～hyper-mega method～

2014/6/10

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THE 1st WORKSHOP ON NEW PILE FOUNDATION TECHNOLOGIES IN VIETNAM 20/6/2014, Ho Chi MinhTHE 1st WORKSHOP ON NEW PILE FOUNDATION TECHNOLOGIES IN VIETNAM 20/6/2014, Ho Chi Minh

INTRODUCTION OF BASE ENLARGEDPRE-BORING METHOD WITH NODULAR PILE

～HYPER-MEGA METHOD～

Yusuke Homma

THE 1st WORKSHOP ON NEW PILE FOUNDATION TECHNOLOGIES IN VIETNAM 20/6/2014, Ho Chi Minh

Introduction of Hyper-MEGA methodDiameter : φ440-300 ～ φ1200-1000

（nodule diameter – shaft diameter)Length : The maximum length is up to 68.5m.

There are many cases of more than 60m length.

Material：Nodular pile : PHC & PRCSpun pile : PHC, PRC, SC, Steel

Concrete strength : 85, 105, 123N/mm2 & more

ω ： enlarged ratio （1≦ω≦2）

ω＝ De ／（ Do +0.05）

De：enlarged excavation diameterDo：nodule diameter

Enlarged ratio ω

Conventional = 1.15↓

Hyper-Mega = 1.0～2.0

more than 2 times bearing capacity

Nor

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2m o

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of P

ile L

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rt 2m

Enla

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Shaf

t Par

t

Low strengthcement

High strengthcement 1,

000m

m

Enlarged Excavation Diameter De

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Procedure of Hyper-MEGA method

①excavation ②expanded blade～enlarged excavation

Expanded blade and enlarged excavation

③mixing repeatedly

Mixing and S

tirred while

injecting cement slurry

④ forming the grouted base ～pull out

Forming the grouted base

then Pull -up

⑤setting pile

Setting pile

Excavation


Overview of the Hyper-MEGA method Welding Pitching Pile Setting Pile

Enlarged auger-head

Screw

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Alloable vertical bearing capacity of soil

Equation of vertical bearing capacity

Soil of pile-toe Hyper-Mega methodJapanese general pre-boring method

TCXD-205 in Vietnam

sandy and gravelly

α=240ω1.5＋90ω（330～858）

250 300 or 400

clayeyα=210ω1.25＋90ω

（300～679）250 300 or 400

( ) ψγβα cussp LqLNANRu ++=

End bearing capacity factor：α

Ru

αN Ap

End bearing capacity: Ultimate bearing capacity

: End bearing capacity factor: Average N value for pile toe: Cross section of end nodular diameter


Procedure of Hyper-MEGA method

Equation of vertical bearing capacity

( ) ψγβα cussp LqLNANRu ++=

SoilHyper-mega method Japanese

general pre-boring method

TCXD-205in VietnamStraight part

Nodular pile of enlarged part

β Ns(sand and gravelly)

5.0 Ns （30+5.5Ｎs）ω 3.3 Ns 2.0Ns

γ qu (clayey) 0.7 qu （20+0.5qu）ω 0.5 qu 0.5qu

Shaft bearing resistance factor : β, γ

Β,γ NsLsquLc

: Shaft bearing resistance factor: Average of N value of sandy soil: total length of pile in contact with sandy soil: Mean value of axial compressive strength : total length of pile in contact with clayey soil

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Result of loading test

0.0

5.0

10.0

15.0

20.0

25.0

30.0

35.0

0 2000 4000 6000 8000 10000 12000

Dept

h G

.L－

(m)

Load (kN)

20 40N Value

60

10

5

15

0 0

G.L

- (m

)

20

25

30

35

0

5000

10000

0 50 100 150

Pile

hea

d ｌo

adPo

(kN

)

Pile head displacementSo, Pile toe displacementSp (mm)

Pile head displacement

Pile toe displacement

These database is used to get license of"ASSESSMENT OF TECHNOLOGY FOR BUILDING CONSTRUCTION GBRC FOUNDATION" (GBRC 05-23A-001～003)and "INFRASTRUCTURE AND TRANSPORATION MINISTRY" (TACP-0210～0214).

Static loading tests were carried out in 53 locations.

・pile：φ500-400 + φ500・pile length：30m・ω=2.0

Load-displacement curve Axial force distribution


Study of end bearing capacity＜CONVENTINAL method＞

Pp＝α・N・Ap

α＝250 (1)

＜Hyper-Mega method＞

*Constituted by the combination of resistance Ppp of the pile bottom face and the friction Ppf of the grouted base.

*considered to change of the base grouted diameter

Pp＝Ppp＋Ppf

α＝αp＋αf＝aωb＋cω (2)

Pp

Gro

uted

Bas

e

Shaf

t fr

ictio

n of

gro

uted

bas

e P p

f

load bearing capacity of the bottom face of the grouted base

Ap

position 2m above the pile toe

lowermost nodebottom face

pile toe about 0.35m

Ppp

Ppf 2.0m

Pp=Ppp+Ppf

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End Bearing Capacity Factor ( α )

Sandy & Gravelly：α＝240ω1.5＋90ω

0

200

400

600

800

1000

1 1.2 1.4 1.6 1.8 2

αp＝

qpp

/ N (

kN/m

2)

enlargement ration ω

sandy soilgravelly soilregression curve：315.7 1.455 calculation：240 1.5

0

2000

4000

6000

8000

10000

0 20 40 60 80

（qp

－24

0 ω

1.5

N) /

ω(k

N/m

2)

N

sandy soilgravelly soilregression curve 219.2 lower limit 98.2 calculation 90

ω=1.0 → α= 330, ω=2.0 → α= 858

αp=240ω1.5

Pp

Gro

uted

Bas

e

Shaf

t fr

ictio

n of

gro

uted

bas

e P p

f

Ap

Ppf 2.0m


Ppp

Pp=Ppp+Ppf

αf=90ω


End Bearing Capacity Factor ( α )

Clayey soil：α＝210ω1.25＋90ω

ω=1 → α= 300, ω=2→ α= 679

Pp

Gro

uted

Bas

e

Shaf

t fr

ictio

n of

gro

uted

bas

e P p

f

Ap

Ppf 2.0m


Ppp

Pp=Ppp+Ppf

0

500

1000

1500

2000

2500

1.0 1.2 1.4 1.6 1.8 2.0

α p＝

ｑpp

/N(k

N/m

2 )

enlargement ration ω

clayey soil

excluded data to statistics

regression curve：280.5 1.259

calculation：210 1.25

0

2000

4000

6000

8000

10000

0 20 40 60 80

(qp －

210ω

1.25

N)/ω

(kN

/m2 )

N

calyey soillower limit 99.8 calculation 90

αp=210ω1.25

αf=90ω

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Shaft Resistance Factor (β & γ) for Nodular pile

0

200

400

600

800

0 20 40 60 80

ｆｓ/ω

(kN

/m2)

Ns

sandy soilregression curvemean-1.06σcalculationJapanese generalVietnamese standard

Ｆs ＝ (30＋5.5Ns）ω×DoπLs

0

50

100

150

200

250

0 100 200 300 400

ｆc/ω

(kN

/m2 )

ｑu (kN/m2)

clayey soilregression curvemean - 1.06σcalculationJapanese general & Vietnamease standard

Hyper-Mega method

more than 2 times

more than 20%

Spun Pile Nodular Pile

Ground

In some cases of spun-pile, friction capacity is determined by between shaft cement slurry and pile.→ Spun-pile is proportional to pile-diameter. In case of nodular-pile against that, that is always determined by between shaft cement slurry and soil, because it can get high adhesion force by nodular.→Nodular-pile is proportional to excavation-diameter.

Hyper-Mega method

Sandy soil

Clayey soil

Ｆc ＝ (20＋0.5qu）ω×DoπLc


Comparison of Calculation and Static load test result

Static load test result ＞ Calculation 1.24 times

0

10000

20000

30000

40000

50000

0 10000 20000 30000 40000 50000

Bea

ring

capa

city

by

load

test

Rt (

kN)

Bearing capacity from applied equation Rc (kN)

Toe:Sand

Toe:Gravel

Toe:Clay

Rc=Rt

Ration of average

These database is used to get license of "ASSESSMENT OF TECHNOLOGY FOR BUILDING CONSTRUCTION GBRC FOUNDATION" (GBRC 05-23A-001～003) and "INFRASTRUCTURE AND TRANSPORATION MINISTRY" (TACP-0210～0214).

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Design Procedure on Vietnam

Pile diameter

(mm)

Pile Length(m)

Designedcapacity

(kN)

Minimumplaned

load(kN)

Ultimate capacityby load test

(kN)

1200 60 9,000 18,000 14,400 20% ↓

1000 60 7,000 14,000 9,800 38% ↓

Designed by Cast-in Place Pile

In Vietnam, it is necessary to confirm the designedbearing capacity in advance in construction site.

Loading test must be carried out using designed piles.

If designed capacity can be obtained by loading test,We have to redesign the pile foundation of building.


We can surely determine the specification of pile which is satisfied with designed capacity, from advanced loading test.

Design Proposal using Hyper-MEGA Method in Vietnam

The greatest feature of Hyper-MEGA Method is that this method can be changed the vertical bearing capacity by control of the enlargement excavation rate in the range of 1 to 2 times, under the same specification pile.

ω=1.0 ω=1.2 ω≧1.2The capacity of pile is designed as ω=1.0 .

In investigating the bearing capacity of designed pile, the piles with specification of more than ω=1.0 are constructed in addition to ω=1.0

Even if the bearing capacity of ω=1.0 is less than designed capacity, another pile can fulfill it.

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Design Proposal using Hyper-MEGA Method in Vietnam

In recent year, a new pre-cast pile installation method forhigh load-bearing capacity is being actively developed inJapan. This Hyper-Mega method can set the enlargementfactor to a pile diameter of 1 to 2 times without keeping afixed value, and can get bigger friction resistance by nodularpile. Here is the evaluation of vertical bearing capacitythrough the loading test results.-------------------------------------------------------------------Because now pre-boring method like the Hyper-Mega

method is not general in Vietnam, we want to introduce theHyper-Mega method to Vietnam.

Thank you very much !


～hyper-mega method～

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