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# Shaft Settlement

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

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

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

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.

### Kanwarjot Singh

Kanwarjot Singh is the founder of Civil Engineering Portal, a leading civil engineering website which has been awarded as the best online publication by CIDC. He did his BE civil from Thapar University, Patiala and has been working on this website with his team of Civil Engineers.

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## 4 comments on "Shaft Settlement"

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mahendran says:

very good information, thank you

aldwin R.bacay says:

how it affect to the bearing capacity of soil

maninder singh says:

it is really helping.