Need of Proper Development in Hilly Urban Areas to Avoid Landslide Hazard Dr. Arvind Phukan, P.E. Cosultant/Former Professor of Civil Engineering University of Alaska, Anchorage, USA RI District Governor 2002-03, District 5010 Director Engineers Without Borders - USA
Outline of Presentation Introduction Causes of landslides Types of landslides Landslide hazard analysis & mapping Stabilization of landslides Typical solutions to prevent sediment flow into drainage system causing flooding in the plain area Conclusion
Introduction A landslide is a geological phenomenon which includes a wide range of ground movement, such as rock falls, deep failure of slopes and shallow debris flows, which can occur in various environments including ldi urban settings It is to be noted that t a landslide lid can also occur due to human activities or unusual natural phenomenon including rainfall and earthquake The action of gravity is the primary driving force for a landslide to occur
Global Landslide Risk
Causes of Landslide Landslides occur when the stability of a slope changes from a stable to an unstable condition. A change in the stability of a slope can be caused by a number of factors, acting together or alone. Natural causes of landslide include: - Groundwater (pore water) pressure acting to destabilize the slope - Loss or absence of vertical vegetative structure and soil structure (e.g. after a wildfire)
Causes of Landslide (Cont d) - Erosion of the toe of a slope by various factors including streams, rivers, ocean waves etc. - Weakening of the slope through saturation by heavy rainfall, snow or glaciers melting - Earthquakes adding loads to barely stable slope - Earthquake causing liquefaction and destabilizing slopes - Volcanic eruption
Causes of Landslide (cont d) Landslides are aggravated by human activities. Human causes are: deforestation, cultivation and construction. Construction activities include: - Vibration from machinery or traffic - Blasting - Earthwork which alters the shape of a slope or which imposes new loads on an existing slope - Construction, agricultural or forestry activities (Logging) which change the amount of water which infiltrates the soil
Types of Landslide Debris Flow or Mud Flow Earth Flow Debris Avalanch Shallow Landslide Deep seated landslide
Landslide Hazard Analysis and Mapping Landslide hazard analysis and mapping can provide useful information for catastrophic loss reduction and assist in the development of guidelines for sustainable land use planning The analysis is used to identify the factors that are related to landslides, estimate the relative contribution of factors causing slope failures, establish a relation between the factors and landslides and to predict the land slide hazard in the
Landslide Hazard Analysis (Cont d) Future based on such relationship. The factors that are used for landslide hazard analysis can usually grouped into geomorphology, geology, land use/land cover, and hydrogeology. -Since many factors are considered d for landslide lid hazard mapping, GIS is an appropriate tool. Other tools which h can be used are Remote sensing technique Before and after aerial photographs and satellite imagery
Landslide Hazard Mapping Using satellite imagery in combination with GIS and on-ground studies, it is possible to generate maps of likely occurrences of future landslides. Such maps should show the location of previous events as well as clearly indicate the probable locations of future events. In general, to predict landslides, one must assume that their occurrence is determined by certain geologic factors, and that future landslides will occur under the same conditions as past events.
Landslide Hazard Mapping (Cont d) Therefore, it is necessary to establish a relationship between the geomorphologic conditions in which the past events took place and the expected future conditions.
Stabilization of Landslide The stabilization ti of landslide lid will depend d primarily il on the subsurface conditions (Soil & rock type and groundwater), the slope angle, availability of granular material and potential environmental impact. Some possible techniques are: -Stabilize the steep slope to gentle slope - Provide drainage structure at the toe as well as on the bank of the slope -
Stabilization of Landslide (Cont d) - Install relief wells along the slope to prevent generation of excessive pore water pressure - Prevent loss of vegetative cover on the slope - Prevent erosion at the toe of the slope - Prevent human activities close to the slope that cause slope instability or landslide in the area.
Typical Solution to prevent sediment flow into drainage system