Geotechnical Engineering accounts for 8 to 12 questions on the FE Civil exam. Most of them start from the phase diagram, weight-volume relationships, void ratio, water content and unit weights, and build from there to effective stress, settlement, shear strength and bearing capacity. Making the phase relationships automatic pays off across the entire area.
The problems below come with full solutions that show every substitution, not just the result. Geotech is the area where a correct method combined with a mishandled unit weight produces a wrong answer that still looks reasonable, so read the solutions for where the total versus effective distinction enters, not only for the arithmetic.
Exam weight: NCEES lists Geotechnical Engineering at 8-12 questions (7-11%) of the 110-question FE Civil exam. Work each problem below on paper first, then reveal the worked solution — reading a solution you have not attempted builds recognition, not recall.
What NCEES Tests in Geotechnical Engineering
The NCEES outline covers index properties and soil classification, including USCS and AASHTO, Atterberg limits and gradation, along with phase relationships, effective and total stress, and pore pressure. Expect items that hand you two phase quantities and ask for a third, or that ask for the vertical effective stress at a given depth with a water table somewhere in the profile.
Beyond that it covers permeability and seepage, consolidation and settlement, shear strength through Mohr-Coulomb, slope stability, lateral earth pressure with Rankine and Coulomb coefficients, shallow and deep foundation bearing capacity, and earth retaining structures. Compaction, subsurface exploration and standard penetration testing appear as well, usually as interpretation rather than computation, such as estimating relative density or strength from N-values.
5 Free Geotechnical Engineering Practice Problems
Each problem below comes from the PECivilClick FE Civil question bank and matches the style, difficulty and format of the real exam. Attempt each one under a three-minute limit — roughly the pace the exam demands.
Problem 1
A saturated (no air) soil sample has wet mass = \( 186\,\mathrm{kg} \), dry mass = \( 106\,\mathrm{kg} \), and total volume = \( 0.120\,\mathrm{m^3} \). What is the specific gravity of soil solids \( G_s \)?
A) 2.4
B) 2.55
C) 2.65
D) 2.8
Answer: C) 2.65
Step 1 – Identify given information:
| Wet mass | \( m = 186\,\text{kg} \) |
| Dry mass | \( m_s = 106\,\text{kg} \) |
| Total volume | \( V_t = 0.120\,\text{m}^3 \) |
| Condition | Saturated (\( V_a = 0 \)) |
Step 2 – Specific gravity formula: \( G_s = \dfrac{m_s}{\rho_w \, V_s} \) where \( \rho_w = 1000\,\text{kg/m}^3 \). For a saturated sample, all voids are filled with water so \( V_s = V_t - V_w \).
Step 3 – Solve:
\( m_w = 186 - 106 = 80\,\text{kg} \)
\( V_w = \dfrac{m_w}{\rho_w} = \dfrac{80}{1000} = 0.080\,\text{m}^3 \)
\( V_s = V_t - V_w = 0.120 - 0.080 = 0.040\,\text{m}^3 \)
\( G_s = \dfrac{106}{1000 \times 0.040} = \dfrac{106}{40} = 2.65 \)
Step 4 – Answer: \( G_s = 2.65 \) matches option (C). Typical \( G_s \) values for soil solids range from 2.60 to 2.80. The saturation condition (\( V_a = 0 \)) simplifies the calculation because \( V_v = V_w \).
Correct answer: (C)
Problem 2
An undisturbed soil sample has wet mass = \( 120\,\mathrm{kg} \), dry mass = \( 110\,\mathrm{kg} \), total volume = \( 0.060\,\mathrm{m^3} \), and \( G_s = 2.70 \). What is the void ratio \( e \)?
A) 0.31
B) 0.4
C) 0.47
D) 0.61
Answer: C) 0.47
Step 1 – Water mass and volume:
\(m_w = 120 - 110 = 10 \text{ kg}\)
\(V_w = \frac{10}{1000} = 0.010 \text{ m}^3\)
Step 2 – Solids volume:
\(V_s = \frac{m_s}{G_s \rho_w} = \frac{110}{2.70 \times 1000} = 0.04074 \text{ m}^3\)
Step 3 – Air volume and void ratio:
\(V_a = V_t - V_s - V_w = 0.060 - 0.04074 - 0.010 = 0.00926\)
\(V_v = V_a + V_w = 0.01926\)
\(e = \frac{V_v}{V_s} = \frac{0.01926}{0.04074} = 0.473 \approx 0.47\)
Correct answer: (C)
Problem 3
A soil has percent passing No.200 \( F = 55 \), \( LL = 35 \), and \( PI = 12 \). What is the AASHTO group index \( GI \) (nearest integer)?
A) 0
B) 4
C) 8
D) 15
Answer: B) 4
Step 1 – Identify given information:
| Percent passing No. 200 | \( F = 55 \) |
| Liquid limit | \( LL = 35 \) |
| Plasticity index | \( PI = 12 \) |
Step 2 – AASHTO Group Index formula: \( GI = (F - 35)[0.2 + 0.005(LL - 40)] + 0.01(F - 15)(PI - 10) \). Each term in brackets is taken as zero if it computes negative.
Step 3 – Solve:
\( (F - 35) = 55 - 35 = 20 \)
\( (LL - 40) = 35 - 40 = -5 \), so \( 0.2 + 0.005(-5) = 0.2 - 0.025 = 0.175 \)
First term: \( 20 \times 0.175 = 3.5 \)
\( (F - 15) = 55 - 15 = 40 \), \( (PI - 10) = 12 - 10 = 2 \)
Second term: \( 0.01 \times 40 \times 2 = 0.8 \)
\( GI = 3.5 + 0.8 = 4.3 \approx 4 \)
Step 4 – Answer: \( GI \approx 4 \) matches option (B). The group index is always rounded to the nearest integer and reported as a minimum of 0. Higher GI values indicate poorer subgrade quality.
Correct answer: (B)
Problem 4
A soil has \( D_{10} = 0.20\,\mathrm{mm} \), \( D_{30} = 0.35\,\mathrm{mm} \), and \( D_{60} = 0.80\,\mathrm{mm} \). What is the coefficient of curvature \( C_c \)?
A) 0.45
B) 0.77
C) 1.25
D) 2
Answer: B) 0.77
Step 1 – Identify given information:
| \( D_{10} \) | \( 0.20\,\text{mm} \) |
| \( D_{30} \) | \( 0.35\,\text{mm} \) |
| \( D_{60} \) | \( 0.80\,\text{mm} \) |
Step 2 – Coefficient of curvature formula: From the FE Handbook: \( C_c = \dfrac{D_{30}^2}{D_{10} \times D_{60}} \). For a well-graded soil, \( C_c \) should be between 1 and 3.
Step 3 – Solve:
\( C_c = \dfrac{(0.35)^2}{0.20 \times 0.80} = \dfrac{0.1225}{0.16} = 0.766 \approx 0.77 \)
Step 4 – Answer: \( C_c = 0.77 \) matches option (B). Since \( C_c < 1 \), this soil does not meet the well-graded criterion for \( C_c \) (needs \( 1 \leq C_c \leq 3 \)), even though \( C_u = 4 \) may be adequate.
Correct answer: (B)
Problem 5
A soil has \( D_{60} = 0.80\,\mathrm{mm} \) and \( D_{10} = 0.20\,\mathrm{mm} \). What is the coefficient of uniformity \( C_u \)?
A) 2
B) 3
C) 4
D) 6
Answer: C) 4
Step 1 – Identify given information: \( D_{60} = 0.80\,\text{mm} \) and \( D_{10} = 0.20\,\text{mm} \).
Step 2 – Coefficient of uniformity formula: From the FE Handbook: \( C_u = \dfrac{D_{60}}{D_{10}} \). This coefficient measures the range of particle sizes in a soil; \( C_u > 6 \) for well-graded gravel, \( C_u > 4 \) for well-graded sand.
Step 3 – Solve:
\( C_u = \dfrac{0.80}{0.20} = 4.0 \)
Step 4 – Answer: \( C_u = 4.0 \) matches option (C). Since \( C_u = 4 \) for a sand, this soil barely meets the well-graded criterion for sand. Options (A) 2 and (B) 3 result from incorrect division, while (D) 6 would require \( D_{60}/D_{10} = 6 \).
Correct answer: (C)
Using the FE Reference Handbook for Geotechnical Engineering
Keep the phase diagram and its identities in your head, because everything else in this section builds on them. In the handbook, searching Rankine reaches both the active and passive coefficients at once, and note that the bearing capacity factors Nc, Nq and N-gamma are tabulated against friction angle rather than something you compute under time pressure.
Four Mistakes That Cost Points
- Using total unit weight below the water table Effective stress below the water table uses the buoyant unit weight, saturated minus the unit weight of water. Applying total unit weight all the way down overstates effective stress and then cascades into wrong shear strength and bearing capacity. Sketch the profile, mark the water table, and label each layer before computing.
- Confusing void ratio with porosity Void ratio e is voids over solids; porosity n is voids over total volume, related by e equals n over one minus n. For typical soils the two values are close enough that a swap does not look obviously wrong. Rebuild the definition from the phase diagram instead of recalling a number.
- Applying Rankine when the geometry is not Rankine Rankine assumes a smooth vertical wall face and horizontal backfill. When the problem states wall friction or a sloped backfill, Coulomb applies and the coefficient differs. Read the described geometry before choosing the equation, because the distractors are typically built from the method you did not use.
- Dropping the surcharge term in bearing capacity The Nq term uses the overburden at the footing base, unit weight times embedment depth, not zero. Treating a footing as though it sits at ground surface discards a real share of the ultimate capacity. Confirm the embedment depth and whether the question wants ultimate or allowable capacity.
Frequently Asked Questions
How many geotechnical questions are on the FE Civil exam?
NCEES specifies 8 to 12 questions for Geotechnical Engineering out of the 110 on the exam, about 7 to 11 percent. Because so much of the area chains off the phase diagram and effective stress, a few focused hours making those two topics automatic tends to lift performance across the whole block.
Is soil classification worth memorizing?
Memorize the logic, not the tables. The USCS and AASHTO charts are in the NCEES FE Reference Handbook, but you still need to know that you route first by percent passing the No. 200 sieve, then use Atterberg limits and the plasticity chart for the fines. Knowing the path makes the lookup fast.
Do geotechnical questions require Mohr circle work?
Sometimes, though usually in a light form: given principal stresses, find the shear stress on a plane, or given a failure envelope, find strength at a stated normal stress. You are rarely asked to construct a full circle graphically. Fluency with tau equals c plus sigma tangent phi covers most shear strength items.
What is the fastest way to improve in this area?
Drill phase relationship problems until conversions among void ratio, porosity, water content, specific gravity and unit weights take no thought, then move to effective stress profiles with a water table. Those two skills are prerequisites for consolidation, shear strength and bearing capacity, so gains there show up in questions that look unrelated.
Keep Going
Work through the other FE Civil knowledge areas with more free practice problems, review the full FE Civil exam topic breakdown, or plan your preparation with our FE exam study guide and study timeline.