Explosive welding is planned in an abandon drift which is approximately 10m radius and 9m height. According to the plan the amount of explosive, ANFO will be up to 1000kg per stage. Before the explosive welding experiment, the environmental analysis especially about the air-blast overpressure should be concerned because that the explosive welding is methodologically similar to open pit blasting. The air-blast overpressure could give damages to nearby structures and cause human annoyance. Normally in tunnels and drifts in a mine, a damping ratio of the overpressure is lower than open space because that reflected pressures are easily get together in a sealed condition. In this study we investigate a safety of nearby pillar and upper wall from the overpressure in a drift using the overpressure estimate equations from CONWEP and DDESB. As the results, strength of composed limestone in the drift is higher than the overpressure in a common distance. However the overpressure can cause a weakness of nearby pillar and roof in a drift which contain narrow parallel joints.
An explosive welding was designed in the mining drift. The explosive welding to the nearest pillar was approximately 20m and the ceiling height was 9m. The mining drift 15m×7m was excavated to ventilate gases generated from explosive welding. ANFO is designed to use explosive welding up to 1000 kg in phase. Peak overpressures, caused by explosive welding, are expected to rapidly propagate to the air with hemispherical around. It can also give damage to the nearest pillar and its celling. Thus safety factor analysis should be considered beforehand. In this study, the three equations, a normal equation from large explosion experiment, CONWEP (Convention Weapons Effects Program) overpressure equation depending on distance from an explosion and DDESB (Department of Defense Explosives Safety Board) overpressure equation estimating overpressures by efficiency volume are used for estimating overpressures generating from blasting welding.
If an explosive explodes from the ground or near surfaces, the first overpressure will be reflected to the ground soon. Furthermore the initial and reflected overpressures are going to combine into one single wave which will propagate simultaneously hemispherically [1].
As ANFO was considered for explosive welding at this mine equivalent weights of TNT which is relative to effective charge weights of ANFO should be considered in order to estimate overpressure within those equations.
The Peak overpressure P0 estimated with CONWEP equation can be calculated in the following equation [2]. The blasting welding has many analogies with ground explosions. Therefore reflected over pressures should be concerned since the overpressure will be propagating hemispherically. As a results, if 1000kg of ANFO is used for explosive welding, the peak overpressure which affects to pillars 50m away from the explosion is calculated to 0.03 MPa. Furthermore the peak overpressure onto the roof which is located on the distance of 9m from the explosion is calculated to be 1.36 MPa.
