Impacts of saturation-dependent anisotropy on the shrinkage behavior of clay rocks

Geomaterials such as soils and rocks can exhibit inherent anisotropy due to the preferred orientation of mineral grains and/or cracks. They can also be partially saturated with multiple types of fluids occupying the pore space. The anisotropic and unsaturated behaviors of geomaterials can be highly interdependent. Experimental studies have shown that the elastic parameters of rocks evolve with saturation. The effect of saturation has also been shown to differ between directions in transversely isotropic clay rock. This gives rise to saturation-dependent stiffness anisotropy. Similarly, permeability anisotropy can also be saturation-dependent. In this study, constitutive equations accommodating saturation-dependent stiffness and hydraulic anisotropy are presented. A linear function is used to describe the relationship between the elastic parameters and saturation, while the relative permeability–saturation relationship is characterized with a log-linear function. These equations are implemented into a hydromechanical framework to investigate the effects of saturation-dependent properties on the shrinkage behavior of clay rocks. Numerical simulations are presented to demonstrate the role of saturation-dependent stiffness and hydraulic anisotropy in shrinkage behavior. The results highlight that strain anisotropy and time evolution of pore pressures are substantially influenced by saturation-dependent stiffness and hydraulic anisotropy.

     

Integrating long-term water and sediment pollution data, in assessing chemical status within the European Water Framework Directive

The European Water Framework Directive (WFD) establishes a framework for the protection and improvement of estuarine (transitional) and coastal waters, attempting to achieve good water status by 2015; this includes, within the assessment, biological and chemical elements. The European Commission has proposed a list of priority dangerous substances (including metals such as Cd, Hg, Ni and Pb), with the corresponding list of environmental quality standards (EQS), to assess chemical status, but only for waters. In this contribution, a long-term (1995–2007) dataset of transitional and coastal water and sediment trace elements concentrations, from the Basque Country (northern Spain), has been used to investigate the response of these systems to water treatment programmes. Moreover, the approach proposed in the WFD, for assessing water chemical status (the ‘one out, all out’ approach), is compared with the integration of water and sediment data, into a unique assessment. For this exercise, background levels are used as reference conditions, identifying the boundary between high and good chemical status. EQS are used as the boundary between good and moderate chemical status. This contribution reveals that the first approach can lead to misclassification, with the second approach representing the pattern shown by the long-term data trends. Finally, the management implications, using each approach are discussed.     

Lattice Boltzmann method with two relaxation times for advection–diffusion equation: Third order analysis and stability analysis

The objectives of this study are to investigate the third order accuracy and linear stability of the lattice Boltzmann method (LBM) with the two-relaxation-time collision operator (LTRT) for the advection–diffusion equation (ADE) and compare the LTRT model with the single-relaxation-time (LBGK) model. While the LBGK has been used extensively, the LTRT appears to be a more flexible model because it uses two relaxation times. The extra relaxation time can be used to improve solution accuracy and/or stability. This study conducts a third order Chapman–Enskog expansion on the LTRT to recover the macroscopic differential equations up to the third order. The dependency of third order terms on the relaxation times is obtained for different types of equilibrium distribution functions (EDFs) and lattices. By selecting proper relaxation times, the numerical dispersion can be significantly reduced. Furthermore, to improve solution accuracy, this study introduces pseudo-velocities to develop new EDFs to reduce the second order numerical diffusion. This study also derives stability domains based on the lattice Peclet number and Courant number for different types of lattices, EDFs and different values of relaxation times, while conducting linear stability analysis on the LTRT. Numerical examples demonstrate the improvement of the LTRT solution accuracy and stability by selecting proper relaxation times, lattice Peclet number and Courant number.     

The application of a Marine Biotic Index to different impact sources affecting soft-bottom benthic communities along European coasts

Following the European Water Framework Directive (2000/60/EC), the authors proposed, in a previous contribution, a Marine Biotic Coefficient (BC) to establish the ecological quality of soft-bottom benthos within European estuarine and coastal environments. The present study examines the application of the BC to the Atlantic (North Sea; Bay of Biscay; South of Spain) and Mediterranean (Spain and Greece) European coasts. The investigation assesses also the usefulness of the BC, in relation to different impact sources (e.g. drilling cuts with ester-based mud, submarine outfalls, heavy metals, industrial and mining wastes, jetties and sewerage works). The results obtained are consistent with those obtained using several methods and parameters, such as richness, diversity, evenness, Abundance-Biomass comparison plots and univariate and multivariate statistical analyses. The BC values provide a simple and clearly defined way to establish the ecological quality of soft-bottom benthos, complementary to the above mentioned methods.     

Implementation of the European water framework directive from the Basque country (northern Spain): a methodological approach

The European Water Framework Directive provides a challenge in the development of new and accurate methodologies. It addresses assessment of Ecological Quality Status within European rivers, lakes, groundwaters, estuaries and coasts. Although this directive is simple and flexible in its concept, it is necessary to develop an approach based upon scientific knowledge; however, at the same time it should be as simple as possible, in order to achieve both requirements and comparability of results throughout European waters. This contribution presents the first methodological approach to the problem, as used for estuaries and coasts of the Basque Country (northern Spain), in: selecting typologies and reference conditions; determining biological quality and ecological status; and identifying some problems in implementing the WFD. As such, the present paper could serve as the basis for a discussion document for other regions and countries, throughout Europe.     

Thermoplasticity and strain localization in transversely isotropic materials based on anisotropic critical state plasticity

Geomaterials such as soils and rocks are inherently anisotropic and sensitive to temperature changes caused by various internal and external processes. They are also susceptible to strain localization in the form of shear bands when subjected to critical loads. We present a thermoplastic framework for modeling coupled thermomechanical response and for predicting the inception of a shear band in a transversely isotropic material using the general framework of critical state plasticity and the specific framework of an anisotropic modified Cam–Clay model. The formulation incorporates anisotropy in both elastic and plastic responses under the assumption of infinitesimal deformation. The model is first calibrated using experimental data from triaxial tests to demonstrate its capability in capturing anisotropy in the mechanical response. Subsequently, stress‐point simulations of strain localization are carried out under two different conditions, namely, isothermal localization and adiabatic localization. The adiabatic formulation investigates the effect of temperature on localization via thermomechanical coupling. Numerical simulations are presented to demonstrate the important role of anisotropy, hardening, and thermal softening on strain localization inception and orientation. Copyright © 2016 John Wiley & Sons, Ltd.     

Multiphysics hillslope processes triggering landslides

In 1996, a portion of a highly instrumented experimental catchment in the Oregon coast range failed as a large debris flow from heavy rain. For the first time, we quantify the 3-D multiphysical aspects that triggered this event, including the coupled sediment deformation-fluid flow processes responsible for mobilizing the slope failure. Our analysis is based on a hydromechanical continuum model that accounts for the loss of sediment strength due to increased saturation as well as the frictional drag exerted by the moving fluid. Our studies highlight the dominant role that bedrock topography and rainfall history played in defining the failure mechanism, as indicated by the location of the scarp zone that was accurately predicted by our 3-D continuum model.     

Millennial/submillennial-scale sea-level fluctuations in western Mediterranean during the second highstand of MIS 5e

This paper investigates a series of small-scale, short-lived fluctuations of sea level registered in a prograding barrier spit that grew during the MIS 5e. This interglacial includes three highstands (Zazo et al., 2003) and we focus on the second highstand, of assumed duration ～10 ± 2 ka, given that U–Th ages do not provide more accurate data. Geometry and 3D architecture of beach facies, and thin-section petrography were used to investigate eight exposed offlapping subunits separated by seven conspicuous erosion surfaces, all interpreted as the result of repeated small-scale fluctuations of sea level.Each subunit records a relatively rapid rise of sea level that generated a gravelly shoreface with algal bioherms and a sandy uppermost shoreface and foreshore where most sand accumulated. A second range of still smaller-scaled oscillations of sea level has been deduced in this phase of sea-level fluctuation from lateral and vertical shifts of the foreshore-plunge-step-uppermost shoreface facies.Eventually, progradation with gently falling sea level took place and foreshore deposits underwent successive vadose cementation and subaerial dissolution, owing to relatively prolonged exposure. Later recovery of sea level re-established the highstand with sea level at approximately the same elevation, and there began deposition of a new subunit. The minimum sea-level variation (fall and subsequent rise) required to generate the observed features is 4 m. The time span available for the whole succession of events, and comparison with the Holocene prograding beach ridge complex in the nearby Roquetas (Almería) were used to calculate the periodicity of events. A millennial-suborbital time scale is suggested for fluctuations separating subunits and a decadal scale for the minor oscillations inside each subunit.