Scott Lidster of Australian Earth Training provides the dirt on dirt, and why soil testing is an important tool.
If you’re in the earthmoving game, you’ve probably heard a fair bit about soil testing.
But what’s it all about, really? Think of soil testing as the foundation of your project – quite literally. Before you start shifting dirt or laying down concrete, you need to know what you’re dealing with beneath the surface.
I caught up with Matt Neville, acting GM and Lab Manager at Benchmark Geotechnical, to learn more about the “Dirt Doctor” game!
Why bother with soil testing?
You might be thinking “Why do I need to test the soil? It’s just dirt, right?”
Well, not exactly. The soil on your site can make or break your project. Whether you’re building a road, setting up a structure, or digging out a trench, the type of soil underfoot matters.
Imagine laying a foundation on soil that’s prone to sinking or cracking.
Not good, is it? Soil testing helps you suss out any potential issues before they become full- blown disasters.
It tells you things like how much load the soil can handle, how well it drains, and whether it’s likely to shift around when wet.
It’s about being prepared, so you’re not caught off guard halfway through the job.
Soil testing conducted during the project also provides quality assurance of the works you’re performing allowing the completed project to be signed off and moved onto the next step leaving you with peace of mind.
The key tests you’ll need
Now, let’s get into the nitty-gritty of what soil tests you might come across. First up, primarily before any works are conducted or even designs are finalised, soil classifications are performed.
This is done via site investigations engineers using drill rigs to drill numerous bore holes throughout the site to visually inspect the soil at various depths.
During this process, samples are taken back to the laboratory for testing to determine the characteristics of the soil.
Tests such as PSDs (particle sieve distribution for gravels), Atterbergs (plasticity for clays) and CBRs (bearing strength of the soil) are commonly performed. This provides data to confirm whether the soil is a gravel, sand, clay or silt based which is necessary as all these soils behave very differently, so this is crucial info.
Next, there’s the moisture content test.
This one’s pretty self-explanatory – it measures how much water is in the soil.
Too much moisture can turn the soil into a sloppy mess, while too little can make it dusty and tricky to work with.
Moisture content tests are generally performed on all most other tests as this is considered a critical factor.
Design specifications will often state an “Optimum Moisture Content” on all soils on the project. Hitting that sweet spot often gives you the best outcomes in using the soil saving time in the long run.
Then there’s the field density/compaction test: the most commonly performed test on projects and no doubt you would have seen a soil tester using a bright yellow gauge on soils just recently compacted.
This test is about determining the current density of the compacted soil onsite and comparing this with the maximum density compaction that soil can achieve.
A soil tester will collect density readings from the gauge of that soil on site, retrieve a sample where the gauge was and take this back to the laboratory.
A compaction test is done to determine the max density this soil can achieve, comparing this data with the density readings on site allows a density compaction ratio result to be given.
In short, if the field density readings are too low then often further compaction on the soil on site is required.
Ultimately this is to avoid uncontrolled settlement of this soil after the project’s completion and prevent damage to the new structure built over that area.
Every time you see a pothole on the road, think poor compaction. This one’s all about finding the sweet spot for compacting the soil.
You want it packed just right, so it’s solid and stable under whatever you’re building.
Tools of the trade
Now, let’s talk about the gear you’ll need to get the job done.
With such a wide range of soil tests that can be performed, specialised equipment is required.
Each laboratory would house sieve shakers, drying ovens, load bearing machines, compaction machines and numerous others. Each apparatus is calibrated regularly to NATA requirements for quality assurance to provide accurate results.
In most cases, you’ll only ever see the nuclear density gauge (yellow machine) which is used on sites for compaction which all soil testers are required to be trained and accredited to use.
Wrap-up
So, there you have it – the basics of soil testing in a nutshell, plus the tools you’ll need to get the job done.
It might seem like an extra step, but trust me, it’s worth the effort. By knowing what’s going on beneath the surface, you can tackle your earthmoving projects with confidence, avoiding those costly and time-consuming headaches down the track.
Whether you’re a seasoned pro or just starting out, getting a handle on soil testing is a smart move. So, give it a go, and keep your projects rock-solid from the ground up!
Soil testers are there to assist and help provide input on how to best achieve high quality standards. Think of them as a guide to getting the job done right and not a hindrance.
Ultimately completing a project on time, within budget and to a high-quality standard is everyone’s objective. We all drive on these roads or use structures where this process has been performed prior.
Australian Earth Training scott@australianearthtraining.com.au www.australianearthtraining.com.au