a) Ignoring the end bearing in calculating ultimate loads of piles in rock. b) R
ID: 1710144 • Letter: A
Question
a) Ignoring the end bearing in calculating ultimate loads of piles in rock. b) Reducing the adhesion factor "a" for stiffer clays surrounding pile shafts. c) Having a constant end-beating for piles in sand after exceeding certain pile depth. d) The need of laboratory field testing to estimate bearing capacity of pile of in rock. e) Utilizing E_ (not E_lab) in estimating settlement of foundations on rock. f) Using long piles for Doha towers in spite of having pile bearing capacity controlled by the structural requirements g) Using the factored column load in the structural design of pile caps. h) Using inclined (not horizontal) ties for most of anchored sheet-pile walls.Explanation / Answer
a) In end bearing piles, the bottom end of the pile rests on a layer of casted concrete or strong soil or rock. The load of the building is transferred through the pile onto the strong layer. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is safely transferred to the strong layer.
End bearing will resist pile from further settlement into soil. More the extent of area and depth of end bearing provided, more the resistance offered from soil below the end bearing against settlement of pile.
In present case, pile is constructed on rock bed which is hard enough to resist settlement of pile as rock acts as end bearing. Hence we can ignore the end bearing in calculating the ultimate loads of pile in rock. It is enough to consider only frictional resistance offered.
b) Adhesion factor, mainly depends on undrained shear strength Cu of the soil. Smaller the undrained strength, softer the consistency of soil and greater the tendency for the soil to adhere to the pile. For this case, alpha will tend close to 1.
For stiff or over consolidated clays, skin friction resistance is higher because, the undrained shear strength Cu is more in stiff clays. So alpha can be as low as 0.3.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.