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Joint Properties
An Swedge analysis requires the orientation and shear strength of two joint planes to be defined. Swedge determines if a removable wedge can be formed by the intersection of the joint planes with the slope surface, and calculates the safety factor of the wedge.
Intersection of joint planes forming a wedge
Joint properties are entered in the Input Data dialog. The required joint properties are:
Optional joint properties include:
For a Deterministic Analysis the joint properties are assumed to be exactly known. For a Probabilistic Analysis, the joint properties can be defined as random variables, and a probability of failure is calculated.
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Joint Properties: Orientation
Joint Orientations in Swedge are defined by Dip and Dip Direction, and can be entered in the Input Data dialog or imported from a Dips file.
Joint orientation input data (Deterministic)
For a Probabilistic Analysis, the joint orientations can be defined as random variables.
Probabilistic joint orientation (Fisher Distribution)
For a Combination Analysis, multiple joint orientations can be defined, and Swedge will analyze all possible combinations of two joints.
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Joint Properties: Strength
The shear strength of the joint planes can be modeled using the following strength criteria:
Mohr-Coulomb
Barton-Bandis
Power Curve
The strength criteria define the relationship between effective normal stress on a wedge plane, and the shear strength of the wedge plane.
Mohr-Coulomb shear strength equation and input parameters
Barton-Bandis shear strength equation and input parameters
Power Curve shear strength equation and input parameters
For a Probabilistic Analysis, the joint strength can be defined as a random variable. There are two methods available - you can specify statistical distributions for the individual strength parameters (e.g. cohesion and friction angle), or you can specify a variability of shear strength about the mean strength envelope, as illustrated below.
Random shear strength option (Mohr-Coulomb envelope)
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Joint Properties: 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 Swedge. 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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Joint Properties: Water Pressure
The effect of water pressure on the joint planes can have a great effect on wedge stability, decreasing the safety factor. Water pressure can be applied to the joint planes with the Water Pressure option in the Input Data dialog.
Water Pressure option in Input Data dialog
The Water Pressure can be defined by specifying the water level in the slope, or by specifying the pressure on each joint plane.
For more information see the Water Pressure topic in the Swedge help system.
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