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8 | INSTALLATION | GEOKON
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 Soils
Materials
Weight
Water
30 gallons
Portland Cement
94 lbs. (one sack)
Bentonite
25 lbs. (as required)
The 28-day compressive strength of this mix is about
Notes
50 psi, similar to very stiff to hard clay. The modulus
is about 10,000 psi
TABLE 1: Ratios for Two Grout Mixes.
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 the Weak Grout
Method section above, 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.
2.2.2 INSTALLATION OF MODEL 4810 CONTACT ("FAT BACK") PRESSURE
CELL
This section details installation instructions for Model 4810 earth pressure cells,
which are used for the measurement of earth pressures on structures. In
backfills for piers, piles, bridge abutments, retaining walls, culverts and other
structures the cells may be installed either inside a concrete structure being
poured or directly on the surface of an existing structure. For slurry walls, the
Model 4820 earth pressure cell is used as described in Section 2.2.4.
INSTALLATION IN POURED CONCRETE
When pouring concrete, the cells can be held to the forms using nails through
the lugs welded to the edge of the cell. Position the cell so that the thin pressure
sensitive plate is directly against the concrete form. Nail the plates to the form
lightly in such a manner that they engage the concrete sufficiently and will not
pull out of the concrete when the forms are removed. Route the cable inside the
concrete to a convenient readout location or to a block out inside where excess
cable can be coiled. Protect the cable from damage during concrete placement
and vibration by tying it to adjacent rebar. See Figure 11.
Grout for Soft Soils
Ratio by Weight Weight
2.5
75 gallons
1
94 lbs. (one sack)
0.3
39 lbs. (as required)
The 28-day strength of this mix is about 4 psi,
similar to very soft clay.
1:
Ratio by Weight
6.6
1
0.4
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