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UNDERPINNING AND UNDERPINNING AND SHORINGSHORING

Engr. Yusuf Mohamed YusufEngr. Yusuf Mohamed Yusuf

2005-Ms-C-Stru-932005-Ms-C-Stru-93

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I- UNDERPINNINGI- UNDERPINNINGWhat is foundation underpinning?What is foundation underpinning?What is the purpose of underpinning?What is the purpose of underpinning?When foundation underpinning is When foundation underpinning is

required?required?What are the methods used for What are the methods used for

underpinning?underpinning?

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What is foundation underpinning?What is foundation underpinning?

Foundation underpinning is a means of Foundation underpinning is a means of transferring loads to deeper soils or transferring loads to deeper soils or bedrockbedrock . .

Underpinning is the securing, Underpinning is the securing, stabilizing, or supporting of an stabilizing, or supporting of an existing foundationexisting foundation..

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What is the purpose of What is the purpose of underpinningunderpinning??

To obtain additional foundation To obtain additional foundation capacitycapacity

To modify the existing foundation To modify the existing foundation systemsystem

To create new foundations to which the To create new foundations to which the existing load may be wholly or partially existing load may be wholly or partially transferred into deeper soil transferred into deeper soil

Underpinning is generally used for Underpinning is generally used for remedial purposesremedial purposes

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When foundation underpinning When foundation underpinning is requiredis required??

Underpinning is required when:Underpinning is required when:The original foundation is simply not stable The original foundation is simply not stable

enough. enough. The usage of the structure has changed. The usage of the structure has changed. The properties of the soil supporting the The properties of the soil supporting the

foundation may have changed or was foundation may have changed or was mischaracterized during planning. mischaracterized during planning.

The construction of nearby structures The construction of nearby structures necessitates the excavation of soil necessitates the excavation of soil supporting existing foundations. supporting existing foundations.

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What are important parameters to be What are important parameters to be considered before Underpinningconsidered before Underpinning? ?

Height of the buildingHeight of the buildingColumn spacingColumn spacingWall thicknessWall thicknessType and material of constructionType and material of constructionDifferent loads acting on the buildingDifferent loads acting on the buildingCondition of the buildingCondition of the building

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What are the methods used for What are the methods used for underpinning underpinning??

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1-Pit Underpinning1-Pit Underpinning

The most common and oldest method of The most common and oldest method of underpinning is by installing piers under a underpinning is by installing piers under a structure’s foundation, filling them with structure’s foundation, filling them with concrete and wedging up to transfer the concrete and wedging up to transfer the load to the new piersload to the new piers

Pit underpinning requires careful and skilled Pit underpinning requires careful and skilled work as loss of ground will cause building work as loss of ground will cause building settlementsettlement

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Pit UnderpinningPit Underpinning… …

ProcedureProcedureColumn/ wall above the affected Column/ wall above the affected

footing should be braced as much as footing should be braced as much as possiblepossible

A pit of 3’ wide, 4’ long and 5’ depth A pit of 3’ wide, 4’ long and 5’ depth is excavated in front of the footing to is excavated in front of the footing to be underpinnedbe underpinned

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Pit UnderpinningPit Underpinning… …

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Pit UnderpinningPit Underpinning… …

Pit is extended laterally to reach under the Pit is extended laterally to reach under the footing to be underpinned and then is footing to be underpinned and then is deepened several feet below the subgradedeepened several feet below the subgrade

A vertical formwork is built in the pit and A vertical formwork is built in the pit and then is concreted up to the footingthen is concreted up to the footing

Dry packing operation is then carried outDry packing operation is then carried out

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Pit UnderpinningPit Underpinning… …

CommentsComments

This method is limited to dry ground This method is limited to dry ground because it is difficult to dig below because it is difficult to dig below water level otherwise more building water level otherwise more building settlement may occur.settlement may occur.

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Helical Pier SystemHelical Pier System

HelicalHelical pierspiers are used to support are used to support foundation of existing structures.    foundation of existing structures.    Using a hydraulic motor attached to Using a hydraulic motor attached to a backhoe. a backhoe.

The pier is drilled into the ground to a The pier is drilled into the ground to a specified depth or until refusal.  specified depth or until refusal. 

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Helical Pier SystemHelical Pier System

Damaged FoundationDamaged Foundation Repaired FoundationRepaired Foundation

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ProcedureProcedureExcavate down to the footing at each Excavate down to the footing at each

designated     pier location designated     pier location Notch out foundation footing to Notch out foundation footing to

accommodate     support bracket accommodate     support bracket Screw piers into excavated site to a Screw piers into excavated site to a

desired depth using a hydraulic desired depth using a hydraulic motor attached to a backhoe motor attached to a backhoe

Connect bracket to base of Connect bracket to base of foundation and the     top the pier foundation and the     top the pier

Backfill all excavated pier locations Backfill all excavated pier locations

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CommentsCommentsFast installationFast installationEconomicalEconomicalCan be installed in confined spaceCan be installed in confined spaceMinimum disturbance to site.Minimum disturbance to site.Immediate loading.Immediate loading.All weather installation. All weather installation. Applicable for saturated soil Applicable for saturated soil

conditions conditions

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22 - -Pile UnderpinningPile Underpinning

The pile underpinning technique is used to The pile underpinning technique is used to overcome the extremely difficult working overcome the extremely difficult working circumstances encountered when pit circumstances encountered when pit underpinning action become unsuitable underpinning action become unsuitable due to high ground water leveldue to high ground water level

Piles are often used where water condition Piles are often used where water condition make it difficult to dig below the footingmake it difficult to dig below the footing

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Special Underpinning MethodsSpecial Underpinning Methodsa)a) Chemical groutingChemical grouting

Perforated pipes are drilled into the Perforated pipes are drilled into the ground with suitable spacing and a ground with suitable spacing and a solution of Sodium Silicate is solution of Sodium Silicate is pressure-injected into the ground pressure-injected into the ground and then Calcium or magnesium and then Calcium or magnesium chloride is injected as the pipe is chloride is injected as the pipe is withdrawn.withdrawn.

The two chemicals interact to form a The two chemicals interact to form a gel that binds the soil particles into gel that binds the soil particles into a mass similar to sandstonea mass similar to sandstone

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Special Underpinning Special Underpinning MethodsMethods

b) Microfine Groutingb) Microfine Grouting

A perforated pipe is drilled into ground A perforated pipe is drilled into ground and fluid grout mixture is injected by and fluid grout mixture is injected by pressurepressure

The mixture consist ofThe mixture consist of

1- water + Cement1- water + Cement

2- water + cement + fly ash or lime2- water + cement + fly ash or lime

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22 - -SHORINGSHORING

Definition :Definition :

“ “Structural system made of metal or Structural system made of metal or timber that supports the sides of an timber that supports the sides of an excavation trench and is designed to excavation trench and is designed to prevent side collapse."prevent side collapse."   

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Shoring action depend onShoring action depend on::soil type soil type moisture content moisture content depth of foundation/ trenchdepth of foundation/ trenchvibration effectsvibration effectsadjacent buildings and structures adjacent buildings and structures adjacent weight (surcharge) adjacent weight (surcharge) weather weather

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Surcharge pressureSurcharge pressure

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Surcharge pressureSurcharge pressure

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Where shoring is requiredWhere shoring is required??

Demolishing and excavating under the Demolishing and excavating under the existing footing,existing footing,

Pouring a new footing at the required Pouring a new footing at the required depth.depth.

Supporting loose soil or waterSupporting loose soil or water   

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Foundation repairingFoundation repairing

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Loose soilLoose soil

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Embankment protectionEmbankment protection

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WaterWater

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Wall Shoring ( Soldier pile)Wall Shoring ( Soldier pile)

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THANKSTHANKS