Environmental Engineering Reference
In-Depth Information
The information is particularly important for the design of long, high-capacity
piles penetrating several formations where design analysis based on laboratory test
data is often not reliable, especially in formations which are difficult to sample undisturbed.
Instrumentation
Deflections at the pile top shown in
Figure 4.36
are monitored by dial gages and optical
surveys. Deflections at the pile tip and at various locations along the pile's length are mon-
itored with tell tales and strain gages. A load or pressure cell installed at the base provides
data on the end bearing pressure.
During horizontal testing, dial gages and optical surveys monitor deflections at the top
and the inclinometer monitors deflection along the length.
Dynamic Load Testing
The Case-Goble method of dynamic pile testing (Goble and Rausche, 1970; Rausche et al.,
1971; La Fond, 1977) utilizes transducers and accelerometers attached near the pile top. For
each hammer blow, a “Pile Driving Analyzer” processes the signals to calculate the hammer
energy, pile stresses, and pile bearing capacity. Instrumentation removes the need to evaluate
the unknown factors of energy loss in the driving system and allows the indirect elimination
of the dynamic pile characteristics. It thus provides a more accurate measurement of driving
resistance. The data are input to the wave equation method of dynamic pile analysis.
4.5.3
Excavation Retention
Objectives
A retaining structure in an open excavation must be designed to provide adequate support
for the excavation sides and to restrict wall deflection to a minimum in urban areas. As the
Dial gages to read tell tales and
pile head deflection
Deflections are checked also
by optical survey
(L) Inclinometer for lateral
load test
(u) Tell-tale and /or strain
gage (v) or (w)
Fill
Pile
Soil no. 1
(u) Tell-tale and /or strain
gage (v) or (w)
(u) Tell-tale and /or strain
gage (v) or (w)
Soil no. 2
Anchors
Rock
(u) Tell-tale and load
pressure cell (s, t)
FIGURE 4.36
Instrumentation for pile load test.
