Australian Geomechanics Society Newcastle, New South Wales Chapter – 2006 Meetings

• February 7, 2006

  2005 Poulos Lecture “Soft clay engineering: site characterisation and design of shallow foundations and anchoring systems”

  Professor Mark Randolph, ARC Federation Fellow

  The worldwide trend in the offshore industry is towards ever deeper water, where the seabed sediments mostly comprise normally or lightly overconsolidated soft, fine-grained sediments. This has brought particular challenges in characterising the soil, with much greater reliance on in situ testing, and designing seabed foundation and anchoring systems. The upper 0.5 to 1 m, where the shear strengths may be 5 to 10 kPa or lower, is particularly critical for pipelines in respect of embedment depth and resistance to buckling brought on by temperature changes. The lecture will focus on offshore applications, but address many issues that are very relevant for onshore design in soft clay, in particular site characterisation, including interpretation of ‘full-flow’ penetrometer data, and the effects of strength gradient and geometry on the bearing capacity of shallow foundations. Establishing an appropriate shear strength profile is critical for design, but this is complicated by secondary effects such as strength enhancement due to high strain rates and strain softening during penetration of objects into the seabed. Further applications including plate anchors, and dynamically penetrating torpedo anchors will be described briefly.

• May 17, 2006

  “Who Needs Constitutive Models?”

  Professor John Carter, Pro-Vice Chancellor, Faculty of Engineering and the Built Environment. University of Newcastle

  Constitutive models are essential in any rational theoretical modelling in geotechnics. How the stress-strain response of soil or rock is represented in these models is usually the key to successful prediction of the behaviour of geotechnical structures. However, the important details of these models, particularly the idealizations that are made, are often poorly understood or ignored, sometimes at significant cost to the unwary analyst. Indeed, the capabilities and the shortcomings of these models, especially the more advanced models, are not always easy to ascertain. In some cases determination of the input parameters is not straightforward. Consequently, it may be difficult to determine which model to select for a particular task.

  The lecture will chart the development of constitutive models used to represent the mechanical behaviour of soils and provide an overview of the principles and the main features and components of existing, widely used constitutive models for soil. The clear intention is to emphasise the physical basis theses models, rather than their mathematical complexity. While the focus is on saturated soil mechanics, the behaviour of unsaturated soils will also be mentioned. Some of the constitutive models encoded in the software packages used routinely in geotechnical practice are reviewed, and discussion is also provided on their specific limitations. Examples of practical applications, including problems involving soil-structure interaction, will be used to illustrate both the advantages and some of the pitfalls of the commonly used models. A brief description of recent developments in this area of geotechnical research will also be included.

• August 2, 2006

  Recent applications of the “square” impact roller

  Derek Avalle, Technical Manager Broons Hire (SA) Pty Ltd

  Impact roller technology has been available in Australia since 1985, and it has found use in a wide range of applications. Examples of some of these show the breadth of innovative projects and how the Australian civil and geotechnical fraternity have embraced the concept. More recent applications in the mining sector and on large-scale earthworks projects have resulted in the development of wider and heavier units, and four models of the “square” impact roller are now available. The use of impact rollers on projects in the Middle East is the main focus of this presentation. Construction of a huge new international airport in Doha, Qatar, by reclamation and filling over 22 square kilometres, has utilised a fleet of 8t and 12t impact rollers since the first quarter of last year. Another project in Doha using impact rollers for the earthworks, the prestigious residential development known as the “Pearl of the Gulf”, involves reclamation works to develop islands incorporating marinas, 5-star hotels, apartments and villas, as well as private islands. More recently still, this year, an “square” impact roller has commenced work on port facilities in Dubai, UAE, in conjunction with deep ground improvement by vibro-floatation.

• August 17, 2006

  Characteristics of Vacuum Consolidation

  Prof. Jin-Chun Chai, Department of Civil Engineering, University of Japan

  Laboratory consolidation tests under odometer conditions were conducted under both vacuum pressures and surcharge loads. The characteristics of vacuum consolidation have been investigated by comparing vacuum pressure and surcharge load induced consolidations. Firstly, regarding the magnitude of consolidation settlement, vacuum pressure induced less or the same settlement as that by a surcharge load with the same magnitude. If a vacuum pressure alone is larger than the lateral pressure required to maintain a k0 condition (no lateral displacement), there will be inward lateral displacement and the vacuum pressure will induce less settlement than that of a corresponding surcharge load. Secondly, regarding the effects of drainage boundary conditions, under a vacuum pressure, two-way drainage resulted in less settlement than that of one-way drainage. Theoretically, under a vacuum pressure one-way and two-way drainage cause consolidation at the same rate because for both cases the water in the soil is only allowed to drain out from the top surface of the samples. Thirdly, regarding the effect of the order of soil layers in a two-layer system, under one-way drainage conditions, for both surcharge load and vacuum pressure cases, the order of soil layers only influenced the rate of consolidation but not the final settlement. When a layer with a relative lower value of hydraulic conductivity (k) was located immediately adjacent to the drainage boundary, the consolidation rate was lower. However, for vacuum pressure applied under two-way drainage conditions, the order of the soil layers not only influenced the rate of consolidation but also the magnitude of settlement. Based on the laboratory test results, a method of predicting vacuum pressure induced deformation has been proposed. The method has been applied. This method has been applied to three case histories reported in the literature, two cases in China and one case in Japan. It is shown that the field-measured data are simulated reasonably well, suggesting that the method is useful for the design of vacuum consolidation projects.

• August 30, 2006

  Hydraulic Containment at Landfill Sites

  Kane Mitchell, Environmental Scientist, Environ Australia Pty Ltd, Hunter Valley

  A hydraulic containment system of some description is commonly required to abate the offsite migration of leachate and/or contaminated groundwater at landfill sites, and to a lesser extent other contaminated sites (i.e. industrial facilities). In Australia, these systems typically comprise pumping leachate/groundwater from a series of extraction bores to maintain an inward hydraulic gradient, with the extracted leachate/groundwater transferred to a treatment plant, or to sewer. The construction of a cut-off wall may be a more appropriate approach where saltwater intrusion is an issue, subsurface conditions are not favourable for groundwater extraction (i.e. low hydraulic conductivity aquifer) or a high level of certainty is required regarding the containment of the targeted groundwater/leachate due to site sensitivity. The lecture will provide a brief background on the application and limitations of cut-off walls in groundwater remediation projects (landfill and other contaminated sites) as well as a case study of a groundwater remediation project conducted at a 40Ha former landfill site situated adjacent to a canal in the Sydney metropolitan area, including discussion of: the design and construction of a soil/bentonite cut-off wall (1.5km in length, 0.8m wide, max. depth 15m) and associated leachate collection/treatment system; the usefulness of a full scale pilot test conducted prior to full commitment to the soil/bentonite slurry approach; the development of an innovative means of validating the performance of cut-off walls in tidal groundwater systems; The demonstrated performance of the wall to date.

• September 1, 2006

  Hydraulic Containment at Landfill Sites

  Nathan Juchau, RLMC; Charles Spalding, Austress-Menard; Stephen Jones, Douglas Partners; Dr Gary Schmertmann, URS Australia Pty Ltd

  The world’s deepest continuous trench groundwater barrier wall is currently under construction at the former Newcastle Steelworks site. Contractor Austress-Menard (A-M) was engaged by the Regional Land Management Board (RLMC) to design and construct the barrier wall to reduce migration of contaminated groundwater to the adjacent Hunter River, as part of the remediation strategy for the site (refer to attached summary for further information). The following presentation and site inspection provide a rare opportunity to observe construction of the wall first hand, and understand the technical and practical considerations for design.

• October 18, 2006

  Solid Waste Landfill Geotechnics

  Dr Gary Schmertmann, URS Australia Pty Ltd

  Solid waste is a particulate material that is analogous to soil in many respects, although with somewhat extreme engineering properties. The presentation concerns the application of geotechnical engineering concepts to solid waste landfill behaviour. A number of applicable geotechnical engineering analysis approaches will be discussed and illustrated. The major topics covered by the presentation comprise solid waste properties, slope stability and settlement. Issues relating to geosynthetic materials (e.g. geomembranes, GCLs, geotextiles) will also be addressed. The slope stability discussion includes static and seismic loading, material properties of waste, waste pore pressure, and shear strength of lining systems and interfaces. Settlement issues include self-weight compression of waste during landfilling, as well as continuing waste settlement/decomposition after landfill closure. Landfill project examples will be presented to illustrate typical geotechnical analysis and design results.

• October 25, 2006

  Numerical algorithms for large deformation analysis in geomechanics

  Majid Nazem, Discipline of Civil, Surveying and Environmental Engineering, The University of Newcastle

  Large deformation analysis is very important in some problems of geomechanics. Soft clays experience large amounts of settlements under applied loads and consolidation, for which the small deformation assumption does not result in precise solutions. The large deformation considerations are vital for these problems especially in Australia, since there is a large amount of soft soils along the east coast of the continent. Studying the footings behaviour under such circumstances demands for large deformation formulation by which load bearing capacity and settlements can be estimated more precisely and therefore more reliable design methods and techniques will be achieved. Two well-known methods for analysing large-deformation geotechnical problems are studied in this work. These methods include the Updated-Lagrangian (UL) and the Arbitrary-Lagrangian-Eulerian (ALE). The ALE method in this study is based on the operator-split technique during which the analysis is performed in two steps; an UL step followed by an Eulerian step. In the first step, a common UL procedure is undertaken to achieve the equilibrium. In the second step, the distorted mesh is refined and all kinematic and static variables are then transferred from the old mesh to the new mesh. Most ALE algorithms require mesh generation to refine the mesh during Eulerian step. This study introduces a new method for mesh refinement which can be used in general cases regardless of problem dimension and element types. The performance and efficiency of the UL and the ALE methods in solving some interesting problems in geomechanics are compared.

• October 27, 2006

  “Student Membership Function: Geotechnical Design 2006 - University of Newcastle”

  Chris Bozinovski, AGS Newcastle Chairman, Douglas Partners

  To celebrate the completion of the 2006 Geotechnical Design Project at the University of Newcastle, the Newcastle Chapter of the Australian Geomechanics Society invited its members to join the 4th year design students to a Students Function on 27 October 2006 (just after they submitted their major assignment work). Once again, it proved to be an excellent opportunity for our imminent graduates to meet members of the local geotechnical profession and discuss potential career opportunities. The Chapter was also fortunate to sign up additional student members as a result of the function.

• November 15, 2006

  41st Karl Terzaghi Lecture: Unsaturated Soil Mechanics in Engineering Practice

  Professor Del Fredlund

  Unsaturated soil mechanics has rapidly become a part of geotechnical engineering practice as a result of solutions that have emerged to a number of key problems (or challenges). The solutions have emerged from numerous research studies focusing on issues that have a hindrance to the usage of unsaturated soil mechanics. The primary challenges to the implementation of unsaturated soil mechanics can be stated as follows:

  1. The need to understand the fundamental, theoretical behaviour of an unsaturated soil;
  2. the formulation of suitable constitutive equations and the testing for uniqueness of proposed constitutive relationships;
  3. the ability to formulate and solve one or more nonlinear partial differential equations using numerical methods;
  4. the determination of indirect techniques for the estimation of unsaturated soil property functions, and
  5. in situ and laboratory devices for the measurement of a wide range of soil suctions.

  This presentation outlines the nature of each of the previous challenges and describes the solutions that have emerged from research studies. breakthroughs in the in situ and laboratory measurement of soil suction are allowing unsaturated soil theories and formulations to be verified through use of the ‘observational method’.