14-06-2014, 02:13 PM
Tunnelling Methods
Tunnelling Methods.ppt (Size: 1.09 MB / Downloads: 128)
The choice of tunnelling method may be dictated by:
geological and hydrological conditions,
cross-section and length of continuous tunnel,
local experience and time/cost considerations (what is the value of time in the project),
limits of surface disturbance, and many others factors.
tunnel construction methods
Classical methods
Mechanical drilling/cutting
Cut-and-cover
Drill and blast
Shields and tunnel boring machines (TBMs)
New Austrian Tunnelling Method (NATM)
Immersed tunnels
Special methods
The process for bored tunnelling involves all or some of the following operations:
Probe drilling (when needed)
Grouting (when needed)
Excavation (or blasting)
Supporting
Transportation of muck
Lining or coating/sealing
Draining
Ventilation
Classical Methods
Among the classical methods are the Belgian, English, German, Austrian, Italian and American systems. These methods had much in common with early mining methods and were used until last half of the 19th century.
Excavation was done by hand or simple drilling equipment.
Supports were predominantly timber, and transportation of muck was done on cars on narrow gauge tracks and powered by steam.
Progress was typically in multiple stages i.e. progress in one drift, then support, then drift in another drift, and so on.
The lining would be of brickwork.
These craft-based methods are no longer applicable, although some of their principles have been used in combination up to present day. Nevertheless some of the world’s great tunnels were built with these methods
The English method
method, figure left) started from a central top heading which allowed two timber crown bars to be hoisted into place, the rear ends supported on a completed length of lining, the forward ends propped within the central heading. Development of the heading then allowed additional bars to be erected around the perimeter of the face with boards between each pair to exclude the ground. The system is economical in timber, permits construction of the arch of the tunnel in full-face excavation, and is tolerant of a wide variety of ground conditions, but depends on relatively low ground pressures