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Shaft Settlement

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To find the shaft settlement, Empirical correlations or load-deformation compatibility analysis are widely used. In case of tensile and lateral loads by straight shaft drilled shafts, the procedure to determine shaft settlement is same that of pile foundations.

According to Meyerhof,G. G. and Adams,J. I.,“The Ultimate Uplift Capacity of Foundations,” Canadian Geotechnical Journal, 5(4):1968, for rigid shafts with characteristic length T greater than 3, the equation becomes

shaft-settlement-1
where
Qut = ultimate resistance to uplift of a belled shaft.
D= Shaft Diameter
Db=Bell Diameter
w= Shear strength reduction factor
Nc= bearing-capacity factor
cu = the undrained shear strength of the soil just above the bell surface

The failure surface of the friction cylinder model is assumed to be vertical. So
shaft-settlement-2
where
fut is the average ultimate skin-friction stress in tension developed on the failure plane; that is, fut= 0.8cu for clays
Ws and Wp represent the weight of soil contained within the failure plane and the shaft weight, respectively.

SHAFT RESISTANCE IN COHESIONLESS SOILS

shaft-settlement-3

At displacement-pile penetrations of 10 to 20 pile diameters (loose to dense sand), the average skin friction reaches a limiting value fl.

For relatively long piles in sand, K is typically taken in the range of 0.7 to 1.0 and delta is taken to be about phi-5, where phi is the angle of internal friction, degree. For piles less than 50 ft (15.2 m) long, K is more likely to be in the range of 1.0 to 2.0, but can be greater than 3.0 for tapered piles.

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Comments
  • Sian May 28, 2007 at 2:07 pm

    Shaft Settlement???? i was wishing to know something about that and then i came across Your Site

  • mahendran November 24, 2008 at 5:49 pm

    very good information, thank you

  • aldwin R.bacay September 27, 2010 at 9:09 pm

    how it affect to the bearing capacity of soil

  • maninder singh July 20, 2011 at 4:13 am

    it is really helping.

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