ABSTRACT:

Potential soil liquefaction is always a concern for structures located in seismically active regions. The phenomenon of liquefaction is the strength loss and subsequent fluid like behavior which may be exhibited by saturated soils during earthquakes. The main concerns for piles in liquefied soils are:

  1. loss of axial capacity leading to punching or pullout,

  2. loss of lateral capacity causing increased horizontal displacements, pile head damage, and lengthening of structure period and

  3. kinematic forces from lateral spreading or uncoupled movements of non-liquefied crust.

This paper presents a recent example of foundation design for a steel jacket in potentially liquefiable soils. The site is located in the Nile Delta offshore Egypt; partial liquefaction of the soils in the area is expected under the ductility level earthquake (DLE). Conditions at the site are particularly difficult, as the zone of liquefaction is expected at depth. In this case there is the risk that a non-liquefied soil crust will develop over the liquefied stratum. Similar conditions have caused significant well documented foundation damage in a number of recent earthquakes. The pile design required special attention to the potential effects of liquefaction. Specifically, design addressed loss of axial capacity, lateral resistance and kinematic soil-structure interaction with the non-liquefied crust. This experience shows that standard offshore foundations can be adapted to even these difficult conditions with minimal cost impacts

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