RIMS Update - Guideline for Pavement Strength Testing
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Transcript of RIMS Update - Guideline for Pavement Strength Testing
Guideline for Pavement Strength Testing
2012 Road Asset & Information Forum
The Project•The project is commissioned by the RIMS Group•Researcher - Graham Salt et al of Tonkin and Taylor Ltd•Project Manager – Theuns Henning•RIMS Champion – Jim McQueen
Project ObjectivesTo provide a good practise guideline to assist Road Controlling Authorities in understanding the collection and interpretation of pavement strength data using the falling weight deflectometer.
The Falling Weight Deflectometer (FWD)FWD is currently the most practical system for accurate measurement of deflection responseGeophones determine the deflection bowl produced by the impulse of the falling weight.
Background•RCA’s are required to manage assets in cost effective and sustainable
manner•Understanding failure modes and strength of pavements at project level
promotes design of best long term treatments•Knowledge of pavement strength at network level aids sustainable long
term renewals planning•Pavement strength data stored in AMIS is utilised in optimised decision
making and deterioration modelling (eg dTIMS)•FWD testing has been widely used in NZ for may years for design and
network level management•As testing becomes more affordable authorities are increasingly
surveying extended parts of their networks
Background (cont)•Technology behind analysis of FWD data is well advanced•Various reports cover many aspects of FWD testing and
analysis for project and network level•There is no commonly adopted sampling approach adopted
by authorities in NZ•Combining information available into one guideline would
assist asset owners•In recent research, Salt et al (2010) have developed
structural indices for rutting, roughness, flexure and shear•Testing of these indices indicate their potential value
Aspects covered by Guideline•Use and basic principles of FWD testing•Explanation of empirical bowl parameters and structural
indices (SI)•Guidance for planning surveys and sampling•Data requirements•FWD data that should be stored in AMIS•SI concepts for alternative pavement types (unbound
granular, thin AC, stabilised etc)•SI application at network and project level•Reporting for Project/network
Sampling for network analysisProject level testing carried out for pavement rehabilitation requires sufficient data to provide reliability in terms of the 5 or 10 percentile parameters applied to design.
Network testing for asset management is often constrained by budget and to get coverage spacing of tests is extended.
The following table is used for network level testing(The remaining life can be determined as survey progresses)
dTIMS network level FWD spacings
Centreline Length
FWD Test Spacing based on Field Calculation of Residual Life
Life > 15 Years Life < 15 Years
0 m ‐ 200 m 5 Tests (3 in IRP lane, 2 in DRP lane)
200 m ‐ 500 m 100 m intervals in each lane
500 m ‐ 2 km 10 tests in IRP lane only 10 tests in each lane
2 km ‐ 5 km 200 m intervals in IRP lane only 200 m intervals in each lane
> 5 km 200 m intervals in each lane, or 400 m intervals if geologically uniform terrain
Structural indices•The SNP while being easy to calculate, has a limitation that it
does not distinguish between the various modes that can lead to the failure of a pavement
•The SNP could suggest a strong pavement with a long life ahead but failure occurs sooner due to tensile failure in surface
•A set of “Structural Indices” has been introduced by Salt et al(2010), representing a structural number for each of the common distress modes
Structural indices and Distress Modes•SI Rutting – Vertical surface deformation, initially some
bedding in then a rapid increase at end of pavement life•SI Roughness – loss of shape longitudinally from variations
in rut depth and shear failures•SI Flexure – Surface cracking caused by surface tensile
strain in the deflection bowl as the wheel travels along the road and also in structural AC on the bottom of the layer
•SI Shear – lateral deformations or shoving due to shear failure in the pavement layers.
Obtaining the structural indices•Supplied by FWD provider after mechanistic analysis•Calculated by dTIMS analyst after mechanistic analysis
outlined in guideline•Generated by regressions currently being considered as an
application within RAMM•Analyst might generate SIs using a more rigorous approach
(layered elastic theory) using data in RAMM - may need to get additional data from the FWD provider
Mechanistic approachEach SI is mechanistically derived and has the same range and general distribution as the traditional SNP
The following chart shows a process of determining Structural indices (Stevens et al 2009)
Mechanistic approach (cont)
No
Yes
Establish general form of relationships for determining ESA to a term inal condition for each distress mode
Using known distress and traffic data (from LTPP sites or specific case histories), determine coefficients for each distress general form relationship
Create a transfer function that maps the refined relationship onto a structural index with the same range
Use structural index until more data comes to hand that can fu rther refine the above models
Determine layer moduli, stresses and strains at LTPP sites under 1 ESA
More pavement performance data now available?
Mechanistic approach (cont)Data from LTTP sites is used to determine coefficients in transfer functions that derive SIsChart shows distribution of SNP for all national LTTP sites.
Mechanistic approach (cont)The pavement structural life (Rutting) is converted to the corresponding structural index using a transfer function
An example of SIs and SNP from one LTTP site BM01
Chainage SNP SIRUTTING SIROUGHNESS SIFLEXURE SISHEAR
0.10 3.9 4.5 4.9 3.1 3.6
0.15 3.9 4.6 4.7 3.5 3.8
0.20 3.5 4.0 3.9 3.3 3.6
0.25 3.6 4.1 3.8 4.0 3.9
0.30 1.8 2.6 2.7 4.2 4.2
0.35 2.2 3.1 3.1 3.8 3.8
Application of Structural Indices•The application of Sis has been tested on some networks (eg
Hastings)•Correlations between SIs and Radius of curvature etc have
been tested (Ashwin Sashi and Sine Foulgar) at Auckland university
•The box and whisker plot below is sample from wellington
Application of Structural indices (cont)
This is a section of Motorway that is AC on a relatively stiff base. The chart supports the expected behaviour with isolated areas indicated as cracking risk with other indices not an issue.
Some Conclusions•Structural indices give an indication of the bearing capacity
of road lengths in terms of specific failure modes•Capable of highlighting performance issues which may not
yet be visible – risk of future failure•Provides strong supporting evidence for maintenance
•Indices cannot be used in isolation as deterioration is also a function of traffic loading
•May also be a function of material types
Progress with Guideline ProjectThe document has been written and will go to the review stage next
Peer review and final editing to be completed – approx 2 months
Publishing will be later in this calendar year
Questions?More Information?www.rims.org.nz
Presenter NameJim [email protected]