Environmental Engineering Reference
In-Depth Information
TABLE 4.2
Instrumentation: Simple vs. Complex Methods and Devices
Applications
Simple
a
Complex
b
Surface movements
Optical surveys of monuments,
Global positioning system (GPS)
settlement plates
Water-level device
Electrical tiltmeter
Simple strain meter
Electrical strain meter
Wire extensometer
Vertical extensometer
Subsurface deformations
Settlement points
Inclinometer
Borros points
Deflectometer
Rock bolt and rod-type
Wire-type MPBX (extensometer)
MPBX extensometers
Shear-strip indicator
Acoustical emissions
In situ
pressures and stresses
Tell tales (pile load tests)
Pneumatic and electric piezometers
Open-system piezometers
Strain gages
Pressure cells
Vibrating-wire stress meter
Residual rock stresses
Strain meter on rock surface
Borehole devices
Flat jacks
a
Simple types are read optically or with dial gages. They are less costly to install and less subject to malfunction.
b
Complex devices are attached to remote readouts, and many can be set up to monitor and record changes con-
tinuously. The device and installation are more costly, and reliability will usually be less than that of the sim-
pler types. In many cases, however, there is no alternative but to use the more complex type.
TABLE 4.3
Instrumentation of Movements, Deformations, and Stresses
Method/Instrument
Applications
Surface Movements
Survey nets
Vertical and horizontal movements of slopes, walls; settlements by precise
leveling, theodolite, or laser geodimeter. Requires stable bench mark. Slow
except with laser. GPS to monitor slope movements
Water-level device
To monitor building settlements optically
Settlement plates
Installed at base of fills and read optically for settlement monitoring
Remote settlement monitor
Installed at base of fills, over tunnels in soft ground, adjacent to excavations
(settlement extensometer)
to monitor vertical deflections
Reference point installed below in rock or strong soils
Instrument connected electrically to readout or recorder
Tiltmeters
Measure rotational component of deflection electronically
Used in buildings, on walls, and rock-cut benches
Pendulums
Monitor tilt in buildings adjacent to excavations
Convergence meters
Measure convergence in tunnels, between excavation walls, and down cut
slopes in rock
Surface extensometers
Measure linear strains downslope or across faults. Small
or strain meters
strain meters for joints
Terrestrial
Monitor movements of slopes, retaining structures, and
stereophotography
buildings. Less accurate than optical systems
Vibration monitoring
Monitor vibrations caused by blasting, pile driving, traffic, etc.
Subsurface Deformations
Vertical rod extensometer
Settlement points installed at various depths allow measurement of
increments of vertical deflection. Borros points, cross-arm device, and the
remote settlement monitor also are used
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