Very Costly

Does not require much timbering or supports

Extreme care required in carrying out the work

Over cutting of the section is to be avoided

Allows tunneling operations to be carried out

at many sections along the tunnel length

Construction of Shafts

Transferring C/L to the inside of tunnel

Deciding method of excavation

Setting up and drilling holes for blasting

Filling up of explosives

Carrying out the blasting operations

Providing ventilation and removing dust after

blasting

Carting muck at suitable place outside tunnel

Pumping and removing groundwater

Providing supports inside tunnel

Lining of tunnel

Opening tunnel for use

System of vertical shaftsOn tunnel line, at suitable points, shafts are sunk. n shafts (2n + 2) faces of attackSystem of Pilot Tunnelslateral or horizontal approach shorter compared to deep vertical shaftsSmall size tunnel called plot tunnel driven parallel and close to proposed tunnel and short cross connecting tunnels to reach proposed main tunnel

Cross Headings – convenient places to store

tools and materials during construction

Less costly than shaft

Avoids dislocation of strata at sides of tunnels

After work completion, cross headings can be

used for repairs and maintenance

Means of artificial ventilation by use of fans

Drift Method

Heading and Bench Method

Full Face Method

Cantilever car dump Method

Consists of driving small sized heading , centrally at top or bottom of face , which is enlarged by widening and benchingTop drift method- popular –Boring or blasting a top centre heading of drift end to endWidening & EnlargingBenching in stages

Drift 2m x 3m size is driven end to end of tunnel

As heading proceeds, C/L is checked and marked on iron dogs fixed on roof

Widening is commenced by blasting sides of drift

Completes top heading

Benching is carried out in stages and lowered down to grade in a series of sloping and horizontal cuts

Supporting platforms not required for drilling

operations

During heading, mucking work goes on

undisturbed

Small preliminary section for full length driven

and so economization of excavation work

Good ventilation for workers

Enlargement work only after central hole is

constructed for full length

As enlarging and benching commences,

mucking trucks have to shifted frequently from

bench to bench - costly

Central Drift – time consuming – but provides

good ventilation, requires less quantity of power.

Side Drift – used for tunneling work of large

tunnels in bad ground

Bottom Drift – Platforms can be avoided

Involves driving of top portion of tunnel in advance of the bottom portionHard and self supporting rock Top heading proceeds one round over the bottomHeading is always ahead of benchingLess explosive compared to full face method

Adopted for tunnels of small C/s area -

diameter < 6m & face areas < 19 m2 -

through stable and self supporting rocks

Full face is opened out once for all and driven

Extra units of tunneling equipment necessary

TBMs – well suited for full face excavation

Simplicity of operationMinimizes total magnitude of ground disturbance and settlementWork completed easily and speedilyAdvantage in sensitive ground conditions where multi- phase excavation could generate unacceptable ground pressure and settlement effectsMucking trucks could laid on tunnel floor

Improved arrangement of throwing muck from bench to floor of tunnel

2 plate girders fixed at 1.80 m centre to centre

Belt Conveyor runs on the plate girders

Ends of plate girders project beyond full face of bench

Front ends of girders – supported by means of struts from top of tunnel