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 Topic: Geotechnical design and analysis Subject: Consolidation Settlement
 Author: Brandon 2001-01-17 Somebody can tell me is it logical to have a consolidation settlement so much so that the settlement (based on conventioanal Terzaghi formulae ) is almost equal or even exceed the the height of embankment placed (loading). i.e. there will be no net height gain even say a fill of 1m (about 20 kPa) is palced while the computed settlement is also 1m by calculation ? This sounds very unrealistic isn't it ? Reply to this posting
Follow-up:
 Author: Bengt Broms 2001-01-17 It is entirely possible that the settlement calculated from e.g. the results from oedometer (consolidation) tests can exceed the height of the fill. The compression index Cc had to be high, 2.0 to 3.0. The submerged unit weight of the compressible soil had to be low, 2 to 3 kN/mcu and the ground water table had to be very high, close to the ground surface. For e.g. a 10 m thick layer with peat with a compression index of 2.5, a unit weight of 12.6 kN/mcu and an initial void ratio eo of 5 the estimated settlement for a 1 m high fill is about 1 m when the ground water table is located at the ground surface. (The stress increase is reduced from 20 to 10 kPa as the fill is submerged.) The net increase of the effective vertical stress is 10 kPa throughout the clay layer when the width of the fill is large compared with the thickness of the clay layer. The settlement caused by the lateral displacements of the soft soil is neglected as well as the long term settlements caused by secondary consolidation and creep. If the thickness of the fill is reduced to 5 m the estimated settlement is reduced to 0.8 m. In order to reach a settlement of about 1 m when the thickness is 5 m then compression index had to be about 3. It is thus possible that the calculated settlement of a fill can reach or even exceed the height of the fill. This is not uncommon for organic soils like peat and gyttja.
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Follow-ups:
 » Bengt Broms, 2001-01-17 » Bengt H. Fellenius, 2001-01-20 » Liew Shaw Shong, 2001-05-18 » MG, 2003-02-19 Show all follow-ups