Marine Prefabricated Vertical Drains for
the Craney Island Eastward Expansion
P R E S E N T E D BY:
IRA BROTMAN, PE
M O F FAT T & N I C H O L
OCTOBER 18, 2012
Craney Island Eastward Expansion
1
CIEE Layout
CIEE Main
Dike
I
CIDMMA
East Dike
Existing
CIDMMA
CIEE
Cross Dike
(typ)
Subsurface Stratigraphy
2
CIDMMA Dikes (1954)
CIDMMA Dikes (1954)
3
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
Limit Inappropriate Construction Claims
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
4
Selected Low Cost, Low Risk Cross Dike
Final target elevation = +18 ft (MLLW)
900 ft Wide
Built in 3 Stages
Hydraulic
Elevation in feet (MLLW)
60
Sand Fill
Zone of
PVDs
40
20
0
-20
-40
Marine PVDs
-60
Marine PVDs
Land PVDs
Upper Norfolk Clay (Qnu)
-80
-100
-120
Pleistocene/Pliocene Sands (Qnl/Tys)
-140
-160
.50
-0.45
-0.40
-0.35
-0.30
-0.25
-0.20
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
0.45
Distance in feet (x 1000)
PVDs
PVD Design
Design for long‐term (20‐30 feet) settlement
Use Dike Lifts for Surcharge Load
PVD Spacing
Constructability
Overwater – minimize due to cost
Verticality Control
Production
5
PVD Design Parameters
Long Term Consolidation
Settlement Effects Critical
• Buckled Discharge
Critical
• ISO/EN Methods for
Testing
Ref: Bucket Tests by Cortlever, 1983
Ref: EN 15237, 2007
Typical PVD
6
Discharge Capacity Test
ISO 12958 & EN 15237
PVD Test Results – Discharge Capacity
PROPERTY
SPECIFIED VALUES
TEST RESULTS
# Tests
Average
Standard
Deviation
Discharge capacity
ISO 12958 & EN 15237
0.3 gpm @ 65 psi
22
0.32
gpm
0.18
Discharge Capacity
Buckled
ISO 12958 & EN 15237
2.0 gpm @ 35 psi
16
2.32
gpm
1.07
American Wick Drain, Soil Drain 1000
7
Construction Sequence
Place Initial Lift
Install Marine PVDs
Initiate Strength Gain
Place Second Lift
Allow Additional Strength Gain
Place Third Lift
Summary
Contractor Innovation
Spillbarge
Specialized Barge
Positioning /Tracking System
Observational Method Success
QA of PVD testing
PVD installation verification
Measure behavior of foundation during filling
Validate Lift placement schedule and hold times
Control project risk
Thank You
Special thanks to:
Virginia Port Authority
Corps of Engineers, Norfolk District