Consolidation behaviour of finely laminated clays

Thin highly permeable laminations have a significant influence on the rate of consolidation of many natural clays. Horne [1] presented analytical solutions for a particular type of problem. The range of solutions has been extended by the authors, who have used the more general finite element technique to solve consolidation problems of finely laminated clays under various geometry, load, and boundary conditions. Solutions are presented in graphical form to enable engineers to predict the rate of settlement for strip loads imposed on the surface of laminated clays. The effect of the laminations on the pore water pressure distribution, and the significant difference between a laminated (composite) material and an anisotropic material, are examined.     

A Nondestructive Technique for Predicting the In Situ Void Ratio for Marine Sediments

This study tests the hypothesis that the in situ void ratio of surficial marine sediments may be predicted from shear wave velocity-depth data with a reliability equal to that of other methods currently available. Shear wave velocity is fundamentally controlled by the number of grain-to-grain contacts per unit volume of material and by the effective stress across those contacts. In this study, three previously established empirical formulae are used to predict void ratio from velocity-depth data. Field data were acquired along a transect off the northern Californian coast across which water depth increased from 35 to 70 m and seafloor sediment type varied from sand to silty-sand, respectively. A towed seafloor sled device was used to collect shear wave refraction data, and a marked, systematic decrease in velocity was observed along the line, ranging from 35-70 m/s for the coarse, near-shore material to 25-40 m/s for the finer, offshore deposits. Void ratios predicted from these velocities were compared with data measured directly from box-core samples. Of the formulae used for prediction, two agree remarkably well with the control data. Both predicted and control values increase from 0.6-0.8 for the sandy material to 1.1-1.5 for the silty-sand. Thus, this study does not disprove the hypothesis set and demonstrates the potential of field shear wave velocity-depth data as a means of delineating spatial variation in void ratio for surficial marine sediments in a remote, nondestructive manner.     

Assessment of three interface elements and modification of the interface element in CRISP90

To model the interaction between a buried pipeline and the surrounding soil either special interface elements or thin conventional elements may be used. In this study the CRISP90 interface element, the DRCRISP interface element and a conventional 8-noded quadrilateral element have been examined and their behaviour compared for a variety of loading conditions. Initial studies reveal that all these elements have limitations and are only suitable for monotonic loading and situations where tensile conditions do not occur across the interface. In the light of these findings the CRISP90 interface element has been modified by introducing a limiting adhesive strength in the normal direction; a flag system has also been introduced to track the various conditions of separation and closure for any gap that is formed. The results of single element and other benchmark tests show that the modified element can satisfactorily model the different modes of deformation relevant to soil–structure interface problems.     

A Particle Tracking Model for Non-Fickian Subsurface Diffusion

In this paper, a new particle tracking technique is described which can simulate non-Fickian diffusion within porous media. The technique employs fractional Brownian motions (fBms), a generalization of regular Brownian motion. These random fractal functions allow both super- and subdiffusive particle paths to be produced and hence non-Fickian diffusion of the resulting panicle clouds can be modeled. In recent years, fBm trace functions have been used by many authors to reproduce self-affine random fields to simulate various porous media properties. In contrast, a method is detailed herein which uses self-similar spatial fBm trajectories to simulate directly non-Fickian behavior of the particle clouds. Although fractal trajectories have been previously suggested as the basis for possible methods of modeling non-Fickian diffusion, the authors believe that this paper contains the first algorithm to be presented which does not require an a priori knowledge of the end condition of the random walk and, more importantly, allows both a definable scaling exponent and (fractal) diffusion coefficient to be specified. The resulting non-Fickian diffusion using the new algorithm is illustrated and some applications are discussed. The purpose of this paper is to bring the potential usefulness of fBm trajectories in simulating non-Fickian processes within homogeneous media to the attention of numerical modelers active in the simulation of subsurface diffusive processes. The method has a particular environmental application in the simulation of the non-Fickian dispersion of groundwater contaminants through porous media.     

A Nondestructive Technique for Predicting the In Situ Void Ratio for Marine Sediments

Abstract

This study tests the hypothesis that the in situ void ratio of surficial marine sediments may be predicted from shear wave velocity-depth data with a reliability equal to that of other methods currently available. Shear wave velocity is fundamentally controlled by the number of grain-to-grain contacts per unit volume of material and by the effective stress across those contacts. In this study, three previously established empirical formulae are used to predict void ratio from velocity-depth data. Field data were acquired along a transect off the northern Californian coast across which water depth increased from 35 to 70 m and seafloor sediment type varied from sand to silty-sand, respectively. A towed seafloor sled device was used to collect shear wave refraction data, and a marked, systematic decrease in velocity was observed along the line, ranging from 35–70 m/s for the coarse, near-shore material to 25–40 m/s for the finer, offshore deposits. Void ratios predicted from these velocities were compared with data measured directly from box-core samples. Of the formulae used for prediction, two agree remarkably well with the control data. Both predicted and control values increase from 0.6–0.8 for the sandy material to 1.1–1.5 for the silty-sand. Thus, this study does not disprove the hypothesis set and demonstrates the potential of field shear wave velocity-depth data as a means of delineating spatial variation in void ratio for surficial marine sediments in a remote, nondestructive manner.