unit-3 (part-3) tunnelling techniques
TRANSCRIPT
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