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For a reliable prediction of the time-development of soil deformations, a detailed characterization of both primary and secondary deformations is required. Nevertheless, in the current engineering practice the estimation of the primary and secondary deformations relies on the assumption of a constant coefficient of consolidation and a constant creep index respectively. However, high plasticity overconsolidated clays have reportedly complex stiffness and permeability relationships that challenge the validity of those assumptions. Analytical solutions of the one dimensional consolidation have been proposed, accounting for variation in permeability and oedometer modulus. Nevertheless, the methods assume a simplified log-linear and linear relationship with void ratio and effective stress for the two parameters, respectively. One-dimensional oedometer and constant rate of strain testing were employed to investigate the time-deformation development of a particular high plasticity overconsolidated clay. A dependency of the time until the end of primary deformations on the stress path was observed, with the majority of the unloading steps extending well beyond the 24 h typical duration of a load increment. It was revealed that the coefficient of consolidation generally increases during consolidation, and it may vary by more than one order of magnitude at the early stages of the consolidation process. This variation has been attributed to a transient effect noticed in the permeability, which has not been previously reported. The linear relationship between primary and secondary deformation indices was confirmed as an upper bound. In an effort to better characterize the time dependent behaviour a new index, the primary time deformation index, was defined as the slope at the inflection point of the time-curves. This parameter was found to be linearly related to the creep index, presenting thus a potential of better predictions of the duration and magnitude of consolidation deformations for the engineering practice.

This paper presents an approach for evaluating the horizontal stresses that develop in geotechnical Direct Simple Shear (DSS) tests through the use of high-resolution distributed fiber optic sensing. For this aim, fiber optics were embedded in 3D printed rings used for confining the soil in the test procedure. An analytical approach linking the measured spatially-distributed strain profile and the internal soil-ring contact stresses is developed in the paper. The method is based on representation of the contact stresses by a Fourier series expansion, and determining the coefficients of the series by minimizing the difference between the measured strain and the analytical strain within the linear elastic ring. The minimization problem results in a linear set of equations that can easily be solved for a given measurement. The approach is demonstrated on a set of drained DSS tests on clean sand specimens. Stress paths using the evaluated horizontal stresses are plotted together with Mohr circles at failure. These illustrate how, in these specific tests, the horizontal stress increases and principal stress direction rotates, until failure occurs along horizontal planes.

The Pleiades Volcanic Field (PVF) of northern Victoria Land (Antarctica) is made up of a dozen scoria cones whose erupted products present an unusually complete evolutionary trend from alkali-basalt to trachyte. With the aim of reconstructing the evolution of the PVF plumbing system, we have investigated the petrography and chemistry of main mineral phases using scanning electron microscopy (SEM-EDS) coupled with major element analyses using an electron probe microanalyser (EPMA-WDS). We further focussed on clinopyroxene phenocrysts obtaining a more detailed characterization by means of trace laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) element analyses coupled with machine learning thermobarometry. The results indicate that fractional crystallization and magma mixing are the major processes determining the development of the complete evolution trend. While fractional crystallization is a persistently active process in all parts of the plumbing system, mixing among differently evolved magma batches pertaining to the same association is responsible for the formation of intermediate compositions in the differentiation lineage at a specific pressure range (0.4–0.5 GPa). These processes are compatible with significant residence time of magmas at depth, resulting in multiple episodes of magma mixing, as testified by resorption and overgrowth textures in phenocryst assemblage occurring under isobaric conditions. The prolonged residence time likely increased the efficiency of the mixing process, leading to the formation of magmas with intermediate composition. In turn, the build-up of volatiles during the magma differentiation at depth could have favoured the eruption of these (variably differentiated) magmas. Considering that the PVF is situated in a glacial region, a process forcing long magma residence time can be envisaged associated with increased ice loading during glacial stages. This study specifically considers the ice fluctuations in the last 100 ka, theorizing the possibility of a climate-controlled volcano plumbing system. [ABSTRACT FROM AUTHOR]