H. Mohammadi; M. A. Ebrahimi Farsangi; H. Jalalifar; A. R. Ahmadi; A. Javaheri
Abstract
In advance longwall mining, the safety of mine network, production rate, and consequently, economic conditions of a mine are dependent on the stability conditions of gate roadways. The gate roadway stability is a function of two important factors: 1) characteristics of the excavation damaged zone (EDZ) ...
Read More
In advance longwall mining, the safety of mine network, production rate, and consequently, economic conditions of a mine are dependent on the stability conditions of gate roadways. The gate roadway stability is a function of two important factors: 1) characteristics of the excavation damaged zone (EDZ) above the gate roadway and 2) loading effect due to the caving zone (CZ) above the longwall working, which can extend the EDZ size. Generally, due to the coal seam dip, the failure possibility of main gate roadway is more severe than tail gate roadway. The aim of this work is to determine the longwall working effect on the EDZ extension above main gate roadway. To achieve this purpose, considering three factors involved in the CZ characteristics, the coal seam properties (dip and thickness) and the geomechanical properties of hangingwall, a new geometrical model is developed. Then, based on the geometrical calculations, a new relationship is presented to determine the working influence coeffiecint. Furthermore, taking into account the new geometrical model, an algorithm is suggested for the stability analysis of main gate roadways. Validation of the new geometrical model is carried out by the instrumentation and monitoring results of a longwall working carried out in the Parvade-2 coal mine of Tabas, Tabas, Iran. The results obtained show that there is a good agreement between the values obtained by the new model and the actual measured values. Finally, a sensitivity analysis is carried out on the effects of pillar width, bearing capacity of support system, and coal seam dip.
H. Mansouri; M. A. Ebrahimi Farsangi
Abstract
A linear superposition method was used for modeling the time history of the production blast vibrations and optimizing the blast sequence to reduce vibration levels in Sar-Cheshmeh copper mine, Kerman, Iran. A single-hole blast for modeling and two double-hole blasts with time delays of 25 and 65 ms ...
Read More
A linear superposition method was used for modeling the time history of the production blast vibrations and optimizing the blast sequence to reduce vibration levels in Sar-Cheshmeh copper mine, Kerman, Iran. A single-hole blast for modeling and two double-hole blasts with time delays of 25 and 65 ms between two holes for modeling validation were carried out. The generated vibrations were measured at seven points with different distances and directions around the blasts. These records contain information about the complex mechanism of seismic energy radiation from an explosive source as well as the filtering effect of the signal travel path. Totally, 40 seismograms were synthesized (3 components for each point) for two blasts using the linear superposition method. The results obtained presented a good correlation between the synthetic and measured seismograms. Also, a comparison was made between the measured peak particle velocities (PPVs) and those obtained from the scaled-distance method and linear superposition modeling. This shows the merits of linear superposition modeling to predict PPVs. Moreover, the recorded seismograms of the single-hole blast were used to simulate the vibrations produced by a production blast at seven points. Furthermore, by using a systematic variation of firing delay in the modeling procedure, the effect of delay on the production blast vibrations was studied. The production blast simulations showed that for Sar-Cheshmeh copper mine, the blasts carried out with the inter-row delays more than 40 ms can significantly reduce vibration levels.
