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V1.4 March 15
7.3 Buoyancy
QJ Inclinometer Casing
will be buoyant if the borehole is filled with water or grout and
should therefore be filled with water to counteract this. The addition of grout to the borehole
will however make the Casing become buoyant again as grout is denser than water and
becomes worse the denser the grout used.
If buoyancy is expected to be a major problem casing anchors can be used or weight can be
applied at the base of the casing by installing a steel pipe or drill rods.
DO NOT APPLY WEIGHT TO THE TOP OF THE CASING AS THIS WILL
PUT THE CASING UNDER COMPRESSION AND DISTORT ITS PROFILE.
PLACE ANY WIEGHT INSIDE THE CASING AND AT THE BASE.
7.4 Grouting
Grouting is required to connect the surrounding ground to the inclinometer Casing and the
grout mixture should be mixed to match the strength and deformation properties of the
ground. The design of the grout is the responsibility of the Site Engineer.
Grout equipment should comprise of the following:-
•
Grout mixer
•
Grout pump
•
Pipe or hose for Tremie or grout valve method
DO NOT MIX GROUT MANUALLY
USE A PROPER HIGH SHEAR GROUT MIXER AND PUMP
Correctly mixed grout must be of a “just pump able” consistency but thick enough to set in a
reasonable time and be free of lumps. If the mixture is too watery excessive shrinkage will
occur leaving the upper part of the borehole un-grouted.
During the grouting process care should be taken to balance the differential pressures
between the inside and outside of the Casing and it is also important to monitor the water
level in the Casing.
When mixing the grout add the cement to the water first and then add the Bentonite to the
correct consistency. If the grout is too thin the solids and the water will separate. If too thick
it will be difficult to pump.
