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Pertemuan 08 GEOTEKNIK

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Title: Judul Author: Debby Tanamal Last modified by: Amelia Makmur Created Date: 4/16/2005 3:08:17 AM Document presentation format: On-screen Show Company – PowerPoint PPT presentation

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Title: Pertemuan 08 GEOTEKNIK


1
Pertemuan 08GEOTEKNIK
  • Matakuliah S0182/Studi Kasus Dalam Teknik Sipil
  • Tahun Juli 2005
  • Versi 01/01

2
Learning Outcomes
  • Mahasiswa dapat membandingkan kasus-kasus yang
    terjadi dengan berbagai alternatif yang dipilih ?
    C4

3
Outline Materi
  • Analisa pemecahan masalah
  • Beberapa alternatif pemecahan masalah
  • Kasus kegagalan konstruksi yang mungkin terjadi

4
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.

5
Slope Failures
6
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.

7
Slope Failures
8
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9
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.

10
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
11
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.
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