Sub-base design

Sub-grade assessment

The typical way to measure the strength of the soil is California Bearing Ratio (CBR), this rating should be obtained by testing. The table below gives typical strengths (CBR) for sub-grades found in the UK.

Initial steps

It’s highly recommended that a site survey is done to establish what the site conditions are, as the sub-grade strength and soil characteristic are important to identify, so the correct construction depth is calculated to avoid pavement collapse or subsidence.

Table 1 Sub-grade assessment Table 2 Soil Characteristic Sub-base depths