TUNNELS: Construction Methods
Introduction to Tunnels
In this chapter, the purpose of tunneling, tunneling methods, and tunnel lining are discussed. Tunnels are primarily used for roads and rail transportation but also serve various other purposes such as mining, public works, transportation, and drainage.
Purpose of Tunnels
- Tunnels are mainly used for roads and rail transportation.
- They can also be used for drainage purposes in areas with heavy rainfall.
Tunneling Methods
- The choice of tunneling method depends on factors such as ground type, conditions, length of the tunnel, expertise available, required type of tunnel, economics, and rock stability.
- Definitions:
- Heading: The work face where tunnel activities occur.
- Lining: The material used to complete the face (e.g., steel or concrete).
- Pipe jacking: Method to install pipes into the soil.
- Full face: Refers to the entire area of the heading.
- Conventional shield: A steel casting used to protect the heading.
Types of Tunnels
- There are three main types of tunnels:
- Mining tunnels
- Public works tunnels
- Transportation tunnels
- Other uses include drainage systems and hydro conduits for conducting electricity.
Tunneling Methods
There are six main tunneling methods discussed in this chapter. These include drilling and blasting, tunnel boring machines (TBM), tunneling with shields, pipe jacking, freezing methods, and immersed tubes.
Drilling and Blasting
- Used when excavating in rock where the diameter is too small for large excavating machines or in short lengths of the tunnel.
- Techniques include advanced heading without support, advanced heading in segments followed by full face support, and heading in segments followed by progressive support.
- Process: Holes are drilled into the rock, explosives are inserted and detonated, rubble is removed, and the tunnel is reinforced.
Tunnel Boring Machines (TBM)
- Widely used method employing sophisticated machinery for longer tunnels.
- Limitations include frequent changes in ground nature (soft to hard) and confined spaces.
- Examples of previous TBM use: Durban Harbor undersea tunnel (4.4m diameter, completed in 2007) and Lesotho Highlands Water Project (6 TBMs used for three tunnels).
Tunneling with Shields
- Used when tunnels go through soft soil that requires temporary support.
- Shields act as a protective structure during excavation.
Pipe Jacking
- Hydraulic jack used to push specially made pipes behind the TBM to create tunnels under existing structures.
Freezing Methods
- Used on unstable soil by freezing the excavation area before conventional tunneling methods are employed.
Immersed Tubes
- Mentioned as an additional method but not discussed further in the transcript.
The remaining part of the transcript was not provided.
New Section
In this section, the speaker discusses the different methods of building and why manual construction is sometimes necessary. They also mention other techniques such as sprayed concrete method, rock bolting method, stiffening ribs, liner plates, and full lining.
Methods of Building
- Manual Construction: Sometimes it is necessary to build structures by hand.
- Sprayed Concrete Method: This technique involves using sprayed concrete to construct structures.
- Rock Bolting Method: In this method, rocks are physically bolted into position.
- Stiffening Ribs: Stiffening ribs are used to reinforce structures.
- Liner Plates: Liner plates are used for lining structures.
- Full Lining: Full lining is another technique used in construction.
For more details on support systems and lining, refer to pages 163-164 of the material.