PILE FOUNDATION FOUNDATIONS S
The conditions that require pile foundations (Vesic, (Vesic, 1977) When one or more upper soil layers are highly compressible and too weak to support the load transmitted by the superstructure, piles are used to transmit the load to underlying bedrock or a str stronge ongerr soil soil lay layer
The conditions that require pile foundations (Vesic, (Vesic, 1977) When bedrock is not encountered at a reasonable depth below the ground surface, piles are used to transmit the structural load to the the soil soil gr grad adua uall lly y
The conditions that require pile foundations (Vesic, (Vesic, 1977) When subjected to horizontal forces, pile foundations resist by bending, while still supporting the vertical load transmitted by the superstructure
The conditions that require pile foundations (Vesic, (Vesic, 1977) In many cases, expansive and collapsible soils may be present at the site of a prop propos osed ed struc tructu turre. Howe owever, er, pile foundations may be considered as an alternative when piles are extended beyond the active zone, which is whe where swellin ling and shrinki inkin ng occur.
The conditions that require pile foundations (Vesic, (Vesic, 1977) •
The foundations of some structures, such as transmission towers, offshore platforms, and basement mats below the water table, are subjected to upli uplift ftin ing g force orces. s.
The conditions that require pile foundations (Vesic, (Vesic, 1977) •
Bridge abutments and piers are usually constructed over pile foundations to avoid the loss of bearing capacity that a shallow shall ow foundation might suffer because of soil erosion at the ground surface.
PILE CATEGORIES Depending on their lengths and the mechanisms of load transf t ransfer er to the soil: 1. point int be beari aring pi piles 2. Friction piles 3. compac paction ion piles
POINT BEARING PILES
ULTIMATE PILE LOAD, Qu
FRICTION PILES
LOAD TRANSFER MECHANISM
LOAD TRANSFER MECHANISM
LOAD TRANSFER MECHANISM resistance per unit area area at any depth z may be determined as The frictional resistance
where p = perimeter of the cross section of the pile
PILE CAPACITY The ultimate load-car load-carrying rying capacity Qu of a pile is given by the equation
PILE CAPACITY
POINT BEARING CAPACITY, Q P
POINT BEARING CAPACITY
FRICTIONAL RESISTANCE
ALLOWABLE LOAD
MEYERHOF’S METHOD FOR
ESTIMATING Qp SAND – c’ = 0
MEYERHOF’S METHOD FOR
ESTIMATING Qp CLAY –
’=0
VESIC’S METHOD FOR ESTIMATING
SAND – c’ = 0
Qp
VESIC’S METHOD FOR ESTIMATING
CLAY –
’=0
Qp
COYLE AND CASTELLO’S METHOD FOR
ESTIM ESTIMA ATING TING Qp IN SAND SAND Coyle and Castello (1981) analyzed 24 large-scale field load tests of driven piles in sand. On the basis of the test results, they suggested that, in sand,
CORRELATIONS FOR CALCULATING Q P WITH SPT AND CPT RESULTS MEYERHOF (1976)
CORRELATIONS FOR CALCULATING Q P WITH SPT AND CPT RESULTS BRIAUD ET AL. (1985)
CORRELATIONS FOR CALCULATING Q P WITH SPT AND CPT RESULTS MEYERHOF (1956)
FRICTION CAPACITY, Q S
FRICTIONAL RESISTANCE (Q S) SAND
Estimation of f The unit frictional fri ctional resistance, f, f, is hard to estimate. In f, several important factors making an estimation of f, must be kept in mind: 1. The natur nature e of of the the pile pile insta installa llation tion.. For For driv driven en piles piles in in sand, the vibration caused during pile driving helps densify the soil around the pile. The zone of sand densification may be as much as 2.5 times the pile diameter, diameter, in the sand surrounding the pile.
Estimation of f 2. The The unit unit ski skin n frict friction ion incr increas eases es wit with h dept depth h more more or less linearly to a depth L’ of and remains constant thereafter. thereafter. The magnitude of the critical depth L’ may be 15 to 20 pile p ile diameters.
Estimation of f 3. At simi similar lar dept depths, hs, the the unit unit skin skin fri fricti ction on in in loose sand is higher for a high displacement pile, compared with a low-displacement pile. 4. At simil similar ar dept depths, hs, bor bored, ed, or jet jette ted, d, piles piles will will have have a lower unit skin sk in friction compared with driven piles.
Estimation of f
Coyle and Castello (1981)
Coyle and Castello (1981)
CORRELA CORRELATION TION WITH WITH ST STANDAR ANDARD D PENETRA PENETRATION TION TEST RESULTS RESULTS MEYERHOF (1976)
HIGH DISPLACEMENT DRIVEN PILES LOW DISPLACEMENT DRIVEN PILES
CORRELA CORRELATION TION WITH WITH ST STANDAR ANDARD D PENETRA PENETRATION TION TEST RESULTS RESULTS BRIAUD ET AL. (1985)
CORRELATION WITH CONE PENETRATION TEST
FRICTIONAL FRICTIONAL RESISTANCE RESISTANCE (Q (Q S) CLAY METHOD (Vija Vijayver yvergiy giya a and and Focht ocht (1972 (1972))
l method in layered soil
FRICTIONAL FRICTIONAL RESISTANCE RESISTANCE (Q (Q S) CLAY METHOD
FRICTIONAL FRICTIONAL RESISTANCE RESISTANCE (Q (Q S) CLAY METHOD
METHOD for normally consolidated clays
for overc overconsolida onsolidated ted clays clays
THE TOT TOTAL FRICTI F RICTIONAL ONAL RESIST R ESISTANCE ANCE
CORRELATION WITH CONE PENETRA PENETRATION TION TEST RESULTS RESULTS •
Nottingha Nottingham m and and Schmertman Schmertmann n (1975) (1975) and Schmertmann Schmertmann (1978) (1978) found found the correla correlation tion for for unit skin friction in clay (with f = 0 ) to be
POINT BEARING CAP CAPACITY ACITY OF PILES RESTING ON ROCK Goodman, 1980
FS ≤ 3
BEARI BEARING NG CAPACI CAPACITY TY,, Q U
Meyerhof Qu = kb x NSPT x Ab + kf x NSPT x As kb
= 40 for Sands = 30 for Silts = 4.5 for Clays
ks
= 0.20 for Sands = 0.17 for Silts = 0.50 for Clays
Luciano Decourt Qu = kb x NSPT x Ab + ( kb
= 40 for Sands = 25 for Clayey Silts = 20 for Silty Clays = 12 for Clays
+ ) x As
Schmertman Qu = kb x NSPT x Ab + kf x NSPT x As kb
= 32 for Sands = 16 for Silts = 7 for Clays
ks
= 0.19 for Sands = 0.40 for Silts = 0.50 for Clays
Ab As
= Luas Luas pena penampa mpang ng tiang tiang = Luas Luas sel selimu imutt tiang tiang
