An effective way of increasing the stability of quays

Abstract

The design of the main wall of the sheet-piled quay of the general cargo berths at Umm Said, Qatar, called for the excavation of a trench in the rock over which an embankment was constructed, the sheet piles were driven and excavation in front of the wall and backfilling behind it then proceeded in the usual manner. This resulted in a silt layer accumulating in the bottom of the trench considerably reducing the stability of the wall under full operating conditions. The circumstances that led to the presence of the silt layer and the mechanics whereby it was formed were investigated. A scheme involving the drilling and pumping of sand columns in front of the wall was foreseen as a viable solution. A laboratory and field testing programme on different mixes was undertaken to assess the behaviour and design characteristics of the columns, and to check the durability. Empirical equations relating the standard penetration test values to the unconfined shear strength of the strengthened soil were established. The interaction between the stabilized mass and its neighbouring soil and wall were studied by a plane-strain, finite-element programme and the minimum area to be stabilized determined by examining horizontally the shear stress pattern of the soil in proximity of the wall. Extensive deformation measurements of the wall showed the appropriateness of the parameters used in the analysis and the effectiveness of the method in arresting the wall displacements.