Rock mass classification systems - Geotechnical Investigation and Design Tables - page 236

Table 18.18 Approximate support required using Q value (adapted from Barton at al., 1974).

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

Poor Poor Fair Good

Description

Exception Extremely Very OK/very Ext./Exc.

1.7-2.3 m

Shotcreted
No
shotcrete

1.0-1.3 m 1.3-1.7 m 2.3-3.0 m N/R

Bolt
spacing

1.0-1.3 m 1.3-2.0 m 2.0-4.0 m N/R

Typical shotcrete
thickness

300 mm 250 mm 150 mm 120 mm 90 mm N/R

1 < --- 150 mm shotcrete --- > 50
1 < --------- 120 mm shotcrete ------- > 70
1 < ---------- 90 mm shotcrete ---------- > 80

Bolt
length
(m)

Span or
height (m)
/ESR

1.5 < -- 50 mm shotcrete -- > 60

1 1.2 150 mm 110 mm 75 mm

2 1.5

2.4

200 mm 140 mm 90 mm 45 mm

5 250 mm 175 mm 120 mm 60 mm 40 mm

10 3.0 300 mm 225 mm 150 mm 90 mm 40 mm

20 5

7

300 mm 210 mm 120 mm 50 mm N/R

30 300 mm 135 mm 75 mm

50 11

20

150 mm 100 mm

100

Steel ribs 0.5 m 0.5-1.0 m 1.0-2.5 m 2.5-5 m N/R

- Barton et al.'s research was primarily for tunnel support requirements. Since

that time many relationships to other parameters have been developed. Many
practitioners have suggested this is beyond its initial scope. However as in
many engineering relationships it does provide useful initial guidance to other
parameters.

- Some of these relationships are presented in Table 18.18.

18.19 Prediction of velocity using Q values
•

The prediction of the P - wave velocity based on the Q value is shown in the Table
18.19.

•

This is for hard rock, near the surface.