Geotechnical Manual for Slopes

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10.5 LOADS AND STRESSES
10.5.1 Load Cells for Rockbolts and Anchors
Only load cells suitable for long-term monitoring of rockbolt and anchor
loads are considered in this Section.
The anchor load can either be determined at intervals, by measuring the
force required to jack the anchor head away from its seating, or it may be
monitored continuously with a compression load cell between the anchor head
and bearing plate. The types of load cell available and their advantages and
disadvantages are given in Table 10.3.
10.5.2 Earth Pressure Cells
Measurement of earth pressure is unlikely to be required in soil slopes
in Hong Kong. In large excavations, cells may be specified to measure the
contact pressure between the soil and a retaining structure. Effective stress
can be computed by installing pressure cells with piezometers. The type and
position of a cell should be chosen with great care, because the introduction
of the cell into the soil causes a redistribution of the stresses around it,
and the errors depend on the geometry of the instrument. Details of the types
of cell available and the problems that may be encountered when using them are
given by Hanna (1973).