Slope stability analysis and the new (New Zealand) National Seismic Hazard Model
By Ian Brown.
For many sites in New Zealand, the recently announced National Seismic Hazard Model (NSHM) 
has indicated levels of shaking that will make it difficult, in some cases, to establish site stability when calculated in a conventional 2D limit equilibrium slope stability analysis. We provide an example that shows when 3D effects are taken into account, the out of plane (third dimension) resisting forces provide sufficient additional restraint that indicates stability of the 3D volume of soil. Read more.
Development of 3D models of slope failure during Canterbury earthquake sequence
By C J Skinner, I R Brown.
Christchurch City and its surrounds experienced a series of damaging earthquakes in 2010 and 2011. During the 22 February 2011 earthquake, extensive cracking and movement of the ground occurred in some areas of the Port Hills. We have used a geological modelling package, Leapfrog3D®, to build 3D models of three of the well documented landslide areas. The surfaces that were developed in Leapfrog3D® have been used in TSLOPE, a new slope stability package, to investigate the 3D effects on slope stability. An objective of our study was to develop a number of slope models that could be used to calibrate computational methods used to predict seismic displacements, and to make these available to other researchers. Read More
Estimation of in situ strength from back-analysis of pit slope failure
By Ian Brown, Peter Wood & Mark Elmouttie
Using a software package that can be used for either three or two-dimensional (2D) slope stability analyses
of the same model we analyse the stability of columns (3D) or slices (2D) overlying a shear failure surface. The failure surface can be any shape, such as that formed by interconnecting fault surfaces in an open pit slope failure that we analyse. We show that there is a significant difference in the factors of safety calculated using 3D analyses, compared with 2D sections through the same model. This means that different shear strength parameters will apply when the values are varied to obtain a Factor of Safety of 1.0.
Systematic back-calculations of open pit slope failures using appropriate 3D analysis methods can give a better understanding of appropriate shear strengths to use in forward 3D analyses. This should lead to more efficient pit slope designs. Read More
3D terrain and geological modelling for the design of a cut slope in Wellington, NZ
By Matt Brown
A 3D terrain and geological model has been used to assist in the design of a cut slope for a proposed house in Wadestown, Wellington. The natural slope of the site is ~30º and consists of colluvium overlying fractured greywacke. A 3D geological model was built from site investigation data, a topographical
survey, and from point cloud data generated via photogrammetry (utilising photographs obtained by a UAV). The 3D model was analysed using TSLOPE; a 3D limit equilibrium slope stability package. This enabled calculation of the appropriate parameters for design of slope reinforcement. Read More
On the Limitations of Limit Equilibrium Slope Stability Analyses
By Robert Pyke Ph.D., G.E.
The history of slope stability analyses by the method of slices or columns in geotechnical engineering is well documented in the textbook by Duncan, Wright and Brandon (2014) and elsewhere. The procedures used for slope stability analysis started out as hand or graphical methods, but with the introduction of limit equilibrium methods of analysis most calculations became computerized. Many engineers seem to believe that these computer programs automatically give the correct answer, but, in addition to the “garbage in – garbage out” rule still holding, these analyses are simplified and thus approximate at best. Read More
3D Effects in Slope Stability Analyses
By Robert Pyke Ph.D., G.E.
The short answer to the question “what is the difference between 2D and 3D analyses of slope stability by the Method of Slices” is that it can be significant and varies in surprising ways. The examples below illustrate some of the differences, but these are just the tip of the iceberg. Read More
Selection of seismic coefficients for use in pseudo-static slope stability analyses
By Robert Pyke Ph.D., G.E.
Analyses of seismic slope stability problems using limit equilibrium methods in which the inertia forces due to earthquake shaking are represented by a constant horizontal force (equal to the weight of the potential sliding mass multiplied by a coefficient) are commonly referred to as pseudo-static analyses. Read More
