FE Civil Geotechnical Engineering Practice Problems

The current FE Civil specification assigns 10-15 of the 110 exam questions to Geotechnical Engineering. Form A contains 12 original problems in this area. The sample below is published in full, with the same worked-solution format used throughout the book.

A saturated clay specimen has a water content of 40% and a specific gravity of solids of 2.70. The saturated unit weight of the specimen is most nearly:

(A)8.0 kN/m³
(B)12.7 kN/m³
(C)17.8 kN/m³
(D)24.3 kN/m³

Show worked solution

Answer: (C)

Saturation forces e = wG_s = 1.08, and the phase relation returns γ_sat = 17.8 kN/m³.

Saturation ( $S = 1$ ) fixes the void ratio through $S e = w G_{s}$ .

e = w G_{s} = 0.40 \times 2.70 = 1.08

With $e$ known, the unit weight follows directly, taking $γ_{w} = 9.81$ kN/m³.

γ_{s a t} = \frac{( G _{s} + e ) γ _{w}}{1 + e} = \frac{( 2.70 + 1.08 ) ( 9.81 )}{1 + 1.08} = 17.8 kN/m^{3}

FE Reference Handbook — Geotechnical: Phase Relationships (Unit Weight Equations)

Why the other choices appear

(A)Reports the buoyant (submerged) unit weight, 17.83 − 9.81 = 8.0 kN/m³, instead of the saturated unit weight.
(B)Reports the dry unit weight, G_s·γ_w/(1+e) = 12.7 kN/m³, omitting the pore water.
(D)Computes the void ratio as e = w/G_s = 0.148, giving (2.70 + 0.148)(9.81)/1.148 = 24.3 kN/m³.