Foundation, Concrete and Earthquake Engineering

What Mitigation Measure Should be Taken for Using Collapsible Soil as Foundation Bed?

Several mitigation options are used to deal with collapsible phenomenon of these soils. We are providing a list of mitigation measures below. Any of them or combination of them can be used in field application depending on the characteristics of soils. Soils are investigated carefully before application of these measures. Houston (1996) provides some measures that are provided below:

1. The soils that are sensitive to moisture have to remove.

2. The removal should follow replacement or providing compaction to them.

3. Restricting wet environment

4. These soils may be stabilized with chemical or grouting

5. Prewetting techniques sometimes is used successfully

6. Providing controlled wetting

7. Dynamic compaction of soil

8. Deep foundation like pile/pier foundations

9. Providing foundation that is not susceptible to differential settlement

The measures stated below are suitable only when wetting moisture is occurred from ground surface or from near ground surface infiltration. These measures are:

1. Restricting wetting from irrigation

2. Restricting landscape vegetation near structures

3. Surrounding paved surface is sometimes expected to restrict infiltration of moisture. The extent of paved surface is determined by economy and practicability.

4. Sewer lines and water lines should be kept leak free. For this purpose double pipes and sometimes troughs are used.

5. Forming a low permeable soil to have a barrier to wetness penetration by removal and or replacement and compacting surface layer of foundation soil. In providing barrier for water, soils that are insensitive to moisture is used.

Risks of collapse are avoided as the wetting reduced or controlled to desire degree. Analysis should be performed to compare total cost involved for these measures to economical loss due to suspected collapse settlement of designed or repair of foundation of structures and various alternatives are compared considering these. 

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