Western Australia Chapter

Young Geotechnical Engineers’ Evening Seminar &
The 15th Dr Baden Clegg Award – 2016

This annual event gives a platform for our younger (under 35) geo-professionals to present their work, gain feedback from experienced colleagues and become involved in AGS activities. Please support them by coming along to what should be a varied, interesting and exciting evening.

There will be three presentations, each 15 minutes long, with 5 minutes for questions after each talk. The Dr Baden Clegg Award will be presented to the best contribution.

Pizzas and drinks will be provided after the presentations.

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:

Cathal Colreavy

Arup

Youngho Kim

Centre for Offshore Foundation Systems (COFS), UWA

David Wade

Golder Associates

Their Presentations

Cathal Colreavy

Arup

Advantages of using full-flow penetrometers for soft soil sites

Abstract

The worldwide population increase and associated increased demand for space means that structures are now being considered for areas of soft ground that were previously considered unsuitable for development, e.g. the new Perth Stadium. Furthermore, the recent emphasis on finding new sources of offshore energy requires offshore structures to be located in deep water where the seabed sediments are generally soft. Soft ground presents unique challenges to geotechnical engineers; this challenge is underpinned by the difficulty in accurately determining the available undrained shear strength of the soft soil and accurately assessing the rate at which the strength will increase during consolidation. Difficulty in obtaining undisturbed and representative samples means there is a heavy reliance on in situ tests. In recent years, the potential for “full-flow” penetrometers (a variation of the cone penetrometer) to solve this major technical obstacle has been demonstrated, particularly offshore. However this potential has not yet been fully realised and exploited by the engineering community, particularly onshore, as there is inexperience and some key unanswered questions surrounding the framework for interpreting penetrometer test data. Onshore, full-flow penetrometers such as the T-bar or piezoball, are infrequently used.

This presentation aims to demonstrate some of the key advantages of using a full-flow penetrometer, particularly the ball, over the traditional cone penetrometer in estimating strength and consolidation characteristics of very soft to soft soil. Results from in situ full-flow penetrometer tests from a number of Australian and European sites will be presented and compared with other field and laboratory test results. The benefits of using T-bar or ball tests on soft soils, such as in Perth’s Swan River Alluvium, will be described.

Youngho Kim

Centre for Offshore Foundation Systems (COFS), UWA

Investigation of Dynamically Installed Anchor (DIAs) in Clay and Silt

Abstract

Dynamically installed anchors (DIAs) are a recent type of mooring technology that have been shown to provide a cost-effective alternative to other forms of anchoring system in deep water clayey sediments. They are also being increasingly considered in relatively shallower water, with silty and sandy deposits, by changing the geometry and pad-eye position. These anchors are released from a designated height above the seafloor, causing the anchor to penetrate into the seabed by the kinetic energy obtained through ‘free-fall’ and through the self-weight of the anchor. Challenges associated with DIAs include prediction of the anchor embedment depth and the subsequent capacity. The former is complicated by the very high strain rate (exceeding 25 s-1) at the soil anchor interface, resulting from the high penetration velocities. The latter is also difficult to predict if the anchor has a diving potential.

In this research, a series of three-dimensional dynamic finite element analyses have been undertaken to provide insight into the behaviour of DIAs during dynamic installation and pullout in non-homogeneous clay and calcareous silt. The large deformation finite element (LDFE) analyses were carried out using the coupled Eulerian-Lagrangian approach, modifying the simple elastic-perfectly plastic Tresca soil model to allow strain softening, and incorporate strain-rate dependency of the shear strength using the Herschel-Bulkley model. The results were validated against field data and centrifuge test data prior to undertaking a detailed parametric study, exploring the relevant range of parameters in terms of anchor geometry and type; drop height and soil strength. The pullout angle at the mudline was also varied to encompass various mooring systems. To predict the behaviour of DIAs in the field, an improved rational analytical model, based on strain rate dependent shearing resistance and fluid mechanics drag resistance, has been proposed, with the LDFE data used to calibrate the model.

David Wade

Golder Associates

Remote Sensing for Potential Road Gravel Sources

Abstract

Western Australia has a vast rural road network comprising sealed and unsealed roads throughout the state. Construction and maintenance of a road network of this scale requires an immense and continuous supply of quality gravel for use as pavement basecourse and subbase material. At the current time, a limited supply of material is available from existing gravel pits. Many of these pits are nearing or have reached exhaustion and new sources will be required. Current methods used to identify potential gravel sources for use in road construction typically requires information from a number of sources including:

  • Geological mapping
  • Topographical mapping
  • Vegetation type
  • Drainage
  • Local knowledge

In addition to the above sources, satellite imagery could provide a useful tool to target potential road building materials. Materials have a varying reflectance across the electromagnetic spectrum that is dependent on their chemical composition, crystal structure and texture. The use of satellite imagery provides the ability to refine search areas and analyse large areas efficiently by utilising the spectral response of known gravel sources and identifying potential gravel areas displaying a similar response.

Satellite imagery (remote sensing) was recently used to identify potential gravel sources in the Pilbara region including along the alignments of Northwest Coastal Highway and Nanutarra Road. For this project, Landsat 8 Operational Land Imager (OLI) multispectral imagery was obtained for a corridor along the road alignment. Existing Main Roads Western Australia gravel pits were used as training sites for the classification of potential sites by remote sensing. Once the classification process was complete, a site visit was carried out to assess the quality of the classification of potential gravel areas that were accessible. The classification was found to have a variable success rate depending on the quality of the training sites selected. As the available technology continues to improve, it is expected that the quality of results would also increase, leading to discovery of new local gravel sources which reduce the need to import road construction materials over large distances.

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.