Palmer Road Sub Division

Broome, WA

Background

CMW Geosciences were contracted to investigate the extent of collapsible soils at a proposed residential sub division on Palmer Road, Broome. CMW assessed the collapse potential of the soil and developed an economical engineering ground remediation solution, to mitigate the effects of long term foundation settlement, at significant time and cost savings for our client.

Scope

CMW initially travelled to site to complete test pits and ‘cut cube’ tests, from undisturbed samples at varying depths, to determine if in fact the soil was likely to be collapsible. ‘Cut cube’ testing involves cutting a uniform block of sand from the test pit wall, wetting and mechanically disturbing the sample and then observing whether a volume change occurs when the cube is reconstituted. Results from the ‘cut cube’ test indicated that there was collapse potential of the soil. Collapse potential plate load tests were subsequently carried out to more accurately determine the amount the soil would collapse under wetting up and load.

Collapse potential plate load results indicated that the settlement exceeded 20mm at the pressure of 100kPa.

Findings/Challenges

It was concluded that the top 500mm of insitu soil material had to be reworked wetted up and re-compacted such that a dry density of at least 95% of the modified maximum dry density (MMDD) was achieved. The ground material at a depth greater than 500mm below the surface did not require any remediation work.

CMW completed three site visits during the earthwork phase to ensure that the top 500mm of material was being mixed, moisture conditioned and compacted in accordance with the specified solution. Nuclear density and dynamic cone penetration tests were observed by CMW on the completed site to ensure that at least 95% MMDD had been achieved. Once earthworks was complete CMW signed off the earthworks to a level 2 standard in accordance with AS3798.