Behaviour of model foundations on sand

  • A. Siraty

    Student thesis: Doctoral Thesis


    - The aim of the present research is to examine the behaviour of foundation/sand interaction under load at a pre-failure stage generally known as "Serviceability". The semi-full scale foundation used is a purpose designed bolted steel box, instrumented to measure contact stresses and displacements at selected points. Three types of foundation/sand interaction cases were examined, namely: smooth surface, rough surface and smooth embedded.
    The sand used was Leighton Buzzard, placed under controlled conditions in a 3.0m diameter by 3.0m deep concrete tank. The vertical and horizontal displacements of the sand were monitored using displacement transducers and inclinometers.
    - The former were also used to monitor the deformation of the foundation. Stress measuring transducers were installed at the underside of the foundation to record the normal and shear stresses at the soil/structure interface. Density changes within the sand were measured before and after loading.
    - Each test was controlled using a "Management" program. Raw data were recorded using a Data Logger which was interfaced with a micro computer.
    - Finite Element analysis was used to model the foundation/ soil behaviour and the testing environment. The variation of both displacements and stresses, once processed, was plotted with position. The results were then compared with experimental data using back analysis techniques. Various parameters were subsequently established and verified.

    The main findings of this investigation are:

    Contact stresses increase from zero to twin peak distributions positioned symmetrically about the centre line of the foundation.

    The variation of normal stress with depth is such that only residual stresses remain at a depth of z=2.0B.

    The inclusion of base roughness was found to mobilize the stresses and displacements in the sand within a boundary closer to the loaded foundation.

    The imposition of surcharge resulted mainly in increased magnitude of stresses and displacements while their variation with depth remained similar to those of the smooth surface condition.

    Both experimental and F.E. results indicated the existence of a zone referred to as the tensile zone, the depth and boundary of which depended on the characteristics of the foundation i.e. base roughness and depth of embedment.
    Date of AwardApr 1992
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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