Seminar on Landslides prevention & control

1. Seminar on Landslides prevention & control Presented by: Geologist Planet

2. ROCK SHED NEW ZEA Land

3. CONTENTS • Introduction • Subject:Landslides • Landslides Prevention • Landslides mitigation in India • Quiz • Glossary

4. Landslide is a type of disastrous natural hazard cause…… > 1 people/ year/ 100sq. Km. killed in Colombia, Tajikistan, India, China, and Nepal. Loss of 1- 2% of the gross national product in many developing countries. Thatsby Prevention of landslides is necessary.

5. Definition of landslide Landslide defined as a process involving the downward and outward movement of a part of the slope forming material due to the action of gravity, other forms of mass movements like falls, flows, topples and creeps are generally included in the term landslides. Source: NDMA 2009

7. Mechanism of landslides Stability of slope or slope failure evaluated by factor of safety= Fs resistance force Fs= driving force When Fs < 1.25 slope will fail & landslide occur

8. Simple slope failure dry wet cohesion = c angle of shearing resistance = ϕ the area of the base of the block = A

9. Different corrections made for determination of Fs of wedge failure, topple failure.

10. Landslide causes •An increase of shear stress •A decrease of material strength

11. An increase of shear stress Removal of lateral and underlying support (erosion, previous slides, road cuts and quarries) Increase of load (weight of rain/snow, fills, vegetation) Increase of lateral pressures (hydraulic pressures, roots, crystallisation, swelling of clay) Transitory stresses (earthquakes, vibrations of trucks, machinery, blasting) Regional tilting (geological movements)

12. Reduction of material strength Decrease of material strength (weathering, Change in state of consistency ) Changes in intergranular forces (pore water pressure, solution) Changes in structure (decrease strength in failure plane , fracturing due to unloading

14. Landslide prevention ? It is geotechnical measure to mitigate landslides problem aided by remote sensing , geology, civil engineering, hydrology.

15. Why prevention ? Because… ………in India 3600 Million Rs. economic damage – affect at least 15% of land area of India exceeding 0.49 million km2 – In 2007‐2008 : 445 landslides in which 226 people were killed – in 2008‐2009: 59 landslides 82 people lost their lives (Baghchi et al., 2009 Sources: Ministry of Home Affairs J.P. Sharda, GSI

17. Where landslide prevention ? • Location selection with the help of…. • Landslides Hazard Zonation (LHZ) map • Real time monitoring of active landslide

18. Landslide Hazard Zonation Map

19. Landslide Hazard Zonation map of India by GSI

21. Real time monitoring of active landslide

22. REMEDIAL MEASURES/METHODS • Direct methods: • Restraining structure, for exam pile; retaining walls, anchored walls, restraining piles, • Easing of pressure by excavation; • Reconstruction of slope using reinforced earth; • Rock reinforcement. • Indirect methods - Erosion Control Measures • Surface Drainage • Sub-Surface Drainage -recommended by BIS (2002)

23. 1. Restraining structures Retaining concrete walls

24. Debris flow retaining wall in Japan

25. Gabion walls - Wire mesh filled with boulders

26. Concrete pile with shortcrete

27. ROCK SHED NEW ZEA Land

28. Rock shelter

29. 2. Easing of pressure by excavation

30. 3. Reconstruction of slope using reinforced earth Soil nailing by steel rods

31. Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain Used in Tanzania

32. Geomembrane is very low permeability synthetic membrane liner or barrier used with any geotechnical engineering related material so as to control fluid (or gas) migration in a human­made project.

33. 4. Rock reinforcement. WIRE MESH

34. ROCK BOLTING

36. 5. Erosion Control Measures Schematic and photograph of a crib wall check dam

37. VEIVER GRASS SYSTEM USED IN CONGO

38. CAUSEWAYS

40. Straw wettles

41. 6. Surface Drainage By trench

43. 7. Subsurface drainage

45. Landslides mitigation in India

46. Overall system governed by NDMA • Geotechnical investigation(LHZ Map) working by GSI • Remedial methods recommended by BIS • DST working for Geotechnical work • The GSI is the nodal agency for monitoring landslide activity and its mitigation.

48. GLOSSARY Landslide - Landslide denotes downward and outward movement of slope forming materials under the action of its own weight. Main Scarp - A steep surface on the undisturbed ground around the periphery of the slide, caused by the movement of slide material away from the undisturbed ground. Crown - The material that is still in place, practically undisturbed and adjacent to the highest parts of the main scarp. Toe - The margin of displaced material most distant from the main scarp. Flank - The side of the landslide. Head - The upper parts of the slide material along the contact between the displaced material and the main scarp. Foot- That portion of the displaced material that lies downslope from the toe of the surface of rupture. Displaced Material- The material that ha s moved away from its original position on the slope. Zone of Depletion- The area within which the displaced material lies below the original ground surface.

49. Sikkim Landslide

50. References BOOCKS David George Price, 2009, Engineering Geology Principles and Practice , Springer-Verlag Berlin Heidelberg John A. Hudson and John P. Harrison, 1993, Engineering rock mechanics an introduction to the principles, ELSEVIER SCIENCE Ltd UK E DWAR D A. KE L L E R , 2011, Environmental Geology 9 EDITION, Pearson Prentice Hall Pearson Education Guidelines to landslide mitigation by Geological Survey Of India Bureau Of Indian Standards United States Geological Survey