Table 1 - Ratios For Two Grout - Geokon 4820 Instruction Manual

The cells (Model 4800-1-1P, complete with pinch tubes and lugs) are positioned on a thin
layer of non-shrink, sand cement grout, and are nailed in position using the lugs on the
cells provided for this purpose. The excavated pocket is then backfilled to a depth of 300
mm with a weak concrete in 100 mm layers, vibrated with a poker vibrator. After 24
hours, the cells are pressurized by pinching the pinch tubes until the pressure in the cell,
displayed on a connected Readout Box, starts to change.
The instrument location containing the grouted cells and the cable trench is then
backfilled in 250 mm layers, using the same material as the main fill placed by hand and
compacted with pneumatic or gasoline backfill tampers, or vibratory trench rollers. After
this, standard construction filling and compaction practices can continue.
Earth Pressure Cells clusters, placed according to the methods outlined above, may be
installed either in trenches, below the temporary embankment grade, or in ramps above
the temporary embankment grade. In dams, for example, it is usually convenient to install
in trenches in the impervious rolled fill core, and in ramps in the filter zones and
compacted rockfill shell zones. In earth embankments, it is convenient to install in
trenches. By doing so, adequate degrees of compaction of the backfill can be more easily
obtained without damage to the cell clusters or cable arrays. As the cells are being
covered and compacted, repeated readings should be taken to ensure that the cells are
continuing to function properly.
See Section 2.3 for cable installation and protection.
Application
Grout for Medium to Hard
Materials Weight
Water 30 gallons
Portland 94 lbs.
Cement (One sack)
Bentonite 25 lbs.
(as required)
Notes
The 28-day compressive strength of this
mix is about 50 psi, similar to very stiff to
hard clay. The modulus is about 10,000 psi
2.2.1.2 Alternative Method
In this method, the pressure cell used to monitor vertical earth pressures is placed directly
in the fill. The procedures are similar to those in Section 2.2.1.1, except that the pressure
cell does not have a pinch tube and the layer of weak grout is dispensed with. Instead, the
cell is placed on a pad of quick-setting mortar. This is done to ensure uniform contact
with the soil at the bottom of the trench. The cell is then covered by soil placed in
300 mm layers and compacted as before.
Soils
Ratio by
Weight
2.5
1
0.3
Table 1 - Ratios for Two Grout Mixes.
Grout for Soft Soils
Weight Ratio by
Weight
75 gallons
94 lbs.
(One sack)
39 lbs.
(as required)
The 28-day strength of this mix is about
4 psi, similar to very soft clay.
9
6.6
1
0.4