What is Slope Failure – Its 4 Types | Causes | Effects & Prevention of Slope Failure

What is a Slope?

The incline angle of the surface is called slope.

The slope is the evaluation of the inclination of a line or a segment of a line that is attached with the two points. The slope of a line is assigned to the ratio of the quantity that y extends as x increases some amount. The slope is unvarying (equivalent) anywhere on the line.

Depending on the construction, the slope is classified into two types:

• Natural slope
• Artificial slope

Depending on the extent, the slope is classified into two types:

• Infinite slope
• Finite Slope

What is Slope Failure?

The slope failure can be defined as the incident in which a slope fails as the outcome of the weak bearing capacity of the soil because of heavy rainfall, earthquake, landslides, and other natural disasters or factors.

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Cause of Slope Failure

The slope failure is caused by several human activities as well as natural factors. Some of the major causes are defined briefly as follows:

1.  Earthquake: Earthquake is the major cause of slope failure and instabilities in soil. In the action of the earthquake, the slope is subjected to the vertical and horizontal forces that result in stresses in the slope. Earthquakes have dynamic forces which accordingly decrease the shear strength and bearing of the soil makes it too liable to fail.
2. Rainfall: Another major cause of slope failure is rainfall. Heavy rainfall occurs for a period of time which softens the soil and makes it liable to erosion. The rainwater enters the cracks and reduces the strength(bearing capacity) of soil which may cause slope failure.
3. Erosion: Erosion is the process by which soil particles get eroded by wind and rainwater etc. The erosion of the soil particles develops changes in the geometry of the slope that results in slope failure. The utmost condition, it may also lead to landslides.
4. Construction Work: The construction activities are carried out near the toe of the existing slope which eliminates the resistance that causes slope failure.
5. Geological characteristics: Some of the major and unidentified geological characteristics can cause landslides (slope failure).
6. External loading: The various types of loads that are imposed on the top of the surface (slope) add additional load to the gravitational load and this causes slope failure.
7. Increase in shear force: When the loading on the soil is more than the binding capacity of the particles of soil gets decreases. There are some reasons by which it happens is mentioned below:
   • Because of a sudden increase in the dynamic force of the soil mass like an earthquake.
   • When the slope of the soil is increased
   • Because of external force.
   • Increase in weight of the soil due to absorption of rainwater.
8. Decrease in shear force of soil: When the bond between soli particles gets weak and loses its bearing capacity or loses its strength.

Effects of Slope Failure

• Slope failure causes landslides that may cause loss of life and properties.
• It reduces the bearing capacity of the soil.
• Damage to the road causes slope failure.
• It significantly affects humans and their lives.

Types of Slope Failure

It is classified into four types

1. Rotational failure
2. Translational failure
3. Compound failure
4. Wedge failure

Rotational failure

In the condition of the rotational failure, the failure occurs by the rotation on the slip surface, usually by the outward and inward movement of soil, and the shape of the slip surface is curved.

Types of Rotational Failure

1. Base failure: The failure which is occurred in the weak soil strata and failure plane passes through of base of the slope is called base failure
2. Toe failure: Toe failure is the most common type in which the failure plane is passed through the toe of the slope.
3. Face failure: The failure which occurs on the surface of the slope which is passed through the toe of the slope is called Face failure or slope failure. It happens when the soil is above the toe which contains weak strata.

Translational Failure 

The slope failure occurs in an infinite slope( the slope which has no boundaries) in which the movement of the soil is along the level surface. It happens, mostly in the layered material.

Compound failure

The compound failure is the combination of translation and rotational. The slope failure. In this condition, the failure surface is curved at two ends, and plain at the middle portion is called compound failure, and generally, this happens, when the hard stratum is below the toe at considerable depth

Wedge Failure

Generally, the wedge failure is also referred to as block failure or plane slope failure and it occurs along an infinite plane. It mostly happens when the wedges and distinct blocks of the soil mass get separated. It is also common when there is a soil layer that has the weak bearing capacity, joints, or fissures and the slope has two different materials.

This is similar to translation Failure and the main difference is that the translation Failure occurs in the situation of the finite slope only but the wedge failure occurs in both conditions ( finite and Infinite slopes).

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How to Prevent Slope Failure?

Many majors are adopted to prevent slope failure like we need to proper drainage, benching, terracing, build retaining walls, soldiers piles and we can use rock bolts to maintain the stability of soli to prevent the slope failure.

Some of the factors are used to prevent slope failure is as follows:

1. Slope failure can be prevented by managing proper drainage on the slope to reduce the waterlogging and seepage forces. Because when the soli absorbed rainwater in the excessive amount it’s lost its bearing capacity or strength.
2. Slope failure can be improved by the plantation because the roots of the plant make the soil stable.
3. Slope failure can be prevented by grouting (a thin and coarse layer of mortar is poured into various joints to consolidate into solid mass) which increases the stability of the soils.
4. It can be improved by the provisions of sheet piles and retaining walls which provide lateral support to soil and make it stable or the soil doesn’t move through it.
5. It can be improved by the process of densification in which the density of soil is increased by the use of explosion or terra (earth) probe, it helps to increase the bearing capacity or strength of the cohesionless soil particles, and hence stability is also increased.
6. Slope failure can be prevented by providing a berm (horizontal surface between exterior slope) below the toe of the slope which increases the resistance force to movement of the soil and this is the best way to avoid base failure.
7. Consolidated by the electroosmotic, injection of cement or many other methods helps in increasing the stability of the slope.

The slope failure of the soil mass can be improved and make it stable or reusable by increasing its strength or by reducing the soil mass. Due to the improvement of the slope failure which reduces any kind of accident.

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