The process of sliding down large soil mass along a plane or a curved surface with respect to the remaining mass is known as slope failure. In this post we will discuss different types of slope failure in soil.
Our earth is made of soil having different slope and height. These slopes may be either natural or artificial.
Some time slope of soil become an obstacle for us while sometime it should be made ourselves for different services like railway formation, highway embankments, earth dam, canal banks etc.
The failure of a slope may cause loss of huge amount of properties as well as life. Also, the stability of soil is required to remain various structure like an earthen dam, bridge etc to remain in stable condition.
So, it is very important to know the methods of improvement of slope failure to prevent it. But, before knowing cause and types of slope failure it is impossible to apply the suitable improvement in slope failure. Hence at first, we are going to discuss about cause and types of slope failure.
Causes of slope failure
Generally, slope failure occurs mainly for two reasons. They are as follows:-
1)Increase in shear force:-
When loading on soil mass increases then it a capacity of binding together between particles of soil decreases and slope failures occur. This happens due to the following reason.
- Due to the sudden dynamic force applied to soil mass like an earthquake.
- Due to the increase in the slope of the soil mass.
- Due to an external load applied on it like constructing the building.
- Due to the increase in unit weight of soil by rain. e.t.c
2)The decrease in shear strength of soil
When the bond between soil particles are loosened then it also loses its shear strength. And this happens due to the following reason.
- Increase in pore water pressure.
- Due to weathering.
- Due to erosion or loss of cementing materials.
- Due to the increase of water within it.
Now let us move toward different types of slope failures. Generally, there are four types of slope failure.
Types of slope failure
- Translational Failure
- Rotational Failure
- Wedge Failure
- Compound Failure
Translational Failure
The failure occurs in an infinite slope along a long failure surface parallel to the slope having uniform soil properties is known as a translational failure. This occurs above hard strata at a shallow depth of soil.
This types of failures generally occurred in nature where the bed of rocks is found below the certain depth of the soil mass along the slope and soil above it slide due to a decrease in the bond between them.
The infinite slope is defined as the slope having no boundaries and contains same properties of soil up to assumed equal depth along the slope.
Rotational Failure
The failure occurs by rotation along a slip surface by a downward and outward movement of the soil mass is known as a rotational failure.
The shape of the slip surface is circular when the soil is homogenous while the shape is non-circular when the soil is non-homogenous. This types of failure can be seen at finite slope failure like earthen dam, landslide etc.
Further rotational failure may occur in three different ways :
- Slope failure or Face Failure:- The failure which occurs along the surface that passes through the toe is known as slope failure. It occurs when soil above the toe contains a weak stratum. In this case, the failure plane intersects the slope above the toe.
- Toe failure:- The failure in which the failure plane passes through the toe of the slope is known as toe failures.
- Base failure:- The failure which occurs when there is a weak soil stratum under the toe and failure plane passes through the base of the slope is known as a base failure.
Compound Failure
The failure of the slope by a combination of translational slide and the rotational slide is known as a compound failure.
In this failure, the slip surface is curved at two ends of the rotational slip surface and flat at the translational slip surface. The slip surface becomes flat due to the hard soil layer at a considerable depth from the toe.
Wedge failure
The slope failure occurred along the plane of the soil mass is known as wedge failure. It is also known as block failure or plane failure.
This type of failure occurs when there are fissures, joints, or weak soil layers in slope, or when a slope is made of two different materials.
Unlike translational, wedge failure can occur in both finite and infinite slopes.
Improvement of slope failure
Slope failure can be improved by flattening the slope which will reduce the mass of soil and make it light.
- It can be improved by providing a berm below the toe of the slope to increases the resistance to movement. It is best to avoid the base failure of the slope.
- It can be improved by managing drainage on the slope to reduce seepage forces. Because water inside the soil makes its shear strength low.
- It can be improved by densification by use of explosives, or terra probe because it helps in increasing the shear strength of cohesionless soils and thus increasing the stability
- Consolidation by surcharging, electro-osmosis or other methods helps in increasing the stability of slopes in cohesive soils.
- It can be improved by Grouting and injection of cement or other compounds into specific zones. It catches soil around it and does not let it slide.
- It can be improved with the help of Sheet piles and retaining walls to provide lateral support and do not let soil to move through it.
- It can be improved by the method of the plantation.
In this way, the improvement of slope failure is done according to the economy and factor of safety needed at that place.
Why to do Improvement in Soil?
The slope’s failure of the soil mass can be protected and make it reusable by improving their shear strength or by reducing soil mass by the various mean. Due to improvement of the slope which is susceptible to failure can be prevented and reduce the chance of any kind of accident.
Hence, these are the types of slope failure, Causes, and Improvement of Slope failure of soil.
Read Also,
Differences between compaction and consolidation process of Soil mass
Relation between Discharge velocity and Seepage velocity in soil mass
Numerical to calculate the plastic limit of soil |Plasticity index
