Physical modeling of the pile over pile condition

In certain conditions, the need may exist for installing an open ended pile over an already placed pile as a means of remediation or increasing the capacity of the existing foundation. The objectives of this program of testing were to investigate the presence of an existing pile's effect on the drivability of an outer pile, and on the pull-out resistance of an outer pile. Laboratory testing was conducted using normally consolidated test beds to model offshore conditions that would be reflective of the typical scenario in which such a method would be implemented. First, a series of tests were conducted with single piles to determine the set-up time for the inner pile. This set-up time was then used in the pile-over-pile tests to model a fully set-up condition for the existing pile. Three series of pile over pile tests were conducted, modeling various diameter ratios between the two piles. For each test series, three pile over pile tests were conducted in the same test bed, with a free field control test with a pile of the same diameter as the outer pile used as a comparison. A separate test bed was used to run seismic testing, with a geophone sensor array, to better understand how the properties of the test bed changed with time around the pile. The major conclusion was that there is no discernible increase in push-in resistance due to an inner pile, provided the piles do not come into contact. The pull-out capacity is similarly unaffected and is consistent with the prediction based on the API design method. If piles come into contact, the push in resistance increased. Spacers placed at the top of the inner pile were shown to mitigate the problem of pile to pile contact.