Lecture 31, 32, 33Temporary Earth Retaining StructuresJuly 29, 2009Meeting 11

CofferdamsTemporary Structures to keep out water and soil to permit construction in the dryTypesSheet Pile Wall with bracing (used for compact structures)Cellular cofferdams (used for large construction areas)

Typical Z Section Piling

Cofferdam Construction StepsPre-dredge to remove soft material and level area

Install temporary support pilesSet bracing frame and hang from temp piles

Drive Sheet Pile Wall using frame a guideExcavate bottom of cofferdamPlace concrete sealDewater and commence construction

Tremie PipeConcrete Seal

Compact CofferdamSteel Sheet PilesBracingConcrete Seal

Cellular CofferdamsMainCellConnecting Arc

Cellular CofferdamsUsed to dike off a large construction areasPractical to depths of 75 ft.Cells are filled with granular material

Cellular Cofferdam ConstructionFalsework ring templates must be usedGuide rings are temporarily supported by temporary pilesSheeting installation starts with the Y section.Pile layouts should be marked on the guide ringAfter Sheet piling is complete Cells are filled

Typical Flat Sheet Pile SectionsFabricated Y

Cofferdam Example

Cofferdam Detail

Other Earth Retaining Structures

Trench Boxes Prefabricated structure that is moved as the work progresses

Trench Box

Vertical Wood SheatingVertical woodsheatingTimber waleTimber cross bracing

Steel Soldier Piles and Horizontal SheatingHorizontal sheating set behind the flangeDriven sheet H piles

Braceless Systems Using Tie BacksTendonStressing UnitGrout

Tie back Example

Installing Tie backs

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