Handbook for Marine Geotechnical Engineering

7/23/2019 Handbook for Marine Geotechnical Engineering

1/257

*

Handbook for

00

Marine

Geotechnical

Engineering

L/'

D5

I

Technical

Editor

LI Karl

Rocker,

Jr.

*

March 1985

DEEP OCEAN TECHNOLOGY

NAVAL CIVIL ENGINEERING LABORATORY

PORT HUENEME, CA 93043

85 8:6

043

Approed for

public release; distribution

unlimited.


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BY

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ODES

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AND/OR

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SECURITY

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OF

THIS

PAGE

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DWO

.I.Ened)REDIS

UC

ON

REPORT

DOCUMENTAT;ON

PAGE

BEFORECOPLTIG

OR M

N-ro"6161

2. GOVT

ACC2SSION NO. 3. MECIPICNT'S

CATALOG

MU&IUER

DN

987083

4.

TITLE

tods Wbitio)

C. TYPE

OF REPORT 6

P919100 COVERED

Handbook

for Marine GeqL

echnical

.

Final

Engineering-Deep Ocean

Technology

-Oct 1979

-

Dec

1983

6

PEaRFORMIN

ORG.

REPOrT NummnR

7. AUT MO(.j

6.

CONTRACT 0OR

GRANT

NUMOER(.J

Kar~l Rocker,

Jr., Technical

Editor

9.

PERFORMING ORGANIZATION

NAME

AND.00CtESS

to. PROGRAM ELEMEINT.

PRO ECT. TASK

AREA &

WORN

UNIT NUNSERSI

Naval

Civil

Engineering

Laboratory PE

637 13 N

Port Huenieme,

CA 93043

2.11001

11I.

CONTROLLING

OFFICE MNAM

AND ADDRESS

IS.

REPORT OATE

Naval Sea

Systems Command

March 1985

Washington,

DC

20362

'3

IVNE~%4AO

14.

MONMITORING

AGENCY

NAMCE& ADORESUIP1

Ififfter.

NInl C..te..jiin

Off-C.)

IS. SECURITYV

CLASS.

(of

060

.pMtj

Unclassified

IS. CLASSIVICATION'DOWNGRAOINd

SCHEDULE

19. OISTRIUUTION STA'?CMENT

lotI thll

R*p.fI

Approved

for

public

release;

distribution

is

unlimited.

17.

DISTRIBUTION STATEMENT

(04

Me

obeftec

owo,

inBlock

M.

At

-dlofo...

Anfi

ASPA9)

IS9.

SUPOLEMENKTARYNOTIES

IS. KEY WORDS

(COg.U... M IOf.. 5155

IlRt . 555I

SHr

104

#~#(Y AV

N0

geotechnics,

marine

soils, sediments,

engineering

properties

ocean

technology,

ocean

engineering,

3ite

surveying,

seiamic

profiling,

penetrometers-,

side-scan~

sonar,

foundations,

anchors,

sampling,

coring.

gilea.

Mang

q~~e

tptgmanl~

OSTMSYACT Coem...r

an

ro.aw.

*Ad*

H

"etteOSWt

Red5559Ip

bflockEw

This

handbook

discusses the application

of

engineering

tetdh-

niques

and

scientific

knowledge

to the' investigation

of

sea-

floor

materials,

'their

characteristics,

and

theirresponses

to foundation

and

mooring

loads.

Its

prim~ary

thrust

is

with.

problems

engineers

will

encounter

beyond

the

continental

shelf

or

below

600

feet

but

the information

is

also

applicable

to

shallow

water

tasia.

*

00

','OM1473

EYU@IN@Sil@SIt3Unclassified

SSCURITY

Cl.AUfCBjAIOU 00

TNIS VAE39 w

9


4/257

ACKNOWLEDGMENTS

Much of

the

background material for the

Handbook for Marine

Geotechnical Engineering

was developed by

the Naval

Civil

Engineering

Laboratory (NCEL).

These materials were updated

and supplemented

with

experience

from

the

private

sector by a number of

contractors.

Initial

,-diting

and

consolidation of the chapters

was carried out by

Brian

Watt

Associates, Inc.

Technical

review

of

the Handbook

was also made by

Dr. Robert H.

Mayer, Jr.

(U.S.

Naval

Academy) and

Mr.

Homa

J. Lee. The

primary contributor

for

each of the

chapters

is as

follows:

Chapter

Primary Contributor

1 Brian

Watt Associates,

Inc., Houston,

TX

2 The Earth

Technology Corporation,

Long Beach, CA

3 Prof. I. Noorany, San

Diego

State Univ.,

San

Diego,

CA

4 The

Earth

Technology

Corporation,

L6ng

Beach,

CA

5

Woodward-Clyde Consulta nts,

Santa Ana, CA

6 Brian

Watt

Associates, Inc., Houston,

TX

"7 Brian Watt

Associates, Inc., Houston,

TX

8 Brian Watt

Associates,

Inc., Houston, TX

9

Mr. H.J. Lee, U.S.

Geological Survey, Menlo

Park, CA

10 Mr.

N.J. Atturio, Naval

Civil

Engineering

Laboratory,

Port Hueneme, CA

11 Dr.

D.A. Sangrey, Carnegie-Mellon

Univ. , Pitts.

PA

:::i:

-. -i


5/257

CONTENTS

Page,

Chapter

1- INTRODUCTION ...................... .....................................

1-1

1.1 OBJECTIVE .............................................................

.. 1-1

1.2 HANDBOOK

ORGANIZATION .

......................................................

1-1

1.3

SELECTION OF

FOUNDATION/ANCHOR

TYPE

........... ........................... .. 1-3

1.4

REFERENCES

.............................................................

1-6

Chapter

2 -

SITE SURVEY

AND IN-SITU TESTING

................

............................ 2-1

"2.1 INTRODUCTION 2-1

2.11.uros.....................................................-

2.1.1 Purpose .

. . . . . . . . . . .

. . .

2-1

" 2.1.2 Factors Influencing the Site Survey

..........

....................... .. 2-1

2.2

PRELIMINARY

STUDY ......... ..... ... ....... ................... ......... 2-3

2.2.1

Information

Sources

..................

...............................

2-3

"2.2.2 Typical Ocean Soils . .

..................

.............................

2-4

2.3 REGIONAL

SURVEY

................. ......................................

2`12

2.3.1

General ..................

..................................... ..

2-12

2.3.2

Seismic

Profiling ................

................................. 2-12

2.3.3

Limited

Sampling ............................................ ....... 2-14

2.3.4 Side-Scan Sonar ..... ................................. 2-14

2.3.5

Visjal

Observation

.............. ................................ ..

2-14

2.3.6

Survey

Line

Spacing.

.............. ........................

........ 2-14

2.4

SITE-SPECIFIC

SURVEY .....................................................

2-1s

2.4.1

General

........ .............................. ......... ........ 2-15

2.4.2 Shallow

Sampling ......

........................................... 2-16

2.4.3 Deep

Sampling

......................... ........................... 2-19

2.4.4 Sample Handling ........... ..................... .

.............. ..

2-20

S,2.5 IN-SITU

TESTING ...........................................................

2-21

2.5.1 General ............................................. . ...........

2-21

2.5.2

Vane

Shear Tests ................. ...................... ........ 2-22

2.5.3 Cone Penetration Tests

(CPT)

...... ............................ . .

.2-23

2.5.4

Pressuremeter Tests

........

....................................... 2-25

2.5.5 Dynamic Penetrometer .............................

..........

...... 2-25

2.5.6 Borehole

Logging Techniques

. .......................................... 2-25

2.6

SEISMICITY

SURVEY

.......

......

......

....

. .

............

.........

225

-.- ..7 REFERENCES

. .

.

...

.............................................

.........

2-26

2.8

SYMBOLS

............................................................

2-27

* .

Chapter 3

- LABORATORY DETERMINATION

OF SOIL

PROPERTIES

...........

.................

-1

3.1

INTRODUCTION

......................................................

.....

3-1

3. .1

Sc p

. . . . . .

.

. . ..

. ...

. . .

.

. .

... .

.

.. . . .

. 3-

"-'" 3.1.1 Scop ........

m

r"""............

.... 3"1I

3.1.2 Special Considerations

...............................................

3-1

3.2 SOIL CLASSIFICATION

......

.................... ........................ 3-1

3.2.1 Classification by Origin

..............................................

3-1i

"3.2.2 Classification by

Grain

Size

1.....

3.2.3 Classification by Grain Size and B'eav*ier

'..

. ....

3-2

"3.3 INDEX

PROPERTY TESTS

............

......................... . . . 3-4

3.3. 1 Gener&l

......

.....................................

3-4

3.3.3 2 Sample Preparation . . . . . .. . . . ... . . . . . ... . . . . . . . . . . . . . 3-4

' ' 3.3.3 Water Content

..................

.....................

.............

3-4

* ; 3.3.4 Unit Weight ......................................................... 3-?


6/257

Page

3.3.5 Specific Gravity ............................. ..........

37

3.3.6 Liquid

Limit,

Plastic Limit, and Plasticity Index ...... ................

3-7

3.3.7 Grain Size

Analysis

................... ............................. 3-9

3.3.8 Carbonate and

Organic

Carbon

Content

.......

....................... ..

3-9

3.4

ENGINEERING PROPERTY TESTS ..................................................

3-9

3.4.1

General

...................

.....................................

.. 3-9

3.4.2

Vane

Shear

Test

..............

.................................

3-10

3.4.3 Unconfined Compression

Test .............................

.. 3-12

3,4.4

Unconsolidated,

Undrained Triaxial Compression

Test

........

............... 3-13

3.4.5

Consolidated-Undrained

and

Consolidated-Drained

Triaxial

Compression

Tests . . . 3-13

3.4.6 Consolidated-Drained

Direct

Shear

Test ......... ......................

.. 3-13

3.4.7

Considerations

for Triaxial

Testing of

Marine

Soils

........

............... 3-13

3.4.8

One-Dimensional

Consolidation

Test ...............................

3-13

3.5 PROPERTY

CORRELATIONS

......................................................

3-14

3.5.1 General .... ......

............. ................

.................

3-14

3.5.2

Nearshore

Sediments

..................

...............................

3-14

3.5.3 Deep Sea

Sediments

..............

................................

.. 3-16

3.6

REFERENCES

......

................

.........

.......................

3-17

3.7 SYMBOLS .......................

.........................................

3-18

Chapter

4 - SHALLOW FOUNDATIONS

AND DEADWEIGHT ANCHORS.

.

..................... 4-1

4.1

INTROCUCTION

....................

......................................

4-1

4.1.1

General ..................................................

......

.

4-1

4.1.2

Definitions/Descriptions

................

.............................

4-1

4.2 DESIGN CONSIDERATIONS

................

..................................

4-3

4.2.1

General ..............................................

..........

4-3

4.2.2 Site

.......

..........................

.

........

...............

4-4

4.2.3

Structure

.................. ......................................

4-4

4.2.4

Loading .................

............................

. ..........

4-4

4.2.5

Geotechnical ....................

. .

.........................

4-4

4.2.6 Factor of Safety

.................

......................

4-5

4.3 DESIGN

METHODOLOGY AND

PROCEDURE ........... .......................

. ....... 4-5

4.3.1

General

............................

....... .4-5

4.3.2

Bearing Capacity

. ..............................................

. ...

4-7

4.3.3' Lateral

Load Capacity ...........

..................................

4-11

4.3.4

Overturning

Resistance

............ . .......

....................

4-13

4.3.5

Shear

Key Design ..............

.................................

..

4-14

4.3.6

Foundation

Settlement ................................................

4-15

4.3.7

Installation and

Removal

........... ...........................

.. .

4-17

4.4 EXAMPLE

PROBLEMS .......... ......

.................................

4-17

4.4.1

Problem 1 - Simple Foundation

on ohesive Soil ..... .....

..............

4-17

4.4.2 Problem

2 -

Simple Foundation

on Ohesionless Soil

..................... 4-24

4.5

REFERENCES

..... .....................

.. ............

.................. 4-28

4.6 SYMBOLS ............. . ........... ...................

................. 4-28

Chapter 5 - PILE FOUNDATIONS AND ANC14CRS

.................

............................

5-1

5.1

INTRODUCTION

....................................

5-1

5.2

PILE DESCRIPTIONS .

. . . . . . . . . . . . . . . . . . 5 "1

5.E ECITIN....................

...........

....

...... .. . o... ..

5.2.1 Pile Types

................. . ....

...................

....

5-1

5.2.2

Mooring Line

Connections . . . . . ........

. ..........

...... 5-1

5.2.3 Modifications for

Increasing Lateral Load

Capacity..-...........

.....

5-1

5.3

DESIGN PROCEDURES

FOR

SIMPLE

PILES

IN

SOl SEAFLOORS . ........................

5-1

5.3.1 General . .........................

..........

.............

51

5.3.2

Soil

Properties .... ....... ....... ................. .... .... . . ...-5


7/257

Page

5.3.3

Pile Design

Loads

.....

......... ........ ....................... ..5-6

5.3.4 Lateral

Load

Analysis

.................. .............................. 5-7

5.3.5

Axial

Load

Analysis ..................

.......................... . . 5-9

5.3.6

Steel

Stress Analysis

............. ........ ....................

5-11

5.3.7 Special

Cases ................

..................................

.. 5-12

5.4 DESIGN OF PILE ANCHORS IN

ROCK

SEAFLOORS

........... ........................ ..

5-13

5.4.1 Lateral

Capacity ....... .

...........

............................. .. 5-14

5.4.2

Uplift Capacity .................... ................................. 5-15

5.5 PILE

INSTALLATION.5-15

5.5.1 Driven

Piles ............................ .....

................. .. 5-15

5.5.2

Drilled and

Grouted Piles

.......... .........................

5-17

5.5.3 Jack-in

Piles

.......................................................

5-18

"5.5,4

Jetted

Piles ................ ...................................

.. 5-18

5.6 EXAMPLE

PROBLEMS

.....................

....................................

5-18

"5.6.1

Problem

1--Pile

Design

in

a

Cohesive

Soil

........

....................

..

5-18

"5.6.2

Problem

2--Pile Design

in a Cohesionless Soil ..........

.................. 5-25

5.7 REFERENCES

................................................................

5-29

5.8

SYMBOLS

............. . ............... ..............................

5-30

Chapter

6 - DIRECT-EMBEDMENT

ANCHORS .... ...........

........... ................... 6.1

6.1 INTRODUCTION

....................

......................................

6-1

6.1.1 Purpose ...........

.....................

. .....

.......... ......

6-1

6.1.2 Function . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . 6-1

6.1.3

Features

. . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. .

6-1

6.2

DIRECT-EMBEDNENT

ANCHOR TYPES

AND SIZES .............. ......................

6-1

6.2.1

Propellant-Oriven Anchor ...........................

6-1

6.2.2 Vibratory-Driven

Anchors

............... .......................... 6-6

6.2.3

Impact-Driven

Anchors 6-6

6.2.4 Jetted-In Anchors

.................. ................................

6-7

6.2.5 Auger Anchors ......................

...............................

6-7

6.3

SITE DATA

NEEDED ......................................................

.... 6-8

6.3.1

General

.......... ................................

...............

6-8

6.3.2 Preliminary

Penetration Estimate

.......................................

6-8

a.3.3 Topography,

Strata Thicknesses, Type. . ......................

6-8

. - .6.3.4 Engineering Propetties

. . . . . . . . .

. . . . . . . . . .. . . . . . . . .

.. 6-8

6.3.5 Complicating or Hazardous

Conditions ..... ..............................

6-10

6.3.6 Specialized Survey

Tools........ .......................

6-11

6.4

FLUKE PENETRATION AND KEYING

......

....................................-

11

"6.4.1

Penetration

Prediction

.

...

......................

...

... 6-11

6.4.2

Keying

Prediction

............. ..................... ..

............ 6-11

6.5

STATIC

HOLDING

CAPACITY

........................... ................

6-12

6.5.1

Loading

Conditions.

. .....................

6-12

6.5.2

Deep

and Shallow Anchor

Failure ..... ...............

. ...... .........

6-12

6.5.3

Short-Term

Capacity in

Cohesive Soils ..............

.... .............. 6-13

6.5.4 Long-Term

Capacity in

Cohesive Soils

.......

....................... .. 6-14

6.5.5

Short-

and

Long-Term Capacity

in Cohesiofess

Soils

.. .......

............

6-15

6.5.6 Disturbance Corrections

.......... .............

..........

. ....... 6-15

"6.5.7 Factors ef Safety

..

..............

...........................

. ..

6-16

"6.6 DYNAMIC HOLDING

CAPACITY...................................

.......... 6-16

..

._ 6.6.1

Loading

Conditions

. . . . .

. . .

. . . ... .

. . .

. . . I

. . . . . .

. . .

. . -1

.-..

6.6.2 Cyclic Loading .........

. ....... .

.......

.....................

6-16

vii


8/257

Page

6.6.3 Earthquake Loading

................

.............................

.. 6-19

6.6.4

Impulse Loading

....................

.................................

6-19

6.7 OTHER INFLUENCES ON

HOLDING

CAPACITY

..................................

....

6-23

6.7.1

Holding Capacity

on

Slopes ............

............................

.. 6-23

6.7.2

Creep

Under

Static

Loading

............

............................

.. 6-24

6.8 HOLDING CAPACITY

IN CORAL AND

ROCK

. ..........................

6-24

6.8.1 Coral

....................

......................................

6-24

6.8.2 Rock... ....... .

..........

..... .. .... ........ ........

..

..

6-24

6.9 EXAPLIE

PROBLEMS .............. .. ......................

6-24

6.9.1 Problem

1--An Embedment

Anchor

Used in Cohesivei

Soil

......................

6-24

6.9.2 Problem 2--An Embedment

Anchor

Used

in Cohesionless

Soil

..................

.. 6-28

6.10

REFERENCES

..................

.........................................

.

6-31

6.11 SYMBOLS .................................................................

6-32

Chapter 7 -

DRAG-EMBEDMENT ANCHORS

................

.................................

7--1

7.1

INTRODUCTION

................

...........................................

7-1

7.1.1 Purpose and Scope

..................

................................

7-1

7.1.2 Drag

Anchor

Description ..............................................

7-1

7.1.3

Types

of

Drag Anchors

..................

..............................

7-2

7.1.4

Application

of Drag

Anchors ...........

............................

7-3

7.2

FUNCTIONING OF A DRAG

ANCHOR ..................

..............................

7-3

7.2.1 General .

7-3

7.2.2 Tripping

... .....................................

7-4

7.2.3

Embedment

....................

..............

......................

7-5

7.2.4

Stability

...........

..........................................

.. 7-6

7.2.5 Soaking ............... ......................... . ................ 7-8

7.3

SITE

INVESTIGATION

......

... .. ..........................

...

..

.. . .

...

7-B

7.3.1 Site Data Needed

.......

..... .......................

.......... ..

,7-

7.3.2

Topography

and Layer

Thickness ...........................

............ 7-8

7.3.3 Sediment

Type and Strength ...

..................

7-9

7.3.4 Site

Investigation Summary ..... ....

..........

. ..... .............

. 710

7.4 SELECTING A

DRAG ANCHOR ...................................

7-11

7.4.1

General . . . ............

..............

.......... ...

7-11

7.4.2 Tripping and Penetration

Performance ..............................

.. 7-12

7.4.3 Stability

Performance

.... .............

........

..................

7-12

7.4.4

Holding Capacity

Performdnce ............

................ ...........

7-12

7.4.5 Selection

of

Anchor

Type .........

.

......

.....

..................

...

7-12

7.5

SIZING-A DRAG

ANCHOR ......................................

7-12

7.5.1

Efficiency Ratio

Method....................................

......

7-12

7.5.2

Power

Law

Method

............

...................

................

7-13

7.5.3

Analysis Based

on

Geotechnical

Considerations ......

.... ..............

.. 7-17

7.5.4 Factor

of Safety ............ ..... ........................ . . .7-18

7.6 TROUBLESHOOTING. ..

.. ........ ............ ........ ... ........ ............

.... 7-19

7.6.1

Soft

Sediments ..............................

7-19

7.6.2

Hard Sediments .............................................

7-20

7. IB X N

. . . . ..

. . . . . . . . . . . . . . .

. . . . . .. . .

. . . . . . 7

7.7

PIGGYBACKING......................................................7-20

7.7.1 Field

Practice . . .

...............

..........................

...

7-20

7.7.2 Results

and Field Problems.

. ........................

...... 7-22

7.7.3 Recommended

Practice .... ..........................

. .

...

, ....... ..

7-23

viii


9/257

Page

7.8

REFERENCES .........................................................

7-23

h

7.9

SYMBOLS

..................

.........................................

..

7-24

Chapter

8 - PENETRATION

OF OBJECTS

INTO

THE SEAFLOOR ............

....................... 8-1

8.1 INTROOUCfION ................... ......................................

.. 8-1

"8.1.1

Purpose ..................

.....................................

.. 8-1

8.1.2 Scope ......... . .... .................................. 8-1

8.2 STATIC PENETRATION ................... ...................................

8-1

8.2.1 Application ................. ...........................

....... 8-1

8.2.2 Approach

..................

..................................... 8-1

- 8.2.3

Method

,for

Predicting

Shallow Static

Penetration

.......... ...... ......... 8-2

8.2.4

Methods

for Predicting Deep

Static

Penetration ...... .................. ..

8-5

8.3

DYNAMIC

PENETRATION

......................................................

8-7

8.3.1

Application

................

...................................

.. 8-7

8.3.2 Approach . .......................................................... 8-7

8.3.3 Method for Predicting Dynamic Penetration ...... .....................

.. 8-7

8.4 EXAMPLE PROBLEMS ..................... .................................... 8-11

8.4.1

Problem 1--Slow

Penetration of a

Long

Cylinder

...... .................. .. 8-11

8.4,2 Problem 2--Rapid

Penetration of a

Long Cylinder

....... .................

8-14

"

8.5 REFERENCES ............................................................. 8-19

8.6

SY B L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . .

8 2

- 8.6 SYMBOLS........................................................ 8-20

Chaptar 9 - BREAKOUT

OF

OBJECTS FROM

THE SEAFLOOR ..................................... 9-1

9.1

INTRODUCTION..................

. .......................................

9-1

9.1.1 Applications

. . . . . . .

..............

............................ 9-1

9.1.2

General Concepts

.............

................................. .. 9-2

9.1.3

Definitions

................

.............

.....................

..

9-2

9.2

REQUIRED INFOR14ATION ................ ................... ...............

9-4

L 9.2.1

Object Embedment

Characteristics

............ .........................

9-4

9.2.2 Sediment

Chardcteristics

............. ................ ........ ..... 9-4

"9.2.3

Bearing

Capacity

(Cohesive Sediments)

.......

...................... ... 9-5

9.3 SHORT-TERM (IM4EDIATE)

BREAKOUT

.......

.................................... 9-5

"9.4

LONG-TERM BREAKOUT

TIME

PREDICTION

.... ........ .................. ........ .9-6

9.5 BREAKOUT AIDS

.................................... . .................. 9-7

9.5.1 Jetting

and Drainage Tubes

...... .....................

9-8

9.5.2

Eccentric

Loading

................................................... 9-9

-'" 9.. 3

Cyclic Loading

..... .

..............................

9-9.

9.5.4 Rocking or

Rolling ..........................................

9-9

-

9.5.5 Breakaway

Parts .........................

.....................

. 9`9

9.5.6

Altering

Buoyant Weight

.......... ........

......................

.

.

9-9

9.6 OTHER

FACTORS

....

........................................

.. . 9-10

"*

9.6.1 Irregular Shape or Neauniform Embedment Depth.

.

........ .................. 9-10

9.6.2 Waiting

Time

........................................................

9-10

9.6.3

Foundation Skirts

.... ........................................... 9-10

9.7 EXAMPLE PROBLEMS . . ...... ....... ..................... ... . ............ 9-10

-

9,7.1 Problem

I - Recovery of a Large Long Cyliiler .................. .........

9-10

9.7.2

Problem

2 " Recovery of a Skirted Foundation

.........

........ 9_13.


10/257

Page

9.8 REFERENCES ......................

......................................

9-16

9.9

SYMBOLS .................................. .......... 9-17

Chapter

10 -

SCOUR ..... .....................

.................................

.. 10-1

10.1 INTRODUCTION

. . . . . . . . . . . . .. . . . . . . . . . . . . 10-1

10.1~

TOUTO............................................

,........10-1

~

10.1.1 Objectives ..................

....................................

10-1

10.1.2 Theory

.....................

...................................... 10-1

10.1.3

Modeling

..................

..................................... .. 10-1

10.2

SCOUR

TYPES ...................

....................................... .. 10-2

10.2.1 Seasonal and

Local

Scour ......... .................................. 10-2

10.2.2 Deep Water Wave-Induced Scour

.......................................... 10-2

10.3

ESTIMATING

SEASONAL

SCOUR...........

.......................

ln-2

10.4

ESTIMATING

LOCAL SCOUR

AT,

SEAFLOOR STRUCTURES

......... ...................... .. 10-3

10.4.1

Effect

of

Seafloor Factors

on

Scour

...................................

10-3

10.4.2-Structures Piercing the Water

Surface

...........

....................... 10-5

10.4.3 Structures Resting

on the

Seafloor ......................................

10-9

10.4.4

Time for Scour Development

................

............................ 10-11

10.5 MINIMIZING SCOUR . ... ..............

..

.

. . ........ 10-12

10.5.1

Scour-Resistant Structures

..........................................

10-12

10.5.2

Sco-ir

Protection

Measures .................

............................ 10-12

10.6 REFERENCES ....................

.......................................

..

10-16

10.7 SYMBOLS

...................................................................

10-18

Chapter 11 - SLOPE STABILITY ASSESSMENT ......

.............................. ...... .11-1

11.1 INTRODUCTION .................

......................... .

....

............ 11-1

11.2

FORMS OF INSTABILITY ....................

.................................. 11-2

11.2.1

Translational

Slides.........

. . .

.............................

..

11-3

11.2.2 Rotational

Slides ..........

..................................... .. 11-3

11.2.3 Flow Slides ....................................

11-3

11.2.4

Turbidity Currents

...................................................

11-5

11.3

LOADING ..........

.............. ...............................

11-5

11.3.1 Loading Mechanisms .............................

... 11-5

11.3.2

Probabilistic

Preaoction

of Load ........................ . .

..........

11-5

11.4 IMPORTANT SOIL PROPERT!SS .............. ................................

.. 11-6

11.4.1 Gene-al

.................... ....................... ..

.U11-6

11.4.2

Special Conditions:

Underconsolidated

Sediments

..................

11-6

11.4.3

Repetitive

and Dynamic Loading

Response of

Sediments .....................

11-7

11.5

LEVEL OF

ANALYSIS ................................................

11-7

11.6

SITE ,INVESTIGATION ................. ................. .

.................

11-7

11.6.1

General ...................

..............................

....... 11-7

11.6.2 Preliminary

Studies

..................

...............................

11-8

11.6.3

Ar.oustic

Surveys

..............

................... ...............

11-9

11.6.4 Sampling

of

Sediments . . .... . ... ...................

................

11-11'

11.7

EVALUATION PROCEDURES ..................................

11-12

11.6

REFERENCES

.... ................... ................ .... . 11-15

11.9

SYMBOLS .....................

......................................

.

.. 11-16


11/257

LIST

OF TABLES

Table

Page

1.3-1 Features

of

Shallow

Foundations

and Deadweight

Anchors

....... .................

..

1-3

1.3-2 Features

of Pile Foundation

and

Anchor

Systems . .. .. ......

..................

..

1-4

1.3-3

Features

of

Direct-Embedment

Anchors..........

... ..........................

1-5

1.3-4

Features of Drag-Embedment

Anchor Systems

.........

........................

.. 1-5

1.3-5

Performance

of

Foundation

and

Anchor

Types

as a

Function of Seafloor

and

Loading

Conditions

........ ..... ... .................................. ..1-6

2.1-1

Site

Data

Requirements

for

Categories of

Geotechnical

Engineering

Applications .....

... 2-2

2.1-2

Soil

Engineering Parameters

Normally

Required

for Categories

of

Geotechnical

Engineering

Applicatiolis..

............ .....

.............................

2-2

2.1-3 Historical

Environmental

Information

Needed

to

Assess

Geotechnical Hazards

.........

.. 2-3

2.3-1

Steps

in a Typical Regional

Survey

..........

...

...........................

.. 2-12

2.4-1

Steps in

a

Typical

Site-Specific

Survey

.........

.......

........................

2-1b

2.4-2

Shallow Soil

Sampler

Types and

Applications .........

.......................

2-16

2.4-3

Characteristics

of

Some Free-Fall

and Lowered

Corers

.......

.... ....... 2-19

2.5-1

In-Sitqi Tests,

Applications,

and

Some.Equipment

Characteristics

....

.............

.

2-22

3.2-1

Size

Range Limits

for

Two Soil Classification

Systems ....

.......

................

3-2

3.3-1

Requirements

for

Indtx

Property Tests

.........

.....

........................ ..3-5

3.3-2

Some Index

and

Engineering

Properties

of Ocean

Sediments

(Most Data Limited

to

Upper

2

Meters

of

Seafloor)

...........

......................

...........

3-6

3.4-1

Requirements

for Engineering

Property

Tests

...........

......................

.. 3-11

4.2-1

Soil Properties

Required

for

f.maysis

and

Recommended Factors

of, Safety

.........

...

4-5

4.3-1-

Suimary

of Steps

in

the

Design

of Shallow

Foundations

and Deadweight

Anchors ........

4-7

4.3-2

Coefficient

of Friction

Between

Cohesionless

Soils

and

Some Marine

Constructicn

Materials ........

.........

................................

4-12

5.2-1

Pile Types ..........

............

.......................................

5-2

5.2-2

Mooring Line Connections

..........

.....

.....

................................

5-3

5.2-3

Techniques

to Improve Pile

Lateral

Load Capacity

........

....................

..

5-3

5.3-1

Properties

of

CohESionless

Soil Useful in

Pile Design

......... ..................

5-5

5.3-2

Properties

of

Cohesive

Soils Useful

in

Pile Design ........

..... ..............

5-5

5.3-3 Properties

of

Calcareous

Soil Useful in

Pile Design ......

...................

.. 5-6

5.3-4

Bearing

Capacity

Factors for Chain

Lateral Force

in Sand

......

................

5-7

5.3-5

Recommended

Limiting

Values

for Unit Skin

Friction

and End Bearing

for

Cohesionless

Soils.

.......

............

..................................

5-9

5.4-1

Rock Properties

.........

..... ...

.....................................

..

5-14

6.2-1

Propellant-Driven

Embedment Anchors

for Ocean

Use

.....................

6-3.

6.2-2

Parameters

for

Navy

Propellar..-Embedded

Anchors

.....................

6-4

6.3-1 Conditions

Complicating

or

Hazardous

to Direct-Embedment

Anchor

Use ...............

.

6-10

6.5-1 Values

for

Strength Reduction

Factor for

Use in Equation

6-3 .....

.............

.. 6-16

6.6-1 Average

Values

of Soil Permeability

......... ...

..........................

..

6-18

6.7-1

Factors

Associated

With

Direct-Embedment

Anchors

Which Can

Influence Submarinp:

Slope

Stability

. . . . . . .

. . .

. . . . . . .

. . .

. . .

. . .

6-24

7.3-1

Estimated

Maximuo Fluke

nip

Penetrattou

of

Some

Drag Anchor

Types

in

Hard

,and Soft

Soils

.......

...........

. ..........

..........

7-9

7.4-1

Rating

of Drag

Anchor Types

Based on Tripping

and Dig-In,

Roll

Stability,

and Holding Capacity

Efficiency

......... .......

............................

7-11

.7.6-1

Parnmeters

HR

and

b Used

in Equation

7-2

.

.............

. .....

..............

7-14

7.5-2

Parameters

N

and

f

Used for

Clays

and Cohesive

Silts

in

Equation

7-3

.............

..

7-18

7.6-1

'Troubleshooting

Procedures

for

Correcting

Drag Anchor

Performance

Problems

....

....... 7-19

&.2-1

Correlation

Coefficients

Between Dutch

Cone Penetration

Resistance

and Thin-Walled

Skirt and

DowlPenetration

Resistance

........ .....

..................

.....

8-6

8.3-1

Values

of Constants

Used

in Equation

8-12

.........

........................

.. 8-9

8.4-1

Summary of

Calculations

for

Problem

1

....

. .........

......................

.

8-14

8.4-2

Sumary

of

Calcuiations

for Proolem

2

.........

..... .....

.......

..... .....

.....

.8-19

11.2-1

Movement Models for

Submarine

Slides in

Soft and

Loos* Sediment

.........

.....

11-2

11.7-1

Level I Slope

Stability

Survey

..........

.....

.............................

.. 11-13

11.7-2

Level

II Slope Stability

Survey ...........

..... .........................

.. 11-14


12/257

LIST OF

FIGURES

Figure

Page

1.3-1

Simplified

anchor types

..............

........... .......................

3

2.2-1 Ocean sediment distribution

......... ....... ............................... 2-6

2.2-2

Topography

of the carbonate

compensation depth (CCD) .

..... ..........

..... .... 2-7

2.2-3

Marine geological

provinces

probable soil types

....... ..................

2-8

2.2-4

Typical

strength

profile for

hemipelagic

terrigenous

silty

clay

. . ... .......... 2-9

2.2-5 Typical

strength profiles

for proximal

and

distal turbidites ...

..................

2-9

2.2-6

Typical

strength profiles

for

calcareous

ooze

.

... .. .. .....................

.. 2-10

2.2-7

Typical

strength profiles for

pelagic clay .......... .......................

.. 2-10

2.2-8

Typical

strength

profile

for

siliceous

ooze .......

...

............

..... ......

2-11

2.3-1 Acoustic profiling

systems

... .............................................

2-13

2.4-1 Grab

samplers

and

dredges .... .....

.... .........

.......................

.

-16

2.4-2

Box corer and

its

operation

sequence ..............

........................

.. 2-17

2.4-3

Long piston corer operation sequence with

a short corer used

as

a

trigger weight

. . .. 2-18

2.4-4

Alpine vibracore

sampler .......... .....

.. ...............................

2-20

2.5-1 Correction factor for

vane determined shear strength

. . ;

'..............

2-23

2.5-2 Electric

friction-cone

penetrometer

tip .

..

....... .......................

.. 2-23

2.5-3 Correlation

between cone

tip resistance and sand relative

density .................

.. 2-24

2,5-4

Estimation

of

sand

friction angle,

*, from material

relative densitj ..............

. ..

-2 4

2.6-1

Seismic

risk

map of United

States coastal

waters

...

........................... 2-26

3.2-1

Trilineal soil classification

plot -

normally

used

with Wentworth grade

limits . ...

.

3-2

3.2-2

Unified soil classification

chart........

.....................

3-3

3.4-1 Miniature vane blade geometry

.......... ..............

.... .. .... -12

3.5-1

Relationship

between

s

/P and

P1

for

normally consolidated

late glacial

clay

... ....

3-14

3.5-2 Relationship between

fIiclton angle and

P1 for normally

consolidated

fine-grained soils

. ......... .....

.... ...... .. .... .... ......

.... ..

3-15

3.5-3

Correlation between

coefficient of consolidation

and liquid

limit .........

..... ...

3-15

,3.5-4 Range of

PI

values

for pelagic clay .....

: ......................

3-16

3.5-5

Correlation

between

water content and

C

/(I

+ e

)

for

pelagic

clay

and

calcareous ooze

.c.. . . .

. . .

.

.

,

. . . . . . . . . . . . . . . . . .

. . . . 3-17

4.1-1

Features

of

simple shallow

foundation .....

.....................

4-1'

4.1-2 Types

of

shallow

foundations .............................

4-2

4.1-3

Types and significant

characteristics

of deadweight anchors

...... ...............

4-3

4.3-1

Flow

chart for

the

design

of shallow foundations

and

deadweight

anchors

....

......... 4-6

4.3-'2 Bearing

capacity

factors

N , N , and N as

a function of the

snil friction angle . .

.. 4-8

4.3-3

Area

reductior,

factors

forqeccintr~ca]Yy

loaded

foundations

.....

................. 4-10

4.3-4

Possible

failure modes, when sliding

resistance

is

exceeded

..... ............ .....

4-11

4.3-5

Forces considered

in

the overturning

analysis

...............................

4-14

4.3-6 Soil stress

increase beneath

a rectangular

foundation ........

....... ......

416

4.4-1 Foundation

sketch for example problems

I

and

2 ......

........................

.. 4-18

4.4-2

Forces

considered

in the overturning

analysis for example

problem 1.... ...........

4-23

4.4-3

Forces considered

in the overturning

analysis for-example

problem2 .... ......... 42 7

5.3-'1

Flow

chart for

the

pile design procedure

... ..... ...........

. ... ..........

..5-4

5.3-2

Design values

for nh

for cohesionless

soils . . ....... ..

....................

5-7

5.3-3 Design

values for n

for

cohesive

soils

........ .. ..... ..............

.......

5-8

5.3-4

Deflection coefficients A

and B at the nround surface

.................

....... .

5-8

5.3-5

Influence values

for a

piYe

withyapplied

lateral load

or

moment

.... .............

.5-11

5.4-1

Failure modes

for pile anchors in'a

rock

seafloor

...........

. ................

5-13

5.5-1

Pile installation

techniques ... .....................

.....

...............

5-16

5.5-2 Drilled~and

grouted

pile

......... .......

..............................

.. 5-17

5.6-1 Problem

sketch

for

example problems

1

and

2

....... .......................

..

5-19

5.6-2 Soils

data for example

problem I ............

..... .................

......... 5419

6.2-1

Installation sequence for a propellant-embedment

anchor ....... .......

. ........ 6-2

6.2-2

NCEL 10K propellant-embedment

anchor showinq

sand and clay flukes

..........

.........

6-5

6.2-3

Coral

and

rock flukes

for NCEL propellant-embedment

anchor systems

. . .

..

...... .6-5

6.2-4 Impact-driven

anchors

.

. .............

..... .....

..... ..........

6-6

6.2-5 Jetted-in

anchors

......... ... ..............................

......

. . 6-7

6.3-1

Flow chart for

predicting the holding

capacity of a direct-embedment

anchor ..........

6-9

6.5-1 Failure

modes

for

shallow and deep

embedded plate

anchors .....

. . . . . .

.......

6-12

6.5-2

Short-term

holding capacity

factors

for cohesive

soil where

full

suction

develops

beneath

the

plate..

. . ...........

..............

. ........ ..

6-13

6.5-3 Long-term holding

capacity factors and

short-term no-suction

factors for

cohesive

soils . . . .................

..................

6-14

6.5-4

Holding

capacity factors for cohesionless

soils

..........

........ .

...... . 6-15

xi.


13/257

Figure

"" 6.6-1

Nomenclature

for types

of

non-steady

loading .

. . ...................

6.6-2

Time

required

for

dissipation

of

stress-induced

excess

pore

pressure

.....

..........

S6.6-3

Maximum

cyclic load

capacity

without

soil strength

loss .

...........

.....

..... ...

6.6-4 Maximum

(lifetime) cyclic

load capacity

without

development

of cyclic creep

....... .

"6.6-5 Strain-rate

factor,

1, for

cohesive

soil ...... .........

........................

6.6-6

Inertial factor, If,

for cohesive

and

cohesionless

soils

.

. . ........

. .........

6.6-7

Strain-rate factor,

I,

for

cohesionless

soil ........ ......

...............

..

6.9-1

Mooring

sketch for

example problem

1

........................................

6.9-2

Soil strength profile for example problem 1

........ ..... . ... .............

.6

6.9-3 Mooring sketch for

example problem 2 ...... .......

...........................

4..

7.1-1

Features

of a

drag anchor .......

.......................

....

..........

,...- 7.1-2

Example

of a movable fluke anchor: STEVIN cast .......

....... ..............

7.1-3 Example

of a fixed fluke

anchor:

BRUCE cast .

... .. . ...............

7.1r4 Examples

of

bilateral

fluke

anchors

.

. .

. ......

.. ........

.................

7.1-5

Example of

a

soft soil

anchor: STEVMUD.

...........

.................

.......

7.2-1 Development

of

a tripping problem

in

soft

seafloors

with an improperly

set

anchor .

. . .

7.2-2

Proper

anchor setting

sequence

using two

floating

platforms

. ......

..............

7.2-3

Development

of a

tripping problem

in

hard

seafloors.......

. ..................

7.2-4

Penetration

and orientation

behavior of

ananchor

in hard

and soft

seafloors

.........

S-

7.2-5

Forces on unstabilized

and

stabilized

anchors in sand

7.2-6 Anchor

in soft

soil, after

balling-up

and pullinC-out

. .

............

....

7.3-1 Site

survey plan

decision flow

chart .........

.

.

....

...... .................

7.5-1

Anchor

chain system

holding

capacity

at the

mudlinein soft

soils

.....

.............

7.5-2

Anchor chain

system holding

capacity

at

the

mudline

in

hard soils ....

,.......

...

7.6-1

Typical

perforaance

of drag

anchors

when operating

properly

and improperly

....

.......

7.7-1

A pendant

line and

buoy arrangement

for semisubmersibles

.........

.............

..

7.7-2

Chain

chaser used

to

assist

anchor

deployment and

recovery

..... ...............

..

7.7-3

Tandem/piggyback

anchor

arrangements

......

.....

... ..........................

7.7-4 Parallel anchor

arrangement ............ ..... .... ....

.... ...... .... ....

8.2-1

Shallow

static penetration

model ......

.....

..................

.......

.

.

. .

8.2-2 Relationships

for

calculating

sinkage

resistance

in-cohesionless

soils;

for =

30

and

40

.....

..................................

8.2-3

Flow chart

of the

calculation

procedure for

predicting

static

penetration

.... ........

8

.2-4

Location

of the

critical

shear

strength

zone

B for

blunt and

conical

penetrators

. .

.

8.3-1 Forces

acting

on~a

penetrator before

and after

contact with

the

seafloor ...........

.

8.3-2

Flow

chart

of

the

calculation

procedure

for

predicting

dynamic

penetration

....

.......

8.4-1

Problem

sketch

and

soils

data for

example

problem

1 .........

...................

"8.4-2

Plot of predicted

soil resistance to EPS penetration

...... ..... .... .... ......

8.4-3 Sketch for

example problem 2 ........

.................

. . . ...

9.1-1

Flow chart

for procedures

to determine

immediate

breakout

force and

time required

for long-term breakout under a lower

force ..

.......

... ....... .......

""

9.3-1

Normalized immediate

breakout

force

as a

function

of

relative

embedment

depth

.........

9.4-1

Normalized long-term

breakout force

as

a function

cf breakout

time

parameter

.. ......

9.7-1 Problem

sketch

and data

for

example problem

I .

. ...... ..

...........

.........

9.7-2

Problem sketch

and-data

for

example

problem 2

........

....... .... ....

......

10.4-1

Clear

water

scour

and general

sediment

transport

near

a pile .....

.

. . ..

10.4-2

Variation

of maximum

clear water

scour

depth with

seafloor material

diameter

04

,at a

cylindrical pier

..........

............

....

.....

............ ...

"

0.4-

Idealized wave-induced

flow and

scour

patterns around a vertical

cylinder ........

" 10.4-4

Summary

plot of field

and

model scour

depth

data at

single piles and

pile

groups .

. .

10.4-5

Scour

comparison

for

very

large

circular,

square

and

hexagonal

cylinders

of equal

1046

cross-sectional area

where

a/D


14/257

Chapter

1

INTROOtkTION

1.1

OBJECTIVE

aspects of

engineering problems

associated

"*

the

facilities

are

difficult

for

Navy eng

"Marine

geotechnical

engineering

is

the

to address

because of the highly

speci

application

of

scientific

knowledge and engi-

nature

of

most

geotechnical topics.

Also

neering

techniques to

the

investigation

of

to

a general

lack

of

historical

precedenc

seafloor

materials and the

definition

of

their

seafloor construction,

a

low level of

.

physical properties The responses of these standing of seafloor soil behavior

exists.

seafloor materials

to

foundation

and mooring of

what does exist Is

published

in documen

"elements

are the

engineering

aspects

of

marine

widely distributed. The Handbook

brings

- geotechnology which are addressed in this

docu-

information together.

It is

intended

for

' ment.

This Handbook for Marine Geotechnical Navy

engineers

who do not have an

ext

Engineering

brings

together

the

more important background

in

geotechnical

engineering.

- aspects of 5eafloor behavior for application to Ha 'ook

Is

not an all-inclusive design m

. Navy

deep ocean

ungineering

problems.

Rather,

the

objective

of the

Handbook

' The Navy installs,

or

may

require installa- famillariz engineers

with

geotechnical a

* tion

of,

a variety

of facilities fixed to the of problem,

serve

as a design guide for

*4, continental shelves

and slopes, to the submarine

tively unc

licated. problems,

and

be

a

-

slopes

of seamounts

and

islands,

and

to the deep nical

directo

to

more

complete discussio

ocean floor.

Some of

these facilities rest on

to more

sophi ticatedanalysis and

design

shallow foundations resebling a

spread

footing dures. Alt ugh i t is intended for us

or on pile*-like

foundations.

Others rmy

be deep ocean p llef

(nominally beyond th

Ssurface-

r

subsurface-moored types

where a

tinental

she f

or

below

about 600 feet)

buoyant

element

is

tethered to the seafloor by information tained in

the

Handbook is

uplift-reSisting foundations or piles or by cable to p lem

in

shallow

water

as

propel*,ant-embedment or drag-ebedeent anchors.

Behavior

of

the mooring

elements

lying

on

or

"embedded

in the

seafloor

is

dependent

on the 1.2

HANDOOK ORGANIZATION

physical properties of the

materials making

up

the

'seafloor

In the

imesdiate

area. In addi- This Manlfok has 11 chapters;

an Int

"

tion, .cour

and

slope

stability problems

may tion, and 1 technical

chapters

grouped

exist or

my

be

created

by the placement of

three major tions: PROPERTIES DETERMIN

these elements.

DESIGN OF F )UE0ATIONS AND ANCHORS, and

Navy military and ivilian engineer's will SEAFLOOR

LEKS.

. be

required

to

plan

for, design,

supervise

The

Int

odu:tion

serves

as a guide

construction

of, or

have

-technical

respondt- remaining

ch pters. It lists

ginhalizd

.

bilitty

for 'these facilities.

Geotechnical tuo for each

type of foundatioa and

a

7 f@ e


15/257

and can assist the reader in selection

of

an

In

the Other Seafloor Problems section

appropriate

foundation

or anchor type based on

other aspects

of marine geotechnical engine

environmental

conditions and

structural require-

are

discussed. Chapter 8

describes

techni

ments.

for

predicting the

depth of penetration

The Properties

Determination section,

objects

into

the seafloor.

The

techniques

"consisting of Chapters

2

and

3, discusses on- be used

for penetration

prediction% with

-

site

and

laboratory determination of soil prop- and small

objects of

various

shapes (suc

erties and presents physical

property

models

for

lost hardware, instrument packages, or

fou

major seafloor soil types.

Chapter

2

describes

tion

elments)

impacting

the

seafloor at hig

the

various

aspects

of surveying

a site,

includ- low

initial velocities.

The procedures

ing

preliminary reference information

gathering Chapter 8

can also be

used

to

predict

the

" and survey

planning

through

brief descriptions

required

to

embed

a given

object

to

a spec

of remote survey equipment,

shallow

and deep

subbottom depth (shear keys below

a

bo

sampling equipment, and

in-situ soil properties resting

foundation,

for

example). Chap

"testir.g

equipment.

Additional

information on

prescnts

techniquesi

.dar predicting the

forc

.

site surveying for

the assessment of

slope

tim required

for breakout of objects emb

""

stability is given in

Chapter 11. Chapter

2

in

the seafloor and discusses conditions

*

also contains a section on

estimating soil

prop-

can have

a significant effect on brea

erties

for use

in a

preliminary design when no

Analytical techniques are

given

for two sig

,

field

data

are

available. Chapter

3

describes

cantly different

cases--full-suction and

""

the laboratory tests

performed

on

recovered soil

suction--along with a discussion

of

mecha

- samples

to generate

index

and

engineering prop-

techniques

that can reduce

the

breakout

f

"" erties

data required

for analysis and design of and

time requirements.

Chapter

10

desc

seafloor structures. Use of index properties to scour prediction

techniques.

It

is

dire

classify the soil and

to

correlate with

engi-

primarily toward

scour problems around

ob

nearing

properties is

also described,

on the seafloor (Tocal

scour), but

includ

The

Design

of Foundations

and

Anchors

discussion of nearshore

seasonal seafloor

-

section, consisting of Chapters 4

through 7, file

changes. Most

information on scou

describes the

use

of

topographic, stratigraphic, drawn from

historical observations and

and soil

properties information

necessary

to

studies

of nearshore and

river

condit

"predict

capacities

of

foundation and anchor Insight

from

these studies

is

extrapolate

*

systems.

Chapter

4

covers the

design

of founda- conditions

more likely to exist

in deeper

m

*"tions

and deadweight anchors

bearing on the enviianme-ts.

Chaptcr

11

discusses

"

seafloor

surface.

Design of piles

for use

as stability

in qualitative

terms. 'Techniques

foundations or

anchors

is

discussed in described for surveying a site

to determine

Chapter

S. Plate-shaped anchors

embedded

in

the potential

for slope instability. The metho

seafloor are

treated in

Chapter 6, with emphasis

stability analysis are

described but are

"given

to the

propellant-embedment

anchor

systems presented in detail.

Considerable

tech

recently incroduced

into the

Navy's

Ocean Con- interoretiv skills

are

required

for

evalu

struction Equipment

Inventory.

Chapter

7

covers of site information and

application

of

the selection

and sizing

of

drag-embedment

analytical procedures.

anchors;

only the resistance developed

from Each chaoter has a list,

of references

" anchor and

chain interaction with

seafloor symbols visd

In that chapter. Example prob

materials is

discussed

and

not

the design

of

a which

outline

design or

calculation proced

complete

mooring

system. References 1-1, 2-Z,

are presented

at

the

end of each chapter

and 1-3 can be

consulted for

information

regard-

Inchlaes

design

procedures.

Ing complete

mooring

systems..


16/257

"1.3 SELECTION

OF FOUNDATIOM/ANCHOR TYPE

SChapters

,

5,

6,

and 7

each describe

a

idfferent

type of foundation

or

anchor--

. .

.

...

.

. .

.

=

.': ::::'.."

deadweight, drag-embedment,

pile, and direct-

embedent

(Figure 1.3-1].

Each of

these

founda-

(a)deadweight

tion

and

anchor

types

has

strong

points or

features. This

section summarizes

these fea-

tures

[Tables

1.3-1

through

1.3-4]

to

provide

.

....

guidance on

selecting the

optiomu foundation

or

-

..

.

...............

anchor

type

for a given

set of problem

condi-

tions. (b) drag-ebedment

Shallow

foundations

and deadweight anchors

are

widely

used

in

the

deep ocean environment

because

they are simple

and readily

sized for

most

seafloor

and loading

conditions. However,

they do

not

perform

well on

steep sloping sea-

floors.

In addition,

deadweight

anchors

are not

verj

efficient (that is,

the rstio of lateral

%

-

'.'-

load

resistance

to

anchor

weight

is

very

low

"-.

compared to other lateral-load-resisting

anchor

types). Table

1.3-1 lists

these and other

features

of

the shallow

foundations and

deaar-

kc)

pifon(aiso

us(d asdideep"

weight anchors. foundation) (d) directembedment

Figure

1.3-1. Simplified

anchor types.'

Table

1.3-1. Features of Shallow Foundations

--

and

Deadweight Anchors.

Features

of Shallow Foundations

and Deadweight

Anchors

1. Simple,

on-site

construction feasible, can be

tailored to

task.

2.

Size limited

only

by

load-handling equipment.

3. Reliable on

thin

sediment

cover over

rock.

4. Lateral

load resistance

decreases rapidly with

increase in

seafloor

slope.

Addktional

Features

of

Deadweight

Anchors

1.

Vertical

mooritng

component can be

large, permitting shortermooring

line scope.

2. No

setting distance

required.

3. Reliable

resisting force, because most

resisting force

is

directly due to anchor

mess.

4.

Material

for

construction

readily available and economical.

5.

Mooring line

connection

easy to

inspect

and service.

6. A good

energy absorber

when

used

as a

sinker

in

conjunction

with

nonylelding

anchors

(pile and plate

anchors).

7. Works

well as

a

sinker in combination

with

drag-lebedient

Qnchors

to

permit shorter mooring

line scopes.

Lateral

load resistance is

low

compered

to

other anchor

types.

9.

In

shallow

water, the large

mass

can

be an

undesirable

obstruction.


17/257

p/

I

Ple foundations and

anchors

are

used

where Direct-embedment anchors can be

driven

into

,

less expensive

types of shallow

foundations and

seafloor

soils

by propellant,

vibratory,

or

anchors cannot.

mobilize

sufficient

resistance.

hsmer-driving

systems.

The

propellant-

A

principal drawback of piles

for the deep

ocean

embedment

systems

are

particularly amenable

to

is

the

highly

specialized equipment

needed

foy

use

in

the

ocean because

of

the

relatively

short

installation and the associated

very high

mobil-

time peried

required

for installation

and the

tzation and installation

costs.

Table

1.3-2

few

limitations

on operating

depth. Other

"lists

features

of piles used

for foundations and features of

direct-embedment anchors are

listed

anchors

on

the

seafloor,

in Table

L3-3.

Table

1.3-2. Features of Pile

Foundation

and Anchor

Systems

Features of Pile Foundations

and Pile

Anchors

J

1.

Requires

highly

specialized

installation equipment.

2. Transmits high axial

loads

through

soft s-rficial

sells

down

to competent

bearing

soil

or rockL

3.

Can

be designed to

accomodate scour

and

resist

shallow

mudflows.

4.

Can be

installed

and performs well

on stbstantial

slopes.

5.

Can be

installed

in hard

seafloors (rock

and

coral)

by

drill-and-grout

technique.

6.

Orilled-and-groutod

piles

require more specialized

skills

P

and

installation equipment

and incur high

Installation

7. Vide range

of sizes

and shapes are

possible

(pipe,

structural

shapes).

8.

Field modifications

permit

piles to be tailored

to suit

requirements

of particular

applications.

9.

Costs are high

and

increase rapidly

in

depe-

water

or

exposed

locations where more

specialized

Installation

vessels

and

driving

equipment

are

required.

10.

Accurate soil

properties are

required

far design.

Additional

Features of Pile

kAncbr

*

1.

High

lateral capacity (greater than

10),0

lb)

achievable.

2.

Resists

high

uplift

as well as

lateral leads,

permitting

use with

short mooring line

scopes.

3. Anchor setting not

required.

4. Anchor dragging eliminated.

5.

Short mooring line scopes

permit

use I* areas

of

limited

sea

room or where

vessel excursions must

be irmiimzed.

6. Pile

anchor

need

not protrude

above seaflor.

7. Driven piles

art cost

competitive with

ethe hfgh-capacity

anchorslwhen

driving

equipment

Is available.

8. Special equipment

(pile

extractor)

my

be

required to

retrieve

or

refurbish

the

mooring,

or

raw

pile

and pendant

must be installed.

9.

More

extensive

and better quality

site data

are required

than the data required for

other

anchor types.

10. Pile capacity goes to

zero when its capacity

as an anchor

is exceeded

and pullout occurs

(is

a

nsmyielding'

anchor).

It


18/257

Table 1.3-3.

Features of Direc'-Embedment Anchors

Features of All

Direct-Embedment

Anchors

1.

High

capacity

(greater

than 100,000

lb)

achievable.

S2.

Resists

uplift as well

as

lateral

loads, permitting

moorings

of short scope.

3.

Anchor

dragging eliminated.

4. Higher

holding-capacity-to-weight

ratio

than other

anchor

types.

S.

Handling

is

simplifiad

due to

relatively

light

weight.

6. Accurate

anchor

placement

is

possible; no

horizontal

"-

setting

distance

necessary.

7. Does

not

protrude above

the

seafloor.

8.

Possibly

susceptible

to

strength

reduction accompanying

cyclic

loading

Yhen used in taut

moorings

in

loose

sand

and

"coarse

silt

seefloors.

9.

For

critical

moorings,

soil engineering

properties

required.

10.

Anchor

typically not

recoverable.

11.

Anchor

cable

may be

susceptible to

abrasion or'

fatigue.

Features

Unique

to

Propellant-Driven

Plate Embedment

Anchors

1.

Can be placed

on

moderate

slopes, and in rock and

coral

* A-.'. seafloors.

S2.

Installation

is simplified

as

compared

to

other

typei

because

they

can

be embedded immediately

on seafloor

contact.

3.

Special

consideration

neemed for

ordnance.

"4. Gun' system

not

generally

retrieved

in water

deeper than

approximately 1,000

ft.

Features Unique

to

ScreowIn,

Vibrated-In,

and Hammer-Driven

Plate

Anchors

1.

Can better

accommodate

loyered

seafloors (seafloors

with

variable

resistance) because

of continuous power

expenditure

during

penetration.

..".-.-

2.

Penetration

is

controlled

and

can be monitored.

3. Surface vessel

must

maintain position

during installation.

"4. Operation

with

surfaced-powered

equipment

limited

to

shallow

depths by power and strength

umbilicals as

well

as

.

the

mooring line.

5.

Operation limited

to sediment

seafloors.

Table

1.3-4.

Features

of

Drag-Embedment

Anchor

Systems

-

1.

Wide range

of

anchor

types

and

sizes

available.

*

2. High

capacity

(greater

thean

100,000 lb)

achievable.

3. Nest

anchors

are standard off-the-shelf

equipment.

'

4.

Broad

experience

with use.

S*..--.

S.

Can

provide

continuous

resistance

even though

maxim.um

capacity

has

been ecceeded.,

.

,,.

6. Is recoverable.

7.

Does

not

function well in

rock seafloors.

8.

Behavior

is

erratic

in

layered

seafloors.

*

z*,"9.

Low

resistance

to

uplift

loads;

therefore, large

line scope

required

to cause

near horizontal

loading at

seafloor.

"10.

If

dragging is

not

acceptable, anchor must

be

pulled

horizontally at

high loads

to

properly penetrate

and

set.

11. Oragging

of anchor

to

achieve

penetration

can damoge

pipelines,

cables, etc.

12.

Loading must

be limited

to one direction

for most anchoer

types

and

applications.

13. Exact

anchor

plact-ent

limited

by

ability to

estimate

.setting

distance.

(

4 J


19/257

Table 1.3-5. Performance of Foundation and

Anchor Types as a

Function

of Seafloor

and

Loading Conditions

Performancea

for

Following Types--

Item Dirct

Deadweight

Pile Embedment

Brag

Seafloor Material Type

Soft clay,

mud ++

+ 4+ +4

Soft

clay

layer (0-20 ft

+

+4

+.

thick)

over hard

layer

Stiff clay

44

++

++

++

Sand

++

++

++

++

Hard

glacial

till

+

++

++

+

Boulders

++ 0

0 0

Soft

rock

or

coral

++

a4

4

Hard, monolithic rock ++

+

+

0

Seafloor

Topography

Moderate slopes,

10 deg

o

++ 44 o

Loadina Direction

Downward

load

component

+4

++

o

o

(foundations)

Omni-directional (not down) 4+

++ 0

Uni-directional

(not down)

++

4+ 44

4.

Large uplift

component 4+

+4 a

Lateral

Load

Range

To 100,000

lb

.+

+ + 44

100,000 to

1,00C,000

lb + +4

+

Over

1,000,000 lb o +4

0 a

"a

4

- functions

well

* s normally is not the preferred

choice

o

does

not

function well+

Table' 1.3-4 l ists features of

drag- 1.4

REFERENCES

embedment

anchors.

Although

these anchors can

develop

high capacities,

the

load on a drag 1-1. Design

manual, harbor

and coastal

facili-

anchor 1s usually limited

to

one direction,

and ties, Naval

Facilities Engineering

Command,

the mooring-

line

angle at the seafloor

must be

,NAVFAC

DN-26. Washington. D.C.

Jul

1968.

virtually horizontal.

The holding capacity

of

drag

anchors

decreases very

quickly

as mooring 1-2. AF

recoimmmded practice

for the analysis

line

angles

exceed

approximately

6

degrees. To

of spread

mooring

systems

for floating

drilling

assist in

understanding the advantages

and

units, American Petroleum Institute,

API RP

2P.

disadvantages of the various anchor

types, Dallas,

Tex.,

.My

1981.

Table

1.3-5

compares

how

well

they

function

under different conditions.

Judgments

of

1-3. Rules

for

building

and clessing mobile

expected performance

have

been made primarily

on offshore

drilling units,

American

Bureau

of

the basis

of holding

capacity

'and relative cost.

Shipping. New York,

N.Y., 1980.

It

should

be

noted that Table 1.3-5 is

an

expeditious

guide, for general

use,

and

special

ci-cumstances

can shift the

performance ratings.


20/257

fI

Chapter 2

SITE SURVEY

AND

IN-SITU TESTING

2.1 INTRODUCTION

topography on drag anchor

performance

or

(2)

a

technical

inability to use

this

data

element

in

S-2.1.1

Purpose

design

because

analysis techniques are no t

developed,

as

in the inability

to use

dynamic

This

chapter sumarizes considerations

and

soil properties

in

drag anchor design due to an

"methods

for

selecting and

characterizing

a site absence

of

a

performance-related

model.

for

bottom-resting

or

moored

platforms

in the

Table 2.1-2 lists geotochnical parameters

deep

ocean.

requirad for each of the

applications.'

&.1.2 Factors Influencing

the Site Survey

2.1.2.3

Regional

Versus

Site-Specific

Surveys.

Some

projects

or project

phases

2.1.2.1

Constraints.

The

type and

detail

require

general Information

from a

large region,

of

site

data sought will

be

a

function of: wt.reas

others

require more accurate

data

from a

small geographic

area. For example, a manned

""

Value

and

replacement

cost

of platform

habitat

installation

may

require

low-precision

Impact

of platform failure (primarily) date resulting

from

a

regional survey over

a

on

human life

-

Purpose of

the

platform

large area to determine

an adequate or a

best

.Topography and

seafloor

materil

type

location

for

Its placement, while design

for the

"' Any presurvey

requirements for an exact

geographical location habitat's

foundation requires high-precision

Types

of

man-induced

and environmental

date

frU

e select

ste.

'',loadi

ngs$=t

sletdst*

a Type and size

of the

foundations

or Since regional

surveys compare

Handbook for Marine Geotechnical Engineering

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Transcript of Handbook for Marine Geotechnical Engineering