Humboldt H-4140 GeoGauge - Manual (Page 14)

14
variability. Be prepared to question and understand what you are doing with
all the measurements you make, not just the GeoGauge. Process control for
material structures is new and will take different thinking to effectively
implement it.
6.0: GeoGauge Seating
A good GeoGauge measurement arises from good seating, the foot to surface
contact. It cannot be emphasized enough that preparing the soil surface is
key to good seating. Merely having a level material surface is not enough, the
foot must have sufficient direct contact with the soil. Experience shows that
~ 100% of the foot's surface in contact with the material surface is needed. If
a measurement precision represented by a Coefficient of Variation of < 10 %
is achieved from repeated measurements at a single location, then seating is
sufficient.
On loose or soft materials, place the GeoGauge on the ground. Rotate the
GeoGauge no more that 1/2 of a revolution by holding the side or bottom of
the gauge. Now you can take the measurement
Lifting the gauge from the measured spot and observing the imprint made can
readily judge the degree of foot contact. Occasionally, the material is hard and
smooth enough or rough and irregular enough that the imprint made by the foot
cannot be seen. This is where measurement precision will be the judge.
If the imprint made by the foot cannot be readily seen, the simple solution is to
apply a thin patted layer of clean moist mortar sand per ASTM C144-02, about
5 to 10 mm thick (1/8 to 1/4 inches), on the spot to be measured. Level and pat
down firmly with your hand to roughly 10 mm thick. Place the GeoGauge on the
packed moist sand. Rotate the GeoGauge no more that 1/4 of a revolution by
holding the side or bottom of the gauge. Now you can take the measurement.
When adding water to the mortar sand, there is not enough water if it does
not clump when squeezed in your hand. There is too much water if water
squirts between your fingers. It is essential to be consistent in using moist sand
and in the seating of the GeoGauge. The influence of the moist sand in the
measurement is negligible.
Use just enough moist sand that when the GeoGauge is placed on it, the sand
does not bunch up and touch the bottom of the internal or exterior flanges. It is
important that no sand or other material come into contact with the foot flanges
or the underside and sides of the GeoGauge body. Only the ring foot surface
should contact the soil. A small area on the sides of the ring foot may touch the
soil if the soil there is loose.
Dry sand or other cohesionless materials do not help the seating of the
GeoGauge. In fact dry sand will serve to decouple the GeoGauge from
the ground.