COFFERDAMS

CEM 250Construction Methods & Materials

Main Purpose

Construct in areas under water

Rivers LakesOceans

Points of Concern

Safety Failure Worker well being

Forces Soils Water Currents Waves Ice Seismic Activity

Soil

Internal and External SupportGeotechnical study is key

Proper designAsset or LiabilityUltimate success of project

Water Currents

Normal ProjectionDrag Force

Flat vs. Indented Sides

Waves

Primary Cause – WIND and BOATS3 feet above surface water elevationHigher walls for open water applications

Large baysLakesOceans

ICE

Frozen-over Static Force 4000 lb/ft² design

Flowing Dynamic Force 12,000 – 14,0000

lb/ft² design

Seismic

Not commonly concerned except for:Large Jobs Important JobsDeep JobsHigh Seismic Areas

Failure

Does not release or distribute the load like other failures. “ Progressive Collapse”Provisions to prevent failurePartial Failure lead to total Failure

Steps In Construction

PredredgingTemp. support piles and bracing installedDrive pilesFurther excavationLeveling courseConcrete sealDewatering Process

Predredging

Remove loose soil for baseEliminates unbalanced forcesLowers excavation costs

Support Piles

Resisting structureVertical piles supported by lateral

bracingPrefabricated and then placedMultiple units can be used on top of each

other for higher applications

Driving Piles

Alignment important for later stepsPopular shapes – Z, H and O pipeTie and block sheet metal to solidify

structureBolts over welds

Prevents fracture Vibratory and non-uniform loads

Further Excavation

Few feet below final gradeDon’t disturb bracingClay removalAllows good seal in next step

Leveling Course

Prepares for underwater concrete placing

Concrete Seal

Mat ties all Piles togetherPrevents upliftLower support strutSeals from upward flow of waterPlaced by pipe or grout-induced

aggregate methodReinforcing if needed

Dewatering

Empty the water out of the cofferdam area Massive pumps start dewatering Natural materials to help seal

Sand and Sawdust Canvas or Plastic to fully seal in harsh

conditions Pour footing

Cracking

Demo Cofferdam

FloodingEqualize water levelDemo Structure

Bolt rather than weldFaster demoLess damage

Reuse material

Portadam

12’ deep max Portable Free standing struct. Fabric Membrane Cheaper and faster

assembly Any configuration Uneven ground

Aqua Dam

Short term Ballon type Rubber/fabric mem. Filled with water Gravity and friction Uses

Emergencies, diversions, const, repairs and open water

Uses

Oil rigsConstruct and repair

BridgesFooting placing

DamsDiversions, repairs

Building shipsBuild and repair

Deep Water

Enclosed cofferdamPressurizedAccessed through tubes and hatchesAir suppliedWorker safety

Casey Canal CofferdamSavannah, GA

Blocking Canal

Ship Repair