lect landslide mar -2k11
TRANSCRIPT
Landslide and Slope StabilityJune-2010
n.k.agarwal
geo-consultant
Geological, Geotechnical, Environmental & Allied ServicesHydro Power, Environment, Mineral Resources, Disaster Damage Reduction, Integrated Watershed
Management, Technical Auditing & Site Inspection
Phone: +91 135 2650373/2654487, Mob.:+91 9760099015, Fax: +91 135 2657748
Landslides Impact and Remediation
Landslides Cause Accidents and Disasters
Identification
Processes
Remediation
Landslide Management
Types Studies
Academic/Documentation
Inventory
Type and Mechanism
R & D
Disaster
Rescue & Relief
Zonation
Mitigation
Management
Prevention, Stabilisation
Active Landslides
Inactive Landslides
Palaeo Landslides
Landslide and Slope Failure are a part of Mass Wasting
Processes
All objects have a tendency to acquire lowest potential
energy level
Landslide is a Generic term for a wide variety of
perceptible downslope and outward movement of
rocks and soil.
Usually Landslide occurs on steep slopes
Can also occur on low relief area
Landslides can be triggered by natural as well as
anthropogenic changes in the environment.
Natural changes include reduction in shear strength
and increase in weight of the rock/soil.
Anthropogenic changes include modification of slope
profile and surface-groundwater regime.
Many types of Mass Movements are included in Landslide
Landslide - Generic
Mass Wasting
Mass wasting is the down slope movement
of materials under the influence of gravity.
Mass wasting can occur at rates of only a
few cm/year and cause little damage and
no loss of life, or it can occur at over 100
150km/hr and result in great loss of life and
property damage.
Type of Movement BedrockSoils/Overburden
Classification of Landslides
Types of Landslides and Movements
S.No. Type Movement
1 Falls Abrupt outward and downslope movement of detached material from cliffs, steep slopes- free fall, rolling, bouncing.
2 Topple Block of Rock tilts-rotates outward and falls- rolls down slope, bounces.
3 Slide 1) Rotational Landslide : movement along an upward concave surface of rupture, the moved mass is tilted backward
2) Translational Landslide : movement is essentially outward a and no backward tilt.
4 Lateral Spread
Nearly horizontal movement on very gentle slopes mainly due to saturation and liquefaction.
5 Flows 1) Creep : Slow downslope movement of rock debris and soil.2) Debris flow : Rock debris and soil moves down slope as a slurry
mass along narrow gullies and gorges.3) Debris Avalanche : An extremely rapid movement of Debris
flow downslope.4) Mud Flow : Rapid movement of wet mud (50% sand, silt, clay)
downslope5) Lahar Flow ; Rock or Mud flow downslope of Volcanoes.
Slump Flow
NKA-2010
Types
Root Cause of Mass Wasting
Root Cause of Mass Wasting is the Force of Gravity.
There are other Factors that increase the risk of Slope Failure.
When One or more of these risk factors is high, Mass Wasting is
likely to occur
No Movement
Safety Factor = Shear Strength/Shear Stress
If Safety Factor becomes <1, Slope Failure is Expected
Slope Failure
F = Shearing Strength
mg sinə = Shearing Stress
Landslide and Slope Failure
Site characteristics
(1) Groundwater and seepage conditions.
(2) Lithology, stratigraphy, and geologic details disclosed by borings and
geologic interpretations.
(3) Maximum past overburden at the site as deduced from geological
evidence.
(4) Structure, including bedding, folding, and faulting
(5) Alteration of materials by faulting
(6) Joints and joint systems.
(7) Weathering.
(8) Cementation.
(9) Slickenside.
(10) Field evidence relating to slides, earthquake activity, movement along
existing faults, and tension jointing.
Causes of Slope Instability/Landslides
Geological causes
Weak or sensitive materials
Sheared, jointed, or fissured materials
Adversely oriented discontinuity (bedding, schistosity, fault,
unconformity, contact, and so forth)
Contrast in permeability and/or stiffness of materials
Morphological causes
Tectonic or volcanic uplift
Fluvial, wave, or glacial erosion of slope toe or lateral margins
Subterranean erosion (solution, piping)
Deposition loading slope or its crest
Vegetation removal (by fire, drought)
Thawing
Freeze-and-thaw weathering
Shrink-and-swell weathering
Anthropogenic causes
Excavation of slope or its toe
Loading of slope or its crest
Drawdown (of reservoirs)
Change in land use
Drain seepage
Deforestation
Irrigation
Mining
Artificial vibration
Water leakage from utilities
Vibrations due to explosions
Causes of Slope Instability/Landslides (contd.)
Important Triggers for Slope Failure/ Landslides
Water
Slope saturation by water due to intense rainfall,
snowmelt, changes in ground-water levels, and water-
level changes along coastlines, earth dams, and the
banks of lakes, reservoirs, canals, and rivers. Toe removal
Slope Modification by cut slopes, river erosion,
Head loading
Adding material a slide mass increases its driving
force.
Strength reduction
Weathering ultimately weakens all slope materials; slow
creep causes restructuring of clays stressed within
slopes; slow processes eventually reach critical points.
Cyclic and temporarily increased stresses may cause
soil restructuring or rock fracturing. Earthquakes
Earthquakes, generally of magnitude 6 and above,
inducing ground intensities of greater than or equal to VI,
trigger landslides in the critical reaches of hill slopes. Vibration
Artificial vibrations, as from heavy road traffic.
Important Triggers for Slope Failure/ Landslides (contd.)
Steep High Cut Slopes in Debris fan - Cut Slope Failed during the next rains
Inviting problem
Distant View of Sonapur Landslide
(Jaintia Hills, Meghalaya
Creeping landslide
• The trained eye of a geologist can discover
• Clues if a land is currently moving.
• Clues if the land has moved in the past.
• Evidence that the land is moving includes cracks
appearing where the land is being slowly pulled apart
from the hillside.
• These cracks are called tension cracks.
• With time, the ground on one side of the tension crack
may slide downhill forming a scarp and leaves a scar.
• A fresh scar has a lighter color and no/sparse
vegetation in comparison to adjoining slopes.
• Bulging- lobate landforms-soil profiles indicate old
slides.
Telltale marks of landslide
Hummocky Landforms indicate landslide or soliflucttion
Initiation of detachment
1. Date and time of occurrences:
2. Location:
i) Village / Town
ii) Tehsil / Taluka
iii) District
iv) State
v) Co-ordinates and Toposheet No.
3. Dimensions:
i) Length
ii) Breadth
iii) Height
4. Type:
i) Rock Slide / Fall
ii) Overburden Slide / Fall
5. History
i) Old
ii) New
6. Material Involved:
i)Rock / Overburden
7. Whether in road cutting / river bank / natural hill slopes
8. Structure Affected:
i) Road / Railway line
ii) Houses
iii) Land
a) Barren
b) Cultivated
c) Forest
iv) Civil Projects
9. Casualties:
i) Human
ii) Livestock
First Information Report
10. Rain fall:
i) During last 24 hours
ii) During the week prior to slide
iii) If rainfall data are not available, local
assessment may be given
11. Causes of Slide:
i) As per local assessment
12. Existing Remedial Measures:
and recommendations if any
Signature:
Name:
Address:
Email:
Ph. No.
First Information Report (contd.)
Geological Survey of India as a
Nodal Agency is responsible
for:-
Coordinating and undertaking
geological studies for landslide
Hazard Mitigation
Carrying out landslide hazard
zonation
Monitoring landslides and
avalanches
Studying the factors responsible
for sliding and suggesting
precautionary as well as
Preventive measures
Is there a landslide in your locality?
Send the First Information to Nodal Officer, GSI
(Fax: 011-29051328/26053532, 033-22861656) or email :[email protected]
Formulation Uniform Methodologies for LHZ on Macro and Meso
Scales
LHZ of Vulnerable Areas on Macro Scales
LHZ of identified areas on Meso Scales
Real Time Monitoring of Slides
Development and Validation of Early Warning System
Guidelines and training for Scientists, Engineers, Planners &
Decision makers
Inventory/ Database on LHZ
Formulation Strategy for Prevention and Reduction Loss
Environmental
Life, Livestock & Property
• Awareness Generation
Scope for Action
Massive Landslide – La Conchita-California (1995)
Physical weathering
NKA-2010
Planar Failure
Wedge Failure
When the rock mass is cut across by two or
more joint planes such that they cut each other,
with the minimum requirement of four planes
WITH either two free surfaces and two joint
planes or at least one free space with three
unfavorably oriented joint or discontinuity
planes ,
constituting a tetrahedral or trapezoidal wedge,
failure may initiate either along their line of
intersection or on one of the gentler dipping
planes.
Such type of failures are called 'wedge failure'.
Landslide Management
Reduction in Shearing Stress
Enhancing Shearing Strength
Strategy
Geotechnical + Bio-engineering Treatment
Reduction in Shear Stress
• Removal of Head Load of the Slide
• Grading of Slope
• Benching of Slopes
• Removal of Loose and Unstable Material
Enhancement of Shearing Strength
• Over burden laden Slope treatment by geotextile/geogrid
• Grading of over burden laden slopes
• Dressing of
• Sealing of Cracks
• Rock bolting/anchors/cable anchors
• Shotcreting
• Consolidation grouting and pile shafts in the weathered rock mass
• Drainage
Landslide Hazard Zonation
Macro Scale – 1:50,000 to 25,000 scale
Meso Scale - 1:25,000 to 1:15,000 scale
Micro Scale – 1:15,000 to 1:5,000 Scale
Zonation Map Validation
Field - Slope Instability Incidences
Statistical - Frequency Correlation
Varunavat Landslide Treatment
Initiation of varunavat Landslide
Lateral Cracks
Lateral Cracks
July-August 2003
GSI officer Noticed these cracks (21-24th August 2003)
24-25 Sep 2003
24th-25th September varunavat Slope
Failed and huge quantities of debris
rolled down on residential and
commercial buildings in Uttarkashi
• Proterozoic Garhwal Group rocks comprising
• quartzite, phyllite and metabasics are exposed.
• Rocks dip at 15o-45o in N010o-040o direction i.e. into the hill.
• The rocks are highly weathered, destressed, decomposed, jointed and
fractured.
• The hill slopes are steep 45o-60o in general, the top of the hill has
gentler slopes.
• The top varunavat hill is laden by unconsolidated, overburden mass.
• The top is at El± 1800m and the toe of the hill is at EL ± 1100m m.s.l.
• The overburden/rock contact is exposed at El ± 1660m.
Geological Set Up
Geological-Geotechnical Investigations
Contouring of Landslide Area on 1:1000 scale
Geological Mapping on 1:1000 scale
Identification of Structural Discontinuities/Lineaments
Geophysical Surveys – depth of OB
Geomechanical Characterisation of OB for
stabilisation analysis.
Monitoring of Slope movement
Major Works at Varunavat Area
S.No. Description of Work s
1 Varunawat Parvat Treatment Works
2 Additional and post Treatment Works
3 Miscellaneous Works
4 Removal of Muck from Masjid Mohalla
5 Barethi- Tekhla bye-pass road
6 Gyansu Nala Treatment
7 Relocation of Govt. Offices
8 Relocation of Private Property
9 Relocation of Commercial Property
10 Relocation of Shops
11 Rehabilitation of landslide affected villages of Bhatwari/Dunda
12 Rehabilitation of landslide affected villages of Naitwar & Fafrala
13 Construction of Roads & Bridges in Mori Tehsil
Treatment works at the Crown
DEVELOPMENT OF PLATFORMS AT EL ± 1670 AND ±1710 IN THE ENTIRE LENGTH ACROSS THE AFFECTED ZONE.
A TOTAL OF 1.51 LAC CUM LOOSE MATERIAL REMOVED FROM THE CROWN AREA AND 1.87 LAC CUM MUCK HAS BEEN REMOVED TILL 19 NOV. 2004.
CONSTRUCTION OF EARTHEN DYKE ON THE EDGE OF THE PLATFORM 3-4 M HIGH.
REMOVAL OF DEBRIS LYING ON THE HIGHWAY AT THE TOE AND CONSTRUCTION OF PROTECTION DYKES BY WAY OF WIRE CRATES AND CONCRETE BLOCKS.
STRENGTHENING OF PROTECTION MEASURES IN THE BUFFER ZONE.
CHANNELISING THE SURFACE RUN-OFF IN THE CROWN AREA TO AVOID ITS ENTRY INTO THE SURFACE CRACKS.
• Grading of Slopes to ,300 between EL 1660m and EL
1800 with berms
• Development of Platform at the contact of OB/Rock at
EL 1660m
• Weathered Rock mass strengthing at the Platform by
Pile shafts and consolidation grouting
• Strengthening of rock mass with rock bolting, cable
anchoring and reinforced shotcreting
• Laying geogrid at EL 1660m
• Development of contour drain on rocky slopes
between EL 1650m and toe of hill connected with
chute drains
• Main toe drain
• Retaining structure at the toe of the hill
Treatment (contd.)
Varunavat Landslides
Landslides along Chutes
Chutes due to landslides
varunavat Parvat - Pre September 2003 Landslide
Uttarkashi Township
Stabilisation by Geojute between EL 1790m to 1780m
Stabilisation of Overburden by Geogrid
Treatment at Crown
Geogrid treatment at Crown
NKA-2010
Cable Anchors at Crown
Stabilisation of Rocky Slopes by Rock bolts and shotcreting
Stabilisation by Cable Anchors
Excavation of Platform at Crown Area
Cellular Wall at Ram Lila Ground (settlement)
nk. agarwal
Geo-Consultant & Advisor
HIGEOS India