Week 7

Question 1

Types of piles

Answer 1

Timber pile
Steel piles
Concrete piles
Composite piles

Question 2

Types of steel pipes

Answer 2

Steel H pile

Steel pipe pile

Question 3

Types of concrete piles

Answer 3

Precast piles (prestressed, reinforced or cylinder piles)
Cast in place (driven or uncased)

Question 4

Types of composite piles

Answer 4

Precast concrete - steel pile
Wood composite pile
Pipe-corrugated shell pile
Composite tapered precast (TPT)

Question 5

Up to which SPT value steel H pile can be used?

Answer 5

Up to 200, very common in HK

Question 6

What is the plug problem in steel H and pipe piles?

Answer 6

Soil will easily get stuck in the profile section creating driving resistance

Question 7

Common piles in HK?

Answer 7

H and bored piles

Question 8

When peak support is used?

Answer 8

When the firm stratum can be reached

Question 9

When the pile works by friction

Answer 9

When there is no firm stratum

Question 10

When should deep foundations be considered?

Answer 10

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)

Question 11

Effects of pile driving in cohesion-less soils (sand or gravel soil)

Answer 11

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.

Question 12

Why pile driving induces negative pore water pressure?

Answer 12

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

Question 13

What is the consequence of negative pore water pressure? How is the phenomena called?

Answer 13

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.

Question 14

Effects of driving in cohesive soils (clay or silt saturated )

Answer 14

Much smaller influential zone
Ground surface heave upward
Exhibits positive pore water pressure

Question 15

What are the effects of positive pore water pressure? How is the phenomena called?

Answer 15

The opposite of the negative pore water pressure, called set up.

Question 16

Static Analysis Methods for estimation of pile capacity?

Answer 16

Laboratory determined soil rock shear strength
Standard penetration test
In-situ test data

Question 17

Ultimate bearing capacity formula and its components

Answer 17

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)

Question 18

For what types of soil Meyerhof method is used? And type of pile?

Answer 18

For cohesion-less soils only for estimating purposes.

Question 19

Types of soil used in alpha method

Answer 19

Cohesive soils only

Question 20

Types of soils used in effective stress method?

Answer 20

For both cohesive on cohesion less, good design approach better than undrained analysis

Question 21

Landa method for offshore piles type of soil?

Answer 21

Cohesive soils only

Question 22

Meyerhof’s fs value for driven displacement piles?

Answer 22

2*N’ lesser than 100kpa

Question 23

Meyerhof’s driven non displacement pile fs value?

Answer 23

N’ lesser than 100 kpa

Question 24

How much percentage of shaft resistance of the total bearing capacity is put into driven piles in cohesive soils

Answer 24

80 to 90%. Calculated by the product of the undrained cohesion times alpha

Question 25

Shaft resistance values or adhesion typical values for piles in cohesive soils? What are the variables?

Answer 25

Depend on pile material and diameter.

From 10 to 90 kpa. Direct proportionality with undrained shear strength

Question 26

What does the Effective stress method (b method) model?

Answer 26

The long term drained shear strength

Question 27

How does the landa value variate?

Answer 27

Through depth, the deeper the smaller

Question 28

How are the lateral loads and moments resisted by single piles?

Answer 28

By flexural stiffness of the pile and mobilized soil resistance

Question 29

How is the lateral capacity controlled in short piles?

Answer 29

By the ultimate soil resistance

Question 30

How is the lateral capacity controlled by long piles?

Answer 30

By the lesser of:
Horizontal load required to cause soil failure
The horizontal load required to cause the yielding of the pile