1. Slope Stability in Jointed Rock Masses
Maurice B. Dusseault
Porous Media Research Institute
University of Waterloo, Waterloo ON Canada

2. Uncertainty in Slope Design
What are joint patterns at slip surfaces?
What are the joint properties?
What will the loads be over time?
Pore pressures can be seasonal, or a storm
Earthquake loads are hard to predict
Will the rock strength deteriorate over time?
Geochemical changes in shale
Dissolution of limestones
Did blasting affect properties?
A highly indeterminate design problem

3. Solutions to Uncertainty
Deterministic slope stability models have now reached their useful limits
We need probabilistic models
Fabric from oriented core + stochastics
Likely property variations (e.g. c, )
Return period probabilities on pore pressure
Same for earthquake loads
Cohesion loss with time in shales
Safety factor method is not adequate
Monitoring vital in critical cases

4. Some Factors Depth of tension cracks Earthquake loads Joint properties
Cohesion deterioration in regions of high stresses
Seasonal pore pressure variations

5. How do we extrapolate jointing data from the surface to depth?
Fabric Uncertainty
How to extract fabric data from boreholes?
How do we extrapolate jointing data from the surface to depth? ??

6. Geometry and Pore Pressure
Joint intensity decreases with depth?
Are there sub-parallel stress joints?
Do joint properties vary with depth?
Which is the most critical slip plane?
What is the p response to rainfall?

7. Whither Slope Mechanics?
Since the advent of 3-D block models, there is nothing new in slope stability models
Also, the continued pursuit of better deterministic models is a futile effort.
The random “noise” because of uncertainty exceeds the precision of models
Therefore, the only realistic developments are in the area of stochastic (probabilistic) approaches to stability, combined with monitoring

8. Mining and Civil Approaches
Civil slopes are designed conservatively, using Factor of Safety approaches
Minimize risk to people and structures
Long service life required
Minimal long term deformations
Mining slopes are almost always empirically built to be close to failure at all times
As steep as possible to minimize excavation
Monitored carefully for deformations
Generally experience continued slow movement

9. FS is not necessarily same as Pf
Factor of Safety
FS = 1.6
FS is not necessarily same as Pf
FS = 1.9
Pf = 0.05
Pf = 0.01
Safety factor

10. Monitoring Methods Displacement gauges, alarm tapes
Piezometric measurements
EDM 3-D measurements, resolved to give a map of movement vectors with time
Satellite InSAR interferometry
Direct visual measurements by mine personnel (face raveling…)

11. Protecting People Rock catching berms, ditches
Deflecting devices and diversion structures
Wire mesh blankets to minimize acceleration of individual blocks
Surface block scaling (removal)
Horizontal drains into slip planes
Shotcrete or concrete coat the entire surface
Controlled deliberate inducing of failures
Massive cable anchors, etc…