1.

W18 [Accumulated ESALs]

Zr
Std Dev
PSI
2. Subgrade M[r]
a[i]
D[i], inches
m[i]
3. Reliability, %

648,000
-1.28
0.45
1.70
9500
Surface mix
0.44
4.00
90

ZR
S
DPSI
psi
Base mix
0.34
0.00
1.00
R

4. Initial and terminal serviceability

PSI
Provided SN

Po
4.20
3.70

Pt
2.50

Required SN (Solver will fill in)

2.95

Adequate

log10(W18) =

5.81
5.81
0.00

left side
right side

target cell

P.A.B.
0.14
6.00
1.00

subbase
0.11
10.00
1.00

inches

Instructions
1. If the Excel-> Add-ins--> Solver has not been activated, do that first.
(Excel 2003: Tools->Add-ins, check the
In Excel 2010, it's File->Options->Add-ins->click on [Go] Button at the bottom by "M

2. Fill in the values for the cells in light blue for reconstruction (all new layers).
It is not necessary to fill in these values here. Filling them in allows the labeling of "A
For rehabilitation, please check the value in B16 against the result of filling in the tabl
The value in B16 gets carried onto that tab, so once the Solver has been run (step 3)
3. Open the Solver (Tools->Solver). Cell B20 should already be the
target cell. "By Changing" should be "sn" (B16).
In Excel 2010, it's in the [Data] tab at the top toolbar, then under the "Analysis" categ
It is already set up to run in the appropriate cell with the appropriate values. Click OK
4. The structure provided is adequate when the provided SN exceeds
the required SN (and is indicated on cell C16).
You may use either the a[i] and D[i] rows here for the provided SN or you may use the
If you use the next sheet, do not change the Provided SN in the green cell because it
NOTE:
Disclaimer: No claims of accuracy are made about the answers provided
by this tool.
This tool calculates the required SN. The Provided SN depends on
whether this is new construction or a rehabilitation.
Please see the AASHTO 1993 Pavement Design Guide for guidance
on rehabilitation design as well as calculations for ESALs.
(There are some calculators online, too).

Please note that the structural coefficient of the base layer (0.34) is a function of its position
within the pavement structure and not necessarily material properties. It was derived from
empirical relationships at the AASHTO Road Test and therefore a hot-mix-asphalt base should
be considered at 0.34 per inch and not 0.44 per inch.

KEYS: Fill in cells in light blue. (D[i] cells aren't necessary but they can help see the adequacy of a design)
1.
The W18 value is the value obtained in the bright yellow cell in ESALCALC.xls, the ESAL calculator.
2.

Subgrade resilient modulus.

Gravels
10,000-12,000 psi
Tills
10,000 psi
Sands
7500-10000 psi
Silts
6000-7500 psi
Clays
4000-6000 psi

<---- this value should be used unless there is clear information to use someth
(low end for silty/clayey sands, high end for gravelly sands)

3.

Reliability should be 95% for Interstates, Expwys, 90% elsewhere.

4.

Terminal serviceability should be 2.5, but collectors and local roads may use 2.0.
The remaining inputs, Std Dev and Zr should not be varied from defaults.

D[i]

Depth of each layer being constructed.

This is not related to the required SN but

rather to the provided SN. It is not necessary except
to check the adequacy of the design.
For rehabilitation, existing layers will have different
coefficients. That calculation needs to be done
separately but is straightforward. (depth x coeff, add layers).

Tools->Add-ins, check the Solver option)

Button at the bottom by "Manage Excel Add-ins", then select Solver Add-In in the dialog box that opens, click OK.

n allows the labeling of "Adequate" in yellow. This is a quick shortcut for reconstructed pavement.
e result of filling in the table in the SN eff tab (next Excel tab).
lver has been run (step 3) you can move over to the SN eff tab to do those calculations.

under the "Analysis" category at the far right top, there is the "Solver" option. Click it.
propriate values. Click OK and then "Keep Solver Solution".

ded SN or you may use the next tab (SN eff).

n the green cell because it will override the formula.

adequacy of a design)
the ESAL calculator.

s clear information to use something else.

gravelly sands)

ot necessary except

will have different

eds to be done
(depth x coeff, add layers).

The effective (existing) Structural Number is a straightforward calculation. Please see the [Layer Coefficients for Sneff] tab to
Remember to take out layers that will be removed by milling.
Layer
HMA surf.
HMA surface
HMA base
Subbase
available
available
available
available
available
available
available
(1)

New/Existing (1)
N
E
E
E
available
available
available
available
available
available
available

Thickness (in) Layer coefficient

2.5
2
4
8
0
0
0
0
0
0
0

Drainage coefficient
0.44
0.25
0.15
0.08
0
0
0
0
0
0
0

1
1
1
1
1
1
1
1
1
1
1

Enter N for new layers, E for existing layers

Required SN
from previous tab
In this example, the SN after rehab is only 2.84 - more
SN needs to be provided.
This could be achieved by paving 3 inches instead of 2.5
Change the HMA surface to 3.0 and see the answer
(3.06, which exceeds 2.95, so OK)

yer Coefficients for Sneff] tab to find appropriate layer coefficients.

SN

Use Drainage Coefficient of 1 unless you have specific site information to vary it.
1.1
0.5
0.6
0.64
0
0
0
0
0
0
0
1.74 SN effective (existing)
2.84 SN with new layer(s)
2.95

s only 2.84 - more

Use SN effective with the SN required to calculate the required SN of the overlay
if a rehab project (SN ol = SN required - SN effective)
Or, if you are checking the adequacy of an overlay, include the overlay as an "N" and check the
SN with new layer(s) number agains the SN required.

inches instead of 2.5

see the answer
Or, type "N" under New/Existing with appropriate layer coefficients to get the SN provided.
(This can be done in the 'flexible pavement' tab, D[i] row, too).

For extra layers, you may use rows 9-15 in addition to the ones provided.
Remember always to not include layers that are being milled in these calculations.
For instance, the values shown in rows 5-8 result in a structure that is less than the required SN
Therefore, the overlay thickness should be increased.
If you use 3" overlay, the SN with new layer(s) becomes 3.06 and that would be adequate.

of the overlay

lay as an "N" and check the

o get the SN provided.

se calculations.
is less than the required SN

hat would be adequate.

MATERIAL

AC Surface (hot mix asphalt, HMA)

Stabilized Base (includes HMA base)

Granular Base or Subgrade

SURFACE CONDITION

COEFFICIENT RANGE

Little or no alligator cracking and/or only lowseverity transverse cracking

0.35 0.40 per inch

< 10% low-severity allig ckg and/or <5%

medium- and high- severity transverse cracking

0.25 0.35 per inch

>10% low-severity allg ckg and/or

<10% medium-severity allig ckg and/or 0.20 0.30 per inch
>5-10% medium- and high- severity
trans. cracking
>10% medium-severity allg ckg and/or
<10% high-severity allig ckg and/or

0.14 0.20 per inch

>5-10% medium- and high- severity

trans. cracking
> 10% high-severity allig ckg and/or
0.08 0.15 per inch
>10% high- severity transverse cracking
Little or no alligator cracking and/or only lowseverity transverse cracking

0.20 0.35 per inch

< 10% low-severity allig ckg and/or

<5% medium- and high- severity transverse
cracking

0.15 0.25 per inch

>10% low-severity allg ckg and/or

<10% medium-severity allig ckg and/or 0.15 0.20 per inch
>5-10% medium- and high- severity
trans. cracking
>10% medium-severity allg ckg and/or
<10% high-severity allig ckg and/or
>5-10% medium- and high- severity
trans. cracking

0.10 0.20 per inch

> 10% high-severity allig ckg and/or

0.08 0.15 per inch
>10% high- severity transverse cracking
No evidence of pumping, degradation, or
contamination by fines

0.10 0.14 per inch

Some evidence of pumping, degradation, or

contamination by fines

0.00 0.10 per inch