ABSTRACT:

In this paper the performance of an instrumented landfill resting on soft silty and clayey soils with vertical wick drains is discussed, and the results of a numerical back-analysis of the main parameters controlling the consolidation process are presented. The test was performed in Egypt, within the Nile Delta area. A 2.5m thick sand-fill was laid throughout the plant area, and the wick drains were installed to speed up primary consolidation in a soft shallow formation (Unit 1). The test zone was selected in the centre of the plant area, far from the fill edges. The instrumentation included surface settlement plates, deep settlement monitoring devices and a few piezometers. The numerical settlement analysis confirmed that Unit 1 is overconsolidated as inferred from strength measurements, and showed that the behaviour of the wick drains was satisfactory and predictable, in spite of the scattered results of the cone dissipation tests. The computed pore pressure variations match reasonably well with the recorded values. A thicker delta-clay formation, which is not affected by the drains, might be slightly overconsolidated due to ageing, but the settlement in this unit was too small to reach a final conclusion.

INTRODUCTION

Vertical wick drains are often adopted, in combination with a surface surcharge, in order to improve soft clayey soils. Although experimented design methodologies are today available (e.g. Barron, 1948; Hansbo, 1981), prediction of the settlement vs. time relation involves uncertainties due to the many variables affecting the consolidation process. In The test was performed during construction of a gas and condensate treatment plant owned by the Petrobel Belayim Petroleum Company, Egypt. The site lies on the Mediterranean coast about 10km West of Port Said, within the Nile delta area, and is adjacent to the Manzala Lake. The site elevation is close to the mean sea level.

This content is only available via PDF.
You can access this article if you purchase or spend a download.