David Muir Wood

Mechanical behaviour of soils under environmentally induced cyclic loads

T. Wichtmann, T. Triantafyllidis: Behaviour of granular soils under environmentally induced cyclic loads. - D. Muir Wood: Constitutive modelling. - C. di Prisco: Creep versus transient loading effects in geotechnical problems. - M. Pastor et al.: Mathematical models for transient, dynamic and cyclic problems in geotechnical engineering. - M. Pastor: Discretization techniques for transient, dynamics and cyclic problems in geotechnical engineering: first order hyperbolic partial diffential equations. - M. Pastor et l.: Discretization techniques for transient, dynamic and cyclic problems in geotechnical engineering: second order equation. - C. di Prisco: Cyclic mechanical response of rigid bodies interacting with sand strata. - D. Muir Wood: Macroelement modelling. - M. F. Randolph: Offshore design approaches and model tests for sub-failure cyclic loading of foundations. - M.F. Randolph: Cyclic interface shearing in sand and cemented solis and application to axial response of piles. - M. F. Randolph: Evaluation of the remoulded shear strength of offshore clays and application to pipline-soil and riser-soil interaction.

Microscale biogeotechnical differences in intertidal sedimentary ecosystems

Abstract Intertidal sediments are inhabited by organisms that can modify the geotechnical and sedimentological properties of the sediment. We have analysed small scale differences in these properties at four closely adjacent sites on Ardmore Bay, Clyde Estuary, Scotland. The sites were an Enteromorpha algal mat site (EAM), a Corophium volutator site (CV), the head shafts of Arenicola marina (AMHS) and the tail shafts of Arenicola marina (AMTS) burrows. Three replicate cores were taken from each site. We measured load resistance, particle size parameters of mean particle size, sorting, skewness and kurtosis, and total organic matter (TOM) and carbonate. Load resistance was measured with a newly developed microscale load resistance penetrometer which measured load resistance of the sediment at 1 mm intervals through the sediment core from the surface to 100 mm. Sediment cores were then sectioned every 10 mm and particle size, total organic matter and carbonate content measured. In situ shear strength measurements were also taken at the four sites. The data were analysed by bivariate correlation analysis and multivariate cluster analysis. There was a number of significant positive and negative correlations between the parameters at the four sites. Significant down-core changes in the sediment parameters and their correlations were noted. These differed between the four sites. The CV site had the largest number of significant correlations, the EAM site had the least. Cluster analyses of the sites showed that in general the sites clustered separately, although there were a number of overlaps. The EAM site showed distinct clusters for its three separate replicate cores, while the CV site clustered into a top part and a bottom part of the core. Cluster analyses of the depths across all the sites identified a break in the data at depths of between 40 and 70 mm. There was a linear relationship between field shear strength and laboratory penetration resistance. The results are discussed in relation to the fine-scale geotechnical and sedimentological heterogeneity of intertidal sediments, and the effects of biological activity.

Introduction: models and soil mechanics

Use of models in engineering Scientific understanding proceeds by way of constructing and analysing models of the segments or aspects of reality under study. The purpose of these models is not to give a mirror image of reality, not to include all its elements in their exact sizes and proportions, but rather to single out and make available for intensive investigation those elements which are decisive. We abstract from non-essentials, we blot out the unimportant to get an unobstructed view of the important, we magnify in order to improve the range and accuracy of our observation. A model is, and must be, unrealistic in the sense in which the word is most commonly used. Nevertheless, and in a sense, paradoxically, if it is a good model it provides the key to understanding reality. (Baran and Sweezy, 1968) Engineering is concerned with understanding, analysing, and predicting the way in which real devices, structures, and pieces of equipment will behave in use. It is rarely possible to perform an analysis in which full knowledge of the object being analysed permits a complete and accurate description of the object to be incorporated in the analysis. This is particularly true for geotechnical engineering. The soil conditions under a foundation or embankment can be discovered only at discrete locations by retrieving samples of soil from boreholes or performing in situ tests; soil conditions between such discrete locations can be deduced only by informed interpolation.

Elastic-plastic model for soil

Introduction In this chapter we build a general but simple elastic-plastic model of soil behaviour, starting with the experimental observation of the existence of yield loci that was discussed in Chapter 3. Other features are added as necessary, and their selection is aided sometimes by our knowledge of well-known characteristics of soil response and at other times by knowledge of the elastic—plastic behaviour of metals. Broadly, having established that yield surfaces exist for soils, it follows that, for stress changes inside a current yield surface, the response is elastic. As soon as a stress change engages a current yield surface, a combination of elastic and plastic responses occurs. It is necessary to decide on the nature of the plastic deformations: the magnitudes and relative magnitudes of various components of plastic deformation and the link between these magnitudes and the changing size of the yield surface. It must be emphasised again that we are attempting to produce a simple broad-brush description of soil modelling which cannot hope to match all aspects of soil behaviour. Some of the shortcomings of such models are discussed in Chapter 12. For convenience of presentation, the discussion is largely restricted to combinations of stress and strain that can be applied in the triaxial apparatus, and the model is described in terms of triaxial stress variables p and q and strain variables e p and e q .

A particular elastic—plastic model: Cam clay

Introduction In the previous chapter, elastic—plastic models for soil were discussed in a general way. Yield loci and plastic potentials were sketched, but no attempt was made to suggest possible mathematical expressions for these curves. In this chapter, a particular model of soil behaviour is described and used to predict the response of soil specimens in standard triaxial tests. In subsequent chapters, this model is used to illustrate a number of features of soil behaviour. This particular model can be regarded as one of the set of volumetric hardening models covered by the discussion in Chapter 4. When the model was originally described in the literature by Roscoe and Burland (1968), it was called ‘modified’ Cam clay to distinguish it from an earlier model called Cam clay (Roscoe and Schofield, 1963). The qualifier modified is dropped here because the modified Cam clay model has probably been more widely used for numerical predictions. The ‘original’ Cam clay model is mentioned in Section 8.4. The model is described here in terms of the effective stress quantities p and q which are relevant to the discussion of soil response in conventional triaxial tests. Most of the examples given are for triaxial compression, though it is tacitly assumed that triaxial extension can be accommodated merely by allowing the deviator stress q to take negative values. The extension of the model to other more general states of stress is described briefly in Section 10.6.2.