What standards does your soil mechanics laboratory follow?

Our laboratory operates in accordance with British Standards (BS 1377) and Eurocode 7. All testing procedures are accredited under ISO 17025, ensuring compliance with UK regulatory requirements for geotechnical investigations.

How long does a typical soil testing program take?

Standard classification tests such as granulometry and Atterberg limits are completed within 5–7 working days. Advanced triaxial and consolidation tests may require 2–4 weeks, depending on the number of samples and drainage conditions.

Do you provide services for small-scale projects?

Yes, our firm supports projects of all sizes, from residential extensions to major infrastructure. We offer flexible sampling kits and remote consultation to accommodate smaller budgets while maintaining full technical rigor.

Sand Equivalent Calculator — SE

The Sand Equivalent (SE) is an indirect and rapid measure of the quality and quantity of plastic fines (clay) in a granular soil. It is based on the sedimentation separation of sand and clay fractions in a graduated cylinder with flocculating solution. This calculator applies the BS 1377-2 / BS EN ISO 17892-4 formula from the readings of sand height (h2) and total clay + sand height (h1), with typical acceptance ranges from the UK Highways Agency Manual of Contract Documents for Highway Works (MCHW) and BS 882 for concrete aggregates. It is the fastest mandatory test for aggregate quality control.

What is SE and when to apply it?

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

Formulas applied

Formula BS 1377-2 / BS EN ISO 17892-4:

SE (%) = (h2 / h1) · 100

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

h2 = height reading of settled sand only

Standardised procedure: 85 ± 5 ml of material passing a 4.75 mm sieve is placed in a cylinder with calcium chloride flocculating solution; agitation for 45 s in a mechanical shaker; rest for 20 min; reading h1 (upper) and h2 (lower, with weighted cone)

Acceptance criteria (MCHW Series 800):

Granular base CBR 80: SE ≥ 50 %

Sub-base 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 C30
Source	River Cachapoal, lot 14/May
Volume of sample passing 4.75 mm sieve	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 complies for structural concrete. Interpretation: there is ~20 % clayey-silty fraction over the total sedimentation, acceptable for concrete mixes. If the same sand were used in a CBR 80 granular base, the criterion would be SE ≥ 50 and it would comply comfortably. 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 review of the stockpile origin.

Result: SE = 80.6 % · Passes ≥ 75 % · Suitable for structural concrete C30.

Interpretation of results

SE = 80 % is typical of washed river sands of good quality. SE < 50 suggests significant clay contamination: washing or rejection is required. The historical trend of the test per quarry is as important as the point value: sharp drops indicate a change in the extraction face. For high-strength structural concretes (> C40) some projects require SE ≥ 80 %. The test does not replace chemical analysis of salts or particle size analysis, but detects variations in minutes.

Reference standards

BS 1377-2 — Methods of test for soils for civil engineering purposes — Classification tests
BS EN ISO 17892-4 — Geotechnical investigation and testing — Laboratory testing of soil — Part 4: Determination of particle size distribution
BS EN ISO 17892-12 — Geotechnical investigation and testing — Laboratory testing of soil — Part 12: Determination of liquid and plastic limits
Manual of Contract Documents for Highway Works (MCHW) — Volume 1 Series 800 (SE requirements)
BS 882 — Specification for aggregates from natural sources for concrete

Frequently asked questions

How many tests per lot?

MCHW requires at least 1 SE per 500 m³ of material or 1 per quarry stockpile, whichever is less. For concrete, BS 8500 requires 1 per 200 m³ of sand. For statistical control, a minimum of 5 tests per month on an active quarry is recommended.

What if SE varies greatly between tests?

A coefficient of variation > 15 % indicates a heterogeneous sample or source. It is recommended to increase test frequency, identify the source of variation (quarry face, stockpile, operator) and use 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 a 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 clayey-silty fraction is removed and SE increases significantly (10-20 points). This has energy and water costs. Alternative: blend with clean sand from another source until an acceptable average SE is reached.