This page gives a selection of different applications in which
geotechnical instruments might be used.
Either scroll down the page, or choose an application from the
drop-down list below:
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Braced Excavations |
| The design of
projects such as these is based largely on past experience, and a monitoring
program
may not be necessary, provided that the design is very
conservative, there is sufficient previous experience in similar situations
and that the consequences of poor performance will not be severe. |
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| Outside of these
conditions, a monitoring program will normally be required, to check that
the excavation is stable and that nearby structures and utilities are not
adversely affected. The monitoring may apply to the wall and bracing, the
ground beneath and adjacent to the excavation or nearby structures and
utilities. |
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Instruments possibly applicable: |
| For measurement
of |
Instruments |
Settlement of ground surface and
structures
|
Rod Extensometers (in conjunction
with surveying techniques) |
Horizontal deformation of ground surface and
structures
|
Tape Extensometers, Jointmeters |
| Change in width of cracks in
structures |
Crackmeters |
| Subsurface horizontal ground deformation |
Vertical and In-place Inclinometers,
Magnetic Probe and Vibrating Wire Extensometers |
| Subsurface settlement of ground
and utilities |
Magnetic Probe and Vibrating Wire
Extensometers |
| Load in internal bracing |
Weldable Strain Gauges |
| Load in external bracing |
Load Cells, Weldable Strain
Gauges |
| Groundwater pressure |
Piezometers |
| Heave of ground under excavation |
Horizontal/Inclined
Extensometers,
Magnetic Probe and Vibrating Wire Extensometers |
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Drilled Shafts and Bored Piles |
Drilled shafts
(or drilled piers, caissons, drilled piles, bored piles, drilled caissons or
cast-in-place piles) are made by drilling a hole, reinforcing it, and
filling it with concrete. Design and performance considerations are, as with
driven piles, largely to do with the load-movement relationships. |
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Instruments possibly applicable:
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| For measurement
of |
Instruments |
Load-movement relationships
|
Pressure Cells, Load Cells,
Embedment Strain Gauges |
Changes in pore-water pressure
|
Piezometers |
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Driven Piles |
| Piles can be
deformed during driving, especially if driven to bedrock, or certain types
of pile can cause large displacements, affecting pore-water pressure in
surrounding soil and therefore neighbouring piles or general site stability.
Instrumentation can be used to measure the effects of pile driving and thus
help with planning this aspect of the project. |
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| Static load tests
are usually carried out, either during the design phase or at the beginning
of construction. |
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Instruments possibly applicable: |
| For measurement
of |
Instruments |
Load-movement relationships
|
Pressure Cells, Load Cells,
Strain Gauges |
Changes in pore-water pressure
|
Piezometers |
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Embankments on soft ground (other than
water-retaining) |
| In the design and
construction of embankments on soft ground, however "conservative" the soil
parameters are, there is always an element of uncertainty. Instrumentation
therefore has a significant role in the verification and, if needed,
modification of the design and construction technique. |
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| Instrumentation is
primarily used to monitor the process of consolidation and to determine
whether or not the embankment is stable. It may occasionally be considered
necessary to build a test embankment; in this case, instrumentation will
play a vital role in evaluating the performance of the test model. |
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Instruments possibly applicable: |
| For measurement
of |
Instruments |
Vertical deformation of original
ground surface below embankment
|
Settlement gauges, Horizontal
Inclinometers |
Vertical deformation and compression of subsurface
|
Settlement gauges, Magnetic Probe and Vibrating
Wire Extensometers |
| Groundwater pressure |
Standpipe, Pneumatic and
Vibrating Wire Piezometers |
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Embankment Dams |
| Including earthfill
dams of various types, rockfill dams with impervious earth cores and
rockfill dams with upstream concrete or asphaltic concrete facings. |
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| The primary function
of instrumentation in embankment dam construction and operation is to study
whether or not the dam is behaving according to design predictions. These
can either involve special conditions or uncommon design features, or simply
be related to general behaviour. |
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| It should be noted
that the instruments themselves can be the cause of problems occurring. This
is generally where compaction has been imperfect, due to the presence of
vertical pipes, tubes or cables as filling was in progress. |
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| (The general role of
instrumentation in embankment dams is described by the
International Commission on Large Dams (ICOLD) |
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Instruments possibly applicable: |
| For measurement
of (in order of priority) |
Instruments |
Leakage downstream
|
V-Notch Weir Monitors |
Performance of relief wells
|
V-Notch Weir Monitors, Standpipe Piezometers |
| Pore-water pressure within the
embankment |
Standpipe, Pneumatic and
Vibrating Wire Piezometers |
| Vertical deformation within the embankment |
Double Fluid Settlement Gauges, Horizontal
Inclinometers, Magnetic Probe Extensometers |
| Lateral deformation within the
embankment |
Magnetic Probe Extensometers,
Vibrating Wire Soil Extensometers , Inclinometers |
| Total stress at contact points between embankment
and any structures |
Vibrating Wire Pressure Cells |
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| Further monitoring
techniques may also be advisable which are outside the scope of Geotechnical
Instrumentation, e.g. Precipitation Gauges, Satellite-based distance
measuring systems, Strong Motion Accelerographs, Microseismographs and so
on. |
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Excavated and Natural Slopes |
| With excavated or
natural slopes, the main concern is always the stability of the slope. The
causes of instability are different for soil and rock. In soil, stability is
a factor of the ratio between the available shearing resistance along a
potential failure surface and the shear stress on the surface. In rock,
failures usually occur as a result of sliding or separation along
discontinuities in the rock, which contain water under pressure. |
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| Use of
instrumentation can be divided into two phases - analysis of the ground
prior to excavation and stability monitoring during excavation. The analysis
prior to excavation will consists of, for example, geological surveying or
installation of piezometers to monitor ground water pressure. For monitoring
during excavation, attention should be paid to monitoring surface and
sub-surface deformation and groundwater pressure. |
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Instruments possibly applicable: |
| For measurement
of |
Instruments |
Surface deformation
|
Crackmeters, Tiltmeters |
Subsurface deformation
|
Inclinometers, Magnetic Probe and Vibrating Wire
Slope Extensometers, Piezometers |
| Groundwater pressure |
Standpipe, Pneumatic and
Vibrating Wire Piezometers |
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Underground Excavations |
| These may include
tunnels in soil or rock, subway stations, underground nuclear waste
repositories and mines. As with excavated slopes, the factors affecting
stability vary depending on whether the excavation is in soil, clay or rock.
For soil and clay, stability is related to shear strength ratios; for rock,
it depends on discontinuities containing water under pressure. |
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| Full-scale
instrumented test sections can be of great benefit in helping to determine
design adequacy and economy, especially where the following four conditions
obtain: |
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little precedent for excavations
under similar circumstances |
|
new methods are to be used |
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likelihood of cost or safety
benefits arising from an increased understanding of the factors affecting
excavation and support |
|
the effects of scale make
exploratory excavations unhelpful |
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Instruments possibly applicable: |
| For measurement
of |
Instruments |
Deformation of ground surface,
utilities and structures
|
Settlement gauges, Tiltmeters |
Change in cracks in structures
|
Crackmeters and jointmeters |
| Deformation within excavation |
Tiltmeters, Bassett Convergence
System |
| Deformation of ground around tunnels |
Extensometers, Inclinometers |
| Stress in or loading on tunnel
liners in soft ground or on supports in rock |
Strain Gauges, Load and Pressue
Cells |
| Groundwater pressure |
Piezometers |
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