Search

Dump slope failure has become a recurring incident in Nigeria's major mine sites while the visible signs of instability in Nigeria's waste rock dumps are the most dangerous situation. This paper aims to present intrinsic poor safety conditions of dump slopes in Nigerian mines. Twenty-one samples were collected from three mining provinces (7 samples from each province) and were subjected to various geotechnical tests such as particle size distribution, Atterberg limits, triaxial, compaction, consolidation and permeability tests. Results obtained were analyzed using numerical simulation models. From the laboratory data, the waste dumps were proven to be cohesive materials despite their high sand content. The wastes were described by the geo-mechanical characterization of the samples as competent materials with moderate strength and low compressibility, indicating materials with intermediate engineering capabilities. However, both field observation and numerical simulation of the waste dumps revealed that high slope height and angle, as well as excessive material saturation caused by high seasonal rainfalls, could compromise the stability of the dump slopes. According to stability analysis, the most crucial failure modes would be superficial plane and polygonal failures, as well as deep circular failures on rare occasions, all of which are governed by the mines' local geology. The waste dumps' factor of safety, probability of failure and reliability index values all suggested slope instability, especially during the rainy season. To prevent future waste dump slope failures, the authors advocate recycling and reusing waste rocks as engineering materials, particularly for tailing dam structures. [ABSTRACT FROM AUTHOR]

The aim of this work was to evaluate reliability index (RI) with respect to fatigue and rutting within the different seasons peculiar to Nigeria, in order to improve Empirical-Mechanistic flexible pavement design approach, using First Order Reliability Method (FORM). Flexible pavement design involves many uncertainties, variabilities, and approximations regarding the input parameters like material properties, traffic loads. Others include subgrade strength, drainage conditions, construction, compaction procedures and climatic factors such as temperature, rainfall, and snowfall, etc. The combination of the variances associated with input parameters contributes to components and system uncertainty, and this combination of variances can have a significant effect on the predicted performance of the pavement. Reliability in pavement design is introduced to consider these uncertainties. Layers thicknesses, material properties, and Equivalent Standard Axle Load (ESAL) were entered into a multi-layer elastic theory software, ELSYM-5, which in turn were used to calculate strains and stresses for different seasons. The results obtained were entered into Nigerian fitted transfer function distress models to compute allowable ESALS. Miner's hypothesis theory equation was used to calculate the cumulative damage due to stress and strains generated. A Framework was generated for finding individual reliability index (RI), systemic reliability index (SRI), and probability of failure. The findings showed that Season I (Winter) recorded the highest component reliability index for fatigue (5.63 for Normal Distribution). Season II (Summer) recorded the lowest component reliability index (β) for rutting (5.4 for Normal Distribution). Season III (Spring) recorded the lowest component reliability index for fatigue (1.85 for Normal Distribution) [ABSTRACT FROM AUTHOR]

Effective generator maintenance scheduling (GMS) is very important to a power utility for the economical and reliable operation of a power system. An optimal GMS increases the operation reliability, reduces power generating cost and extends the generator lifetime. The GMS problem has been formulated as a combinatorial optimisation task, with explicit and simultaneous treatment of multiple objectives: maximisation of reliability, minimisation of fuel costs and minimisation of constraint violations. Many mathematical methods and heuristic search techniques have been reported to find the optimal solution of GMS problem. However, these methods have many limitations and require valid approximations. This paper formulates a general GMS problem using a reliability criterion and a novel bio-inspired search technique, namely artificial bee colony (ABC), is applied to determine the optimal generator maintenance schedule. The performance and effectiveness of the proposed algorithm in solving the GMS problem is illustrated and compared with the recent reports on the standard 21-unit test system with two different peak load demands and crew requirements and a practical 49-unit Nigerian power system. The simulation results show that the proposed ABC is a very effective method for GMS problems. [ABSTRACT FROM AUTHOR]