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Support
There are various options for modeling support in Swedge, including:
Different support types can be combined (e.g. bolts and shotcrete), and the required support parameters necessary to achieve a given factor of safety can be readily determined.
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Support: Bolts
Rock bolts can be graphically added to the wedge with the Add Bolt option. Simply click on a point on the wedge face, and you will first see the following dialog.
Bolt Properties dialog
Enter the desired bolt properties and select OK. The bolt will be added to the model and the safety factor will be recalculated. Any number of bolts can be individually added to the model, and bolt properties and orientation can be easily edited if necessary.
Wedge with three bolts added
Note the following features of the Bolt Properties dialog:
Bolt Capacity - you can either specify the Bolt Capacity or the Factor of
Safety. If you choose the Factor of Safety option, Swedge will calculate the
required bolt capacity to achieve the specified Factor of Safety.
Optimize Orientation - if you choose the Optimize button, the bolt
orientation will be automatically optimized to give the maximum Factor of
Safety for the given bolt capacity
Active / Passive - a bolt can be specified as either Active or Passive.
Passive force increases the resisting force in the safety factor
calculation. Active force decreases the driving force in the safety factor
calculation. In general, a Passive support force gives a lower safety factor
than an Active force with the same magnitude, and is therefore a more
conservative design assumption.
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Support: Shotcrete
Shotcrete can be applied to the slope face by selecting the checkbox in the Shotcrete dialog and entering the thickness and shear strength of the shotcrete. Shotcrete is always applied as a Passive support force.
Shotcrete properties dialog
When shotcrete is applied, you will notice that the slope face is shaded gray, to indicate the presence of shotcrete. Shotcrete is NOT applied to the upper slope of the model. The support force provided by the shotcrete is obtained by adding the trace lengths of Joint 1 and Joint 2 on the slope face, and multiplying by the shotcrete thickness and shear strength.
Shotcrete applied to slope face (grey shading)
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Support: Pressure
The Pressure option allows you to specify a distributed force which is applied to the slope face and / or the upper face of the wedge. The pressure is specified in terms of force per unit area, and may represent:
support pressure (for example, rock bolts applied to the slope face of the
wedge)
loading pressure (for example, a distributed surcharge load on the upper
face of the wedge)
The Pressure option is the easiest way to model the effect of pattern bolting or distributed loads.
Pressure dialog
When pressure is applied, the corresponding wedge face is shaded and an arrow is displayed as shown below.
Pressure applied to slope face (shading and arrow)
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Support: External Force
Support (or loading) can also be represented as an External Force, with a given direction and magnitude. External forces are defined in the Input Data dialog.
External force definition
NOTE: an External Force in Swedge is exactly equivalent to an Active bolt, with the same orientation and capacity. An External Force is displayed as an arrow applied to the wedge.
Display of External Force (side view)
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Support: Sensitivity Analysis
The Sensitivity Analysis option makes it easy to determine the required support parameters necessary to achieve a given factor of safety. Simply enter a range of values for a support parameter (e.g. bolt capacity, shotcrete thickness, support pressure), and from the sensitivity plot you can determine the parameter value which corresponds to a desired factor of safety.
For example, in the following sensitivity plot, a support pressure of approximately 3.8 tonnes/m2 is necessary to achieve a safety factor = 1.5.
Support pressure versus factor of safety
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