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| INSTALLATION | GEOKON
5:
FIGURE 5:
High Air Entry Filter
In partially saturated fills (if only the pore air pressure is to be measured), the
standard tip is satisfactory. It should be noted that the standard coarse tip (low
air entry) measures the air pressure when there is a difference between the pore
air pressure and the pore water pressure. The difference between these two
pressures is due to the capillary suction in the soil. The consensus is that the
difference is normally of no consequence to embankment stability.
The coarse tip filter is suitable for most routine measurements. Both the
installation shown in Figure 5 and the installation shown in Figure 6 may be
used with the standard piezometer filter.
6:
FIGURE 6:
Low Air Entry Filters ONLY
4.4
INSTALLATION BY PUSHING OR DRIVING INTO SOFT SOILS
The Model 4500DP piezometer is designed to be pushed into soft soils. In soft
soils, it can be difficult to keep a borehole open. The 4500DP may eliminate the
need for a borehole altogether. The unit is connected directly to the drill rod
(AW, EW, or other) and pressed into the ground, either by hand or by means of
the hydraulics on the rig (see Figure 7). The units can also be driven into the soil,
but there is a possibility that the driving forces may shift the zero reading.
The ground conditions need to be relatively soft for the 4500DP to be effective.
Soft soils (like clays or silts) with SPT blow counts under 10 are ideal. In stiffer
soils, it is possible to drill a hole and then push the 4500DP only a few feet below
the bottom of the hole. If the soil is too stiff, the sensor may overrange or break.
