The document discusses the Saito effect in the context of landslide prediction, highlighting its significance in understanding the time of failure through a characteristic hyperbolic increase in displacement rate. It examines theories related to state-dependent friction and crack growth processes that may explain this effect, alongside laboratory testing with varying pore pressures to analyze movement styles. The study concludes that Saito linearity is observable in brittle materials, which can aid in predicting failures, while non-brittle materials do not exhibit this behavior.

1. Temporal prediction in landslides – understanding the Saito effect David Petley Durham University, United Kingdom Derek Petley Warwick University, United Kingdom Robert Allison Sussex University, United Kingdom

2. Worldwide fatal landslides - 2007 Large fatal landslides occur mainly in less developed countries Prediction may be a key tool to reduce their impact

3. The Saito Effect During final failure, some slopes show a hyperbolic increase in displacement rate with time Manifested by a linear trend in a plot of inverse displacement rate against time This is the Saito effect Can be used to predict the time of failure if (and only if) we understand the when and why it applies Time Displacement rate Time Displacement rate -1 Failure

4. Theory one: state and rate dependent friction Friction inversely related to strain rate What causes the Saito effect?

5. Theory two: crack growth processes Behaviour related to growth of shear surface through subcritical crack growth What causes the Saito effect? Diagram from: Scavia, C. 1995. A method for the study of crack propagation in rock structures. Géotechnique , 45 , 447-463.

6. Movement analysis in the laboratory Aim: to simulate movement styles with increasing pore pressures using stress path testing Apply constant deviator stress Increase pore pressure Allow development of strain

7. Black Ven landslide, United Kingdom

8. Conventional drained testing of undisturbed Foxmould

9. “ Pore pressure reinflation” tests

10. p’ = 100 kPa PPR test

11. Remoulded and undisturbed samples have different form of strain accumulation Remoulded Undisturbed

12. Different behaviour using a Saito plot Remoulded Undisturbed

13. P’ = 1000 kPa Saito plot

14. Relationship with peak strength envelope Peak strength envelope

15. Saito linearity is a brittle phenomenon Only occurs in materials in which rupture surface formation is occurring Non-brittle materials do not show this behaviour - therefore it is not possible to use Saito linearity to predict failure in non-brittle materials Linearity results from stress concentrations in final stages of failure Laboratory testing allows likely behaviour to be understood Conclusion