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Loading
The default loading, which is always applied to the wedges in Unwedge,
is gravity loading due to the self-weight of each wedge. In most cases,
this is the primary driving force leading to wedge movement and instability.
There are several other ways in which loads can be applied to wedges
to simulate stabilizing or de-stabilizing forces including:
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Seismic loading
Field stress
Pressure
Bolt force
Water Pressure
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Loading: Seismic Loading
Seismic Force can be included in the Unwedge analysis by
selecting the Seismic Force checkbox under the General
tab of the Input Data dialog.
Seismic force option in Input Data dialog.
There are four different methods of specifying the direction and magnitude
of the seismic force:
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Sliding – seismic coefficient is applied in the sliding
direction for
each wedge
Local X / Y / Z – seismic coefficients can be independently
specified
in the local X, Y and Z directions
North / East / Down – seismic coefficients
can be independently specified
in the global North / East /
Up directions
Trend / Plunge – seismic
coefficient is specified at a given Trend / Plunge |
The Seismic Force option in Unwedge is a simple pseudo-static
analysis, in which the seismic coefficient(s) are multiplied by the
mass of the wedge and acceleration due to gravity to compute the additional
body force on each wedge. The seismic coefficients are dimensionless
numbers defining the seismic acceleration as a fraction of the acceleration
due to gravity.
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Loading: Field Stress
By default, the actual stress field in the rock mass surrounding the
excavation is NOT taken into account. With the Field Stress
option, the user may choose to include the effect of “clamping
stress” on the wedge stability. This will determine the actual
stress distribution around the excavation and then will compute the
resultant normal and shear stresses on each joint plane for each wedge.
In general, this can only increase the safety factor of a wedge; it
will never lower the safety factor in the Unwedge implementation.
For further details about the Field Stress option, see the Stress
Analysis page.
Normal stress contours on wedge planes.
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Loading: Pressure
In Unwedge, the support Pressure option
can be used to simulate the equivalent applied load of any type of
support system. However the Pressure option could also be used to
model any type of general loading that could be represented as a pressure
on the excavation boundary.
For further details about the Pressure option, see the Support
page.
Support pressure applied to sidewall wedge.
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Loading: Bolt Force
Loading is also applied to wedges by bolt support in Unwedge.
Several different bolt models are available, which allow you to explicitly
model the effects of various bolt types.
The most basic bolt model in Unwedge is the Simple
Bolt Force model. With this option, the specified bolt capacity
is applied in the direction of the bolt, regardless of how the bolt
intersects the wedge. The Simple Bolt Force model can therefore be
used to apply a line load of known magnitude and direction to a wedge.
In conjunction with the Spot Bolting option, this is useful for specifying
a known external line load to a wedge.
For further information about bolt support, see the Support
page.
Bolt Properties – Simple
bolt force option.
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Loading: Water Pressure
Another type of loading which can be applied to wedges is Water
Pressure. Water Pressure is specified as a joint property,
and allows you to define a Constant or Elevation based water pressure
to individual joint planes. Application of Water Pressure will decrease
the effective normal stress on the joint planes, and lower the wedge
safety factor.
For further details about Water Pressure, see the Joints
page.
Joint Properties – Water
Pressure option.
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