Landslide and Slope Stability

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CE 4745:Landslides, Slope Stability

and Earth Retaining

Structures

Dante Fratta

Spring 2004


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Introduction

Landslides

Slope Stability

Need for Earth Retaining Structures and

Flooding Protection

Discussion of Factors Influencing Design

References and Bibliography


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Landslides

The Mamayes, Puerto Rico, landslide, 1985. This landslide destroyed 120 houses and killedat least 129 people, the greatest number of casualties from any single landslide in North

America. The catastrophic block slide was triggered by a tropical storm that producedextremely heavy rainfall. Contributing factors could also have included sewage directly

discharged into the ground in the densely populated area, and a leaking water pipe at the topof the landslide.

URL:landslides.usgs.gov


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Landslides

La Conchita, California-a small seaside community along Highway 101 south of SantaBarbara. This landslide and debris flow occurred in the spring of 1995. Many people wereevacuated because of the slide and the houses nearest the slide were completely destroyed.Fortunately, no one was killed or injured.



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Landslides

Fire-related debris flows from Storm King Mountain, Colorado. Debris flows blocked Interstate-70 during Labor Day weekend, 1994. A very hot and fast-moving wildfire in July of that year onthe slopes of Storm King Mountain denuded the slopes of vegetation. An intense rainstormgenerated debris flows from material on the burned hillslopes and in the channels betweenhills. Interstate traffic was disrupted for a day and caused serious delays for emergencyvehicles and hospital access, due to the fact that Interstate-70 is the only access route throughthis part of the Rockies. The Interstate-70 corridor through the Rocky Mountains experiencesnumerous problems from landslides, debris flows, and rockfalls.



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Landslides

The 1983 Thistle landslide at Thistle, Utah-This landslide began moving in the spring of 1983 inresponse to groundwater buildup from heavy rains the previous September and the melting ofdeep snowpack for the winter of 1982-83. Within a few weeks the landslide dammed theSpanish Fork River, obliterating U.S. Highway 6 and the main line of the Denver and RioGrande Western Railroad. The town of Thistle was inundated under the floodwaters rising

behind the landslide dam. Total costs (direct and indirect) incurred by this landslide exceeded$400 million, the most costly single landslide event in U.S. history.

UL:landslides.usgs.gov


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Landslides

The Madison Canyon landslide near Yellowstone Park. This landslide occurred after theHebgen lake earthquake (Richter Scale Magnitude = 7.5) in Montana, in 1959. The earthquakecaused a great slide of rock, soil, and trees to fall from the steep south wall of the MadisonRiver Canyon. Twenty-eight people camping in the area were killed as they were overtaken by

this 21 million cubic meter mass. The landslide formed a barrier that completely blocked thegorge and the flow of the Madison River, and created a lake.

UL:landslides.usgs.gov


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Landslides

Rock and snow avalanche, Mount Huascaran, Peru. In 1970, an earthquake-induced rock andsnow avalanche buried two towns. The death toll from the Debris Avalanche was 18,000 (totalfatalities from the earthquake and the debris flow was 66,000). The avalanche started as asliding mass of glacial ice and rock about 3,000 feet wide and one mile long. The avalancheswept about 11 miles to the village of Yungay at an average speed of more that 100 miles an

hour. The fast-moving mass picked up glacial deposits and by the time it reached Yungay, it isestimated to have consisted of about 80 million cubic yards of water, mud, and rocks.



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Landslides

Melting snow and ice on the north flank of Washington's Mount St. Helens, triggered this lahar(an Indonesian term for a "volcanic debris flow"), which rapidly traveled down the flanks of themountain with the North Fork of the Toutle River. The melting snow and Ice resulted from the1982 eruption of Mount St. Helens



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Landslides

Sinkhole at Winter Park Florida-Sinkholes (1981): Subsidence occurs when carbonate layersthat lie below the surface dissolve. When the weight of the overlying ground becomes toogreat, or the dissolved area too large, the surface collapses into the void. These features

occur in what is known as karst topography which is common in FL, KY, MO, PA, and TN

URL:

landslides.usgs.gov


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Landslides

The Problem Landslides constitute a major geologic hazard because

they are widespread, occurring in all 50 states, and

cause $1-2 billion in damages and more than 25fatalities on average each year.

Landslides pose serious threats to highways, lifelines,and structures that support fisheries, tourism, timber

harvesting, mining, and energy production as well asgeneral transportation.


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Landslides

The Problem (cont.) Landslides commonly occur with other major natural

disasters such as earthquakes and floods that

exacerbate relief and reconstruction efforts andexpanded development and other land use hasincreased the incidence of landslide disasters.

Source: The National Landslide Hazards Program (2002)


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Landslides

The Problem (cont.)

(Nelson 2004)


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Landslides

Triggering Mechanisms Intense Rain-Fall

Water-Level Change

Ground Water Flow

Rapid Snowmelt

Volcanic Eruption

Earthquake Shaking

Human activity


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Landslides

Landslide: General term for any perceptible down slopemovement of rock or soil Can include bedrock, soil, or a mixture of these

Classified according to the mechanisms responsible for the

movement and the velocity of the movement

Slope Failures - sudden failure of the slope resulting intransport of debris down hill by slumping, rolling, falling,or sliding

Slumps Falls

Slides

Sediment Flows - debris flows down hill mixed with water or air

(Nelson 2004)


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Landslides

Types and Processes

(Canada Natural Resources 2002)


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Landslides

Landslides Types

Fall: is the detachmentof soil or rock fromsteep slopes along thesurface. Little or noshear displacement(e.g. loess).

Topple: is the forwardrotation of soil or rockmass about a point.

(Turner and Schuster 1996)


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Landslides

Landslides Types

Slide: is the downslope displacement of soil or rockmasses. It includes: rotational, translational, anddebris slide



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Landslides

Landslides Types

Flow: continuousmovement of soilmasses where shearsurfaces are shortlived.

Spread: is the suddenmovement of waterbearing rock masses



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Slope Stability

Slope Stability Analysis (Abramson et al. 2002) understand the development and shape of natural

slopes

determine the short-term and long term stability

conditions evaluate the possibility of failure of natural or

engineering slides

analyze and understand failure mechanisms

enable the retrofit of failed slopes understand the effect of seismic loading on slope and

embankments


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Slope Stability

Effect of Water on Soils Dry sand grains will form a pile. The slope angle is determined by

the angle of repose (i.e., the steepest angle at which a pile ofunconsolidated grains remains stable - controlled by the frictionalcontact between the grains. It usually lies between about 30 and 37

degrees.

(Nelson 2004)

Dry sand

Angle ofrepose

Grain-to-grain frictional contact


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Slope Stability

Effect of Water on Soils Slightly wet soil materials exhibit a very high angle of repose

because surface tension between the water and the grains tends tohold the grains in place.

(Nelson 2004)

Wet sand

Angle ofrepose

Surface tension thin film


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Slope Stability

Effect of Water on Soils When the material becomes saturated, the strength may reduced to

a very small values and it may tends to flow water (between the

grains) eliminates grain to grain frictional contact.

(Nelson 2004)

Angle ofrepose

Fully saturatedsand

Water surrounds the grain andprevent grain-to-grain contact


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Slope Stability

Slope Stability Failure

(after Duncan)


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Slope Stability

Slope Stability Failure

(after Duncan)


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Need for Earth Retaining Structures

Each year flooding causes more property damage inthe United States than any other natural disaster.

Annually, flood damages average over $3 billion(Lilli damages expected to raise to $ 600 million -

Levitan). In 1985 the estimated flood damage was $6 billion

and affected over 250,000 structures.


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Average flood damage for a home is approximately$20,000 per flood and is much higher for industrialbuildings.

Flooding is not only expensive to the homeowner

and the taxpayer, but also causes despair and worryfor its victims.

Effective flood protection and preventive measurescan significantly reduce the expense and traumacaused by flooding

Source: National Flood Proofing Committee (2002).


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The Landslide Problem

Slope failure near McClure Pass, Colorado (TheNational Landslide Hazards Program 2002)


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Flooding Protection

Incomplete List Retaining walls

Sheet piles

Dams and reservoirs Levees

Embankments

Other: diversion channels, retaining ponds,etc


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Flooding Protection

Retaining walls and sheet piles (Bowles 1988)

Retaining walls are structures used to retained soils or othergranular materials.

Materials: masonry, concrete, wood, metal sheeting, reinforce

earth, etc. The analysis and design of retaining walls is governed by the

stiffness of the wall: rigid or flexible.

Sheet pile

Drainage pipe

(Cheifetz 2002)


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Flooding Protection

Dams and reservoirs (US Society on Dams 2002) A dam is built to control water. Dams are made from earth, rocks

or concrete.

Dams are usually constructed on rivers to store water in areservoir.

Dams help people have water to drink and provide water forindustry, irrigation, fishing and recreation, hydroelectric powerproduction, navigation in rivers, etc. Dams also serve people byreducing or preventing floods.

(from McCarthy1998)


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Flooding Protection

Levees(The Academy of Science of Saint Louis 2002): Levees are low ridges or earthen embankments made of

silt, sand or clay, built along a stream of water.

They help in the prevention of flooding of the adjacentland.

Levees can be either naturally occurring or man-made.

Man-made levees consist of an impermeable coresurrounded by an earthen material, with some type ofprotection to minimize erosion.


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Flooding Protection

Levees(The Academy of Science of Saint Louis 2002): Dimensions of a levee are typically 2.5 m across the top,

the height 0.30 m above the level of a predicted floodhaving once in 50-year frequency, the slope on the river

side being three up per one across and the slope on landside five feet up per one foot across.

There are federal standards for dimensions dependingon the local material available, anticipated force of the

river and the amount of development in the area.


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Flooding Protection

Levees (McMillan, J. - TheAdvocate 2002)

Deep fissures on the batture - landbetween the levee and theMississippi River - reveal theground is again sinking at the spotwhere the levee collapsed in 1983.


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Discussion of Factors InfluencingDesign

Social Requirements

Engineering Requirements

Economical Constrains

Environmental Actions Water level

Rain: intensity and duration

Wind action

SoilsMaterial Properties

Grain size distribution Degree of saturation

Void ratio

Strength


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References and Bibliography

Abramson, L. W., Lee, T. S., Sharma, S., and Boyce, G. M. (2002). SlopeStability and Stabilization Methods. Wiley and Sons.

Bowles, J. E. (1988). Foundation Analysis and Design. McGraw-Hill.

Canada Natural Resources (2002). Geoscape Calgary. URL:http://www.nrcan.gc.ca/gsc/calgary/geoscape/index_e.html

Cheifetz, D. (2002). Slope Stability. URL: http://soilslab.cfr.washington.edu/ESC311-507/2001/FinalProjects/DAVID-CHEIFETZ/

Eckel, E. B. (1958). Landslides and Engineering Practice. HighwayResearch Board. Special Report 29. NAS-NRC Publication 544.Washington DC. 232 pages.

The National Landslide Hazards Program (2002). URL:http://landslides.usgs.gov/html_files/landslides/program.html

Louisiana Floods (2002). URL: http://www.louisianafloods.org/

McCarthy, D. (1998). Essential of Soil Mechanics and Foundation. Prentice-Hall.
http://www.nrcan/http://soilslab.cfr.washington.edu/http://landslides.usgs.gov/http://www.louisianafloods.org/http://www.louisianafloods.org/http://landslides.usgs.gov/http://soilslab.cfr.washington.edu/http://www.nrcan/

Landslide and Slope Stability

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