Civil Engineering PE Basic Civil Engineering PE 5 — Questions and Answers
Question 1: In a soil consolidation test, the time to reach 50% consolidation (t_50) is 10 minutes for a 1-inch thick doubly drained sample. What is the coefficient of consolidation c_v?
- 0.00197 in²/min
- 0.0197 in²/min (Correct answer)
- 0.197 in²/min
- 1.97 in²/min
Correct answer: 0.0197 in²/min
c_v = T_50·H_dr²/t_50 = 0.197×(0.5)²/10 = 0.197×0.25/10 = 0.00493 in²/min — using H_dr = 0.5 in (half of 1 in for double drainage) and T_50 = 0.197.
Question 2: Which type of prestressed concrete system applies prestress after the concrete has hardened and reached adequate strength?
- Pre-tensioned
- Post-tensioned (Correct answer)
- Partially prestressed
- Pretensioned with debonding
Correct answer: Post-tensioned
In post-tensioning, steel tendons are stressed after concrete cures, typically using hydraulic jacks against anchorage devices at the member ends.
Question 3: The design flood for a major highway culvert crossing typically corresponds to which return period?
- 10-year
- 25-year
- 50-year
- 100-year (Correct answer)
Correct answer: 100-year
AASHTO and FHWA guidelines recommend the 100-year (1% annual chance) flood for design of major culverts and bridges on principal highways.
Question 4: In a CPM schedule, if Activity A has an Early Start (ES) of Day 5, an Early Finish (EF) of Day 12, a Late Finish (LF) of Day 15, the total float is:
- 0 days
- 3 days (Correct answer)
- 7 days
- 10 days
Correct answer: 3 days
Total Float = LF − EF = 15 − 12 = 3 days (or equivalently LS − ES = (15−7) − 5 = 8−5 = 3 days).
Question 5: In wastewater treatment, the Biochemical Oxygen Demand (BOD) test measures:
- Total dissolved solids in effluent
- Oxygen required by bacteria to decompose organic matter (Correct answer)
- Chemical oxygen demand from inorganic compounds
- Turbidity of the wastewater
Correct answer: Oxygen required by bacteria to decompose organic matter
BOD quantifies the amount of dissolved oxygen consumed by aerobic biological organisms when decomposing organic matter in a water sample at a given temperature over a specific time period.
Question 6: A 12-inch diameter concrete pipe flows full with Manning's n = 0.013 and slope S = 0.005. The approximate full-flow discharge Q is:
- 0.85 cfs
- 1.70 cfs (Correct answer)
- 3.40 cfs
- 0.43 cfs
Correct answer: 1.70 cfs
A = π(0.5)² = 0.785 ft²; R = D/4 = 0.25 ft; V = (1.486/0.013)(0.25)^(2/3)(0.005)^(1/2) ≈ 2.17 ft/s; Q = 0.785×2.17 ≈ 1.70 cfs.
Question 7: Which factor does NOT affect the lateral earth pressure coefficient at rest (K_0) for a normally consolidated soil?
- Friction angle (φ')
- Overconsolidation ratio (OCR)
- Depth of soil layer (Correct answer)
- Poisson's ratio (ν)
Correct answer: Depth of soil layer
K_0 for NC soil is estimated as 1−sinφ' (Jaky's formula) or via Poisson's ratio; it is a material property and does not change with depth in a uniform deposit.
Civil Engineering PE Basic Civil Engineering PE 5
In a soil consolidation test, the time to reach 50% consolidation (t_50) is 10 minutes for a 1-inch thick doubly drained sample.
What is the coefficient of consolidation c_v?