Influence of geometry on the bearing capacity of sheet piled foundations

Bored concrete piles are commonly used to support moderate loads from buildings in urban areas. At the end of their 25-30 year lifespan these structures are decommissioned but their foundations are left in place. These cannot be inspected hence the bearing capacity cannot be accurately verified. A hybrid foun- dation comprising sheet piles and a pilecap to mobilise shaft friction and end bearing was demonstrated to be a feasible and sustainable alternative to cast in-situ concrete piles. This research investigated the influence of sheet pile geometry on ultimate bearing capacity. A centrifuge test at 50 g was performed in over- consolidated clay where a square hybrid sheet pile group was ax ially loaded and vertical settlements recorded. Results indicated a square sheet pile group offers 70% greater capacity than a circular sheet pile group of similar surface area and 24% improved performance over the solid p ile loaded in the same test. Analysis of results suggested that the ultimate bearing capacity of the square sheet pile group compared with a solid pile of equivalent base area were within 0.2%, emphasising the importance of shape on capacity and the feasibility of the hybrid system as a viable foundation solution

Bearing Capacity of Sheet Piled Foundations

Bored concrete piles have been used widely on commercial developments in London for about the last 50 years. The life of a commercial building is between 25 – 30 years and, as each building is demolished and rebuilt, the piles from the previous buildings remain in the ground causing obstructions to the new foundations. This paper describes a preliminary study to explore the viability of sheet piled foundations as a genuine alternative to cast in situ concrete piles and all of the complications inherent in their construction and the obstruction they create to subsequent foundations. If it is possible to use steel piles as foundations they can be easily removed, recycled and will not cause obstructions for future developments. However, individual sheet piles have relatively low capacity when axially loaded and it is therefore necessary to consider a sheet pile group in conjunction with a pilecap, which can be considered a hybrid foundation; a combination of shallow (pilecap) and deep (sheet pile). A short series of centrifuge tests is reported in which model sheet pile groups in over-consolidated clay were loaded axially whilst vertical displacements were measured. Equivalent cast in place piles were similarly tested alongside the sheet pile groups by way of comparison

Autism in Special and Inclusive Schools: 'there has to be a point to their being there'

What kind of schools are most suitable for pupils affected by autism? This article reviews meanings of autism and autistic spectrum disorders (ASD). We report evidence from observations in schools and interviews with pupils and adults, drawing on a qualitative study of special education in two contrasting education authorities one with special autistic schools, the other with inclusive schools. Current theory, policy and practice in the education of pupils with autistic tendencies are discussed in relation to the data

Mapping urban infrastructure interdependencies and fuzzy risks

This is the final version of the article. Available from Elsevier via the DOI in this record.In this study, we considered the relationships between different types of CI and services to simulate possible cascading effects during extreme hazard conditions brought on by climate change and how to analyse impacts with limited data resources. An area in central Bristol, UK, was used as the case study to investigate the interdependencies among select assets and services. A wide range of plausible scenarios caused by pipe bursts in the area were simulated using the CADDIES 2D modelling framework, to identify the hotspots with high risk. The impact on CI, including water supply, electricity, wastewater, solid waste, transportation, telecommunication, and emergency services were assessed by the HAZUR tool. The analysis demonstrated that with limited data resources the dynamics of the interdependencies between CI networks can be highlighted and a basis of risk quantification can be established. The same procedure can be repeated to evaluate the impact of other types of hazards, or the compound hazard scenarios to provide a holistic assessment. Therefore, urban planners and managers can further explore options of interventions for setting up strategies to strengthen city resilience.This study is supported by the RESCCUE (RESilience to cope with Climate Change in Urban arEas) project, funded by the European Union Horizon 2020 research and innovation programme (Grant Agreement No. 700174)

Sheet pile groups as an alternative foundation solution to cast in-situ concrete piles

Concrete piles have become a common high load bearing foundation solutions providing end bearing and frictional resistance along the shaft. They are typically used for founding commercial or residential blocks with a design life of approximately 50 years. Following this the superstructure is decommissioned and may be demolished. However, piles are difficult to remove and therefore future developers can incur significant expense and programme delays in preparing the site to avoid obstructions. If removed, concrete piles are required to be broken down which is a slow and laborious process. However, a foundation solution has been developed that allows foundations to be installed and extracted with relative ease whilst still achieving a similar, if not improved capacity. This solution has been defined as a hybrid foundation comprising deep sheet piles for shaft resistance and a pile cap as a shallow foundation. The hybrid pile offers significant advantages over concrete piles include ease of installation, extraction, reuse and economy. Axial capacity of individual sheet piles is low, however geometrically arranging sheet piles; was shown to offer comparable or improved capacity over conventional concrete piles. The results from a series of centrifuge tests are presented in this paper

A method for creating larger clay samples with permeability anisotropy for geotechnical centrifuge modelling

Long-term ground movements associated with geotechnical constructions are predominantly caused by the dissipation of excess pore-water pressures and are governed by the permeabilities of both the soil and the geotechnical structure. Natural soil has inherent anisotropy due to the layering and structure as a result of the natural deposition process. A significant factor that influences the rate of consolidation and seepage in natural soils is that the horizontal permeability can be orders of magnitude larger than the vertical permeability. This is often considered in numerical modelling during geotechnical design however, due to the lack of reliable field measurements available, validating these numerical models can be difficult. Geotechnical centrifuge techniques have successfully been used to investigate responses to complex construction events but are, generally, models created from reconstituted soil. This results in models with well-defined but homogeneous properties. There is a fundamental difference between centrifuge models and natural soil deposits. As a result, centrifuge models are better suited to simulating the short-term response of the soil to a construction event. The work presented outlines a procedure for creating large clay models suitable for geotechnical centrifuge testing with a sedimented structure. These models have anisotropy of the horizontal and vertical permeability allowing for more representative soil behaviour (in terms of dissipation of pore-water pressures) which can be used to investigate the long-term movements resulting from geotechnical construction events

Tests of varied sample preparation methods for centrifuge modelling

Centrifuge modelling is an established technique capable of investigating the ground’s response to complex geotechnical events. Centrifuge models are often created from reconstituted soil, with well-defined boundary conditions and known soil parameters. Clay soil models may be prepared by mixing clay powder with distilled water to form a slurry. This slurry is placed within a soil container and subjected to a vertical stress (usually in a consolidation press or consolidated inflight). This creates an isotropic model but there is a fundamental difference between this soil model and naturally occurring soil deposits. The structure and fabric present within a naturally occurring clay is not reproduced by this preparation process. It is well-established that structure and fabric in naturally deposited soils are as significant in their effect on soil behaviour as, for instance, the stress history. Inherent structure and fabric within clay soils creates anisotropy which can vary with depth, this is particularly apparent when considering the permeability. Creating a soil model for centrifuge modelling with representative permeability anisotropy would allow for a better representation of consolidation driven events and the ability to observe long-term behaviour of complex geotechnical events. Currently, there are limited methods of doing so, leading to a considerable gap in knowledge associated with the behaviour of layered ground. This paper describes the development of the equipment and experimental procedure for quantifying the structure developed by different sample preparation techniques for centrifuge modelling

A Microchip CD4 Counting Method for HIV Monitoring in Resource-Poor Settings

BACKGROUND: More than 35 million people in developing countries are living with HIV infection. An enormous global effort is now underway to bring antiretroviral treatment to at least 3 million of those infected. While drug prices have dropped considerably, the cost and technical complexity of laboratory tests essential for the management of HIV disease, such as CD4 cell counts, remain prohibitive. New, simple, and affordable methods for measuring CD4 cells that can be implemented in resource-scarce settings are urgently needed. METHODS AND FINDINGS: Here we describe the development of a prototype for a simple, rapid, and affordable method for counting CD4 lymphocytes. Microliter volumes of blood without further sample preparation are stained with fluorescent antibodies, captured on a membrane within a miniaturized flow cell and imaged through microscope optics with the type of charge-coupled device developed for digital camera technology. An associated computer algorithm converts the raw digital image into absolute CD4 counts and CD4 percentages in real time. The accuracy of this prototype system was validated through testing in the United States and Botswana, and showed close agreement with standard flow cytometry (r = 0.95) over a range of absolute CD4 counts, and the ability to discriminate clinically relevant CD4 count thresholds with high sensitivity and specificity. CONCLUSION: Advances in the adaptation of new technologies to biomedical detection systems, such as the one described here, promise to make complex diagnostics for HIV and other infectious diseases a practical global reality