What is shaft in tunnel construction?

In civil engineering a shaft is an underground vertical or inclined passageway. Shafts are often entered through a manhole and closed by a manhole cover. They are constructed for a number of reasons including: For ventilation of a tunnel or underground structure. As a drop shaft for a sewerage or water tunnel.

How are shafts constructed?

Using this technique the shaft is constructed by removal of the ground using excavators and cranes followed by the installation of precast concrete segments directly in their final place, which hang from the previously constructed ring.

What are the main methods of tunnel construction?

There are three basic types of tunnel construction in common use:

• Cut-and-cover tunnel, constructed in a shallow trench and then covered over.
• Bored tunnel, constructed in situ, without removing the ground above.
• Immersed tube tunnel, sunk into a body of water and laid on or buried just under its bed.

How are tunnels constructed?

There are three basic types of tunnel construction in common use. Cut-and-cover tunnels are constructed in a shallow trench and then covered over. Bored tunnels are constructed in situ, without removing the ground above. Finally, a tube can be sunk into a body of water, which is called an immersed tunnel.

What’s the difference between a tunnel and a shaft?

Shaft: a long, narrow, typically vertical hole that gives access to a mine, accommodates a lift in a building, or provides ventilation. Tunnel: an artificial underground passage, especially one built through a hill or under a building, road, or river.

What is pipe jacking in construction?

Pipe jacking is a trenchless construction method to install product pipe through the ground on line and grade for new service lines, sewer tunnels and utilities. Pipe jacking is done from a launch shaft to a reception shaft with advancement provided by a hydraulic jacking frame located in the launch shaft.

What are tunneling techniques?

Rock tunnels are excavated through the rocks either by drilling or by blasting. The tunneling method utilizes mechanized excavators in case of soft rocks or rock tunnel boring machines (TBM). Sequential Excavation Method (SEM) is also used in some cases.

How are tunnels built underground?

Today, underwater tunnels are often created with humongous tunnel-boring machines (TBMs) — sometimes called moles. They then sink pre-made steel or concrete tubes in the trench. After the tubes are covered with a thick layer of rock, workers connect the sections of tubes and pump out any remaining water.

What materials are used to build tunnels?

The different types of materials used in tunnel construction include explosives, concrete, steel, shotcrete material, lattice girders, geomembranes, rock bolts/anchors, admixtures, fibres and rock reinforcement.

What is the best material for shaft?

The material used for ordinary shafts is mild steel. When high strength is required, an alloy steel such as nickel, nickel-chromium or chromium-vanadium steel is used. Shafts are generally formed by hot rolling and finished to size by cold drawing or turning and grinding.

How do you choose shaft material?

The material used for shafts should have the following properties : 1. It should have high strength (Strong). 2. It should have good machinability (easily machined).

What are the ventilation systems in tunnel construction?

These ventilation systems in tunnel construction are discussed in this article. The tunnel construction works are mainly carried out by drill and blast method, which have many safety and health issues due to the emission of dust and many poisonous gasses. Hence it is essential to provide ventilation systems in in tunnel during construction.

What are the uses of shafts in construction?

Shafts Shafts provide access to tunnels and deep pipe networks, but also enable construction of underground structures such as escalators to subway stations, for ventilation, to launch and retrieve tunnel boring machines, or facilitate jacked tunnel construction.

What are the disadvantages of tunnel ventilation system?

But in long tunnels, these systems have a disadvantage of fogging the atmosphere inside the tunnel when the smoke, dust and foul air move out. The system incorporates an exhausting duct near the working face, into which, the foul air and the dust are let. By this fresh air is maintained within the tunnel, through the entrance.

What are the advantages of transverse ventilation tunnel?

A consistent level of temperature and the pollutants will be maintained if this system is employed. The system can be either fully or semi-transverse. Transverse or semi-transverse ventilation tunnel is better than a longitudinal one for the tunnels that are longer than 4 to 5 km.