IPWEA NZ Wellington/Taranaki Branch Meeting

Civil Engineering Testing Frequently Asked Questions

A presentation by Bob Smith, Principal Engineer,and Rhys Jones, Laboratory Manager, Opus Wanganui.

Scratching the surface

When you specify a test, do you understand how you will use the result?

Fundamental question to be answered

“The test result is only as good as your sample.”

Sampling

• What is the target density for this material?• Is there a quick and easy way to test

(especially compaction of small lots)?• How can compaction be over 100%? Can

you over-compact soil/aggregate?• What is the difference between Standard,

Heavy, and Vibrating Hammer compaction? Which one should we use?

• What can we do when we can not achieve the compaction requirements in the specification?

Frequently Asked Questions

• Is this compaction curve okay – shouldn’t it be a regular parabolic curve?

• How many tests are required – one or one lot?

• What are Density Index (ID) and Relative Density (RD)? Are they the same?

• What should we do if two labs give different results?

• Can you find these test methods for me – Sand Equivalent NZS4402 Part 1:1980 Test 7, Wet Sieving NZS4401:1986 Test 2.8.1?

Frequently Asked Questions

• What is the best method to compact sand?• How much sample do you need for testing?• Can you explain what this report is telling me?• What does IANZ accreditation cover?• Why do a wet grading when a dry grading is

quicker?• Why do we have to do Insitu CBR tests on the

subgrade?• What testing does the specification require me to

get carried out?• Why does M/4 require CBR to be tested without a

surcharge? Is it done? Does it make a difference?

Frequently Asked Questions

Typical Compaction Curves

SILT material compaction curveNote: Flat dry side, drops off steeply on wet side.

Vibrating compaction curveNote: Sometimes flicks up on dry side of optimum

• Max Dry Density (MDD) is 1.60 t/m3, therefore 98% of MDD is 1.57 t/m3.

• Water content range for 98% of MDD is approx. 21% to 24%.

• Should be able to achieve >98% compaction between these water content ranges.

Cohesive Soils

But … beware

Compaction Curves

• Standard Compaction - General earthworks

• Heavy Compaction - Building foundations - Civil structures foundations e.g bridge abutments

• Vibrating Compaction - Highways/roads (B/2) - Carparks/driveways

Which one should we use?

Achieving Compaction

• Each test method measures something specific. - Scala Penetrometer - Clegg Impact Value - Nuclear Density Meter - Benkelman Beam - CBR

What does the equipment measure?

• “Specifiers should talk to the laboratory before writing the specification if they want anything other than normal quality tests. Find out the appropriate test method …”

Where to from here?

• “… the best time to talk to the laboratory is BEFORE taking the sample, rather than after.”

Where to from here?

• “Communication between Contractor, Client, Contractor’s Laboratory, and Consultant’s Laboratory can result in great benefits for all parties. … Working towards the same end.”

Where to from here?

Contact details

Bob SmithPrincipal EngineerPO Box 654Wanganui 4540Ph 06 349 6616Email: Bob.Smith@opus.co.nz

Rhys JonesLaboratory ManagerPO Box 654Wanganui 4540Ph 06 349 6640Email: Rhys.Jones@opus.co.nz