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50 PSI Grout for Medium
Water
Portland
94 lb. (one sack)
Cement
Bentonite
25 lb. (as required)
The 28-day compressive strength of this mix
Note:
is about 50 psi, similar to very stiff to hard
clay. The modulus is about 10,000 psi
Add the measured amount of clean water to the barrel then gradually add the cement in the
correct weight ratio. Slowly add the bentonite powder so that clumps do not form. Keep adding
bentonite until the watery mix turns to an oily/slimy consistency. Let the grout thicken for 5 to
10 minutes. Add more bentonite as required until it is a smooth, thick cream, similar to pancake
batter. It is now as heavy as it is feasible to pump.
When pumping grout (unless the tremie pipe is to be left in place,) withdraw the tremie pipe after
each batch, by an amount corresponding to the grout level in the borehole.
CAUTION! If the grout is pumped into the hole, rather than tremie piped, there is a
danger that the piezometer will be overranged and damaged. Pumping directly into the
bottom of the borehole should be avoided. It is good practice to read the piezometer while
pumping.
For more details on grouting, refer to "Piezometers in Fully Grouted Boreholes" by Mikkelson
and Green, FMGM proceedings Oslo 2003. Copies are available from Geokon.
4.3 Installation in Fills and Embankments
Geokon piezometers are normally supplied with direct burial cable suitable for placement in fills
such as highway embankments and dams, both in the core and in the surrounding materials.
For installations in non-cohesive fill materials, the piezometer may be placed directly in the fill,
or, if large aggregate sizes are present, in a saturated sand pocket in the fill. If installed in large
aggregate, additional measures may be necessary to protect the cable from damage.
In fills such as impervious dam cores, where subatmospheric pore water pressure may need to be
measured, (as opposed to the pore air pressure,) a ceramic tip with a high air entry value is often
used. This type of filter should be carefully placed in direct contact with the compacted fill
material. (See Figure 3).
Cables are normally installed inside shallow trenches with the fill material consisting of smaller
size aggregate. This fill is carefully hand compacted around the cable. Bentonite plugs are placed
at regular intervals to prevent migration of water along the cable path. In high traffic areas and in
materials that exhibit pronounced "weaving", heavy-duty armored cable should be used.
to Hard Soils
Ratio by
Amount
30 gallons
Table 1 - Cement/Bentonite/Water Ratios
4 PSI Grout for Soft Soils
Amount
Weight
2.5
75 gallons
1
94 lb. (one sack)
0.3
39 lb. (as required)
Ratio by
Weight
6.6
1
0.4
The 28 day strength of this
mix is about four psi,
similar to very soft clay.
7
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