An Appreciation of Modified Cam Clay
by G.T. Houlsby
ABSTRACT: This paper presents an appreciation of the importance of the paper “On the generalised stress-strain behaviour of ‘wet’ clay” by Roscoe and Burland (1968), which sets out the Modified Cam Clay (MCC) framework for understanding the behavior of clays. In the last 50 years MCC has become one of the most important theoretical tools for understanding and modelling soil behaviour. Here I present a number of different aspects of the influence of MCC, as a simple conceptual model which allows hand calculations, as the basis of numerical modelling software, as the starting point for some of the most sophisticated of constitutive models developed today, and as a vehicle for discussion of fundamental features of soil behavior as a scientific topic.
KEYWORDS: Clay, Modified Cam Clay, Plasticity Theory
Integrated Research into the Foundation Behaviour of Offshore Energy Production Platforms
by Richard J. Jardine, David W. Hight and David M Potts
ABSTRACT: This paper revisits research undertaken by the Authors with Professor J B Burland in which key contributions were made to the pioneering Magnus Foundation Monitoring Project (FMP), Hutton Tension Leg Platform (TLP) and Gullfaks-C platform oil production platform projects in the North Sea. Close liaison with industry and an integrated approach that combined high quality laboratory and in-situ testing with cutting-edge numerical analysis and accurate observations of full-scale field behaviour were central to the improvements achieved in analysing the foundations of these and similar structures. The paper asserts the central importance of understanding regional geology before reviewing how teams led by John Burland developed new laboratory and field monitoring instruments, as well as experimental and numerical approaches that have had a lasting impact in many areas of geotechnical engineering. Recent developments that sprang from the projects and the associated research programmes are highlighted. Particular attention is given to subsequent improvements to pile design methods whose development started with the first two cited case histories, as these and later developments are now contributing to a worldwide shift towards renewable, low-carbon, wind-energy production.
KEYWORDS: Foundations, Offshore energy, Field monitoring, Advanced laboratory testing.
Stress Components in Unsaturated Soils
by D. G. Toll
ABSTRACT: In 1959, Bishop published his classic paper on “effective stress” in unsaturated soils, combining together the components of net stress and suction into a single stress variable using the empirical χ factor. Jennings and Burland (1962) criticised this approach, identifying limitations in the use of an “effective stress”. In particular, the approach failed to explain volumetric collapse of soil when wetted. Burland followed up this criticism in 1965 by pointing out that the role of suction was two-fold; not only did it increase the contact stress between particles but the presence of air-water interfaces (menisci) also had a stabilising effect. He suggested that we should not try to combine the stress variables into a single “effective stress” but that we should treat the two stress components of net stress and suction differently. This approach was adopted by Fredlund and Morgenstern (1977) and led to the widely used ∅b approach. Thus, in critiquing the Bishop approach, John Burland had a highly significant input into the direction of unsaturated soil research and practice over a number of decades. In this paper, Burland’s contribution to the debate on stress components in unsaturated soils will be examined through reinterpretation of a set of experimental data from triaxial testing of an unsaturated lateritic gravel. The results confirm that attempting to combine net stress and suction into a single variable is not sufficient for interpreting unsaturated soil behaviour.
KEYWORDS: Unsaturated soil, Effective stress, Suction
Reflections on the Importance of Small Strain Non-Linearity in Soils
by Andrew J. Whittle
ABSTRACT: It is widely accepted today that most soils exhibit non-linear stress strain properties even at very small strain levels and that improved representation of these stiffness properties is needed to understand and interpret many practical problems involving soil-structure interactions. Much of this understanding relates to research carried out at Imperial College led by John Burland and his colleagues during the 1980’s. This work included the development of devices for routine measurements of local strains in laboratory element tests (Burland & Symes, 1982; Jardine et al. 1984), documentation of small strain stiffness properties for a range of reconstituted and natural soils (Jardine et al. 1984), and representation of these nonlinear stiffness properties in finite element simulations involving a range of soil-structure interactions (Jardine et al. 1986). This information was then synthesized in Burland’s seminal Bjerrum Lecture ‘Small is beautiful’ (Burland, 1989) and linked to the performance of foundations, excavations and tunnels. This paper reviews the importance of small strain non-linearity from the perspectives of i) advancing knowledge of soil behavior, ii) development of more reliable constitutive models, and iii) evaluating impacts in the computed performance for practical geotechnical problems.
KEYWORDS: Soil stiffness properties, Laboratory tests, FE analyses, Constitutive models, Foundations, Excavations, Tunnels
Aqueous Gel in Sands; a Friend or Foe?
by V.N. Georgiannou, E-M. Pavlopoulou and F.C. Chortis
ABSTRACT: The response of sands stabilized with colloidal silica aqueous gel is examined in the laboratory. The role of colloidal silica on subsequent sand behaviour is examined with the aid of monotonic loading tests to establish the mechanical response and the resistance of the treated sand to liquefaction. It appears that depending on the loading conditions while the strength of the treated sand is enhanced, its stiffness may reduce and its compressibility increase. This contradictory behaviour is investigated on the basis of an extended database including direct shear, triaxial and normal compression tests.
KEYWORDS: Soil stabilization, Laboratory tests, Sands
John Burland’s Deep-Excavation- and Tunnelling-Related Research and Industry Involvement
by J. R. Standing
ABSTRACT: During the time that Professor John Burland was an expert witness for the Parliamentary hearings for the Jubilee Line Extension Project (JLEP), he realised that although tunnels had been constructed in London for more than a century, there were very few well documented case studies describing the response of buildings to tunnelling-induced settlement. Professor Burland had extensive knowledge of the effects of ground movement on buildings, having studied and published his seminal work with Professor Peter Wroth in the 1970s which he with others developed into a staged process for assessing potential structural damage from excavation-induced ground movements. Construction of the JLEP provided an ideal opportunity to compile a set of exemplary case studies (involving different structural forms, foundation types, tunnelling methods and geological conditions) and he harnessed this to its full extent. At the start, a number of ‘gaps in knowledge’ were identified and these were addressed over the following years of monitoring and data analysis. The research culminated in a two-volume book that is still widely referenced almost twenty years later.
In this paper a background to Professor Burland’s tunnelling- and deep-excavation-related research is given and the gaps in knowledge are summarised along with how they were answered through the JLEP research findings. They are reinforced with other more recent tunnelling projects in London that he has been involved with, in particular the Crossrail project, thus furthering the understanding of ground and structural response to tunnelling, benefitting both industry and academia.
KEYWORDS: Deep excavations, Tunnels, Field monitoring
Mechanical Models for Hazard and Risk Analysis of Structures in Creeping Landslides
by Philipp W. Oberender, Dimitri V. Val and Alexander M. Puzrin
ABSTRACT: Inspired by John Burland’s outstanding work on stabilizing the Leaning Tower of Pisa, this paper proposes a novel approach that allows risk assessment for another historic tower – the Leaning Tower of St. Moritz. The leaning of the St Moritz Tower is caused by differential displacements of the permanent landslide in which it is embedded, making its risk assessment challenging due to difficulties in predicting displacements and loads in creeping slopes. This paper proposes a methodology for hazard assessment in terms of expected displacements and ultimate loads making use of two novel approaches: (i) observation guided constitutive modelling (where visco-elastic-plastic models of the landslide are calibrated using observations) and (ii) assessment of landslide pressure via limit analysis. In order to complete the formulation for the assessment of risk, exemplary exposure models (for weather variables including the effect of climate change) and simple vulnerability functions are proposed.
KEYWORDS: Landslide, Creep, Risk analysis, Leaning tower
Reflections on Recent Tailings Dam Failures and How the Application of Burland’s Soil Mechanics Triangle Concept May Avert Future Failures
by A. Fourie
ABSTRACT: In his Nash Lecture in 1989, Burland presented the concept of what he referred to as the Soil Mechanics Triangle. The three apexes of the triangle were identified as Ground Profile, Soil Behaviour and Applied Mechanics, and embedded within the triangle and linked to all three apexes the notion of empiricism and well-winnowed experience. Burland used this concept to emphasise the critical and interlinked nature of the three triangle apexes when teaching Soil Mechanics to undergraduate students. This paper applies the triangle to the current state of practice regarding tailings dam management, highlighting how lack of attention to the concepts embedded in Burland’s approach have resulted in sometimes catastrophic consequences. Using the published forensic reports on two recent, major tailings dam failures around the world, the paper illustrates how they may have been avoided if a proper appreciation of the three pillars of good practice suggested by Burland had been adhered to. It also argues for more rigorous training in geotechnical engineering and engineering geology of practitioners working in the field of tailings engineering.
KEYWORDS: Teaching soil mechanics, Tailings dam, Failures, Soil mechanics triangle
From Particles to Constrictions: Scientific Evolution of Enhanced Criteria for Internal Stability Assessment of Soils
by Buddhima Indraratna, Jahanzaib Israr, and late Peter R Vaughan
ABSTRACT: Internal instability occurs when steady seepage forces erode the finer fractions from non-uniform soils along pre-existing openings such as cracks in cohesive soils and voids in non-cohesive soil to induce permanent changes in the original particle size distribution. Given that the drainage characteristics of soils are significantly influenced by the shape, packing arrangement, compaction, and size distribution of their particles, even limited erosion can markedly alter their drainage characteristics. The geometrical assessment of internal instability potential is normally conducted using classical filter retention criterion based on mere particle size distribution and without giving due consideration to the above factors. These methods would determine the risk of instability by approximating the soil’s constrictions based on its particle size distribution; these constrictions are pore channels connecting neighbouring void spaces that would control both permeability and retention phenomena. However, recent advances in mathematical computations have facilitated the exact delineation of constriction sizes and the introduction of more accurate constriction based methods. This study purports to shed light on the scientific evolution of particle and constriction based methods over the past four decades, including the enhanced accuracy, reduced bias, and robustness associated with the latter. An interesting case study from our experience of using these approaches for a permeable barrier design at Bomaderry, NSW (Australia) for subsurface flow treatment is presented, and recommendations for their use by practicing engineers are made to conclude this study.
KEYWORDS: Internal instability, Granular soils, Particles sizes, Constriction sizes, Relative density
