Ch.4 Learning Goals
1. Explain how the Landslides occur when the gravitational force pulling the slop material
socioeconomic down exceeds the slop material’s internal resistance to shear or failure.
impact of landslides
depends on the type Landslides can be more devastating to areas with a high population density,
and characteristics low levels of preparedness, and poorly made infrastructure. This is most
of the landslide frequently found in third world countries.
The reason why it is more devastating is because the weak infrastructure
collapses more easily in the face of landslides, causing more damage and
the high population density makes evacuation efforts more difficult and
there are more people to be injured.
The economic impact is usually more severe in developed countries
because of the high cost of building new well-made infrastructure
2. Distinguish Fall: occur on very steep slopes and material (usually rock) detaches from
between the these slopes due to weakness. They are very fast and are propelled by
different modes of gravity.
failure (falls, flows,
slides, topples, and Topple: forward rotation of material (rocks) about a pivot point below the
spreads) and how center of gravity of the unit or in the slope. There is no debris topple
they are influenced because debris is unsorted with varied sizes while topples consist of
by geology coherent blocks
Slides: move as a coherent mass along a surface of failure, and are usually
composed of soil, rock, or debris. If the surface is curved, the slide is
rotational, moving at an intermediate speed with weak material. If it is a
translational slide, it can be slow to fast moving, made of strong material
moving on planes of weakness.
Flows can range in speed from very slow to very fast. They are composed
of wet amerial such as soil and mud. Water is very important to flows.
There can be a fluid or plastic flow of material. Soil creep is an example of
flow, although it is very slow.
Type of Type of Material
Bedrock Debris (Unsorted soil) Earth (Sorted soil)
Falls Rock Fall Debris Fall Earth Fall
Topples Rock block -- Earth block
Slides Rock slump Debris slide Earth slump
Rock slide Earth slide
Spreads Rock spread -- Earth spread
Flows Rock creep Debris flow Sand flow slide
Slope sagging Mud flow Silt flow slide
Debris avalanche Earth flow slide Soil creep Dry sand flow
Solifuction Earth flow
3. Define the chief
4 compare and Slope failure occurs when the force of gravity parallel to the slope (shear
contrast landslide stress) become greater than the strength of the material that make up the
causes and how they slope, which is acting to hold itself in place (shear strength)
differ from landslide
triggers Landslide causes are long-term factors leading to the instability of a given
slope, and they reduce the shear strength of a slope. However, they do not
initiate any movement.
A trigger is a factor that translates instability into motion. They are usually
short event and only one is required to start a mass movement.
5. Asses the balance The factor of safety (Fs) is the ratio of shear strength to shear stress. If
between the Fs>1, the slope is stable. If it is <1, failure occurs.
strength of the slope Shear strength is the resisting force, made up of friction and cohesion.