Summary of Modelling Safety Factors of Slope Stability in A Tar-Sand Quarry: A Case Study

Ajibola Rasidat Oyebamiji, Alao David Afolayan, Mopa Bassagi, Olarewaju Tajudeen


This research studies the importance of slope stability during open-pit mining of tar sand within the Dahomey basin, Southwest Nigeria. It involved the geotechnical characterization of the layers of Laterites and Alluvium which it underlies. In addition, SLOPE/W software of the GeoStudio package was utilized for deducing and modeling the bench face angles which had higher safety factors, through the Morgenstern Price method of slices. It was discovered that the lateritic soil layer possessed higher values of unit weight, cohesion and internal frictional angle than those of the Alluvial Sand layer. Factors of safety were generated for bench face angles ranging from 10o to 90o at 1m, 4m and above 40m groundwater levels; over a 10m bench width and 6m bench height. However, for heavy equipment, a bench width of 20m and height of 6m were assumed. This resulted in factors of safety varying between 3.58 and 1.73 for bench face angles between 10o and 30o during higher precipitation (and water tables). Thus, this suggests that stable slopes predominate at bench face angles of 10o to 30o. This can be further enhanced when sufficient drainage systems are constructed.



Dahomey Basin, Geotechnical Characterization, Open-Pit Mining, Tar Sand

Full Text:



S.O. Adegoke, B.D. Ako, E.I. Enu, S.W. Petters, A.C.W. Adegoke M.O. Odebode, W.O. Emofurieta (1976). Tar sand Project Phase II; Estimation of Reserves, Materials testing and Chemical Analyses. Unpublished report, Geological Consultancy Unit, Department of Geology, University of Ife, Ile-Ife, pp75.

O.S. Adegoke, A.C. Ibe, (1982). The Tar sand and Heavy Crude Resources of Nigeria. Proceedings of the 2nd International Conference on Tar sands and Heavy crude, pp 280-285.

S.O. Adegoke, B.D. Ako, E.I. Enu, S.W. Petters, A.C.W. Adegoke M.O. Odebode, W.O. Emofurieta, (1980). Geotechnical Investigations of the Ondo State Bituminous Sands. Report by the Geological Consultancy Unit, Department of Geology, University of Ife, Ile-Ife, pp25.

D.A. Alao. Nigerian Tar Sands: Potential for direct application in road pavement design and construction. A paper presented at the Southern interdisciplinary round table on African studies (SIRAS) March 30-April1st 2006, Kentucky State University Frankfort Kentucky 40601, USA.

D.A. Alao, M. Bassagi Modeling Safety factors of slope stability in a Tar-sand quarry: A Casey Study 1st Annual Civil Engineering Conference, University of Ilorin Nigeria 26-28 August 2009(p.185+195).

R.D. Adelu, E.A. Fayose (1991, August). Development prospects for the bituminous deposits in Nigeria. In Proceedings 5th UNITAR/UNDP International Conference on Heavy Crude.

S.I. Bankole, E. Schram, B.D. Erdtmann et al. (2006). Palynostratigraphic age and paleo environments of the newly exposed section of the Oshosun formation in the Sagamu Quarry, Dahomey basin SW Nigeria. NAPE Bulletin, 19(2), 25-27.

M. Bassagi (2007) Computer simulation of slope stability safety factors for tar sand quarrying at Loda Village, Ore Southwestern Nigeria.162p.M.Sc. Thesis submitted to Department of Geology, University of Ilorin. (Unpublished).

C.W. Duncan, C.W. Wyllie (2004). Rock Slope Engineering. 4th edition, spon press, UK. 480p.

E.I. Enu (1985). Textual Characteristics of the Nigerian Tar sands. Sedimentary Geology vol. 44, pp 65-81.

E.I. Enu, O.I.S. Adegoke, C. Robert, B.D. Ako, T.R. Ajayi, Adediran, S.A. A. Oriyomi, (1981). Clay mineral Distribution in the Nigerian tar sand sequence. In: Van Olphen and F. Variable (Eds.). International Clay Conference 1981. Development in Sedimentology, 35. Elsevier Amsterdam, pp 321-323.

H. Gebhardt, O.A. Adekeye, S.O. Akande (2011). Late Paleocene to Initial Eocene Thermal Maximum (IETM) foraminiferal biostratigraphy and paleoecology of the Dahomey basin, southwestern Nigeria. Jahrb. Geol. Bundesanst, 3, 407-419.

C.A Kogbe (Ed.). (1989). Geology of Nigeria. Rock View (Nigeria) Limited.

E.H. Mandzic (1992). Mineral water Risk in Open pit slope Stability. Mine water and the Environment, Vol. Ii No.4, pp 35-42.

W.L. Schroeder, S.E. Dickinson (1996), Soils in Construction, Prentice Hall.



  • There are currently no refbacks.

Creative Commons License
This work is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.