Environmental Engineering Reference
In-Depth Information
Procedure
Ceramic plates are cemented to the surface at locations to be monitored. The plates con-
tain pegs that which serve as reference points for aligning the tiltmeter and measuring the
angular deflection. Changes in tilt are found by comparing the current reading to the ini-
tial reading.
Pendulums
Application
Pendulums are used to measure the horizontal distance between two points at different
elevations. They are installed in the highest elevations of structures adjacent to open exca-
vations areas or over tunneling operations, where ground subsidence may cause differen-
tial settlement and tilting.
Instrument
The two general pendulum types, direct and inverted, are illustrated in
Figure 4.4.
Mercury Pools Set in Piers
Application
Mercury pools set in piers were installed by National Oceanic and Atmospheric
Administration's (NOAA) Earthquake Mechanism Laboratory, Stone Canyon, California,
adjacent to the San Andreas Fault to monitor ground surface movements over a large area
(Bufe, 1972).
Anchorage
Injected plug
Pendulum
Support
Scales
wire
Concrete
base
Scales
Borehole,
150-mm
casing
Wire
Suppo
Weight
Injected plug
Anchor
Oil tank
(b)
(a)
FIGURE 4.4
Pendulums of Soil Instruments Ltd: (a) direct pendulum, (b) inverted pendulum. (From Franklin, J.A.,
Int. J. Rock
Mech. Miner. Sci. Geomech. Abstr
., 14, 163-192, 1977. With permission.)
