How the Drilling Process in Tunnel Carried Out?
Let have a look towards the Basic of Drilling
- Percussion Drill:Machine which break rock into small peices by the impact of repeated blows
- Abrasion Drill: In this bit rotate in hole
- Jack Hammer/Sinkers:Itis an air operated percussion drill type(reciprocate @ 2200 blows per minute) Weight - 20 to 25 kg
- Drifter – Similar to jack hammer but make hole bigger in size about 11.25cm in dia Wagon drill: Mounted on mast supported by two or more wheels
- Stopper:It is air operated percussion type drill,used for overhead drilling Churn drill : To make deep holes more than 15cm dia
- Shot drill: work on principle of abrasion upto 750mm dia hole can be drilled
- Diamond drill:used to obtain core samples
- Depth per bit:Depth of hole which can be drilled by bit before replacing Drilling rate:No. of metres of hole drilled per hour per drill
- Burden:Horizontal distance from face back to first row of drill hole
- Face : Vertical surface extending upward from floor of pit to level@which drilling is done
- Piston Drill/Quarry Master:Action similar to wagon drill.It strikes 200 blows per minute Drilling can be done upto 21m
- Mast hole drill:Self propelled drill.Used to drill hole on soft to medium rocks.used to drill upto 100m
Let not get in a Hurry!!
As we have to further look at the mode of selection of Drilling Methods
Selection of Drilling Equipment
- For exploration purpose – for small cores-Diamond drill & for large cores – Shot drills
- Blasting – For holes upto 11.25cm in dia use jack hammer or wagon drill.If terrain is rough jack hammer is used.If job is large and terrain permit use of wagon drill prove useful
- For holes between 12.5cm to 17.5cm in dia choice is Quary Master ,Blast hole drill and churn drill
- In soft to medium rock upto 21m deep hole either of above can be used .
- For depth greater than 21m deep hole quarry master is not used.
- For harder rock blast hole drill not satisfactory .
- Then in harder rock more than 21m deep hole churn drill is satisfactory.
- For core drilling upto 7.5cm outside hole dia ,Diamond drill is satisfactory.
- For 5 to 20cm diamond or shot drill is used.
- A diamond drill can drill a hole in any direction while shot drill can drill in vertical direction only
MOUNTING OF DRILL FOR SMALL TUNNEL
- For small tunnel ,bar and column are satisfactory but for large tunnel it is convenient to mount drill on jumbos.
- Inclined hole with inclination 45° prove efficient.If charge of explosive is placed equidistant from two free face it will break 2.25 times more material and if charge of explosive is placed equidistant from three face it will break 3.5 times material than single face quary
- Igneous rock require more hole than sedimentary rock
- Maximum efficiency obtain from suitable charge of explosive is when line of resistance is @90° to axis of bore hole and minimum efficiency when two are coincident.
- Depth of hole: The angle between line of least resistance and axis of bore hole.
- Depth of hole not more than 5/8 times the diameter of tunnel
Have A look towards the Drilling Pattern
- In Hard rock generally pyramid or wedge cut pattern is employed
- The innermost hole called cutholes are 15cm to 23cm deeper than other hole.
- Next hole are called Easier’s or reliever hole and are more heavily loaded and outer hole are called rim holes
- Horizontal wedge cut:Used when height of tunnel greater than width .When drilling done from bar
- Pyramid Cut: For circular or horseshoe tunnel. Apex of cuthole not more then 15cm apart and angle at apex is 50° to 60°
- Vertical wedge cut:Best when drilling done from column
- Bottom cut : Common in mining and is more efficient . In wide heading modified form of this pattern is used.Modified form called Top cut or Side cut
- Buster cut : Also called Baby cut.Used when drilling usually have deep holes. It is drilled about half depth of regular cut holes. Buster cut may be single hole
BASIC DIFFERENCES IN CUT
For Drilling Cut For Shaft Cut
1. Horizontal 1.Central
2. Vertical 2. Alternate
3. Pyramid 3. Pyramid
Tunnel construction Cycle
- Railway bridge and Tunnel Engineering by Rangwala
- Harbour dock and Tunnel Engineering by R.Srinivasan
- Roads, Railways Bridges and Tunnel Engineering by Ahuja & Birdi