This study investigates physical and mechanical characteristics of the Pleistocene coral limestone of Kenya's coastal plain by laboratory experiments based on ASTM standards. The experiments have done include uniaxial compression test, indirect tensile test, ultrasonic pulse velocity (UPV) test, saturation porosity for porosity and direct shear test. Engineering properties of brittleness, Schmidt's rebound number, fracture index and drillability index are calculated from empirical equations based on the tensile strength and uniaxial compressive strength available in published literature. The various moduli are also calculated from equations based on the P-wave and Swave velocities from UPV test. The average values of the investigated physical properties include bulk density (2199kg/m 3 ), porosity (8.47%). The average investigated mechanical properties values include uniaxial compressive strength (16.41MPa), tensile strength (1.61MPa), Elastic modulus(31.62GPa), cohesion(133.33kPa) and friction angle (410). The P-wave and S-wave velocities are 4797m/s and 2288m/s respectively. The results presented in this work highlight the influence of rock porosity as an inherent structural feature that affects intact rock properties. The results are discussed with a focus on the variation of properties with porosity, with the conclusion that empirical relationships developed for porous rock should include porosity as a parameter which contributes to variations in rock properties. This paper presents the first published geomechanical data of coral limestone from the reef coral rock formation making up Kenya's coastline.

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The stability of underground excavations has become an important issue in order to extend underground mining operations and extract deeper deposits. The increasing demand for Tin-Tungsten (Sn-W) for industry and its market price has created a motivation for mining companies to extract deep-seated Sn-W ore deposits in Myanmar. Thus, this paper aims to investigate the stability of underground openings, especially, the stope with considering the mining methods. To meet the objective, FLAC 3D 5.0 simulation was used for the assessment of stope under different stress ratios, 0.5, 1.0, and 1.5 for two types of underground mines; Open stoping and Cut and Fill stoping. The results show that the risk of instability of stope is high under the stress ratio of K = 0.5 than that of K = 1.0 and K = 1.5 in both mining methods. However, the stability of the stope in open stope method is lower than that of cut-and-fill method obviously. This result shows that the appropriate mining method has to be selected for extraction of Sn-W deposit carefully in terms of the balance of safety and cost.

The investigation of the influence of in situ stress in Open Pit Mine (OPM) projects has not been accorded a deserved attention despite being a fundamental concern in the design of underground excavations. Hence, its long-term potential adverse impacts on pit slope performance are overly undermined. Nevertheless, in mines located in tectonically active settings with a potential high horizontal stress regime like the Songwe mine, the impact could be considerable. Thus, Using FLAC3D 5.0 software, based on Finite Difference Method (FDM) code, we assessed the role of stress regimes as a potential triggering factor for slope instability in Songwe mine. The results of the evaluated shearing contours and quantified strain rate and displacement values reveal that high horizontal stress can reduce the stability performance of the pit-wall in spite of the minimal change in Factor of Safety (FoS). Since mining projects have a long life span, it would be recommendable to consider “in situ stress-stability analyses” for OPM operations that would be planned to extend to greater depths and those located in tectonically active regions.