qnf=(2/3)cNc’+ (Nq’-1)σ +0.5 Ny’ bΎ
= (2/3) 30X11.8 + (3.9-1) X 18 X1 + 0.5X 1.7 X 1.5 X18
= 311.15 kn/m²
qs = qnf /2.5 + ...