-Craney Island Eastward Expansion Hydraulically Constructed Dikes - PowerPoint PPT Presentation

-Craney Island Eastward Expansion Hydraulically Constructed Dikes “40 Years of Dredging and Environmental Innovation” P R E S E N T E D B Y: I R A B ROT M A N , P E M O F FAT T & N I C H O L O C T O B E R 2 5 , 2 0 1 2

Craney Island Eastward Expansion

CIEE Layout I CIEE Main Dike CIDMMA East Dike Existing CIDMMA CIEE Cross Dike (typ)

Subsurface Stratigraphy

CIDMMA Dikes (1954)

CIDMMA Dikes (1954)

CIDMMA Dikes (1954)

Cross Dike Objectives  Experiences with CIDMMA (built to +5’)  Minimize Mud Waves  Minimize Deformation  Minimize Instability – Now and Future  Minimize Ultimate Sand Volume  Predictable Schedule

Cross Dike Alternatives  High strength geotextile/geogrid  Pre-dredge  Deep Soil Mixing  Prefabricated Vertical Drains (PVD)  Build dikes in lifts/stages  Allow increase in shear strength  Achieve by specifying lift thicknesses and hold times

Selected Low Cost, Low Risk Cross Dike  Final target elevation = +18 ft (MLLW)  900 ft Wide  Built in 3 Stages Hydraulic Sand Fill 60 Zone of 40 PVDs Elevation in feet (MLLW) 20 0 -20 -40 Marine PVDs Marine PVDs Land PVDs -60 Upper Norfolk Clay (Qnu) -80 -10 0 -12 0 Pleistocene/Pliocene Sands (Qnl/Tys) -14 0 -16 0 0.50 -0.45 -0.40 -0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0.0 0 0.0 5 0.1 0 0.1 5 0.2 0 0.2 5 0.3 0 0.3 5 0.4 0 0.4 5 Distance in feet (x 1000) PVDs

Construction Sequence  Place Initial Lift  Install Marine PVDs  Initiate Strength Gain  Place Second Lift  Allow Additional Strength Gain  Place Third Lift

South and Division Cross Dikes

Cross Dikes – Stage 1 Hydraulic Sand Fill, Stage 1

Cross Dikes Stage 1 – Marine PVDs PVDs Outer 3rd PVDs PVDs

Cross Dikes Stage 2A – Sand Fill Hydraulic Sand Fill, Stage 2A

Rendering Post Stage 3

Rendering Southeast Cell Closed

Borrow Source Atlantic Ocean Channel CIEE

GLDD – Stage 1

Sand Placement

GLDD – Stage 1 – Marine PVDs

PVD Installation Record

PVD Tip Elevations

Multibeam Survey

Multibeam Survey

Geotechnical Instrumentation

Instrumentation Website

Settlement

Summary  Schedule Challenges  TOY: Turtles  Contractor Innovation  Spillbarge  Specialized Barge for PVDs  Positioning /Tracking System  Observational Method Success  Measure behavior of foundation during filling  Validate Lift placement schedule and hold times  PVD installation verification  Control project risk

Thank You Special thanks to:  Virginia Port Authority  Corps of Engineers, Norfolk District