IDENTIFICATION AND ASSESSMENT OF PROBLEMATIC EXPANSIVE SOILS

Published ThesisIn the last few decades the construction of small dwellings, particularly government subsidy houses, has increased markedly in South Africa. Large numbers of these light structures have suffered severe damage and many have been demolished after being occupied for only a small fraction of their expected life-span. The research detailed in this thesis deals with a search for reasons for these widespread failures and investigations into economically feasible solutions. The investigation began with an assessment of the current methods of identification and assessment of potentially problematic expansive soils. This revealed serious shortcomings in a number of the standard testing procedures. These shortcomings may have consequences for a wider range of engineering projects than just housing development. Progress towards more reliable testing methods has led to an appreciation of the importance of variability of soil properties and the necessity of taking this into account in engineering design. Investigation of clay fraction determination by the hydrometer has led to the realization that the unreliability of this procedure has been a cause of failure in subsidy housing projects as well as other light structure developments. Assessment of expansive potential cannot safely rely on hydrometer determination of clay fraction, which is a principal parameter for a number of popular design procedures. It was also established that attractive alternatives in the form of automatic particle sizing equipment (designed for the analysis of industrial powders) are not suitable for natural soils containing the clays commonly found in South African soils. Alternative procedures, particularly small-scale suction testing, have been found to provide more reliable insights into design for expansive clays. The investigations suggest that some form of Reliability Based Design, which takes account of specific variability in soil properties, may be the only way to achieve rational design for foundations on expansive clay

The evolution of galaxies in massive clusters

We present a study of the evolution of galaxies in massive X-ray selected clusters across half the age of the Universe. This encompasses galaxies on the red sequence from the Brightest Cluster Galaxy (BCG) to the faint red population. We begin at the tip of the red sequence with an investigation into the near infrared evolution of BCGs since z =1. By comparing the BCG Hubble diagram and near-infrared colour evolution to a set of stellar population and semi-analytic models we constrain the evolution and formation redshift of these massive galaxies. Moving down in luminosity from the BCG, in chapter 3 we study the build up of the red sequence in massive clusters. To achieve this we compare the luminosity functions for red galaxies in a homogeneous sample of ten X-ray luminous clusters at z ~ 0.5 to a similarly selected X-ray cluster sample at z ~ 0.1. We quantify this result by measuring the dwarf to giant ratio to ascertain whether faint galaxies have joined the red sequence over the last 5 Gyr. In chapter 4 we study the evolution of the red sequence slope in massive clusters from z=l to present day. We compare our observed slope evolution to that predicted from semi- analytical models based on the Millennium simulation. We also look for trends between the red sequence slope and other cluster observables, such as X—ray luminosity, to investigate whether this will effect cluster detection methods which search for a colour-magnitude relation. In the final science chapter we present the details of our own cluster detection algorithm. This simple algorithm is based on finding clusters through the near-infrared and optical properties of the red sequence, drawing on our galaxy cluster evolution research. We describe the application of the algorithm to object catalogues from the UKIDSS DXS fields in order to find clusters at z ~ 1. To confirm the presence of the clusters we employ deep multi-object spectroscopy on the photometric members. The clusters found in this study are fed back into the high redshift regime of our galaxy evolution research

Duplicate Testing Conducted On The Input Parameters For The Estimation Of Potential Expansiveness Of Clay

Conference: 16Th African Regional Conference on Soil Mechanics and Geotechnical Engineering, At unisia, Volume: Innovative Geotechnics for Africa - Bouassida, Khemakhem & Haffoudhi (Eds.) 2015This paper presents a study conducted on three active clay soils analysed at seven commercial laboratories in South Africa. Commercial test results are often used as input parameters for prediction models used to estimate potential heave expected from active clays, especially when designing foundations for light structures. This paper briefly looks at the typical results obtained from such laboratories and comments on the correlation achieved

The moose, purine degradation, and environmental adaptation

It is accepted that allantoin is the end-product of purine degradation in mammals, except that uricase activity has been lost during the evolution of humans in which uric acid protects the brain from oxidative damage. However, we have found that the moose Alces americanus excretes extremely low urinary concentrations of allantoin and high concentrations of uric acid very similar to those of humans. Exposure to extreme cold is known to cause oxidative damage, and we suggest that the retention of uric acid by the moose represents an adaptation enabling the species to survive at high latitudes.Weiqi Zhang, Philip Stott, Minghai Zhan

Changing trends in the management of intertrochanteric hip fractures - a single centre experience

With an annual incidence greater than 65,000 in the UnitedKingdom, hip fractures are a common but debilitating injury predominantlyaffecting those over 65. Treatment is based on the anatomical location ofthe fracture relative to the capsule of the hip joint - fracturesoccurring within it are treated by arthroplasty, while extracapsularfractures are an indication for fixation. Intertrochanteric fractures arefurther grouped as stable (AO/OTA 31A1/A2) or unstable (31A3) which inturn governs in the current UK guidelines whether this fixation isachieved with a dynamic hip screw or intramedullary device. Anecdotally,some units are tending towards intramedullary devices for 31A2 fracturesas well, a practice which from the evidence does not appear to conferbenefit and carries an excess cost. We reviewed our data submitted to theNational Hip Fracture Database over the last five years and identifiedall intertrochanteric fractures, from which cohort we identified allpatients with 31A2 fractures by review of radiographs. The cohortcomprised 370 patients. We then recorded age, gender, ASA grade,abbreviated mental test score, residence from where admitted, length ofstay, destination on discharge and whether any further operations wererequired. There was no significant difference in the demographics of thegroups, year-on-year, except gender mix. There was a significant, twentyfoldrise in the use of intramedullary devices between 2011 and 2015.Length of stay, length of overall episode of care, revision rates,mortality and destination on discharge were unchanged. This use is notsupported by NICE guidelines and this study offers no evidence tocontradict this position. We advocate all centres examine their practiceto avoid a costly intervention without clinical benefit

Stratospheric Flow during Two Recent Winters Simulated by a Mechanistic Model

The authors have used a spectral, primitive equation mechanistic model of the stratosphere and mesosphere to simulate observed stratospheric flow through the winters of 1991–92 and 1994–95 by forcing the model at 100 hPa with observed geopotential height. The authors assess the model’s performance quantitatively by comparing the simulations with the United Kingdom Meteorological Office (UKMO) assimilated stratosphere– troposphere data. Time-mean, zonal-mean temperatures are generally within 5 K and winds within 5 m s⁻¹; transient features, such as wave growth, are mostly simulated well. The phase accuracy of planetary-scale waves declines with altitude and wavenumber, and the model has difficulty correctly simulating traveling anticyclones in the upper stratosphere. The authors examine the minor warming of January 1995 which was unusual in its depth and development and which the model simulated fairly well. The authors also examine the minor warming of January 1992, which the model missed, and a major warming in February 1992 that occurred in the model but not in the observations

Interpretation and application of carbon isotope ratios in freshwater diatom silica

Carbon incorporated into diatom frustule walls is protected from degradation enabling analysis for carbon isotope composition (δ13Cdiatom). This presents potential for tracing carbon cycles via a single photosynthetic host with well-constrained ecophysiology. Improved understanding of environmental processes controlling carbon delivery and assimilation is essential to interpret changes in freshwater δ13Cdiatom. Here relationships between water chemistry and δ13Cdiatom from contemporary regional data sets are investigated. Modern diatom and water samples were collected from river catchments within England and lake sediments from across Europe. The data suggest dissolved, biogenically produced carbon supplied proportionately to catchment productivity was critical in the rivers and soft water lakes. However, dissolved carbon from calcareous geology overwhelmed the carbon signature in hard water catchments. Both results demonstrate carbon source characteristics were the most important control on δ13Cdiatom, with a greater impact than productivity. Application of these principles was made to a sediment record from Lake Tanganyika. δ13Cdiatom co-varied with δ13Cbulk through the last glacial and Holocene. This suggests carbon supply was again dominant and exceeded authigenic demand. This first systematic evaluation of contemporary δ13Cdiatom controls demonstrates that diatoms have the potential to supply a record of carbon cycling through lake catchments from sediment records over millennial timescales

VIS3COS:III. nature and nurture in galaxy structure and morphology

We study the impact of local density and stellar mass on the morphology of ~500 quiescent (Q) and SFGs from the VIS3COS survey. We perform B/D decomposition of the SBPs and find ~41% of 10^10 Msun galaxies to be best fitted with 2 components. We complement our analysis with non-parametric measurements and qualitative visual classifications. We find that galaxy morphology depends on stellar mass and environment for our sample as a whole. We only find an impact of the environment on galaxy sizes for galaxies more massive than 10^11 Msun. We find higher n and B/T in high-density regions when compared to low-density counterparts at similar stellar masses. We also find that higher stellar mass galaxies have steeper light profiles compared to the lower ones. Using visual classifications, we find a morphology-density relation at z~0.84 for galaxies more massive than 10^10 Msun, with elliptical galaxies being dominant at high-density regions and disks more common in low-density regions. However, when splitting the sample into colour-colour selected SF and Q sub-populations, there are no statistically significant differences between low- and high-density regions. We find that Q galaxies are smaller, have higher n, and higher B/T when compared to SF counterparts. We confirm these trends with non-parametric quantities, finding Q galaxies to be smoother and having most of their light over smaller areas than SFGs. Overall, we find that the dependence of morphology on stellar mass is stronger than with local density and these relations are strongly correlated with the quenching fraction. The change in average morphology corresponds to a change in the relative fractions of blue disk-like galaxies and red elliptical galaxies with stellar mass and environment. We hypothesize that the processes responsible for the quenching of SF must also affect the galaxy morphology on similar timescales