serviceability index in the traditional AASHTO pavement design).
The reliability level needed is similar to that currently used in the traditional AASHTO process.
c. Site conditions and factors. Here, information is needed on truck traffic (including axle-load distributions, speed limit to account for the effect of truck speed on pavement distress, and monthly and hourly distributions of truck-travel), climate (including hourly temperature, precipitation, wind speed, relative humidity and cloud cover), and detailed soil information (strength, variability, etc.).
d. Material properties. Detailed information on new-pavement material properties is needed. This information is along the lines of the structural coefficient values and concrete-strength measurements used in the traditional AASHTO pavement design (although at a significantly higher level of detail).
3. With the above, the MEPDG software can then be run and software outputs will include calculated changes in pavement layer properties, various distresses (such as rut depth, cracking, and faulting), and the International Roughness Index over the design life of the pavement. The designer can then determine if the criteria for a successful pavement design have been met (critical distresses do not cross values that can be considered a failure of the pavement over its design life). If these criteria are not met, the pavement design is altered and the process is continued until an acceptable pavement design is achieved.
Currently, the use of the mechanistic-empirical pavement design process and the MEPDG software is increasing; however, many highway and transportation agencies still use the traditional AASHTO pavement-design approach (AASHTO Guide for Design of Pavement Structures, 1993).
Problems
131 REFERENCES
AASHTO (American Association of State Highway and Transportation Officials). AASHTO Guide for Design of Pavement Structures. Washington, DC:
AASHTO, 1993.
AASHTO (American Association of State Highway and Transportation Officials). Mechanistic-Empirical Pavement Design Guide ʊA Manual of Practice.
Washington, DC: AASHTO, 2008.
Carey, W., and P. Irick. The Pavement Serviceability- Performance Concept. Highway Research Board Special Report 61E, AASHO Road Test, 1962.
Federal Highway Administration. "2006 Status of the Nation’s Highways, Bridges, and Transit:
Conditions and Performance; Report to Congress",
United States Department of Transportation, Washington, DC, 2007.
Li, S., S. Noureldin and K. Zhu. Upgrading the INDOT Pavement Friction Testing Program. Final report FHWA/IN/JTRP-2003/23, West Lafayette, Indiana, 2003.
Sayers, M., T. Gillespie, and W. Paterson. Guidelines for the Conducting and Calibrating Road Roughness Measurements. World Bank Technical Paper No. 46.
The World Bank, Washington, DC, 1986.
Yoder, E. J., and M. W. Witczak. Principles of Pavement Design, 2nd ed. New York: Wiley, 1975.
PROBLEMS
Flexible Pavement Design (Sections 4.3–4.4)
4.1Truck A has two single axles. One axle weighs 12,000 lb and the other weighs 23,000 lb. Truck B has an 8000-lb single axle and a 43,000-lb tandem axle. On a flexible pavement with a 3-inch hot-mix asphalt (HMA) wearing surface, a 6-inch soil-cement base, and an 8-inch crushed stone subbase, which truck will cause more pavement damage? (Assume drainage coefficients are 1.0.)
4.2 A flexible pavement has a 4-inch hot-mix asphalt (HMA) wearing surface, a 7-inch dense-graded crushed stone base, and a 10-inch crushed stone subbase. The pavement is on a soil with a resilient modulus of 5000 lb/in2. The pavement was designed with 90% reliability, an overall standard deviation of 0.4, and a ¨PSI of 2.0 (a TSI of 2.5). The drainage coefficients are 0.9 and 0.8 for the base and subbase, respectively. How many 25- kip single-axle loads can be carried before the pavement reaches its TSI (with given reliability)?
4.3 A highway has the following pavement design daily traffic: 300 single axles at 10,000 lb each, 120 single axles at 18,000 lb each, 100 single axles at 23,000 lb each, 100 tandem axles at 32,000 lb each, 30 single axles at 32,000 lb each, and 100 triple axles at 40,000 lb each. A flexible pavement is designed to have 4 inches of sand-mix asphalt wearing surface, 6 inches of soil- cement base, and 7 inches of crushed stone subbase.
The pavement has a 10-year design life, a reliability of 85%, an overall standard deviation of 0.30, drainage coefficients of 1.0, an initial PSI of 4.7, and a TSI of
2.5. What is the minimum acceptable soil resilient modulus?
4.4 Consider the conditions in Problem 4.3. Suppose the state has relaxed its truck weight limits and the impact has been to reduce the number of 18,000-lb single-axle loads from 120 to 20 and increase the number of 32,000-lb single-axle loads from 30 to 90 (all other traffic is unaffected). Under these revised daily counts, what is the minimum acceptable soil resilient modulus?
4.5 A flexible pavement was designed for the following daily traffic with a 12-year design life: 1300 single axles at 8,000 lb each, 900 tandem axles at 15,000 lb each, 20 single axles at 40,000 lb each, and 200 tandem axles at 40,000 lb each. The highway was designed with 4 inches of hot-mix asphalt (HMA) wearing surface, 4 inches of hot-mix asphaltic base, and 8 inches of crushed stone subbase. The reliability was 70%, overall standard deviation was 0.5, ¨PSI was 2.0 (with a TSI of 2.5), and all drainage coefficients were 1.0. What was the soil resilient modulus of the subgrade used in design?
4.6 A flexible pavement has a structural number of 3.8 (all drainage coefficients are equal to 1.0). The initial PSI is 4.7 and the terminal serviceability is 2.5. The soil has a CBR of 9. The overall standard deviation is 0.40 and the reliability is 95%. The pavement is currently designed for 1800 equivalent 18-kip single-axle loads per day. If the number of 18-kip single-axle loads were to increase by 30%, by how many years would the pavement’s design life be reduced?
4.7 An engineer plans to replace the rigid pavement in Example 4.3 with a flexible pavement. The chosen design has 6 inches of sand-mix asphalt wearing surface, 9 inches of soil-cement base, and 10 inches of crushed stone subbase. All drainage coefficients are 1.0 and the soil resilient modulus is 5000 lb/in2. If the highway’s traffic is the same (same axle loadings per vehicle as in Example 4.3), for how many years could you be 95% sure that this pavement will last? (Assume that any parameters not given in this problem are the same as those given in Example 4.3.)
4.8 A flexible pavement is designed with 5 inches of hot-mix asphalt (HMA) wearing surface, 6 inches of hot-mix asphaltic base, and 10 inches of crushed stone subbase. All drainage coefficients are 1.0. Daily traffic is 200 passes of a 20-kip single axle, 200 passes of a 40- kip tandem axle, and 80 passes of a 22-kip single axle.
If the initial minus the terminal PSI is 2.0 (the TSI is 2.5), the soil resilient modulus is 3000 lb/in2, and the overall standard deviation is 0.6, what is the probability (reliability) that this pavement will last 20 years before reaching its terminal serviceability?
4.9 A flexible pavement is designed with 4 inches of sand-mix asphalt wearing surface, 6 inches of dense- graded crushed stone base, and 8 inches of crushed stone subbase. All drainage coefficients are 1.0. The pavement is designed for 18-kip single-axle loads (1290 per day). The initial PSI is 4.5 and the TSI is 2.5. The soil has a resilient modulus of 12,000 lb/in2. If the overall standard deviation is 0.40, what is the probability that this pavement will have a PSI greater than 2.5 after 20 years?
4.10 A flexible pavement has a 4-inch sand-mix asphalt wearing surface, 10-inch soil cement base, and a 10- inch crushed stone subbase. It is designed to withstand 400 20-kip single-axle loads and 900 35-kip tandem- axle loads per day. The subgrade CBR is 8, the overall standard deviation is 0.45, the initial PSI is 4.2, and the final PSI is 2.5. What is the probability that this pavement will have a PSI above 2.5 after 25 years?
(Drainage coefficients are 1.0.)
Rigid Pavement Design (Sections 4.5–4.6)
4.11 Consider the two trucks in Problem 4.1. Which truck will cause more pavement damage on a rigid pavement with a 10-inch slab?
4.12 You have been asked to design the pavement for an access highway to a major truck terminal. The design daily truck traffic consists of the following: 80 single axles at 22,500 lb each, 570 tandem axles at 25,000 lb each, 50 tandem axles at 39,000 lb each, and 80 triple
axles at 48,000 lb each. The highway is to be designed with rigid pavement having a modulus of rupture of 600 lb/in2 and a modulus of elasticity of 5 million lb/in2. The reliability is to be 95%, the overall standard deviation is 0.4, the drainage coefficient is 0.9, ¨PSI is 1.7 (with a TSI of 2.5), and the load transfer coefficient is 3.2. The modulus of subgrade reaction is 200 lb/in3. If a 20-year design life is to be used, determine the required slab thickness.
4.13 A rigid pavement is being designed with the same parameters as used in Problem 4.5. The modulus of subgrade reaction is 300 lb/in3 and the slab thickness is determined to be 8.5 inches. The load transfer coefficient is 3.0, the drainage coefficient is 1.0, and the modulus of elasticity is 4 million lb/in2. What is the design modulus of rupture? (Assume that any parameters not given in this problem are the same as those given in Problem 4.5.)
4.14 A rigid pavement is designed with a 10-inch slab, anEc of 6 million lb/in2, a concrete modulus of rupture of 432 lb/in2, a load transfer coefficient of 3.0, an initial PSI of 4.7, and a terminal serviceability index of 2.5.
The overall standard deviation is 0.35, the modulus of subgrade reaction is 190 lb/in3, and a reliability of 90%
is used along with a drainage coefficient of 0.8. The pavement is designed assuming traffic is composed entirely of trucks (100 per day). Each truck has one 20- kip single axle and one 42-kip tandem axle (the effect of all other vehicles is ignored). A section of this road is to be replaced (due to different subgrade characteristics) with a flexible pavement having a structural number of 4 and is expected to last the same number of years as the rigid pavement. What is the assumed soil resilient modulus? (Assume all other factors are the same as for the rigid pavement.)
4.15 Consider the loading conditions in Problem 4.3. A rigid pavement is used with a modulus of subgrade reaction of 200 lb/in3, a slab thickness of 8 inches, a load transfer coefficient of 3.2, a modulus of elasticity of 5 million lb/in2, a modulus of rupture of 600 lb/in2, and a drainage coefficient of 1.0. How many years is the pavement expected to last using the same reliability as in Problem 4.3? (Assume all other factors are as in Problem 4.3.)
4.16 Consider Problem 4.15. How long would the rigid pavement be expected to last if you wanted to be 95%
sure that the pavement would stay above the 2.5 TSI?
4.17 Consider the traffic conditions in Example 4.3.
Suppose a 10-inch slab was used and all other parameters are as described in Example 4.3. What
Problems
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would the design life be if the drainage coefficient was 0.8, and what would it be if it was 0.6?
4.18 Consider the conditions in Example 4.4. Suppose all of the parameters are the same, but further soil tests found that the modulus of subgrade reaction was only 150 lb/in3. In light of this new soil finding, how would the design life of the pavement change?
4.19 Consider the conditions in Example 4.4. Suppose all of the parameters are the same, but a quality control problem resulted in a modulus of rupture of 600 lb/in2 instead of 800 lb/in2. How would the design life of the pavement change?
Pavement Design with Design-Lane Traffic (Sections 4.3–4.6)
4.20 You have been asked to design a flexible pavement, and the following daily traffic is expected for design: 5000 single axles at 10,000 lb each, 400 single axles at 24,000 lb each, 1000 tandem axles at 30,000 lb each, and 100 tandem axles at 50,000 lb each. There are three lanes in the design direction (conservative design is to be used). Reliability is 90%, overall standard deviation is 0.40, ¨PSI is 1.8, and the design life is 15 years. The soil has a resilient modulus of 13,750 lb/in2. If the TSI is 2.5, what is the required structural number?
4.21 A three-lane northbound section of interstate (with the design lane conservatively designed) has rigid pavement (PCC) and was designed with a 10-inch slab, 90% reliability, 700 lb/in2 concrete modulus of rupture, 4.5 million lb/in2 modulus of elasticity, 3.0 load transfer coefficient, and an overall standard deviation of 0.35.
The initial PSI is 4.6 and the TSI is 2.5. The CBR is 2 with a drainage coefficient of 1.0. The road was designed exclusively for trucks that have one 24-kip tandem axle and one 12-kip single axle. It is known from weigh-in-motion scales that there have been 13 million 18-kip–equivalent single-axle loads in the entire northbound direction of this freeway so far. If a section of flexible pavement is used to replace a section of the PCC that was removed for utility work, what structural number should be used so that the PCC and flexible pavements have the same life expectancy (the new life of the flexible pavement and the remaining life of the PCC)?
4.22 A rigid pavement is designed with an 11-inch slab thickness, 90% reliability, Ec = 4 million lb/in2, modulus of rupture of 600 lb/in2, modulus of subgrade reaction of 150 lb/in3, a 2.8 load transfer coefficient, initial PSI of 4.8, final PSI of 2.5, overall standard deviation of 0.35, and a drainage coefficient of 0.8. The pavement has a 20-year design life. The pavement has three lanes and is
conservatively designed for trucks that have one 20,000- lb single axle, one 26,000-lb tandem axle, and one 34,000-lb triple axle. What is the daily estimated truck traffic on the three lanes?
4.23 A rigid pavement is on a highway with two lanes in one direction, and the pavement is conservatively designed. The pavement has an 11-inch slab with a modulus of elasticity of 5,000,000 lb/in2 and a concrete modulus of rupture of 700 lb/in2, and it is on a soil with a CBR of 25. The design drainage coefficient is 1.0, the overall standard deviation is 0.3, and the load transfer coefficient is 3.0. The pavement was designed to last 20 years (initial PSI of 4.7 and a final PSI of 2.5) with 95%
reliability carrying trucks with one 18-kip single axle and one 28-kip tandem axle. However, after the pavement was designed, one more lane was added in the design direction (conservative design still used), and the weight limits on the trucks were increased to a 20-kip single and a 34-kip tandem axle (the slab thickness was unchanged from the original two-lane design with lighter trucks). If El Niño has caused the drainage coefficient to drop to 0.8, how long will the pavement last with the new loading and the additional lane (same volume of truck traffic)?
4.24 A four-lane northbound section of interstate has rigid pavement and was designed with an 8-inch slab, 90% reliability, a 700 lb/in2 concrete modulus of rupture, a 5 million lb/in2 modulus of elasticity, a 3.0 load transfer coefficient, and an overall standard deviation of 0.3. The initial PSI is 4.6 and the TSI is 2.5.
The pavement was conservatively designed (assuming the upper limit of the W18 design lane load) to last 20 years, and the CBR is 25 with a drainage coefficient of 1.0. A design mistake was made that ignored 1000 total northbound (daily) passes of trucks with 22-kip single and 30-kip tandem axles. What slab thickness should have been used?
Multiple Choice Problems (Multiple Sections) 4.25 A flexible pavement is constructed with 5 inches of sand-mix asphaltic wearing surface, 9 inches of dense-graded crushed stone base, and 10 inches of crushed stone subbase. The base has a drainage coefficient of 0.90 while the subbase drainage coefficient is 1.0. Determine the structural number of the pavement.
a) 4.47 b) 4.31 c) 4.76 d) 3.98
4.26 A flexible pavement is designed to last 10 years to withstand truck traffic that consists only of trucks with two 18-kip single axles. The pavement is designed for a soil CBR of 10, an initial PSI of 5.0, a TSI of 2.5, an overall standard deviation of 0.40 and a reliability of 90%, and the structural number was determined to be 6.
On one section of this roadway, beneath an underpass, an engineer uses an 8-inch rigid pavement in an attempt to have it last longer before resurfacing. How many years will this rigid-pavement section last? (Given the same traffic conditions, modulus of rupture = 800 lb/in2, modulus of elasticity = 5,000,000 lb/in2, load transfer coefficient of 3.0 and drainage coefficient of 1.0.).
a) 11.33 b) 13.22 c) 18.44 d) 25.65
4.27 A flexible pavement at an access road to a sports stadium parking lot is designed with a 4-inch sand-mix asphaltic concrete surface, 5-inch aggregate bituminous emulsion base, and a 10-inch crushed stone subbase.
There are 95 scheduled baseball and football games at the stadium per year. The access road to the parking lot is three lanes in each direction (conservatively designed). The pavement was designed for recreational vehicles with one 20K single axle and one 20K tandem axle. There are 9,000 recreational vehicles estimated at each event. Given that drainage coefficients are 1.0, the overall standard deviation of traffic is 0.45, reliability is 90%, and the soil's resilient modulus is 15,000 lb/in2, how many years will the access road last if the initial PSI is 4.0 and the terminal serviceability index is 2.5?
a) 7 b) 9 c) 12 d) 14
4.28 A rigid pavement on a new interstate (3 lanes each direction) has been conservatively designed with a 12- inch slab, an Ecof 5.5 u 106 lb/in2, a concrete modulus of rupture of 700 lb/in2, a load transfer coefficient of 3.0, an initial present serviceability index of 4.5, and a terminal serviceability index of 2.5. The overall standard deviation is 0.35, the subgrade CBR is 25, and the drainage coefficient is 0.9. The pavement was designed for 600 30-kip tandem axles per day and 1400 20-kip single axle loads per day. If the desired reliability was 90%, how long was this pavement designed to last?
a) 18 b) 32 c) 42 d) 46
4.29 A flexible pavement was designed to have a 6- inch sand-mix asphaltic surface, 8-inch soil-cement base and a 21-inch crushed-stone subbase (all drainage coefficients are 1.0). The pavement was designed for 800 12-kip single axles and 1600 34-kip tandem axles per day in the design direction. The reliability used was 90%, the overall standard deviation was 0.35, initial PSI was 4.7, the TSI was 2.5 and the soil resilient modulus was 2582 lb/in2. If the road has three lanes in the design direction (and was conservatively designed), for how many years was the pavement designed to last?
a) 8 b) 43 c) 53 d) 63