1. TAGAsoft - TSLOPE TAGA Engineering Software Ltd TSLOPE Presentation February, 2014 Robert Pyke

2. 2D or not 2D – that is, 3D Traditionally slope stability analyses have been conducted using two dimensional cross sections, if only because in the early days of geotechnical engineering such analyses were done by hand and three dimensional analyses were unthinkable. But with modern computers anything is possible. The big question is does it make a difference. The answer is YES, it can. The factor of safety for a three dimensional sliding surface can be less than or greater than a two dimensional one by up to 25 percent. TAGAsoft - TSLOPE

3. The next slide shows a long embankment forming one side of a canal that leads to a hydropower plant. A two dimensional analysis is usually satisfactory for geometries like this, but note that if, for instance, there was a short section with a different, weaker, foundation material, a two dimensional analysis might be overly conservative because the “end effects” would not be properly accounted for. TAGAsoft - TSLOPE

5. The following slide shows a dam that very clearly has three dimensional geometry. In this case both the curvature of the dam and the buttressing effect of the abutments means that a standard two dimensional analysis is likely very conservative. On the other hand, if the back and side slopes of a fill open out, as was the case at the Kettleman Hills landfill, which is shown subsequently, the three dimensional factor of safety might be lower than the two dimensional factor of safety. TAGAsoft - TSLOPE

7. Presentation outline Introduction A short history Slope stability analysis - discussion TSLOPE Three examples – open pit, landslide, landfill Where to from here

8. TAGAsoft - TSLOPE Who we are Web site http://www.tagasoft.com TSLOPE v2 development by Peter Wood, Wellington, New Zealand Technical direction from Drs Robert Pyke (California) and Ian Brown (Wellington) Web based delivery of software and support

9. TAGAsoft - TSLOPE A short history …. 1970:

10. TAGAsoft - TSLOPE 1978:

11. TAGAsoft - TSLOPE 1985:

12. TAGAsoft - TSLOPE TAGAsoft history 2D slope stability programs, TSLOPE and TSTAB developed in early days of personal computers by Robert Pyke and his team in Berkeley, California. First version of TSLOPE3 developed in 1989 for design of Puente Hills landfill, using LA County method of force equilibrium. New version of TSLOPE3 developed in 2003 for Windows with 3D graphics using Ordinary Method of Columns (OMC). TSLOPE v2.0.1 (2009), with Spencer’s method extended to 3D; both 2D and 3D analyses combined into one slope stability program.

13. TAGAsoft - TSLOPE Before we get started: From TSLOPE/TSTAB Users’ Manual

14. TAGAsoft - TSLOPE Why do we carry out slope stability analyses ? To get a numerical value that we can assign to the stability (or otherwise) of a slope – the factor of safety. To confirm something we already know – the slope is stable, or it is unstable. To back calculate the material strength following observed slope failure. To satisfy a regulatory requirement eg. factor of safety greater than 1.5. To provide insight into slope behaviour. To assist with slope design – excavation geometry, drainage, reinforcement

15. TAGAsoft - TSLOPE Why do we continue to use 2D limit equilibrium slope stability analysis ? There is a long history of use. Conventional wisdom says: 2D factor of safety will always be lower than 3D provided comparable limit equilibrium approaches are used. Slope geometry does not vary in the direction perpendicular to the cross section analysed. Valid reasons: Few acceptable 3D programs; they generally use simplified assumptions that limit applicability to real problems. Alternative finite element codes are complex and require material properties that are difficult to measure.

16. TAGAsoft - TSLOPE Why we should carry out 3D slope stability analyses We now work in a 3D world with most other computer applications (GIS, CAD, geological modelling, mine planning). 3D geometry often has significant influence on slope stability, e.g. wedge like geometry. 3D slope data becoming increasingly easy to acquire (e.g. laser scanning) and use. Ability to model detailed failure surfaces rather than assumed planar surfaces. All this leads to a better understanding of the nature of slope failure mechanisms.

17. TAGAsoft - TSLOPE TAGAsoft – TSLOPE TSLOPE - a new program for 2D and 3D slope stability analysis; from wedge failures in open pit mines defined by rock structure, to landfills where failure is possible along a geofabric liner. Development of a slope stability analysis “tool box” to assist with slope design. Breakthrough in 3D limit equilibrium analysis: implementation of Spencer’s method in 3D is able to satisfy full force and moment equilibrium. OMC provides alternate approach, provides for calculation of local factors of safety and the highlight the potential for progressive failure.

18. TAGAsoft - TSLOPE Spencer’s method Spencer’s method now extended to 3D with vertical columns. Side force assumed to be at a constant angle. Shear strength – Mohr Coulomb, or Hoek Brown. Search routine determines side force angle to provide force and moment equilibrium, as well as the direction of sliding.

19. TAGAsoft - TSLOPE 3D Spencer’s analysis method details Use minimization to determine best estimate for global equilibrium, including sliding direction. For symmetric problems, achieving “exact” global equilibrium is often possible. For asymmetric problems, typically get within a few percent of “exact” global equilibrium. Method is robust. It also calculates out of balance forces and moments, thus providing estimate for “error” of the result. Always get a solution – we don’t have an error message “algorithm failed to converge”.

20. TAGAsoft - TSLOPE 3D Ordinary Method of Columns Calculates overall factor of safety as ratio of sum of driving forces over sum of resisting forces. Always get a solution – there are no iteration or convergence issues. Needed as starting point for Spencer’s analysis. Automatically get local factors of safety for individual columns. Local factors of safety provide an indication of the potential for progressive failure. Simple definition of factor of safety allows for much easier inclusion of driving water pressures and external forces of all kinds.

21. TAGAsoft - TSLOPE Slope model definition Multiple surfaces can be input. Complex slope geology accommodated with layers or zones. Geology independent of topography and excavation surfaces. Slope failure surfaces pre-defined, arbitrary 3D shapes, or complex surfaces developed constrained by layers. Groundwater as phreatic surfaces, or pore pressure surfaces. Import drillholes (AGS), geo-referenced images. Tension crack outlines.

22. TAGAsoft - TSLOPE Example 1 Open pit mine slope failure

23. TAGAsoft - TSLOPE Geological model exported from TECHBASE

24. TAGAsoft - TSLOPE

30. Example 2 Karaka Bay, Auckland Coastal area of Auckland city, overlooking Hauraki Gulf. Geology – low strength sedimentary rocks dipping towards sea. Mapped landslide, controlled by bedding plane failure. Topography obtained from LIDAR. Limited subsurface information.

31. TAGAsoft - TSLOPE

38. Factors of safety 3D OMC 1.194 Spencer’s 3D 1.328 Spencer’s 2D 1.256

39. TAGAsoft - TSLOPE

43. Factors of safety 3D OMC 1.003 Spencer’s 3D 1.052 2D OMC 1.205 Spencer’s 2D 1.216

44. TAGAsoft - TSLOPE Where to from here ? TSLOPE presently available for beta testing Tasks to be completed include full software documentation, client/server implementation. Software to be licensed using SaaS model. 1 week US$200, 4 weeks US$500 per IP address Details to be announced http://www.tagasoft.comhttp://www.tagasoft.com Enquiries: info@tagasoft.com