Retaining walls - Geotechnical Investigation and Design Tables - page 261

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Limitation of soil nails:
- Some minor movement is acceptable.
- No water table, or water table can be reduced.

20.15 Driven soil nail designs
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Driven or fired soil nails have a lower tensile capacity than driven or drilled and
grouted type. The latter has a larger area and tensile strength, and with a larger
spacing.

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Driven nails are usually not applicable in weak rocks.

Table 20.15 Driven nails - typical designs (adapted from Phear et al., 2005 and Clouterre, 1991).

Typical slope angle Facing type Length Area per nail (m 2 ) Nails per m 2

70 to 90 ◦ Hard 0.5 to 0.7 H 0.4 to 1.0 1 to 2.5

45 to 70 ◦ None 0.5 to 0.7 H 0.7 to 1.2 0.8 to1.4

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Typical strength of a driven nail is 50 to 200 kN.

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Table assumes a level ground at the top.

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Gravel or Rock fills would typically have some difficulty. Using a sharpened edge
angle iron instead of a bar provides a stiffer inclusion that may work for small
enough particle sizes.

20.16 Sacrificial thickness for metallic reinforcement
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Sacrificial nail thickness or other barriers need to be applied for corrosion
protection based on service life.

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For driven nail barriers are not possible.

Table 20.16 Corrosion protection for soil nails (Schlosser et al., 1992).

Environment Sacrificial thickness (mm) for minimum service life (yrs)

18 months 1.5 to 30 yrs 100 yrs ≤

A little corrosive 0 2 mm 4 mm

Fairly corrosive 0 4 mm 8 mm

Corrosive 2 mm 8 mm Plastic barrier

Strongly corrosive Compulsory plastic barrier Sacrificial thickness above +

20.17 Design of facing
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The design of the facing depends on the uniform pressure acting on the facing and
tension in the nails at the facing T o .

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=

Spacing (S) maximum of S V and S H .