Marine Prefabrcated Vertical Drains -05 Brotman

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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

South and Division Cross Dikes

8

Cross Dikes – Stage 1

Hydraulic Sand
Fill, Stage 1

Cross Dikes Stage 1 – Marine PVDs

PVDs Outer 3rd

PVDs

PVDs

9

Cross Dikes Stage 2A – Sand Fill

Hydraulic Sand
Fill, Stage 2A

Rendering Post Stage 3

10

Rendering Southeast Cell Closed

GLDD – Stage 1

11

GLDD – Stage 1 – Marine PVDs

12

PVD Monitoring - Observational Method
Assess Progress and Validate Strength Grains
 Lab Testing
 PVD Installation Records





12 MLF of PVDs Installed
100,000 Individual PVDs
To depths over 130 ft
Avg 500 PVDs / day

 Surveys
 In‐situ Testing
 Geotechnical Instrumentation

13

PVD Installation Record

PVD Tip Elevations

14

Multibeam Survey

Multibeam Survey

15

Geotechnical Instrumentation

Instrumentation Website

16

Settlement

Inclinometer

17

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

18

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