ABSTRACT:

A geomechanical analysis of a shallow small scale landslide in the harbour of Saba was carried out to calculate the risk of new landslides and in order to advise local authorities on practical measures to improve safety. Geotechnical investigations and geological mapping were carried out to study the failure mechanism and slope stability. Comparison of shear box tests, field natural slope angle observations and calculations of slope stability probability showed a good agreement.

INTRODUCTION

In February 1997 a small scale landslide occurred on the island of Saba (Netherlands Antilles) in the Caribbean Sea. The landslide occurred during heavy rainfall in the harbour Fort Bay on the southern coast of Saba. The landslide is located along a road cut at the westerly part of the harbour. The unsafe situation on the slope was recognised quickly as a serious threat to historical building and harbour works at the toe of the slope (Figure 1). Initial site investigations and research were carried out because of large threatening boulders hanging halfway up the collapsed slope. Engineering geological studies were focused on deformation mechanism of the landslide, stability analysis and practical measures to increase safety. The studies have been carried out in corporation with Witteveen+Bos for the local governmental authority. The landslide is described as small scale, brittle and superficial with a depth of a less than 5m and a toecrown angle of approximately 50°. The Saba landslide has a width of 20m and a length of 30m (including the toe of the landslide) and is located at the southern side of Bunker Hill. According to the work of Varnes (1958) the landslide is classified as a debris slide: slip surfaces are not visible and large boulders are displaced significantly. The landslide occurred in a zone with slightly weathered volcanic deposits and slope debris.

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