The stability of geodemographic cluster assignments over an intercensal period

A geodemographic classification provides a set of categorical summaries of the built and socio-economic characteristics of small geographic areas. Many classifications, including that developed in this paper, are created entirely from data extracted from a single decennial census of population. Such classifications are often criticised as becoming less useful over time because of the changing composition of small geographic areas. This paper presents a methodology for exploring the veracity of this assertion, by examining changes in UK census-based geodemographic indicators over time, as well as a substantive interpretation of the overall results. We present an innovative methodology that classifies both 2001 and 2011 census data inputs utilising a unified geography and set of attributes to create a classification that spans both census periods. Through this classification, we examine the temporal stability of the clusters and whether other secondary data sources and internal measures might usefully indicate local uncertainties in such a classification during an intercensal period.     

Effects of pore water pressure dissipation on rate dependency of shear strength in localised failure of soils

The paper presents analytical solutions for the evolution of excess pore pressures in the vicinity of a shear band in a rate‐dependent, strain‐softening permeable soil, with the aim to explore, both qualitatively and quantitatively, the potential variation of failure shear stress in the shear band. The solutions encompass both dissipation of a pre‐existing pore pressure regime within the main soil domain, and the effects of generation of additional pore pressure within the shear band itself. The simplified analytical solutions were checked by numerical inversion of exact solutions in Laplace transform space, confirming their high accuracy. The solutions show that it is possible for the failure shear stress to rise initially because of short‐term dissipation of the pre‐existing excess pore pressure at a faster rate than generation of new excess pore pressure within the shear band. This apparent strain hardening in a strain‐softening soil can be misleading in that it can temporarily slow down the sliding mass and create a false sense of stabilization of the slope. It can also result in additional temporary shear resistance for sliding foundations or pipelines on the seabed. Copyright © 2015 John Wiley & Sons, Ltd.     

Fast multipole displacement discontinuity method (FM‐DDM) for geomechanics reservoir simulations

The displacement discontinuity method (DDM) is frequently used in geothermal and petroleum applications for modeling the behavior of fractures in linear‐elastic rocks. The DDM requires O(N²) memory and O(N³) floating point operations (where N is the number of unknowns) to construct the coefficient matrix and solve the linear system of equations by direct methods. Therefore, the conventional implementation of the DDM is not computationally efficient for very large systems of cracks, often limiting its application to small‐scale problems. This work presents an approach for solving large‐scale fracture problems using the fast multipole method (FMM). The approach uses both the DDM and a kernel‐independent version of the FMM along with a preconditioned generalized minimal residual algorithm to accelerate the solution of linear systems of equations using desktop computers. Using the fundamental solutions for constant displacement discontinuity in a two‐dimensional elastic medium, several numerical examples involving fracture networks representing fractured reservoirs are treated. Numerical results show good agreement with analytical solutions and demonstrate the efficiency of the FMM implementation of the DDM for large‐scale simulations. Copyright © 2015 John Wiley & Sons, Ltd.