TUNNELLING TECHNIQUES

METHODS Firm groundSoft groundRunning groundRock

TUNNELLING IN FIRM GROUND

Full face method Top heading and benching method Drift method

TUNNELLING IN FIRM GROUND (FULL FACE METHOD)

When the excavated portion can hold itself…. Suitable for tunnel of small size

TUNNELLING IN FIRM GROUND (TOP HEADING AND BENCHING

METHOD) When the excavated portion cannot hold itself…. Heading is excavated first and supported to full

length… Benching is started

TUNNELLING IN FIRM GROUND (DRIFT METHOD)

Size of the tunnel is large Pilot tunnel or drift is made at the center Drill holes are driven from the drift towards the

periphery Drift provide the suitable arrangement for

supporting the excavation

TUNNELLING IN SOFT GROUNDFORE POLING METHOD

Boards are driven ahead to support ground (spiles)

TUNNELLING IN RUNNING GROUND

Tunnelling with liner platesEmployed in medium stiff groundFirst liner plate is placed as the crown

Two adjacent liner plates are attached to it after widening the hole

The arch section is widened gradually down

TUNNELLING IN ROCKS

Drilling holes on the rock face Loading the holes with explosives Blasting Removing the debris Disposing off the broken rocks

TUNNEL LINING Tunnel lining is indented to withstand the

following loads

Weight and pressure of surrounding ground Water pressure Super imposed loading Service loads (railway, highway) Temporary loads during construction Weight of the structure Self weight of tunnel material

TUNNEL LINING Brick masonry lining Stone masonry lining

Timber lining

Concrete lining (extensively used. Not suitable for fore

poling method)

Cast iron lining (suitable for fore poling) method)

Structural steel lining ( less weight when compared to cast iron)

Used in earlier days

Used as a semi permanent lining

TUNNEL DRAINAGE

Pre drainageDewateringPermanent drainage

PRE DRAINAGE

Diverting surface drainage

Depending on the topography the surface water may reach the tunnel

Cross drainage at right angle to the tunnel Water may be collected and diverted to a

sump

PRE DRAINAGE

Preventing hydrostatic pressureExcess hydrostatic pressure can be prevented by providing cover over the tunnel

Existence of any hole along the tunnel may be blown out

DEWATERING

If gravity condition prevails side

drains can be provided In flat gradient water is pumped out

PERMANENT DRAINAGE

Provision of drain pipesConcrete liningContinuous open gutterGrouting

BOX JACKINGPIPE JACKING