Use of In Situ Material the Key to Dirt Cheap Earthworks

Wednesday, January 27th, 2016
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The use of readily available in situ material is the key to creating strong earthworks for buildings and infrastructure at minimal cost.

“The word ‘earthworks’ itself is all about dirt to the layperson, and that means that the structures themselves should also be dirt cheap,” said Burt Look, geotechnical engineer with Foundations Specialists Group.

Look is one of Australia’s leading experts on earthworks engineering, having been named Queensland’s Engineer of the Year in 2014. In addition to serving as FSG’s senior principal engineer, he is also the facilitator for Engineering Education Australia’s earthworks technical engineering course.

“Earthworks is the process of using soil and rock materials and actually even man-made materials to build earth structures for a broad range of purposes, including embankments for roads or railways or land development platforms for buildings,” he said. “They can be built from the most common ground materials that are available everywhere.”

Look notes that the ability to employ readily available dirt and soil for the earthworks of construction projects can achieve a dramatic reduction in associated costs.

“If you want to use other materials which aren’t dirt cheap, such as concrete, then you could be moving from say 10 dollars a cubic metre to as much as 200 dollars a cubic metre, increasing expenses by as much as a factor of 20,” he said.

The use of in situ dirt and soil can further reduce costs by dispensing with the need to source material from quarries that are located far from building sites, thus avoiding increased transportation costs as well as environmental impacts.

“If you import material from elsewhere, you’ve already increased the costs by a factor of five to 10,” said Look. “In order to transport it from quarries, you need enough trucks running along various roadways and through people’s suburbs, which can be expensive and is not the environmental thing to do.

“Earthworks should be built by economical use of the material which is readily available all around us, which is dirt. We’ve got to use what’s available.”

This may sound simple, yet Look notes that the use of in situ material to create solid yet economical earthworks is a complex engineering feat involving a broad range of considerations and approaches.

“While in a simple sense it’s just digging dirt and placing it somewhere else, you have to make sure the quality is appropriate, you need to understand how to excavate it, you need to understand how to position it, and also how to bring it back to the required strength,” he said.

“It involves the quality of material, how you place it, the compaction process, type of equipment, the thickness of materials you need to use, the quality control procedures in terms of the acceptance criteria and when it’s okay and when it’s not to apply them – these are just some of the factors that must be considered.”

According to Look, the key to creating successful yet dirt cheap earthworks is to first acquire an understanding of what kind of materials are involved before engaging in the flexible application of engineering principles.

“First all you have to determine the type of material, and once you classify the material you then look at different strategies for placement and compaction,” he said. “In some instances it may involve additives to enhance strength if repeated compaction would be insufficient, while in others cases it will involve zonal strategies of where you place it and how you place it.”

Look emphasises that given the sheer variety of dirt types and site conditions, it’s critical that earthworks engineers be adaptable in their use of principles and refrain from adopting a “one size fits all” approach.

“There are thousands of permutations of dirt, and because there are thousands of permutations it’s about trying to clarify the key principles underlying those permutations,” Look said. “We can easily be misled by a single project and transfer it to another project when it’s a different type of soil.

“The course I run is essentially geared toward people with some experience, and teaching them not to be misled into thinking that one experience is a universal practice that applies to all cases.

“People should build on experience so that they can effectively connect theory and practice – this what we have to understand.”


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