NAVFAC Dm7-02 (Foundations and Earth Structures) Complete Manual

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An Annotated Reproduction of

NAVFAC Design Manual 7.2

Foundations and Earth Structures

PLEASE NOTE This is the second volume of an extraordinary document, published in 1982, that is now considerably out‐of‐date and is no longer a sanctioned publication of the US Government. NAVFAC DM 7.2 is provided here as a reference because of the incredible density of highly practical geotechnical design guidance it contains. It is also of significant historical interest, and when combined with DM 7.1, it represents perhaps THE principle compendium of geotechnical knowledge used by designers between 1982 and around the turn of the century. The importance of the Federal labs (particularly FHWA, Bureau of Reclamation, Army and Navy labs) in pushing the practice of geotechnical engineering forward between 1930 and around the time of the publication of this manual cannot be overstated, and this manual is a testament to that heritage. Thus, you are holding in your hands (or in your computer memory) a great reference for preliminary design guidance and a knowledge artifact that will be recognized by nearly every senior practicing geotechnical engineer. This copy of NAVFAC DM 7.2 (1982) has been updated to comply in spirit with NAVFAC DM 7.02 (1986). DM 7.02 was actually a very minor update of DM 7.2 made mostly to correct some out‐of‐date numbers that referenced relatively obscure Federal publications. This reproduction has considerable advantages over the widely‐distributed and much‐appreciated PDF version that has been floating around the net. That version was hosted at Vulcan Hammer’s site (many thanks!) for years. The asterisks and parentheses that were the artifact of an early PDF conversion have been replaced in this version with the lines originally intended. Further, Greek symbols and the size of the figures are as per the original paper publication of 1982 rather than the shrunken versions. The resulting file size is much bigger, of course, but I believe the improved quality is worth it. Enjoy this historic document, but please use it with caution. J Ledlie Klosky

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ABSTRACT

Design guidance i s presented for use by experienced engineers. The c o n t e n t s include: excavations; compaction, earthwork, and hydraulic f i l l s ; a n a l y s i s of walls and r e t a i n i n g s t r u c t u r e s ; shallow foundations; and deep foundations.

For sale by the Superintendent of Documents, U.S. Government Printing Of6e.e Washington. D.C. 20402

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FOREWORD

This design manual for Foundations and Earth Structures is one of a series

that has been developed from an extensive re-evaluation of the relevant

portions of Soil ~echanics

,

Foundations, and Earth Structures, NAVFAC D W 7

of March 1971, from surveys of available new materials and construction

methods, and from selection of the best design practices of the Naval

Facilities Engineering Command, other Government agencies, and private

industry. This manual includes a modernization of the former criteria and

the maximum use of national professional society, association and institute

codes. Deviations from these criteria should not be ma$e without the prior

approval of the Naval Facilities Engineering Command Headquarters (NAVFAC

HQ)

.

Design cannot remain static any more than can the naval functions it serves,

or the technologies it uses. Accordingly, this design manual, Foundations

and Earth Structures, NAVFAC DM-7.2, along with the companion manuals, Soil

Mechanics NAVFAC DM-7.1 and Soil Dynamics, Deep Stabilization, and Special

Geotechnical Construction, NAVFAC DM-7.3, cancel and supersede

-

Soil

Mechanics. Foundations. and Earth Structures. NAVFAC DM-7 of March 1971 in

its entirety, and all changes issued.

!;zot",~:A

CEC, U. S. Navy

'Commander

\

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PREFAC

This manual c o v e r s t h e a p p l i c a t i o n of b a s i c e n g i n e e r i n g p r i n c i p l e s of s o i l mechanics i n t h e d e s i g n of f o u n d a t i o n s and e a r t h s t r u c t u r e s f o r n a v a l s h o r e f a c i l i t i e s . Companion manuals (NAVFAC DM-7.1 and DM-7.3) c o v e r t h e p r i n c i - p l e s of s o i l mechanics and s p e c i a l a s p e c t s of g e o t e c h n i c a l e n g i n e e r i n g . These c r i t e r i a , t o g e t h e r w i t h t h e d e f i n i t i v e d e s i g n s and g u i d e l i n e s p e c i f i c a t i o n s of t h e Naval F a c i l i t i e s E n g i n e e r i n g Command, c o n s t i t u t e t h e Command's d e s i g n guidance. These s t a n d a r d s a r e based on f u n c t i o n a l r e q u i r e m e n t s , e n g i n e e r i n g judgment, knowledge of m a t e r i a l s and equipment, and t h e e x p e r i e n c e g a i n e d by t h e Naval F a c i l i t i e s E n g i n e e r i n g Command and o t h e r commands and bureaus o f t h e Navy i n t h e d e s i g n , c o n s t r u c t i o n , o p e r a t i o n , and maintenance of n a v a l s h o r e f a c i l i t i e s .

The d e s i g n manual s e r i e s p r e s e n t s c r i t e r i a t h a t s h a l l be used i n t h e d e s i g n o f f a c i l i t i e s under t h e cognizance of t h e Naval F a c i l i t i e s E n g i n e e r i n g Command. The d i r e c t i o n and s t a n d a r d s f o r p r o c e d u r e s , methods, d i m e n s i o n s , m a t e r i a l s , l o a d s and s t r e s s e s w i l l be i n c l u d e d . Design manuals a r e n o t t e x t - books, but a r e f o r t h e u s e of e x p e r i e n c e d a r c h i t e c t s and e n g i n e e r s . Many c r i t e r i a and s t a n d a r d s a p p e a r i n g i n t e c h n i c a l t e x t s i s s u e d by Government a g e n c i e s , p r o f e s s i o n a l a r c h i t e c t u r a l and e n g i n e e r i n g g r o u p s , and t r a d e a n d i n d u s t r y groups a r e s u i t a b l e f o r , and have been made i n t e g r a l p a r t s o f , t h i s s e r i e s . The l a t e s t e d i t i o n of e a c h p u b l i c a t i o n s o u r c e s h a l l be u s e d . B i b l i o g r a p h i e s of p u b l i c a t i o n s c o n t a i n i n g background i n f o r m a t i o n and a d d i - t i o n a l r e a d i n g on t h e v a r i o u s s u b j e c t s a r e i n c l u d e d i n t h e manuals. T h i s m a t e r i a l , however, i s n o t a p a r t of t h e c r i t e r i a , n o r i s a r e a d i n g of t h e s e s o u r c e s n e c e s s a r y f o r t h e u s e of t h e c r i t e r i a p r e s e n t e d i n t h e manuals. To avoid d u p l i c a t i o n and t o f a c i l i t a t e f u t u r e r e v i s i o n s , c r i t e r i a a r e p r e - s e n t e d o n l y once i n t h i s s e r i e s a s f a r a s p o s s i b l e . C r i t e r i a having g e n e r a l a p p l i c a t i o n s a p p e a r i n t h e b a s i c manuals numbered DM-1 t h r o u g h DM-10 (numbers DM-1 1 t h r o u g h DM-20 were unassigned i n t h e o r i g i n a l i s s u e s ) . Manuals numbered DM-21 and above c o n t a i n c r i t e r i a t h a t u s u a l l y a r e a p p l i c a b l e o n l y t o t h e s p e c i f i c f a c i l i t y c l a s s covered by e a c h manual. When c r i t e r i a f o r o n e f a c i l i t y a l s o have an a p p l i c a t i o n i n a n o t h e r f a c i l i t y c l a s s , . t h e b a s i c r u l e h a s been t o p r e s e n t s u c h c r i t e r i a i n t h e b a s i c , o r l o w e s t numbered, manual and c i t e i t by r e f e r e n c e where r e q u i r e d i n l a t e r manuals.

The s p e c i f i c d e s i g n manuals (DM-21 and a b o v e ) , w i t h b u t t h r e e e x c e p t i o n s , l i s t d e s i g n c r i t e r i a f o r s p e c i f i c f a c i l i t i e s i n t h e o r d e r of t h e c a t e g o r y codes. The e x c e p t i o n s a r e :

(1) Drydocking F a c i l i t i e s , NAVFAC DM-29, which i n c l u d e s b o t h C a t e g o r y Codes 213 and 223.

( 2 ) C r i t e r i a f o r f a c i l i t y c l a s s 800, U t i l i t i e s and Ground Improvements, which have been i n c l u d e d i n t h e b a s i c manuals on m e c h a n i c a l ,

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( 3 )

Weight Handling Equipment and S e r v i c e C r a f t , NAVFAC DM-38, which i n c l u d e s t h e d e s i g n c r i t e r i a f o r t h e s e f a c i l i t i e s under t h e c o g n i - zance of t h e Naval F a c i l i t i e s E n g i n e e r i n g Command t h a t a r e n o t c l a s - s i f i e d a s r e a l p r o p e r t y . These i n c l u d e weight and l i n e h a n d l i n g equipment, d r e d g e s , yard c r a f t , and p i l e d r i v i n g equipment.

F o r t h e e f f e c t i v e u s e of t h e s e c r i t e r i a , t h e d e s i g n e r must have a c c e s s t o :

(1) The b a s i c and s p e c i f i c d e s i g n manuals a p p l i c a b l e t o t h e p r o j e c t . See l i s t on page ix.

( 2 ) P u b l i s h e d c r i t e r i a s o u r c e s .

( 3 ) A p p l i c a b l e d e f i n i t i v e d e s i g n s , D e f i n i t i v e Designs f o r Naval Shore F a c i l i t i e s , NAVFAC P-272.

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LIST OF DESIGN MANUALS

Title

Number

BASIC MANUALS

I

UUL

of Date

I

Architecture

...

Civil Engineering

...

Cold Regions Engineering

...

Cost Data for Military Construction

...

Drawings and Specifications

...

Electrical Engineering

...

Foundations and Earth Structures

...

Fire Protection Engineering

...

Mechanical Engineering

...

Soil Dynamics. Deep Stabilization and

Special Geotechnical Construction

...

Soil Mechanics

...

Structural Engineering

...

SPECIFIC MANUALS

Administrative Facilities

...

Airfield Pavements

...

Communications. Navigational Aids. and Airfield Lighting

...

Community Facilities

...

Drydocking Facilities

...

Family Housing

...

Harbor and Coastal Facilities

...

Hospital and Medical Facilities

...

Land Operational Facilities

...

Liquid Fueling and Dispensing Facilities

...

Maintenance Facilities

...

Production Facilities

...

Research. Development. and Test Facilities

...

Supply Facilities

...

Training Facilities

...

Troop Housing

...

Waterfront Operational Facilities

...

Weight Handling Equipment and Service Craft

...

INDEX MANUAL

NAVFAC DM-1

NAVFAC DM-5

NAVFAC DM-9

NAVFAC DM-10

NAVFAC DM-6

NAVFAC DM-4

NAVFAC DM-7.2

NAVFAC DM-8

NAVFAC DM-3

NAVFAC DM-

7.3 NAVFAC DM-

7.1 NAVFAC DM-2

NAVFAC DM-3

4 NAVFAC DM-21

NAVFAC DM-23

NAVFAC DM-37

NAVFAC DM-29

NAVFAC DM-35

NAVFAC DM-26

NAVFAC DM-33

NAVFAC DM-24

NAVFAC DM-22

NAVFAC DM-28

NAVFAC DM-30

NAVFAC DM-31

NAVFAC DM-32

NAVFAC DM-27

NAVFAC DM-36

NAVFAC DM-25

NAVFAC DM-38

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CHAPTER

1 .

EXCAVATIONS

Section

1 .

Introduction

...7.

2-1

Section

2 .

Open Cuts

...7.

2-1

Section

3 .

Trenching

.

...7.

2-2

Section

4 .

Braced Excavations

...7.

2-13

Section

5 .

Rock Brcavation

...7.

2-19

Section

6 .

Groundwater Control

...7.

2-27

....

Section

7

.

Excavation Stabilization. Monitoring. and Safety

7.

2-27

CHAPTER

2 .

COMPACTION. EARTHWORK. AND HYDRAULIC FILLS

Section 1 .

Introduction.

...7.

2-37

Secfion

2 .

Embankment Cross-Section Design

...7.

2-38

...

Section

3 .

Compaction Requirements and Procedures

7.

2-45

Section

4 .

Embankment Compaction Control

...7.

2-50

Section

5 .

Borrow Excavation

...7.

2-52

Section

6 .

Hydraulic and Underwater Fills

...7.2

-54

CHAPTER 3 .

ANALYSIS OF WALLS AND RETAINING STRUCTURES

Section 1 .

Introduction

...7.

2-59

Section

2 .

Computation of Wall Pressures

...

7.

2-59

Section

3 .

Rigid Retaining Walls

...

7.

2-82

Section

4

.

Design of Flexible Walls

...7.

2-85

Section

5 .

Cofferdams

...7.

2-116

CHAPTER

4 .

SHALLOW FOUNDATIONS

Section

1 .

Section

2 .

Section 3 .

Section

4 .

Section

5 .

Section

6 .

Section

7 .

Section

8 .

.

Introduction

...7.

2-129

...

Bearing Capacity Analysis

7.

2-129

...

Spread Footing Design Considerations

7.

2-146

...

Mat and Continuous Beam Foundations

7.

2-150

Foundations on Engineered Fill

...

7.

2-159

Foundations on Expansive Soils

...

7.

2-159

Foundation Waterproofing

...7.

2-163

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Page CHAPTER 5

.

DEEP FOUNDATIONS

S e c t i o n 1

.

I n t r o d u c t i o n

...

..

...

.7.2.177 S e c t i o n 2

.

_{Foundation Types and D e s i g n Criteria}

...

_{7 -2-178} S e c t i o n 3

.

_{Bearing C a p a c i t y and S e t t l e m e n t . . . 7 .} _2-191 S e c t i o n

4 .

P i l e I n s t a l l a t i o n and Load T e s t s

...

. 7 0 2-213 S e c t i o n

5 .

D i s t r i b u t i o n o f Loads on P i l e Groups

...

7 . 2-230 S e c t i o n 6

.

_{Deep Foundations o n Rock}

...

_.7.2-232 S e c t i o n 7

.

_{L a t e r a l Load C a p a c i t y}

...

_{7 -2-234} BIBLIOGRAPHY

.

1

APPENDIX A

-

L i s t i n g o f Computer Programs

...

. 7 . 2 - A-1 GLOSSARY*.

...

m7.2- G-1 SYMBOLS

.*....~...

....moo ...ooe~.-.~ - 7 - 2 - s - 1

I N D E X * * * . . . . . . . . . . .

..

. .o . . . . . . . . . . . . . . . . 1

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Figure FIGURES T i t l e Page CHAPTER 1 S l i d i n g Trench S h i e l d

...

7. 2-7 Skeleton Shoring

...

7. 2-10

Close (Tight) Sheeting

...

7. 2-11

BOX Shoring

...

7. 2-12

Telescopic Shoring

...

7. 2-12

Support System

-

Walled Excavation

...

7. 2-15

General Guidance f o r Underpinning

...

7. 2-20

R i p p a b i l i t y of Subsurface M a t e r i a l s Related t o L o n g i t u d i n a l

...

Seismic Velocity f o r a Heavy Duty Ripper (Tractor-Mounted) .7.2-22

Suggested Guide f o r Ease of Excavation

...

7. 2-23

Cube Root Scaling Versus Maximum P a r t i c l e V e l o c i t y ...7. 2-24

Guideline f o r Assessing P o t e n t i a l f o r Damage Induced by B l a s t i n g V i b r a t i o n t o R e s i d e n t i a l s t r u c t u r e Founded on

Dense S o i l o r ~ o c k

...

7. 2-25

Guide f o r P r e d i c t i n g Human Response t o V i b r a t i o n s and

B l a s t i n g E f f e c t s

...

7. 2-26

Methods of C o n s t r u c t i o n Dewatering

...

.7. 2-31

...

Limits of Dewatering Methods Applicable t o D i f f e r e n t S o i l s 7. 2-33

CHAPTER 2

1 _{Resistance of E a r t h}D m Bnbankment M a t e r i a l s t o Piping and

Cracking

...

7. 2-42

CHAPTER 3

E f f e c t of W a l l Movement on Wall P r e s s u r e s

...

7. 2-60

Computation of Simple Active and P a s s i v e P r e s s u r e s ...7. 2-62

Active and P a s s i v e C o e f f i c i e n t s . Sloping B a c k f i l l

.

(Granular S o i l s )

...

....

... ...

...

- 7 2-64

P o s i t i o n of F a i l u r e Surface f o r Active and Passive Wedges

(Granular S o i l s )

...

.7. 2-65

Active and P a s s i v e C o e f f i c i e n t s w i t h W a l l F r i c t i o n

(Sloping Wall)

...

7. 2-66

Active and P a s s i v e C o e f f i c i e n t s with W a l l F r i c t i o n

( Sloping B a c k f i l l )

...

.7. 2-67

Computation of General Active P r e s s u r e s

...

7. 2-68

C o e f f i c i e n t s KA and

Kp

f o r Walls w i t h Sloping Wall and

F r i c t i o n . and Sloping B a c k f i l l

...

7. 2-69

Computation of General P a s s i v e P r e s s u r e s

...

7. 2-71

E f f e c t of Groundwater Conditions on Wall P r e s s u r e s

...

.7. 2-72

H o r i z o n t a l P r e s s u r e s on Rigid Wall from Surface Load

...

7. 2-74

L a t e r a l P r e s s u r e on a n Unyielding Wall Due t o Uniform

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F i g u r e T i t l e Page CHAPTER

3

( c o n t i n u e d )

...

Horizontal P r e s s u r e on Walls from Compaction E f f o r t

7. 2-77

Values of F f o r Determination of Dynamic L a t e r a l P r e s s u r e

C o e f f i c i e n t s

....

...7.

2-79

Example C a l c u l a t i o n s f o r Dynamic Loading on Walls

...

7. 2-80

Design C r i t e r i a f o r Rigid R e t a i n i n g Walls

.

7 .

2-83

Design Loads f o r Low R e t a i n i n g Walls ( S t r a i g h t Slope B a c k f i l l )

..7. 2-86

....

Design Loads f o r Low R e t a i n i n g Walls (Broken Slope B a c k f i l l )

7. 2-87

...

Design C r i t e r i a f o r Anchored Bulkhead ( F r e e E a r t h Support)

7. 2-88

Reduction i n Bending Moments i n Anchored Bulkhead from Wall

F l e x i b i l i t y

...7.

2-89

...

Design C r i t e r i a f o r Deadman Anchorage

7.2-91

Example of Analysis of Anchored Bulkhead

.

7 .

.

2-93

...

Sand Dike Scheme f o r C o n t r o l l i n g Active P r e s s u r e

7. 2-94

Analysis f o r C a n t i l e v e r Wall

...7.

2-95

C a n t i l e v e r S t e e l Sheet P i l e Wall i n Homogeneous Granular S o i l

...

7. 2-97

C a n t i l e v e r S t e e l Sheet P i l e Wall i n Cohesive S o i l w i t h

Granular B a c k f i l l

...7.

2-98

Pressure D i s t r i b u t i o n f o r Brace Loads i n I n t e r n a l l y Braced

F l e x i b l e Walls

...7.

2-100

Design C r i t e r i a f o r Braced F l e x i b l e Walls

...

7. 2-102

S t a b i l i t y of Base f o r Braced Cut

.

7 .

2-104

P r e s s u r e D i s t r i b u t i o n f o r Tied-Back W a l l s

...

7. 2-105

Example of Analysis of P r e s s u r e s on F l e x i b l e Wall of Narrow

Cut i n Clay

-

Undrained Conditions

.

7 .

2-107

Example of Excavation i n S t a g e s

...7.

2-108

Culmann Method f o r Determining P a s s i v e R e s i s t a n c e of E a r t h

Berm (Granular S o i l )

...7.

2-113

P a s s i v e Pressure D i s t r i b u t i o n f o r S o l d i e r P i l e s ...7.

2-114

Gabion Wall

.

7 .

2-115

Reinforced E a r t h

...7.

2-117

Design C r i t e r i a f o r C r i b and Bin Walls

...7.

2-118

Design C r i t e r i a f o r C e l l u l a r Cofferdams

.

7 .

2-119

CHAPTER

4

Ultimate Bearing Capacity of Shallow Footings w i t h Concentric

b a d s

.

7 .

2-131

Ultimate Bearing Capacity w i t h Groundwater E f f e c t

...7. 2-132

Ultimate Bearing Capacity of Continuous Footings w i t h I n c l i n e d

Load

.

7 .

2-133

E c c e n t r i c a l l y Loaded Footings

...

.

7 .

2-134

U l t i m a t e Bearing Capacity f o r Shallow Footing Placed on o r

Near a Slope

.

7 .

2-135

Bearing Capacity F a c t o r s f o r Shallow Footing Placed on o r

Near a Slope

.

7 .

2-136

Ultimate Bearing Capacity of Two Layer Cohesive S o i l (@PO)

...

7. 2-137

Examples of Computation of Allowable Bearing C a p a c i t y Shallow

(13)

Figure T i t l e Page CHAPTER 4 (continued)

Examples of Computation of Allowable Bearing Capacity Shallow

Footings on Granular S o i l s

...

7. 2-140 Allowable Bearing P r e s s u r e f o r Sand from S t a t i c Cone

P e n e t r a t i o n T e s t s

...

7. 2-147

...

Example of Proportioning Footing S i z e t o Equalize Settlements 7. 2-148 Computation of Shear. Moment. and Deflection. B e r m s on

E l a s t i c Foundation

...

7. 2-153 Functions f o r Shear. Moment. and Deflection. Beams on Elastic

'Foundations

...

7. 2-154 Functions f o r Shear. Moment. and Deflections.

Mats

on Elastic

...

Foundations 7. 2-157

Limits of Compaction Beneath Square and Continuous Footings

...

7. 2-160

...

Construction Details f o r Swelling S o i l s 7. 2-162

...

Typical Foundation Drainage and Waterproofing 7. 2-167

...

Capacity of Anchor Rods i n Fractured Rock 7. 2-170

Resistance of Footings and Anchorages t o Combined T r a n s i e n t

...

Loads 7. 2-171

...

Tower Guy Anchorage i n S o i l by Concrete Deadman 7. 2-172

CHAPTER 5

...

Load

Carrying Capacity of Single P i l e i n Granular S o i l s 7. 2-193 U l t i m a t e h a d Capacity of S i n g l e P i l e o r P i e r i n Cohesive

...

S o i l s 7. 2-196

Bearing Capacity of P i l e Groups i n Cohesive S o i l s

...A

2-206 Settlement of P i l e Groups

...

7. 2-210 P r i n c i p l e s of Operation of P i l e Drivers

...

7. 2-222 I n t e r p r e t a t i o n of P i l e

Load

Test

...

7. 2-229 h a d Test Analysis Where Downdrag A c t s on P i l e s

...

7. 2-231 Example Problem

-

Batter P i l e Group a s Guy Anchorage

...

-7. 2-233 C o e f f i c i e n t of Variation of Subgrade Reaction

...

7. 2-236 Design Procedure f o r L a t e r a l l y Loaded P i l e s

...

7. 2-237 Influence Values f o r P i l e with Applied L a t e r a l

Load

and

Moment (Case I

.

F l e x i b l e Cap o r Hinged End Condition)

...

7. 2-238 Influence Values f o r L a t e r a l l y U a d e d P i l e (Case I1

.

Fixed

Against R o t a t i o n a t Ground Surface)

...

7. 2-239 Slope C o e f f i c i e n t f o r P i l e with L a t e r a l

Load

o r Moment

...

7. 2-240

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Table

TABLES

Title

Page

CHAPTER

1

Factors Controlling Stability of Sloped Cut in Some

...

Problem Soils

7 . 2-3

...

2

Factors Controlling Excavation Stability

7.2-4

...

3

OSHA Requirements (Minimum) for Trench Shoring

7.2-8

4

Types of Walls

...7. 2-14 5

Factors Involved in Choice of a Support System For a Deep

...

Excavation

(> 20

feet)

7 . 2-16

...

6 Design Considerations for Braced and Tieback Walls

7 . 2-17

7

Methods of Groundwater Control

...

7 . 2-28

CHAPTER

2

1

Typical Properties of Compacted Soils

...

...7.

2-39 2

Relative Desirability of Soils as Compacted Fill

...

7.

2-40

...

3

Clay Dispersion Potential

7 . 2-44

...

4

Compaction Requirements

..7. 2-46

5

Compaction Equipment and Methods

...

7.2-48 6

Methods of Fill Placement Underwater

...

7 . 2-55

CHAPTER

3

1

Friction Factors and Adhesion for Dissimilar Materials

...

7 . 2-63

CHAPTER

4

1

Presumptive Values of Allowable Bearing Pressure for Spread

Foundations

...

7 . 2-142 2

Selection of Allowable Bearing Pressures for Spread

Foundations

...

7 . 2-144 3

Definitions and Procedures. Analysis of Beams on Elastic

Foundation

...

7 . 2-151 4

Definitions and Procedures. Mats on Elastic Foundations

...

7 . 2-155 5

Requirements for Foundation Waterproofing and Dampproofing

...

7.2-164

CHAPTER

5

1

Design Criteria for Bearing Piles

...7. 2-179 2

Characteristics of Common ExcavatedIDrilled Foundations

...

7 . 2-184 3

Design Parameters for Side Friction for Drilled Piers in

...

Cohesive Soils

7 . 2-198

(15)

Table T i t l e Page CHAPTEK

5

( c o n t i n u e d )

5 T y p i c a l Values of C o e f f i c i e n t Cp f o r E s t i m a t i n g S e t t l e m e n t

of a S i n g l e P i l e ...7. 2-208

6

General C r i t e r i a f o r I n s t a l l a t i o n of P i l e Foundations

...

7. 2-214 7 Supplementary Procedures and Appurtenances Used i n P i l e

Driving

...

7.2-218 8 Impact and V i b r a t o r y P i l e - D r i v e r Data

...

7. 2-219

...

9 Treatment of F i e l d Problems Encountered During P i l e D r i v i n g 7. 2-226 10 D r i l l e d P i e r s : C o n s t r u c t i o n Problems.

...

7. 2-227

(16)

ACKNOWLEDGEMENTS

Figure or Table

Acknowledgement

Figure 13,

Chapter 1 Figure

1,

Chapter 2 Figures 5, 6

&

7, Chapter 3

Figure 16

&

17

Chapter 3 Figures 23, 24

&

25, Chapter 3

Figure 36,

Chapter 3 Figures 10

&

11, Chapter 4

Figure 14,

Chapter 4 Figw-e 2,

C1'

3cl8.i?r

5

( d.;p f

panel

,

rignt)

Mazurkiewicz, D.K., Design and Construction of Dry Docks,

Trans Tech Publications, Rockport,

MA.,

1980.

Sherard, J.L., Influence of Soil Properties and

Construction Methods on the Performance of Homogeneous

Earth Dams, Technical Memorandum 645, U.S. Department of

~~~~~ -

the Interior, Bureau of Reclamation.

Caquot, A., and Kerisel, J., Tables for the Calculation of

Passive Pressure, Active Pressure and Bearing Capacity of

Foundations, Gauthier-Villars, Paris.

Terzaghi, K. and Peck, R.B., Soil Mechanics in Engineering

Practice, John Wiley

&

Sons, Inc., New York,

NY.

U.S. Steel, Sheet Piling Design Manual, July, 1975.

Portland Cement Association, Concrete Crib Retaining

Walls, Concrete Information No. St. 46, Chicago, IL., May,

1952.

Hetenyi, M., Beams on Elastic Foundation, The University

of Michigan Press, Ann Arbor, MI.

Parcher, J.V., and Means, R.E., Soil Mechanics and

Foundations, Charles E. Merril Publishing Company,

Columbus, OH., 1968.

Skempton, A.W., The Bearing Capacity of Clays,

(17)

(18)

CHAPTER

1.

EXCAVATIONS

S e c t i o n 1. INTRODUCTION

1.

SCOPE. This c h a p t e r c o v e r s t h e methods of e v a l u a t i n g t h e s t a b i l i t y of shallow and deep excavations. There a r e two b a s i c types of e x c a v a t i o n s : ( a ) "open excavations" where s t a b i l i t y

i s

achieved by providing s t a b l e s i d e

s l o p e s , and (b) "braced excavations" where v e r t i c a l o r sloped s i d e s a r e main- t a i n e d w i t h p r o t e c t i v e s t r u c t u r a l systems t h a t can be r e s t r a i n e d l a t e r a l l y by i n t e r n a l o r e x t e r n a l s t r u c t u r a l elements. Guidance on performance m o n i t o r i n g i s given i n DM-7.1, Chapter 2.

2.

METHODOLOGY. I n s e l e c t i n g and d e s i g n i n g t h e e x c a v a t i o n system, t h e p r i - mary c o n t r o l l i n g f a c t o r s

w i l l

i n c l u d e : ( a ) s o i l type and s o i l s t r e n g t h parameters; ( b ) groundwater c o n d i t i o n s ; ( c ) s l o p e p r o t e c t i o n ; (d) s i d e and bottom s t a b i l i t y ; and ( e ) v e r t i c a l and l a t e r a l movements of a d j a c e n t a r e a s , and e f f e c t s on e x i s t i n g s t r u c t u r e s .

3 .

RELATED CRITERIA. For a d d i t i o n a l c r i t e r i a on e x c a v a t i o n s , s e e t h e f o l - lowing source :

Subject Source

Dewatering and Groundwater Control of Deep Excavations....NAVFAC P-418

S e c t i o n 2. OPEN CUTS

1.

SLOPED CUTS.

a. General. The depth and slope of an excavation, and groundwater con- d i t i o n s c o n t r o l t h e o v e r a l l s t a b i l i t y and movements of open e x c a v a t i o n s . I n g r a n u l a r s o i l s , i n s t a b i l i t y u s u a l l y does n o t extend s i g n i f i c a n t l y below t h e excavation provided seepage f o r c e s a r e c o n t r o l l e d . I n rock, s t a b i l i t y i s c o n t r o l l e d by d e p t h s and s l o p e s of excavation, p a r t i c u l a r j o i n t p a t t e r n s , i n

s i t u s t r e s s e s , and groundwater c o n d i t i o n s . I n cohesive s o i l s , i n s t a b i l i t y t y p i c a l l y i n v o l v e s s i d e s l o p e s b u t may a l s o i n c l u d e m a t e r i a l s w e l l below t h e base of t h e excavation. I n s t a b i l i t y below t h e base of e x c a v a t i o n , o f t e n r e f e r r e d t o as bottom heave, i s a f f e c t e d by s o i l type and s t r e n g t h , d e p t h of c u t , s i d e s l o p e and/or berm geometry, groundwater c o n d i t i o n s , and construc- t i o h procedures. Methods f o r c o n t r o l l i n g bottom heave a r e given i n DM-7.1, Chapter

6.

b. Evaluation. Methods described i n DM-7.1, Chapter 7 may be used t o e v a l u a t e t h e s t a b i l i t y of open excavations i n s o i l s where behavior of s u c h s o i l s can be reasonably determined by f i e l d i n v e s t i g a t i o n , l a b o r a t o r y test- i n g , and a n a l y s i s . I n c e r t a i n geologic formations ( s t i f f c l a y s , s h a l e s , s e n s i t i v e c l a y s , c l a y t i l l s , e t c . ) s t a b i l i t y i s c o n t r o l l e d by c o n s t r u c t i o n procedures, s i d e e f f e c t s during and a f t e r excavation, and i n h e r e n t g e o l o g i c p l a n e s of weaknesses. Table 1 (modified from Reference

1,

E f f e c t s of Con- s t r u c t i o n

on

Geotechnical Engineering, by Clough and Davidson) p r e s e n t s a

(19)

summary of t h e primary f a c t o r s c o n t r o l l i n g e x c a v a t i o n s l o p e s i n some problem s o i l s . Table 2 (modified from R e f e r e n c e 1 and R e f e r e n c e 2, S o i l s and

Geology, Procedures f o r Foundation Design of B u i l d i n g s and O t h e r S t r u c t u r e s , Departments of Army and A i r F o r c e ) summarizes measures t h a t c a n be used f o r e x c a v a t i o n p r o t e c t i o n f o r b o t h c o n v e n t i o n a l and problem s o i l s .

2. VERTICAL CUTS. Many c u t s i n c l a y s w i l l s t a n d w i t h v e r t i c a l s l o p e s f o r a p e r i o d of time b e f o r e f a i l u r e o c c u r s . However, changes i n t h e s h e a r s t r e n g t h o f t h e c l a y w i t h time and s t r e s s r e l e a s e r e s u l t i n g from t h e e x c a v a t i o n c a n l e a d t o p r o g r e s s i v e d e t e r i o r a t i o n i n s t a b i l i t y . T h i s p r o c e s s c a n be r a p i d i n s t i f f , h i g h l y f i s s u r e d c l a y s , b u t r e l a t i v e l y slow i n s o f t e r c l a y s . ( S e e DM-7.1, Chapter 7 f o r c r i t i c a l h e i g h t s f o r v e r t i c a l c u t s i n c o h e s i v e s o i l s . ) For c u t s i n hard unweathered r o c k , s t a b i l i t y i s m o s t l y c o n t r o l l e d by s t r e n g t h a l o n g bedding p l a n e s , groundwater c o n d i t i o n , and o t h e r f a c t o r s ( s e e DM-7.1,

Chapter 6 and Reference 3 , S t a b i l i t y of S t e e p S l o p e s on Hard Unweathered ~ o c k , by Terzaghi f o r d e t a i l e d d i s c u s s i o n on t h e e f f e c t s of r o c k d i s c o n t i n u i t i e s ) . Cuts i n rock can s t a n d v e r t i c a l w i t h o u t b o l t i n g o r a n c h o r i n g depending on r o c k q u a l i t y and j o i n t p a t t e r n .

S e c t i o n 3 . TRENCHING

1. SITE EXPLORATION. I n d i v i d u a l t r e n c h i n g p r o j e c t s f r e q u e n t l y e x t e n d o v e r l o n g d i s t a n c e s . A n e x p l o r a t i o n program should be performed t o d e f i n e t h e s o i l and groundwater c o n d i t i o n s over t h e f u l l e x t e n t of t h e p r o j e c t , so t h a t t h e d e s i g n of t h e s h o r i n g system can be a d j u s t e d t o s a t i s f y t h e v a r y i n g s i t e con- d i t i o n s .

2. TRENCH STABILITY. P r i n c i p a l f a c t o r s i n f l u e n c i n g t r e n c h s t a b i l i t y a r e t h e l a t e r a l e a r t h p r e s s u r e s on t h e w a l l s u p p o r t system, bottom heave, and t h e p r e s s u r e and e r o s i v e e f f e c t s of i n f i l t r a t i n g groundwater ( s e e Chapter 3 and DM-7.1, Chapter 6 ) . E x t e r n a l f a c t o r s which i n f l u e n c e t r e n c h s t a b i l i t y i n c l u d e :

a. S u r f a c e Surcharge. The a p p l i c a t i o n of any a d d i t i o n a l l o a d between t h e edge of t h e e x c a v a t i o n and t h e i n t e r s e c t i o n of t h e ground s u r f a c e w i t h t h e p o s s i b l e f a i l u r e p l a n e must be c o n s i d e r e d i n t h e s t a b i i i t y a n a l y s e s f o r t h e e x c a v a t i o n .

b. V i b r a t i o n Loads. The e f f e c t s of v i b r a t i n g machinery, b l a s t i n g o r o t h e r dynamic l o a d s i n t h e v i c i n i t y of t h e e x c a v a t i o n must be c o n s i d e r e d . The e f f e c t s of v i b r a t i o n s a r e cumu1ati;e o v e r p e r i o d s of t i m e and c a n be p a r t i c u - l a r l y dangerous i n b r i t t l e m a t e r i a l s such a s c l a y e y sand o r g r a v e l .

c . Groundwater Seepage. Improperly dewatered t r e n c h e s i n g r a n u l a r s o i l s c a n r e s u l t i n q u i c k c o n d i t i o n s and a complete l o s s of s o i l s t r e n g t h o r bottom heave. (See DM-7.1, Chapter 6.)

d. S u r f a c e Water Flow. T h i s c a n r e s u l t i n i n c r e a s e d l o a d s on t h e w a l l

s u p p o r t system and r e d u c t i o n of t h e s h e a r s t r e n g t h of t h e s o i l . S i t e d r a i n a g e should be d e s i g n e d t o d i v e r t water away from t r e n c h e s .

(20)

TABLE 1

Factors C o n t r o l l i n g S t a b i l i t y of Sloped Cut i n Some Problem S o i l s

i

SOIL TYPE PRIMARY CONSIDERATIONS FOR SLOPE DESIGN

2

S t i f f - f i s s u r e d Clays and Shales

F i e l d s h e a r r e s i s t a n c e may be l e s s t h a n s u g g e s t e d by l a b o r a t o r y tests. Slope f a i l u r e s may occur p r o g r e s -

s i v e l y and s h e a r s t r e n g t h s reduced t o r e s i d u a l v a l u e s compatible w i t h r e l a t i v e l y l a r g e deformations. Some c a s e h i s t o r i e s s u g g e s t t h a t t h e long-term performance i s c o n t r o l l e d by t h e r e s i d u a l f r i c t i o n a n g l e which f o r some s h a l e s may b e a s low a s 12'. The most r e l i a b l e d e s i g n procedure would i n v o l v e t h e u s e of l o c a l e x p e r i e n c e and recorded o b s e r v a t i o n s .

Loess and Other C o l l a p s i b l e S o i l s

Strong p o t e n t i a l f o r c o l l a p s e and e r o s i o n of r e l a t i v e - l y d r y m a t e r i a l upon wetting. Slopes i n l o e s s a r e f r e q u e n t l y more s t a b l e when c u t v e r t i c a l t o p r e v e n t i n f i l t r a t i o n . Benches a t i n t e r v a l s can be used t o reduce e f f e c t i v e s l o p e angles. E v a l u a t e p o t e n t i a l f o r c o l l a p s e a s d e s c r i b e d i n DM 7.1, Chapter 1. ( S e e DM-7.3, Chapter 3 f o r f u r t h e r guidance.)

Residual S o i l s _{S i g n i f i c a n t l o c a l v a r i a t i o n s i n p r o p e r t i e s can be} expected depending on t h e w a t h e r i n g p r o f i l e from p a r e n t rock. Guidance based on recorded o b s e r v a t i o n provides prudent b a s i s f o r design.

S e n s i t i v e Clays Considerable l o s s of s t r e n g t h upon remolding g e n e r a t e d by n a t u r a l o r man-made d i s t u r b a n c e . Use a n a l y s e s based on unconsolidated undrained tests o r f i e l d vane

t e s t s .

T a l u s Talus i s c h a r a c t e r i z e d by l o o s e a g g r e g a t i o n of r o c k t h a t accumulates a t t h e f o o t of rock c l i f f s . S t a b l e s l o p e s a r e commonly between 1-114 t o 1-314 h o r i z o n t a l t o 1 v e r t i c a l . I n s t a b i l i t y i s a s s o c i a t e d w i t h abun- dance of w a t e r , mostly when snow i s melting.

Loose Sands May s e t t l e under b l a s t i n g v i b r a t i o n , o r l i q u i f y ,

s e t t l e , and l o s e s t r e n g t h i f s a t u r a t e d . Also prone t o e r o s i o n and piping.

(21)

TABLE 2 F a c t o r s C o n t r o l l i n g E x c a v a t i o n S t a b i l i t y 4 Comments I n v e s t i g a t e s o i l c o m p r e s s i b i l i t y and e f f e c t of d e w a t e r i n g on s e t t l e m e n t of n e a r b y s t r u c t u r e s ; c o n s i d e r r e c h a r g i n g o r s l u r r y w a l l c u t o f f . Examine f o r p r e s e n c e of lower a q u i f e r and need t o dewater. I n s t a l l piezometer i f needed. Consider e f f e c t s of d e w a t e r i n g i n c a v i t y - l a d e n l i m e s t o n e . Dewater i n advance of e x c a v a t i o n . Analyze s a f e s l o p e s ( s e e DM-7.1, Chapter 7 ) o r b r a c i n g r e q u i r e m e n t ( s e e Chapter 3 ) , e f f e c t s of s t r e s s r e d u c t i o n on over- c o n s o l i d a t e d , s o f t o r s w e l l i n g s o i l s and s h a l e s

.

Consider hor i z o n t a 1 and v e r t i- c a l movements i n a d j a c e n t a r e a s due t o e x c a v a t i o n and e f f e c t on n e a r b y s t r u c - t u r e s . Keep equipment and s t o c k p i l e s a s a f e d i s t a n c e from t o p of e x c a v a t i o n . See Chapter 3 f o r w a l l d e s i g n . Reduce e a r t h movements and b r a c i n g s t r e s s e s , where n e c e s s a r y , by i n s t a l l i n g l a g g i n g on f r o n t f l a n g e of s o l d i e r p i l e . Con- s i d e r e f f e c t of v i b r a t i o n s due t o d r i v - i n g s h e e t p i l e s o r s o l d i e r p i l e s . Con- s i d e r d e w a t e r i n g r e q u i r e m e n t s a s w e l l a s w a l l s t a b i l i t y i n c a l c u l a t i n g s h e e t i n g depth. Movement m o n i t o r i n g may be w a r r a n t e d .

C o n s t r u c t i o n A c t i v i t y

Dewatering

Excavation and Grading

Excavation Wall C o n s t r u c t i o n > O b j e c t i v e s To p r e v e n t b o i l i n g , s o f t e n i n g , o r heave i n e x c a v a t i o n bottom, r e d u c e l a t e r a l p r e s s u r e s on s h e e t i n g , r e d u c e seepage pres- s u r e s on f a c e of open c u t , e l i m i n a t e p i p i n g of f i n e s t h r o u g h s h e e t i n g . Pipe t r e n c h i n g , basement e x c a v a t i o n , s i t e g r a d i n g . To s u p p o r t v e r t i c a l e x c a v a t i o n w a l l s , t o s t a b i l i z e t r e n c h i n g i n l i m i t e d space.

(22)

TABLE 2 (continued) Factors C o n t r o l l i n g Excavation S t a b i l i t y Construction A c t i v i t y B l a s t i n g Anchor o r S t r u t I n s t a l l a - t i o n , Wedging of S t r u t s , P r e - s t r e s s i n g T i e s Objectives To remove o r t o f a c i l i t a t e t h e removal of rock i n the excava- t i o n . To o b t a i n support system s t i f f n e s s and i n t e r a c t i o n . -- - Comments Consider e f f e c t of v i b r a t i o n s on s e t t l e - ment o r damage t o a d j a c e n t a r e a s . Design and monitor o r r e q u i r e t h e c o n t r a c t o r t o design and monitor b l a s t i n g i n c r i t i c a l a r e a s ; r e q u i r e a pre-construction survey of nearby s t r u c t u r e s .

Major excavations r e q u i r e c a r e f u l i n s t a l - l a t i o n and monitoring, e.g., c a s e anchor h o l e s i n c o l l a p s i b l e s o i l s ; measure

(23)

3. SUPPORT SYSTEMS. Excavation s u p p o r t systems commonly used a r e a s f o l - lows :

-

a. Trench S h i e l d . A r i g i d p r e f a b r i c a t e d s t e e l u n i t used i n l i e u o f s h o r i n g , which e x t e n d s from t h e bottom of t h e e x c a v a t i o n t o w i t h i n a few f e e t of t h e t o p of t h e c u t . P i p e s a r e l a i d w i t h i n t h e s h i e l d , which i s p u l l e d ahead, a s t r e n c h i n g p r o c e e d s , a s i l l u s t r a t e d i n F i g u r e 1 (from R e f e r e n c e

4 ,

Cave-In! by P e t e r s e n ) . T y p i c a l l y , t h i s system

i s

u s e f u l i n l o o s e g r a n u l a r o r s o f t c o h e s i v e s o i l s where e x c a v a t i o n d e p t h d o e s n o t exceed 1 2 f e e t . S p e c i a l s h i e l d s have been used t o d e p t h s of 3 0 f e e t .

b. Trench Timber Shoring. Table 3 i l l u s t r a t e s t h e Occup&tional S a f e t y and H e a l t h A c t ' s minimum r e q u i r e m e n t s f o r t r e n c h s h o r i n g . B r a c e s and s h o r i n g of t r e n c h a r e c a r r i e d a l o n g w i t h t h e e x c a v a t i o n . . Braces and d i a g o n a l s h o r e s o f timber should n o t be s u b j e c t e d t o compressive s t r e s s e s i n e x c e s s o f :

where : L = unsupported l e n g t h ( i n c h e s )

D = l e a s t s i d e of t h e timber ( i n c h e s )

S = a l l o w a b l e compressive s t r e s s i n pounds p e r s q u a r e i n c h of c r o s s s e c t i o n

Maximum R a t i o

LID

= 50

( 1 ) S k e l e t o n Shoring. Used i n s o i l s where c a v e - i n s a r e e x p e c t e d . A p p l i c a b l e t o most s o i l s t o d e p t h up t o 20 f e e t . See F i g u r e 2 (from Refer- e n c e 4 ) f o r i l l u s t r a t i o n and guidance f o r s k e l e t o n s h o r i n g . S t r u c t u r a l com- p o n e n t s should be d e s i g n e d t o s a f e l y w i t h s t a n d e a r t h p r e s s u r e s .

( 2 ) Close ( T i g h t ) S h e e t i n g . Used i n g r a n u l a r o r o t h e r r u n n i n g s o i l s , compared t o s k e l e t o n s h o r i n g , i t i s a p p l i c a b l e t o g r e a t e r d e p t h s . S e e i l l u s t r a t i o n i n F i g u r e 3 (from R e f e r e n c e 4 ) .

( 3 ) Box Shoring. A p p l i c a b l e t o t r e n c h i n g i n any s o i l . Depth l i m i t -

ed by s t r u c t u r a l s t r e n g t h and s i z e of timber. U s u a l l y l i m i t e d t o 4 0 f e e t . See i l l u s t r a t i o n i n F i g u r e 4 (from R e f e r e n c e 4 ) .

( 4 ) T e l e s c o p i c Shoring. Used f o r e x c e s s i v e l y deep t r e n c h e s . See i l l u s t r a t i o n i n F i g u r e 5 (Reference 4).

c. S t e e l S h e e t i n g and Bracing. S t e e l s h e e t i n g and b r a c i n g c a n be u s e d i n l i e u of t i m b e r s h o r i n g . S t r u c t u r a l members should s a f e l y w i t h s t a n d water

and l a t e r a l e a r t h S t e e l s h e e t i n g w i t h t i m b e r w a l e s and s t r u t s h a v e a l s o been used.

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(25)

TABLE 3

C6HA Requirents (Minjmum) hr Trench Sbring

Trench jacks may be

used

i n

lieu

of, or i n canbination d t h , cross braces.

Where desirable, steel s k t piling a d bracirg of equal strength may be substituted for mod.

J Depth of Trench Feet 5 to 10 11 t o 15 v Maxinnm Spacing Vertical Feet 4 4 4 4

4

4 4 a d Spacirg of Menbers cross &aces1 Ibri- zontal Feet 6 6 6 6 6 6 6 6 Kid or Condition of Earth Hard, canpact Likely to crack Soft, s d y , or filled Hydrostatic pressure Hard Likely to crack Soft

,

s a d y o r f illed Hydrostatic pressure 1 3 t o 1 5 feet Incks 6 x 8 6 x 8 8 x 8 8 x 8 8 x 8 8 x 8 8 x 1 0 8 x 1 0 Size Trench l o t 0 1 2 feet Inches 6 x 5 6 x 6 6 x 8 6 x 8 6 x 8 6 x 8 8 x 8 8 x 8 Upto 3 feet I n c k s 2 x 6 2 x 6 4 x 4 4 x 4 4 x 4 4 x 4 4 x 6 4 x 6 Stringers Minimun Dimension Inches

...

4 x 6 4 x 6 6 x 8 4 x 6 4

x

6 4 x 6 8 x 10 Uprights f i i m u n Dimmion Inches 3x4 or 2x6 3x4 or 2x6

3x4

or 2xfj 3x4 o r 2x6 3x4 or 2x6 3x4 or 2x6

3x4

or 2x6 3x6 Maxhuu Spacing Feet

...

4 4 4 4 4 4 4 MPcirmm Spcing Feet 6 3 Close sktirlg Close sheeting 4 2 Close s k t i n g Close sheeting 4 t o 6 feet Inches 4 x 4 4 x 4 4 x 6 4 x 6 4 x 6 4 x 6 6 x 6 6 x 6 Width of 7 t o 9 feet I n c k s 4 x 6 4 x 6 6 x 6 6 x 6 6 x 6 6 x 6 6 x 8 6 x 8

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(27)

R e q u i r e m e n t s f o r S k e l e t o n S h o r i n g

NOlES:

CLOSE: Close u p r i g h t s up t i g h t . c-c: Center-to-Center

( a ) Minimum: Two s t r i n g e r s , one on top and one on bottom. ( b ) Minimum: Two s t r u t s t o 7' depth and t h r e e t o 10'.

( c ) Minimum: Three s t r i n g e r s , placed top, bottom and center. ( d ) Minimum: Three s t r u t s t o 13' depth and four t o 15'.

FIGURE

2 S k e l e t o n S h o r i n g 7.2-10

-

TRENCH

Width Up t o 42" Over 42" Up t o 42" Up t o 42" Ikpth 4' t o 10' 4' t o 10' 10' t o 15' Over 15'

UPRIGHTS

Size 2" x 6" 2" x 6" 2" x 6" 2" x 6" b r i z o n t a l SPC~% 3'

cc

3' c-c 3' c-c ( X E E

s-Size 2"

x

6"

4"

x 6"

2"

x 6" 4 " x 1 2 "

s m

Vert id S p a c i s (a) 4' c-c ( c ) 4 ' c c Size 2"x61'(b) 4" x 6"(b) 2" x 6"(d) 4 " x 1 2 " b r i z o n t a l S p a c i s 6 ' c - c 6' c c 6'

crc

6' c c

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Requirements f o r C l o s e S h e e t i n g

N(7IES:

-

CLOSE: Close uprights up t i g h t . c-c: C e n t e r - t o a n t e r

( a ) Minimum: Two s t r i n g e r s , one on top and one on bottom. ( b ) Minimum: Two s t r u t s t o

7'

depth and t h r e e t o

10'.

( c ) Minimum: Three s t r i n g e r s , placed top, bottom and center. ( d ) Minimum: Three s t r u t s t o

13'

depth and four t o

15'.

FIGURE

3 C l o s e ( T i g h t ) S h e e t i n g SIRUrS Size

4"

x

6"

4"

x

6"

/ 7

V x 6 "

4"x12"

sTmmRs r mENQI Ibrinmtal

s@%

6'

c-c

6'

cc

6'

c c

6'

e c

size

4"x6"

V x 6 '

4 " x 6 "

4"x12"

mGI.rJs Width

-

Up t o

42"

O\Rr

42"

Up

t o

42"

Up to

42"

Vertical s@% (a) (a) (b)

4'-

Size

2" x

6"

2"

x 6"

2" x

6"

2" x 6"

Depth

4'

t o

10'

4'

t o

10'

t o

15'

Over

15'

Ibrizuntal s@% UDSE UDSE U X 3 3 UDSE

(29)

FIGURE 4

Box Shoring

FIGURE

5

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Section 4. BRACED EXCAVATIONS

1. WALL TYPES. Commonly used wall types and l i m i t a t i o n s t o be c o n s i d e r e d i n s e l e c t i o n a r e given i n Table 4. Schematics of support systems a r e shoyn on Figure 6. A d e s c r i p t i o n of w a l l types l i s t e d i n Table

4 i s

presented

i n

Reference

5,

L a t e r a l Support Systems and Underpinning, by Goldberg, e t al.

2.

SELECTION OF SUPPORT SYSTEM. F a c t o r s t o be considered i n s e l e c t i n g types of support systems a r e given i n Table 5.

3. EARTH PRESSURES. The

t m

l i m i t i n g pressures which may

act

on the w a l l , _{a r e t h e s t a t e s of a c t i v e pressure and passive pressure.} _{D e f i n i t i o n s and}

methods f o r computing e a r t h pressures a r e presented i n Chapter 3.

For most p r a c t i c a l c a s e s , c r i t e r i a f o r e a r t h p r e s s u r e s do not e x a c t l y conform t o t h e s t a t e of a c t i v e , passive o r a t

rest

pressure. Actual e a r t h p r e s s u r e depends on

w a l l

deformation and t h i s i n t u r n depends on s e v e r a l f a c t o r s . Among t h e p r i n c i p a l f a c t o r s a r e : (1) s t i f f n e s s of

w a l l

and support systems; (2) s t a b i l i t y of t h e excavation; and (3) depth of excavation and w a l l

d e f l e c t i o n .

The e f f e c t s of w a l l d e f l e c t i o n on p r e s s u r e d i s t r i b u t i o n , and d i f f e r e n c e s between s t r u t l o a d s computed from a c t i v e e a r t h pressure theory and those a c t u a l - l y measured f o r deep excavation i n s o f t c l a y , a r e i l l u s t r a t e d i n Reference 6 , s t a b i l i t y of ~ l e x i b l e S t r u c t u r e s by

Bjerrum,

e t a l . A s many d i f f e r e n t v a r i a - b l e s a f f e c t p r e s s u r e s a c t i n g on w a l l s , many types of a n a l y s e s a r e a v a i l a b l e f o r s p e c i a l s i t u a t i o n s . ( D e t a i l s concerning t h e s e a r e given i n Reference 7, Braced Excavation by Lambe.) Examples of e a r t h p r e s s u r e computations

are

given i n Chapter 3.

4. OTHER DESIGN AND CONSTRUCTION CONSIDERATIONS. Several f a c t o r s o t h e r t h a n e a r t h p r e s s u r e s a f f e c t t h e s e l e c t i o n , d e s i g n and t h e performance of braced excavations. See Table 6 f o r a summary of t h e s e f a c t o r s .

5.

LATERAL

MOVEMENTS. For

w e l l

constructed s t r u t t e d excavations i n d e n s e sands and till, maximum l a t e r a l w a l l movements a r e o f t e n

less

than 0.2% of excavation depth. L a t e r a l movements a r e u s u a l l y less f o r t i e d back

w a l l s .

I n s t i f f f i s s u r e d c l a y s , l a t e r a l movements may reach 0.5% o r higher depending on q u a l i t y of c o n s t r u c t i o n . In s o f t c l a y s , a major p o r t i o n of movement o c c u r s below excavation bottom. L a t e r a l movement may be i n t h e range of 0.5% t o

2%

of excavation depth, depending on the f a c t o r of s a f e t y a g a i n s t b o t t a n i n s t a - b i l i t y . Higher movements a r e a s s o c i a t e d w i t h

lesser

f a c t o r s of s a f e t y .

6. SOIL SETTLEMENTS BEHIND WALLS. , Reference

8,

Deep Excavations and Tunnel- i n g i n S o f t Ground by Peck, provides guidance based on e m p i r i c a l o b s e r v a t i o n of s e t t l e m e n t behind wall. Settlements up t o about

1%

of t h e e x c a v a t i o n d e p t h have been measured behind

w e l l

c o n s t r u c t e d

w a l l s

f o r c u t s i n sand and

i n

medi-

um

s t i f f c l a y s . In s o f t e r c l a y s , t h i s may be a s high a s

2%

and c o n s i d e r a b l y

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TABLE 4 Types of Walls N a m e ( 1 ) S t e e l S h e e t i n g ( 2 ) S o l d i e r P i l e and Lagging ( 3 ) Cas t-in-place o r Pre-cast Con- c r e t e S l u r r y Wall (diaphragm w a l l s , s e e

DM-

7.3, Chapter 3 ) ( 4 ) Cylinder P i l e Wall T y p i c a l E I Values P e r Foot ( k s f ) 900

-

90,000 2,000

-

120,000 288,000

-

2,300,000 115,000

-

1,000,000 Comments

-

Can be impervious

-

Easy t o h a n d l e and c o n s t r u c t

-

Easy t o h a n d l e and c o n s t r u c t

-

P e r m i t s d r a i n a g e

-

Can be d r i v e n o r a u g e r e d

-

Can be impervious

-

R e l a t i v e l y h i g h s t i f f n e s s

-

Can be p a r t of permanent s t r u c t u r e

-

Can be p r e s t r e s s e d

-

R e l a t i v e l y less l a t e r a l w a l l movement pe mi t t ed compared t o ( 1 ) and ( 2 )

-

High i n i t i a l c o s t

-

S p e c i a l t y c o n t r a c t o r r e q u i r e d t o c o n s t r u c t

-

_{Very l a r g e and heavy}_{w a l l}

must be used f o r deep systems

-

P e r m i t s y i e l d i n g of sub- s o i l s , b u t p r e c a s t c o n c r e t e u s u a l l y shows l e s s y i e l d i n g t h a n s t e e l s h e e t i n g o r s o l d i e r p i l e procedures.

-

Secant p i l e s impervious

-

R e l a t i v e l y h i g h s t i f f n e s s

-

Highly s p e c i a l i z e d equipment n o t needed f o r t a n g e n t p i l e s

-

S l u r r y n o t needed

(32)

A. CANTILEVER WALL B. CROSS-LOT BRACED WALL

F;DUNDATION SLAB

C. RAKER SYSTEM D. ANCHOR OR TIEBKK WALL

E.

EARTH

BERM

SUPPORT

FIGURE 6