Grouting if flushing water is lost during pilot hole drilling

In such a case that weak or fractured rock conditions are encountered during the pilot hole drilling, it may become necessary to grout. The decision is based on observations such as rock instability or loss of flushing water and the normal procedure is as follows.

1. The drill string is pulled out from the pilot hole.

2. The quantity of grout, a mixture of cement, sand and water, required is estimated and pumped or poured into the pilot hole. If possible, the pilot hole is filled from the bottom in order to avoid separation of the material.

3. When the grout has hardened, after approximately 24-30 hours, the drill string is lowered and the pilot hole is re-drilled through the grouted part.

The procedure may have to be repeated until the conditions become satisfactory.