| In this paper, in order to study the mechanical properties of the roof, bearing capacity of pine props and the motion laws of the overlying strata systematically, some methods including the indoor experiments, the field monitoring and the theoretical analysis were used based on the 2351 paste backfilling face of Daizhuang Coal Mine as engineering geological prototype. In addition, based on the experimental results and the actual measurements, supporting of the paste backfilling face was optimized and got some useful achievements.In order to understand the mechanical properties of the roof, the tensile tests and the uniaxial compression tests were carried out using Servo-controlled Testing System MTS815.03. As a result, the average value of tensile strength is 7.3125MPa and the average value of uniaxial compression strength is 53.85MPa. In order to test the bearing capacity of the northeast larch pine props which were taken from the wood filed of Daizhuang Coal Mine, the AG-X250 electronic universal testing machine was used. The results show that the samples which were taken from the same prop have little difference on the compression strength parallel to grain, but the compression strengths perpendicular to grain are varied greatly. It is mostly dependent on the loading surface. The compression strength parallel to grain is the key point when the pine is used as the single prop and its overall average compression strength perpendicular to grain is about 12.5% of the overall average compression strength parallel to grain. There is a compact relationship between the strength and the moisture content of the pine. Both the compression strength parallel to grain and the compression strength perpendicular to grain have an obvious tendency of decreasing with the increasing of the moisture content. In other words, the higher drying, the bigger strength the pine will have.The monitoring results show that the backfilling technique of the 2351 paste backfilling face achieved good results. Because there is a good result in the supporting effect of the paste to the overlying strata and the gravity of the overlying strata mainly forces on the coal wall ahead of the coal face and the paste of the goaf, the motions of the overlying strata are not obvious. With the progressive of the face, overlying strata are gradually transformed from the "C" type space structure into articulated rock beam with unequal height supports. The immediate roof of working face is the main roof; the first weighting interval is 33.6m, and the periodic weighting length are 18.3m,8.8m,13.7m and 9m respectively for the last four times. The overburden gravity mainly act on coal wall in front of face and backfill paste, which has little effect on roof advance stress, and the influence scope is less than 15m. Under the current technology conditions of the 2351 paste backfilling face, the reasonable maximum value of the roof-control distance is 8.8m, the reasonable working resistance of support backfilling is 27MPa, the value of setting load is 21MPa and the maximum value of the filling drawing pace is 4m.Finally, based on the mine rock mechanics theory and the practical underground pressure theory and combining the results of the indoor experiment and the field monitoring, the technologies of the paste backfilling face support and the crossheading advanced support were optimized to further improve the productivity. |
