Week 7 Flashcards
(30 cards)
Types of piles
Timber pile
Steel piles
Concrete piles
Composite piles
Types of steel pipes
Steel H pile
Steel pipe pile
Types of concrete piles
Precast piles (prestressed, reinforced or cylinder piles) Cast in place (driven or uncased)
Types of composite piles
Precast concrete - steel pile
Wood composite pile
Pipe-corrugated shell pile
Composite tapered precast (TPT)
Up to which SPT value steel H pile can be used?
Up to 200, very common in HK
What is the plug problem in steel H and pipe piles?
Soil will easily get stuck in the profile section creating driving resistance
Common piles in HK?
H and bored piles
When peak support is used?
When the firm stratum can be reached
When the pile works by friction
When there is no firm stratum
When should deep foundations be considered?
Foundation subject to vertical or lateral load or the combination of both.
In the case of offshore structure, anchorage, highway embankment , liquefaction, scour zone or swelling soils ( expansive soils)
Effects of pile driving in cohesion-less soils (sand or gravel soil)
First: ground surface subsidence
Second: large impact zone, large influential zone
Third: increase density of the soil due to vibration and lateral displacement inducing negative pore water pressure.
Why pile driving induces negative pore water pressure?
If the soil is saturated the driving will create severe shearing increasing the volume but it cannot. Consequence is the negative pore water pressure, suction take place
What is the consequence of negative pore water pressure? How is the phenomena called?
Increase effective stress and bearing capacity in the short term. In the long term consolidation will dissipate the negative pore water pressure reducing the bearing capacity. The phenomena is called relaxation.
Effects of driving in cohesive soils (clay or silt saturated )
Much smaller influential zone
Ground surface heave upward
Exhibits positive pore water pressure
What are the effects of positive pore water pressure? How is the phenomena called?
The opposite of the negative pore water pressure, called set up.
Static Analysis Methods for estimation of pile capacity?
Laboratory determined soil rock shear strength
Standard penetration test
In-situ test data
Ultimate bearing capacity formula and its components
Qu = Rs + Rt
Where Rs is the shaft resistance (Asfs shaft surface times unit shaft resistance) And Rt is the toe resistance (qtAt unit toe resistance times pile toe area)
For what types of soil Meyerhof method is used? And type of pile?
For cohesion-less soils only for estimating purposes.
Types of soil used in alpha method
Cohesive soils only
Types of soils used in effective stress method?
For both cohesive on cohesion less, good design approach better than undrained analysis
Landa method for offshore piles type of soil?
Cohesive soils only
Meyerhof’s fs value for driven displacement piles?
2*N’ lesser than 100kpa
Meyerhof’s driven non displacement pile fs value?
N’ lesser than 100 kpa
How much percentage of shaft resistance of the total bearing capacity is put into driven piles in cohesive soils
80 to 90%. Calculated by the product of the undrained cohesion times alpha
