8
Figure 3 - 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 3 and the installation shown in Figure 4 may be used with the standard piezometer filter.
Figure 4 - Low Air Entry Filters ONLY
