Grout injection is the pumping of grout (a thin cement mortar or injection fluid) under pressure into soil, rock, masonry or voids, in order to fill, strengthen or seal them. The grout flows into pores, cracks and cavities and, once set, forms a solid, load-bearing or sealing mass.
Aims of grout injection
- Ground improvement — filling the pores between sand or gravel grains, making the ground stronger and less permeable
- Water sealing — closing cracks and joints so water can no longer flow through (for example in excavation bases)
- Void filling — filling cavities beneath floors, in quay walls or in old masonry
- Underpinning — strengthening the ground beneath a settled foundation
- Compensation grouting — targeted injection during tunnelling or boring to offset settlement of buildings above
Execution
The grout is placed through injection tubes or drilled holes (injection lances) under controlled pressure. Key points are:
- Injection pressure — too high a pressure can lift or fracture the ground (hydrofracture)
- Grout mix — the fluidity and setting time are matched to the soil type and purpose
- Monitoring — the injection progress and the volume taken are recorded
Grout injection is specialist work, carried out mainly by dedicated foundation and injection contractors.
Related terms
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