Retaining walls - Geotechnical Investigation and Design Tables - page 254

•

The table below is based on the pier Diameter (D).

•

Sands and gravels assume some minor clay content.

•

Without some clay content and where a high water table exist, the pier spacing
would need to be reduced.

Table 20.5 Typical pier spacing.

Type of material Strength Typical pier spacing

Intact rock High

>

5D

Low 5D

Fractured rock High 5D

Low 4D

Gravel Dense 3D

Loose 2.5D

Sand Dense 2.5D

Loose 2.0D

Silts Very stiff 2.0D

Firm 1.5D

Clays Very stiff 2.0D

Firm 1.5D

20.6 Wall drainage
•

All walls should have a drainage system.

Table 20.6 Typical wall drainage measures.

Wall Drainage measure Typical design detail for rainfall environment

height

1000 mm 1000 mm < >

1m Weep holes at 250 mm from base 50 mm Weep holes at 75 mm Weep holes at < • • •

of wall or as low as practical 3.0 m spacing, or 3.0 m spacing, or

Geotextile wrapped 75 mm 200 mm drainage gravel 200 mm drainage gravel

• • •

perforated pipe at base of wall behind wall behind wall

with outlet.

1-2 m Weep holes and Geotextile 50 mm Weep holes at 75 mm Weep holes at • • •

wrapped 75 mm perforated pipe 3.0 m spacing, and 3.0 m spacing, and

at base of wall with outlet. 200 mm drainage gravel 200 mm drainage gravel • •

behind wall behind wall

2-5 m Weep holes and Geotextile 75 mm Weep holes at 75 mm Weep holes at

• • •

wrapped 100 mm perforated pipe 3.0 m horizontal and 2.0 m horizontal and

at base of wall with outlet. vertical spacing vertical spacing

(staggered), and (staggered), and

200 mm drainage gravel 300 mm drainage gravel • •

behind wall behind wall

Internal drainage system to be Filter drainage material Filter drainage material

• • •

considered inclined with a minimum inclined with a minimum

thickness of 300 mm thickness of 300 mm

( Continued )