Geotechnical Engineering 101 and more…

Building firm foundations

Significance of Geotechnical Engineering – Part I – Differential Settlement

Posted by Kshitija Nadgouda on April 5, 2006

Geotechnical Engineering is the study of soil in relation to man-made structures that stand on it. Every structure that is built, has a foundation that rests on the soil underneath and transfers the load (weight) from the structure to the ground. It is the job of the geotechnical engineer to assess the properties of the soil and determine wheather the structure is feasible at the proposed location.

Soil in its natural state is very heterogenous and non-uniform. It can vary greatly from place to place and also with depth. Soil investigations need to be performed to determine the type of soil present at a location. Based on the collected data, the geotechnical engineer determines the soil bearing capacity and estimated settlement of the structure.

The bearing capacity of the soil is simply the capacity of the soil to bear the weight (load) of the structure built on it, without undergoing failure. The settlement of the structure is the amount the structure will “sink” during and afer construction. It is the role of the geotechnical engineer to ensure that this settlement is within tolerable limits.

Settlement is broadly classified as total settlement and differential (uneven) settlement. Total settlement refers to the uniform settlement of the entire structure and occurs due to weight of the structure and imposed loads. Differential or uneven settlement can occur if the loads on the structure are unevenly distrbuted, variations in the soil properties or due to construction related variations.

Probably the most talked about and classsic “failure” in terms of differential settlement is La Torre Di Pisa (The Tower of Pisa) in Italy. Imagine a building meant for habitat (residential or commercial) structure showing so much inclination!!!

Leaning Tower Of Pisa

Leaning Tower of Pisa
(Courtsey Wikipedia )

The Leaning Tower of Pisa is the bell tower of the Cathedral. Its construction was commenced in 1173 and contiued haltingly over a period of 200 years! The tower began “leaning” soon after construction began in 1173. The inclination of the tower is attributed to the non-uniform, sponge-like saturated clay soil on which the foundation of the tower rests. The softer area within this strata has settled more causing the tilt.

Several engineers have proposed plans to “straighten” the tower. However, with its 800+ years of “leaning” history, locals do not want the tower to be straightened. Every few years some form of restoration is performed to ensure that the tower does not become unstable or collapse.

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Copyright Kshitija Nadgouda.

17 Responses to “Significance of Geotechnical Engineering – Part I – Differential Settlement”

  1. […] This is a continuation, rather the next part, of the topic I posted earlier on Differential Settlement. Total settlement is the uniform “sinking” of the structure due to various factors such as the self-weight of the structure, the loads imposed on it, the nature of the soil on which the structure’s foundation rests, etc. […]

  2. Russell said

    Thanks for the useful info, this has really helped me with my project work.

  3. Russell,

    You are most welcome! If there is any particular topic related to Geotechnical Engineering or related fields that you would like to read about, do let me know. I will try and write about it.

    Good luck!

    • Ziko said

      I would like to know wat geotechnical information can be said about the pagoda tilting tower in shanghai

  4. Anonymous said

    i’d like to get more info about soil profile of the pisa tower site. anyone has any suggestion? thank you…


  5. Rachel said

    Your simple way of explaining terms
    is simply nice,it really helped me

  6. Emm.. I like the way you react to my luscious export I have a nice fresh joke for you people) Where do young dogs sleep when they camp out? In pup tents.

  7. rahim said

    How much is the toolerance(in mm) of differential settlement of a newly improvd compacted soil sub base. Soil compacted by Dynamic Replacement method.

  8. rahim said

    Also if the soil compacted by Dynamic compaction, how much is the differential settlement tollerance.

  9. Nancy said

    In residential construction, in your opinion what steps could be taken to prevent differential settlement?

  10. Anonymous said

    awesome stuff thanks very much, I am doing a project on earthquake SSSI dynamics and am trying to model the soil and foundation, im a mechanical engineer — great start — long way to go.

  11. olabisi sulaimon said

    good work sir, but i would like to know the role of geotechnical in civil engineering construction

  12. so nice

  13. Monique Forbes said

    Helped a lot as additional reading, thanks.

  14. […] Differential settlement is a deceptively destructive failure that commonly occurs when the building site has not been properly analyzed. Differential settlement will occur when “the soil beneath a structure cannot bear the weights imposed. The settlement of a structure is the amount that the structure will ‘sink’ during and after construction,” [a]. A well-known example of differential settlement is the Leaning Tower of Pisa, which leans due to insufficient bearing capacity of the soil beneath one side of the tower [b]. […]

  15. Corky said

    Seems that several years ago the current solution to the differential was addressed by small diameter directional boring beneath the “stiffer” clays that were not settling as fast; this allowed the “high” side to settled and compress into the void left by the borings, reducing the total differential to a level that does not threaten the structure.

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