There is not an exact ratio for each kind of soil. It depends from many factors that could change for every geological and geotechnical situation. Anyway the grouting should be similar to the soil even if is not really possible to match both characteristics.
Approximate Cement/Water/Bentonite mix ratio are:
- for hard and medium soil: 1 / 2.5 / 0.3 (i.e. 50kg / 125kg / 15kg)
- for soft soil: 1 / 6.5 / 0.4 (i.e. 50kg / 325kg / 20kg)
The right way to mix the materials is:
1. mix the water and cement
2. add and mix the bentonite
The results have to be similar to an heavy cream.
The ratio of the cement and water determine the strength of the grout. More water decrease the strength.
- A grout too thick will be difficult to pump.
- A grout too thin solidifies and the water will separate from it.
- A mix too watery could separate cement ( on the bottom) from water and bentonite (on the top).