In Situ Testing “Game Changers”

Major advances in CPT and DMT

Allan McConnell

TOPIC 1: A New CPT For Extremely Soft Soils And Tailings Sediments

CPT is a great tool when used well. However, there is a problem in that up to now no commercially available CPT cones can detect and measure very very low (ie teeny tiny) sleeve friction (fs) values. This means that tests in extremely soft soils and in ooze-like tailings sediments are almost always compromised.

An “elephant in the room”, this is hardly ever talked about – sometimes ignored – sometimes disputed – sometimes taken into account – but mostly just glossed over. This presentation will demonstrate.

A new CPT has been developed to overcome this very critical problem. With this new tool it’s possible to repeatedly measure teeny tiny qc and fs values. This is a very nice cone, and works very well; it’s incredibly sensitive and repeatable. However, if used trivially, following “usual” conventions for calibration, it may disappoint.

A paper was presented and well received on this development, by this Speaker, at the very recent CPT’22 Conference in Bologna Italy.

TOPIC 2: The Medusa (automated) DMT – A New Tool – A Very, Very Good One

The Flat Plate Dilatometer (DMT) is, arguably, the second-most-used in situ testing tool. It provides much useful geotechnical data, some direct and some via algorithms developed by the tools’ developer, the late Professor Silvano Marchetti. DMT started life in the early 1980s in Italy.

The original DMT has many strengths, two being simplicity and robustness. But like all testing tools it also has some weaknesses: (a) it is slower to use than a CPT; (b) for complex test routines, eg dissipation tests, tedious and repetitive operator input is required; and (c) in very deep tests a pressurisation time-lag occurs that can lead to test uncertainty.

The Medusa DMT is a fully automated DMT of much higher resolution than the original tool. It is faster. It makes easy work of complex routines such as dissipation tests, which can even run overnight. There is nil time lag in the system. Now new complex DMT test routines are not just possible, they are “every day”. There is now no gas bottle at the surface; no operator opening and closing valves; no reason for operator error, tedium or boredom.

This sounds at first like a nice improvement to an old tool, but the Speaker sees this as basically a new in situ tool altogether; a very, very good one.

About the speaker

Allan McConnell Founder of Insitu Geotech Services (IGS)

Allan McConnell is a geotechnical engineer, with 50+ years experience in Australia, SE Asia and the Pacific. He is the founder of the company Insitu Geotech Services (IGS).

Allan is known for his past consulting work on major projects, including many on soft soil sites, and for his passion-driven “crusade” to reduce risk and uncertainty in geotechnical engineering. It is this passion for reducing risk and uncertainty that led to the evolution of IGS.

Allan is a Fellow of Engineers Australia, a Registered Engineer in Queensland, a long-term Committee Member of the Australian Geomechanics Society, Queensland Division, and a Committee Member of the Queensland Tailings Group. He was Chair of the 2015 ISC’5 (International Site Characterisation) Conference on The Gold Coast. During his time as a consultant Allan won three prestigious ACEA Excellence Awards, the Sole Practitioners Award, and the President’s Award.

He presented a paper on his Topic 1 and participated in a focus discussion on CPT uncertainty at the CPT’22 Conference in Bologna Italy in June this year – just a few weeks ago.

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