These are the questions I faced in my literature review I could not find an answer for them. Just for the record, I am going to do the CBR test on laboratory compacted base materials in the pavement.
1- In which moisture content and dry density this test is accomplished (generally for the scientific purpose). I mean, CBR can be employed directly after the compaction or after soaking in water for four days. Should the CBR test be done with various moisture content? Should it be done in 95% of MDD (as the compaction in field is usually 95% of compaction in the lab)?
2- What is the number of layers in the compaction process (if the vibratory hammer is used for the compaction)? 2 or 3 layers?
3- What would be the weight of surcharges if the pavement design includes an asphalt layer of 10 cm and a basecourse of 30 cm and the materials are to be used in the base layer?
4- While soaking aggregates in water, what should be the elevation of water above the sample?
Kind regards,
It is an empirical way of determining the soil strength for engineering purposes.
AASHTO T 193 will be useful.
Hi Ebrahim,
I notice that you are a PhD student at the University of Auckland, so I would imagine you will be looking at the problem from the New Zealand point of view on pavement design? If so, you should hopefully find all the answers you are looking for in this document:
New Zealand Standard NZS 4407:2015: Methods of sampling and testing road aggregates. This is the latest standard that details the test methods and procedures for testing aggregates for the purpose of road pavement construction and replaces the older standard NZS 4407.3.15:1991 Methods of testing road aggregates - Laboratory tests - Test 3.15 The California Bearing Ratio (CBR).
While AASHTO T 193 (2017) - Standard Method of Test for The California Bearing Ratio - may provide some help, as suggested by others above, it is the standard used by the American Association of State and Highway Transportation Officials. There are many other countries whose standards for CBR testing could be used if you are not confined to New Zealand's perspective, e.g. Australian AGPT02-17 Guide to Pavement Technology Part 2: Pavement Structural Design, and its subsequent 2018 supplement that in Chapter 5 details CBR testing. There are the British Standards too, where the Specification for Highway Works Series - Series 0800, Road Pavements - Unbound, Cement and Other Hydraulically Bound Mixtures - contains a wealth of information and requires the use of BS1377-4:1990 Compaction-related tests for CBR testing.
Good luck with the PhD research, and I hope the above helps.
Best wishes,
Anne
Very simply speaking there is a specialization named "Soil Mechanics and Foundation Engineering" and another one named "Soil Mechanics and Road Engineering".
If you are constructing a a foundation, find the soil strength using the Triaxial Test. If you are constructing a road find the soil strength using the CBR.
Dear Ebrahim,
CBR is an evaluation of the load-bearing capacity of natural ground, subgrades and base courses essentially for highways or even airstrips. Since various countries have their respective various standards, it will be useful for you to adopt the most relevant standard and workflow applicable to your target area.
for granular soils, it is recommended that the CBR test is conducted at optimum moisture content and maximum dry density. In case of expansive soils, not necessarily to compact at optimum moisture content.
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