FE Civil Geotechnical Engineering practice problems
6 free FE Civil Geotechnical Engineering practice problems with answers and full worked solutions. Geotechnical Engineering carries 10–15 of the 110 questions on the FE Civil exam (NCEES specification effective July 2020). Pick an answer to check it, then read the worked solution and why each wrong choice is wrong.
6 worked Geotechnical Engineering problems
Question 1 of 6
A clay has a liquid limit of 66 and a plastic limit of 25. Its plasticity index is most nearly:
Show the answer and the reasoning
Why C
Given: LL = 66, PL = 25. Relation: PI = LL - PL, the range of water content over which the soil is plastic. Substitute: PI = 66 - 25. Result: PI = 41.
Why A is tempting
Reversed the subtraction. The liquid limit is always the larger of the two.
Why B is tempting
Took a ratio rather than a difference.
Why D is tempting
Added the two limits. The plasticity index is the width of the plastic range, so it is a difference.
Question 2 of 6
A soil has a porosity of 0.34. Its void ratio is most nearly:
Show the answer and the reasoning
Why C
Given: n = 0.34. Relation: e = n/(1 - n); void ratio is voids over solids, porosity voids over the total. Substitute: e = 0.34/0.66. Result: e = 0.515.
Why A is tempting
Used a plus sign in the denominator, which converts a void ratio to a porosity rather than the reverse.
Why B is tempting
Reported the porosity. Void ratio is voids over solids, while porosity is voids over the total volume.
Why D is tempting
Took the reciprocal of the porosity.
Question 3 of 6
A sand has a maximum void ratio of 0.70, a minimum of 0.35, and an in-situ void ratio of 0.472. Its relative density is most nearly:
Show the answer and the reasoning
Why D
Given: emax = 0.70, emin = 0.35, e = 0.472. Relation: Dr = (emax - e)/(emax - emin) x 100. Substitute: Dr = (0.70 - 0.472)/(0.35) x 100. Result: Dr = 65.1%.
Why A is tempting
Divided by the maximum void ratio rather than the range between the two limits.
Why B is tempting
Reversed the numerator. A soil at its minimum void ratio is at 100% relative density, not zero.
Why C is tempting
Treated the void ratio as a porosity.
Question 4 of 6
The water table sits 9 ft below the ground surface and hydrostatic conditions apply. The pore water pressure at a depth of 12 ft is most nearly:
Hydrostatic profile with the water table 9 ft below ground; the pore pressure is required at 12 ft. Show the answer and the reasoning
Why A
Given: water table at 9 ft, point at 12 ft, hydrostatic. Relation: u = gamma_w x (depth below the water table). Substitute: u = 62.4(12 - 9) = 62.4(3). Result: u = 187.2 psf.
Why B is tempting
Used the depth to the water table as the pressure head.
Why C is tempting
Measured the pressure head from the ground surface. It is measured from the water table.
Why D is tempting
Added the depth to the water table rather than subtracting it.
Question 5 of 6
A dense sand has an effective friction angle of 27 degrees. The Rankine passive earth pressure coefficient is most nearly:
Show the answer and the reasoning
Why B
Given: phi = 27 degrees. Relation: Kp = tan^2(45 + phi/2). Substitute: Kp = tan^2(58.5). Result: Kp = 2.66. Check: (1 + sin phi)/(1 - sin phi) gives the same; passive resistance needs far more wall movement to mobilise than active.
Why A is tempting
Did not square the tangent.
Why C is tempting
Cubed the tangent. The Rankine coefficients are squares of the tangent, not cubes.
Why D is tempting
Used the full friction angle rather than half of it.
Source NAVFAC DM-7, Soil Mechanics and Foundations — DM-7.02 Chapter 3, lateral earth pressure
Question 6 of 6
An unconfined compression test on a saturated clay gives qu = 3600 psf. The undrained shear strength is most nearly:
Show the answer and the reasoning
Why B
Given: qu = 3600 psf, unconfined so sigma3 = 0. Relation: the Mohr circle runs from 0 to qu, and its radius is the undrained strength: su = qu/2. Substitute: su = 3600/2. Result: su = 1,800 psf.
Why A is tempting
Quartered the compressive strength.
Why C is tempting
Reported the unconfined compressive strength itself. The undrained shear strength is half of it.
Why D is tempting
Doubled the compressive strength rather than halving it.
Going further
Frequently asked questions
How many Geotechnical Engineering questions are on the FE Civil exam?
Between 10 and 15 of the 110 questions, according to the NCEES FE Civil specification effective July 2020.
Are these real NCEES exam questions?
No. NCEES does not release its exam questions. These are original FE-style problems written to the NCEES specification and the FE Reference Handbook; every calculated key is checked by two independent solution methods.
Are these Geotechnical Engineering practice problems free?
Yes. All 6 problems on this page, with answers and full worked solutions, are free and need no account.
Check where you stand, free
The quick diagnostic is eight FE Civil questions in about ten minutes, with no account. The free mock is a full 110-question, 5 hour 20 minute FE Civil paper with a worked solution for every question.