Free PE Civil: Geotechnical exam Practice Questions

Sample Practice Questions

Try these 10 sample questions from the PE Civil: Geotechnical exam practice bank. Each includes the answer and explanation. Continue with the interactive practice above to review the full question set.

1. 1An engineer is screening the upper 4 ft of soil along a proposed roadway for preliminary USCS classifications and Atterberg-limit data. Which existing data source most directly provides this combination?

   1. A. USGS bedrock geologic maps
   2. B. NRCS Soil Survey Geographic Database
   3. C. USGS topographic quadrangle maps
   4. D. Historical aerial photographic archives

   Answer: B

   Explanation: FHWA states that SSURGO "often provides quantitative soil classification data such as USCS (Unified Soil Classification System) and AASHTO soil classification, moisture characteristics, Atterberg limits". It is appropriate for preliminary shallow-soil screening; site-specific investigation remains necessary.

   Reference: FHWA Geotechnical Site Characterization (GEC No. 5) — Section 3.2.1, p. 3-4

2. 2A soil specimen weighs 150 g before drying and 120 g after oven drying; both masses exclude the container. What is its gravimetric water content?

   1. A. 20 percent
   2. B. 25 percent
   3. C. 80 percent
   4. D. 125 percent

   Answer: B

   Explanation: FHWA defines water content using "the weight of the water" relative to "the weight of the solids." Water mass is 30 g, so w = 30/120 × 100 = 25 percent. Using wet mass gives 20 percent; dry/wet and wet/dry ratios give 80 and 125 percent.

   Reference: FHWA Soils and Foundations Reference Manual, Volume I — Section 2.1.2, pp. 2-4–2-5, Equation 2-4

3. 3A compacted fill has a field dry unit weight of 114 pcf. The specified laboratory compaction test gives a maximum dry unit weight of 120 pcf. What is the relative compaction?

   1. A. 5 percent
   2. B. 95 percent
   3. C. 105 percent
   4. D. 114 percent

   Answer: B

   Explanation: FHWA defines RC as "the ratio of the desired field dry unit weight, γd field, to the maximum dry density measured in the laboratory, γd max". Thus RC = 114/120 × 100 = 95 percent. The other values use deficiency, reverse the ratio, or confuse a unit weight with a percentage.

   Reference: FHWA Soils and Foundations Reference Manual, Volume I — Section 5.8.3, p. 5-77, Equation 5-19

4. 4In a crosshole seismic test, the actual source-to-receiver distance at the test depth is 4.0 m and the corrected shear-wave travel time is 20 ms. What shear-wave velocity is measured?

   1. A. 100 m/s
   2. B. 200 m/s
   3. C. 400 m/s
   4. D. 2,000 m/s

   Answer: B

   Explanation: FHWA states that velocity is obtained by "dividing the distance between the boreholes at the depth of measurement by the measured travel times." Vs = 4.0/0.020 = 200 m/s. Doubling or halving the travel time gives 100 or 400; a decimal conversion error gives 2,000.

   Reference: FHWA Geotechnical Site Characterization (GEC No. 5) — Section 8.4.1, p. 8-7, Crosshole Seismic Method

5. 5An embankment will preload a thick compressible clay layer. What is the principal mechanism by which prefabricated vertical drains accelerate consolidation?

   1. A. They increase the compressibility of the soil skeleton
   2. B. They shorten the drainage path for excess pore water
   3. C. They increase the permanent weight of the embankment
   4. D. They replace the clay with a load-bearing granular column

   Answer: B

   Explanation: FHWA states that vertical drains accelerate settlement "by reducing the drainage path the water must travel". They facilitate pore-pressure dissipation; they are not structural granular columns or a means of adding preload weight.

   Reference: FHWA Soils and Foundations Reference Manual, Volume I — Printed page 7-46, Wick Drains

6. 6At a point in an aquifer, elevation head is 8 m and pressure head is 12 m relative to the selected datum. Velocity head is negligible. What total hydraulic head should be used in the seepage analysis?

   1. A. 4 m
   2. B. 8 m
   3. C. 12 m
   4. D. 20 m

   Answer: D

   Explanation: FHWA identifies “total” head, “elevation head” and “pressure” head and states, "the potential for flow through soil and rock is predominantly driven by elevation and pore water pressure." Neglecting velocity head, total head is 8 + 12 = 20 m. Subtracting the components gives 4 m; using only one component gives 8 or 12 m.

   Reference: FHWA Geotechnical Site Characterization (GEC No. 5) — Section 10.2, Equation 10.1, pp. 10-2–10-3

7. 7Wetting under the anticipated field load produces 2% collapse strain in a loess specimen. If the entire uniform 4-m layer beneath a foundation is wetted under that loading, what collapse settlement is estimated?

   1. A. 0.008 m
   2. B. 0.020 m
   3. C. 0.080 m
   4. D. 0.800 m

   Answer: C

   Explanation: FHWA explains, "Conceptually, C is a strain." Equation 5-16 applies collapse strain to the wetted layer thickness: 4(2/100) = 0.080 m. The alternatives reflect an extra decimal conversion, using strain as displacement, or an insufficient percent conversion.

   Reference: FHWA Soils and Foundations Reference Manual, Volume I — Section 5.7.2, Equation 5-16, p. 5-69

8. 8An unyielding wall retains level, normally consolidated sand with effective friction angle 30°. Using Jaky's approximation, what at-rest earth-pressure coefficient applies?

   1. A. 0.33
   2. B. 0.50
   3. C. 1.50
   4. D. 3.00

   Answer: B

   Explanation: FHWA gives "K o = 1 − sin φ′" for near normally consolidated soil. Thus K₀ = 1 − sin30° = 0.50. The value 0.33 is the Rankine active coefficient, 3.00 is passive, and 1.50 results from adding rather than subtracting sin30°.

   Reference: FHWA Soils and Foundations Reference Manual, Volume II — Section 10.2.1, Equation 10-2, p. 10-10

9. 9For an ASD footing design, ultimate bearing pressure divided by the selected safety factor is 300 kPa. The pressure meeting the specified settlement limit is 180 kPa. What allowable bearing pressure governs?

   1. A. 180 kPa
   2. B. 240 kPa
   3. C. 300 kPa
   4. D. 480 kPa

   Answer: A

   Explanation: FHWA states, "the allowable bearing capacity of a spread footing is defined as the lesser of" the shear-based and settlement-based limits. Thus 180 kPa governs. Averaging, selecting the larger value, or adding the limits would violate the settlement criterion.

   Reference: FHWA Soils and Foundations Reference Manual, Volume II — Section 8.3, p. 8-12

10. 10A single pile's ultimate shaft resistance is 1,200 kN and ultimate toe resistance is 800 kN. Assume both are fully mobilized compatibly. What ultimate geotechnical axial resistance is obtained by the conventional component-sum approach?

    1. A. 400 kN
    2. B. 800 kN
    3. C. 1,200 kN
    4. D. 2,000 kN

    Answer: D

    Explanation: FHWA gives "Qu = Rs + Rt" and cautions that the components must move sufficiently to develop their ultimate resistances simultaneously. Under the stated assumption, 1,200 + 800 = 2,000 kN. Subtraction or using only one component produces the other values.

    Reference: FHWA Soils and Foundations Reference Manual, Volume II — Section 9.5.1.1, Step 10, p. 9-35; compatibility discussion p. 9-22