Geotechnical analysis of slope failure at a Kaolin quarry

                          ABSTRACT

Over 40 complexes of the younger granites of Nigeria are found on the Jos plateau. The Ganawuri complex is one of the high level granitoid bodies in the Younger Granite Province. During the period of this research, a massive kaolin deposit at Kurra was studied. The sequence of the studied area comprises of five layers: a lateritic layer, an older basalt layer, reddish kaolin, pure white kaolin and a migmatite layer. It has been proposed that the kaolin formed as a result of the hydrothermal alteration of the migmatite. Mining activities are presently been carried out on site and slope movements have been noticed in form of slides in the sequence. Instability of slopes may be as a result of internal and external factors which include the effect of ground water and pore water within the rock and also human activities.

Samples were collected from each of the layers in the sequence for analysis. Soil properties such as moisture content, unit weight, specific gravity, plastic limit, liquid limit, plasticity index, cohesion and angle of internal friction were obtained from the samples. The mineral constituent of the samples were determined by XRD analysis. Furthermore, the factor of safety was calculated by the Morgernstern- Price method using Geostudio slope/w software.

Results from engineering tests indicate that soils are of CL group having low to medium plasticity and a high bearing capacity. XRD analysis shows that the sample consists of talc, kaolin, smectite, illite, gibbsite, ilmenite, heamatite and others. From the amount of the minerals it is deduced that the samples have low shrinkage and swelling potential. Using Geostudio slope/w software the factor of safety was calculated as 2.84 in the rainy season. This value indicates that slope failure is not immediate in this area since sampling was done during the rainy season when materials are most susceptible to failure. It is recommended that better methods be used in mining the kaolin and mining should be done within the safe angle provided by the Geostudio slope/w