New Austrian Tunneling Method (NATM)

The New Austrian Tunnelling Method is expressed by German The method was developed by L. von Rabcewicz, L. Müller. and F. Pacher from 1957 to 1964 .It was originally developed for weak ground, i.e. where the materials surrounding the tunnel require rock supporting works because they are over-stressed .

Before the use of NATM method, a wood and steel frame construction were temporary buffered.The NATM construction method is about flexibility—drilling and designing depending on the results of the ongoing monitoring. 

Principles

There are seven features on which NATM is based:

• Work start with survey work , Firstly surveyor give the profile it may take time of ( 30 minute to 50 minute )

• Then Drilling work is start after drilling work ( Typical Drilling Time 2 to 4 Hour )

• Charging work ( Charging means fill up of hole with Cartridged Explosives ) is start ,then mechanized Charging with Bulk Explosive

• Then Blast And Ventilation ( It Take typical Time of 1 Hour )

• Then Loading of Soil n rock work is start , Dumpers & trucks carry rock and soil out from the tunnel

• Shotcrete protection – Loosening and excessive rock deformation must be minimised. This is achieved by applying a thin layer of shotcrete immediately after face advance.

• Every deformation of the excavation must be measured

• Rock Bolting with Jumbo machine (Rock bolt, in tunneling and underground mining, steel rod inserted in a hole drilled into the roof or walls of a rock formation to provide support to the roof or sides of the cavity. Rock bolt reinforcement can be used in any excavation geometry, is simple and quick to apply, and is relatively inexpensive. ) Process is start after face support layer of shotcrete

• After Rock Bolting ,steel Arches ( Latice Grider ) is just installed in poor ground condition for proper support of soil

• Closing of invert – Quickly closing the invert and creating a load-bearing ring is important. It is crucial in soft ground tunnels where no section of the tunnel should be left open even temporarily.

• After Lactice grider one more layer of shotcrete is just Apply on it

• After it Fibre sheet and PVC membrane is apply on it

• After Final process is start , That is Lining of tunnel with the help of gantry

Advantages

1. Flexible – Support provide as required by the ground conditions .
2. Safe – Able to deal with locally unexpected ground condition, minimizing claims.
3. Economical – Support provided as required by the encountered ground conditions, in contrast to TBM segments, which are designed for
   worst load case – if needed or not, therefore overdesigned.
4. Adaptable – Optimizing equipment and crews, allowing multiple heading operations concurrent.

Disadvantages

1. High level of coordination, cooperation and communication.
2. Lower production rates.
3. Interruptions in excavation and support works have to be avoided as much as possible.

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NOTE :-

1. Tunnel Lining – Sprayed Concrete.
2. Typical Performance – 1m to 3m per day. Actual performance and costs will depend on ground conditions and tunnel diameter.