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1.4 landslide

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1.4 landslide

  1. 1. LANDSLIDE Presented byCT.Lakshmanan B.Arch., M.C.P. SRM School of Architecture SRM University Prepared by CT.Lakshmanan 1
  2. 2. What is Landslide ?downward and outward movement ofslope forming materials composed ofrocks, soils, artificial fills or combination ofall these materials along surfaces ofseparation by falling, sliding and flowing,either slowly or quickly from one place toanother. Prepared by CT.Lakshmanan 2
  3. 3. An idealized slump-earth flow showing commonly used nomenclature for labeling the parts of a landslide. Prepared by CT.Lakshmanan 3
  4. 4. Classification with respect to depth of slide Type Maximum depth (m)Surface slide < 1.5Shallow slide 1.5 – 5Deep slide 5 – 20Very deep slide > 20 Prepared by CT.Lakshmanan 4
  5. 5. Types of landslides Prepared by CT.Lakshmanan 5
  6. 6. Rotational and Translational landslide Prepared by CT.Lakshmanan 6
  7. 7. Block slide & Rockfall Prepared by CT.Lakshmanan 7
  8. 8. Topple & Debris flow Prepared by CT.Lakshmanan 8
  9. 9. Debris Avalanch & Earth flow Prepared by CT.Lakshmanan 9
  10. 10. CreepPrepared by CT.Lakshmanan 10
  11. 11. Lateral spread Prepared by CT.Lakshmanan 11
  12. 12. Types of rapid mass movement Prepared by CT.Lakshmanan 12
  13. 13. SlumpPrepared by CT.Lakshmanan 13
  14. 14. Factors that control slope stability Prepared by CT.Lakshmanan 14
  15. 15. Factors that control slope stability Prepared by CT.Lakshmanan 15
  16. 16. Factors that control slope stability Prepared by CT.Lakshmanan 16
  17. 17. Factors that control slope stability Prepared by CT.Lakshmanan 17
  18. 18. CAUSES OF LANDSLIDES• Geological Weak material• Erosion• Intense rainfall• Human Excavation• Earthquake shaking• Volcanic eruption Prepared by CT.Lakshmanan 18
  19. 19. Causes of LandslidingGeologists use a variety of classificationschemes to describe causes of landslides.Because of wide variety of causes, nosingle scheme has yet been developedthat address or describe all types oflandslides. Prepared by CT.Lakshmanan 19
  20. 20. External Geometrical change1. Gradient2. Height3. Slope length Unloading1. Natural2. Human-induced Loading1. Natural2. Human-induced Shocks and Vibrations1. Single2. Multiple/continuous Prepared by CT.Lakshmanan 20
  21. 21. Internal Progressive failure (internal response to unloading, etc.)1. Expansion, swelling2. Fissuring3. Strain softening4. Stress concentration Weathering1. Physical property changes, swelling2. Chemical changes Seepage Erosion1. Removal of cements2. Removal of fines Water Regime Change1. Saturation2. Rise in water table3. Excess pressures4. DrawdawnSource: The Royal Academy of Engineering. 1995. Landslides Hazard Mitigation. Westminster, London: The Royal Academy of Engineering. Prepared by CT.Lakshmanan 21
  22. 22. Human causesa. Excavation of slope or its toeb. Loading of slope or its crestc. Drawdown (of reservoirs)d. Deforestatione. Irrigationf. Miningg. Artificial vibrationh. Water leakage from utilities Prepared by CT.Lakshmanan 22
  23. 23. Prepared by CT.Lakshmanan 23
  24. 24. Prepared by CT.Lakshmanan 24
  25. 25. Major Landslides of India Prepared by CT.Lakshmanan 25
  26. 26. Major Landslides of India Prepared by CT.Lakshmanan 26
  27. 27. Major Landslides of India Prepared by CT.Lakshmanan 27
  28. 28. MAIN MITIGATION STRATEGIESHazard mappingLand useRetaining WallsSurface Drainage Control WorksEngineered structuresIncreasing vegetation coverInsurance Prepared by CT.Lakshmanan 28
  29. 29. MAIN MITIGATION STRATEGIESHazard mapping will locate areas proneto slope failures. This will permit to identifyavoidance of areas for buildingsettlements.These maps will serve as a tool formitigation planning. Prepared by CT.Lakshmanan 29
  30. 30. MAIN MITIGATION STRATEGIESLand use practices such as:• Areas covered by degraded natural vegetation in upper slopes are to be afforested with suitable species. Existing patches of natural vegetation (forest and natural grass land) in good condition, should be preserved• Any developmental activity initiated in the area should be taken up only after a detailed study of the region and slope protection should be carried out if necessary.• In construction of roads, irrigation canals etc. proper care is to be taken to avoid blockage of natural drainage• Total avoidance of settlement in the risk zone should be made mandatory.• Relocate settlements and infrastructure that fall in the possible path of the landslide• No construction of buildings in areas beyond a certain degree of slope. Prepared by CT.Lakshmanan 30
  31. 31. Prepared by CT.Lakshmanan 31
  32. 32. MAIN MITIGATION STRATEGIESRetaining Walls can be built to stop landfrom slipping (these walls are commonlyseen along roads in hill stations). It’sconstructed to prevent smaller sized andsecondary landslides that often occuralong the toe portion of the largerlandslides. Prepared by CT.Lakshmanan 32
  33. 33. MAIN MITIGATION STRATEGIESSurface Drainage Control Works. Thesurface drainage control works areimplemented to control the movement oflandslides accompanied by infiltration ofrain water and spring flows. Prepared by CT.Lakshmanan 33
  34. 34. Prepared by CT.Lakshmanan 34
  35. 35. MAIN MITIGATION STRATEGIES• Engineered structures with strong foundations can withstand or take the ground movement forces.• Underground installations (pipes, cables, etc.) should be made flexible to move in order to withstand forces caused by the landslide Prepared by CT.Lakshmanan 35
  36. 36. MAIN MITIGATION STRATEGIESIncreasing vegetation cover is thecheapest and most effective way ofarresting landslides. This helps to bind thetop layer of the soil with layers below,while preventing excessive run-off and soilerosion. Prepared by CT.Lakshmanan 36
  37. 37. MAIN MITIGATION STRATEGIESInsurance will assist individuals whosehomes are likely to be damaged bylandslides or by any other natural hazards.For new constructions it should includestandards for selection of the site as wellas construction technique. Prepared by CT.Lakshmanan 37
  38. 38. Flattening of the slopeSlope at the point of failure may bestabilised by grading the slope to a flatterangle on the basis of proper geotechnicalinvestigationDone either by regarding the slope frombottom to the top with benching, wherevernecessary or cut in upper hills. Prepared by CT.Lakshmanan 38
  39. 39. Prepared by CT.Lakshmanan 39
  40. 40. Stitching of the debris cover to the rockMovement of surface soil can becontrolled by stitching the debris to thebase rock with help of micro-piles (e.g.timber piles) Prepared by CT.Lakshmanan 40
  41. 41. Retaining wallsBuilt at the bottom of the slope but thebase of the wall should be properlyanchored into the rock.Big landslides cannot be controlled byretaining walls Prepared by CT.Lakshmanan 41
  42. 42. GroutingEffective method of improving the shearstrength and decreasing the permeabilityof coarse-grained soil. Suitable for fillingvoids in the rock mass.Cement grouts are injected underpressure to close the voids in the rock Prepared by CT.Lakshmanan 42
  43. 43. GeotextilesGeotextiles wrapped filler drains areinserted into the slope extending beyondthe estimated slip surface.They are connected to a crib wall at thebase which is made of crushed rock toprovide drainage of water from thetransverse drain. Prepared by CT.Lakshmanan 43
  44. 44. Rockfall ProtectionIn many areas rock faces are‘stitched’ with massive steel bolts totry to keep material from being lost toactive weathering.Alternately, surfaces can be coveredwith strong mesh or boulder catchingnets can be used. Prepared by CT.Lakshmanan 44
  45. 45. Mudflow BarriersThese kinds of barriers aredesigned to catch mostsediment, but are not capableof stopping very large and veryfast moving debris. Prepared by CT.Lakshmanan 45
  46. 46. Debris BasinsThese require periodic (regular) removal of trapped material. d e b r is f lo w h e a d in g to w a r d n e ig h b o r h o o d d e b r is t r a p p e d in c o n c r e t e - lin e d b a s in Prepared by CT.Lakshmanan 46
  47. 47. The hazard from landslides can be reducedby avoiding construction on steep slopesand existing landslides, or by stabilizing theslopes. Prepared by CT.Lakshmanan 47
  48. 48. Stability increases when ground water isprevented from rising in the landslide mass by(1) covering the landslide with an impermeableMembrane(2) directing surface water away from the landslide(3) draining ground water away from the landslide(4) Minimizing surface irrigation. Slope stability is also increased when a retaining structure and/or the weight of a soil/rock berm are placed at the toe of the landslide or when mass is removed from the top of the slope. Prepared by CT.Lakshmanan 48
  49. 49. Thank you Prepared by CT.Lakshmanan 49

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