CE 4745 Landslides Slope Stability and Earth Retaining

CE 4745: Landslides, Slope Stability and Earth Retaining Structures Dante Fratta Spring 2004

Introduction • Landslides • Slope Stability • Need for Earth Retaining Structures and Flooding Protection • Discussion of Factors Influencing Design • References and Bibliography

Landslides URL: landslides. usgs. gov

Landslides URL: landslides. usgs. gov The Mamayes, Puerto Rico, landslide, 1985. This landslide destroyed 120 houses and killed at 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 produced extremely 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 top of the landslide.

Landslides URL: landslides. usgs. gov La Conchita, California-a small seaside community along Highway 101 south of Santa Barbara. This landslide and debris flow occurred in the spring of 1995. Many people were evacuated because of the slide and the houses nearest the slide were completely destroyed. Fortunately, no one was killed or injured.

Landslides URL: landslides. usgs. gov 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 on the slopes of Storm King Mountain denuded the slopes of vegetation. An intense rainstorm generated debris flows from material on the burned hillslopes and in the channels between hills. Interstate traffic was disrupted for a day and caused serious delays for emergency vehicles and hospital access, due to the fact that Interstate-70 is the only access route through this part of the Rockies. The Interstate-70 corridor through the Rocky Mountains experiences numerous problems from landslides, debris flows, and rockfalls.

Landslides UL: landslides. usgs. gov The 1983 Thistle landslide at Thistle, Utah-This landslide began moving in the spring of 1983 in response to groundwater buildup from heavy rains the previous September and the melting of deep snowpack for the winter of 1982 -83. Within a few weeks the landslide dammed the Spanish Fork River, obliterating U. S. Highway 6 and the main line of the Denver and Rio Grande 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.

Landslides UL: landslides. usgs. gov The Madison Canyon landslide near Yellowstone Park. This landslide occurred after the Hebgen lake earthquake (Richter Scale Magnitude = 7. 5) in Montana, in 1959. The earthquake caused a great slide of rock, soil, and trees to fall from the steep south wall of the Madison River 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 the gorge and the flow of the Madison River, and created a lake.

Landslides URL: landslides. usgs. gov Rock and snow avalanche, Mount Huascaran, Peru. In 1970, an earthquake-induced rock and snow avalanche buried two towns. The death toll from the Debris Avalanche was 18, 000 (total fatalities from the earthquake and the debris flow was 66, 000). The avalanche started as a sliding mass of glacial ice and rock about 3, 000 feet wide and one mile long. The avalanche swept 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 is estimated to have consisted of about 80 million cubic yards of water, mud, and rocks.

Landslides URL: landslides. usgs. gov 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 the mountain with the North Fork of the Toutle River. The melting snow and Ice resulted from the 1982 eruption of Mount St. Helens

Landslides URL: landslides. usgs. gov Sinkhole at Winter Park Florida-Sinkholes (1981): Subsidence occurs when carbonate layers that lie below the surface dissolve. When the weight of the overlying ground becomes too great, 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

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 25 fatalities 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 as general transportation.

Landslides The Problem (cont. ) • Landslides commonly occur with other major natural disasters such as earthquakes and floods that exacerbate relief and reconstruction efforts and expanded development and other land use has increased the incidence of landslide disasters. • Source: The National Landslide Hazards Program (2002)

Landslides The Problem (cont. ) (Nelson 2004)

Landslides Triggering Mechanisms • • Intense Rain-Fall Water-Level Change Ground Water Flow Rapid Snowmelt Volcanic Eruption Earthquake Shaking Human activity

Landslides • Landslide: General term for any perceptible down slope movement 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 in transport 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)

Landslides • Types and Processes (Canada Natural Resources 2002)

Landslides • Landslides Types – Fall: is the detachment of soil or rock from steep slopes along the surface. Little or no shear displacement (e. g. loess). – Topple: is the forward rotation of soil or rock mass about a point. (Turner and Schuster 1996)

Landslides • Landslides Types –Slide: is the downslope displacement of soil or rock masses. It includes: rotational, translational, and debris slide (Turner and Schuster 1996)

Landslides • Landslides Types – Flow: continuous movement of soil masses where shear surfaces are short lived. – Spread: is the sudden movement of water bearing rock masses (Turner and Schuster 1996)

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

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 of unconsolidated grains remains stable - controlled by the frictional contact between the grains. It usually lies between about 30 and 37 degrees. Dry sand Angle of repose Grain-to-grain frictional contact (Nelson 2004)

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 to hold the grains in place. Wet sand Angle of repose Surface tension thin film (Nelson 2004)

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. Fully saturated sand Angle of repose Water surrounds the grain and prevent grain-to-grain contact (Nelson 2004)

Slope Stability Failure (after Duncan)

Slope Stability Failure (after Duncan)

Need for Earth Retaining Structures • Each year flooding causes more property damage in the 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.

Need for Earth Retaining Structures • Average flood damage for a home is approximately $20, 000 per flood and is much higher for industrial buildings. • Flooding is not only expensive to the homeowner and the taxpayer, but also causes despair and worry for its victims. • Effective flood protection and preventive measures can significantly reduce the expense and trauma caused by flooding • Source: National Flood Proofing Committee (2002).

Need for Earth Retaining Structures The Landslide Problem Slope failure near Mc. Clure Pass, Colorado (The National Landslide Hazards Program 2002)

Flooding Protection • Incomplete List… – Retaining walls – Sheet piles – Dams and reservoirs – Levees – Embankments – Other: diversion channels, retaining ponds, etc…

Flooding Protection Retaining walls and sheet piles (Bowles 1988) • Retaining walls are structures used to retained soils or other granular 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)

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 a reservoir. • Dams help people have water to drink and provide water for industry, irrigation, fishing and recreation, hydroelectric power production, navigation in rivers, etc. Dams also serve people by reducing or preventing floods. (from Mc. Carthy 1998)

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 adjacent land. • Levees can be either naturally occurring or man-made. • Man-made levees consist of an impermeable core surrounded by an earthen material, with some type of protection to minimize erosion.

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 flood having once in 50 -year frequency, the slope on the river side being three up per one across and the slope on land side five feet up per one foot across. • There are federal standards for dimensions depending on the local material available, anticipated force of the river and the amount of development in the area.

Flooding Protection Levees (Mc. Millan, J. - The Advocate 2002) “Deep fissures on the batture - land between the levee and the Mississippi River - reveal the ground is again sinking at the spot where the levee collapsed in 1983. ”

Discussion of Factors Influencing Design • • Social Requirements Engineering Requirements Economical Constrains Environmental Actions – Water level – Rain: intensity and duration – Wind action • Soils – Material Properties – – Grain size distribution Degree of saturation Void ratio Strength

References and Bibliography • • Abramson, L. W. , Lee, T. S. , Sharma, S. , and Boyce, G. M. (2002). Slope Stability and Stabilization Methods. Wiley and Sons. Bowles, J. E. (1988). Foundation Analysis and Design. Mc. Graw-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/ ESC 311 -507/2001/Final. Projects/DAVID-CHEIFETZ/ Eckel, E. B. (1958). Landslides and Engineering Practice. Highway Research 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/ Mc. Carthy, D. (1998). Essential of Soil Mechanics and Foundation. Prentice. Hall.

References and Bibliography • • • Mc. Millan, J. (2002). “Fissures near old site worry corps officials”. The Advocate Online. URL: http: //www. theadvocate. com Nelson, S. (2004). Mass-Wasting and Mass-Wasting Processes. URL: http: //www. tulane. edu/~sanelson/geol 204/masswastproc. htm National Flood Proofing Committee (2002). URL: http: //www. usace. army. mil/inet/functions/cw/cecwp/NFPC/nfpc. htm. The Academy of Science of Saint Louis (2002). URL: http: //www. jracademy. com/~mlechner/archive 1999/link-levee. html. Turner, A. K. and Schuster, R. L. , Ed. (1996). Landslides. Investigation and Mitigation. Special Report 247. Transportation Research Board. National Research Council. Washington DC. 673 pages. US Geological Survey (2004). Landslide Hazards. URL: http: //landslides. usgs. gov/