Analysis of shallow and deep foundations using soil-structure interaction techniques

  • Anthony James Jones

    Student thesis: Doctoral Thesis


    Methods of analysis are presented which enable the performance of both piled and plain raft foundations to be predicted. Throughout the work the substructure is modelled using a beam-column idealization. This allows the superstructure configuration to be readily incorporated into the model enabling the soil-structure interaction of the complete system to be investigated.

    The supporting soil is modelled using a discrete spring representation as in the simplified subgrade reaction theory (S.S.R.T.). The idealized model is analysed using a standard structural program. Relationships are developed between spring stiffness values and soil moduli for a range of axially and laterally loaded pile-soil configurations. The results are verified by comparison with more rigorous solutions and the measured performance of single piles.

    The work is extended to consider the interaction of axially and laterally loaded pile groups and piled raft foundations. A simplified treatment of interaction is proposed for approximately uniformly loaded piles. For piles which carry substantially different loads due to interaction effects, a more rigorous procedure is presented.

    Consistent matrices are presented to idealize the uniform distribution of soil stiffness along both axially and laterally loaded pile elements. Parametric studies demonstrate that very few elements are required to model laterally loaded piles. The S.S.R.T. method indicates that the results are very sensitive to the number of pile elements used.

    The limitations of the proposed method for the analysis of plain raft foundations is investigated. It is demonstrated that soil-structure interaction generally cannot be modelled by varying the soil stiffness across the raft. Consequently, a method of analysis is developed which combines the grillage idealization with the Surface Element Method. A program is developed for the analysis which incorporates the superstructure configuration. The proposed method is verified by comparison with results from the measured performance of existing buildings and other rigorous solutions.

    Finally, the combined S.S.R.T./stiffness approach is successfully developed to predict the non-linear performance of single piles. This is achieved using established non-linear load-displacement curves. The solution process involves less iterations than traditional non-linear methods. The computed results are correlated with the measured performance and other solutions of both axially and laterally loaded piles.
    Date of Award1991
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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