Engineering and Mineralogical Characterization of Okeluse Limestone Deposit, Dahomey Basin, Southwestern Nigeria

Abstract: Limestone is very useful for various purposes especially as chief raw material for manufacturing Portland cement which is the most common and extensively used adhesive in the construction industries. Hence, it is imperative in designing excavations in rocks to evaluate the mechanical properties and know the strength characteristics of the available rock materials so as to apply them to their appropriate uses. Thirty samples were collected from three different locations (ten from each) for analyses and their point load strength index, slake durability, natural moisture content, Schmidt hammer rebound values and their bulk density were determined as well as mineralogical composition. The limestone is found to be very durable as its slake durability after the first and second cycles ranges 99.68% and 99.34% respectively and falls within high strength rocks. It has low natural moisture content which accounts for the high strength of the rock. It was also observed that the uniaxial compressive strength (UCS) estimated with the aid of point load index has strong correlation than the UCS estimated with the aid of Schmidt rebound hammer values when compared with other parameters, this indicate that point load index is likely to be more accurate than that of the Schmidt rebound hammer. The average values of the point load test index of the samples from each of the three locations are 6.42, 5.91 and 5.67 respectively with Omi-Alayo phase 1 having the highest value. The average UCS ranges from 124.40 to 216.24Mpa, 93.06 to 228.48Mpa and 77.82 to 190.57Mpa respectively. Hence, the UCS for the three locations is 144.08Mpa. The average bulk density of the limestone is 2.64 which justify the high UCS values obtained from the Schmidt hammer rebound values which make the deposits at Omi-Alayo phase 1 and Phase 2 have a high UCS. It is observed that Omi-Alayo phase 1 has the lowest value of natural moisture content with 79% while the phase 2 has the highest with 99%. Result shows very low correlation and indirect relationship between the natural moisture content and the UCS values.

Limestone, rock mechanics, durability, geotechnical enginmeering

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