Young Geotechnical Engineers’ Evening Seminar & 17th Dr Baden Clegg Award

Jarrad Coffey, Andrew Lim and Sam Stanier

The Western Australian Chapter of the Australian Geomechanics Society invites participants for the 2018 Young Geotechnical Professional’s Seminar Evening. Participants must be under 35 years of age on 30 June 2018 and may be geotechnical engineers, geologists, mining engineers, hydrogeologists or other geotechnical professionals working in industry or academia.

Three speakers will be chosen to give a 15 minute presentation, based on an abstract of about 300 words. Talks need not be overly technical or theoretical, but should reflect interesting and challenging aspects of the speaker’s work that would be of interest to the geotechnical community.

Prizes

First Place

Trophy, $500 + a copy of the Australian Geomechanics Journal Collection on USB.

Runners up

$100 + a copy of the Australian Geomechanics Journal Collection on USB.

Most of the WA geotechnical community will be represented on the night and the speakers will be given great exposure. There will be food and drinks available before the talks and opportunities to network with representatives from various geotechnical companies.

This year’s speakers are:

Jarrad Coffey

Andrew Lim

Sam Stanier

Their presentations:

Jarrad Coffey

Rio Tinto

Reducing the energy consumed in mine haulage through pavement engineering

Abstract

The load and haul process is a significant cost to most mining operations. It has been estimated to represent as much as 25% of the total cost of production and sales combined (de la Vergne, 2003). Running costs of haul trucks can be key contributor, which in-turn, is related to the rolling resistance experienced while traversing haul roads.

Rolling resistance generated due to pavement condition is most often attributed to roughness and texture. However, pavement deflection has been found to be a significant contributor for flexible, unsurfaced haul roads. This was determined through full-scale testing where pavement texture, roughness and deflection were measured through the use of a terrestrial laser-scanner. Haul truck rolling resistance was determined through logging of electric wheel-motor torque by software installed on the truck’s central operating system and post-processing of the resulting data. Pavement deflection was shown to contribute approximately 25% of the total rolling resistance while the haul truck was unloaded and 50% when the truck was loaded to its nominal maximum payload.

This finding highlights that energy and cost savings may be achievable through updating the haul road pavement design methods that have been applied in practice until now. Such methods are typically empirical and aim to limit sub-grade deformation, which is estimated with the application of axisymmetric and linear-elastic pavement models. The ability of such techniques to predict measured pavement deflections has been compared to non-linear, 3D Finite Element Analysis methods. Consequently, it was found that existing methods cannot properly account for effects such as variation in tyre-pavement contact geometry/stress and wheel load interaction.

It is proposed that optimisation of energy consumption in haulage be adopted as the basis for a new pavement design method for haul roads. Further, in order to maximise the benefits of adopting such a method, the Finite Element Analysis discussed above would need to be implemented as the basis of the associated pavement model in order to adequately consider the impact of the pavement’s structural response.

Andrew Lim

SRK Consulting (Australasia)

Tube sampling disturbance – how well do we understand the effects?

Abstract

Soil parameters used in geotechnical design and analysis are obtained through laboratory and in situ tests. In situ tests can provide information on the variation of soil properties with minimal disturbance but are plagued by interpretation issues. Despite this, laboratory tests are still preferred to in situ tests, because the boundary and drainage conditions of the tests can be well controlled, as well as the soil stress path. In order for laboratory tests to be carried out, soil samples need to be retrieved from the ground and transported to the laboratory. Among the available sampling techniques, tube sampling is still the most common choice because of its cost and time effectiveness. Tube sampling using Shelby tubes such as U50 and U75 are still very common, especially in Australia, for retrieving undisturbed soil specimens for element tests. However, a key question is, ‘are the specimens retrieved undisturbed’?

The presentation will focus on understanding the effects of sampling disturbance on a soft estuarine clay, known as Ballina clay. Different sampling methods, such as an open push tube sampler (Shelby tube), fixed and free piston sampler and block sampler (Sherbrooke sampler) were used to retrieve soil samples in order to investigate the effects of sampling methods in geotechnical designs. The study includes extensive experimental tests such as one-dimensional compression tests, simple shear tests with cell pressure confinement and small strain stiffness measurement using bender elements and a resonant column apparatus for Ballina clay. Finally, mechanical soil properties derived from retrieved specimens using the different samplers are used in the prediction of two classical problems in soil mechanics: the settlement and excess pore pressure response underneath an embankment, as well as the settlement and bearing capacity of a shallow footing. These two examples are used here to highlight the consequences of poor sampling in practice.

Sam Stanier

Centre for Offshore Foundation Systems, UWA

Shallow penetrometers emerging from the RIGSS JIP for measuring pipeline-soil interaction properties

Abstract

One of the principle activities of the RIGSS JIP – co-sponsored by Fugro, Shell, Total and Woodside – has been the development of the so-called shallow penetrometers, which were envisaged to more directly measure pipeline-soil interaction properties for subsea pipelines.

The toroid and hemiball are annular or hemispherical devise with a ‘pipe-like’ cross section, and the ring is a flat based toroid that provides a direct measure of interface friction that is comparable with interface shear box tests – the current de-facto standard for pipeline interface friction measurement. A suite of properties can be measured in a single test using these shallow penetrometers, including: (i) strength properties during penetration; (ii) consolidation characteristics by monitoring the dissipation of penetration induced excess pore pressures; and (iii) the mobilisable friction on the interface during rotation of the devices, which is analogous to axial sliding of a pipeline.

This presentation will demonstrate that the measurements derived using shallow penetrometers are comparable with current de-facto industry standard tests for measuring strength and pipeline-soil interaction properties, with the added advantage that they are faster to perform, can be conducted ex-situ on the deck of a survey vessel and provide additional data that is useful in pipeline design. Over the past year, these devices have been successfully trialled on three live projects in various oil and gas producing locations around the globe in collaboration with all four industry partners and we are now considering how best to commercialise the technology and encourage adoption within the industry.

Venue location

Engineers Australia members participating in AGS technical sessions can record attendance on their personal CPD logs. Members should refer to Engineers Australia CPD policy for details on CPD types, requirements and auditing guidelines.