J. B. Burland

Kinematic hardening plasticity formulation of small strain behaviour of soils

An objective of this paper is to demonstrate that the small strain model developed by the authors can be incorporated into the conventional kinematic hardening plasticity framework to predict pre-failure defor mations. The constitutive model described in this paper is constituted by three elliptical yield surfaces in triaxial stress space. Two inner surfaces are rotated ellipses of the same shape, representing the boundaries of the linear elastic and small strain regions, while the third surface is the modified Cam clay large-scale yield surface. Within the linear elastic region, the soil behaviour is elastic with cross-coupling between the shear and volumetric stress–strain components. Within the small strain region, the soil behaviour is elasto-plastic, described by the kinematic hardening rule with an infinite number of loading surfaces defined by the incremental energy criterion. Within the large-scale yield surface, the soil behaviour is elasto-plastic, described by kinematic and isotropic hardening of the small strain region boundary. Since the yield surfaces have different shapes, the uniqueness of the plastic loading condition imposes a restriction on the ratio between their semi-diameters. The model requires 12 parameters, which can be determined from a single consolidated undrained triaxial compression test. Copyright

Thermomechanical formulation of a small-strain model for overconsolidated clays

A constitutive model for the stress‐strain behaviour of overconsolidated clays at small and intermediate strains is presented. The model had previously been formulated by Puzrin & Burland in terms of classical plasticity theory with certain additional assumptions. It is presented here within a rigorous formalism based on thermomechanical considerations, described by Puzrin & Houlsby and termed the ‘continuous hyperplastic’ method. The entire constitutive behaviour is derived from the specification of two scalar functionals. The model serves as the first example of the derivation of a non‐trivial constitutive model within this approach.

A Miniature Soil Inclusion for Measuring Axial Force and Radial Stress

This paper describes the design, development, and manufacture of a miniature soil inclusion 175 mm long and 8 mm in diameter for measuring axial force and radial stress at three points along its length. The individual devices rely on strain gages for their operation and were found to be stable in a laboratory environment. The axial force and radial stress measurements can be resolved to less than 1 N and 1 kPa, respectively. The model inclusion has been used in a study to investigate the development of shear stress along a soil nail. The instrumentation allowed the influence of arching to be positively identified. The paper includes discussion of factors such as calibrating for cross-effects, converting the electrical outputs to engineering units, and cell-action effects. These factors along with the soil stiffness govern the accuracy of measurement.

Pisa goes critical

Abstract The Leaning Tower of Pisa is not just a quaint curiosity but a magnificent architectural treasure. Over the years its inclination has been increasing inexorably to the point where it is about to fall over. Moreover the stresses in the masonry induced by the lean have brought it close to structural failure. Stabilisation of the tower represents the ultimate civil engineering challenge. This paper describes the history of the tower and the mechanics of its behaviour, understanding of which has proved vital in the development of stabilisation measures. Early stabilisation was first achieved by placing temporary lead weights on the foundation masonry on the opposite side from the lean. Long term stabilisation commenced in February 2000 using a controversial method of soil extraction to reduce the inclination by about 10% – not enough to be visible but enough to substantially increase the safety. A long, tense journey lies ahead of the tower.