C Sawmliana

Blast induced air overpressure and its prediction using artificial neural network

Abstract Air blast is considered to be one of the most hazardous environmental disturbances created by blasting operation. Prediction of air overpressure (AOP) generated owing to blasting is difficult due to the influence of several factors in the air wave transmission. Blast design parameters, wind direction and speed, atmospheric temperature, humidity and topography, etc. are all affecting AOP. In this paper, an attempt has been made to predict AOP using artificial neural network (ANN) by incorporating the most influential parameters like maximum charge weight per delay, depth of burial of charge, total charge fired in a round and distance of measurement. To investigate the effectiveness of this approach, the predicted values of AOP by ANN were compared with those predicted by generalised equation incorporating maximum charge weight per delay and distance of measurement. Air overpressure data sets obtained from four different mines in India were used for the neural network as well as to form generalised equation. The network was trained by 70 data sets and validated with 25 data sets. The network and generalised predictor equations were tested with 15 AOP data sets obtained from another two mines. The results obtained from neural network analysis showed that the depth of burial of the charges and maximum charge weight per delay were among the blast designed parameters that have most influence on AOP. Based on the ANN result, depth of burial of charge has more relative sensitivity and weight than the maximum charge weight per delay. The average percentage of prediction error for ANN was 2·05, whereas for generalised equation, it was 5·97. The relationship between measured and the predicted values of AOP was found to be more logical in the case of ANN (correlation coefficient: 0·931) than that of generalised equation (correlation coefficient: 0·867).

A New Blastability Index for Hard Roof Management in Blasting Gallery Method

The presence of hard and massive sandstone above the coal seam in underground coal mines often leads to delay in caving of overlying rock beds thereby causing excessive load on supports and posing danger to underground workings. The problem is more prominent in blasting gallery (BG) as well as longwall mining methods in Indian coal mines. Induced caving by blasting is a promising means for hard roof management in underground coal mines. Based on extensive studies and data collected from different mines in India, a Blastability Index (BI) has been developed which can be used for the classification of roof according to the degree of ease in caving by induced blasting. Different charge factors have also been suggested based on the Blastability Index. Due to wide change in the method of extractions, ‘Cavability Index’ for longwall panel was found ineffective in case of BG method of working as well as bord and pillar working. For this reason, this proposed Blastability Index would be of immense help for caving of hard roof by induced blasting.

Safety of dam structures from ground vibrations due to demolition blasting of coffer wall of a hydroelectric project in India

The National Hydroelectric Project Corporation (NHPC) Limited, a Government of India Undertaking, while constructing a 132 MW Hydroelectric Project on the river Teesta at the district of Darjeeling in West Bengal built one concrete coffer wall on the upstream of the river to facilitate the construction of barrage and spillway. One end of the coffer wall was abutted to the barrage pier and the other end to the left bank onto the cellular wall. The demolition of the said coffer wall by controlled blasting was entrusted to CSIR-CIMFR by NHPC. The paper deals with the scientific methodology resorted by CSIR-CIMFR for accomplishing the job successfully with full safety to the nearby structures viz. barrage, spillway, Intake, penstocks, surface powerhouse, tail channel, pot head yard etc.

Blast-induced ground vibration damage assessment for foundation work at a thermal power project in India

This paper presents the extensive trial blasts conducted for damage assessment due to blast-induced ground vibrations for removal of hard rocks as well as establishment of safe blasting zones during excavation work at a proposed thermal power project in India. During the excavation work it was feared that the impact of blasting may cause damage to the rocks or extension of cracks to the nearby foundations/foundation bases for various types of sensitive structures. A number of trial blasts with varying designs and charging patterns were carried out at the site. The impact of ground vibration waves were assessed on nearby structures/foundations. Ground vibrations were monitored at varying distances in a straight line, to find out the characteristics of wave propagation in the particular medium. Based on the analyses of recorded vibration data, it was suggested that no blasting should be carried out within 5 m when the foundation work is in progress. Within 5–15 m, controlled blasting should be carried out with 32 mm diameter Jack Hammer Drilling Machine while beyond 15 m and up to 25 m, 100 mm diameter drill machine can be used with hole depths up to 3.0 m. Within the zone of 25 m to 35 m from the foundation, the depth of blastholes may be more than 3.0 m but it should not be greater than 4.5 m. Beyond 35 m zone, the depth of blast holes should be between 4.5–6.0 m. It was also suggested that a clearance of at least 0.5 m from both the edges of the blasting face should be used between the boundary of excavation line and the last row of holes to minimize over break beyond the excavation line. Lighter explosive charges with longer delay periods should be used for the blastholes adjacent to the excavation boundary.

Effective blasting using mixture of ammonium nitrate, fuel oil, sawdust and used oil at limestone mine

Abstract The efficacy of a mixture of ammonium nitrate prills, sawdust, fresh diesel and used oil (engine oil, hydraulic oil, transmission oil, etc.) as an efficient explosive was investigated in a limestone mine of Adhunik Cement Limited, Jaintia Hills, Meghalaya, India. An air decking column of 1 m length wooden spacer was used in each blast hole. The method was proved to be well effective in not only improving the blasting performance but also reducing the cost of blasting. The paper highlights scientific explanation of the methodology buttressed by data generated during the investigation. This method will open up an effective approach to the utilisation of waste materials like sawdust and used oil in blasting operation.

Environmental Impact of Detonation of Explosives in Seismic Survey Operations

Seismic survey operations are short-term, although, they can cause annoyance to the surrounding inhabitants. These annoyances may be due to generation of ground vibrations and noise and their possible impact on the surrounding houses and other structures. The paper discusses a case study of experimental trials conducted at three different exploration sites of Oil India Limited in Assam, India. The impact of ground vibrations and noise generated due to detonation of explosives were investigated on the surrounding environment and structures in various working conditions. The maximum magnitude of vibration recorded near a residential house was 53.01 mm/s at a distance of 20 m from the blast site with the dominant peak frequency of 56.8 Hz. No adverse impact on the structure was observed. The analyses of data revealed that the ground vibrations generated due to the detonation of explosives were having their most of the energy in higher dominant frequency bands i.e. more than 30 Hz. The analyses of data clearly indicated that the magnitude of ground vibration enhances when the shot holes are stemmed. In general, the enhancement in vibration was 9–29 % but in some cases, it was observed up to 31.7 %. The level of vibration also increases as the depth of burial of explosives is increased. It was observed that whenever the confinement of explosives will be more, higher magnitude of vibrations would be generated. The magnitude of noise generated during seismic survey operations were well within the safe limits.