Ultimate vs Nominal Load Reality Check

A grade name is a class label. An ultimate compression test is a short-term failure load. Neither is what your engineer designs to. This tool applies the CIRIA C680 material partial factor so you can see how far a supplier’s headline number falls once the first divisor lands — and it stops there, because one divisor is not a design method.

Tested ultimate figure

CIRIA C680 material partial factor (F_m) Where a supplier will not name the factor they applied, assume 2.75.

Compare against a nominal grade label

Material-factor value (upper bound, not a design-allowable)

170 kN/m²

≈ 17.4 t/m² · from 468.52 kN/m² ÷ 2.75

The divisor removes 63.6% of the tested number.

A nominal SG-L30 label reads 30 t/m². The material-factor value is 17.4 t/m². Both are true; they answer different questions.

One divisor is not a design method. C737 (2016), which supersedes C680, applies further partial factors for installation, temperature and design life on top of the material factor — so the figure above is an upper bound and your engineer’s allowable will be no higher. Lateral earth pressure, cover depth, groundwater and combined vertical-plus-lateral load cases all sit outside this arithmetic. Per CIRIA C737, most geocellular failures trace to installation, temporary works and ground conditions rather than to inadequate long-term strength. Always ask a supplier for the lateral figure as well as the vertical one.

Request the SGS and Intertek test reports