Flexible Pavement Design Tool.xls

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Flexible Pavement Design Tool

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Post on 09-Dec-2015

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flexible pavementKEYS: Fill in cells in light blue. (D[i] cells aren't necessary but they can help see the adequacy of a design)1. W18 [Accumulated ESALs]648,0001.The W18 value is the value obtained in the bright yellow cell in ESALCALC.xls, the ESAL calculator.Zr-1.28ZRStd Dev0.45S2.Subgrade resilient modulus.PSI1.70DPSIGravels10,000-12,000 psi2. Subgrade M[r]9500psiTills10,000 psi Add-ins--> Solver has not been activated, do that first.(Excel 2003: Tools->Add-ins, check the Solver option)In Excel 2010, it's File->Options->Add-ins->click on [Go] Button at the bottom by "Manage Excel Add-ins", then select Solver Add-In in the dialog box that opens, click OK.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 "Adequate" in yellow. This is a quick shortcut for reconstructed pavement.For rehabilitation, please check the value in B16 against the result of filling in the table in the SN eff tab (next Excel tab).The value in B16 gets carried onto that tab, so once the Solver has been run (step 3) you can move over to the SN eff tab to do those calculations.3. Open the Solver (Tools->Solver). Cell B20 should already be thetarget cell. "By Changing" should be "sn" (B16).In Excel 2010, it's in the [Data] tab at the top toolbar, then under the "Analysis" category at the far right top, there is the "Solver" option. Click it.It is already set up to run in the appropriate cell with the appropriate values. Click OK and then "Keep Solver Solution".4. The structure provided is adequate when the provided SN exceedsthe 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 next tab (SN eff).If you use the next sheet, do not change the Provided SN in the green cell because it will override the formula.NOTE:Disclaimer: No claims of accuracy are made about the answers providedby this tool.This tool calculates the required SN. The Provided SN depends onwhether this is new construction or a rehabilitation.Please see the AASHTO 1993 Pavement Design Guide for guidanceon 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 positionwithin the pavement structure and not necessarily material properties. It was derived fromempirical relationships at the AASHTO Road Test and therefore a hot-mix-asphalt base shouldbe considered at 0.34 per inch and not 0.44 per inch.

SN eff (existing)The effective (existing) Structural Number is a straightforward calculation. Please see the [Layer Coefficients for Sneff] tab to find appropriate layer coefficients.Remember to take out layers that will be removed by milling.LayerNew/Existing (1)Thickness (in)Layer coefficientDrainage coefficientSNUse Drainage Coefficient of 1 unless you have specific site information to vary it.HMA surf.N2.50.4411.1HMA surfaceE20.2510.5HMA baseE40.1510.6SubbaseE80.0810.64availableavailable0010availableavailable0010availableavailable0010availableavailable0010availableavailable0010availableavailable0010availableavailable00101.74SN effective (existing)(1)Enter N for new layers, E for existing layers2.84SN with new layer(s)Required SN2.95Use SN effective with the SN required to calculate the required SN of the overlayfrom previous tabif a rehab project (SN ol = SN required - SN effective)In this example, the SN after rehab is only 2.84 - moreOr, if you are checking the adequacy of an overlay, include the overlay as an "N" and check theSN needs to be provided.SN with new layer(s) number agains the SN required.This could be achieved by paving 3 inches instead of 2.5Change the HMA surface to 3.0 and see the answer(3.06, which exceeds 2.95, so OK)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 SNTherefore, 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.

Layer coefficients for SNeffMATERIALSURFACE CONDITIONCOEFFICIENT RANGEAC Surface (hot mix asphalt, HMA)Little or no alligator cracking and/or only low-severity transverse cracking0.35 0.40 per inch< 10% low-severity allig ckg and/or 10% low-severity allg ckg and/or0.20 0.30 per inch 5-10% medium- and high- severity trans. cracking >10% medium-severity allg ckg and/or0.14 0.20 per inch 5-10% medium- and high- severity trans. cracking> 10% high-severity allig ckg and/or0.08 0.15 per inch>10% high- severity transverse crackingStabilized Base (includes HMA base)Little or no alligator cracking and/or only low-severity transverse cracking0.20 0.35 per inch< 10% low-severity allig ckg and/or0.15 0.25 per inch10% low-severity allg ckg and/or0.15 0.20 per inch 5-10% medium- and high- severity trans. cracking >10% medium-severity allg ckg and/or0.10 0.20 per inch 5-10% medium- and high- severity trans. cracking> 10% high-severity allig ckg and/or0.08 0.15 per inch>10% high- severity transverse crackingGranular Base or SubgradeNo evidence of pumping, degradation, or contamination by fines0.10 0.14 per inchSome evidence of pumping, degradation, or contamination by fines0.00 0.10 per inch