Humboldt H-4140 GeoGauge - Manual (Page 13)

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5.0: Get Acquainted With The GeoGauge ®
Before using the GeoGauge to make measurements that matter, get acquainted
with it. Get used to what it takes to make a precise measurement. Get
acquainted with how the stiffness of prepared materials varies.
Select a site that is representative of the material you will be measuring. Bases
or subbases with high aggregate contents should be avoided for awhile until the
technician gains some experience.
Layout measurement locations in a straight line, with the increment between
locations being about .6 meter (2 ft) or less. Walking over measurement
locations will not disturb the surface and affect a measurement. The physical
properties of prepared construction materials can be extremely variable.
They can be much more variable than expected. Over a .6 meter (2 ft)
increment, it is not uncommon for soil stiffness to vary more than 1 MN/m! So,
the initial over-sampling of a material is desirable to develop accurate profiles.
During the actual compaction, the engineer will specify the measurement
interval. Intervals of 15 m (50 ft.) to 145 m (500 ft.) are typical for material quality
control measurements.
The site and layout of measurement locations should allow for repeated
measurements. Six (6) locations is a good number. Site conditions are continually
changing, such as: varying moisture content, sandy soils drying out rapidly,
and clays drying slowly. Making a comprehensive set of measurements rapidly
assures material characterization under one set of conditions (e.g., with in ~ 1 hr.
of compaction). Knowing site conditions is critical to characterizing a material.
Repeat measurements at each location at least three times. These repeated
measurements will get you familiar with GeoGauge precision for the
corresponding surface conditions. Seating the GeoGauge to the ground is
the most important part of the measurement (see GeoGauge Seating below).
Always remove the GeoGauge between measurements and do not touch the
GeoGauge during a measurement. The number of repeated measurements
depends on the site. Don’t confuse the measurement precision (repeatability)
with location-to-location variability in the material.
Perform GeoGauge measurements first, before other companion measurements.
Performing measurements such as FWD or nuclear gauge measurements will
disturb the material and affect any subsequent measurements.
Again, practice making measurements before performing the measurements
that matter. Site conditions and the type of material will affect how you will
want to place the GeoGauge on the surface. Knowing how to properly seat the
GeoGauge’s foot on the surface, as described below, and being consistent in
how you use the GeoGauge is critical to good measurements.
Remember, compacted materials are not as structurally uniform as most people
expect. Stiffness is a sensitive enough measurement of a material to reveal this