EN ISO 17892-5 and ASTM D2435: where the two diverge

Updated: September 30, 2026 · ISKRIT

Both standards run the same test on the same apparatus and report the same quantities. The differences are in procedure and in what counts as a completed loading step, and they change results rather than paperwork.

Common ground

Incremental loading, a laterally confined specimen, void ratio against effective stress, compression index Cc on the logarithmic plot, coefficient of consolidation from the time-settlement curve of each step. A calculation engine treats them identically, which is why our tool applies one computational branch to both and differs only in the label it prints.

Where they part

The load increment ratio, the criterion for ending a step and the treatment of secondary compression are handled differently. ASTM D2435 defines two methods, one on a fixed 24-hour step and one on a rate-of-deformation criterion; the European standard leans on the deformation criterion and expects the report to state which was used. On a soil with pronounced creep the two give measurably different void ratios at the same stress, because a 24-hour step captures secondary compression that a rate criterion cuts off.

Specimen height to diameter ratios and permitted trimming disturbance also differ, which matters most for stiff overconsolidated clays where the recompression slope is small and disturbance flattens it.

What to write in the report

Whichever standard is cited, the report is only usable if it states the stress interval each modulus refers to, the initial void ratio, the step duration criterion and whether the specimen was saturated before loading. Without those four items a Cc or an Eoed cannot be compared with another laboratory's number, and cross-laboratory comparison is the usual reason someone opens the report.

Questions

Do EN ISO 17892-5 and ASTM D2435 give the same results? They run the same test and report the same quantities, but differ in the load increment ratio, the criterion for ending a step and the treatment of secondary compression. On a soil with pronounced creep the void ratios at the same stress differ measurably.

Why does the choice of a 24-hour step matter? A fixed 24-hour step captures secondary compression that a rate-of-deformation criterion cuts off, so the report has to state which criterion was used.

Select the standard on the oedometer calculator; the label travels into the output, so the report states which tradition the numbers belong to.