Landslides with case studies Presentation by Anand Swaroop Jaichandran

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Transcript of Landslides with case studies Presentation by Anand Swaroop Jaichandran

  2. 2. Landslides are defined as mass movement of rock, debris or earth down a slope and have come to include broad range of motions whereby falling, sliding and flowing under the influence of gravity dislodges earth material. Take place in conjunction with I. Earthquakes II. Floods/ prolonged rainfall III. Volcanoes Hilly terrain is highly sensitive to landslides Himalayas and Western Ghats Landslides can do great damage and change the land very quickly. If a slippery material is present below soil then soil can become heavy with rainwater and prone to landslide. It is a downward or outward movement of soil, rock, vegetation due to gradient. This movement can be fall, flow, slide, spread or topple. Landslides occur usually at steep slopes but these may occur in areas with low slope gradient.
  3. 3. LATERAL SPREAD- Spread is defined as an extension of a cohesive soil or rock mass combined with a general subsidence of the fractured mass of cohesive material into softer underlying material. ROTATIONAL SLIDES- It move along a surface of rupture that is curved and concave. TRANSITIONAL SPREAD- In translational slides the mass displaces along a planar or undulating surface of rupture, sliding out over the original ground surface. CREEP- It is spatially continuous movement in which surfaces of shear are short-lived, closely spaced, and usually not preserved its speed is extremely slow. ROCK FLOW- Extremely rapid, massive, flow like motion of fragmented rock from a large rock.
  4. 4. In the following table shows a schematic landslide classification adopting the classification of Varnes 1978 and taking into account the modifications made by Cruden and Varnes, in 1996. Some integration has been made by using the definitions of Hutchinson (1988) and Hungr et al. 2001
  5. 5. A. Natural Factors Gravity works more effectively on steeper slopes Geological factors weak, sensitive or weathered materials Heavy and prolonged rainfall rapid rise in water level and saturation Earthquakes plate tectonic moves the soil that covers it also moves Forest fire causes erosion and induce floods and landslides Volcanoes kill vegetation over extensive area and spreads volcanic rocks, subsequent rainy season will trigger landslides Waves can erode the beach or the toe of a bluff, cutting into slope Freezing and Thawing Landslides occurs when several factors converge:-
  6. 6. B. ANTHROPOGENIC FACTORS Inappropriate drainage system natural drainage lines on slopes are blocked by terracing/ contour bounding Cutting and deep excavations on slopes for buildings, roads, canals and mining modification of natural slopes, blocking of surface drainage, loading of critical slopes and withdrawal to toe support Change in slope/ land use pattern, deforestation, settlements, agricultural practices on steep slope. C. HUMAN ACTIVITIES Deforestation, Cultivation and Construction when destabilize the already fragile slopes. Vibrations from machinery or traffic, blasting, Construction. In shallow soils, the removal of deep-rooted vegetation that binds colluviums to bedrock. Landslides occurs when several factors converge:-
  7. 7. Landslides destroys everything and anything that comes in their path. Roads Rail lines Lines of communication Settlements River flows/ Damming Agricultural production Land area Flooding Water availability, quality and quantity Flora and Fauna Fatalities depends on the place and time of occurrence. Estimated casualties per year, world-wide: 600 - 1000 persons. HOTSPOTS Anywhere with steep slopes and weathering High mountain ranges, sheer cliffs, and steep sided river valleys Where volcanoes erupt and along coasts
  8. 8. EXAMPLE S
  9. 9. Springs, seeps, or saturated ground in areas that have not typically been wet before. New cracks or unusual bulges in the ground, street pavements or sidewalks. Soil moving away from foundations, and ancillary structures such as decks and patios tilting and/or moving relative to the house. Sticking doors and windows, and visible open spaces. Broken water lines and other underground utilities. Leaning telephone poles, trees, retaining walls or fences. Sunken or dropped-down road beds. Rapid increase in a stream or creek water levels, possibly accompanied by increased turbidity (soil content). Sudden decrease in creek water levels even though rain is still falling or just recently stopped.
  10. 10. Prevent landslides and neighborhood drainage problems in landslide prone areas:- Water is the most common cause of unstable slopes, landslides, and erosion. Check your home's drainage system. Maintaining the drainage system on private property is the owner's responsibility. Make sure your drainage system directs water away from your foundation and not on to your neighbor's property. Never discharge water over the side of a steep hill. Clean your gutters and downspouts. Check your gutters once a week during fall and winter. Just one wind or rainstorm can clog a well-flowing drainage system. Clean your gutters and downspouts. Check your gutters once a week during fall and winter. Just one wind or rainstorm can clog a well-flowing drainage system. In general, trees and plants with strong root structures help prevent soil erosion but do not prevent landslides Never block any part of the city's drainage system. Do not put leaves, dirt, grass clippings, or any materials in ditches, culverts, or drains. Doing so can cause flooding. It is against the law to dump any material into the drainage system.
  11. 11. MEASURES TO REDUCE THE CHANCE OF LANDSLIDES: Vegetation cover protects land from landslides and soil erosion. Therefore efforts should be made to maintain greenery particularly on slopes. Provisions should be made at community level to prevent people from excavating, removing materials from the soil or cutting trees. Trees should be planted on slopes and slopes base to prevent erosion. Record of erosion, landslide masses and falling rocks should be maintained. During construction a building on a slope design that suits the natural slope should be adopted. Vegetation and trees should not be removed while constructing. Natural streams or drainage paths should not be constructed during construction. Surface water should be diverted towards the natural galley enabling water to quickly drain away from the slope. Quickly move out of path of the landslide or debris flow. If inside a building, stay inside and take cover under a desk, table or other sturdy furniture. If escape is not possible, curl into tight ball and protect your head. PRECAUTIONS DURING LANDSLIDE:
  12. 12. PRECAUTIONS DURING LANDSLIDE: Check for injured and trapped persons, without entering the slide and direct and assist rescuers. Help vulnerable group persons in neighbourhood for emergency assistance. Listen to local radio or television station. Watch for flooding, which may occur after a landslide or debris flow. Look for and report damaged utility lines to authorities. Replant damaged ground as soon as possible since erosion caused can lead to flash flooding. Seek professional advice for evaluation of landslide hazard and designing corrective techniques to reduce landslide risk. LANDSLIDE IN HILLY AREADEMOLISHED ROAD
  14. 14. Western Ghats A: Kerala: small catchment B: Nilgiri: transportation corridor Himalayas: C: Okhimath: high Himalaya, large area D: Darjeeling: middle Himalaya, watershed .
  15. 15. Aruvikkal catchment : 9.5 km2 Sub catchment of Tikovil River History of debris flows during the monsoons Dominant rock type: Charnokites UNUITC CESS debris flow research catchment Rubber plantation area Clear relation landuse landslides
  16. 16. Kurseong in the Darjeeling district Elevations in the study area vary from 236 m to 2189 m Annual precipitation in the area varies from 2000 to 5000 mm metamorphic rocks of the Himalayan FoldThrust Belt (FTB) foreland molasse basin in the south Main Boundary Fault (MBT) Main Central Thrust
  17. 17. Most landslides are structurally controlled (a) A deepseated rock wedge (W_Fol x J2) within Daling metasediments, (b) Plane failure (P_Fol) along foliation surface (Fol) in sheared phyllonitic rocks (c) Toppling (T_J1) caused by steepdipping SWdipping joint plane (J1) within quartzofeldspathic gneiss Retrogression of a deepseated rock wedge slide.
  18. 18. EXAMPLES
  19. 19. CASUALTIES
  20. 20. A kind gesture can reach a wound that only compassion can heal.