Announcement: Award-winning papers in 2015 Free

The paper describes a three-phase single-point material point method formulation of coupled flow (water and air) for hydro-mechanical analysis of geotechnical problems involving unsaturated soils. The governing balance and dynamic momentum equations are discretised and adapted to material point method characteristics: an Eulerian computational mesh and a Lagrangian analysis of material points. General mathematical expressions for the terms of the set of governing equations are given. A suction-dependent elastoplastic Mohr–Coulomb model, expressed in terms of net stress and suction variables is implemented. The instability of a slope subjected to rain infiltration, inspired from a real case, is solved and discussed. The model shows the development of the initial failure surface in a region of deviatoric strain localisation, the evolution of stress and suction states in some characteristic locations, the progressive large strain deformation of the slope and the dynamics of the motion characterised by the history of displacement, velocity and acceleration of the unstable mass.

The Geotechnical Research Medal, presented for the best paper on geotechnical research, was awarded to Vrakas & Anagnostou (2015).

This paper presents a novel, very simple, accurate, theoretically well-founded and widely applicable relationship expressing the tunnel convergences obtained from large strain elasto-plastic analyses as a hyperbolic function solely of the corresponding small strain convergences. It can thus be used for ‘self-correcting’ small strain solutions, removing the need for large strain elasto-plastic analyses at least at the preliminary design stage and quantifying a hitherto unknown error caused by disregarding the geometric non-linearity. The proposed relationship can be proved rigorously for the plane strain rotationally symmetric ground response problem with a general elasto-plastic constitutive law with or without dilatancy and hardening. Numerical analyses of characteristic two- and three-dimensional excavation problems show that this relationship is generally applicable, irrespective of the in situ stress state and the tunnel geometry. It is therefore very useful from an engineering point of view for the design of tunnels crossing heavily squeezing ground, where the convergences may be so large (sometimes well in excess of 10% of the tunnel radius) that the usual small strain elasto-plastic analyses are deficient.

The David Hislop Award, presented to the best paper published on heavy marine design and construction with particular reference to offshore engineering, was awarded to Tian et al. (2015).

This paper proposes an analytical approach to evaluate the ultimate embedment depth and holding capacity that plate anchors can potentially achieve. Based on a plasticity model for anchor–soil interaction and compatible chain solution, detailed derivations are presented that allow the main dimensionless groups of input parameters to be identified. For typical cases where the weight of the anchor is negligible relative to its holding capacity, explicit expressions are provided in non-dimensional form for ultimate embedment and anchor capacity. A thorough parametric sensitivity study highlights the major factors affecting these quantities. Two practical examples are considered that demonstrate the proposed analytical approach for different types of anchors, in one case revealing significant scope for improved design of plate anchors in order to optimise performance.