Program Assumptions

There are some important limitations and assumptions of the RocSlope2 program that should be considered when interpreting the results.

RocSlope2 produces results for three Analysis Methods at once (Wedge, Planar, and Toppling) and assumes the following context given each of the different analyses:

Wedge Analysis

• Block Failure should be analyzed along slopes cut in hard rock where discontinuities are discrete (finite) and perfectly planar.
• Displacements take place along the joints and blocks move as rigid bodies with no internal deformation or cracking.
• The Orientation and extents of joints dictate possible Joint Intersections and formation of blocks (i.e., non-ubiquitous Joints). How and if Joints intersect will determine if a block can form, its Geometry and dimensions (i.e., volume).
• Rock mass strength and rock bridging is not considered where joints do not sufficiently persist to form closed volumes.
• Without the consideration of external Loads and Supports, only gravitational loading due to self-weight is modeled as the driving force in limit equilibrium analysis to compute the Factor of Safety.
• Without the consideration of external Loads and Supports, only Shear Strength along sliding Joints is modeled as the resisting force in limit equilibrium analysis to compute the Factor of Safety.

Planar Analysis

• The following geometrical conditions are assumed for a Planar Analysis:
  • A sliding or failure plane that strikes parallel or approximately parallel (within 20 degrees) to the face of the slope.
    
  • The failure plane daylights into the face of the slope. This condition occurs when the failure surface dips at an angle shallower than the slope face.
  • The presence of release surfaces at the lateral boundaries of the block that have insignificant resistance to sliding.

In Rocslope2 Planar Analysis, the slope slice analyzed is taken perpendicular to the face of the slope and is assumed to have unit thickness.

RocSlope2 performs the limit equilibrium analysis of a sliding block. The Factor of Safety of the slope or sliding mass is defined as the ratio of the total forces resisting down-slope sliding to the total forces inducing sliding. The resisting forces comprise the Shear Strength of the sliding surface, artificial reinforcement of the slope, or other stabilizing External Forces, if present. The driving forces consist of the down-slope component of the weight of the sliding block, forces generated by seismic acceleration, forces due to water pressures acting on various faces of the block, and external loads on the upper slope surface.

The limit equilibrium model in RocSlope2 assumes that all forces operating on a sliding block act through the centroid of the block; it ignores overturning moments. When an analysis involves a tension crack, it is assumed that the tension crack, just like the failure plane, strikes parallel to the slope face.

While many planar wedge analysis programs consider only vertical tension cracks, RocSlope2 allows for non-vertical tension cracks as well. Non-vertical tension cracks in RocSlope2 can have angles of inclination from the horizontal that are greater or less than 90 degrees.

Toppling Analysis

• The analysis is two-dimensional and is based on a unit width of slope in the out-of-plane direction (i.e., block weights are calculated assuming a unit thickness of 1 meter or 1 foot according to the unit system chosen, and all applied forces are normalized per unit out-of-plane dimension, such as bolt support forces, point loads, and distributed loads).
• The Toppling Blocks are automatically generated based on the Slope Geometry, and it is assumed that the discontinuities are equally spaced.
• The base of each toppling block is assumed to be perpendicular to the Dip Angle of the block (i.e., all blocks are rectangular).
• The three-dimensional view in is for visualization purposes, but keep in mind that the analysis is two-dimensional.
• Although the program considers Toppling, Sliding, and Flexure Toppling failure modes of individual blocks during the limit equilibrium calculations, keep in mind that the overall analysis is designed for toppling stability of rock slopes.