Civil Engineering Reference
In-Depth Information
by making appropriate assumptions, upper and lower limits to the settlement may be
established.
9.2.5 Special pile instrumentation
To obtain a greater understanding of the pile-soil behaviour, it is sometimes desirable
to install further instrumentation in the test piles. It should be stressed that such instru-
mentation demands significant investment in cost and manpower, if reliable results are
to be obtained. In general, for site use simple robust equipment should be used to obtain
the necessary information, albeit with some loss of accuracy. There are several case
histories reported in the literature (Reese
et al
., 1975) for fully instrumented piles;
these are really research projects and are not considered in detail here.
9.2.5.1 Distribution of load
Special high-capacity load cells were originally developed by the BRE (Whitaker,
1963). The cells are steel multi-column devices, the strain being measured by elec-
tric resistance strain gauges (Figure 9.19). Simpler modular load cell systems have
subsequently been developed by the BRE (Price and Wardle, 1983; Price
et al
., 2004).
The load transducer comprises a steel tube fitted with an internal vibrating wire gauge.
Load is transferred to the transducer, across a discontinuity in the pile formed by a
soft rubber sheet, by steel bars bonded into the concrete. Load cells of the required
Figure 9.19
BRE pile load cells. (Building Research Establishment: reproduced by permission of the
Controller, HMSO. Crown copyright.)
