Browsing by Author "Kyulule, Ananias L."

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    Residual shear strength of tropical soils.
    (University of Dar es Salaam, 1977) Kyulule, Ananias L.
    For many years failure of slopes and earth-structures has been a matter of concern to civil Africa where little investigation (if any) has been done so far to combat these problems. To obtain economical and satisfactory results an engineer involved in handling landslide, slope instability and embankment design problems should have the knowledge on residual strength of soils. This research has been carried out, therefore, in order to obtain some residual strength values of tropical soils as a start to tackle such problems. A literature review on residual strength of clays from temperate zones is presented and discussed in this paper. Since residual strength values obtained in temperate countries using the ring shear apparatus are quite reliable and easy to analyse, it was decided to use the same device for this purpose. Eleven soils samples mainly from Tanzania and few from West Africa have been investigated in the Soil Mechanics Laboratory of the University of Dar Es Salaam. These soils are bentonite, black cotton soil, pumice, volcanic ashes, lateritic soil, micaceous soil, Accra shale and weathered mudstone. The descriptions and properties of the soils are also presented. Also presented in this paper is the general layout of the ring shear apparatus as assembled in the Faculty of Engineering, Dar Es Salaam. Essentially the apparatus consists of divided confining rings (outer diameter = 24cm, inner diameter = 16cm) and the sample thickness is 16mm. The testing techniques are fully narrated in the text. Only remoulded samples have been tested. The results of ring shear tests and a discussion on them is also presented in the paper. The residual shear strength values of tropical soils cover a wide range. Bentonite and black cotton soil exhibit angles of residual shear strength fr of about 8.50 and 110; brittleness indices (IB) of 57% and 50% respectively. The Accra shale and weathered mudstone give somewhat higher fr values (»220) and much lower IB value (16-34%). The highest fr values (»300) and the lowest IB values (<2%) are given by volcanic ashes and residual soils (lateritic and micaccous soils).