Geotechnical Engineering 101 and more…

Building firm foundations

Consolidation of soil

Posted by Kshitija Nadgouda on November 20, 2006

I talked about compaction of soil and how removal of the air voids in the soil makes it more dense. Consolidation is the removal of water from soil. In other words, it is the squeezing out of water from the soil to make it more dense.

In case of coarse grained soils like sands and gravels, the removal of this pore water is easy since water freely moves from one region to another within these soil types. However, in case of fine grained soils like silty or clayey soils, consolidation is a time consuming process.

As an analogy, consider soil mass to be like a sponge that is slightly wet. If we press the sponge, it will deform by compressing the air out of it. If we squeeze it further, water will be removed and the sponge will be compressed further. If the sponge (soil mass) is completely wet or soaked, it is termed as saturated. This is the condition when all voids are filled with water and no air voids exist.

Soil-Water Phase
Courtsey: Dr. Kamal Tawfiq

In case of fine grained soil on which a structure is to be built, high water content is not desired as the weight of the structure may cause sinking (consolidation settlement) of the structure in due time. Typically the permeability (ability of water to move through the soil voids) of fine grained soils is low, hence it takes a long time for consolidation process. So two aspects of consolidation settlement are important: the rate at which the consolidation is taking place and the total amount of consolidation.

It is very important to note that unlike settlement in sands and other coarse grained soil, consolidation settlement of fine grained soil does not occur immediately. Hence, it is common practice to ensure that the consolidation process is expedited and that most of the consolidation takes place during the various phases of construction.

If the soil is such that it has never experienced pressure of the current magnitude in its entire history, it is called a normally loaded soil. The soil is called pre-consolidated (or over-consolidated) if at any time in history, it has been subjected to a pressure equal to or greater than the current pressure applied to it. In case of normally consolidated soils, the consolidation will be greater than that for a pre-consolidated soil. That is because the pre-consolidated soil has previously experienced greater or equal pressure and has undergone at least some consolidation under that pressure. So a pre-consolidated soil is preferred over a normally consolidated soil.

The rate at which consolidation will take place, will depend on the nature of soil, the degree of saturation (how many percent voids are filled will water), the amount and nature of the load on the soil, the soil history (normally or over -consolidated), etc.

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29 Responses to “Consolidation of soil”

  1. Dharmananda Mazumdar said

    It will be very useful if you write something about soil consolidation by using sand or band drain with preloading. The coal terminal at Vizag sea port use this method for consolidating the coal stack area.

  2. I will try and find out more about it and definitely write about it. Thanks again for your valuable inputs.

  3. imtek said

    There is also some information of soil consolidation with band drains PVD ‘s)

    http://geosynthetic.blogspot.com/

  4. Thomas Berriman said

    Cheers for the info. Is there any chance you could let me know what the difference is betwwen consolidation and compaction in terms of how they are performed (e.g. compaction: rammers, vibrating plates, rollers etc.).

    Thank you very much

    Thomas Berriman

    (Student: University of Manchester)

    • uvt said

      Static method of compaction and consolidation (without blows and vibrations) the bases, roads, at reconstruction of industrial targets, in city centre.

    • parmesh choudhary said

      In consolidation there are two phase only where as in compactoin there are three phase after applied load.

      parmesh choudhary
      (IIT delhi , india)

  5. Anonymous said

    can the void ratio be greater than 1?

  6. Anonymous said

    yes it can

  7. marilyn murray said

    can clay soil be compacted under an existing house by using lime?

  8. Yes, it can. But there are several issues you will have to consider before you go for compacting soil under an existing house – for example the settlement and possibly cracks its may cause to the house.

    I recommend you hire a professional Geotechnical Engineer to look at your particular case and solve your problem.

  9. Anonymous said

    Nicely explained the difference b/w normally and over consolidated soil. its useful, thanks…

  10. Bilal Shirazi said

    Nicely explained the difference b/w normally and over consolidated soil. its useful, thanks…

  11. Bilal Shirazi said

    In Triaxial Shear Test, how will we know to conduct which type of test from these three?
    1 CD test
    2 CU test
    3 UU test
    As all of three are used to find out the parameters of shear.
    Is it related with the type of soil sample we are taking for test or there is some other factor?

  12. Mickey said

    one query , if a pool is cleaned after a long time and the water is drained of for that purpose, and it is filled once more. But in the concrete shell of the pool there is a crack and later it is observed that the pool has risen abt 1 m.
    This will be the case when there is swelling in soil ? am i right ?
    but here is the thing . if the cracks were already there when the water was drained of , y didnt the pools length increase when the water was filled? and y is that only when it was drained of and filled again that the pools length increased?

  13. kevin carradine said

    what are the different and similarities between compaction and consolidation?

  14. We are interested for a product which could relevel concrete and at the same time consolidate soil/ fill voids.
    An early responce shall be highly appreciated.
    RAJIV SAHAI

  15. Anonymous said

    Consolidation is the removal of pore water from soil to make the soil dense,while compaction is the expulsion of air in the void spaces of a soil mass by the application of stress

  16. spino said

    thanks for the information. its been of a lot of help.

  17. Smith said

    It would be better if you explain more about soil saturation. Can i know the factors on which the rate of consolidation of soil depends?

  18. Superb website…

    […]always a big fan of linking to bloggers that I love but don’t get a lot of link love from[…]……

  19. Anonymous said

    nothing is clear………..

  20. mewael gessesse said

    its important if u write about the method of settlement calculations of partially saturated soils!

  21. Thanks for sharing those info. Its help me a lot’s. Now I know which soil is the best for geotechnical Instrumentation works before we start the construction on the site.
    Cheers! :)

  22. Write more, thats all I have to say. Literally, it seems
    as though you relied on the video to make your point. You
    definitely know what youre talking about, why waste your
    intelligence on just posting videos to your weblog when you could be giving us something enlightening to
    read?

  23. Teslim said

    Nice one

  24. The compression of soil can occur due to Compression of solid particles and water in the voids,Compression and expulsion of air in the voids,Expulsion of water in the voids..

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