Underpinning Hystorical Buildings

Historical Constructions, P.B. Lourenço, P. Roca (Eds.), Guimarães, 2001 1003

1 INTRODUCTION

The development of new underpinning techniques has allowed the adoption of a wide number of solutions, progressively more adapted to the singularities and restraints of each scenario, spe-cially when sensitive, old or historic, constructions founded on weak soils have to be underpinned. In this context, the solutions comprising micropiling and jet grouting techniques should be pointed out due to their versatility and advantages related to the limitation of vibrations, as well as the possibility to be adopted in small spaces with low head rooms and restricted access. These tech-niques also allow the soil improvement, minimising the soil disturbance due to the boreholes small diameter, drilled with suitable equipment (Bullivant and Bradbury 1996).

On the following chapters, after the presentation of the main aspects of these two techniques, some practical case histories, where micropiling and jet grouting underpinning techniques were used, are presented. In each case, the following topics are presented: scenario, main restraints, main conception and execution criteria.

2 UNDERPINNING TECHNIQUES

2.1 Micropiling

Micropiling is a very old technique initially adopted with wood driven piles, which has been de-veloped in the last years mainly due to the bearing capacity improvement (lateral friction at the bond length) related with the use of high pressure grout injection techniques (bigger than 4MPa) and high resistance steel hollow tubes (see Fig. 1). These improvements have allowed to design micropiles with steel hollow tubes (external diameter lesser than 130mm) to carry axial service loads greater than 700kN (Bustamante et al. 1997, Bustamante and Doix 1985).

2.2 Jet Grouting

Jet grouting technology have initially been developed in Japan, the UK and Italy. For about 20 years it has been applied worldwide. In Portugal the technology has been applied in the last 6 years, mainly on Lisbon Metro extension works. Recently, vertical jet grouting solutions have

Underpinning solutions of historical constructions

Alexandre Pinto Tecnasol FGE – Fundações e Geotecnia S.A., R. das Fontainhas nº 58, 2700 – 391, Amadora, Portugal

Sandra Ferreira Tecnasol FGE – Fundações e Geotecnia S.A., R. das Fontainhas nº 58, 2700 – 391, Amadora, Portugal

Vasco Barros Tecnasol FGE – Fundações e Geotecnia S.A., R. das Fontainhas nº 58, 2700 – 391, Amadora, Portugal

ABSTRACT: The aim of this paper is to present the main design and construction criteria con-sidered on some underpinning solutions performed by Tecnasol FGE. After a brief description of micropiling and jet grouting underpinning techniques, some practical case histories where these techniques were adopted are presented. Finally the main advantages and limitations of the pre-sented techniques are pointed out.

1004 Historical Constructions

also become competitive and advisable in several and more usual scenarios, like foundations, earth retaining and underpinning works (Falcão et al. 2000, Greenwood 1987).

According to the definitions of the European Standard on Jet Grouting (CEN/TC 288), jet grouted structures consist of interlocking jet grouted elements. An element is the volume of soil treated through a single borehole, which may be a cylindrical jet grouted column or a planar jet grouted panel (Kutzner 1996).

Jet grouting has nothing to do with common grouting, as according to the jet grouting tech-nique the soil is disintegrated by a jet of water or grout at very high pressure (bigger than 30MPa), obtained through the transformation of the high pressure flow (potential energy) into the high speed jet directed to the soil (kinetic energy) due to the very small diameter nozzles effect, and is subsequently mixed with the grouting material (see Fig. 2). A part of the mixed material returns to the surface along annular space around the drill rods or along neighbouring boreholes, serving for necessary pressure relief.

Figure 1: Micropiling: technology and main construction phases.

Figure 2: Jet grouting: technology and main construction phases.

3 CASE A – UNDERPINNIG THE FAÇADES OF AN OLD BUILDING IN LISBON

3.1 Scenario

The building is located in Lisbon at the historic quarter of “Bairro Alto”, close to “S. Pedro de Alcântara” terrace. The construction of a basement with 3 floors above ground level, inside (12 x 20 m2) and outside the existent building, demanded the demolition of the existent brick and ma-sonry structure, persevering, for architectural reasons, the external façades (Pinto et al. 2000).

Micropiles

Thread connectors

Manchette valves

hMicropiling technology

Steel hollowtubes

hJet grouting technology

High pressurejetting nozzle(water test)

1st Phase 2nd Phase 3rd Phase 4th Phase

Drilling theborehole withsmalldiameter rodtill themicropilebase

Placement ofthe steel hollowtube inside theborehole andfilling of thetube/soilannular spacewith grout

Post-groutinghigh pressureinjection throughmanchettevalves in orderto create thebond length (Ls)

Filling of theinternal spaceof the steelhollow tubewith grout

L S

hMicropiling: construction phases

1st Phase 2nd Phase 3rd Phase 4th Phase

Conclusion ofthe drillingoperation whenthe rod’s jetnozzle reachesthe base of thecolumn

Drawing up androtation of therod togetherwith the jettingof grout at veryhigh pressurethrough rod’snozzle

End of the jetgroutingopertations whenthe jet rod´snozzle reachesthe top of thecolumn

hJet grouting columns (type 1): construction phases

Drilling theborehole withsmalldiameter rod

A. Pinto, S. Ferreira and V. Barros 1005

3.2 Main restraints

As main restraints could be pointed out: the geological conditions, the surrounding conditions (site at the historical quarter of “Bairro Alto”), as well as the geometry and degradation of the fa-çades to be persevered, which had to be braced during the excavation works (see Fig. 3).

Figure 3: Site localization and view of the existent façades at the beginning of the works.

3.3 Main conception and execution criteria

Due to the building structure and degradation (see Fig. 3), as well as its tight geometry and low head room, restricted by the façades bracing system, the façades were underpinned with two rein-forced concrete walls, supported vertically by micropiles and horizontally with tie rods. The ex-cavation and construction of both walls followed the “Berlin” technique (see Fig. 4).

Figure 4: Excavation phases: underpinning and earth retaining solutions.

D. Pedro V Street

Adjacent oldbuilding with

3 floors Ext

ern

alex

cava

tio

n

Free ground

Façades to beperservered

Internalexcavation

h Localization Plan

N

hFaçades to be preservered: view from backyard

Miocenicclays

-6m

Micropiles

hPhase I - execution of micropiles

Landfill

D. Pedro V Street

Miocenicclays

-6m

Tie rod

Ground anchors

LandfillInternal

excavationExternal

excavation

D. Pedro V Street

h Phase III - 2nd phase of excavation, includingexecution of tied/anchored retaining walls

Landfill

Miocenicclays

-6m

D. Pedro V Street

Internalexcavation

Externalexcavation

h Phase IV - 3rd phase of excavation

Miocenicclays

-6m

Ground anchors

Internalexcavation

Externalexcavation

Tie rod

h Phase II - 1st phase of excavation, includingexecution of tied/anchored retaining walls

Landfill

D. Pedro V Street

1006 Historical Constructions

4 CASE B – UNDERPINNIG OF AN HISTORIC BUILDING IN AVEIRO

4.1 Scenario

The building with brick and masonry structure, 4 floors and an area of 14x32m2 is located at the down town of Aveiro. The construction of a basement with 1 floor above ground and water level on a 12x12m2 lateral area demanded, by architectural reasons, the demolition of 2 existent ma-sonry columns and the construction of 3 new reinforced concrete columns (see Fig. 5).

Figure 5: Drilling works inside teh building and localization plan.

4.2 Main restraints

As main restraints could be pointed out: the geological conditions, which demanded the excava-tion above ground water table and the building structure and low head room, as works had to be done inside the building (see Fig. 5).

Figure 6: Excavation and underpinning phases.

Existent columns

hPhase I - Drilling works on low head roomfor the execution of jet grouting columns

G.W.

Cobble

-2m

Landfill

Cretacic stiff clays

hPhase I - Execution of underpinning jet groutingcolumns

G.W.

-2m

hPhase II - Excavation works

Cretacic stiff clays

Landfill

Cobble

G.W.

-2m

hPhase III - Execution of new r.concrete columns

Landfill

Cobble

Cretacic stiff clays

• Localization Plan

Bel

ém d

o P

ará

Str

eet

Internalexcavation

Existentcolumns(to bereplaced)New

columns

Main Square

Main entrance

Peripherical jet grouting wall

G.W.

-2m

hPhase IV - Demolition of the existent masonry columns

Landfill

Cobble

Cretacic stiff clays

A. Pinto, S. Ferreira and V. Barros 1007

4.3 Main conception and execution criteria

Due to the building geometry (low head room) the façades were underpinned with a watertight single row jet grouting wall, formed by columns ∅0,80m, spaced 0,70m. The demolition of the internal columns was done just after the excavation and the execution of the 3 new reinforced concrete columns, which demanded the underpinning of the existent columns with two ∅1m jet grouting columns (see Fig. 6 and 7) (Pinto et al 2000).

Figure 7: Excavation and underpinning phases of existent columns.

5 CASE C – UNDERPINNIG OF AN OLD CHIMNEY IN LISBON

5.1 Scenario

The chimney with more than 30m height, brick and masonry structure, belonged to an old chemi-cal factory, named “União”, and is located at the quarter of “Alcântara”. The construction of a new residential and commercial complex with 2 floors above ground level for parking purpose, intersecting partially the chimney masonry foundation, demanded the underpinning of the chim-ney, which, for architectural reasons, had to be refurbished (see Fig. 8 and 11).

Figure 8: Localization plan and cross section.

5.2 Main restraints

As main restraints could be pointed out: the geological conditions, the bed rock (Volcanic Com-plex) is located at a depth of 17m and the execution of a 7m depth excavation located 1m from the chimney shaft, intersecting the chimney original brick and masonry foundation.

New reinforcedconcrete columns

Jet groutingunderpinning

columns

hPhase III -Excavation works

New reinforced concrete columns

hPhase IV - Demolition of the existant masonry columns

G.W.-3m

-17m

Chimney to be perservered)

Internalexcavation

hScenario (cross section 1-1)

Volcanic Complex

Alluvium

0m

+30m

-7m

hLocalization Plan

Ceu

ta A

v.

7m depthexcavation

Chimney to beunderpinned F. Silveira Street

Font

ainh

as S

treet

Periphericaldiaphragm wall

1

1

1008 Historical Constructions

Figure 9: Underpinning solution.

5.3 Main conception and execution criteria

Due to the chimney structure and slenderness, the underpinning solution comprised the execution of 16 micropiles with 24m length, including 6m of bond length on Volcanic Complex. The mi-cropiles were caped by concrete beams, which were connected to the chimney structure with prestressed tie rods (see Fig. 9). The performance of the chimney was analysed through a Moni-toring and Survey Plan, comprising reflective targets located at different levels at the chimney shaft. During excavation works data was collected at least once a week (see Fig. 10).

Figure 10: Chimney Monitoring and Survey Plan.

Figure 11: Excavation works and perspective of the chimney at the end of the works.

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Time

Time

Dy[mm]

Dz[mm]

Target 10 Target 8 Target 6 hMonitoring and Survey Plan

Chimney

Dy[mm]

7m

18m

21m

26m

T10

T8

T6

Dy[mm]

(reflective targets at chimney shaft)

Dz[mm]Chimney

hPerspective of the chimney at the end of the works

Chimney

hUnderpinning solution

Tie rod level 2 and 3 - Plan

Tie rod level 3 and 4 - Plan

Micropiles

Tie rod

View

Level 1

Level 4

Cap beam

hView of micropiles cap beam

Tie rod

hView of excavation works turning aside thechimney

A. Pinto, S. Ferreira and V. Barros 1009

6 CASE D – UNDERPINNIG OF AN OLD PALACE IN LISBON

6.1 Scenario

Built at the beginning of the XXth century, with french classic style, brick and masonry structure, the Palace has 3 floors, an area of 30x30m2 and is located in the center of Lisbon, being sur-rounded by important streets, like F.P.Melo Avenue (see Fig. 12). In order to face the new pro-ject, which demanded a 24m average height excavation on Lisbon Miocenic soils around the Pal-ace (see Fig. 14), as well as the construction of one gallery bellow its structure, the Palace was underpinned internally with micropiles and externally with contiguous bored piles (see Fig. 13). According to the new project, the Palace will become an hotel and the underground areas will be used mainly for parking and shopping purposes.

Figure 12: Palace localization and view from Palmeiras Square at the beginning of the XXth century.

6.2 Main restraints

As main restraints could be pointed out: the geological conditions, the surrounding conditions, the Palace structure and geometry and the construction schedule (see Fig. 15 and 17).

6.3 Main conception and execution criteria

Due to the Palace structure and geometry (low head room), the internal walls were underpinned with micropiles caped by a grillage of prestressed concrete beams, which were connected to the masonry walls with pairs of prestressed “Gewi” bars (see Fig. 13).

Figure 13: Grillage of cap beams and internal underpinning works.

Grillage of prestressed concrete cap beams

Existent walls (brick and masonry structure)Grillage of prestressed concrete beams

• Underpinning solution for internal walls

Underpinningmicropiles

Drilling operation

GewiMicropiles

Load transference

Cap beamUnderpinned wall

Prestressedcables

• Localization - urban area:view from F.P.Melo Avenue

1010 Historical Constructions

The underpinning of external walls was done with a contiguous bored piles (∅0,80m spaced 1,0m) wall, connected to the masonry walls trough the piles cap beam. The piles were lined with sprayed concrete. Due to Palace geometry and the existence of the internal micropiles, the piles were braced at 6 levels by concrete ring beams. These beams were cast against the ground and their levels were defined in order to coincide with the final underground slabs. The beams were supported by vertical steel profiles in order to restrain their deformation (see Fig. 14).

Figure 14: Underpinning solution for external walls.

Figure 15: Sequences of excavation and construction of the underground slabs around the Palace. The Palace performance was analysed through a wide Monitoring and Survey Plan, compris-

ing: topographic marks (reflective targets) and inclinometers (located inside the bored piles). Data was collected at least once a week (see Fig. 16).

Figure 16: Palace Monitoring and Survey Plan.

May 2000

June 2000

July 2000

August 2000

Vista da cortina de estacas e das vigas de cintagemMarch 2001

April 2001

Dezember 2000

Landfill

Miocenic soils

OligocénicoG.W. G.W.

-24m

FontesPereira deMelo Av.(WEST)

After excavationBefore excavation

Sousa MartinsStreet (EAST)

• Underpinning solution for external walls

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A5 A6 A7 A8

DZ[x10-3m]

Time

Time

Time

DY[x10-3m]

DX[x10-3m]

Font

es P

erei

ra d

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Ave

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Reflective tragets at thePalace façades (1st floor)

Martens Ferrão Street

Andaluz Square Palmeiras

Square

Sou

sa M

artin

s St

reet

Lisb

on M

etro

Tun

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A7

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• Monitoring and Survey Plan

Inclinometers(inside piles)

Palace

Contiguousbored piles

Ringprestressed

concretebeams

Prestressed cableslayout

A. Pinto, S. Ferreira and V. Barros 1011

Figure 17: Final phases of excavation and construction of underground slabs around the Palace.

7 MAIN CONCLUSIONS

The demand for underpinning has increased steadily in the last years as renewals and refurbish-ment works have gained popularity. As example, the presented cases proved how the versatility of some underpinning techniques can fit the uniqueness and restraints of complex scenarios, involv-ing old and historic sensitive buildings, sometimes founded on weak soils. On the figures below two comparative analyses between micropiling and jet grouting technologies (see Fig. 18) and be-tween these techniques and the conventional ones are presented (see Fig. 19).

Figure 18: Comparative analysis between micropiling and jet grouting underpinning techniques.

Figure 19: Comparative analysis between micropiling/jet grouting and conventional techniques.

General view of the excavation around the Palace (final phase - Dez 2000) Execution of underground concrete slabs around the Palace(final phase - May 2001)

Main restraints

4 Mobilization of lateral frictiononly on competent soils(NSPT>40 )

4 Lower stiffness

4 Lower end bearing capacity

Main advantages

4 Bigger tensile resistance

4 Lower cement consumption

4 Easier execution control

Main advantages

4 Mobilization of lateral frictionin any kind of soil, speciallyon weak soils

4 Bigger stiffness

4 End bearing capacity

4 Water tightness

Main restraints4 Higher cement consumption

4 Difficult execution control

Jet grouting Micropiling

• Micropiling vs Jet Grouting columns

Weak ground

Axial load [kN]

Dep

th [

m]

500 750250 10000

2,5

5,0

7,5

10,0

12,5

15,0

∅0,5m ∅0,8m

0

Micropiles

Foundation ground

Jet Grouting type 1

• Micropiling vs Jet Grouting columns

Cross section 1-1

1 1

Plan

Existent wall

Existent foundation

New foundation

Pit solution

Jet Grouting equipment

Pit

h Underpinning techniques solutions

Main restraints4 Solutions depending

on workmanship

4 Bigger soildisturbance

4 More risk and longerworks schedule

Main advantages4 Lower cost at shallow

depth (less than 2m)

4 Easier constructioncontrol of the under-pinning elements

Main advantages4 Small dimension and versatility of

equipment

4 Minimization of soil disturbancedue to small diameter of boreholes

4 Improvemente of soilcharacteristics, including watertightness (jet grouting)

4 Solutions depending ontechnology (specialist under-pinners): shorter works schedule

Main estraints4 Solutions depending on technical

expertise (equipment and staff)

Micropiling, Jet Grouting Other conventionalsolutions (ex: pits)

1012 Historical Constructions

In this context, it is also important to point out that underpinning works requires expertise at the design and execution levels, along with safe working practices, specially when the under-pinned building has an old structure and a special architectural/historical interest and therefore is protected from demolition or alteration. In these situations, considerable care is required on pre-vious tasks, as for example: monitoring and survey, geological and geotechnical site investigation, stiffen, grout, shore struct, in order to prepare these old buildings and their original foundations for the underpinning works. As example, some of the presented cases proved how important is the role of the Monitoring and Survey Plan in this kind of works, mainly as a risk management tool, allowing to survey and predict the performance of the underpinned structures and, if necessary, to adjust in time the initial solution.

ACKNOWLEDGMENTS

The authors acknowledge the Owners of the presented underpinned structures for his permission to the presentation of this paper. The authors must also point out that the presented works were performed by a Tecnasol FGE multitask team, involving experts from different areas, ranging from structural and geotechnical design to geological investigation, commercial, monitor-ing/survey and site management teams.

REFERENCES

Bullivant, R. A. and Bradbury, H. W. 1996. Underpinning – A practical guide. Oxford, Blackwell Sci-ence.

Bustamante, M. and Doix, B. 1985. Une méthode pour le calcul des tirants et des micropieux injectés (in french). Bull. Liasion Labo. P. et Ch., nº140, p.75-92.

Bustamante, M. et al. 1997. Underpinning of the Bordeaux Pont-de-Pierre: A First Empire masonry. Geotechnical Engineering for the Preservation of Monuments and Historic Sites, p. 551-559. Rot-terdam, Balkema,.

Falcão, J. et al. 2000. Case histories and work performance of vertical jet grouting solutions. Proceed-ings of the 4th International Conference on Ground Improvment, Geosystems, Helsinki, Finland, June 7-9, 2000, p. 165-171. Building Information Ltd.

Greenwood, D. 1987. Underpinning by grouting. Ground Engineering, April 1987. Kutzner, C. 1996. Grouting of Rock and Soil. Rotterdam, Balkema. Pinto, A. et al. 2000. Casos Práticos de Soluções de Reforço de Fundações (in portuguese). Proceedings

do 7º Congresso Nacional de Geotecnia – Vol 2/3, Porto, Portugal, April, 2000, p.1055-1063.