Field Density Test (Sand Cone Method): Procedure, Calculation & Report Format

Rolling a subgrade or embankment layer means nothing until you prove the compaction is actually there. The field density test by the sand cone method is the classic field check: dig a small hole, measure its exact volume with calibrated sand, weigh the soil that came out, and compare the in-place dry density with the laboratory maximum dry density. The result — percent compaction — is what consultants accept or reject a layer on.

Governing Standards (and an Important Correction)

The correct standards for this test are:

• ASTM D1556 / D1556M — “Standard Test Method for Density and Unit Weight of Soil in Place by the Sand-Cone Method”
• AASHTO T 191 — “Density of Soil In-Place by the Sand-Cone Method”

A correction worth making openly: you may find older site documents (including the URL of this very article) referencing “ASTM D1596” for this test. ASTM D1596 has nothing to do with soil — it is the “Standard Test Method for Dynamic Shock Cushioning Characteristics of Packaging Material.” It was simply the wrong number. The soil test is D1556. You will also see “AASHO T-191” on old report formats — AASHO was renamed AASHTO in 1973, so the modern designation is AASHTO T 191.

What the Test Tells You

Field density testing answers one question: what percentage of the laboratory maximum dry density (MDD) did the roller actually achieve in the field?

Typical acceptance values (always confirm your project specifications):

Layer	Usual minimum compaction
Embankment / subgrade	95% of MDD
Sub-base / base course	98–100% of MDD
Shoulders	95% of MDD

Percent compaction is calculated as:

% Compaction = (Field dry density ÷ Maximum dry density) × 100

The MDD and optimum moisture content (OMC) come from the laboratory Proctor test — AASHTO T 99 / T 180 or ASTM D698 / D1557 — run on the same soil.

Apparatus

• Sand cone apparatus: 1-gallon jar, detachable double cone with a valve
• Base plate with a centre hole (also used as a template for digging)
• Calibrated dry sand — clean, dry, free-flowing, of uniform grading (commonly the fraction passing a 2 mm sieve and retained on a 1 mm sieve); its bulk density must be determined in the lab
• Balance (readable to 1 g for field work)
• Moisture tins or a Speedy moisture tester for field water content
• Excavating tools: spoon, chisel, brush — plus a tray to catch every grain of excavated soil

Calibration Before Testing

Two calibrations are needed, and both are done before going to the field:

1. Bulk density of the sand — fill a container of known volume with the calibrated sand (poured, not compacted, in the same way it will flow in the field), weigh it, and divide: bulk density = mass of sand ÷ volume of container.
2. Cone correction — the amount of sand that fills the cone and the base-plate hole. Place the base plate on a flat surface, invert the filled apparatus over it, open the valve until flow stops, close it, and weigh the apparatus. The difference from the starting weight is the cone correction — sand that never reaches the test hole and must be subtracted every time.

Practical note: Re-check the sand bulk density whenever the sand gets damp, is replenished, or the weather changes. A 2% error in sand density becomes a 2% error in every hole volume you measure.

Step-by-Step Procedure

1. Prepare the surface. Trim a level area roughly the size of the base plate. Remove all loose, uncompacted material.
2. Seat the base plate firmly so it does not rock or shift.
3. Dig the hole through the plate opening, for the full depth of the compacted layer. Collect all excavated soil in the tray — nothing is left behind or brushed away.
4. Weigh the excavated soil immediately (wet mass). Take a representative portion for moisture content.
5. Determine moisture content — oven-dry per AASHTO T 265, or on the spot with a Speedy moisture tester (calcium carbide reacts with the soil water, and the pressure gauge reading converts to moisture percent via the supplied chart).
6. Fill the hole with sand. Weigh the apparatus full of sand, invert it over the plate, open the valve, and let sand flow until it stops. Close the valve — do not tap or vibrate the apparatus — and weigh the apparatus with the remaining sand.
7. Calculate: sand in hole = (sand used) − (cone correction); hole volume = sand in hole ÷ sand bulk density.

Worked Example (With Real Numbers)

A test on a compacted subgrade layer:

Reading	Value
Mass of apparatus + sand, before	7,200 g
Mass of apparatus + sand, after	3,950 g
Sand used (hole + cone)	3,250 g
Cone correction	460 g
Sand in hole	2,790 g
Bulk density of calibrated sand	1.42 g/cm³

Step 1 — Hole volume

Volume = 2,790 ÷ 1.42 = 1,965 cm³

Step 2 — Wet (bulk) density

Mass of excavated wet soil = 3,850 g

Wet density = 3,850 ÷ 1,965 = 1.96 g/cm³

Step 3 — Dry density (moisture by Speedy = 9.5%)

Dry density = Wet density ÷ (1 + w) = 1.96 ÷ 1.095 = 1.79 g/cm³

Step 4 — Percent compaction

Laboratory MDD = 1.88 g/cm³ (OMC = 10.2%)

% Compaction = (1.79 ÷ 1.88) × 100 = 95.2%

Required: 95% → the layer passes. Also note the field moisture (9.5%) is close to OMC (10.2%) — soil compacted near OMC compacts most efficiently, which is exactly what the numbers show.

Field Density Test Report Format

Below is a practical report layout adapted from a typical Highway Department sand-cone report (AASHTO T-191). A blank, ready-to-use version of this report format can be downloaded here:

Download FDT Report Template (Sand Cone, AASHTO T-191) — DOCX

A. General

#	Item
1	FDT Test No.
2	Chainage / location
3	Layer No. and depth of hole (cm)
4	Date of testing

B. Moisture Content

#	Item
1	Can No.
2	Mass of empty can (g)
3	Mass of can + wet soil (g)
4	Mass of can + dry soil (g)
5	Mass of water (g)
6	Mass of dry soil (g)
7	Water content (%)
8	Speedy moisture reading (%)

C. Field Density

#	Item
1	Mass of soil excavated from hole (g)
2	Mass of sand + apparatus, before (g)
3	Mass of sand + apparatus, after (g)
4	Mass of sand used, hole + cone (g)
5	Cone correction — sand to fill cone (g)
6	Mass of sand in hole (g)
7	Bulk density of calibration sand (g/cm³)
8	Volume of hole (cm³)
9	Wet density of soil (g/cm³)
10	Dry density of soil (g/cm³)
11	Maximum dry density, lab (g/cm³)
12	Optimum moisture content (%)
13	Compaction obtained (%)
14	Compaction required (%)
15	Result: Pass / Fail

The report is signed by the contractor’s and consultant’s representatives, with chainage, request number, and remarks.

Common Mistakes That Ruin Results

• Using damp or mixed sand. Sand must be oven-dry and from the same calibrated batch. Damp sand bridges in the cone and under-fills the hole.
• Skipping the cone correction. The cone holds a surprising amount of sand; forgetting it inflates the hole volume and under-reports density.
• Losing excavated soil. Every grain that falls outside the tray is density you “lose” — the soil mass must be complete.
• Rocking base plate or a ragged hole. An unstable plate lets sand leak under it; an over-dug, bell-shaped hole is fine (sand measures whatever shape), but undercutting the plate is not.
• Vibrating the apparatus while sand flows — it densifies the sand in the hole and shrinks the measured volume.
• Wrong moisture value. A Speedy reading is fast but less precise than oven drying; know which one your specification accepts.

Practical note: If a test fails, do not just re-test the same spot hoping for a better number. Find the cause — usually moisture far from OMC or an unrolled patch — correct it, re-roll, and test a fresh location.

Field Density Calculator (Sand Cone)

Sand Cone vs Core Cutter vs Nuclear Gauge: Which Method to Use

The sand cone is not the only way to measure field density. Here is how the three common methods compare:

	Sand cone (ASTM D1556)	Core cutter (IS 2720)	Nuclear gauge (ASTM D6938)
Principle	Hole volume by calibrated sand	Steel cylinder driven into soil	Gamma radiation backscatter
Speed	30–45 min per test	15–20 min per test	2–5 min per test
Cost	Very low	Low	Very high + licensing
Accuracy	Reference method	Good in cohesive soils only	Good, needs calibration
Limitation	Slow; not for >38 mm stone	Fails in gravelly/sandy soil	Radiation safety, licensed operator
Best for	Roads, embankments, base	Small earthworks, cohesive fills	Large projects, rapid QC

Practical note: On most Pakistani road projects the consultant’s specification names the sand cone as the referee method. Even where a nuclear gauge is used for speed, its readings must be correlated against sand-cone tests — the gauge is a production tool, the sand cone is the judge.

Worked Example 2: A Failing Test — Diagnose, Don’t Just Re-Test

A second test on the same subgrade, different location:

Reading	Value
Sand in hole	2,610 g
Sand bulk density	1.42 g/cm³
Hole volume	2,610 ÷ 1.42 = 1,838 cm³
Wet soil from hole	3,420 g
Wet density	3,420 ÷ 1,838 = 1.86 g/cm³
Field moisture (Speedy)	14.8%
Dry density	1.86 ÷ 1.148 = 1.62 g/cm³
Lab MDD	1.88 g/cm³ (OMC 10.2%)

% Compaction = (1.62 ÷ 1.88) × 100 = 86.2% — FAIL (required 95%).

But look at the moisture: 14.8% against an OMC of 10.2% — the soil is far too wet. Rolling wet soil just kneads it; no number of passes will fix this. The correct action: stop, aerate the layer (blade it open, let it dry back toward OMC), re-roll, and test a fresh location. I have seen contractors burn a whole day re-rolling a wet layer and failing every test — one hour of drying would have passed it.

Testing Different Soils: Practical Adjustments

• Sandy soils: dig carefully — the hole walls collapse easily. Keep the hole smaller and work fast; collapsed walls let sand fill beyond the true hole and under-report density.
• Clayey soils: moisture control is everything. Test at OMC ± 2%; clay compacted dry of optimum can look dense but swell later.
• Gravelly base course: particles above ~38 mm jam in the cone neck. Switch to the large-hole sand method (ASTM D4914) or the rubber-balloon method (ASTM D2167) rather than forcing the standard cone.
• Rainy weather: never test a rain-soaked surface and call it the layer. Scrape off the wetted crust, test the compacted material below, and record the conditions on the report.

The Site Workflow: From Test Request to Layer Approval

On a running project the field density test sits inside a paper trail. Knowing the flow saves arguments:

1. Contractor finishes rolling a layer and raises a test request (chainage, layer number, date).
2. Consultant’s inspector witnesses the test — un-witnessed tests are routinely rejected.
3. Lab computes percent compaction against the approved Proctor MDD for that soil.
4. Pass (≥ required %): the layer is approved in writing and the next layer may start.
5. Fail: a non-conformance note is issued; the contractor corrects (drying, re-rolling, or re-laying) and requests a re-test at a fresh location.

Practical note: Never place the next layer over a failed or untested one hoping nobody notices. Consultants check layer approvals against pour/rolling records, and uncovering work for re-testing costs far more than the test itself.

More Questions Site Engineers Ask

How deep should the test hole be?
The full depth of the compacted layer being tested — typically 10–15 cm for a subgrade lift. Testing only the top 5 cm of a 20 cm layer proves nothing about the bottom.

Can the field density test be done in the rain?
No — or at least, not honestly. Rain changes the surface moisture and softens the top crust. Wait for the surface to dry back, trim off the disturbed material, and test the true compacted layer.

What test frequency does NHA require?
Follow the contract’s technical specifications — NHA General Specifications typically call for density testing at regular chainage intervals per layer (commonly every 100–200 m per lane, minimum one per day’s work). The specification governs; when in doubt, test more, not less.

Why must the calibration sand be re-checked?
Because bulk density is the foundation of every volume you measure. Sand picks up moisture from humid air, breaks down with reuse, and gets contaminated — any of which changes its bulk density and silently biases every test. Re-check with each new batch and whenever conditions change.

What if my cone correction changes between calibrations?
Investigate before testing. A drifting cone correction usually means sand is sticking in the valve (damp sand) or the cone is damaged. Fix the cause, re-calibrate, and do not use results from the suspect period.

Frequently Asked Questions

How many field density tests are needed per layer?
Follow the project specification. A common field rule is one test per 500–1000 m² of compacted layer, with at least one test per day’s work — but the specification governs, not the rule of thumb.

Sand cone or nuclear density gauge?
The sand cone is the reference method — cheap, simple, and accepted everywhere. Nuclear gauges are faster but need licensing, safety handling, and regular calibration against sand-cone results.

Can the sand cone be used on base course with large stone?
ASTM D1556 suits soils with particles up to about 38 mm (1½ in.). For coarser base material, use the large-hole method (ASTM D4914) or the rubber-balloon method (ASTM D2167).

What if the field moisture is much higher than OMC?
Stop and dry the layer back (aeration, re-mixing) before rolling. Compacting wet-of-optimum soil wastes roller passes and can pump fines to the surface.

Final Thoughts

The sand cone test is nearly a century old and still the backbone of earthwork quality control, because it is direct: it measures the actual soil in the actual layer. Calibrate the sand honestly, dig the hole carefully, and the arithmetic in the worked example above is all that stands between you and a defensible pass/fail decision.

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Written by Mohsin Raza Adil — BSc Civil Engineering Technologist (NTC-registered), Pakistan.