Dewatering, waterproofing and drainage - Tunnel Engineering: Basics and Additional Services for Design and Construction - page 206

5.2.5.1 Grouting process
In the grouting process, the voids in the rock mass are closed by injecting suitable li-
quids. This reduces the water permeability and simultaneously increases the stability of
the ground. According to the type of grout, this can be categorised into cement grouting,
chemical grouting or resin grouting.
The suitability of the ground and the grout material for grouting depend on the following
geological, hydrological and chemical factors:
- Mineralogical composition of the soil.
- Grading.
- Stratum thickness and location of the boundaries.
- Joint network of the ground.
- Water permeability of the ground.
- Hydrostatic pressure of the groundwater.
- Direction and speed of groundwater flow.
- Chemical properties of the groundwater (for example salt content).
Research and development tendencies show that the use of grouting seems particularly
suitable when water pressure in the joints is very high and their volume is small. This
process also enables the surrounding ground to be exploited for load-bearing, which is
especially significant for tunnels under very high water pressure. The further development
of this basic idea is promising as a future method of economic construction of tunnel lin-
ings under high pressure.
A grouted body in the form of a closed ring is created ahead of the advance. Due to the
increased resistance to flow, the potential gradient in the grouted ground produced by
drainage inside the ring is increased, which leads to the grouted ring resisting hydrostatic
pressure (Fig. 5-13).
Figure 5-13 Grouted load-bearing ring
under hydrostatic pressure, from [70].