Computer Modeling of Slope Stability in Mining the Tar Sands of South Western Nigeria

Only available on StudyMode
  • Download(s) : 599
  • Published : February 18, 2011
Open Document
Text Preview
40E

80E

120E

120N

TERTIARY

COMPUTER MODELING OF SLOPE STABILITY IN MINING THE TAR SAND OF DAHOMEY BASIN, SOUTHWESTERN NIGERIA David Afolayan ALAO and Mopa BASSAGI DEPARTMENT OF GEOLOGY AND MINERAL SCIENCES, UNIVERSITY OF ILORIN P.M.B. 1515, ILORIN, KWARA STATE, NIGERIA Abstract The need to have stable slopes in open pit mining of the tar sand deposit of the Dahomey Basin, Southwestern Nigeria is emphasized in this study. In the Loda village, Southwestern Nigeria, samples of the lateritic soil and alluvial sand which overlie the tar sand occurrence were subjected to geotechnical tests. Computer simulation of bench face angles was carried out using the SLOPE/W software to determine the bench face angle(s) with the least susceptibility to failure. Slope failure might lead to loss of lives and valuable heavy equipment thus increasing overall expense of running the mine. Geotechnical tests carried out helped to determine the unit weight (g), cohesion (c) and angle of o friction (f) values. For the lateritic soil, g = 25 kN/m3, c = 45 kPa and f = 41 . Also, values of g = 18 3 o kN/m , c = 0 kPa and f = 34 were obtained for the alluvial sand. These values were inputted into the software program to simulate different bench face angles that could be cut into the two lithologic o o units. Factor of safety values were obtained for 10 to 90 bench face angles at 1 metre, 4 metres and greater than 40 metres ground water level, respectively. 10 metre bench width and 6 metre bench height were used while 20 metre bench width and 6 metre bench height were also utilized to make room for heavier equipment. Factor of safety values ranging between 3.58 and 1.73 were obtained o o for bench face angles between 10 and 30 making this range least susceptible to failure even when inundation is considered. Consequently when mining commences, a utilization of slope angles ranging from 10 to 30 coupled with adequate drainage conditions like digging of perimeter trenches and use of submersible pumps would go a long way in ensuring optimum output for huge economic gain and revenue generation. This will make Nigerian tar sand exploitation viable for sustainable growth of the economy of the country in the foreseeable future. ________________ Corresponding author: Tel. +2348037553842 E-mail address: lomalao@yahoo.com o o

Stratigraphic correlation chart
90N
Abuja

0.8m

Lateritic overburden (LD1C)

1.0m

Lateritic overburden (LD2C) Reddish brown loose sand (Alluvium) (LD2B)

Table 2: Coefficients of permeability for the samples analysed, using Hazen's formula 1.5m

Lateritic overburden (LD2C)

Table 5: Dry density values of samples obtained from the study area Sample No LD1A LD1B LD1C LD2A LD2B LD2C LD3A LD3B LD3C Dry Density (Mg/m ) 1.77 1.82 2.62 1.85 1.88 2.56 1.89 1.90 2.54 (degrees) 10 20 30 40 50 60 70 80 25 18 45 0 41 34 90 Morgenstern-Price Method of Analysis Slope Angle Piezometric Piezometric Piezometric Level 1 m 3.37 2.03 1.56 1.35 1.18 1.05 0.79 0.65 0.35 Level 4 m 3.91 2.26 1.61 1.39 1.37 1.24 1.22 1.07 1.02 Level >40 m 4.20 2.44 1.82 1.58 1.51 1.35 1.25 1.15 1.09 Morgenstern-Price Method of Analysis Slope Angle Piezometric Piezometric Piezometric (degrees) 10 20 30 40 50 60 70 80 90 Level 1 m 3.58 2.41 1.73 1.66 1.52 1.19 0.96 0.83 0.59 Level 4 m 4.20 2.66 1.85 1.51 1.30 1.42 1.28 1.18 1.02 Level >40 m 4.51 2.72 2.16 1.85 1.82 1.59 1.40 1.25 1.09 Table 7. Table showing factor of safety values obtained for different models of bench face angles using a bench width of 10metres and bench height of 6metrres. Table 8. Table showing factor of safety values obtained for different models of bench face angles using a bench width of 20metres and bench height of 6metres. 3

AGE

EOCENE

Lagos

Loda

Akure

30N

PALEOCENE MAASTRICHT IAN TURONIAN BERREMIAN

CRETACEOUS

ABEOKUTA GROUP

Study Area Phanerozoic Sediments Cretaceous –Recent Sediment Pre-Cambrian basement Complex 0 300Km

FORMATION Ako et al.,...
tracking img