Experimental determination and calculation of pillar dimensions for two-level working of the Novo-Kal'inskii bauxite deposit

Autor: Yu. M. Liberman, A. M. Kozina, E. P. Rutkovskaya
Rok vydání: 1971
Předmět:
Zdroj: Soviet Mining Science. 7:403-407
ISSN: 1573-8736
0038-5581
Popis: The ore body of the Novo-Kal'inskii bauxite deposit, which is the subject of our paper, has a dip of 28". The thickness of the ore bank varies from 0.7 m 8.5 m. In accordance with the adopted working procedure, the ore bank is divided into two levels, the mining-out work being performed simultaneously in them. In the upper level work is carried out from the upper boundary of the ore body from a depth of 295 m, in the lower level from a depth of 655 m (the postulated lower limit of the pillar) to 1060 m. An interlevel pillar is formed between the levels. Geological data show that the lower limit of the pillar is overlain at a distance of 70-150 m by water-resisting rocks. With increasing depth these rocks approach the ore body and in the depth range 500-680 m they lie at a distance of 35 to 40 m from the contact of the ore bank. One may therefore assume that as the mining-out workings advance a distance of 100-120 m from the pillar boundary, the caving zone may reach the w ater-resisting layers and the inflow of w ater into the mine workings may increase. Our aim was to determine the redistribution of the rock pressure on the interlevel pillar as the ore body was extracted, and to establish the strength of the pillar and the character and zones of occurrence of caving of the overlying rocks. We found the problem could be solved by physical modeling [1], and it was also possible to calculate the strength of a pillar Simulation by equivalent materials was done with flat beds. 4.5 m long and 0.24 m wide. With the scale used for this work, it was possible m simulate only the central part of the deposit at relative depths of 430-790 m from the surface; for this purpose we assumed that the work in the upper (295-430 m) and lower (790-1060 m) levels had little effect on the abutment pressure distribution within the limits of the postulated pillar. Initially, using the model we worked the lower level from the 655 m mark (the lower limit of the pillar) to the 790 m mark- during this period the work in the lower level must have advanced from the 295 m mark to the 430 m mark; we then worked the upper level from the 430 m mark to the upper limit of the pillar until its fracture was observed - during this period the work in the lower level must have been performed from the 790 m mark or below. To verify this assumption, we developed a model which simulated simultaneously ore extraction in the lower level from the 655 m mark to the end, and in the upper level from the 295 m mark to the upper boundary of flae pillar and to failure of the latter. The thickness of the overlying rocks to a depth of 240 m was simulated by equivalent m aterials. In these simulation procedures we assumed that the ore body had a flat pitch. It was also assumed that caving of the rocks would have approximately the same character as at a dip of 28". To reproduce the necessary depth of occurrence of the bed, the overlying roof rocks, which did not come within the scope of the model, were replaced by an increasing load. The roof displacement was measured by dial-type indicators with a scale value of 0.01 ram, resting on dowels placed in the roof of the ore body during shaping of the model The stress in the rock mass was measured by the same indicators fixed on the elastic base of the stand. The model was worked by 10 em pulls at 20 min intervals. Working of the lower level was begun from the 250 cm mark in the model (the lower limit of the pillar). To solve the problems, we processed five models, the characteristics of which are given in Table 1.
Databáze: OpenAIRE
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