Introduction of ALM1 & ALM2 Rock Strength Models to SVSlope® 2D

SASKATOON, July 15, 2013

SoilVision Systems Ltd. is pleased to announce the addition of the Anisotropic Linear Models (ALM) versions 1 & 2 into the SVSlope® 2D software package. The models allow advanced analysis of the strength of rock masses and are particularly useful in the analysis of open pits. The models have been implemented and benchmarked in the current version of the software and are available for use.

Anisotropic Linear Model (ALM)


Figure 40 Anisotropic Linear Model (ALM1)
Figure 40 Anisotropic Linear Model (ALM1)

ALM is a constitutive model that describes the shear strength of an anisotropic rock mass in relation to the change of Angle of Anisotropy (AoA). The AoA is defined as the angle between the orientations of the plane of shear and the plane of weakness. This model was originally developed by Snowden Mining Industry Consultants in Perth, Australia in 2005. Two generations of the model are now available. The first generation (ALM1) is based on the Mohr-Coulomb criterion.

The bedding and rock mass shear strengths for ALM1 are defined in terms of the Mohr-Coulomb parameters of cohesion and friction angle. In this model, a rock material is defined with the following anisotropic strength parameters:

  • The weakness plane (usually the bedding plane) cohesion and friction angle (c1, phi1), corresponds to the minimum shear strength
  • Rock mass cohesion and friction angle (c2, phi2), corresponds to the maximum shear strength
  • Angle of bedding plane orientation (theta) from horizontal
  • Parameters A and B define a linear transition from bedding plane strength to rock mass strength, with respect to shear plane orientation

ALM1 defines the shear strength relationship to the AoA, rock mass strength, and bedding shear strength. The parameters A and B allow the user to define a linear transition from bedding plane strength to rock mass strength, with respect to shear plane.


Figure 41 Modified Anisotropic Linear Model (ALM2)
Figure 41 Modified Anisotropic Linear Model (ALM2)

Since 2009, Snowden has been undertaking further research and development of the ALM1 method. In the second generation of ALM, the Modified Anisotropic Linear model (ALM2), Snowden recognizes that cohesion, c and friction angle, phi for a typical rock mass and bedding plane are a function of the stress state within the rock mass and along the bedding plane. As a result, the model requires either a shear stress versus normal stress function or a function relating cohesion and friction angle to normal stress.

In ALM2, as shown in Figure 41, with the parameters "A1", "A2", "B1" and "B2", the non-symmetrical shape of the shear strength transition can be modeled. The rate and shape of the transition depends on the bedding to rock mass strength ratio as well as the normal stress. Both the rock mass and bedding shear strengths are now modeled non-linearly in terms of the normal stress.