Overview - Drilling in rock using pneumatic drilling devices is an integral part of blasting activity.
1. Two types of drilling can be incorporated for performing controlled blasting.
a) Using tractor mounted compressor, jack rod drilling to the required depth of hole dia of 30mm.
b) Using crawler mounted drilling equipment resulting in a bigger hole dia of 4.5inch.
2. Hole pattern to be decided based on the strata of the rock & number holes to be blasted depending once again on the hardness of the rock and distance of the blast from the adjoining buildings & road structure.
Overview -The final stage of the controlled blasting procedure involves detonating the charge by using exploder.
The continuity of the circuit is checked using a ohm meter so that a closed circuit is formed, using an exploder with delay detonation switch the charges are denoted thus resulting in controlled blasting.
1. Electric exploder with delay detonation.
2. ohm meter or a multimeter.
Excavation of Blasted Rock
Excavators of capacity 20 tons or above along with required number of dumpers of capacity 16 cubic meter are used for excavation of blasted rock.
Muffling Before Blasting
Muffing of the holes are essential so that no fly rock escapes and causes damage to nearly people and structure.
1. Sand bags are placed on the top of each charged hole.
2. Metal sheets of thickness 18mm are placed on the sand bags and ensured that the entire blast area is covered.
3. Rubber mats or Blasting mats of dimension 8ft in lenght and 5ft in width each weighing approximately 1.2 tones are placed on top of the metal sheet .
By adapting this process of muffling we can be assured that no fly rock occurs and hence protection to people and neighbouring structures.
1. Rubber mats made of car/lorry tyre harnessed together in a shape of mat using steel cables of dimension 8ft by 5ft weighing 1.2 tons each.
2.Metal sheets of thickness 18mm in various sizes.
Stemming Before Blasting
Stemming plays an important role in controlled blasting .These processes are the ones that differentiates from an open blasting operation from a controlled blasting operation.
After the explosives are placed in the drilled hole, stemming mixture is poured and tightly packed till the top of the drilled hole. Stemming ensures that when the explosives are detonated , the pressure is transmitted on a horizontal line creating breakage of rock and further ensures blow outs does not occur.
1. Stemming material is a mixture of gravel and Jelly .
2. Stemming is done using non friction material.
Charging With Explosive
Overview - This process involves loading the drilled ng the drilled holes with nitroglycerine based explosive and connecting all the holes with excel chord so that a closed circuit is established .
a) Charging the holes:- Since there is to water table encountered in the proposed project, explosives are carefully pushed into the hole and placed at the bottom of the drilled hole .
The following type of explosives are used for holes drilled using tractor compressor.
1. Power get or gelatin sticks of 2 times.
2. Short Delay detonators.
3. Excel cord.
The following type of explosives are used for holes drilled using crawler mounted drilling equipment:
1. Booster:- 83mm.
2. Delay detonators: - 25 Millisecond.
3. Excel cord.
The use of Delay detonators & excel chord is mandatory to avoid vibrations being transmitted to the neighboring structures.
Rope Saw Cutting
The rope saw cutting machine is an electric driven cutting machine for which a suitable diesel driven mobile generator of capacity 125 kva or above is required.
Once a loop is formed through the horizontal drilled holes,the cutting machine is started and the cutting process results in the bottom cut of the rock to be excavated.
Similarly a loop is formed with one side of the horizontal hole to the vertical hole resulting in the side cut of the rock to be excavated . This process is repeated for the side cut to happen to the other face of the rock.
Thus by performing the above actions the rock is separated from the bed rock .
After the drilling of the horizontal holes and the vertical holes, the diamond rope is inserted into the horizontal hole on one side which forms a loop along with the horizontal holes on the other side and then connected to the wheel of the cutting machine.
Similar exercise is performed for the vertical hole.
The rock surface which has developed cracks is further subjected to Rock breaking using a suitable excavator with rock breaker attachment.
The fragmented or broken rock is loaded into dumpers for disposal.
The material used for chemical breaking of rock is a group of expansive cement which swells and generates high pressure when diluted with water.
This pressure is exploited for smooth and noiseless cracking of rock.
This chemical can be used for rock which is solid and does not have any cracks.
The chemical application requires a setting time between 4 to 6 hrs and usually poured during early hours of the day or late in the evening.
The chemical which is in powder form is mixed with water in the ratio 1.5 liters to 5 kg .
The mixture is poured into the drilled holes and allowed to set. After a duration of 4- 6 hrs the rock develops cracks .
Using tractor mounted compressor or wheel mounted compressor , using jack hammer holes are drilled on the rock surface.
The pattern of the holes to be drilled be such that they be drilled on the surface of the rock which has a free face .
The distance between the holes should be not more than 1ft, and the distance between the rows should not exceed 2ft.
It is not feasible to have not more than 6 rows of holes for any single operation.
Using jack hammer , a vertical hole is drilled from the top so the vertical hole meets the junction of the two horizontal holes drilled.
This drilled hole enables us to form a loop with the rope wire which can be utilized for performing side cutting of the rock or in simple terms a vertical cut of the rock.
Using Diesel Driven compressor of sufficient capacity horizontal hole of dia 4 inch is drilled on one face of the rock.
Similarly another hole is drilled on the other face of the rock until both the holes meet and a loop is formed so that the rope can be inserted.
This process is performed thus resulting in the bottom cut of the rock.