if needed.
Dig the hole. Dig through the plate's center hole, usually to the depth of the compacted lift. Put every bit of soil in a sealed container right away so no moisture escapes. ASTM sets minimum hole volumes by largest particle size: about 0.05 cubic foot for 1/2-inch material, 0.075 for 1-inch and 0.1 for 1-1/2-inch.
Fill the hole with sand. Seat the cone on the plate, open the valve and let it run until it stops. Close the valve and weigh the jar again.
Weigh the soil and get its moisture. Weigh the wet soil, then dry it (or a portion of it) for water content.
Correct for oversize stone if needed. When the soil has particles retained on the No. 4 sieve, agencies such as INDOT adjust the comparison using AASHTO T 224.

The calculations

Sand in hole = (jar weight before − jar weight after) − cone correction
Hole volume = sand in hole ÷ sand bulk density
Wet density = wet soil weight ÷ hole volume
Dry density = wet density ÷ (1 + moisture as a decimal)
Percent compaction = dry density ÷ lab maximum dry density × 100

Worked example (made-up numbers)

Every number here is invented to show the steps.

Jar before: 15.00 lb. Jar after: 6.10 lb. Sand used: 8.90 lb.
Cone correction: 3.40 lb. Sand in hole: 8.90 − 3.40 = 5.50 lb.
Sand bulk density: 92.0 lb/ft³. Hole volume: 5.50 ÷ 92.0 = 0.0598 ft³.
Wet soil from hole: 7.20 lb. Wet density: 7.20 ÷ 0.0598 = about 120.4 lb/ft³.
Moisture: 10.0 percent. Dry density: 120.4 ÷ 1.10 = about 109.5 lb/ft³.
Lab maximum dry density: 114.0 lb/ft³. Compaction: 109.5 ÷ 114.0 = about 96 percent.

If the spec called for 95 percent, this lift would pass. Many specs ask for 95 or 100 percent of the Proctor value, depending on the layer and the agency.

Common sources of error

Vibration. Traffic, compactors or people stomping near the hole can settle the sand and change the reading.
Lost soil or lost moisture. Every crumb from the hole has to be weighed, and the sample must be sealed fast.
Damp sand. A small amount of absorbed moisture changes the sand's bulk density noticeably.
Hole walls moving. Soft or saturated soils can squeeze in, and loose clean stone can cave. ASTM notes that a calculated saturation over about 95 percent suggests something went wrong.
Mismatched gear. Swapping plates or cones without redoing the cone correction.

Sand cone or nuclear gauge?

A nuclear density gauge gives a reading in minutes and is the everyday tool on many jobs. The sand cone is slower, needs no radioactive source or license, and measures volume directly, so it is common on small jobs and for checking gauge readings. On a home driveway base, neither is usual, but the idea is still useful: a base compacted in thin, damp lifts, as described in compacted lift thickness for a plate compactor, gets close to its target density.

Questions people ask

What is the sand cone test used for?

It checks how dense a compacted layer of soil, fill or base is in the field. The in-place dry density is compared with the lab maximum from a Proctor test to get percent compaction, which is how many specs accept or reject a lift.

How does the sand cone test work?

A hole is dug by hand through a base plate and every bit of soil from it is saved and weighed. The hole is then filled with a clean, dry sand of known density poured from a jar and cone. The weight of sand used tells you the hole volume, and soil weight divided by volume gives density.

What is the formula for the sand cone test?

Hole volume = (sand used minus the sand that filled the cone and plate) divided by the bulk density of the sand. Wet density = wet soil mass divided by hole volume. Dry density = wet density divided by (1 + moisture content as a decimal).

What standards cover the sand cone test?

ASTM D1556 and AASHTO T 191. Both describe the jar, valve and cone apparatus, the calibrations for the cone and the sand, and the field steps.

Sand cone test vs nuclear gauge: which is better?

The nuclear gauge is much faster and gives instant readings, but it needs licensing, training and calibration checks. The sand cone is slower and depends on careful digging, yet it is a direct measurement with no radioactive source, so it is often used to check or correlate gauges.

When should you not use a sand cone test?

ASTM D1556 says it is not suitable for organic, saturated or highly plastic soils that deform, or for loose granular material whose hole walls collapse. It is also meant for soils without much rock over 1-1/2 inches; bigger stone needs a larger test pit method.

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