Which one of the following parameters can be used as a rough guide to ...
Density Index as a Guide to Determine Failure in Soil
Determining the type of failure in soil is crucial for designing safe and stable structures. One parameter that can be used as a rough guide to determine the type of failure in soil is the Density Index.
What is Density Index?
- The Density Index (ID) is a measure of the relative density of a soil, comparing its in-place density to its maximum density.
- It is calculated as the ratio of the difference between the in-place void ratio and the void ratio at maximum density to the difference between the void ratio at minimum void ratio and the void ratio at maximum density.
Role in Determining Failure
- The Density Index provides an indication of the state of stress in a soil mass and its relative density.
- It can help in identifying whether the soil is in a dense, loose, or critical state.
- Dense soils are more resistant to shear failure, while loose soils are more prone to failure.
Application in Failure Analysis
- A high Density Index indicates that the soil is relatively dense and has good shear strength properties.
- In contrast, a low Density Index suggests that the soil is loose and may be susceptible to failure under certain loading conditions.
- By evaluating the Density Index, engineers can assess the potential failure mechanisms in soil and design appropriate mitigation measures.
In conclusion, the Density Index can serve as a useful parameter in determining the type of failure in soil by providing insights into the soil's density and shear strength characteristics.
Which one of the following parameters can be used as a rough guide to ...
In soils, generally three types of shear failure based on relative density are observed which are described below briefly:
1. General shear failure:
- In this a slight downward movement of the footing develops fully plastic zones and a sudden failure takes place with a considerable bulging of the ground surface adjacent to the footing.
- Characterized by well defined failure pattern, consisting of a wedge and slip surface and bulging (heaving) of soil surface adjacent to the footing.
- In general shear failure of soil, sudden collapse occurs, accompanied by tilting of the footing.
- This type of failure occurs in case of dense sand or stiff cohesive soil having relative density greater than 70 percent.
- Failure load is well defined in this case.
- The load-settlement diagram is similar to stress-strain for dense sand or over-consolidated clay.
2. Local Shear Failure:
- In this a large deformation takes place under the footing before the development of failure zones, i.e. large vertical settlement takes place before slight bulging of the ground surface.
- Tilting of footing is not expected.
- Ultimate load is not well defined in local shear failure.
- It takes place in moderately compressible soils or loose sand i.e. occurs in soil of high compressibility and having relative density lying between 35 and 70 percent.
- Yielding takes place close to the lower edges of the footing.
3. Punching Shear failure:
- Failure pattern is not well defined in punching shear failure of soil.
- No bulging of ground surface and no tilting of footing occurs.
- The yield surfaces are vertical planes immediately adjacent to the sides of the foundation.
- The ground surface may be dragged down thus, no bulging of the surface takes place.
- Failure take place immediately below footing and surrounding soil remains relatively unaffected.
- It takes place in weak compressible soils with considerable vertical settlement i.e. in soil of very high compressibility and having relative density less than 35 %.
- It also occurs in the soil of low compressibility, if the foundation is located at considerable depth.
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