Practice Problems: Pavement Design

Table of Contents
1. Question 1
2. Question 2
3. Question 3
4. Question 4
5. Question 5
6. Question 6
7. Question 7
8. Question 8
9. Question 9
10. Question 10
11. Question 11
12. Question 12
13. Question 13
14. Question 14
15. Question 15
16. Question 16
17. Question 17
18. Question 18
19. Question 19
20. Question 20
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Question 1

A pavement engineer is designing a flexible pavement system for a new highway. The pavement structure consists of an asphalt concrete surface layer, granular base, and subbase over a subgrade. Given the following information:
- Design ESAL (18-kip equivalent single axle loads) = 8 × 10⁶
- Resilient modulus of subgrade (M_R) = 6,500 psi
- Structural layer coefficient for asphalt concrete (a₁) = 0.44
- Structural layer coefficient for granular base (a₂) = 0.14
- Structural layer coefficient for granular subbase (a₃) = 0.11
- Required structural number (SN) = 5.0
- Design includes 6 inches of asphalt concrete and 8 inches of granular base
What minimum thickness of granular subbase is required to meet the design structural number?

(a) 10 inches
(b) 12 inches
(c) 14 inches
(d) 16 inches

Question 2

A transportation engineer is evaluating a rigid pavement design for an industrial park access road. The pavement will be constructed using Portland cement concrete. Given the following design parameters:
- Design traffic = 2.5 × 10⁶ ESALs over 20-year design life
- 28-day concrete modulus of rupture (S'_c) = 650 psi
- Concrete elastic modulus (E_c) = 4.0 × 10⁶ psi
- Subgrade k-value = 200 pci
- Load safety factor (LSF) = 1.2
- Allowable working stress = 50% of modulus of rupture
What is the allowable working stress in the concrete pavement?

(a) 260 psi
(b) 325 psi
(c) 390 psi
(d) 520 psi

Question 3

A pavement designer is conducting an AASHTO flexible pavement design for a rural collector road. The following data has been collected:
- Reliability (R) = 90%
- Overall standard deviation (S₀) = 0.45
- Initial serviceability index (p_i) = 4.2
- Terminal serviceability index (p_t) = 2.5
- Subgrade resilient modulus (M_R) = 8,000 psi
- Design ESALs = 5 × 10⁶
What is the change in serviceability index (ΔPSI) for this design?

(a) 1.5
(b) 1.7
(c) 2.0
(d) 2.5

Question 4

A civil engineer is designing a flexible pavement rehabilitation project. Traffic analysis has provided the following axle load distribution for heavy trucks during the design period:
- Single axles at 22 kips: 150,000 applications
- Tandem axles at 38 kips: 80,000 applications
- Triple axles at 50 kips: 30,000 applications
- EALF for 22-kip single axle = 1.97
- EALF for 38-kip tandem axle = 1.48
- EALF for 50-kip triple axle = 1.14
What is the total design ESAL for this project?

(a) 425,000
(b) 448,900
(c) 489,700
(d) 524,300

Question 5

A pavement engineer is analyzing a proposed rigid pavement section for a state highway. The design requires determination of the loss of support factor. Given the following information:
- Type of material: Granular subbase
- Subbase erodibility: Resistant to erosion
- Potential for pumping: Moderate
- Edge drainage quality: Good (drainage coefficient C_d = 1.0)
- Subgrade k-value before adjustment = 150 pci
- Subbase thickness = 6 inches
According to AASHTO guidelines, what is the most appropriate loss of support factor (LSF) for this design?

(a) 0.5
(b) 1.0
(c) 1.5
(d) 2.0

Question 6

A transportation engineer is evaluating the fatigue performance of an asphalt concrete pavement. Laboratory testing has been completed on the asphalt mix. Given the following conditions:
- Critical tensile strain at bottom of asphalt layer (ε_t) = 250 × 10^-6
- Asphalt concrete elastic modulus (E_AC) = 500,000 psi at 68°F
- Design ESALs = 4 × 10⁶
- Asphalt Institute fatigue equation: N_f = 0.00432 × C × (1/ε_t)^3.291 × (1/E_AC)^0.854
- C = 10^M where M = 4.84 × (V_b/(V_b + V_v) - 0.69), and V_b/(V_b + V_v) = 0.80
What is the value of M in the fatigue equation?

(a) 0.43
(b) 0.53
(c) 0.63
(d) 0.73

Question 7

A municipal engineer is designing a new concrete pavement for a city street. The concrete slab design includes the following specifications:
- Slab thickness = 9 inches
- Joint spacing = 15 feet
- Coefficient of thermal expansion (α) = 5.5 × 10^-6 /°F
- Temperature drop from placement = 50°F
- No reinforcement for crack control
What is the expected thermal contraction of the slab over the 15-foot joint spacing?

(a) 0.033 inches
(b) 0.050 inches
(c) 0.066 inches
(d) 0.083 inches

Question 8

A pavement design engineer is conducting a subgrade evaluation for a new airport taxiway. California Bearing Ratio (CBR) tests have been performed on the subgrade soil. Given the following data:
- Field CBR value = 4%
- Standard correlation: M_R (psi) = 1,500 × CBR (for fine-grained soils with CBR ≤ 10%)
- Alternative correlation: M_R (psi) = 2,555 × CBR^0.64
Using the standard correlation for fine-grained soils, what is the estimated resilient modulus of the subgrade?

(a) 4,500 psi
(b) 6,000 psi
(c) 7,500 psi
(d) 9,000 psi

Question 9

A highway engineer is evaluating load transfer efficiency at joints in an existing jointed plain concrete pavement (JPCP). Falling Weight Deflectometer (FWD) testing has been conducted. Given the following measurements:
- Deflection on loaded side of joint (δ_loaded) = 18.5 mils
- Deflection on unloaded side of joint (δ_unloaded) = 13.3 mils
- Applied load = 9,000 lbs
- Temperature at time of testing = 75°F
What is the load transfer efficiency (LTE) at this joint?

(a) 62%
(b) 68%
(c) 72%
(d) 78%

Question 10

A pavement engineer is designing an asphalt overlay for a distressed flexible pavement. The existing pavement condition survey revealed the following:
- Existing structural number (SN_eff) = 3.2
- Required future structural number (SN_f) = 5.8
- Overlay asphalt layer coefficient (a_ol) = 0.42
- Condition factor for existing pavement = 0.85
- No milling of existing surface is planned
What thickness of asphalt overlay is required?

(a) 5.2 inches
(b) 6.2 inches
(c) 7.3 inches
(d) 8.1 inches

Question 11

A civil engineer is analyzing the structural capacity of a composite pavement section consisting of an asphalt concrete overlay on a Portland cement concrete base. Given the following information:
- Asphalt overlay thickness = 4 inches
- PCC base thickness = 8 inches
- Layer coefficient for asphalt overlay (a_AC) = 0.40
- Layer coefficient for PCC base (a_PCC) = 0.28
- Drainage coefficient for PCC layer (m₂) = 1.0
What is the total structural number (SN) of this composite pavement?

(a) 3.44
(b) 3.84
(c) 4.24
(d) 4.64

Question 12

A transportation engineer is designing a full-depth asphalt pavement for a parking lot that will serve heavy truck traffic. The design includes the following parameters:
- Subgrade CBR = 6%
- Design ESALs = 1.2 × 10⁶
- Terminal serviceability (p_t) = 2.0
- Reliability = 85%
- Layer coefficient for full-depth asphalt = 0.44
- Required structural number = 4.5
What is the required thickness of the full-depth asphalt pavement?

(a) 9.5 inches
(b) 10.2 inches
(c) 11.0 inches
(d) 12.5 inches

Question 13

A pavement engineer is evaluating a rigid pavement design using the AASHTO method. The design involves determining the radius of relative stiffness. Given the following parameters:
- PCC slab thickness (D) = 10 inches
- Elastic modulus of concrete (E_c) = 4.5 × 10⁶ psi
- Poisson's ratio for concrete (μ) = 0.15
- Modulus of subgrade reaction (k) = 250 pci
- Radius of relative stiffness formula: ℓ = [E_cD³/(12k(1-μ²))]^0.25
What is the radius of relative stiffness for this pavement section?

(a) 32.5 inches
(b) 36.8 inches
(c) 40.2 inches
(d) 44.6 inches

Question 14

A highway engineer is conducting a pavement management analysis on a rural highway. The current pavement condition index (PCI) has been determined through a detailed distress survey. Given the following information:
- Total deduct value from all distresses = 45
- Number of deduct values greater than 5 = 4
- Maximum corrected deduct value (CDV) from chart = 38
- PCI = 100 - CDV
What is the pavement condition index for this section?

(a) 55
(b) 62
(c) 68
(d) 72

Question 15

A pavement design engineer is analyzing the critical stress location in a jointed plain concrete pavement slab. The pavement will be subjected to heavy truck traffic. Given the following design parameters:
- Slab thickness = 11 inches
- Joint spacing = 15 feet
- Single axle load = 20,000 lbs (dual tires)
- Subgrade k-value = 200 pci
- Load applied at slab edge at mid-length
According to concrete pavement design principles, where does the maximum tensile stress occur for this loading condition?

(a) Top of slab at interior
(b) Bottom of slab at mid-slab interior
(c) Bottom of slab at edge, mid-length
(d) Top of slab at corner

Question 16

A civil engineer is designing a flexible pavement drainage system. The granular base course must be designed with adequate drainage characteristics. Given the following information:
- Base course thickness = 8 inches
- Pavement width = 24 feet (two-lane)
- Cross slope = 2%
- Base permeability = 500 ft/day
- Time to drain to 50% saturation (t₅₀) required = 1 day
- Drainage path length = width/2 = 12 feet
Does this design meet the AASHTO drainage quality rating for "Good" drainage (t₅₀ ≤ 1 day)?

(a) No, drainage time exceeds 1.5 days
(b) No, drainage time is approximately 1.2 days
(c) Yes, drainage time is approximately 0.8 days
(d) Yes, drainage time is approximately 0.5 days

Question 17

A pavement engineer is evaluating rutting potential in a proposed asphalt pavement design. The critical compressive strain at the top of the subgrade must be checked. Given the following conditions:
- Vertical compressive strain at top of subgrade (ε_c) = 350 × 10^-6
- Design ESALs = 3 × 10⁶
- Subgrade rutting equation: N_d = 1.365 × 10^-9 × (ε_c)^-4.477
What is the allowable number of load repetitions before excessive rutting occurs?

(a) 1.8 × 10⁶
(b) 2.5 × 10⁶
(c) 3.2 × 10⁶
(d) 4.1 × 10⁶

Question 18

A transportation engineer is designing dowel bars for load transfer across transverse joints in a jointed plain concrete pavement. Given the following specifications:
- Slab thickness = 10 inches
- Dowel bar diameter = 1.5 inches
- Dowel bar spacing = 12 inches center-to-center
- Dowel bar length = 18 inches
- Lane width = 12 feet
According to typical AASHTO recommendations, how many dowel bars are required across the joint for a single 12-foot lane?

(a) 10 bars
(b) 12 bars
(c) 13 bars
(d) 15 bars

Question 19

A pavement engineer is conducting a life-cycle cost analysis (LCCA) for two alternative pavement designs. The analysis requires calculating the present worth of future maintenance costs. Given the following information for Alternative A:
- Initial construction cost = $850,000
- Overlay cost in year 12 = $250,000
- Major rehabilitation in year 20 = $400,000
- Discount rate = 4% per year
- Analysis period = 25 years
What is the present worth of the overlay cost scheduled for year 12?

(a) $148,500
(b) $155,800
(c) $162,400
(d) $175,200

Question 20

A highway engineer is evaluating the International Roughness Index (IRI) for an existing highway section to determine if rehabilitation is warranted. Field measurements have been collected using an inertial profiler. Given the following data:
- Measured IRI = 180 inches/mile
- Roadway classification = Primary highway
- Posted speed limit = 55 mph
- AASHTO acceptable IRI range for primary highways at 55 mph = 95-170 inches/mile
- IRI threshold for rehabilitation consideration = 170 inches/mile
Based on this data, what is the appropriate recommendation?

(a) Pavement is acceptable; no action required
(b) Pavement requires routine maintenance only
(c) Pavement should be considered for rehabilitation
(d) Pavement requires immediate reconstruction