In general terms, the definition of grouting is: an injection under pressure of fluid material into fractures and cavities in rock, soil or artificial structures.
Grouting in construction basically has three different main purposes: stabilization, strengthening, sealing.
Stabilization:
Stabilization grouting is making a skeleton of grout in weak parts or areas of the ground and to avoid sliding in cracks, fissures or bedding planes. It can also be done as spot grouting at selected location.
Stabilization grouting is also used when a future concrete casting is to be done. This is grouting to support a construction which will have a temporary status, like a pilot tunnel in a civil engineering project or a drift in a mine. This type of grouting is not meant to stop seepage or water intrusion.
For foundation work, stabilization grouting is mainly done to create temporary roads, work site foundations, stabilize trenches, etc. It may later on form a part of a permanent support.
Strengthening:
Strengthening grouting is when the grouted ground is connected together by the grout and acts as one body. Joins, fissures, shear faults and other voids in the rock are filled with grout. This is grouting to reinforce a
structure that will be permanent, such as communication or water tunnels.
In dam foundations, blanket grouting is a process of enhancing the mechanical properties of the ground itself, so it can act as the support of the structure.
In most cases, it is less expensive to utilize the rock thus strengthened in situ instead of drilling, blasting, excavating, crushing, and mixing it with cement to form a concrete which then is cast to form a support for the excavation.
The different variants of consolidation grouting may be considered as mainly strengthening grouting.
Sealing:
Sealing is strengthening grouting developed to almost water tightness, when a tunnel is dry or the seepage underneath a dam negligible. Sealing is divided into different sealing classes, depending on the permissible inflow of water on the particular work site.
Curtain and cover grouting are forms of sealing grouting. In most subsurface constructions. Sealing is done as pre-grouting, the grouted zone should always go beyond the excavation area disturbed by blasting.
A concrete casted lining will not seal the ground or stop a ground water sinking unless it is combined with grouting or an impermeable membrane.
The tunnel can act as a drainage pipe in the ground especially with the air pumping effect from traffic in the enclosed area.
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