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  • 1.  Slab On Grade Design on Peat Soil

    Posted 02-27-2019 07:53 AM
    Edited by Tirza Austin 02-27-2019 02:14 PM
    Currently I'm involved with the design of a slab on grade for a warehouse. According to the geotechnical investigation, 0-3 m sand layer and 3-6 m organic clay and peat soil. We are planing to try with 1m thick aggregates base course compacted layer as a ground improvement at the top and friction piles assisted slab as a substructure. Will consolidation settlement take place largely due to bottom peat layer? 

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    Kuranage Akila Nadishan Perera A.M.ASCE
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  • 2.  RE: Slab On Grade Design on Peat Soil

    Posted 02-28-2019 08:37 AM
    Edited by Tirza Austin 02-28-2019 08:37 AM
    I suggest to check the FHWA design guidelines for stone columns. Also, what is below the peat layer?


    Original Message:
    Sent: 02-27-2019 07:12
    From: Kuranage Akila Nadishan Perera
    Subject: Slab On Grade Design on Peat Soil

    Currently I'm involved with the design of a slab on grade for a warehouse. According to the geotechnical investigation, 0-3 m sand layer and 3-6 m organic clay and peat soil. We are planing to try with 1m thick aggregates base course compacted layer as a ground improvement at the top and friction piles assisted slab as a substructure. Will consolidation settlement take place largely due to bottom peat layer?

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    Kuranage Akila Nadishan Perera A.M.ASCE
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  • 3.  RE: Slab On Grade Design on Peat Soil

    Posted 02-28-2019 08:38 AM
    Edited by Tirza Austin 02-28-2019 08:37 AM
    Your first action should be to contact the project's Geotechnical Engineer for their input.

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    Douglas Sabin M.ASCE
    Materials Testing Consult
    Grand Rapids MI
    (616) 456-5469
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    Original Message


  • 4.  RE: Slab On Grade Design on Peat Soil

    Posted 02-28-2019 10:03 AM
    Edited by Tirza Austin 02-28-2019 10:03 AM

    The scenario you describe is very likely to result in consolidation settlement.  I suggest you consider the following:

    • If the aggregate base course you propose to use under the slab raises the finished grade, it will induce more consolidation settlement. Therefore, if possible, use the excavate-and-replace method for constructing the base course, rather than placing the aggregate on top of the existing grade.
    • Consider using a lightweight aggregate for the base course to minimize additional loads.
    • Using friction piles will aggravate consolidation settlement and will add downdrag (negative skin friction) load on the piles. Friction piles would need to be designed to account for these additional loads. Alternately, consider using helical piles which are essentially non-susceptible to negative skin friction.

    P.S. - I fully agree with Mr. Sabin: contact the Geotechnical Engineer.



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    Fernando Souto
    Cadillac MI
    (231)944-5145
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    Original Message


  • 5.  RE: Slab On Grade Design on Peat Soil

    Posted 02-28-2019 10:04 AM
    Edited by Tirza Austin 02-28-2019 10:03 AM
    There are several ground improvement options to consider.  3m of peat may not be compatible with stone columns.  In addition to discussing with the project geotechnical engineer, consider reaching out to specialty geotechnical contractors who specialize in ground improvement options (stone columns, aggregate piers, rigid inclusions, soil mixing, etc).

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    Kenneth Kniss M.ASCE
    Annapolis MD
    (336)455-3047
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    Original Message


  • 6.  RE: Slab On Grade Design on Peat Soil

    Posted 03-01-2019 12:34 PM
    Edited by Tirza Austin 03-01-2019 12:34 PM
    For ground improvement information, selection, design guidance, example specs, there is on online program developed by FHWA:

    GeoTech Tools: Geo-construction Information & Technology Selection Guidance for Geotechnical, Structural, & Pavement Engineers
    Geotechtools remove preview
    GeoTech Tools: Geo-construction Information & Technology Selection Guidance for Geotechnical, Structural, & Pavement Engineers
    View this on Geotechtools >



    ... try it, it's free!

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    Barry Siel
    Highlands Ranch CO
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    Original Message


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