The variation of N γ with footing roughness using the method of characteristics

By using the method of characteristics, the effect of footing–soil interface friction angle (δ) on the bearing capacity factor N γ was computed for a strip footing. The analysis was performed by employing a curved trapped wedge under the footing base; this wedge joins the footing base at a distance B t from the footing edge. For a given footing width ( B ), the value of B t increases continuously with a decrease in δ. For δ=0, no trapped wedge exists below the footing base, that is, B t / B =0.5. On the contrary, with δ=ϕ, the point of emergence of the trapped wedge approaches toward the footing edge with an increase in ϕ. The magnitude of N γ increases substantially with an increase in δ/ϕ. The maximum depth of the plastic zone becomes higher for greater values of δ/ϕ. The results from the present analysis were found to compare well with those reported in the literature.