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Joints: Orientation
Joint orientations (dip / dip direction) can be defined by selecting
Input Data > Joint Orientations. The orientations of 3 distinct
joint planes must always be defined for an Unwedge analysis.
A stereonet preview of the joint plane great circles and the tunnel
axis orientation is displayed in the dialog.
Joint
orientation defined in the Input Data dialog.
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Joints: Import from Dips
Alternatively, joint orientations can also be imported from a Dips
file, by selecting the Import button. (Dips is a program
for the statistical analysis of orientation data, also available from
Rocscience).
Import joint planes from Dips.
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Joints: Stereonet View
The stereonet can be displayed in its own full view by selecting the
Stereonet View option. Joint orientations can be interactively edited
in the sidebar, while viewing the stereonet. This is an alternative
to using the Input Data dialog.
Stereonet view – joint orientations
can be entered in the sidebar.
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Joints: Multiple Joint Combinations
Unwedge can only consider 3 joint planes for any given
analysis. However, if you have more than 3 joint planes of interest,
you may define and select different combinations
of 3 joints to analyze, as follows:
1. Select Input Data > Joint Orientations, and select the Add
button to
create additional joints.
2. Enter the joint orientations, and assign the joint properties.
3. You can manually select the 3 joints to consider, using the Joint
Combinations drop-list selection boxes.
4. OR, you can automatically analyze all possible combinations
of 3 joint planes, with the Combination
Analyzer option
(see below for more information).
Manual selection of joint combination to be analyzed.
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Joints: Combination Analyzer
If you have defined more than 3 joint orientations, you can automatically
analyze all possible combinations of 3 joints with the Combination
Analyzer option.
1. Select Input Data > Joint Orientations > Combination Analyzer.
2. You will see the Combination Analyzer dialog. In this dialog,
select
the Compute Combinations button.
3. A summary of results will be displayed. This allows you to sort
(rank)
the results according to output such
as Required Support Pressure,
Factor of Safety, Wedge Volume, etc.
4. The analysis summary allows you to determine the most critical
joint
combination(s). Any individual combination
can then be selected from the
list, and further analysis can be
carried out on the selected combination.
Combination Analyzer dialog – summary
of results.
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Joints: Properties
Joint properties (shear strength, water pressure, waviness) are defined
by selecting Input Data > Joint Properties.
Joint Properties defined in the Input Data dialog.
If you require more than one joint property type, you can create any
number of joint property types by selecting the Add button.
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Joints: Shear Strength
Three shear strength models are available in Unwedge:
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Mohr-Coulomb
Barton-Bandis
Power Curve
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Mohr-Coulomb strength parameters.
Note that Tensile Strength can be explicitly defined for the Mohr-Coulomb
model. In addition to Mohr-Coulomb, you may define the shear strength
of a joint using the Barton-Bandis or Power Curve strength models.
Barton-Bandis strength parameters.
Power Curve strength parameters.
Note: for the Power Curve model, tensile strength is represented by
the “d” parameter.
In order to visualize the strength function defined by the parameters
you have entered, you can select the plot button in the dialog. The
plot will be displayed in a separate dialog.
Plot
of shear-normal strength envelope.
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Joints: Waviness
Waviness is a parameter that can be included in calculations of the
shear strength of a joint for any of the strength models used in Unwedge.
It accounts for the waviness (undulations) of a joint surface, observed
over distances on the order of 1 m to 10 m, and has the effect of
increasing the shear strength of the joint.
The waviness angle is equal to the AVERAGE dip of the joint, minus
the MINIMUM dip of the joint. This is illustrated in the figure below.
Definition of joint waviness.
The waviness angle is implemented in the same way as the Mohr-Coulomb
friction angle. The increased shear strength is directly proportional
to the normal stress and the tangent of the waviness angle.
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Joints: Water Pressure
Water Pressure can be accounted for on the joints by defining the
Water Pressure as a Joint Property in the Input Data dialog.
Water pressure option.
There are two options available for defining water pressure in Unwedge:
Constant or Elevation.
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The Constant Water
Pressure option assumes a constant
(ie.
uniform) water pressure, over the entire joint plane.
The Elevation Water Pressure option
allows you to specify the y-coordinate
of
a water table. The Elevation must be consistent with the y-coordinates
of the Opening Section. The water
pressure will be calculated on each
wedge
face, based on the vertical distance from the wedge to the Elevation. |
Generally a Water Pressure of zero is assumed, since underground excavations
are usually free-draining. However the influence of water pressure
on the stability of a wedge may be important in some cases, for example,
when the wedge has been supported with shotcrete and no allowance
has been made for drainage.
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Joints: Assigning Properties
If you are using more than one joint property type (i.e. your joints
have different properties), then the property types are assigned to
the joints under Input Data > Joint Orientations. For each joint,
select a joint property type from the drop-list beside the joint orientation.
Assigning joint properties.
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