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Problems are discussed that were encountered during the raise boring and widening of a surge shaft for a 1 020 MW project in Bhutan involving Himalayan geology, with particular reference to the methods adopted to clear the blockages at various stages during the excavation. Various methods were evaluated for removing the choke during the pilot opening stage and conventional drilling and blasting was found to be the most effective. The choke formed during widening of the shaft was cleared by extending the drainage gallery to the shaft and the use of drilling and blasting., Problems are discussed that were encountered during the raise boring and widening of a surge shaft for a 1 020 MW project in Bhutan involving Himalayan geology, with particular reference to the methods adopted to clear the blockages at various stages during the excavation. Various methods were evaluated for removing the choke during the pilot opening stage and conventional drilling and blasting was found to be the most effective. The choke formed during widening of the shaft was cleared by extending the drainage gallery to the shaft and the use of drilling and blasting.

A database was created of ground vibration due to blasting at 27 limestone quarries located in various parts of India. The database contains peak particle velocity (PPV), frequency, and other vibration-related and blast design parameters. Regression analysis of the data was carried out to derive site constants of the US Bureau of Mines predictor equation for individual quarries. By combining all the data, a generalised predictor equation was developed to assess and control ground vibration. Mean zone of attenuation was delineated using the predictor equations of the individual quarries. The dominant frequency of ground vibration with respect to distance and the possibility of modifying it by changing delay intervals in production blasts are examined., A database was created of ground vibration due to blasting at 27 limestone quarries located in various parts of India. The database contains peak particle velocity (PPV), frequency, and other vibration-related and blast design parameters. Regression analysis of the data was carried out to derive site constants of the US Bureau of Mines predictor equation for individual quarries. By combining all the data, a generalised predictor equation was developed to assess and control ground vibration. Mean zone of attenuation was delineated using the predictor equations of the individual quarries. The dominant frequency of ground vibration with respect to distance and the possibility of modifying it by changing delay intervals in production blasts are examined.

As part of the 6 x 250 MW hydroelectric power project on the Satluj River in Himachal Pradesh, four underground desilting chambers 525 m long, 16 m wide and 27 m high were excavated by drilling and blasting. Major rock types encountered during excavation of the central heading and side slashing were augen gneisses and gneisses, intersected by three major discontinuities. On the basis of its Q values between 1 and 30, the rock mass was classified as good, fair and poor, with class II (good) dominating in chamber 1 and class III (fair) in the other chambers. Excavation was by a nitroglycerine-based gelatine explosive, chosen for its availability and placed at intervals of 200 mm inside split and taped PVC pipes of 25 mm diameter, with detonating cord for ignition, to achieve smoother blasting. The pull in the top central heading was always equal to or greater than 3.5 m (87%), with the critical factor for success the drilling of five 105 mm diameter relief holes. Average overbreak in the chambers was within 10-11%. The Q-system classifications did not correlate well with pull or overbreak., As part of the 6 x 250 MW hydroelectric power project on the Satluj River in Himachal Pradesh, four underground desilting chambers 525 m long, 16 m wide and 27 m high were excavated by drilling and blasting. Major rock types encountered during excavation of the central heading and side slashing were augen gneisses and gneisses, intersected by three major discontinuities. On the basis of its Q values between 1 and 30, the rock mass was classified as good, fair and poor, with class II (good) dominating in chamber 1 and class III (fair) in the other chambers. Excavation was by a nitroglycerine-based gelatine explosive, chosen for its availability and placed at intervals of 200 mm inside split and taped PVC pipes of 25 mm diameter, with detonating cord for ignition, to achieve smoother blasting. The pull in the top central heading was always equal to or greater than 3.5 m (87%), with the critical factor for success the drilling of five 105 mm diameter relief holes. Average overbreak in the chambers was within 10-11%. The Q-system classifications did not correlate well with pull or overbreak.

The controlled blasting is described of a large underground powerhouse cavern at the project. The rock mass consists mainly of phyllites, phyllitic quartzite and quartzite bands. Wall rock damage was assessed using the half cast fraction method and field studies were carried out using vibration monitoring in the near field zone. The results were used to develop controlled blast designs leading to better wall rock profiles with half cast factors of about 70%., The controlled blasting is described of a large underground powerhouse cavern at the project. The rock mass consists mainly of phyllites, phyllitic quartzite and quartzite bands. Wall rock damage was assessed using the half cast fraction method and field studies were carried out using vibration monitoring in the near field zone. The results were used to develop controlled blast designs leading to better wall rock profiles with half cast factors of about 70%.