Step 1 - When a geo - technician performs a field density measurement using the nuclear density/moisture gauge on clay fill, he is measuring the field wet density of the material ie. 1.750 t/m3

Step 2 - He is then required to dig up a sample from beneath the instrument to perform a laboratory compaction test. There are several test methods used depending on the contract specification and the situation of the likely loading of the soil.

Step 3 - The Hilf standard compaction test is a rapid method of determining the laboratory compaction characteristics of the soil and involves breaking the field sample into small pieces.

Step 4 - The prepared sample is then split into three sub-samples which is to be used in the test. Each split sample will be treated differently. It may either have water added, water dried out or used in its current condition depending on the moisture condition of the field sample. Three separate moisture conditions will need to be mixed into the soil.

Step 5 - Each sample is then compacted into a metal 1 litre mould using three equal layers and compacted with a small hand held compaction rammer. Each layer will receive 25 blows of the rammer.

Step 6 - Any excess soil that is protruding from the mould is struck off and mould and soil is weighed to determine the bulk density of the soil. Differing moisture conditions will result in a different bulk density.

Step 7 - The bulk density of the soil will reach a maximum level of compaction at an ideal moisture level. This is moisture level is called the Optimum Moisture Content (OMC). The peak bulk density =1.770 t/m3 will be achieved at this OMC.

Step 8 - The field bulk density reading taken form the nuclear density/moisture meter will then be compared to the laboratory maximum compaction and expressed as a percentage. ie. (1.750 / 1.770 = 99%)

The methods used for testing soils or crushed rock are basically the same, with variation existing in the number of layers used in the laboratory test and the size of the compaction rammer.

PAVEMENT DIPPINGS are performed to determine the profile of the existing road or in areas proposed for duplication. This involves the excavation of a pit through the profile with accurate measurements taken of each layer thickness. Samples may be required of each material type for further analysis to determine the materials classification or physical characteristics. The profile is logged and photos may be required to show layering and documented evidence. Samples may be retrieved from subgrade materials for determination of the Californian Bearing Ratio (CBR).

Melbourne has the most diverse geology in Australia and as such, our available crushed rock products also vary considerably. It is common practise for construction companies to use the local quarry source and may not always be familiar with its characteristics. This document aims to assist our clients obtain some guidance on achieving compaction on the diverse crushed rock product Melbourne quarries have to offer and some general rules for rock placement.

Some of the rock types used in our crushed rock products include Basalts, Scoria, Rhyolite, Rhyodacites, Hornfels, Granites, and Grandiorite blends just to name a few. With each of these rock types there are varying stages of decomposition and rock formations, so we can see that we are dealing with a very diverse product under the umbrella of crushed rocks. The general principals of rock placement are the same although each will vary how they are to be treated.

The basis of achieving compaction!

1. Place the material as close to optimum moisture content as possible. All crushed rock stone types have different optimum moistures.

2. Don’t allow rock to dry out until compaction is complete.

3. Where possible keep traffic off completed crushed rock pavements, as some products will unravel when dry.

4. Test the pavement within 48 hours of compaction. Some products should be tested within 6–24 hours.

5. Do not roll dry crushed rock as it will fracture and crumble

6. Do not roll faster than walking pace

7. Do not expect a light roller to achieve a high level of modified compaction.

8. Do not over roll your rock. If you are unsure of how many passes to apply ask a Ground Science technician to assist you in performing a roller trial.

9. If the roller is bouncing it means you have reached the maximum compaction using that specific method and need to use alternate methods if required.

10. Some products can only be compacted to 95% Modified using a vibrating flat drum and require the final compaction to be carried out using a multiwheel.

11. Crushed concrete products are better placed wet. Generally the product will release some active cement and set up as it dries.

12. Compacting in confined spaces using hand whackers, plates or excavator driven compaction devices require the crushed rock material to be placed in thin layers and compacted slightly wet of Optimum moisture.

13. Placing crushed rock in layers of 75mm or less is problematic and should be avoided where possible.

14. Cement stabilised crushed rock products have a strict time tolerance on achieving compaction. Once you have exceeded the allowable time limit, further roller may cause the pavement to crack and fail. If the product is left sitting in a stockpile for an extended time it begins to form a coagulation of the finer particles and you will have extreme difficulties achieving compaction.

15. A field density test using a nuclear density meter requires a hole to be driven for the probe to be inserted. When testing cement treated crushed rock products, if the material is more than 24 hours old, the method of driving a metal pin into the product may cause the rigid product to crack and result in a lower measured compaction value. By drilling the hole rather than driving a pin, you limit the disturbance of the material and it may result in a more accurate result.

Classes of crushed rocks

In Victoria classes of crushed rock are determined by Vic Roads specifications and are based on key characteristics of the rock. These include the particle size distribution, the plasticity of the fines in the product, the hardness (Los Angeles abrasion) and shape of the rock, the amount of flat particles (flakiness index) in the product and the percentage of lower grade particles (Sound/unsound content).

Each of these characteristics have a tolerance which, for the end users means there is going to be some variation in the materials delivered to site. It is these variations which add to the difficulties in the field compaction testing regime. It is imperative that regular checks on the materials MDD is determined to ensure that the calculation of results is comparable to the characteristics of the supplied material. A 0.02t/m3 variation in a product is a 1% change in field compaction (density ratio).

A guide to achieving Modified compaction when material is within 1% of OMC (AS1289 5.2.1).

 

product	Initial roller type & min mass	No. of passes	Final roller type	No. of passes
20mm class 1 & 2	Flat drum 11 – 13 tonne	6 - 8	Multi wheel	Min 10 passes
20mm class 3	Flat drum 11 – 13 tonne	6 - 8	Flat drum	3 after final trim. Either light or static
20mm class 4	Flat drum 9 tonne	6 - 10	Flat drum
Capping/NDCR/Salamander	Pad foot or flat drum	6-10	Flat drum	Min 2 passes

SATURATED HYDRAULIC CONDUCTIVITY testing used in the sports field industry is another form of soil permeability designed specifically for sand based products. Ground Science has the rights under licence from Rootzone Laboratories International Pty Ltd to perform a specific unique version of this test.