Pertemuan 08 GEOTEKNIK

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Pertemuan 08GEOTEKNIK

• Matakuliah S0182/Studi Kasus Dalam Teknik Sipil
• Tahun Juli 2005
• Versi 01/01

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Learning Outcomes

• Mahasiswa dapat membandingkan kasus-kasus yang
  terjadi dengan berbagai alternatif yang dipilih ?
  C4

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Outline Materi

• Analisa pemecahan masalah
• Beberapa alternatif pemecahan masalah
• Kasus kegagalan konstruksi yang mungkin terjadi

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Slope Failures

•  
• On September 12 of 1717 an avalanche cascaded
  down the Troilet, Italy glacier, gaining speed on
  a cushion of air, reaching a falling velocity of
  320km/hr over a 3600 m fall. Two towns were
  destroyed, with 7 people killed and 120 cows
  lost. The slosh of the avalanche ran up the far
  side of the valley at a speed of 125 km/hr.
• Snow avalanches, rock avalanches, debris flows,
  mud flows, and rock falls are failures of the
  surface under the action of gravity. The basic
  physics controlling the stability or instability
  of landforms is relatively simple and well
  understood, but the hazards are not always
  recognized, even when geological deposits
  indicate past slope failures in the region. In
  many cases, surface instabilities of this type
  are compound events, associated with earthquake
  or volcanic processes, which enhance their
  catastrophic potential. From the surface geology
  perspective, landslides and debris flows are
  important landscape modifying agents, and play as
  large of a role in eroding topography and
  depositing debris as is played by other
  mechanisms such as rainfall and runoff.

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Slope Failures
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Slope Failures

• There are two basic classes of surface failures
• 1. Single rock failures
• These often are blockfalls of individual rocks
  falling from an eroding surface, which is usually
  very steep, or "over steepened" beyond the stable
  angle of repose for the surface materials. The
  blocks pile up in an apron of debris, called a
  talus slope or talus cone.
• 2. Flows of the surface, involving large volumes
  of rocks and soil.
• Slow flows- (creep, solifluction, earthflows)
• Fast flows- (snow avalanches, landslides,
  mudflows, debris flows)
• Fast flows leave jumbled deposits, often piles
  upon piles, that can be recognized in the
  geological record by their shape and the poorly
  sorted (many rock sizes intermixed) nature of the
  deposit. The fast flows tend to be fluidized,
  either by a mixture of rock and air or rock and
  water. The relative components of the mixture
  determines how the failure will be named a
  mudflow is water with lots of clay and silt
  material, which is a runny mud, while a debris
  flow is a jumble of rock fragments with some
  water. The fluidized nature of the flow accounts
  for the last flow velocities attained, and the
  associated hazard posed.

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Slope Failures
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Landslides

• Landslides occur when a portion of a hillslope
  becomes too weak to support its own weight. This
  weakness is generally initiated when rainfall or
  some other source of water increases the water
  content of the slope, reducing the strength of
  the materials. Other causes of landslides include
  earthquakes and loud sounds. Many types of
  landslides move seasonally or periodically and
  may lie dormant for years.
• Landslides are generally classified into slides,
  falls and flows. Slides move as large bodies by
  slipping along one or more failure surfaces.
  Falls of rock or soil originate on cliffs or
  steep slopes. Large rockfalls can be catastrophic
  events. An earthquake off the coast of Peru in
  1970 started a rockfall which accelerated to more
  than 170 miles per hour and buried more than
  18,000 people. Flows are landslides that behave
  like fluids. Mudflows involve wet mud and debris.
  Earthflows involve wet, claylike material.
  Solifluction is the downslope flow of soil that
  occurs on arctic and alpine hillsides when thawed
  ice or snow saturates the soil cover.

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Landslides

• Landslides constitute a major geologic hazard
  because they occur in all 50 states, causing 1-2
  billion in damages and more than 25 deaths each
  year. Landslides commonly occur with other major
  natural disasters, such as earthquakes and
  floods. The 1980 eruption of Mount St. Helens in
  Washington was preceded by the development of a
  large landslide on the north side of the volcano.
  The Northridge earthquake in 1994 in the San
  Fernando Valley triggered thousands of landslides
  in the Santa Susanna Mountains north of the
  epicenter.

Landslides
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Landslides

• Even though landslides are generally not as
  spectacular or costly as earthquakes, major
  floods, hurricanes and some other natural
  catastrophes, they are more widespread and may
  cause more property loss than any other geologic
  hazard. Much of the damage attributed to
  earthquakes and intense storms is really due to
  landslides.
• The most expensive landslide in U.S. history
  occurred in Thistle, Utah, in the spring of 1983.
  It reached 1/2 mile from top to bottom and ranged
  in width from 1,000 feet to about 1 mile. Total
  costs attributable to this landslide exceeded
  500 million. In May of 1970, an earthquake in
  Peru cost about 70,000 lives. In Alberta, Canada,
  in 1903, a mass of about 30.6 million cubic
  meters slipped from the top of Turtle Mountain
  and fell to the floor of the adjacent valley. The
  mass of earth and rock spread across a 2 mile
  wide valley, annihilating the town of Frank and
  killing 70 people.