Soil Profile Logging

Melbourne soils have extreme variations in reactivity and consequently, extreme variations in ground movement. Large variations in geology constantly challenges geotechnicians and compels them to continually improve their knowledge of the geologic process. Just when you understand the geology and conditions of one subdivision, you move onto a new subdivision and the learning process starts again.  

 

Visual and tactical methods although valuable, have their limitations and require significant experience in different soil types and geologies, and a sound understanding of AS 1726-2017. One of these methods main weaknesses is the prediction of the magnitude of reactivity amongst highly reactive soils. A good technician should be able to judge a soil to be highly reactive but due to a soils origin, history and chemical composition it is extremely difficult to assign an actual reactive value (Ips) or range to it. It is therefore often left to an engineer or geologist in the office to guess it’s Ips value from geological maps and local knowledge, despite the fact that most of the outer residual subdivisions are new, untested areas.

 

In the geotechnical field there is increasing interest in testing soils in the laboratory to satisfy the limited requirements of AS 2870-2011 while obtaining enough information to predict ground movement to a reasonable accuracy. Many practitioners in the industry have come to the realisation that the Shrink Swell test results are unreliable since the outcome will vary according to the different starting moisture content of the soil. The Free Swell test, although has some benefits, provides results that are difficult to correlate with the in situ undisturbed soil conditions and derive an Ips value from.

USL group, in conjunction with it’s partners, has devesloped the Core Shrink test so that it is now a relatively quick and accurate test. This modified Core Shrink test is gaining interest in the industry because a Soil Water Characteristic Curve (SWCC) can be derived from the same sample. The SWCC provides a link between soil moisture and suction values and provides actual values to be used in the ground movement model in the AS 2870-2017 which is based on suction ranges.