The development of shaft friction in semi-fullscale piles passing through granular soils

  • William Kay

    Student thesis: Doctoral Thesis


    The present study examines the load transfer mechanism and subsequent soil displacements around a 0.114m diameter pile passing through a sand stratum.

    The available literature on deep foundations is reviewed. It was found that the amount of literature pertaining to pile behaviour in layered soils was limited.

    A model pilot study showed that the most efficient means of eliminating end bearing, while simulating an underlying clay stratum, was by driving the base of the pile into a frictionless cylinder.

    The composite test pile incorporated load cells for the measurement of the load distribution. The sensitivity of the initial ‘Shell’ type cell was found to be insufficient at the smaller loads which were developed near the pile base. Subsequently, the more sensitive 'Core' type cell was designed and -proved satisfactory.

    The test pile was loaded in a 3m diameter by 3m deep concrete testing tank equipped with sand placement machinery and a dust extraction unit. Small plates, linked to transducers, were used to measure the sand displacements around the pile.

    A small dynamic probe was used to monitor the uniformity of placement and degree of compaction of each sand layer.

    A series of loading tests was carried out in loosely placed and compacted sand layers. The test data was recorded on punched tape. Processing and plotting of the test results was accomplished using the facilities of the DECsystem-20 computer. The results showed

    1. the stress transfer curves were similar to those proposed by Vesic, in sand, and those obtained by Meyerhof and Sastry in layered soils. No skin friction was developed at the top or the bottom of the sand,

    2. the vertical sand displacement decreased with increasing depth, radial distance, and sand density,

    3. the CRP, MLT, and pull-out tests showed that the skin friction was dependent on the direction and sequence of testing,

    4. an expression for the coefficient of earth pressure Ks along the pile shaft was determined, based on the experimental data. The values of Ks were found to increase with increasing density and to decrease with embedded length.
    Date of AwardNov 1980
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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