| Stable mine backfill is necessary for safe working conditions, maximum ore recovery and underground and surface stability. Due to the fact that cement costs can be a significant part of the operating costs in large underground mines, the consumption of cement (or binder) should be minimized. Therefore, developing a safe and economical backfilling method for the large underground mining operations is very significant.; In this thesis, first laboratory tests and in-situ tests are implemented to determine backfill material properties and backfill stress distribution. The laboratory tests include high sulphide paste fill property tests and layered backfill tests. Second, a backfill finite element model is presented and it is validated by the results of laboratory tests and in-situ tests. Finally, by using this model, the following subjects are studied, (1) backfill stress distribution; (2) influences of backfill material properties and dimensions on backfill stability; (3) stress distribution of layered backfill; (4) optimum layered backfill. The results show that: (a) The variation of backfill material properties is quite large, the compressive strength of the layered backfill model is much higher than that of the non-layered backfill model, and the backfill vertical stress is much less than that anticipated by the formula, ρgH; (b) During the process of adjacent pillar recovery, the minor principal stress inside a backfill is tensile, and this tensile principal stress causes backfill failure and spalling near the exposed surfaces. The spalling size progressively increases with the height of the exposed surface, and a sliding zone creates and leads to backfill collapse; (c) Optimum backfill material should be high elastic modulus, high Poisson's ratio and low density. Optimum backfill size should be large depth and small width; (d) For layered backfill, no sliding zone occurs during the process of adjacent pillar recovery, so layered backfill can improve backfill stability. The optimum layered backfill should consist of strong layers distributed evenly with thicknesses of 1∼2m and weak layers 2∼2.5 times the thickness of the strong layers. This can save binder consumption by about 11%. |
