Jouko Lehtonen, Jarmo Virta & Jussi Hattara

Post-underpinning Settlement of the Micropile Underpinning

Tähän of the Micropile Underpinning Projects in Turku

syvättykuva

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Post-underpinning Settlement of the Micropile Underpinning Projects in Turku

Post-underpinning settlement has been commonly ignored when only minor e g elastic deformationignored when only minor e.g. elastic deformation has been assumed in practical design of underpinning.

P t d i i ttl t h t b d iPost-underpinning settlement has not been covered in research literature.

This presentation has a goal to be an opening of discussion on post-underpinning behavior of micropile structures.

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www datu infowww.datu.info

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DATU Database on TurkuDATU Database on Turku Underpinning Projects

Number of piles in DATU by pile length

2000

2500

Moisture observation pointsMoisture observations Crack observations

200 parameters

1000

1500

Num

ber o

f pile

s

Jet GroutingMicropiles

ZIP codes

Settlement observations

PK settlement observation #

FK1 settlement observation point No.

Moisture observation points

PK moisture observation point #

FK1 site number

Moisture observations

PK moisture observation #

FK1 moisture observation point No.

Crack observation points

PK crack observation point #

FK1 site number

Crack observations

PK crack observation #

FK1 crack observation point #

Noise observations

Vibration observation points

PK vibration observation point #

FK1 site number

Vibration observations

PK vibration observation #

FK1 vibration observation point #

500Buildings

PK building #

FK1 zip code

PK zip codeSettlement observation points

PK settlement observation point #

FK1 site number

Questionnaires

PK questonnaire #

Noise observation points

PK noise observation point #

FK1 site number

PK noise observation #

FK1 noise observation point #

Pipes

PK pipe #

FK1 site number

Water observations

PK water observation #

FK1 pipe #

Test pits

PK pit #

00…10 m 10…20 m 20…30 m 30…40 m 40…50 m 50…60 m

Length of piles

Sites

PK site number

FK1 building #

FK1 site number FK1 site numberFK2 pipe #

Soil surveys

PK soil survey #

FK1 site number

Moisture measuring equipment

PK moisture measuring equipment #

FK1 site number

Performed works

PK work name

FK1 site numberFK2 work type #

Piles

PK pile #

FK1 site number

Pile types

PK type #

FK1 pile #

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Notes

PK note #

FK1 site numberFK2 category #

Note categories

PK category #

Works

PK work type #

Project workers

PK name

FK1 site number

Costs

PK cost #

FK1 site number

Elements

PK element #

FK1 pile #

Piling methods

PK piling method #

FK1 pile #

Mi il d li i i T kMicropile deliveries in TurkuPiles in DATU by year of installation

900 25 000 m

600

700

800

20 000 m

400

500

600

Num

ber o

f pile

s

10 000 m

15 000 m

PilesPilemeters

100

200

300

5 000 m

01984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006

Year

0 m

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Installation of micropiles in Turku

Drilling

Jacking

Impact driving

Combination in installation jacking/drilling, j g gjacking/driving

In addition, post-jacking for drilled or driven micropilesp

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T t ll 13 l d t f hTotally 13 load transfer cases has been defined

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Totally 13 load transfer structureTotally 13 load transfer structure cases has been classified as 4 categories

T bl C i f l d f i d i i (L h d H ä 2009)Table. Categories of load transfer structures in underpinning (Lehtonen and Hyyppä 2009).

CATEGORIES COVERING CASES OF LOAD TRANSFER STRUCTURES

Direct support or minor load transfer structure

Separate load transfer structure

Small settlement of superstructure after

d i i ( j ki d i

A: 1, 8 B: 2

underpinning (no jacking during installation)

No movement of superstructure after

d i i (i t ll ti ith

C: 9, 10, 13 D: 3, 4, 5, 6, 7, 11, 12

underpinning (installation with jacking)

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Average settlement in relation to the beginning of underpinning

150 mm

100 mm

g of

und

erpi

nnin

g

27

27 driven no pre-loading34 driven no pre-loading

0 mm

50 mm

rela

tion

to th

e be

ginn

ing 27

343856707824

38 jet gr. no pre-loading56 jacked pre-loading70 drilled no pre-loading78 drilled no pre-loading

-50 mm

Sett

lem

ent i

n

24 jacked pre-loading

-100 mm-15 y -10 y -5 y 0 y 5 y 10 y 15 y

Years from the beginning of underpinning

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Speed of settlement before and after underpinningp p g

0 mm/a

-20 mm/a

-10 mm/a

emen

t 273438

27 driven no pre-loading34 driven no pre-loading38 jet gr. no pre-loading56 jacked pre loading

-40 mm/a

-30 mm/a

Spee

d of

set

tle 3856707824

56 jacked pre-loading70 drilled no pre-loading78 drilled no pre-loading24 jacked pre-loading

-60 mm/a

-50 mm/a

-70 mm/a-14y -13y -12y -11y -10y -9y -8y -7y -6y -5y -4y -3y -2y -1y ±0y +1y +2y +3y +4y +5y +6y +7y +8y +9y +10

y

Years from underpinning

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SiteMicropile type

Total settlement

Settlement during underpinning

Post-underpinning settlement

Elastic deformation of pile shaft

24 jacked 45,2 mm 1,0 mm 44,2 mm 7,0 mm

27 driven 44,4 mm 17,4 mm 27,0 mm 22,3 mm

34 driven 33,6 mm 15,3 mm 18,3 mm 11,5 mm

38 jet grouting 0 1 mm 0 9 mm 1 0 mm N/A38 jet grouting 0,1 mm -0,9 mm 1,0 mm N/A

56 jacked 30,2 mm 5,0 mm 25,2 mm 31,0 mm

70 drilled 39,0 mm 11,3 mm 27,7 mm 31,4 mm

78 drilled 55,7 mm 49,3 mm 6,4 mm 55,3 mm

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Observations

Settlement speed of foundations seems to increase during the underpinning phases. T i ll t t ttl 10 t 40 d t ib ti d l d t fTypically superstructures settle 10 to 40 mm due to vibration and load transfer operations in underpinning. Sometimes settlement during underpinning can be even more, 50 to 70 mm.

Settlement continues after underpinning. If the micropile and load transfer structure system are preloaded the settlement should be minimal, but an observed case had settled for additional 25 mm in six years. Typical post-underpinning settlement is less than 30 mm and speed of settlement is less than 3 mm per year.

The settlement after underpinning is typically less than half of the settlement before underpinning.

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Conclusions

Foundations are underpinned mainly to prevent harmful settlement, to enhance bearing capacity, or for seismic retrofit. In many cases, the need for repair work on foundations is due to rot in wooden piles. Many methods are available for foundation underpinning, micropiles and jet grouting having been common in recent times. A new micropile or a jet grouted column is attached to the existing superstructure, often by means of an even highly complex load transfer structure. The aim is often to mobilize the elastic transformation of the micropile already during the installation phase by using jacks.

Leveling of underpinned buildings is highly important during the renovation phases. Post-underpinning observations will be collected to the DATU database in order to create clearer picture on long-term behavior of underpinned foundations.p g p

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