Rock mass classification systems - Geotechnical Investigation and Design Tables - page 240

Figure 18.3 Hoek - brown criteria.

18.26 Prediction of support pressure and unsupported span
using Q values

•

The support as recommended by Barton et al. (1974) was based on the following
pressures and spans.

Table 18.26 Approximate support pressure and spans using Q value (adapted from Barton, 2006).

Rock mass quality, Q value

<

0.01 0.01-0.1 0.1-1.0 1-10 10-100 100-1000

Support pressure (kg/sq cm) 5-30 3-15 1-7 0.5-3 0.1-2 0.01-0.2

Unsupported span (m) 0.5 m 0.5-1.0 m 1.0-2 m 2-4 m 4-12 m 12 m

≤ >