Deep Foundations

Why to use DF?– High / inclined / horizontal loads,– Extremely different loads,– Compressible soil,– Colapssible soil,– High water level and uplift.

Types of Deep Foundations

SoilMecDrillingMachine

Micropiles – boring machine

Tubes withmanchettes

Rotary drilling – eg. Bauer

Flight AugerDrilling

Core Barrel

Bucket Auger

Multiroller Percussion Bits

Design andConstruction ofRetaining Walls

Benotograbber

Problems withBoring:

Cavingor unstable shaft skin:- casing and or- slurry

Drilling with casing

Drilling with Casing (1/2)

Drilling withCasing (2/2)

Drilling with slurry

Drilling with Slurry (1/2)

Drilling with Slurry (2/2)

Auger Cast Pile

„CFA“ –ContinuousFlight Auger

Pressure Injected Pile

PressureInjectedPile

Pressure Injected Pile - Capacity

Pile Load Test (1/2)

Pile Load Test (2/2)

Load – Settlement Curve

A – typical in soft clay

B – typical ofintermediate, stiffclay anf or sandysoils

Load Transfer

Courtesy SOLEXPERTS AG

Courtesy SOLEXPERTS AG

Strain Distribution along Pile Body

Pile Load TestTime [min] Load [MN] Load [MN]

Settlement [mm]

Time [hours]

Settlement of large diameter pile group

b

iin hdb αtan2∑+=( )2/di φα =

iipn hlndl αtan2).1( ∑+−+=

End-bearing Pile on Rock

cdsvd RAU 6,0=

cdsvd RAU 5,0=

cdsvd RAU 8,0=

pswp EA

lVIs ⋅=

Pile Load

F Design – DPC, p.582, F16.1

Vertical:

Compression

Tension

Horizontal and Moment

Stiff and or

Flexible Pile

Pile subjected to Horizontal andMoment Load

F Design – DPC, p.586, F16.6

dzdys =

2

2

dzydEI

dzdsEIM ==

3

3

dzydEI

dzdMV ==

4

4

dzydEI

dzdVp ==

F Design – DPC, p.588, F16.7

Free-head Restrained-head Pure moment

Connection between the Pile and the Structure

zdykP ihii =i

defhi r

Ek

23

= MdzdyEI =− 2

2

2321

2

2 2z

yyydzdy +−

=

nlz =

0=∑H

0=∑M

( )mdi ddr γϕtan2 ⋅+=

How to increaselateralresistance

F Design – DPC, p.617, F16.30

Adapted from Broms (1972)

Ex. No.4: Large diameter pileCalculate bearing capacity of large diameter pile having diameter d and depth Dp being bored with use of bentonite slurry. Soil section consists of 3,0 m soft clay and 40,0 m stiff clay bellow with consistency index Ic. Borehole is supported by bentonite slurry and the pile will be concreted at the maximum within 8 hours after boring. Modulus of elasticity of concrete is E = 23 000 MPa. Soil and pile data acc. to table below:

d [m] Ic [1] 0.6 cu [kPa] 60 Es [MPa] 8

Dp [m] 0.7 70 12

0.8 80 18

s [mm] 10, 15, 20 0.9 90 27

Ex. No.4: Large diameter pileCalculate bearing capacity of large diameter pile having diameter d and depth Dp being bored with use of bentonite slurry. Soil section consists of 3,0 m soft clay and 40,0 m stiff clay below with consistency index Ic. Borehole is supported by bentonite slurry and the pile will be concreted at the maximum within 8 hours after boring. Modulus of elasticity of concrete is E = 23 000 MPa.

Soil and pile data acc. to the table:

d [m] Ic [1] 0.6 cu [kPa] 60 Es [MPa] 8

Dp [m] 0.7 70 12

0.8 80 18

s [mm] 10, 15, 20 0.9 90 27