Tectonic structures — a classification

By considering the ways (symmetric, asymmetric and antisymmetric) in which layer interfaces can mutually deflect (see Fig.2.), and the relative curvatures which occur in waves of each of the interfaces (Fig.1), it is possible to generate a classification of structures which covers a wide range of buckle fold shapes, load casts and interface buckles, some types of boudins and asymmetric folds, in one three-dimensional plot.     

Poroelastic-plastic consolidation — analytical solution

Consolidation of a poroelastic material that yields according to Drucker–Prager or Mohr–Coulomb criteria leads to a Stefan problem for time-dependent pore fluid pressure. The solution to the Stefan problem for a column of infinite depth is known and is adapted to poroelastic/plastic consolidation of a weightless material under a uniform surface load applied instantaneously and subsequently maintained constant. In this approach, the plastic potential and yield criterion need not be the same. If yielding occurs concurrently with application of load, then collapse is instantaneous. Otherwise, yielding may occur during the consolidation period. If so, then the elastic–plastic zone first appears at the surface and subsequently moves down the column. Depth to the elastic–plastic boundary is given by the simple expression Z = 2β√t where β is a constant determined from continuity conditions at the elastic–plastic boundary. Time-dependent surface displacement that occurs during consolidation is directly proportional to Z. There is little difference between elastic–plastic and purely elastic results in a numerical example because there is little difference in the respective consolidation coefficients. Elastic–plastic finite element results obtained from a column of finite depth are in close agreement with analytical results as long as the pore pressure at the bottom of the column does not change significantly from the value induced by application of the surface load. The analytical solution provides for: (1) efficient evaluation of material properties effects on consolidation, including strength and fluid compressibility, and (2) an accurate way of validating poroelastic/plastic computer codes that are based on Drucker–Prager and Mohr–Coulomb criteria. Copyright © 1999 John Wiley & Sons, Ltd.     

Benchmarking the thermomechanical behaviour of clays — a progress report — the CEC interclay project

In 1989 a small-scale exercise conducted by the CEC as part of its research programme into the underground storage of radioactive waste highlighted the difficulty of making accurate predictions a priori, of the geomechanical behaviour of clay. Given source data about the Boom clay from the underground research facility at Mol, three organisations independently performed f.e. analyses of two somewhat hypothetical problems. While the results were very broadly in agreement, they were shown to be sensitive to both the type of constitutive model used and the way data was fitted to the model.

Subsequently, the CEC sponsored a more comprehensive benchmark exercise called INTERCLAY II. This involves eleven organisations from various member states of the EC in a project encompassing the three aspects of software development for predictive modelling: verification, validation on the laboratory scale and the treatment of in-situ tests. The paper briefly describes the exercise currently in progress and presents the main results achieved to date concentrating on validation aspects.     

Heat-flow — heat-generation studies in Norway

Fifteen heat-flow determinations based on data from 34 drill holes throughout central and southern Norway are presented. Five combined heat-flow — heat-generation measurements from homogeneous Precambrian and Permian crystalline rocks from southern Norway confirm a linear relation between heat flow and heat generation of the form Q = Q₀ + bA, where Q is surface heat flow (1hfu = 10⁻⁶ cal cm⁻² sec⁻¹), A is surface heat generation (1hgu = 10⁻¹³ cal cm⁻³ sec⁻¹), and b and Q₀ are constants. The slope of the line (b = 8.4 km) is in good agreement with results obtained from other stable continental areas, but the intercept (Q₀ = 0.48 hfu) is considerably lower, suggesting the presence of a zone of low heat flow in southern Norway.Nine heat-flow determinations are from the Paleozoic, Caledonian orogenic belt. These values range from 1.09 to 1.29 hfu with an average value of 1.18, are consistent with model data from other Paleozoic orogenic areas including the Appalachian system of North America, and do not appear to reflect the low heat flow observed in southern Norway.