The Development of Shaft Friction and End Bearing for Piles in Homogeneous and Layered Soils

  • S. N. Wersching

    Student thesis: Doctoral Thesis


    This thesis examines the behaviour of a 114.0 mm diameter segmental tubular steel pile jacked into loose sand, and loose sand overlying clay. The soil was placed under controlled conditions in a 3.0 m diameter by 3.0 m deep concrete tank.

    The variation in local unit shaft friction and radial effective stress was monitored along the pile shaft, together with the distribution of axial load within the pile. Density changes within the sand were recorded at the end of pile installation. Vertical displacements and vertical effective stresses within the sand were recorded. In the case of the layered soil profile the shear and vertical effective stresses generated on the sand/clay interface were monitored.

    Data from both the pile and soil instrumentation was recorded throughout pile installation and load testing, consisting of CRP, ML and CRU tests, by an Orion Data Logger which was interfaced with a Commodore PET micro computer. Each stage of the test was controlled by a 'Management' program, written by the author. This also recorded the incoming raw data on a floppy disc and reduced the raw data, outputting a hard copy as the test proceeded.

    The results showed:
    (i) The local unit shaft friction and radial effective stress is practically constant along a pile shaft in sand for a given pile embedment, and increases at a diminishing rate with pile embedment.
    (ii) The average coefficient of earth pressure, K , at ultimate load in loose sand exceeds Kp for shallow pile embedments.
    (iii) At full pile embedment and ultimate load the local coefficient of earth pressure, Kza, may greatly exceed K_ near the top of the pile and tend to a lower limiting value of 0.5 near the pile base.
    (iv) Axial stresses within the sand around the pile shaft are reduced by the development of arching. Adjacent to the pile shaft the radial effective stress is the major axial stress.
    (v) The development of shaft friction is directly related to displacements within the surrounding sand and on the sand/clay interface.
    (vi) The presence of an underlying clay layer effects the development of shaft friction to a limited height above the sand/clay interface.
    (vii) The drawdown of sand into the underlying clay had a direct
    effect the local unit shaft friction developed within the clay.

    Date of AwardMar 1987
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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