Infrastructure Engineering - Theses

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    Free surface flow in a circular conduit: a theoretical and experimental investigation of the influence of velocity distributions on flow behaviour
    Grigg, W. L. ( 1963)
    General Introduction: Since Chezy first proposed his well known equation for uniform flow in open channels, many other formulae have been suggested, either to replace the Chezy expression or form determining the value of the coefficient C. Perhaps the major objection to the use of these formulae is that no account is taken of the variation of the boundary effects with Reynolds number — although in some cases this is done indirectly by relating Chezy’s C to the hydraulic mean radius. Following more recent work, notably by Prandtl, there have been attempts to produce relationships between Chezy’s C, Reynolds number and a roughness parameter, (similar to those which exist for pipe flow) but these habe not been generally applied as the effects of the free surface and unsymmetrical flow conditions have not yet been fully evaluated.
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    Stress distribution in discontinuous media
    Chappell, B. A. ( 1967)
    The determination of the stress distribution within a semi infinite medium, which in fact is an infinitely redundant structure, becomes complex when all the relevant factors such as material characteristics, discontinuity patterns, loading conditions and boundary restraints are considered. This complexity is further accentuated when the material has a non-linear stress-strain relationship and a condition of residual stresses associated with the insitu state. Hence as an initial study the blocks making up the semi infinite medium are considered as homogeneous, isotropic and linear elastic. In this particular study, boundary tractions represented in the form of model foundations are applied to a semi infinite medium of uniform characteristics. That is Young's modulus and Poisson's ratio are constant and the discontinuities are controlled in a horizontal and vertical direction. The stresses within the models are determined by applying photoelastic techniques. Analytical and numerical solutions are developed so as to compare results with those obtained experimentally and subsequently define behaviour patterns. Stress distributions at the contact zone between the foundation and subgrade are also studied. The subgrade is initially studied with no side restraint, however in the latter models a side restraint is applied. Studies on an opening in a discontinuous semi infinite subgrade with surface loading are also made. The relatively low stress fields set up in the subgrade require a much more sensitive photoelastic material than is generally encountered. This sensitivity however, should not be acquired at the expense of reducing Young’s modulus. A material meeting this requirement is Araldite D, with an appropriate hardener. The use of this material however requires the development of careful and precise casting techniques. These techniques are fully covered in the thesis presented. To corroborate the experimental findings with an analytical theory which to date is incompletely defined, a review of the fundamentals controlling the stress distribution is essential. The usual requirement of satisfying compatability of strain at the interface is not always satisfied. This appears to affect the stress-strain relationship, in both a micro and macro scale, and hence the stress distribution and redistribution. Four numerical methods of obtaining an approximate solution to a required degree of accuracy are presented and compared with the experimental work. 1) Finite difference approach. 2) Finite element method. 3) Boundary Singular Integral solution. 4) Energy principle approach. It is concluded that the energy principle offers the most promising approach of determining the stress distribution in a nonlinear elastic-plastic semi infinite discontinuous subgrade. Finally the possibilities of failure conditions within the rock being initiated by environmental changes such as surface loads, excavations and tunnelling are considered.
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    A sediment-routing model for alluvial streams
    Wellington, Neil Bruce ( 1978)
    Using the complete one-dimensional equations of momentum and continuity of fluid-flow, the one-dimensional equation of sediment continuity and several appropriate transport relations, a computer simulation model is derived which is capable of routing flow and sediment through a channel reach with a moveable bed and irregular boundaries. Sediment is assumed to be transported in two modes; as suspended-load and as bed-load. The bed-load transport rate is assumed to react instantaneously to local alterations in flow conditions, while the suspended-load is assumed to take a finite time to react to local flow changes. For non-uniform bed-sediments, the total contribution to erosion or deposition at each computational point in the channel is obtained by summing the individual bed-elevation changes arising from changes in the bed-load and suspended-load for each size fraction. Flow conditions computed by the flood-routing component are then adjusted to allow for erosion or deposition before computations proceed to the next time increment. The concept of erosion probabilities, introduced by Einstein (1950) is used, along with implicit allowance for the occurrence of bed-forms on the stream bed. Several examples of model performance are presented, in which the effects of several significant parameters are demonstrated.