Redesigning the geometry of the Makala Coal Mine to improve safety and productivity
Abstract
Makala is a room-and-pillar coal mine situated in the Katanga Province (DR Congo), close to the city of Kalemie (eastern part of the country). It exploits the so-named Lukuga Coal Basin which is composed by four coal seams numbered 1 to 4, but the economically mineable are 1 (about 2m thickness) and 2 (1 to 1.5m thickness). This coal basin shows some similarities with south-African deposits (Cahen 1961, in Carte Géologique du Zaïre). From West the deposit plunges towards East with an average dip of 8°. Mining operations by room-and-pillar method started in 1914 on the northwestern part of the deposit, following the outcrops of coal seams. Currently only seam 1 is being mined out and the workings are being developed southwards to avoid the higher overburden towards East. Despite the increasing thickness of the overburden, the geometry of the method does not vary, and consists in rooms of 4m wide and pillars of 8x6m, leading to a recovery of about 60%. The main gallery lays from North to South for more than a kilometer. Panels situated on the western part of the main gallery are composed with stable pillars, while on the eastern part one can observe some typical problems like pillar fracturing, ground heave and roof falls. In this last case we noticed that the roof of seam 1 is of poor mechanical quality.
In order to understand the geomechanical problems, we first built a 3D geometrical model, updating the mine layout and incorporating both geological and topographical data. This modelling has been achieved using the GEOVIA-GEMS software. The approach helped in assessing as accurately as possible the overburden to be taken into account when calculating the weight to be supported by pillars. From the defined geometry, we used the modified tributary area method (Brady and Brown 1999) to redesign the pillars accordingly. A 2D numerical modelling has been used as well to assess the stability of the roof and dimension timber support used in the mine.References
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