The connections between steel offshore platforms and their piles are generally made oy filling the annulus between each pile and its sleeve with cement grout. Existing design rules for these grouted connections were. derived from tests on relatively small diameter radially stiff piles. Recent _trends in offshore construction have led to the use of much larger diameter piles and the extrapolation of existing rules to this situation is questionable. This paper summarises the results of some 400 tests' on both full scale and accurate scale model sleeve to pile specimens carried out in connection with the design of seven major North Sea platforms. The validity of reduced scale modelling techniques is established.Ultimate strength is shown to. depend on the geometry of the connection, imperfections of the steel, and grout properties. Tests on plain pipes indicate that the reduction in radial stiffness which accompanies increases in pile diameter can lead to unacceptable reductions in ultimate strength. The addition of mechanical shear keys markedly improves bond strength by an amount which is independent of the type of grout, but a function of grout crushing strength and geome try.A conservative design approach is described and tentative recommendations are given for a more comprehensive design procedure which describes the effect of each important parameter on the connection strength.

Since the Forties Field FB Platform, my company has been involved in the design and installation of the following jackets in the British sector of the North Sea; Forties FD; Brent A; Claymore; Heather and Ninian. The Forties Field was underlain by normally consolidated clays, sands and at depth by overconsolidated clay. The other four fields are further north and are underlain by very hard clays and dense sands. No major pile installation problems were encountered at these northern sites. It was reassuring to find that the design methods used for planning pile installations work just as well for preconsolidated sands and clays as they do for normally consolidated soils.Professor T. J. Poskitt, Queen Mary College, London My comments are on the use of the wave equation in driveability analyses and on the problem of plugging.71. By any standards the piles used offshore are extremely large. Load testing is clearly out of the question and it is therefore natural for engineers to seek ways in which they can relate the soil resistance at the time of driving (SRD) to the static capacity. This is proving to be an extremely difficult job because the SRD is essentially a dynamic phenomenon which has to be studied by the wave equation. In addition pore pressure changes and thixotropy in the remoulded soil will produce time dependent changes which are difficult to predict analytically. These are areas of piling behaviour which are not fully understood and research is necessary in order to gain a better understanding of the mechanisms involved.72. The Authors give a comprehensive description of the use of the wave equation in drivability studies. In principle the wave equation is a powerful tool which will enable the designer to take into account the many different factors known to affect piles. However, in my experience considerable skill is needed if it is to give meaningful answers. Parameters such as quake,, damping factors etc., are as important as shear strength. This is not always sufficiently well appreciated by engineers and must have led to many disillusioned users of the wave equation. It is my opinion that where the wave equation is being used intensively as the Authors suggest in 0 7(e)-(g), the determination of the constants for use in the wave equation should have the same priority as is attached to other soil tests.

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