Definition of overconsolidated soil | Why soil becomes overconsolidated

Saturday, January 28, 2012 14:18
Posted in category Soil Mechanics 2
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Overconsolidated soil

Overconsolidated soil may be defined as

“If the initial vertical effective stress of the soil sample is less than the preconsolidation stress, then the vertical effective stress in the field was once higher than its current magnitude, and the soil is called overconsolidated.”

Or

The soil whose present effective overburden pressure is less than that which the soil experienced in the past is called overconsolidated soil. 

The maximum effective past pressure is called preconsolidation pressure.

Why soil becomes overconsolidated ?

There are many processes that causes the soil to become over-consolidated.

  • Extensive erosion or excavation which results in the decrease of ground surface elevation.
  • Extra loading from a glacier, which has since melted.
  • Extra loading from a structure, such as storage tank, which has since been removed.
  • By rising of ground water table, which increases the pore water pressure.
  • Drying of the pore water due to evaporation, absorption by plant roots which produces negative pore water pressure in the soil ( Stark and Duncan, 1991 ).
  • Chemical changes in the soil.
  • Aging effects.

From the term over consolidation it seems that there is an excessive consolidation in the soil. But that is not the case actually. Overconsolidation is almost always a good thing. Except in Cut slopes where overconsolidated soils are less desirable.

Reference :

Principles of geotechnical engineering by braja m. das

Geotechnical engineering principal and practices by Donald P Coduto

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3 Responses to “Definition of overconsolidated soil | Why soil becomes overconsolidated”

  1. Mohammed Islam says:

    September 18th, 2013 at 4:19 am

    “Overconsolidation is almost always a good thing. Except in Cut slopes where overconsolidated soils are less desirable.”

    Are Overconsolidated soils less desirable in cut slopes? Completely wrong. No geotechnical engineer in right mind will desire the other two types of soils, namely, under- and normally- soils over overconsolidated soils in a cut slope. Please do not write something if you are not sure about.

  2. admin says:

    September 24th, 2013 at 11:47 am

    Muhammad Islam Bro as you have seen i have given reference of the above article. For your information i want you to know that i have not written anything with my own research. Its others research not mine.

    “Overconsolidation is almost always a good thing. Except in Cut slopes where overconsolidated soils are less desirable.”

    The above line is written in the book of Donald. P Cudoto, not my own book. If you want i can tell you the chapter name and page number.

  3. suminder says:

    October 26th, 2013 at 12:46 pm

    question : when does soil behaves like dense sand??

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