Jointing and rock slope stability in north-east Freetown, Sierra Leone

Abstract

Summary The main quarries producing quality aggregates for heavy civil engineering and road construction in Freetown can be found along the mountains directly overlooking the north-eastern area of the city. At these sites, the rocks are first dislodged by blasting after which they are crushed down to commonly required sizes. Recently, quarry owners have been beset by two problems arising from slope stability and the threat of closure resulting from claims for damage to private property. Previously the land around quarries was mainly wasteland but the scarcity of land in the city has led to an extension of the area of development so that a greater use is now being made of land occurring around and at the foot of quarry sites. This development has brought property owners directly into conflict with quarry owners who ironically are required to increase their output to meet increasing construction demands. To meet this demand, steeper slopes and more extensive faces are being excavated with the result that the frequency of accidents and instability has increased. This paper presents the results of a discontinuity survey undertaken to determine safe and economic slope inclinations and alignments in the area.