APPENDIX 3 ASPHALT PAVEMENT AND GRAVEL ROAD DESIGN EXAMPLES
APPENDIX 3  PAVEMENT DESIGN EXAMPLES
GRAVEL ROAD DESIGN
The primary design requirements for aggregate surfaced roads
include:
o Predicted future traffic for the design period (see Article
2)
o The lengths of the seasons (see Article 6.6.1e)
o Seasonal resilient moduli of the roadbed soil (see Article
6.6.1f)
o Elastic modulus, E_{BS}(psi), of aggregate base
layer (from HVEEM or other testing. M_{R} value)
o Elastic modulus, E_{BS}(psi), of aggregate subbase
layer (from HVEEM or other testing. M_{R} value)
o Design serviceability loss, ΔPSI (Article
6.6.1c)
o Allowable rutting, RD(inches), in surface layer (Article
6.6.1a), and
o Aggregate loss, GL(inches), of surface layer (Article
6.6.1b)
These design requirements are used in conjunction with the
computational chart in Table 2 in Appendix 2 and the design nomographs for
serviceability (Figure 18, Appendix 1) and rutting (Figure 19, Appendix 1) The
following steps outline the procedure:
Step 1: Select four levels of aggregate base thickness,
D_{BS}, which should bound the probable solution. Prepare four separate
tables, one for each trial thickness, identical to Table 2. On each of the four
tables enter the trial base thickness, D_{BS}; design serviceability
loss, ? PSI; and the allowable rutting, RD in the appropriate boxes.
Step 2: Enter the appropriate seasonal resilient (elastic)
moduli of the roadbed (M_{R}) and the aggregate base material,
E_{BS}, in columns 2 and 3, respectively, of Table 2. The base modulus
values may be proportional to the resilient modulus of the roadbed soil during a
given season. However, a constant value of 30,000 psi was used in the example
which follows since a portion of the aggregate base material will be converted
into an equivalent thickness of subbase material (which will provide some shield
against the environmental moisture effects).
Step 3: Enter the seasonal 18kip ESAL traffic in column 4 of
Table 2. Assuming that truck traffic is distributed evenly throughout the year,
the lengths of the seasons should be used to proportion the total projected
18kip ESAL traffic to each season. If the road is loadzoned (restricted)
during certain critical periods, the total traffic may be distributed only among
those seasons when truck traffic is allowed. Total traffic of 36,500 18kip ESAL
applications (the minimum 5 EDLA and a 20 year design period) and a seasonal
pattern corresponding to U.S. Climatic Region VI was used in the
example.
Step 4: Within each of the four tables estimate the allowable
18kip ESAL traffic for each of the four seasons using the serviceabilitybased
nomograph (Figure 18) and enter the result in column 5. If the resilient modulus
of the roadbed roil (during the frozen season) is such that the allowable
traffic exceeds the upper limit of the nomograph, assume a practical value of
500,000 18kip ESAL.
Step 5: Within each of the four tables estimate the allowable
18kip ESAL traffic for each of the four seasons using the ruttingbased
nomograph (Figure 19) and enter the result in column 7. Again, if the resilient
modulus of the roadbed soil is such that the allowable traffic exceeds the upper
limit of the nomograph, assume a practical value of 500,000 18kip
ESAL.
Step 6: Compute the seasonal damage values in each of the
four tables for the serviceability criteria by dividing the projected seasonal
traffic (column 4) by the allowable traffic in that season (column 5). Enter
these seasonal damage values in column 6 of Table 2 corresponding to
serviceability criteria. Next, follow these same instructions for rutting
criteria, i.e., divide column 4 by column 7 and enter in column 8.
Step 7: Compute the total damage for both the serviceability
and rutting criteria by adding the seasonal damages. When this is accomplished
for all four tables, a graph of total damage versus base layer thickness should
be prepared. The average base layer thickness, D_{BS}, required
is determined by interpolating in this graph for a total damage equal to 1.0.
Figure A35 provides an example in which the design is controlled by the
serviceability criteria.
Step 8: The base layer thickness determined in the last step
should be used for design if the effects of aggregate loss are negligible. If,
however, aggregate loss is significant, the design thickness is determined using
the following equation:
D_{BS} = D_{BS} + (0.5 x
GL)
where GL = total estimated aggregate (gravel) loss (in
inches) over the performance period.
Step 9: The final step of the design chart procedure for
aggregate surfaced roads is to convert a portion of the aggregate base layer
thickness to an equivalent thickness of subbase material. This is accomplished
with the aid of Figure 20. Select the final base thickness desired,
D_{BSf} (6 inches is used in the example). Draw a line to the estimated
modulus of the subbase material, E_{BS}. Go across and through the scale
corresponding to the reduction in base thickness, D_{BSi} 
D_{BSf}. Then for the known modulus of the base material,
E_{BS}, determine the required subbase thickness,
D_{SB}.
As an example to illustrate the described procedure and the
requirements of Article 6, assume the following:
o HVEEM R value of 20 for the roadbed soil.
o The minimum required EDLA of 5, over a 20 year design
period for a total traffic of 36,500 18kip ESAL.
Assume 6, 8, 10, and 12 inches of base thickness for
preparation of the four tables. Per Article 6.6.1, the design serviceability
loss is 3, and the allowable rutting is 2.
Proportion the total projected 18kip ESAL traffic into the
seasonal traffic values for column 4 according to the lengths of season
specified in 6.6.1e.
The results of proceeding according to steps 4, 5, and 6 above
are shown in the example tables, Tables A31 through A34.
Figure A35 shows the graph of total damage versus base layer
thickness for this example. The serviceability criteria require a larger
thickness of base than the rutting criteria. Use the higher value (11.6 inches)
for design.
Gravel loss is specified for design purposes in 6.6.1b as 2
inches, therefore the required thickness, D_{BS}, is:
D_{BS} = D_{BS} + (0.5 x GL) = 11.6 +
(0.5 x 2) = 12.6 inches.
Use Figure 20 (reproduced showing the example as Figure A34)
to determine the amount of subbase material required to reduce the base
thickness by 6 inches.
TABLE 2a  EXAMPLE ASSUMING 6 INCHES BASE COURSE
TRIAL BASE THICKNESS, D_{BS}
(INCHES)____6____

SERVICEABILITY CRITERIA

RUTTING CRITERIA

PSI = ______3_____

RD (INCHES) ____2_____

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

SEASON (ROADBED MOISTURE CONDITION)

ROADBED RESILIENT MODULUS M_{R} (psi)

BASE ELASTIC MODULUS E_{BS} (psi)

PROJECTED 18  KIP ESAL TRAFFIC W_{18}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{PSI}

SEASONAL DAMAGE
W_{18}/(W_{18})_{PSI}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{RUT}

SEASONAL DAMAGE
W_{18}/(W_{18})_{RUT}

WINTER (FROZEN)

20,000

30,000

9,125

32,000

0.29

350,000

0.03

SPRING/THAW (SATURATED)

1,500

30,000

4,563

2,200

2.07

3,500

1.30

SPRING/FALL (WET)

3,300

30,000

9,125

5,000

1.83

4,500

2.03

SUMMER (DRY)

4,900

30,000

13,687

7,000

1.96

7,500

1.82


TOTAL


TOTAL


TOTAL


TRAFFIC =

36,500

DAMAGE =

6.15

DAMAGE =

5.18

TABLE 2b  EXAMPLE ASSUMING 8 INCHES BASE COURSE
TRIAL BASE THICKNESS, D_{BS}
(INCHES)___8___

SERVICEABILITY CRITERIA

RUTTING CRITERIA

PSI = ______3_______

RD (INCHES) ____2_____

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

SEASON (ROADBED MOISTURE CONDITION)

ROADBED RESILIENT MODULUS M_{R} (psi)

BASE ELASTIC MODULUS E_{BS} (psi)

PROJECTED 18  KIP ESAL TRAFFIC W_{18}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{PSI}

SEASONAL DAMAGE
W_{18}/(W_{18})_{PSI}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{RUT}

SEASONAL DAMAGE
W_{18}/(W_{18})_{RUT}

WINTER (FROZEN)

20,000

30,000

9,125

70,000

0.13

400,000

0.02

SPRING/THAW (SATURATED)

1,500

30,000

4,563

4,200

1.09

7,000

0.65

SPRING/FALL (WET)

3,300

30,000

9,125

12,000

0.76

11,000

0.83

SUMMER (DRY)

4,900

30,000

13,687

13,500

1.01

16,000

0.86


TOTAL


TOTAL


TOTAL


TRAFFIC =

36,500

DAMAGE =

2.99

DAMAGE =

2.36

TABLE 2c  EXAMPLE ASSUMING 10 INCHES BASE COURSE
TRIAL BASE THICKNESS, D_{BS}
(INCHES)____10____

SERVICEABILITY CRITERIA

RUTTING CRITERIA

PSI = ______3______

RD (INCHES) ____2______

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

SEASON (ROADBED MOISTURE CONDITION)

ROADBED RESILIENT MODULUS M_{R} (psi)

BASE ELASTIC MODULUS E_{BS} (psi)

PROJECTED 18  KIP ESAL TRAFFIC W_{18}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{PSI}

SEASONAL DAMAGE
W_{18}/(W_{18})_{PSI}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{RUT}

SEASONAL DAMAGE
W_{18}/(W_{18})_{RUT}

WINTER (FROZEN)

20,000

30,000

9,125

120,000

0.08

400,000

0.02

SPRING/THAW (SATURATED)

1,500

30,000

4,563

8,000

0.57

11,000

0.41

SPRING/FALL (WET)

3,300

30,000

9,125

20,000

0.46

21,000

0.43

SUMMER (DRY)

4,900

30,000

13,687

28,000

0.49

28,000

0.49


TOTAL


TOTAL


TOTAL


TRAFFIC =

36,500

DAMAGE =

1.60

DAMAGE =

1.35

TABLE 2d  EXAMPLE ASSUMING 12 INCHES BASE COURSE
TRIAL BASE THICKNESS, D_{BS}
(INCHES)____12____

SERVICEABILITY CRITERIA

RUTTING CRITERIA

PSI = _____3______

RD (INCHES) _____2______

(1)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

SEASON (ROADBED MOISTURE CONDITION)

ROADBED RESILIENT MODULUS M_{R} (psi)

BASE ELASTIC MODULUS E_{BS} (psi)

PROJECTED 18  KIP ESAL TRAFFIC W_{18}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{PSI}

SEASONAL DAMAGE
W_{18}/(W_{18})_{PSI}

ALLOWABLE 18  KIP ESAL TRAFFIC
(W_{18})_{RUT}

SEASONAL DAMAGE
W_{18}/(W_{18})_{RUT}

WINTER (FROZEN)

20,000

30,000

9,125

200,000

0.05

400,000

0.02

SPRING/THAW (SATURATED)

1,500

30,000

4,563

18,000

0.25

22,000

0.21

SPRING/FALL (WET)

3,300

30,000

9,125

30,000

0.30

31,000

0.29

SUMMER (DRY)

4,900

30,000

13,687

40,000

0.34

45,000

0.30


TOTAL


TOTAL


TOTAL


TRAFFIC =

36,500

DAMAGE =

0.82

DAMAGE =

1.35
