Understanding ground deformation mechanisms during multi-propped excavation in soft clay

To maximize the utility of high land cost in urban development, underground space is commonly exploited, both to reduce the load acting on the ground and to increase the space available. The execution of underground constructions requires the use of appropriate retaining wall and bracing systems. Inadequate support systems have always been a major concern, as any excessive ground movement induced during excavation could cause damage to neighboring structures, resulting in delays, disputes and cost overruns. Experimental findings on the effect of wall stiffness, depth of the stiff stratum away from the wall toe and wall toe fixity condition are presented and discussed. © 2012 Taylor & Francis Group.

Spectroscopy of neutron-rich Dy168,170: Yrast band evolution close to the NpNn valence maximum

The yrast sequence of the neutron-rich dysprosium isotope Dy168 has been studied using multinucleon transfer reactions following collisions between a 460-MeV Se82 beam and an Er170 target. The reaction products were identified using the PRISMA magnetic spectrometer and the γ rays detected using the CLARA HPGe-detector array. The 2+ and 4+ members of the previously measured ground-state rotational band of Dy168 have been confirmed and the yrast band extended up to 10+. A tentative candidate for the 4+→2+ transition in Dy170 was also identified. The data on these nuclei and on the lighter even-even dysprosium isotopes are interpreted in terms of total Routhian surface calculations and the evolution of collectivity in the vicinity of the proton-neutron valence product maximum is discussed. © 2010 The American Physical Society.

Discovery of a new 2.3 s isomer in neutron-rich 174Tm

A new program of K-isomer research has been initiated with the 8π spectrometer sited at the ISAC facility of TRIUMF. We discuss in this paper the identification of a new 2.3 s isomer in 174Tm and its implications. © Società Italiana di Fisica / Springer-Verlag 2005.

The nature and origin of deep ocean clay crust from the Gulf of Guinea

Deep ocean sediments off the west coast of Africa exhibit a peculiar undrained strength profile in the form of a crust, albeit of exceptionally high water content, overlying normally consolidated clay. Hot-oil pipelines are installed into these crustal sediments, so their origins and characteristics are of great interest to pipeline designers. This paper provides evidence for the presence of burrowing invertebrates in crust material, and for the way sediment properties are modified through their creation of burrows, and through the deposition of faecal pellets. A variety of imaging techniques are used to make these connections, including photography, scanning electron microscopy and X-ray computer tomography. However, the essential investigative technology is simply the wet-sieving of natural cores, which reveals that up to 60% by dry mass of the crustal material can consist of smooth, highly regular, sand-sized capsules that have been identified as the faecal pellets of invertebrates such as polychaetes. Mechanical tests reveal that these pellets are quite robust under effective stresses of the order of 10 kPa, acting like sand grains within a matrix of fines. Their abundance correlates closely with the measured strength of the crust. While this can easily be accepted in the context of a pellet fraction as high as 60%, the question arises how a smaller proportion of pellets, such as 20%, is apparently able to enhance significantly the strength of a sediment that otherwise appears to be normally consolidated. A hypothesis is suggested based on the composition of the matrix of fines around the pellets. These appear to consist of agglomerates of clay platelets, which may be the result of the breakdown of pellets by other organisms. Their continued degradation at depths in excess of 1 m is taken to explain the progressive loss of crustal strength thereafter.

Optical properties of silicon rich oxides

Thermally treated silicon rich oxides (SRO) used as starting material for the fabrication of silicon nanodots represent the basis of tunable bandgap nanostructured materials for optoelectronic and photonic applications. The optical modelization of such materials is of great interest, as it allows the simulation of reflectance and transmittance (R&T) spectra, which is a powerful non destructive tool in the determination of phase modifications (clustering, precipitation of new phases, crystallization) upon thermal treatments. In this paper, we study the optical properties of a variety of as-deposited and furnace annealed SRO materials. The different phases are treated by means of the effective medium approximation. Upon annealing at low temperature, R&T spectra show the precipitation of amorphous silicon nanoparticles, while the crystallization occurring at temperatures higher than 1000 °C is also clearly identified, in agreement with structural results. The existing literature on the optical properties of the silicon nanocrystals is reviewed, with attention on the specificity of the compositional and structural characteristics of the involved material. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Modeling of strain rate effects on clay in simple shear

The response of clay is highly dependent on straining and loading rate. To obtain a realistic prediction of the response for time dependent problems, it is essential to use a model that accounts for rate effects in the stress-strain-strength properties of soils. The proposed model has been expanded from the existing SIMPLE DSS framework to account for the strain rate effects on clays in simple shear conditions. In accordance with the findings in the existing literature, soil response displays a unique relationship between shear strength and strain rate. The predicting model is illustrated with a limited test data. Copyright ASCE 2006.

Influence of Peripheral Velocity on Vane Shear Strength of an Artificial Clay

Shearing rate is among the most important factors affecting the undrained shear strength of clays. In particular, for seismic or storm-wave loading conditions, the shearing rate is much higher than that used in many common laboratory or field tests. The testing program described here evaluates the effect of peripheral velocity on the undrained strength inferred from the shear vane test. The study was conducted on a lightly cemented bentonite-kaolinite mixture manufactured in the laboratory, which possesses many characteristics similar to those of natural materials. Results show that the shear strength increases with increasing peripheral velocity, while the residual shear strength seems to be nearly independent of rotation rate.

Characterisation of a high plasticity marine clay using a T-bar penetrometer

A series of laboratory-scale T-bar penetrometer tests have been conducted on a clay bed virgin consolidated from reconstituted high plasticity marine clay. This investigation was mainly concerned with the effects on the penetration resistance of rate of penetration and the presence of free water on the surface of the clay bed. The rate of penetration varied between 0.005mm/s and 50mm/s. The results showed that the nature of soil resistance was 'undrained' over the range of speeds studied, and the resistance showed a marked viscous rate effect. The virgin consolidated clay bed exhibited an increase in penetration resistance by up to 35% for a factor 10 increase in rate of penetration much larger than values previously reported for kaolin. The presence of water on the surface of clay bed had a profound impact on penetration resistance, particularly on the remoulded strength obtained by taking the T-bar through successive penetration and extraction cycles. This was true even when the remoulding cycles were conducted without the T-bar breaking through the clay surface.