A 9 m thick XIV seam is being worked on by three ascending slices with hydraulic sand stowing at Noonodih-Jitpur colliery in Jharia coalfield in India. The seam is accessed by two fully concrete lined shafts 4.88 m in diameter and 450 m deep. In early 1976 signs of ground movement were noticed in the shaft pillar area. The ground movement was associated with damage to reinforced concrete lining in shaft insets, distortion and damage of rectangular and arched steel supports in roadways, pump-house, underground sub-station and storage bunker, etc. Roof falls also took place in some roadways.
The Central Mining Research Station, (CMRS), was approached to investigate into the causes and magnitude of ground movement and to suggest methods to deal with the ground movements. This paper describes the investigations, results obtained, and recommendations.
There are nine seams upto an average depth of about 500 m; namely XII, XIII, XIV, XV, XV-A, XVI, XVI-A, XVII and XVIII, in the area where the mine is located. Of these XVII and XVIII have already been extracted by bord and pillar system with caving/hydraulic sand stowing. The XVI and XVI-A seams were being extracted by longwall/bord and pillar system with caving/hydraulic sand stowing. The XV-A seam is unmined and XV seam burnt due to igneous intrusion. The 9-m thick XIV seam was being worked by three ascending inclined slices with hydraulic sand stowing. The XIII seam is burnt and XII seam is unmined. The section of the strata showing relative positions of the seams and the plan of XIV seam shaft pillar and adjoining area are shown in Figure 1. The parting between XIV and XV seam was about 48 m and that between XIV and XVI seam was 181 m.
The XIV seam access shafts have 600 mm thick concrete lining throughout. The J1- shaft is downcast and has a pair of 6 t skips with rigid rail guides for hoisting coal, men, and materials. The J3-shaft has a pair of cages with rigid rail guides.
Figure 1. Plan of XIV Seam Working In Noonodih-Jitpur Colliery Showing Stowed Areas (Available in full paper)
All extraction operations in XIV seam were suspended in March 1977 except essential development. Three panels (BMT-1, BMT-2, and BMT-3) had been extracted in the seam. In BMT-1 panel first slice of 2.1-2.4 m thickness was extracted with a shearer and the remaining two slices were extracted with solid stowing. The BMT-2 panel was similarly extracted, but in this panel the first slice was extracted completely and the second and third slices partially. In the BMT-3 panel only first slice was extracted partially. The thickness of the second and third slices varied between 2.7 m to 3 m. During the extraction of the third slice about 0.6 m to 0.9 m thickness of coal was left along the roof. The faces of the first slices were supported by 40 t friction props and in the second and third slices the faces were supported by wooden props.