International Conference Vajont2013 - 8 October

1. Engineering Geology
Pore Pressure Diffusion in Brittle Translational Rockslides
Simon Loew
Chair of Engineering Geology, ETH Zuerich, Switzerland
Thomas Strauhal
alpS – Centre for Climate Change Adaptation Technologies, Innsbruck, Austria
• Simon Loew
• Chair of Engineering Geology
• ETH Zuerich, Switzerland
• Contributors
• Tokyo University August 31, 2011 & Marc Diederichs
Giovanni Barla
Photo: Alptransit – Gotthard Basistunnel
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Introduction

2. Engineering Geology
Complex Hydrostratigraphy in Brittle Rockslides (Aknes)
Eastern Alps
Central Alps
Western Alps
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Introduction

3. Engineering Geology
Multiple Groundwater Tables & Perched Aquifers separated
by Sliding Planes
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Introduction

4. Engineering Geology
Confined or Artesian Pore Pressures below Basal Sliding
Plane
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Introduction

5. Engineering Geology
Generic Translational Rockslide Model
Potential Recharge:
300mm/year
(=9.5E-9 m/s)
Stable Rock Mass
Saturated Hydraulic Conductivity [m/s]
Rockslide Mass
Clayey Shear Zone
Alluvial Deposits
Base Case
Parameter Var. 1
1.5·10-7
1.5·10-8
8.9·10-5
8.9·10-5
1.2·10-9
1.2·10-9
1.0·10-5
1.0·10-5
Parameter Var. 2
1.5·10-8
8.9·10-7
1.2·10-9
1.0·10-5
Parameter Var. 3
4.5·10-8
8.9·10-7
1.2·10-9
1.0·10-5
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Generic Rockslide Model

6. Engineering Geology
Fully Saturated (a) versus Partially Saturated (b)
Groundwater Flow Lines and Pressure Fields
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Generic Rockslide Model

7. Engineering Geology
No low-K Clayey Shear Zone
One low-K Clayey Shear Zone
Shallow & Limited Extent Rockslide (with/out Shear Zone)
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Steady State Pore Pressure Fields

8. Engineering Geology
No low-K Clayey Shear Zone
Two low-K Clayey Shear Zones
Deep & Slope Extent Rockslide (with/out Shear Zones)
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Steady State Pore Pressure Fields

9. Engineering Geology
Reduction of Stable Mass (Variation 1) & Rockslide Mass
(Variation 2) Hydraulic Conductivity
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Steady State Pore Pressure Fields

10. Engineering Geology
Reactions to Seasonal Groundwater Recharge (Transient
Pressure Gradients below upper Sliding Zone)
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Pore Pressure Transients

11. Engineering Geology
Reactions to Seasonal Lake Level Variations (Transient
Pressure Gradients below/above upper Clayey Shear Zone)
Pressures Above
Shear Zone
Tokyo University August 31, 2011
Pressures Below
Shear Zone
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Pore Pressure Transients

12. Engineering Geology
Superposition of Lake Level and Recharge Transients
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Pore Pressure Transients

13. Engineering Geology
Dutchman’s Ridge Pore Pressure Transients
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Pore Pressure Transients

14. Engineering Geology
Slope Stability with/out Consideration of Shear-StrengthSuction-Relationships (Fredlund 1995)
Tokyo University August 31, 2011
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Generic Rockslide Model

15. Engineering Geology
Summary: Quasi-planer (2D) translational rockslides
• Translational rockslides in brittle materials often developed complex
hydrostratigraphy, composed of multiple water tables, confined pressures or
suction below sliding planes
• Pore pressure conditions are strongly influenced by ratio of recharge rate to
surface layer hydraulic conductivity. Strongly fractured rockslide masses often
show thin layers of (perched) groundwater at the interface to less deformed
ground.
• Unsaturated conditions further decrease hydraulic conductivities, recharge
rates and groundwater table elevations
• Clayey shear bands with reduced hydraulic conductivity favour the
development of large zones with negative pore pressures, and/or strong
pressure gardients (pressure compartments)
• Pore pressure transients from lake evelation and periodic recharge variations
show significant phase shifts when passing through lower permeability layers
• Lake elevation transients are measurable up to a few tens of meters above the
shore line and then become dominated by groundwater recharge from snow
melt
• Significant knowledge gaps refer to saturation-suction relationships in
fractured rock slopes
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Generic Rockslide Model

16. Engineering Geology
Thank you for your attention!
Any Question ?
Open postdoc/lecturer positions in rockslide processes at ETH:
www.engineering-geology.ethz.ch
Vajont Conference 2013
Transient Pore Pressures in Brittle Translational Rockslides
Generic Rockslide Model