Establishing Pavement Strength HTC INFRASTRUCTURE MANAGEMENT LTD

Contents l Definitions l Purpose l Methods l Output

SNP - Background l ‘Structural Number of the Pavement’ l SNC, modified structural number, a measure of a pavement’s structural capacity l Based on the AASHTO’s structural number l Pavement layers are assigned a structural layer coefficient which represents the layer’s contribution to pavement performance

Equations:

Background... l SNP, adjusted structural number, used in HDM-4 to characterise pavement strength l Applies a weighting factor, which reduces with increasing depth l Pavement strength for deep pavements not over predicted, a concern with SNC

Why SNP? l A good overall measure of pavement strength for pavement performance predictions l Required by HDM Models l Unfortunately, not available in RAMM database

Requirements l Must have SNP for each section –either based on existing RAMM data, or, –from other survey/testing data available l Must be able to import this information into the dTIMS dt2699.dbf file for each section

Solution l Using the strength program in conjunction with the interface program Strength Program Other Data RAMM Database dT2699 Interface Program

What does the Strength Program do? l Not a lot … except: Allows the user to calculate a structural number for a particular section by a variety of methods

Currently Available Methods l FWD with Layer Thickness Method l FWD without Layer Thickness Method l CBR Layer Method l Benkleman Beam Method l ARRB Method l Typical Pavement Design Method

Falling Weight Deflectometer (FWD) Method

FWD with Layer Thickness Method l Used when pavement thickness data are available 100 AM 150 BASE 150 SUB-BASE known thicknesses known deflection

FWD with Layer Thickness Method l Rhode’s method: l Subgrade contribution: Source: HDM-4 Study

FWD only Method l Used when pavement thickness data are not available AM BASE SUB-BASE ? known deflection

FWD only Method l Roberts’ formula: l Jameson’s formula: l CBR Contribution:

CBR Layer Method l Based on the thickness of each layer, strength coefficients and subgrade CBR

Source: Parkman and Rolt (1997) CBR Layer Method

Benkleman Beam Method l Granular base pavements: l Cemented base pavements: Source: Paterson (1987)

ARRB Method l An approximate method l Estimation based on traffic volume l Assumes pavement is correctly designed for traffic loading based on design period of 20 years

Source: Roberts and Roper (1998) ARRB Method

Typical Pavement Design Method l Useful when no data is available to utilise the previous methods l Consists of a series of typical pavement configurations and subgrade strengths l Select the most appropriate pavement configuration –dependant on thickness of layers l Select subgrade strength –low, medium or high

Example...

Strength Program Data Sources l RAMM database l Other sources - Excel spreadsheets

Importing RAMM Data l Export required data from RAMM for Windows as text files then save as Excel files –it is important that the fields are in the correct order and that no fields are missing l Import Excel files into Strength program through File - Data Import/Append

Importing Other Data - Excel Spreadsheets l These must be in the format shown in the Strength Discussion Document –it is important that the fields are in the correct order and that no fields are missing (will be improved in later releases) l They are imported into the Strength program the same way as data originating from the RAMM database

Hierarchy of Methods l Pre-defined by the user prior to calculating SNP values l Determines which SNP value is taken when more than one is calculated

Output File / Interface Program l Output can be exported as an Excel file l SNP values are imported into the dt2699 file by the Interface program to be used by the HDM models in dTIMS