Assessment of Compaction Quality Control Methods – NACOE P60 Best Practice Research

The acceptance of earthwork and unbound pavement construction in Australia currently relies mostly on density testing and CBRs for Quality Assurance (QA).

Though its National Asset Centre of Excellence (NACoE) research program, Queensland’s Department of Transport & Main Roads sponsored a vital ARRB research project to update test methods acceptable for use for QA of pavement and subgrade materials. This state-of-the-industry study assessed test methods that have the potential to:

(a) reliably provide a direct measure of the strength or in-situ modulus value; and
(b) offer significant time savings in turnaround time of test results.

We have brought together the key outcomes from the Best practice in compaction quality assurance for pavement and subgrade materials – P60 project.

Methods evaluated included Light Weight Deflectometer’s (LWD’s), PANDA® Instrumented DCP, Clegg Hammer, DCP and Plate Load Testing (PLT). Specifically, the devices evaluated included the Zorn Light Weight Deflectometer, the Anix Instrumented Plate Load Test and PANDA® Instrumented DCP.

In earthworks testing, using density ratios is applied widely in quality control. There are currently many different measuring devices which can provide a more accurate measurement of design parameters (strength or stiffness) and can provide a more direct route for parameter assessment (i.e. limit need for any inclusion of generic relationships).

Comparisons of density with alternative in-situ testing show the latter provides significant benefits to the industry. Accuracy is not the same as precision, and industry’s reliance on density places an emphasis on precision rather than accuracy, data usability or timeliness of results.

This research has found density measurements are, although precise, not very accurate due to poor correlation with the results of other modulus or strength-based tests.

Year 1 Findings

Year 1 Report – Best Practice in Compaction QA for Pavement and Subgrade Materials Year 1 Report Jeffrey Lee, David Lacey & Burk Look NACOE P60 QLD DTMR, Australia Aug 2017

Currently, the acceptance of construction works (e.g. earthwork embankments, subgrade and pavement granular layers) by Australian road regulatory bodies requires in situ density testing to be completed in order that a relative percentage of the laboratory-determined maximum dry density can be determined. Current earthworks specifications often rely on the assumption that there is a direct correlation between density and modulus parameters (i.e. the greater the density achieved, the higher the modulus of the compacted material). However, this assumption may not be valid and it is affected by many properties of the engineering material.

Over the last two decades, some alternative field assessment methods have been developed which either directly measure the in situ modulus or correlate with the resilient modulus. This project focuses on exploring the use of these new assessment methods. Such innovative testing methods can be grouped into the following four main categories:

• penetration test devices
• surface based impact devices
• geophysical methods
• in situ sensors.

Among these four categories, the ‘penetration test devices’ and ‘surface based impact devices’ were identified to have the potential to be adopted in TMR’s current Quality Assurance (QA) framework.

A literature review conducted in 2016/2017 highlighted that some similar international studies had been completed in recent years. Recent projects in Australia also demonstrated the advantages associated with these innovative, commercially-available field assessment techniques.

The project team attempted to rank the different QA methods using a weighted rating approach.

Year 3 Findings

In Year 3, a number of webinars were presented.

Presenters:

• Dr Jeffrey Lee – ARRB
• Dr Burt Look – FSG – Geotechnics + Foundations
• Dr David Lacey – FSG – Geotechnics + Foundations

Part 1: June 2018

Part 1 introduced alternative methods to assess compaction in the field. The advantages, limitations, and fundamentals of the measurement methods are discussed.

NACOE Advanced Methods for Compaction Quality Control – June 2018 Webinar – Part 1 (Webinar Slides)

Part 2: February 2020

Part 2 compared the limitations, benefits and issues associated with traditional density testing and other types of testing with research data various sites.

You can download the presentation slides and view a recording of the webinar. The presenters answered many questions in writing.

Advanced Methods for Compaction Quality Control Webinar Part 2 Question Answers

1. How is moisture ratio taken into account?
2. Modulus is influenced by moisture too; so, shouldn’t a comparison should MDD v Modulus include consideration of moisture content?
3. Was the moisture content/ratio taken into account when comparing the Density vs Modulus?
4. The statistical analysis doesn’t acknowledge some frustrating variables (1) – e.g. Density Ratio v Modulus not considering moisture content.
5. What was the moisture variations within all the testing?
6. Density Ratio can be performed within 1 day as per AS 1289 5.7.1.
7. Most Victorian testing for earthworks is using rapid HILF method which does not normally require curing if within the test method range.
8. He [the presenter] is referring to assigned value and not the HILF compaction.
9. Are there any case history recorded significant numbers of PLT vs LFWD?
10. PLT has shown vice-versa results and how can we take it PLT as reliability test?
11. The statistical analysis doesn’t acknowledge some frustrating variables (2) – e.g. density ratio v CBR not considering material type
12. Embankments need to have a required modulus for strength as well as minimise settlement. Isn’t density a measure of minimising settlement and therefore still important?
13. A dry material with low density will have a high modulus, but is this all we care about?
14. Slide 17 – These are awful results and not representative of road construction projects in NSW. What is the source of this data? PS. You are showing density (ratio) results and not quality test results!
15. Slide 19 – One crucial item is the location of the test results, that is layer and GPS / Chainage and Offset! Why is this mixing?
16. Slide 23 – If you are placing and compacting in 300 mm lifts, the LFWD and PLT will not give you reliable results as it influenced by the underlying layers. Therefore, why would you use this equipment?
17. Slide 25 – You have only tested and analysed one formation material. How can you draw any early conclusions?
18. Slide 29 – Work in the USA has shown the portable hand held FWD devices are susceptible to moisture content of the material being tested and have you taken this into consideration to the reliability of the test results from these devices?
19. Slide 50 – You would have to be a brave road agency engineer to allow a contractor to use 1000 mm lifts for embankments with a 18 T padfoot roller!

Part 3: March 2020

Part 3 focused on the applications and procedures associated with alternative testing to a density-based approach.

You can download the presentation slides and view a recording of the webinar.

Here is the Year 3 Report.

Industry’s familiarity with density-based assessments for the quality assurance (QA) of pavement layers and subgrades currently favours conventional density measurements over other field tests that have the potential to better validate design parameters achieved during construction. Although such alternative tests (e.g. Prima 100 LWD, Geogauge or PANDA probe) are not necessarily as precise as conventional density testing, the density test itself has significant limitations.

These limitations include the time required to undertake the tests and its inability to reliably assess the in situ devices evaluated in this report.

The background to Phase 3 of the study is covered in Section 2 which discusses the interim findings from Phases 1 and 2. The field testing and analysis conducted on a live construction site to evaluate the alternatives test method is summarised in Section 3. A proposed technical specification is outlined in Section 4 and conclusions and recommendations are discussed in Section 5.

Year 5 Findings

Here is the Year 5 Report.

Moving from Density to Modulus – Guidance On Use Of Light Weight Falling Deflectometers (LWDs) – June 2021

National Asset Centre of Excellence (NACOE), a collaboration of Queensland Department of Transport and Main Roads and the Australian Road Research Board (ARRB), has released their report for the Best practice in compaction quality assurance for pavement and subgrade materials – P60 project.

Importantly, in Appendix A of this report, is the Draft Technical Note – Guidance on Use of Light Weight Falling Deflectometers (LWDs) to be Accepted as an Alternative Method for Verification of Earthworks Compaction Requirements – June 2021. This provides guidance on moving from a density based specification for compaction control to a modulus based approach to testing in the field.

This draft technical note provides guidance on implementation of Light Weight Deflectometers including a flow chart showing key steps for assessment/derivation of equivalent acceptance thresholds for LWD use (in lieu of traditional (density) testing minimum thresholds included in MRTS04 – General Earthworks).

We believe this “How to” guide will be very useful for industry on projects across the country. You can visit our website to access the full report and other resources.

If you have any feedback and thoughts on the Draft Technical Note, we’d love to hear them! Contact us.