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Jacked piling is increasingly being used in China, Japan and South-East Asia, and was introduced into Australia in 1998. Jacked piles have the advantages of being vibration free, creating minimal noise, being pollution free, having a high operational accuracy, not generating high transient driving stresses and providing a type of static load test as part of the installation process. However, there are many aspects of jacked piling that require special attention by geotechnical engineers over that of conventional piling methods. Many of these aspects are now incorporated into AS 2159-2009 “Piling-design and installation”. This presentation addresses several of these aspects, based on Dr Mitchell’s experiences over the thirteen year period since the introduction of large scale jacked piling into Australia.

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Skills in interpreting and understanding the geological origins of soil and rock masses, their defects, fabric and anisotropy are essential in the development of high quality ground models on which our ground engineering decisions are based. Alan’s talk will use case histories to show how important engineering properties and behaviour of the ground can be anticipated from geological knowledge. The case histories will include projects involving tunnels, dams, foundations, and slopes in Australia and overseas. The talk will end with discussion on what lessons can be learned on how we approach and carry out geotechnical site investigations.

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Decision makers increasing consider tunneling as an option for developing and improving infrastructure. Tunnels can be constructed in many different ground conditions for many different uses. This presentation gives an overview of tunneling techniques, including excavation and ground support systems. This is followed in more detail by a description of the development of the design of a road tunnel in rock, drawing on experience in the EastLink tunnels in Melbourne.

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Because geotechnical laboratory testing is often expensive, slow, unavailable, difficult to obtain undisturbed samples or only analysing a very small part of the soil, Black Geotechnical have had a focus on in-situ testing for some time.

The need for higher quality data has driven Black Geotechnical to not only consider traditional in-situ tools such as Dynamic Cone Penetrometers, Standard Penetration Tests and Shear Vanes, but also to utilise Cone Penetration Tests (including Piezocones and mechanical cones), full flow penetrometers, Dilatometer Marchetti Tests and Seismic cones.

The need to determine geotechnical parameters on sites which are impenetrable to drill or cone rigs, and the need to test greater areas of ground, has led to the use of Plate Load Tests, Falling Weight Deflectometer tests, impact compaction deceleration response and settlement tests and finally seismic testing, specifically the measurement of Rayleigh waves with the Continuous Surface Wave System and more recently the Multi-channel Analysis of Surface Waves method.

In this talk Black Geotechnical intend to share their learning experiences with these insitu testing methods and will also show some case histories.

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“Liquefaction” is a potentially catastrophic phenomenon in which saturated/near-saturated cohesionless soil loses strength due to increase in pore water pressure under rapid loading (cyclic/static). Liquefied soil may acquire a degree of mobility sufficient to permit movement from meters to kilometres. Although liquefaction has been long recognized, it was more thoroughly brought to the attention of engineers and seismologists by several natural hazards around the world: Niigata and Alaska (1964), San Fernando Dam failure (1971), Loma Prieta (1989), Kobe (1995) and Chi-Chi (1999) earthquakes. The speaker will discuss his experience with the Christchurch (Darfield) earthquake (2010) and wide spread liquefaction in the City of Christchurch

The presentation will also address the relatively little known phenomenon of ‘static liquefaction’ due to static loading, which has direct correspondence with cyclic instability due to cyclic loading, and can trigger liquefaction due to even a moderate earthquake. The concept of critical state soil mechanics will be used to explain why liquefaction occurred in Christchurch even during relatively small aftershocks.

The effect of fines (particle size ≤ 75µm) in sand on liquefaction will be addressed. Laboratory studies have shown that liquefaction resistance decreases with an increase in percentage of fine particles; however field tests based on a liquefaction screening chart (Youd et al. 2001) shows the opposite trend. The speaker will explain that an inconsistent comparison basis is one of the main reasons for this apparent anomaly.

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Studies have show that out of all of the components of an offshore structure, the design of the foundations contains the most uncertainty. Although methods of pile construction have made enormous advances over the last 50 years, the advances in pile design have been more muted and acceptance of these advances has been slower. Recognising that there are limitations to the traditional design methods, the American Petroleum Institute (API) and ISO have included new alternative CPT methods for the design of piles in sand in their international design recommendations.

The presentation will describe the Imperial College Pile (ICP) design methods, also known as the MTD design methods. These were developed over a ten year period involving three PhD projects (Bond, 1989; Lehane, 1992 and Chow, 1997) encompassing detailed field investigations, laboratory testing, analysis and verification against a large database of piles in sand and clay. The verification studies showed that the new design methods were more reliable than traditional methods delivering cost savings or improvements in foundation safety.

In 1996 the design methods were published in “New Design Methods for Offshore Piles”. This was updated in 2005 in “ICP Design Methods for Driven Piles in Sands and Clays”, published by Thomas Telford. The results have been applied on offshore, nearshore and onshore projects from Azerbaijan to Venezuela. The talk will also refer to the effects of pile group installation and changes in pile capacity with time (pile ageing) with illustrations from case histories.

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The purpose of this seminar is to inform engineers about developments in geotechnical investigation and design for major projects. In accepting our invitation to open this seminar Luigi Rossi, Director of the South Road Superway project, writes:

“I started working for the Highways Department constructing the Swanport Bridge in 1978. Since that time I have managed some of the most complex and significant projects undertaken by DTEI, including the Crafers Freeway and Tunnel, the Northern Expressway, and now the South Road Superway. I have also worked in road design, transport planning, materials investigation and pavement design. All this has reinforced my belief in the importance of rigorous and thorough geotechnical investigation for successful delivery of transport infrastructure. Geotechnical investigation is critical at every stage of a project, thorough investigations during planning ensure your project plan is developed cognisant of risk and required changes, during design it ensures you achieve optimum outcomes for form and function, and during construction it ensures your project is delivered safely, on time and on budget as you minimise the risks of delays.”

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For years geotechnical practitioners have commented on the failure of clients to appreciate the value of good site investigation and the benefits of obtaining more detailed information. Some of the benefits of a good ground investigation coupled with appropriate experience, analysis and design in foundation engineering projects are potential savings in construction costs, potential for assessment of foundation alternatives and reduction of risk in ground works. The savings can be significant – of the order of hundreds of thousands if not millions of dollars for the larger projects. Why then do clients seek to “save” money with taking on the lowest price ground investigation?

Littlejohn et al (1994) wrote:

Now and in the future, it is vital that financial decision-makers appreciate that you pay for a site investigation whether you have one or not, and you are likely to pay considerably more if you do not, or if it is inadequately designed, executed or interpreted.

Nothing much seems to have changed since those words were written, for in 2006, Egan reported:

For nearly a third of all the piling and specialist geotechnical contracts surveyed, the site investigation information provided was poor, preventing optimisation of the foundation solution. The cost to clients arising out of poor site investigation far exceeds the savings that could be made by following good practice when investing in a site investigation.

This presentation provides a guide to the various levels of ground investigation, analysis and design which are available and through the use of case histories, illustrates the significant benefits that higher levels of sophistication can bring to the project.