Over the past century, sprayed concrete has replaced the traditional methods of lining tunnel profiles and has become very important in stabilizing the excavated tunnel section. Sprayed concrete is a single term that describes various component of a complete technology:
the material sprayed concrete
the sprayed concreting process
the sprayed concrete system
Sprayed concrete construction is used in many different types of project. The flexibility and economy comes to the fore in above-ground and underground buildings, tunneling and special underground construction, in fact throughout the construction industry. The following uses are widespread:
excavation stabilization in tunnelling and underground construction
tunnel and underground chamber lining
stabilization in mine and gallery construction
concrete repair (concrete replacement and strengthening)
restoration of historic buildings (stone structure)
special lightweight load-bearing structures
In terms of importance, tunnelling, mining and concrete repair head the list. In tunneling and mining, the main uses are for excavation stabilization, temporary and permanent arch lining. Sprayed concrete is also used fir all other appropriate concrete works. Large cavities are often spray filled, for instance. Spray concrete has confirmed and strengthen its position alongside tunnel segment lining (tubbing) and interior ring concrete as the main concreting method. The limits on its use lie in the technical and economic interfaces with the other concreting process and/or construction methods.
Types of construction using sprayed concrete (shotcrete)
Sprayed concrete is used in all areas of tunneling construction – for road or rail tunnels, water drainage and underground military structures, in addition to slope stabilization. Whether tunneling under a building or driving through an obstruction, the construction method is determined by the weight-bearing properties and stability of the substrate tunneled through. The main distinction is between full excavation of the entire section in one operation and partial excavation in many different forms and methods. If full excavation is not possible due to the rock stability, the final profile is often excavated is several phases.
In underground construction, because high stresses would often be exerted on the newly places excavation stabilization and lining. Predetermined deformation of the excavated section is often allowed and only then is the stabilization given a non-positive seal. This causes the stress to be distributed around the excavation section and in the area around the excavation face.