While grouting is in progress, water and thin grout can collect when the grout is not moving rapidly down the hole, such as in a slow take or when a fast take slows down. The near-static column of grout tends to segregate, with thin grout and water floating upwards and thicker grout descending. Density currents can form.
Every 15 minutes or sooner, the hole should be bled to remove these deleterious fluids.
The process of bleeding is shown in the sketches at left.
The bleeder valve should be on the high side of the fittings if the hole is inclined. When the bleeder valve is opened, it might spray grout out: stand clear. If a packer is in use, bleeding is difficult to do properly. When the pressure is released during the bleeding, check that the pressure gauge responds.
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