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Nailed Slopes 

GEO5

Geotechnical software

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Analysis of nails bearing capacity

For each nail the following bearing capacities are either computed or inputted:

Rf nail head strength
Rt nail strength against breaking
Tp pull-out nail bearing capacity

Strength characteristics of a nail represent the basic parameters to compute the actual force in a nail.


The nail strength against breaking follows from:

where: Rt - strength against breaking
ds - nail diameter
fy - strength of nail material
SBT - factor of safety against breaking

The pull-out nail bearing capacity is calculated by one of the following ways:

1. calculate from ultimate bond strength:

where: Tp - pull-out nail bearing capacity [kN/m]
d - hole diameter
gs - ultimate bond strength
SBe - factor of safety against pull-out


2. calculate from effective stress

where:
where: Tp - pull-out nail bearing capacity [kN/m]
d - hole diameter
σz - vertical geostatic stress
φ - effective angle of internal friction of soil
c - effective cohesion of soil
SBe - factor of safety against pull-out

3. calculate according to HA 68/94

where:
where: Tp - pull-out nail bearing capacity [kN/m]
d - hole diameter
σn - average radial effective stress
φ - effective angle of internal friction of soil
c - effective cohesion of soil
SBe - factor of safety against pull-out

Average radial effective stress ón is calculated by following formula:

where: σz - vertical geostatic stress

where:

Nail head strength is evaluated by formula:

where:
where: l - nail length
Smax - maximum spacing of nails in a structure
Rt - nail strength against breaking
Tp - pull-out nail bearing capacity
SBf - factor of safety of nail head strength

If the nail is not anchored to the structure cover, it is possible to set the nail head strength to zero.

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