Reconnaissance engineering geology
of the Laprak landslide,Gorhka
District, western Nepal




William C. Haneberg    AEG 2...
Acknowledgements

• AEG Foundation Research Fund


• Kadoorie Agricultural Aid
  Assocation


• Dr. G.V. Ramana, Departmen...
Geologic setting

                                                              China
                                    ...
Walking to Laprak
View to the east
?




View to the southwest across the Raizo Khola valley
Damage to an occupied home
More damage to another occupied home
Shaded Relief
Illumination from 30°/315°
Slope Angle
with Shaded Relief (30°/360°)
Slope Aspect
with Shaded Relief (30°/360°)
Foliation (335°-355°)
Shears? (300°-320°)




Joints (130°-140°)




                             




                   ...
Bedrock structural controls




Elevation




                                   Easting
                  Northing
Bedrock structural controls

        Metamorphic foliation




Elevation




                                   Easting
  ...
Bedrock structural controls

        Metamorphic foliation
    Foliation-perpendicular joints




Elevation




          ...
Bedrock structural controls

        Metamorphic foliation
    Foliation-perpendicular joints
          Low angle shears?
...
Bedrock structural controls

     Metamorphic foliation
 Foliation-perpendicular joints
       Low angle shears?

        ...
Rainfall and landslide movement
                     1 life
                   10 homes                    6 homes        ...
Laprak 1999 and 2007 extreme rainfall events




Gabet et al Himalayan rainfall threshold

• Compared peak sediment loads ...
Remedial options

• Structural, grading, or drainage
   • Hand labor, limited budget, difficult access

• Resettlement
   •...
Dhanyabat— Thank you
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Laprak landslide

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A reconnaissance visit to the Laprak landslide in a remote portion of the Gorkha District, western Nepal.

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Laprak landslide

  1. 1. Reconnaissance engineering geology of the Laprak landslide,Gorhka District, western Nepal William C. Haneberg AEG 2008 Annual Meeting New Orleans, Louisiana Narayan Gurung
  2. 2. Acknowledgements • AEG Foundation Research Fund • Kadoorie Agricultural Aid Assocation • Dr. G.V. Ramana, Department of Civil Engineering, IIT-Delhi • The people of Laprak
  3. 3. Geologic setting China Laprak Nepal India Source: Geological Map of Nepal (1994) 0 50 km
  4. 4. Walking to Laprak
  5. 5. View to the east
  6. 6. ? View to the southwest across the Raizo Khola valley
  7. 7. Damage to an occupied home
  8. 8. More damage to another occupied home
  9. 9. Shaded Relief Illumination from 30°/315°
  10. 10. Slope Angle with Shaded Relief (30°/360°)
  11. 11. Slope Aspect with Shaded Relief (30°/360°)
  12. 12. Foliation (335°-355°) Shears? (300°-320°) Joints (130°-140°) Dip Direction (Aspect) of Known Planar Structures with Shaded Relief (30°/360°)
  13. 13. Bedrock structural controls Elevation Easting Northing
  14. 14. Bedrock structural controls Metamorphic foliation Elevation Easting Northing
  15. 15. Bedrock structural controls Metamorphic foliation Foliation-perpendicular joints Elevation Easting Northing
  16. 16. Bedrock structural controls Metamorphic foliation Foliation-perpendicular joints Low angle shears? Elevation Easting Northing
  17. 17. Bedrock structural controls Metamorphic foliation Foliation-perpendicular joints Low angle shears? Easting Northing Colluvium wedges controlled by intersecting bedrock structures (upslope view)
  18. 18. Rainfall and landslide movement 1 life 10 homes 6 homes 5 homes 3 homes 12 hectares 5 hectares 4 hectares 2 hectares 5500 4125 Annual 2750 (mm) 1375 0 1500 Maximum 1125 monthly 750 (mm) 375 0 350.0 262.5 Maximum daily 175.0 (mm) 87.5 0 1999 2000 2001 2002 2003 2004 2005 2006 2007
  19. 19. Laprak 1999 and 2007 extreme rainfall events Gabet et al Himalayan rainfall threshold • Compared peak sediment loads in streams with daily rainfall and annual accumulated monsoon rainfall in the Annapurna region of Nepal • Concluded that 850 mm accumulated monsoon rainfall was necessary for sediment- generating landslides to occur each year • Gabet et al, 2004, Geomorphology 63: 131-143
  20. 20. Remedial options • Structural, grading, or drainage • Hand labor, limited budget, difficult access • Resettlement • No suitable nearby locations • Resistance to distant resettlement • Warning system(s) • Rainfall threshold • Movement monitoring • Temporary evacuation • Safer buildings • Lightweight materials • Hand-buildable and affordable design? • Resistant to landslides and earthquakes • Easy to repair
  21. 21. Dhanyabat— Thank you

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