What is the purpose of a soil mechanics laboratory?

A soil mechanics laboratory tests soil samples to determine physical and mechanical properties such as strength, compressibility, and permeability. These data are essential for designing foundations, retaining walls, and earthworks, ensuring structures are safe and stable under expected loads.

Which ASTM standards are commonly used in soil testing?

Common ASTM standards include ASTM D1586 for SPT, ASTM D422 for grain size, ASTM D4318 for Atterberg limits, ASTM D698 for Proctor compaction, and ASTM D2850 for unconsolidated-undrained triaxial tests. These ensure consistency and reliability across laboratories.

How does seismic zone affect foundation design?

Seismic zones, defined by ASCE 7, indicate ground motion intensity during earthquakes. Higher zones require stronger foundations, deeper embedment, and sometimes soil improvement to mitigate liquefaction risk. Our laboratory provides dynamic soil properties for seismic analysis.

Sand Equivalent Calculator — SE

This calculator applies the ASTM D2419 formula from the readings of sand height (h2) and total clay + sand height (h1), with typical acceptance ranges from the AASHTO M 43 and concrete standards. It is the fastest mandatory quality control test for aggregates.

What is it and when to apply SE?

SE detects clay contamination in aggregates: high plastic fines content reduces mechanical strength, increases swelling, and decreases adhesion in concrete and asphalt pavements. It is applied to granular bases, subbases, concrete sand, mortar sand, and drainage filters. It is a routine control test (1-2 hours per sample) that complements grain size analysis and Plasticity Index. It does not replace the PI but detects variations in the material source faster.

Applied formulas

ASTM D2419 formula:

SE (%) = (h2 / h1) · 100

h1 = total height reading (settled sand + clay in suspension), in inches or mm

h2 = height reading of settled sand only

Standardized procedure: 85 ± 5 ml of material passing No. 4 sieve is placed in a cylinder with calcium chloride flocculating solution; agitation for 45 s in a mechanical agitator; rest for 20 min; reading h1 (upper) and h2 (lower, with weighted cone)

Acceptance criteria (AASHTO M 43):

Granular base CBR 80: SE ≥ 50 %

Subbase CBR 40: SE ≥ 30 %

Sand for structural concrete: SE ≥ 75 %

Sand for mortar: SE ≥ 65 %

Drainage filter: SE ≥ 80 %

Calculation example

Input data — concrete sand control, plant in central valley area
Parameter	Value
Material	Sand for structural concrete H-30
Source	Cachapoal River, lot 14/May
Volume of sample passing No. 4	85 ml
Rest time	20 min exact
Reading h1 (clay + sand)	6.2 in
Reading h2 (sand only)	5.0 in
Required criterion	SE ≥ 75 % (structural concrete)

SE = (h2/h1)·100 = (5.0/6.2)·100 = 80.6 %. Since SE ≥ 75 %, the material meets requirements for structural concrete. Interpretation: there is ~20 % clay-silt fraction over total sedimentation, acceptable for concrete mixes. If the same sand were used in a granular base CBR 80, the criterion would be SE ≥ 50 and it would meet with margin. Conversely: if the readings had been h1 = 7.0 and h2 = 4.5, SE = 64.3 %, sand unacceptable for structural concrete (contaminated source), acceptable only for common mortar. Lot history: the same quarry had SE = 78-82 over the last 3 months; current variation suggests reviewing the stockpile origin.

Result: SE = 80.6 % · Meets ≥ 75 % · Suitable for structural concrete H-30.

Interpretation of results

SE = 80 % is typical of good quality washed river sands. SE < 50 suggests significant clay contamination: washing or rejection is required. The historical trend of the test per quarry is as important as the single value: sharp drops indicate a change in the mining face. For high-strength structural concretes (> H-40) some projects require SE ≥ 80 %. The test does not replace chemical analysis of salts or grain size analysis, but detects variations in minutes.

Reference standards

ASTM D2419 — Sand Equivalent Value of Soils and Fine Aggregate
ASTM D2419 — Sand Equivalent Value of Soils and Fine Aggregate
AASHTO T 176 — Plastic Fines in Graded Aggregates and Soils
ASTM D2419 (SE requirements)
ASTM C33 — Standard Specification for Concrete Aggregates

Frequently asked questions

How many tests per lot?

AASHTO T 88 requires at least 1 SE per 500 m³ of material or 1 per quarry stockpile, whichever is less. In concrete, ASTM C33 requires 1 per 200 m³ of sand. For statistical control, a minimum of 5 tests per month in an active quarry is recommended.

What if SE varies greatly between tests?

Coefficient of variation > 15 % indicates heterogeneous sample or source. It is recommended to increase test frequency, identify the source of variation (quarry face, stockpile, operator) and take moving averages of 5 tests to decide acceptance. A single test below the limit may be an outlier; two consecutive tests already constitute rejection.

Are SE and PI the same?

No. PI measures the plasticity of fines (clay quality); SE measures the relative quantity of fines compared to sand. Clean sand has high SE regardless of PI. Sand with much non-plastic clay can have low PI and low SE simultaneously. Both are complementary.

Can sand with low SE be corrected?

Yes, by washing with running water and a 0.075 mm sieve. The clay-silt fraction is removed and SE increases significantly (10-20 points). This has energy and water costs. Alternative: mix with clean sand from another source until an acceptable average SE is reached.