Rectangular silos; Interaction of structure and stored bulk solid

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The main aim of this research is directed towards the study of thin-walled rectangular planform silos with a view to maximising their structural efficiency. In thin plates of the type making up the wall, membrane action may increase the load carrying capability and current design guides make no account of this. Designing rectangular silos with this in mind can lead to significant structural savings. The core of the research involves using the finite element method to study the patterns of pressure exerted by the weight of a granular bulk solid on the walls of the silo structure. The stored granular solid must use an elastic-plastic material law in order to account for large deformations that can occur in a thin-walled structure. The need for this type of constitutive law led to the investigation of bulk solid properties and shows that parameters that have previously been used to categorise bulk solids may not be sufficient to describe all aspects of their behaviour. The finite element model created uses material constitutive laws that can be found in a number of packages. The required granular material parameters can be determined from a number of simple tests. This approach aims to enable engineers to routinely use similar models when designing silos. The results obtained from the finite element model exhibited some anomalies that had been observed in previous work. These were mainly apparent in the form of localised pressure peaks near the base of the model. These effects were investigated and possible mechanisms that lead to them were proposed. The results from the finite element model were compared to previous experimental work and existing theories. The model was then used to conduct parametric surveys on square and rectangular planform silos and the distribution of pressure across the wall compared to previous predictive models. Finally, a scale thin-walled metal silo was constructed and pressure measurements on filling with pea gravel made. These are compared to predictions made by the finite element model.Mr Chris Brow

Towards design rules for rectangular silo filling pressures

An experimentally validated finite element model of filling pressures in rectangular silos with flexible walls is used to predict the stress regime in the stored solid in squat and intermediate aspect ratio silos. The model predicts the state of stress in the stored solid and the pressures imposed on the flexible walls of the silo. The non-uniform horizontal pressure distributions at each depth at the end of filling are explored. It is known that an empirical relation for the horizontal pressure variation on each straight wall derived from experimental observations in an earlier study closely matches the computational predictions. The coefficients of this relation are found to vary with depth below the stored solid surface, and depend on the relative stiffness of stored solid and the silo wall. Following many calculations involving different solids, an empirical relationship is derived that is suitable for practical design for a range of different stored solids for which relevant properties are known. The resulting expression is well suited to the practical determination of filling pressures in rectangular silos, and provides a silo design pressure proposal that is based on theoretical, rather than empirical findings

Explanation for twin tunnelling-induced surface settlements by changes in soil stiffness on account of stress history

In this article, a group of representative centrifuge tests were selected for numerical modelling to explain the surface settlements induced by sequential twin tunnelling. Both Modified Cam Clay model (MCC) and Three-Surface Kinematic Hardening model (3-SKH) were adopted in the simulation, which indicated the use of 3-SKH model conduced to mimicking more closely centrifuge model response. Via performing more contrastive numerical analyses with 3-SKH model, the influence of the first tunnel event on the stiffness of the soil around the second tunnel was quantitatively investigated, whereby the mechanism behind the observed surface settlements was finally made clear

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

Aphelenchoides sp. destroying mushroom mycelium

RESP-357

An addendum for particle image velocimetry in centrifuge modelling

Image-based analysis is a growing field in geotechnical engineering and has a wide range of applications from measuring particle size distribution to observing the three dimensional internal deformation of granular materials. In centrifuge modelling, pre-failure deformation can be captured from the visible vertical plane of the models. This paper describes a new set-up for measuring a two dimensional displacement field using particle image velocimetry (PIV). The system makes use of the texture (intensity of pixel) of images to determine the accurate pattern of pre-failure ground movements. A complementary metal oxide semiconductor (CMOS) sensor is employed rather than a charged couple device (CCD) sensor used in previous studies. Three examples are presented: (1) synthetic experiment using a sliding bed equipped with LVDT behind the window of a strong box to make and measure controlled displacements; (2) strip footing test on glass ballotini under vertical loading; (3) ground movement generated during a shaft construction in clay. These examples provide a range of tests with artificial texture and demonstrate the most important parameters governing the experimental set-up and image analysis. The possibility of using PIV for grain scale investigations is dis-cussed. The study highlights the benefits of new technology and provides guidelines to minimise artefacts in image processing

Service user suicides and coroner's inquests

This is an Accepted Manuscript of an article published by Taylor & Francis in Criminal Justice Matters on 22nd May 2013, available online: DOI:10.1080/09627251.2013.805375The expansion of victimology in the 1980s produced a more nuanced understanding of victims and victimisation. Yet responses of government, criminal justice agencies, media and general public to victims are predictably and predominantly focused on victims of ‘conventional crime’. We challenge this perspective, thus widening the victimological lens. We discuss the impact of self-inflicted deaths and subsequent coronial inquests on practitioners working on behalf of the state

Stem eelworm attacking carrots

RESP-355