A wall reinforced with the Soil Nailing technique reaches pullout failure of the reinforcement when the maximum value of the tensile force acting on the nail, 
, exceeds the resistance against this mechanism, 
. The factor of safety against this failure mechanism is given by the following relationship:
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(13) |
The expression for calculating the resistance against pullout, 
, takes the following form:
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(14) |
Where D is the diameter of the reinforcement, 
is the effective length of the reinforcement (i.e., the length of the part of the reinforcement outside the potentially unstable soil volume), and 
defines the shear resistance against pullout at the contact between the nail and the soil. The latter is calculated as follows:
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(15) |
Where K is a coefficient of interaction between the nail and the soil, dependent on the type of soil, and 
is the vertical stress acting at the average depth of the effective length of the nail.
This verification is performed for each phase, for each of the nails installed up to the considered phase.