Retaining walls - Geotechnical Investigation and Design Tables - page 262

Table 20.17 Design of facing (Clouterre, 1991).

Spacing (S) T o / T max Comments

S 1 m 0.6 Usually driven nails ≤

1m

<

S

<

3 m 0.5

+

(S

−

0.5)/5

S 3 m 1.0 Grouted Nails

≥

-T max = maximum tension in the nail in service = ultimate nail pull-out force.

- V and S H Vertical and Horizontal spacing, respectively.

- Nails are designed with an overall factor of safety against pull out of 1.5 and
1.3 for permanent and temporary walls, respectively.

=

20.18 Shotcrete thickness for wall facings
•

The shotcrete facing for soil nails depends on the load, and the slope angle.

Table 20.18 Typical shotcrete requirements.

Condition Shotcrete thickness and design details

Life Temporary: 75 mm to 150 mm Permanent:125 mm to 250 mm

Slope 70 ◦ : 50-150 mm Near vertical 70 ◦ to 90 ◦ : 150-275 mm

<

Typical nail Bent bars 28 mm Bent bars 28 mm or plate head < >

Typical mesh 100 mm to 200 mm opening 75 mm to 100 mm opening size

Typical layers of Steel mesh on one side to Steel mesh on either side

mesh side with soil 150 mm

Additional mesh locally behind plate if
significant torque

Mandatory for thickness >

Embedment below No requirements 0.2 m in rock

finished level 0.4 m in soil or H/20 whichever is higher

20.19 Details of anchored walls and facings
•

Where horizontal movement needs to be constrained, prestressing is required.

•

Soil nail and anchored walls experience different pressures, with the latter designed
for greater loads.

•

These two types of walls are designed differently. Table below is for walls with
near vertical faces.

•

The cost of soil nailing may be 50% of the cost of a tieback wall.

•

Greater movement can be expected in a soil wall than the tieback wall.

20.20 Anchored wall loads
•

Anchor loads depend on the wall height, material behind the wall, groundwater
conditions and surcharge.