Engineering properties of the Gila Conglomerate at Bagdad,Arizona

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Authors Jacobsen, Wayne Lee, 1943-

Publisher The University of Arizona.

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ENGINEERING PROPERTIES OF THE GILA CONGLOMERATE

AT BAGDAD, ARIZONA

by

W ayne Lee Jacobsen

A T hesis Subm itted to the F acu lty of the

DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING

In P a rtia l Fu lfillm ent of the Requirem ents For the D egree of

MASTER OF SCIENCEWITH A MAJOR IN GEOLOGICAL ENGINEERING

In the G raduate C ollege

THE UNIVERSITY OF ARIZONA

1 9 7 6

STATEMENT BY AUTHOR

This th e s is has been subm itted in p a rtia l fu lfillm ent of re ­quirem ents for an advanced degree a t The U n iversity o f Arizona and is d e p o sited in the U n iversity Library to be made ava ilab le to borrow ers under rule s of the L ib rary .

Brief quo ta tions from th is th e s is are allow able w ithout sp e c ia l p e rm iss io n , provided th a t accu ra te acknow ledgm ent of source is m ade. R equests for perm ission for ex tended quo tation from or rep roduction of th is m anuscrip t in whole or in p art may be gran ted by the head of the m ajor departm ent or the D ean of the G raduate C ollege when in h is ju d g ­ment the proposed u se of the m ateria l is in the in te re s ts of sc h o la r­sh ip . In a ll o ther in s ta n c e s , how ever, perm ission m ust be ob tained from the a u th o r .

SIGNED:7 = ±

APPROVAL BY THESIS DIRECTOR

This th e s is has b een approved on the date show n below :

RICHARD D . CALL DateL ecturer in M ining and G eo log ica l E ngineering

ACKNOWLEDGMENTS

The author is indeb ted to the C yprus Bagdad C opper C orporation

for providing fin an c ia l a s s is ta n c e and u se of mine personnel and f a c i l ­

i t i e s . A ppreciation is ex tended to M e ss rs . P . K. M edhi, R. J . B onn is,

and T . Vaughn for th e ir cooperation and in te re s t in th is p ro je c t. C o lle c ­

tio n and p ro cess in g of da ta would not.have been p o ss ib le w ithout the

continued help of mine p e rso n n e l, e sp e c ia lly M e ss rs . D . H ernandez ,

R. D elgado , and J . D avis and M iss L . Simmerman. Acknowledgm ent is

a ls o made of the a s s is ta n c e of M r. P . V isca of P incock , A llen & H o lt,

I n c . , T ucson , A rizona, who fu rn ished the m odified com puter program

u sed in th is s tu d y .

The au thor w ishes to ex p re ss h is s in cere ap p rec ia tio n to D r.

Richard D . C a ll , th e s is a d v iso r , for h is g u id an ce , p a tie n c e , and advice

throughout th is s tu d y . D rs . W illiam C . Peters and C harles E. G la s s ,

members of the th e s is com m ittee, a ls o offered gu idance and extrem ely

u se fu l su g g e s tio n s .

Hi

TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS........................................................................................ v l

LIST OF TABLES.............................................................................................................. v iii

ABSTRACT.............................................................................. lx

INTRODUCTION ........................................................................................................ 1

P u rp o se ................................................................................................................. 1Study A re a ........................................................................................................... 2

GEOLOGY.................................................................................................................... 4

G ila C onglom erate . . . . . . .Geology of the Bagdad Mine

S tra tig ra p h y ......................G ila Conglom erate a t Bagdad

ENGINEERING PROPERTIES................................................................. 12

Sample S ite L o c a t io n s ..................................................................................’ 12G rain S ize D is tr ib u tio n .................................................................................. 14U nit W eight and Void R a t i o ........................................................... 19Rock Substance S tre n g th ..................................... 19

U niax ia l C om pression T e s t in g ......................................................... 19T riax ia lC o m p ress io n T e s t in g ............................................................ 21In Situ D irec t Shear T e s tin g ............................................................... 22Laboratory D irec t Shear T e s t in g ...................................................... 27

R e s u l ts ................................................................................................................. 37

BACK ANALYSIS............... 41

S tab ility S e c t i o n s ..................................................................... •.................... 41Theory o f Back A n a ly s i s ............................................................................... 41Procedures for Back A n a ly s is ..................................................................... 48R e s u l ts .................................................. 49

COMPARISON OF ENGINEERING PROPERTIES............................................... S3

P h y sica l P roperties and S tren g th .................................. 53Rock Substance S trength and Rock M ass S tre n g th ............................. 56Engineering C la s s i f ic a t io n s ........................................................... 60

iv

tO hx O

)

V

TABLE OF CONTENTS— Continued

Page

CONCLUSIONS.............................................................................. ........................... 62

APPENDIX A: GRAIN SIZE DISTRIBUTION GRAPHS AND DATA................ 64

APPENDIX B: LABORATORY SHEAR-DISPLACEMENT GRAPHS . ................ 83

REFERENCES. . ........................................................................... ............................ 100

LIST OF ILLUSTRATIONS

Figure Page

1. L ocation map for study a r e a ................................. ... ......................... 3

. 2 . D istribu tion o f rocks c a lle d G ila C o n g lo m e ra te ................... 5

3 . S tra tig raph ic re la tio n sh ip s for the Bagdad m in e ................. 8

4 . R epresen tative G ila Conglom erate l i t h o lo g y ............... 10

5 . L ocation map for sam ple s i te s and back a n a ly s is se c tio n s . 13

6. G radation curves for a l l G ila Conglom erate specim ens . . . 15

7 . T ertiary c la s s if ic a tio n o f G ila C o n g lo m era te ....................... 17

8 . Mohr envelopes for sm a ll-g ra in ed tr ia x ia l s a m p le s ........... 23

9 . Mohr envelopes for m edium -grained tr ia x ia l sam ples . . . . 24

10. Mohr envelopes for la rg e -g ra in ed tr ia x ia l s a m p le s .......... 25

11. In s itu d irec t sh e a r specim en ready for t e s t i n g .................. 28

12. In s itu d irec t sh e a r te s t r e s u l t s ................................................ 29

13. Laboratory d irec t sh e a r t e s t r e s u l ts , s ite 1 ................................. 32

14. Laboratory d irec t sh e a r t e s t r e s u l ts , s ite 3 ................................ 33

15 . Laboratory d irec t sh ea r t e s t r e s u l ts , s ite 4 (upper),s ite 2 ( lo w e r ) ..................................................................................... 34

16. Laboratory d irec t sh e a r t e s t r e s u l t s , s ite 7 .......................... 35

17. S trength v a lu es for a l l rock t e s t i n g ......................................... 38

18. P illa r S lid e , looking e a s t ............................................................ 42

19. Slope profile for rad ia l se c tio n 8 ................................................... 43

20 . Slope profile for rad ia l se c tio n 1 1 ................................................... 44

21 . Slope profile for rad ia l se c tio n 1 5 ..................... 45

vi

vii

LIST OF ILLUSTRATIONS--C ontinued

Figure Page

22 . Region of rock m ass stren g th determ ined from backa n a ly s is ........................................... 50

23. R elationsh ip of G ila Conglom erate rock m ass streng thwith pub lished streng th v a l u e s .................................................. 51

24 . R elationship betw een rock su b s tan ce s treng th v a lu esand back a n a l y s i s ........................................................................... 57

25. R elationship betw een the average rock su b stan cestren g th and back a n a ly s i s ............................................................ 58

26 . C la s s if ic a tio n of G ila C onglom erate according tothe P iteau sy s te m ............................................................................... 61

LIST OF TABLES

Table Page

1 . U nified Soil C la s s if ic a tio n for G ila Conglom eratesam ple s i t e s ........................................................................................ 18

2 . Summary o f u n it w eight and void ra tio r e s u l t s ......................... 20

3 . Summary of u n iax ia l com pression te s t r e s u l t s ........................... 21

4 . Summary o f tr ia x ia l te s t r e s u l t s .............................................. 26

5 . Summary o f d irec t sh ea r te s t r e s u l t s ............................................ 36

6 . Summary of rock te s tin g r e s u l t s ...................................................... 39

7 . Rock s treng th param eters u se d in back a n a ly s is ........................ 49

8 . Sources o f sh ea r streng th da ta p lo tted in Figure 2 3 ................. 52

9 . R esult of re g re ss io n a n a ly s is o f p h y s ic a l p ro p e r t ie s ............. 55

viii

ABSTRACT

The G ila Conglom erate a t Bagdad, A rizona, is an unusua l e n g i­

neering m ateria l b ecau se it has the tex tu re of a so il and the s treng th of

a ro ck . To e s tim a te i ts b eh av io r, the eng ineering p roperties of g rain

s iz e d is tr ib u tio n , un it w e ig h t, void ra t io , m oisture co n te n t, and rock

stren g th were m easu red . The rock su b s tan ce streng th w as determ ined

by com pression and d irec t sh e a r te s t in g . Shear s treng th param eters th a t

b e s t approxim ate the rock m ass streng th determ ined from b ack a n a ly sis

were found to be peak cohesion and re s id u a l fric tio n angle v a lu es d e ­

rived from laboratory d irec t sh e a r te s tin g o f sa tu ra ted sa m p le s . Based

on stren g th p ro p e rtie s , th e G ila Conglom erate is c la s s if ie d betw een a

very s tif f so il and a very so ft ro ck .

A co rre la tion betw een eng ineering p roperties w as made to e s t i ­

mate sh e a r streng th beyond the te s t s i t e s . The re s u lts in d ica ted th a t

peak co h esio n is a function o f g ra in s iz e d is tr ib u tio n , un it w e igh t, and

m oisture c o n te n t, in th a t order of im portance . R esidual fric tio n ang le is

a function o f g ra in s iz e d is tr ib u tio n , m oisture c o n te n t, and un it w eigh t.

These re la tio n sh ip s are not ex c lu siv e b ecau se o ther eng ineering p roper­

t ie s not m easured in th is study a lso a ffe c t the sh ear streng th of the

G ila C ong lom erate .

ix

INTRODUCTION

The term "G ila C onglom erate" is app lied to the poorly so rted

conglom erates of approxim ate C enozoic age th a t occur in many p a rts of

A rizona. W hen encoun tered in mining opera tions th is rock type forms a

w aste u n it or "capping" over o re . In o p en -p it m ines th is w aste m ateria l

m ust be s trip p ed back to expose the o r e . The amount of w aste th a t m ust

be s tripped w ill depend in p art on the eng ineering p roperties of the G ila

C onglom erate . Engineering p roperties of G ila Conglom erate have not

been w ell defined in prev ious geo log ic s tu d ie s . C urrently av a ilab le d e ­

s ig n charts do not g ive adequa te d e s ig n param eters b ecau se the G ila has

the tex tu re o f a so il and the stren g th p roperties of a ro ck .

Purpose

This th e s is d e sc rib e s the eng ineering p roperties of the G ila

Conglom erate a t Bagdad, A rizona, where it crops out a s p a rt of an o p e n -

p it s lo p e . The eng ineering p roperties in v es tig a te d are (1) g ra in s ize

d is tr ib u tio n , (2) u n it w eight and void ra tio , and (3) rock s tre n g th . Only

grain s ize d is tr ib u tio n and un it w eight were chosen to d e sc rib e the rock

te x tu re . C om pressive stren g th and sh e a r streng th .were m easured to d e ­

term ine sh ea r s treng th param eters for o p e n -p it slope d e s ig n . Rock

streng th re su lts from th is study should be app licab le to o ther a reas

where sim ila r ty p es of conglom erates are p re s e n t . This study rep re se n ts

a portion of a slope d esig n p ro jec t for the Cyprus Bagdad C opper Com­

pany .

1

Study Area

The study area for th is th e s is is the Cyprus Bagdad Copper

C om pany's o p e n -p it mine in Y avapai C ounty, A rizona, about 60 m iles

w est o f P re sc o tt. The p it is lo ca ted on the edge of the Basin and Range

province a t the sou thw estern end of the Eureka mining d is tr ic t (Fig. 1).

J

3

112°

ARIZC

Study ■ Area • P resco tt

Phoenix

• Tucson

I-----------1----------------------------150 0 100 m iles

Figure 1 . L ocation map for study area

GEOLOGY

G ila Conglom erate

The name "G ila C onglom erate" was f irs t app lied by G ilbert in

1875 to P le is to cen e a llu v ia l d e p o s its in four s tru c tu ra l b a s in s a long the

G ila River in Arizona and New M ex ico . G ilbert d esc rib ed a l l four lo c a l­

i t ie s a s con ta in ing poorly so rted g rave ls of loca l o rig in cem ented by

c a lca reo u s m ateria l and in terbedded w ith coheren t sa n d , t r a s s , b a s a l t ,

and tu ffaceous m a te ria l. Maximum stra tig rap h ic th ic k n e ss o f th ese u n its

is 1 ,500 fe e t .

Over a broader a re a , o ther a llu v ia l d ep o sits are describ ed as

G ila(?) conglom erate on the b a s is o f tex tu ra l and lith o lo g ic s im ila ritie s

and in some p lac es on the b a s is o f co n tin u ity . At p re sen t the G ila and

G ila(?) term s are app lied to a llu v ia l d e p o s its in a t le a s t s ix m ajor s tru c ­

tu ra l and topograph ica l b a s in s covering a 300-sq u are m iles a rea (H eindl,

1962). A nderson, S ch o lz , and Strobe 11 (1955) p ro v is io n a lly nam ed the

conglom erates a t Bagdad as G ila (?) cong lom era te , and Schrader (1915)

app lied the term to sim ila r ty p es of conglom erates a s far sou th as

N o g a les , Arizona (Fig. 2).

H eindl (1962) sum m arized a llu v ia l d ep o sits th a t have e sc a p e d

the G ila name a s :

1. H olocene d ep o sits th a t are c lea rly in a s ta te of ag g rad a tio n .

2 . L ess recen t d e p o s its th a t are c le a rly younger th an the h ig h es t

e ro s io n a l s u r fa c e .

4

5

112°

ARIZ ONA N EW M E X IC O

Bagdad Studv An

Phoenix •"

S afford S ilver C ity

Tucso

E xplanation

a ■Area of O rig inal Area in which G ila term or

D efin ition G ila(?) conglom erate has. b een u sed

M odified & l i n d n r 9 « T lO nO fr0° kS CaUed G lla ^ " g l o m e r a t e -

6

3 . A lluvial d e p o s its o lder th an b a s in f ill th a t are c lea rly re la te d

to v o lcan ic rocks o lder th an b a s in f ill or th a t are in marked a n ­

gu lar unconform ity w ith b a s in f i l l .

In sum m arizing the Ce no zo ic h is to ry of A rizona, H eindl rev iew ed

G ilb e rt 's (1875) type lo c a lit ie s for G ila Conglom erate and recom m ended

th a t the form ational name "G ila" be ra ise d to group s ta tu s (which was

done in 1963) for the follow ing rea so n s :

1. G ila d e p o sits are in sep a ra te topographic b a s in s th a t have d e ­

veloped in sep a ra te though perhaps re la te d s tru c tu ra l b a s in s .

2 . No d irec t con tinu ity a c ro ss or through the m ountains can be

dem onstra ted for the d e p o s i ts .

3 . The d ep o sits for w hich the G ila name w as o rig in a lly app lied

are not a sing le hom ogeneous u n it .

From the foregoing d isc u ss io n it becom es apparen t th a t the

G ila and G ila(?) nam es are p re sen tly u se d to d esc rib e poorly so rted and

w e ll-c o n so lid a ted a llu v ia l g rave ls o f lo ca l o rig in th a t were d e p o sited in

s tru c tu ra l b a s in s during ea rly C enozoic tim e . These d e p o sits are com­

mon throughout sou thw este rn and so u th e as te rn A rizona.

G eology of the Bagdad Mine

The only com prehensive geo log ic study o f the Bagdad a rea was

conducted by A nderson, S ch o lz , and Strobe 11 (1955). Their report covered

38 square m iles and included m ost of the m ineralized a reas periphera l to

the Bagdad s to c k . Anderson e t a l . (1955, p . 6) sum m arized the sequence

of geo log ic e v e n ts .

7

M ost of the rocks exposed in the Bagdad area make up a m eta­m orphosed p re-C am brian com plex o f v o lcan ic ro c k s , tu ffaceous ro c k s , and sedim entary and a s so c ia te d in truded igneous rocks o f d iverse com position . After considerab le e ro s io n , th is p re - Cam brian com plex was covered by rhyo lite tu ff and in truded by a s so c ia te d rhyolite d ik es of la te C re taceous o r e a rly T ertiary a g e . Later s tocks of quartz m onzonite and a s so c ia te d d ikes were em p laced . After e ro s ion carved a surface of considerab le re lie f upon th e se ro c k s , lava flows and v o lcan ic cones damned the p rin c ip a l s tre a m s , cau sin g d ep o sitio n of g rave ls and sand in the main tribu tary can y o n s. This s tag e in the geo log ic h is ­tory culm inated in the outpouring o f w idespread b a s a lt f lo w s, carved into lava m esas by the la te s t in te rval of e ro s io n .

S tra tig raphy

The m ajor rock types in the Bagdad p it are: (1) quartz mon­

z o n ite , (2) G ila(?) cong lom era te , (3) rhyolite tu ff, and (4) Sanders

B a sa lt. The stra tig rap h ic re la tio n sh ip betw een th e se u n its is shown in

Figure 3 .

The quartz m onzonite is the h o s t rock for most of the copper

m inera liza tion a t Bagdad. This rock crops out a s a se r ie s of p lugs and

s tocks trending N . 70° E . th a t have in truded the Pre Cambrian com plex

during Late C re taceous or ea rly T ertiary t im e . After considerab le e ro sio n

of the quartz m onzonite, the G ila(?) conglom erate was d e p o s ite d .

At B agdad, the G ila(?) conglom erate was p ro v is io n a lly named

by Anderson e t a l . (1955) b ecau se of the g en era l s im ila rity in litho logy

to the G ila conglom erate f ir s t d e sc rib ed by G ilb ert. In the Bagdad p it

the G ila is a v a lle y - f i l l d e p o s it ranging in th ic k n ess from 5 to 700 f e e t .

A white rhyolite tu ff bed overlying the G ila is 29 to 50 fee t

th ic k . This n early ho rizon ta l un it is com posed o f pum ice la p illi and a sh

th a t have been la rge ly a lte red to c la y . The tuff is poorly s tra tif ie d and

has a red color a t the c o n ta c t w ith the overly ing b a s a l t .

it Sanders B asa lthyolite Tuff

G ila C onglom erate

•PreCambrian G ran ites S A and S c h is ts /y v P it Floor

Q uartz M onzonite

Figure 3 . S tra tig raph ic re la tio n sh ip s for the Bagdad mine

9

A pproxim ately 120 fee t of Sanders B asalt covers the m esas to

the w e s t, no rth , and n o rth east beyond the study a re a . C oarse v e s ic le s

and c a lc i te - f i l le d am ygdules are common in upper flow la y e rs .

G ila Conglom erate a t Bagdad

G ila Conglom erate forms m oderately dipping a llu v ia l s lo p e s in

the m esa w alls surrounding the Bagdad p i t . In Boulder C reek to the

n o rth w est, the G ila forms v e rtic a l canyon w alls where cu t by stream

e ro s io n . G ila Conglom erate com prises 50 p ercen t of the 45-d eg ree

slop ing p it w alls in the p i t . It re s ts unconform ably above igneous rocks

of PreCambrian and T ertiary a g e . Diamond d rill hole m apping has in d i­

ca ted a 700-foo t th ic k n ess for th is u n i t . An an c ien t stream channel in

which G ila d ep o sitio n occurred trends no rthw esterly through the p it to

Boulder C reek .

B edding-plane a ttitu d e s are d ifficu lt to m easure b ecau se of the

coarse nature of the cong lom era te . In genera l the bedding is h o rizo n ta l,

a s in d ica ted by the f la t- ly in g in te rbeds o f rh y o litic tu ff near the top of

the G ila s e c tio n . G ila Conglom erate exposed in the p it w alls can be

roughly d iv ided in to th ree poorly defined se c tio n s th a t overlap and grade

into each o ther (Fig. 4 ).

The low er u n it com posed of poorly so rte d , w ell-rounded cobb les

and boulders is 10 to 40 fe e t th ic k and is poorly co n so lid a ted and poorly

cem en ted . Pre Cambrian g ran ites and s c h is ts and T ertiary quartz m on-

zo n ites are the predom inant fragm en ts . C arbonaceous m ateria l is p resen t

in the a n c ien t stream channel a t the north side of the p i t .

10

Figure 4. Representative Gila Conglomerate lithology

11

The middle G ila se c tio n is com posed of poorly so rte d , rounded

to subrounded sands and g rav e ls and is approxim ately 450 fe e t th ic k .

This se c tio n is w ell co n so lid a ted and m oderately cem en ted . PreCambrian

g ran ites and s c h is ts are the predom inant frag m en ts .

The upper se c tio n is approxim ately 200 fe e t th ick and is d i s ­

tin g u ish ed from the middle se c tio n by in te rbeds of rhyo litic tu ff . M ost

of the conglom erate in th is se c tio n is poorly so rte d , subrounded to su b -

angu lar sa n d s , g ra v e ls , and s i l ts th a t a re w ell co n so lid a ted and w ell

cem en ted . G ravels where p re sen t are com posed of Pre Cambrian g ran ites

and s c h i s t s . On the b a s is of a fo s s i l cam el jaw bone found a t the 3 ,4 2 0 -

foot e le v a tio n , th is se c tio n of the G ila is being te n ta tiv e ly a ss ig n e d a

P liocene a g e .

ENGINEERING PROPERTIES

Engineering p roperties for slope d esig n work are the m easurab le

p roperties th a t in d ica te or p red ic t how the conglom erate w ill respond to

loads im posed by m ining. The p roperties in v es tig a te d in th is study were

g ra in -s iz e d is tr ib u tio n , un it w eigh t, void r a t io , and rock s tre n g th .

G ra in -s iz e d is trib u tio n was determ ined from sieve a n a ly s is to

iden tify specim en variance be tw een sam ple s ite s and to compare rock

s treng th te s t r e s u l ts . U nit w eight and rock s treng th are input param eters

for slope s ta b il i ty c a lc u la t io n s . The un it w eight and slope geom etry d e ­

term ine the body fo rces ac tin g on a s lo p e . The s ta b il i t ie s of G ila C on ­

glom erate s lo p es were e s tim a te d by u sin g the sh ea r s treng th p a ram ete rs ,

cohesion and fric tio n a n g le , derived from rock s treng th te s t in g .

Sample S ite lo c a tio n s

Sample s ite lo ca tio n s are show n on Figure 5 . S ites for sam ples

for laboratory d irec t sh e a r te s t s were s e le c te d on the b a s is of a c c e s s i ­

b ility and proxim ity to d e s ig n se c tio n s u se d in mine p lann ing and on

th e ir being rep re se n ta tiv e of the im m ediate litho log ic u n it. Specim ens

were ex cav a ted by a trac to r backhoe equipped w ith a ripper to o th . A

hand p ick w as u sed to trim the specim ens to b locks 20 x 20 x 18 in c h e s ,

which were th en se a le d in parafin to p reven t m oisture l o s s .

N X -diam eter (2 inches) core sam ples for com pression te s tin g

were ob ta ined from DDH 5 -7 4 , which w as a developm ent d rill h o le .

12

O o Oo

MILL

OLaboratory D irec t Shear

□In Situ

D irect Shear

VT riaxial

DDH 5-74

8/ 11, 15

Back A nalysis S ections

0 800 ft

Figure 5 . L ocation map for sam ple s i te s and back a n a ly s is se c tio n s

CO

14

Starting a t the 3 , 532-foo t e le v a tio n , 28 specim ens a t le a s t 5 inches long

were chosen from 27 fee t of c o re . Prior to te s tin g the specim ens were

v isu a lly c la s s if ie d into th ree groups of sim ila r litho log ic ch arac te r:

sm a ll-g ra in ed sam ples conta in ing fragm ents sm aller th an 1 /4 inch;

m edium -grained sam ples con ta in ing fragm ents up to 3 /4 in ch es; and

la rg e -g ra in ed sam ples con ta in ing fragm ent s iz e s up to 1 1 /2 in c h e s . All

specim ens were w rapped in p la s tic to p reven t m oisture l o s s . In s itu

d irec t sh e a r specim ens were te s te d on the 3590 lev e l where su ffic ien t

opera ting room was av a ilab le for s ite p reparation and te s tin g w ith the

large equipm ent.

G rain S ize D istribu tion

Sieve a n a ly s is was perform ed on a ll specim ens te s te d for rock

s tre n g th . The sam ples were d is in te g ra te d with w ater an d , if n e c e s sa ry ,

w eak hydrochloric a c id . After wet s iev in g to remove the -200 m esh

m ate ria l, the rem ainder of the specim en was dried and s iev ed through

s ie v e s of the follow ing s iz e s : 1 , 3 /4 , and 1 /2 inch and # 4 , # 10 , # 2 0 ,

# 4 0 , # 7 0 , #100 , and #200 .

The average g rada tion curve for 63 specim ens o f G ila Conglom­

era te is show n in Figure 6. In g en era l the conglom erate is w e ll-g rad ed

and con ta ins 29% g rave l (reta ined on the #4 s ie v e ) , 53% sand (betw een

#4 and #200 s ie v e s ) , and 18% fines (passing the #100 s ie v e ) . The p e r­

cen tage of g ra v e l-s iz e p a rtic le s ranges from 3 to 74 , the percen tage of

s a n d -s iz e p a rtic le s ranges from 18 to 85, and the percen tage of fines

ranges betw een 3 and 61. These ranges are to be expec ted b ecause of

15

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h-

1 70-5> 6 0 -mcc^ 50-

z 40-uiu£ 3 0 -O l

2 0 -

10-

S I L TC L A Y

S A N D G R A V E LFINE MEDIUM | COARSE FINE COARSE

SIEVE , SIZE 2 30 100 40 2 0 10 4 1/2" 1"

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PARTICLE DIAMETER (MM)

— — —— Average g rada tion for 63 sam ples

/ / / / / / Sample range

CD i

Lim its for 1 standard d ev ia tio n

Figure 6 . G radation curves for a ll G ila Conglom erate s p e d -

16

the v a ria b ility in the m ateria l over short d is ta n c e s . G radation curves for

sam ple s i te s are g iven in Appendix A.

Figure 7b show s 63 specim ens of G ila Conglom erated p lo tted on

a te r tia ry c la s s if ic a tio n c h a r t . The th ree end members were chosen as

% g rav e l, % sa n d , and % fines as defined above. Figure 7a show s the

m eans for each sam ple s i t e . T riax ial sam ples th a t were f ie ld c la s s if ie d

a s medium grained do not show a s ig n if ic an t d ifference from sam ples

c la s s if ie d as large g ra in ed . The in s itu d irec t sh e a r specim ens co n ­

ta in ed the g re a te s t g rain s ize v a r ia tio n s .

The U nified Soil C la s s if ic a tio n system is a standard method of

iden tify ing so ils and c la s ify in g them in to ca teg o ries or groups th a t have

sim ila r eng ineering p ro p e rtie s . This sy stem is b a sed on the s iz e of p a r­

t i c l e s , the am ounts of the various s iz e s , and the c h a ra c te r is tic s of the

very fine g ra in s . The advantage o f th is system is th a t a so il can be

read ily c la s s if ie d by fie ld o r labora to ry exam ination by a system th a t is

understood by en g in eers engaged in ea rth w ork.

Table 1 d e sc rib e s each sam ple s ite accord ing to the U nified

Soil C la s s if ic a tio n . The c rite r ia for th is c la s s if ic a tio n were the lab o ra ­

to ry g ra in -s iz e curve and a f ie ld crush ing t e s t for the f in e s . In g e n e ra l,

the conglom erates fa ll into two g ro u p s . One group is s i l ty sands th a t

are m oderately to w ell cem en ted . The second group is w e ll-g rad ed

sandy g rave ls th a t are m oderately to poorly cem en ted . All specim ens

are b ia sed tow ard the sm aller s iz e frac tio n s (< 6 inches) b ecau se of the

d ifficu lty in ob tain ing in ta c t specim ens with la rg e -s iz e frag m en ts . If the

larger s iz e cobb les and boulders are considered in the U nified Soil C la s ­

s if ic a tio n , the s o il name would be prefixed by the term "g ra v e lly ."

17

G ravel

G ravel

Sand

Laboratory D irec t Shear

IDSIn Situ D irec t Shear

S (sm all), M (medium), L (large)T riax ia l

a . M eans for sam ple s i te s

Sand

Laboratory D irec t Shear

50 . In Situ D irec t Shear

▼T riax ial

b . All sam ples

Figure 7 . T ertiary c la s s if ic a tio n o f G ila C onglom erate

Table 1 . U nified Soil C la s s if ic a tio n for G ila Conglom erate sam ple s i te s

SampleSite

GroupSymbol % G ravel % Sand % Fines

C em entation(field)

C om paction(field)

In Situ M oisture

1 SM 28 60 12 w ell w ell

to2 SM 10 72 18 poor poor 9

3 SM 9 66 25 m oderate w ell 7

4 GW -GM 51 40 9 w ell m oderate 5

7 SM 13 61 26 m oderate w ell 10

IDS SM 29 53 18 m oderate m oderate

TX SM 11 67 22 w ell w ell ND

TX GW -GM 49 41 10 m oderate m oderate ND

TX GW -GM 51 39 10 m oderate m oderate ND

1. ND = not determ ined

19

U nit W eight and Void Ratio

U nit w eights and void ra tio s were determ ined for 29 add itiona l

G ila Conglom erate specim ens from laboratory d irec t sh ea r s i te s 1 , 2 , 3 ,

4 , and 7 . Prior to te s t in g , a ll specim ens were a ir dried for 48 h o u rs .

The day -tim e a ir tem perature w as 90°F and the re la tiv e hum idity was

le s s than 20 p e rc e n t. After recording the in it ia l w e ig h t, the specim en

w as se a le d in p a ra ffin and the volume determ ined by the d isp la c e d -w a te r

m ethod. Void ra tio w as c a lc u la te d u sin g a sp e c if ic g rav ity of 2 .7 d e te r­

mined from pycnom eter t e s t s . Table 2 show s the d irec t sh ear sam ple

s i te s ranked in order o f d ec rea s in g un it w e ig h ts . The h ig h es t un it w eight

is found a t s ite 4 follow ed by s i te s 7 , 3 , 1, and 2 .

Rock S ubstance Strength

A specim en of rock th a t forms the in ta c t m ateria l be tw een s tru c ­

tu ra l d isc o n tin u itie s , such as f a u l t s , jo in t s , and bedding p la n e s , is d e ­

fined as the rock su b s ta n c e . The rock m ass is the in s itu rock m ateria l

con ta in ing the d is c o n tin u itie s . Rarely c an the rock m ass be te s te d due

to the s iz e lim ita tion of te s tin g m ach in es . T esting o f the rock su b s tan ce

is commonly done by labora to ry and fie ld m ethods. The te s tin g m ethods

u sed in th is study were u n iax ia l and tr ia x ia l com pression and laboratory

and in s itu d irec t sh e a r .

U niax ia l C om pression T esting

U niax ia l com pressive s tren g th s of seven NX core sam ples of

G ila Conglom erate were determ ined by load ing cy lin d rica l specim ens to

failu re in a S o ilte s t com pression m achine u sing a loading ra te of 1 ,000

p s i/m in . B ecause of the d e tr ita l nature of the cong lom era te , specim en

20

Table 2 . Summary o f u n it w eight and void ra tio re su lts

Assum ed sp e c ific g rav ity = 2 .7 0 .

S ite N o. n M ean U nit W eight s M ean Void Ratio s

4 5 152 .4 lb / f t3 8 .6 8 0 .11 0 .0 6

7 6 139 .7 2 .6 6 .21 .02

• 3 6 137 .7 4 .8 4 .23 .05

1 6 135 .0 5 .5 9 .30 .12

2 6 127.5 4 .8 9 .33 .05

M ean 137 .5 5 .3 0 .2 4 0 .0 6

ends were f itted w ith su lfu r caps and ground p a ra lle l . The specim ens had

a len g th -to -d ia m e te r ra tio (L/D) of 2 . Specim ens te s te d dry were p laced

in an oven a t 125°F for 24 h o u rs . S a tu ra ted specim ens were subm erged

in w ater for 1 hour th en suspended over w ater in an en c lo sed bucket for

24 h o u rs . Based on the m oisture con ten t tak en a fte r te s t in g , it w as e s t i ­

m ated th a t the sam ples were 60 p e rcen t sa tu ra ted or g re a te r . Table 3

show s unconfined com pressive stren g th s for sa tu ra ted G ila specim ens

are low er th an th o se te s te d d ry .

C om pressive stren g th in c re a se s as g rain s ize in c re a s e s . The

in c rease in com pressive stren g th w ith g ra in s iz e ag rees with re su lts

found by Jain and G upta (1974) for unconfined com pression te s ts on

ea rth dam f i l l . The earth dam f ill con ta ined clod p a rtic le s from 3 /16 to

6 inches in s iz e . To avoid d is to rtio n s o f tr ia x ia l t e s t r e s u l ts , o th er

workers (Dvorak and P e te r, 1961) have su g g ested the maximum p a rtic le

21

Table 3 . Summary of u n iax ia l com pression te s t re su lts

Dry Satu rated

C om pressiveStrength

C om pressiveStrength

M oistureC ontent

Sm all g rained 222 p s i 296 p s i 39.18%

Medium grained 1 ,646 630 7 .9 8

Large grained 2 ,624 1,366 4 .5 1

s iz e in tr ia x ia l com pression te s t should not exceed 15 to 20 p ercen t of

the specim en d iam ete r. For a specim en of NX c o re , 2 in ch es in d iam ete r,

the m axim um -sized p a rtic le would be 1 /2 in ch . G ila specim ens c la s ­

s if ied as medium and large g rained con ta ined p a rtic le s up to 2 inches in

s i z e .

T riaxial C om pression T esting

T riax ial com pression was u se d to determ ine cohesion and f r ic ­

tio n angle under con tro lled drainage conditions and cond itions sim ulating

a la te ra l confining p re s s u re . R esu lts from u n iax ia l com pression te s tin g

were u se d for the tr ia x ia l com pression te s t with zero confining p re s su re .

Sam ples w ith a len g th -to -d ia m e te r ra tio o f 2 were f itted w ith

su lfu r caps on each end and th en ground p a ra l le l . At the cen te r o f e ac h

cap a 1 /4 - in c h -d ia m e te r hole w as bored through the cap to allow d ra in ­

age of pore w a te r. Sam ples te s te d dry were oven dried for 24 hours a t

125°F. S a tu ra ted sam ples were subm erged in w ater for 1 hour and th en

suspended over w ater in an e n c lo se d bucket for 24 h o u rs .

Each sam ple was ja c k e te d w ith a rubber sh rink tube membrane

th a t ex tended beyond the upper and low er p la ten s and then p laced in a

tr ia x ia l c e l l . The c e ll was f illed w ith hydrau lic flu id and the sam ple

te s te d by concurren tly in c reas in g the a x ia l and confining load un til a

p redeterm ined confin ing p ressu re w as e s ta b l is h e d . The a x ia l load was

continued a t a ra te of 1 ,000 p s i/m in u n til th e specim en fa i le d . After

te s t in g , a m oisture sam ple was tak en and the maximum ax ia l load r e ­

corded .

The re su lts for a group of specim ens are p lo tted a s a se r ie s of

Mohr c i r c le s . A lin e a r reg re ss io n of the a x ia l and confining s t r e s s e s is

f itted to the da ta p o in ts . The lin ea r co effic ien t slope (m) and in te rcep t

(b) were u sed to o b ta in a Mohr envelope by the follow ing re la tio n sh ip

T = c + n t a n ^

where c = b /2m and tanpf = (m - l ) /2 m .

R esu lts of th is a n a ly s is , show n in F igures 8 through 10, dem ­

o n stra te a lin ea r re la tio n sh ip in agreem ent w ith the Coulomb equation

for sh e a r s tre n g th . A summary o f the te s t re s u lts is g iven in Table 4 .

F ric tion ang les for sa tu ra ted specim ens were 65 p ercen t low er than th o se

for specim ens te s te d d ry . C ohesion ranges from 36 p s i for sm a ll-g ra in ed

specim ens to 397 p s i for m edium - and la rg e -g ra in ed sp e c im en s .

In Situ D irec t Shear T esting

To o b ta in sh ear streng th param eters for und istu rbed ro ck , in

s itu sh ea r te s ts on 12- in c h -sq u a re by 10-in c h -d e e p specim ens were

co n d u cted . Of the th ree p h y s ic a l t e s t m ethods u se d in s itu d irec t sh ea r

was the m ost expensive and d ifficu lt to perform . The n e c e ssa ry

22

She

ar S

tres

s (p

si)

• S

hear

Str

ess

(psi

)23

900-

300-

1500

Normal S tre ss (psi)

Satu rated60 0 -

3 0 0 -

900 1500Normal S tre ss (psi)

Figure 8. Mohr envelopes for small-grained triax ial samples

She

ar S

tres

s (p

si)

. S

hear

Str

ess

(psi

)24

1600-

4000Norm al S tre ss (psi)

S a tu rated

900-

300-

Normal S tre ss (psi)

Figure 9. Mohr envelopes for medium-grained triax ial samples

She

ar S

tres

s (p

si)

She

ar S

tres

s (p

si)

25

2400-

1600-

8 0 0 -

Normal S tre ss (psi)

Satu rated1200 -

8 0 0 -

Figure 10. Mohr envelopes for large-grained triaxial samples

26

Table 4 . Summary of tr ia x la l te s t re su lts

Dry S atu rated

C ohesionFric tion

Angle C ohesionF ric tion

Angle

AverageM oistureC ontent

Sm all g rained 36 p s i 36° 99 p s i I 70 29.75%Medium grained 374 40 206 35 7 .03Large grained 276 40 397 24 7 .0 0

equipm ent for th is te s t was fab rica ted a t the mine s i t e . Seven s i te s were

o rig ina lly p lanned ; how ever, problem s in d e sig n and lack of experienced

personnel reduced th is number to th re e .

T est b locks were iso la te d by d rilling 3-in c h -d ia m e te r ho les on

6-in ch cen te rs around the t e s t b lo c k . On two opposite s id e s of a t e s t

b lo ck , 3-in c h -d ia m e te r h o les were d rilled to a depth of 10 fee t to a c ­

commodate AQ (1 .4 - in c h diam eter) d rill ro d . The sam ple w as trimmed by

a hand p ick to the f in a l 11- in c h -sq u a re te s t s iz e and th en jac k e ted w ith

a th in gage s te e l m em brane. A 3- in c h concrete cap w as poured on top

and le v e le d . Shearing ja c k abutm ents were fab rica ted w ith 8-in c h I

beam s and when cem ented in p lace ex tended 18 inches beyond the s p e c i­

men w id th . All but the upper 3 fee t of the AQ d rill rods were fu lly g rou ted .

Two 5 0 -ton hydrau lic ja c k s f itted with h em ispherica l p la ten s

were u sed to apply a v e r tic a l norm al and a ho rizon ta l shearing fo rc e .

R esis tan ce to the norm al force was provided by a 5 /8 -in c h -d ia m e te r wire

rope cab le fa s ten ed to two AQ d rill ro d s . The shearing jac k was p laced

betw een the specim en and I beam a t a 3 -deg ree ang le to coun te rac t any

27

overturning m om ents. Prior to te s tin g the hydrau lic ja c k s were c a lib ra ted

on a com pression te s tin g m achine u sing a ca lib ra ted U .S . S tandard g ag e .

H orizontal and v e rtic a l d isp lacem en ts were m easured by d ia l gages lo ­

ca ted a t the cen te r line of the te s t specim en . A fin ished s ite ready for

te s tin g is shown in Figure 11.

A predeterm ined normal force was app lied and the in it ia l s e t t le ­

ment reco rd ed . A ho rizon tal shearing force was app lied a t an approxim ate

rate of 0 .5 inches per minute u n til the specim en fa ile d . The maximum

sh ea r load was recorded before attem pting to resum e the t e s t under a

h igher normal lo ad . At th is po in t the I beam s fa iled and the te s t was

h a lte d , thus only one shear-no rm al po in t was ob tained for each s i t e .

After te s tin g th ree sp e c im e n s , the shear and norm al s tre s s e s

were p lo tted on a graph and a Mohr envelope is ob ta ined by a le a s t

squares f i t of the da ta po in ts (Figure 12). The Coulomb equation for peak

shear streng th is

= 18 p s i + N tan 28°

Laboratory D irec t Shear T esting

Laboratory d irec t sh e a r te s tin g was conducted on 32 specim ens

of G ila Conglom erate from five s i t e s . The sh e a r te s tin g was done a t the

U n iversity of A rizona 's Rock M echanics Laboratory u s in g a W ykeham

Farrance sh ea r box with a 22 ,500 pounds ra ted c ap a c ity in both the nor­

mal and sh e a r d ire c tio n s . The shearing force for sam ples up to 11 .8

inches square is reg u la ted by a m otorized gear box w ith 42 ra te of speed

varying betw een 0 .240 to 0 .000005 inches per m in u te . The shearing

28

Figure 11. In situ direct shear specimen ready for testing

Pea

k S

hear

Str

ess

(psi

)

29

90—

30—

Peak Normal S tre ss (psi)-

Figure 12. In s itu d irec t sh e a r te s t re su lts

30

force is app lied from an e le c tr ic -d r iv e n screw ja c k , while the norm al

force is app lied from a hydrau lic ram .

Specim ens were prepared for te s tin g by saw ing a sam ple to a p ­

proxim ately 9 .5 in ch es square by 6 inches h igh . The sam ples were then

c a s t in an 1 1 .8 -in c h p la s te r of p a ris b lo ck . The p la s te r of pa ris was

mixed by a ra tio of 1 part p la s te r to 2 parts w a ter. The c a s t sam ples

were allow ed to cure overnight before cu tting a 1 /8 - in c h - th ic k sh ea r

line through the p la s te r c a s t and ju s t bare ly into the sam p le . The a rea

of the cu t was su b trac ted from the to ta l su rface a rea to determ ine the

area of the sh e a r p la n e . Sam ples te s te d under sa tu ra ted cond itions were

perfo ra ted w ith 1 /2 -in ch -d iam e te r ho les on 3 -in ch cen te rs and p laced in

50 -ga llon w ater drums for a period o f 60 d a y s . All o ther sam ples were

te s te d a t the in s itu m oisture c o n te n t.

T esting began by apply ing a norm al load to a predeterm ined

v a lu e . After in it ia l co n so lid a tio n a shearing force was app lied a t a sh ear

ra te of 0 .048 inches pe r m inu te . After a peak and re s id u a l s treng th had

b een ob tained the norm al load was in c re a sed and the te s t resum ed . This

procedure was rep ea ted u n til the d isp lacem en t c ap a c ity of the m achine

was reached (2 .4 in c h e s ) . At th is poin t the sh ear d irec tio n s were r e ­

v e rsed and the procedure rep ea ted under the sam e norm al loads u se d in

the forward d irec tio n . After te s tin g , the specim en was rem oved and a

m oisture sam ple was ta k e n . For sam ples te s te d under sa tu ra ted cond i­

t io n s , the sh ear box w as f illed w ith w ater prior to te s t in g .

The sh ear load and ho rizon ta l d isp lacem en t for each normal

force app lied were recorded on an XY reco rd er. The re su ltin g d is p la c e ­

m e n t-s tre s s curve show s a r ise in s tre s s with d isp lac em e n t, reach ing a

31

p e ak , then fa llin g off to a re s id u a l v a lu e . S evera l re s id u a l streng th

va lues are ob ta ined by varying the normal lo a d . The sh e a r and normal

loads were converted to sh ea r and normal s tre s s a fte r applying an area

co rrection fac to r determ ined by tak ing the c ro s s -s e c tio n a l a rea of the

specim en a t the ta i l end of the re s id u a l tra c e .

A curved fa ilu re su rface w as formed on 90 p e rcen t of the s p e c i­

mens . D epending on the o rien ta tio n of th is c u rv e , the bottom h a lf of the

sh ear sam ple is forced to ride up when d isp lac in g in the forward d ire c ­

tio n . This rid ing up in one d irec tio n and down in the opposite d irec tio n

g ives a h igher re s id u a l s tre s s lev e l in the forward d irec tion th an in the

reserve d ire c tio n . For th is rea so n the forward and rev e rse v a lu es were

averaged to compute the sh ear streng th p a ra m e te rs . The sh e a r d is p la c e ­

ment graphs for ind iv idual specim ens are g iven in Appendix B.

R esults from laboratory d irec t sh e a r te s tin g are p lo tted on a

sh ear s tre s s -v e rsu s -n o rm a l s tre s s g rap h . A le a s t squares f it of the peak

and re s id u a l s treng th da ta p o in ts g ives the re su lts shown in F igures 13-

16. In g e n e ra l, the da ta po in ts are in good agreem ent w ith the Coulomb

eq u a tio n . A summary of the re su lts show n in Table 5 ind ica te the d irec t

shear sam ple s i te s can be ranked in order of d ecreasin g peak cohesive

s tre n g th . The s tro n g e s t m ateria l was from s ite 1 follow ed by m ateria l

from s i te s 4 , 7 , 3 , 2 , and the in s itu d irec t sh ear s i t e . C ohesive

stren g th s for sa tu ra ted sam ples a re , on the a v e ra g e , 61 p ercen t low er

th an the peak co h esiv e s tren g th s for sam ples te s te d a t the in s itu m ois­

ture c o n ten t. F ric tion angle v a lu es are 2 degrees le s s fo r sa tu ra ted

sa m p le s . The stren g th of the sa tu ra ted sam ples can be ranked w ith the

s tro n g est a t s ite 1, fo llow ed by th a t a t s i te s 7 and 3 .

She

ar S

tres

s (p

sl).

S

hear

Str

ess

(psi

)

32

300-

R esidual

100 -

Normal s tr e s s (psi)a . In s itu m oisture

Peak

R esidual

100-

Normal S tre ss (psi)S atu rated

Figure 13. Laboratory direct shear te s t re su lts , site 1

She

ar S

tres

s (p

si)

She

ar S

tres

s (p

si)

3 00-

Peak

R esidual

Normal S tre ss (psi)

a . In s itu m oisture

Peak200 -

R esidual

100-

Normal S tre ss (psi)

b . S atu rated

Figure 14. Laboratory direct shear te s t re su lts , site 3

34

Peak

300-

R esidual

co 89

Normal S tre ss (psi)a . In s itu m oisture

Peak

R esidual

Normal S tre ss (psi)b . In s itu m oisture

Figure 15. Laboratory d irec t sh ea r te s t r e s u l t s , s ite 4 (upper), s ite 2 (lower)

She

ar S

tres

s (p

si)

She

ar S

tres

s (p

si)

P eak

R esidual

Normal S tress (psi)a . In s itu m oisture

Peak

100- R esidual

200 . 300Normal S tress (psi)

b . S a tu ra ted

Figure 16. Laboratory direct shear te s t re su lts , site 7

36

Table 5 . Summary of d irec t sh ear te s t re su lts

SiteN o.

M oistureC ontent

Peak R esidual

C ohesionFrictionAngle C ohesion

F ric tionAngle

In s itu M oisture

1 6.2% 9 3 .2 p s i 3 3 .0 ° - 4 .8 p s i 3 3 .4 °

4 4 .6 8 9 .0 4 2 .0 2 5 .9 3 3 .0

7 10.1 67 .1 55 .0 20 .9 3 2 .2

3 7 .0 4 3 .9 3 1 .4 1 .2 3 0 .5

2 9 .0 2 3 .8 33 .4 4 .2 30 .1

M ean 7 .4 6 3 .4 3 9 .0 9 .5 3 1 .8

s 2 .2 2 9 .6 9 .9 13 .2 1 .5

in situ d irec t sh ea r 17 .5 27 .9

Saturated

1 13.1 53 .1 30 .1 15 .9 3 1 .4

7 16 .8 4 3 .8 50 .9 1 4 .4 30 .1

3 10 .2 2 5 .6 35 .0 15 .8 29 .3

M ean 13 .4 4 0 .8 3 8 .7 15 .4 3 0 .3

s 3 .3 14 .0 10 .9 .8 1 .1

37

R esults

Figure 17 show s the re la tio n sh ip s betw een sh ear s treng th param ­

e te rs from tr ia x ia l and d irec t sh e a r te s t in g . A s ig n if ic an t d ifference o c ­

curs betw een sam ples having le s s th an 100 p s i co h esio n and sam ples

having more th an 200 p s i c o h es io n . The sam ples w ith more than 200 p s i

cohesion are tr ia x ia l sam ples c la s s if ie d a s medium and large g ra in ed .

Sm all-g rained tr ia x ia l sam ple v a lu es w ith cohesion le s s th an 100 p s i

c lu s te r around laboratory and in s itu d irec t shear v a lu e s .

A summary of the sh e a r stren g th param eters is show n in Table 6 .

R esidual fric tio n an g les for laboratory d irec t sh ea r sam ples have a m ean

va lu es of 31 deg rees with a standard dev ia tio n o f 1 d e g re e . The mean

peak fric tio n angle is 35 degrees w ith a standard d ev ia tio n o f 10 d e g re e s .

In co n tra s t to the sm all variance for re s id u a l fric tion a n g le s , the re s id u a l

cohesion va lu es show more d isp e rs io n . Laboratory d irec t sh e a r sam ples

(sam ples 1, 2 , 3 , 4 , 7) have a re s id u a l co h esio n of 12 p s i w ith a s ta n ­

dard dev ia tio n of 11 p s i . The m ean p eak cohesion value for a ll sam ples

is 123 p s i w ith a s tandard d ev ia tio n of 128 p s i . High com pressive

streng th v a lu es for m edium - and la rg e -g ra in ed tr ia x ia l specim ens are in ­

fluenced by the p resen ce of large p a rtic le s i z e s . The mean for peak

cohesion v a lu e s , exclud ing m edium - and la rg e -g ra in ed tr ia x ia l s a m p le s ,

is 54 p s i w ith a standard dev ia tio n of 29 p s i . For peak fric tio n angle

va lues the m ean is 36 deg rees w ith a standard d ev ia tio n of 11 d e g re e s .

The m ean and standard dev ia tio n for the p eak fric tio n angle are not s ig ­

n ifican tly d ifferen t from the mean of 35 degrees and standard dev ia tio n

of 10 deg rees for a ll s a m p le s , including m edium - and la rg e -g ra in ed t r i ­

ax ia l s a m p le s .

Coh

esio

n (p

si)

38

400-

F ric tion Angle (degrees)

• Laboratory d irec t sh ea r v a lu e s , p eak cohesion and re s id u a l fric tion angle

■ In s itu d irec t sh ear v a lu e s , p eak co h esio n and peak fric tio n angle

▼ T riax ial v a lu es , p eak cohesion and p eak fric tio n ang le ; L = la rg e - g ra in ed , M = m ed ium -gra ined , S = sm all-g ra in ed sam ples

Open sym bols are sa tu ra ted t e s t re s u lts

Figure 17. Strength values for all rock testing

39

Table 6 . Summary of rock te s tin g re su lts

M oisture Peak R esidual

SampleN o . C ondition

AverageC ontent C ohesion

Fric tionAngle C ohesion

Fric tionAngle

Laboratory D irect Shear

1 dry 6.2% 93 p s i 33° -5 p s i 33°sa tu ra ted 13.1 53 30 16 31

2 dry CD

O 24 33 4 303 dry 7 .0 44 31 1 31

sa tu ra ted 10 .2 26 35 16 294 dry

CD 89 42 26 33

7 dry 10.1 67 55 21 32sa tu ra ted 16 .8 44 51 14 30

In Situ D irec t Shear

IDS a ND 18 28

Triaxial*3

TX-SG dry 36 362 9 .8 99 17

TX-MG dry 374 407 .0 206 35

TX-LG dry 276 407 .0 397 24 .... .

M ean 123 35 12 31

s 128 10 11 1

M ean excludingTX-MG and TX-LG 54 36

s 29 11

a . Not determ ined

b . SG = sm all g ra ined ; MG = medium grained; LG = large g rained

40

Based on the findings p resen ted above for the G ila Conglom erate

sam p les , the follow ing co n c lu sio n s are p resen ted :

1. For tr ia x ia l te s t in g , m ost p a rtic le s iz e s larger th an 1 /2 inch

have a s ig n ific an t e ffec t on cohesive s tren th and a sm all e ffec t

on fric tio n a n g le .

2 . For d irec t sh ea r t e s t s , fric tio n angle v a lu es have le s s d isp e r­

sion th an co h esio n v a lu e s . The sm a lle s t d isp e rs io n is found in

re s id u a l fric tio n angle v a lu e s .

3 . Shear streng th param eters are genera lly low er for sam ples te s te d

sa tu ra ted th an for sam ples te s te d a t the in s itu m oisture c o n te n t.

BACK ANALYSIS

In the p revious se c tio n , te s tin g procedures and re su lts were

described for estim ating rock su b s tan ce s tren g th . Hoek (1970) su g g e s ts

th a t th ese te s tin g procedures do not a ccu ra te ly estim ate the rock m ass

s tren g th . This se c tio n d e sc rib e s the p rocedures and re s u lts for back

analyzing fa iled and s tab le s lo p es to define a probable reg ion of rock

m ass s tre n g th . For a fa iled s lo p e , com binations of cohesion and fric tio n

angle w ill co n stitu te an upper lim it of rock m ass s tre n g th . A low er lim it

is determ ined from back a n a ly s is o f a s ta b le s lo p e .

S tab ility S ections

The P illa r S lid e , loca ted on the e a s t side of the p i t , has been

an area of slope in s ta b ility a t Bagdad since a t le a s t 1952. In June 1954,

mining a t the b ase of the G ila co n tac t con tribu ted to a slope fa ilu re th a t

re su lted in the p resen t P illa r s truc tu re (Figure 18). The p o s t-fa ilu re

topography o f the P illa r Slide is shown by rad ia l se c tio n 8 (Figure 19).

This surface was determ ined from the April 1954 p it topographic m ap.

Radial sec tio n s 11 and 15 (Figures 20 and 21) were chosen as rep re se n ­

ta tiv e of s tab le G ila s lo p e s . Subsurface geo log ic co n tac ts for a ll s e c ­

tions were determ ined from diamond d rill h o le s .

Theory of Back A nalysis

In s ta b ili ty a n a ly s is a model is ch o sen th a t defines the slope

geom etry and the m ost probable fa ilu re su r fa c e . The s ta b ili ty is d e te r­

mined by c a lcu la tin g a fac to r of sa fe ty th a t is the ra tio of av a ilab le sh ear

41

Figure 18. Pillar Slide, looking east

1 ICM

QUARTZ MONZONITE

ELEVATION

— 4000

— 3800

_ 3600

— 3400

— 3200

3000

— 2600

Figure 19. Slope profile for rad ia l se c tio n 8

4kCO

oo0CMkJ

1

ELEVATION

L 4000

3800

3600

3400

3200

3000

2800

Figure 20 . Slope profile for rad ia l se c tio n 11

ELEVATION

OOoCM

zI

BASALT----------- TUFF ----------------GILA INTERBEDOED TUFF

GILA CONGLOMERATE

QUARTZ MONZONITE

_ 4000

_ 3800

_ 3600

- 3400

_ 3200

_ 3000

_ 2800

Figure 21 . Slope profile for rad ia l se c tio n 15

cn

\ 46

streng th along the fa ilu re su rface to the sh ea r s t r e s s e s ac ting a long the

failure su rfa ce . A fac to r of sa fe ty g rea te r than or equal to 1 .0 in d ic a te s

a s tab le s lo p e , and a fac to r le s s than 1 .0 in d ica te s an u n stab le s lo p e .

In a s ta b ility an a ly s is the rock stren g th is determ ined by te s tin g and can

be ex p ressed by a co h esio n and fric tio n angle value assum ing a Coulomb

streng th m odel. The m ethods of back a n a ly s is are the sam e a s th o se for

a s ta b ility a n a ly s is w ith one e x c e p tio n . Rather than c a lcu la tin g a sa fe ty

fac to r b ased on a known rock stren g th v a lu e , com binations of co h esio n

and fric tion angle v a lu es th a t y ie ld a fac to r of sa fe ty of 1 .0 are d e te r­

mined by ite ra tio n . A line connecting th ese po in ts rep re se n ts the rock

streng th va lu es required for s ta b il i ty . For a s tab le slope the rock m ass

streng th w ill be above the line ; for a fa iled slope the rock m ass stren g th

w ill be below the l in e . By com paring both a fa iled and a s tab le slope a

probable region of rock m ass stren g th is defined betw een the two s ta ­

b ility c u rv e s .

In order for a back a n a ly s is to be of p ra c tic a l v a lu e , it is n e c e s ­

sary to rev iew and comment on some of the lim ita tions and assum ptions

common to th is and to a l l m ethods of slope s ta b ili ty a n a ly s is . These

param eters have been d is c u s se d in d e ta il by Hoek (1970) and w ill be r e ­

view ed here a s th ey p e rta in to th is s tu d y .

1. The sh ea r stren g th param eters are defined by a co h esio n and

fric tio n angle th a t are re la te d by the Coulomb eq u a tio n ,

T = c + n tan g f.

T riax ial and d irec t sh ea r te s tin g of G ila sam ples supports th is

a ssu m p tio n . The sh e a r streng th envelopes show a Coulomb

47

re la tio n sh ip w ith in the s tre s s range for G ila s lo p es a t the mine

s i t e .

2 . The a n a ly s is is derived for a tw o-d im ensional c a s e . "It is a s ­

sum ed th a t re le a se su rfaces are p resen t so th a t there is no

re s is ta n c e to s lid in g a t the la te ra l boundaries of the failu re "

(Hoek, 1970, p . A114). The P illa r Slide is bounded by a su b -

- p a ra lle l system of f a u l ts . T hese fau lts a c t a s re le a se su rfaces

by offering lit tle or no re s is ta n c e to shearing a t the la te ra l

b o u n d a rie s .

3 . "It is assiim ed th a t the m ateria l p roperties are uniform and

fa ilu re occu rs a s a re s u lt of sim ultaneous fa ilu re a long the

failu re su rface" (Hoek, 1970, p . A114). In ligh t of th e se a s ­

sum ptions , the sh e a r s tren g th param eters derived from a back

a n a ly s is would be an average value and rep re se n t the failu re

p lane s tre n g th .

4 . "It is assum ed th a t the fa ilu re su rface geom etry can be rep re ­

sen ted by a p lane or a c ircu la r arc or a com bination of the two"

(Hoek, 1970, p . A114). The G ila is a s o il- lik e rock whose

m echan ica l p roperties are not dom inated by p lanar s tru c tu ra l

fe a tu re s . I t is therefo re assum ed th a t the m ost probable fa ilu re

geom etry is a c irc u la r a r c .

5 . The s ta b il i ty a n a ly s is assu m es a known p iezom etric s u r fa c e .

The approxim ate lo ca tio n of the p iezom etric surface a t the tim e

o f the P illa r Slide w as reco n stru c ted a fte r d isc u ss io n s w ith mine

p ersonnel who were working on the e a s t side of the p it during

48

the time o f the June 1954 fa i lu re . On the b a s is of th e ir rep o rts ,

a high p iezo m etric su rface was a ssu m ed .

Procedures for Back A nalysis

Since the m ost probable fa ilu re geom etry in the G ila Conglom­

era te is a c ircu la r a rc , the Bishop (1955) m odified method of s l ic e s was

u sed to back analyze the P illa r Slide and two s ta b le s lo p e s . The an a ly ­

s is was perform ed on a DEC-10 com puter u sing a U n ivers ity o f C a lifo rn ia ,

Berkeley, program w ritten by G . L efebvre . Further m odifications for back

a n a ly s is were made by P . V isca (personal comm un. , 1975). This program ,

STABR, o p e ra tes by search in g for a c r i t ic a l s lip c irc le having a minimum

facto r of s a fe ty . The s lip c irc le w as p a sse d through the base of the G ila

slope to agree with the fa ilu re cond itions observed a t the P illa r S lid e .

For the a n a ly s is of a s ta b le slope the fa ilu re su rface w as assum ed to

p a ss through the b a se of the G ila C onglom erate . By ite ra tio n , com bina­

tions of co h esio n and fric tio n ang le v a lu es th a t y ie ld a fac to r of sa fe ty

of 1 .0 were com puted .

E ngineering stren g th p roperties u se d in the back a n a ly s is are

shown in Table 7 . Rock su b s tan ce streng th s for b a s a lt and quartz m on-

zonite were determ ined from B razilian d isk te n s io n and com pression t e s t ­

in g . B ecause o f the frac tu red nature of the b a s a l t , a zero co h esio n was

a s s ig n e d . Laboratory d irec t sh e a r te s tin g provided streng th param eters

for rhyolite and in terbedded tu ffs .

49

Table 7 . Rock streng th param eters u se d in back a n a ly s is

Rock Type C ohesion F ric tion Angle D ensity

B asalt 0 p s i 48 p s i 158 lb / f t3

Rhyolite tu ff 10 13 110

Interbedded tu ff 15 23 a 132

G ila C onglom erate (b) (b) a 152

Q uartz m onzonite 2083 56 165

a . S atu rated

b . V alues c a lc u la te d from b ack a n a ly s is .

R esu lts

Figure 22 show s the re s u lts of b a ck analyzing a fa iled s lo p e ,

se c tio n 8 , and two s tab le s lo p e s , se c tio n s 11 and 15 . The rock m ass

streng th of the G ila C onglom erate lie s in the reg ion bounded by se c tio n s

8 and 15. D irec t sh e a r t e s t re s u lts in d ica te a mean re s id u a l fric tio n

angle of 32 d e g re e s . By using th is m ean v a lu e , the rock m ass co h esio n

is es tim ated from Figure 22 to be betw een 14 and 52 p s i . Figure 23

show s the com parison of th is range o f streng th v a lu es with sh e a r

streng th v a lu es of o ther m ateria ls c a teg o rized by H oek and Bray (1974).

The m ateria l t y p e s , id en tified by num bers on Figure 23 , are g iven in

Table 8 . This com parison in d ic a te s th a t the range for G ila rock m ass

streng th is h igher than m ost repo rted v a lu e s .

50

Section 8

100-

S ection 15

Rock M ass StrengthS ection 11

F ric tion Angle (degrees)

Figure 22 . Region of rock m ass streng th determ ined from backa n a ly sis

51

Jill,25E H *9

i i | !isSi llii•!*li ilfi •o 0̂0

! ? P Ills 3121 imiIni15 n 111? |S *1 liltt : r

76

69

63

*9f - 56

• - 49•f-4cn

-I- 42 aiU

“ 35 c2cn

38 !g ' U

- 21

- 14

- 7

■

i© ©

Q .

©

©G ila Conglom erate

Rock M ass S trength/

©

© 0 ©. Q ©

Undisturbed hard rock masses with no major structural patterns dipping towards slope.

Undisturbed hard rock masses with no through-going structures dipping taiards slope.

Undisturbed jointed so ft rock masses with few structures dipping towards slope

Soft rock masses or jointed hard rock disturbed by blasting or excess loading.Weathered so ft rock or discontinuities in hard rock.

CU« .o i l

F r ic t io n a n g le # — degrees

Figure 23. R ela tionsh ip o f G ila C onglom erate rock m ass s tren g th w ith p ub lished stren g th v a lu e s — Diagram a fte r H oek and Bray (1974)

52

Table 8 . Sources o f sh e a r s treng th d a ta p lo tted in Figure 23—After Hoek and Bray (1974)

PointN o. M ateria l Location

1 D isturbed s la te s and q u a rtz ite s Knob L ak e , C anada

2 Soil — — —

3 Jointed porphyry Rio T in to , Spain

4 Orebody hanging w all G rangesborg , Sw eden

6 Bedding p lan es in lim estone S om erset, England

7 London c lay England

8 G ravelly alluvium Pim a, Arizona

9 Faulted rhyolite Ruth, N evada

10 Sedim entary s e r i e s , P ittsbu rgh , P ennsy lvan ia

11 K aolinized g ran ite (China clay)

C ornw all, England

12 C lay sh a le Fort Peck Dam , M ontana

13 C lay sha le G ardiner Dam , C anada

14 C halk C halk c l i f f s , England

15 B en to n ite /c lay Oahe Dam, South D akota

16 C lay G arrison Dam , North D akota

COMPARISON OF ENGINEERING PROPERTIES

The purpose of co rre la ting the eng ineering p ro p erties is to e s t i ­

mate the G ila rock s treng th in a reas of the p it th a t were not sam pled for

laboratory rock te s t in g . A lin e a r reg re ss io n a n a ly s is was u se d to e s t i ­

mate functional re la tio n sh ip s betw een rock streng th param eters and

p h y sica l p roperties of g ra in s i z e , un it w eigh t, and m oisture c o n te n t.

The functional re la tio n sh ip s e s ta b lish e d from the reg re ss io n were not

a l l in c lu siv e b ecau se the G ila rock s treng th a lso depends on o ther

p roperties th a t were not m easured as p a rt of th is s tu d y . Some of th e se

p roperties include the am ount o f cem en ta tio n , the angu la rity o f frag m en ts ,

and the type of m in e ra ls .

To determ ine appropria te sh e a r s treng th param eters for slope

design work, a com parison was made betw een rock su b s tan ce streng th

v a lu es derived from labora to ry te s tin g and rock m ass streng th v a lu es

derived from back a n a ly s i s .

P h y sica l P roperties and Strength

For the com parison the p h y s ic a l p ro p erties defined by % g rav e l,

% sa n d , % f in e s , un it w e ig h t, and % m oisture con ten t are independent

v a r ia b le s . Shear stren g th p a ra m e te rs , p eak c o h esio n and re s id u a l f r ic ­

tio n a n g le , were ch o sen as dependen t v a r ia b le s . The dependen t v a r i­

ab les are the rock su b s ta n c e stren g th va lu es show n in Table 5 .

A lin ea r re g re ss io n a n a ly s is was perform ed for each indepen­

dent va riab le ra is e d to the follow ing exponen ts: 0 .3 3 , 0 .5 , 1 , 2 , and 3 .

53

54

This procedure acco u n ts for lin ea r and cu rv ilin ea r r e la t io n s h ip s . After

the reg re ss io n a n a ly s i s , the co rre la tio n c o effic ien ts are u sed to rank

the independent v a ria b le s by d ec rea s in g o rd e r . A p o sitiv e co rre la tio n

co effic ien t m eans th a t one v a riab le in c re a se s a s the o ther in c re a s e s ; a

negative co effic ien t m eans th a t one va riab le in c re a se s a s the o ther d e ­

c re a s e s . C orrela tion co e ffic ien ts may be any value betw een -1 and 1,

in c lu s iv e . If the c o e ffic ien t is -1 or 1 the v a ria b le s have a p e rfec t

lin ear re la tio n sh ip .

The re s u lts of th is a n a ly s is are show n in Table 9 . The m ost

s ta t is t ic a lly s ig n if ic an t v a ria b le s in fluencing G ila sh e a r streng th were

the v a riab les m easured by the g ra in s iz e d is tr ib u tio n . For peak co h e­

sion the h ig h es t co rre la tab le v a riab le w as % g rave l follow ed by % sa n d ,

% f in e s , u n it w e ig h t, and % m oisture c o n ten t. For re s id u a l fric tio n

angle the h ig h es t c o rre la tab le v a riab le was % g rave l follow ed by %

f in e s , % sa n d , % m oisture c o n te n t, and un it w e igh t.

A m ultiple re g re ss io n co rre la tio n was perform ed to determ ine

if the dependent v a ria b le s could be p red ic ted from the independen t v a ri­

a b le s . The % fines was not u se d in th is a n a ly s is b ecau se of in te rd e ­

pendence w ith % g rave l and % s a n d . R esu lts show n in Table 9 ind ica te

th a t peak cohesion and re s id u a l fric tio n angle s ta t is t ic a l ly depend on

the percen tage of g ra v e l. Such a co n clu sio n show s the in s e n s itiv ity o f

m ultiple re g re ss io n a n a ly s is b ecau se a ll the p h y s ic a l p ro p erties in ­

fluence sh e a r s tre n g th .

55

Table 9 . Result of reg re ss io n a n a ly s is o f p h y s ica l p roperties

L inear R egression

Peak C ohesion R esidual F ric tion Angle

Independent C orrela tion C orre la tionVariable Exponent C oeffic ien t (r) Exponent C oeffic ien t (r)

% F ines (F) 0 .3 3 -0 .7 4 7 0 .3 3 -0 .7 6 5

% G ravel (G) .5 + .830 .5 + .813

% Sand (S) .33 - .747 3 - .671

U nit w eight (r) 2 + .561 3 + .431

% M oisturecon ten t (W) .33 - .548 .33 - .575

F unctional R elationsh ip

Peak co h esio n f(-K3-5 , - S 3 , -F*3 3 , + 2, - w 33)'

R esidual fric tio n angle f(+G ‘^ , -F *2 2 , S2 , -W :22

M ultip le R egression A nalysis

Peak C ohesion = 2 .6 0 + 1 .38 (G) r = .84

R esidual fr ic tio n angle = 27 .92 + .79 (G) r = .81

56

Rock S ubstance Strength and Rock M ass Strength

The p h y s ic a l te s tin g m ethods in v es tig a te d in th is th e s is were

tr ia x ia l com pression , labora to ry d irec t sh e a r , and in s itu d irec t sh e a r .

Shear s treng th p a ram ete rs , c o h esio n and fric tion an g le , from th ese te s ts

are ind ica to rs of the rock su b s ta n c e s tre n g th . The v a lid ity of u sing

th e se param eters to e s tim ate the rock m ass s tren g th was determ ined by

comparing them w ith sh e a r s treng th param eters ob ta ined from b ack a n a l­

y s i s . This com parison is show n in Figure 24 . Shear s tren g th param eters

from tr ia x ia l and in s itu d irec t sh e a r te s tin g are p lo tted a s peak co h esio n

and peak fric tio n angle v a lu e s . Shear streng th param eters for each la b ­

oratory d irec t sh ear sam ple are p lo tted in term s o f peak and re s id u a l

cohesion and peak and re s id u a l fr ic tio n a n g le . An exam ination of Figure

24 illu s tra te s the e ffe c t of g ra in s iz e on sh ear streng th for m edium - and

la rg e -g ra in ed tr ia x ia l sa m p le s . T hese sam ples give anom alously high

sh ear s treng th v a lu es and are excluded from the follow ing com parative

a n a ly s is .

Rock stren g th v a lu e s bounded by sec tio n s 8 and 15 (Fig. 25)

rep re sen t average s tren g th v a lu e s . Figure 25 a lso show s the average

rock su b s tan ce stren g th p a ra m e te rs . The a reas bounded by the diam ond-

shaped figures rep re se n t one stan d ard d ev ia tio n from the m ean. S e le c ­

tio n of sh ear stren g th param eters th a t b e s t e s tim a te the rock m ass

s treng th is b a sed on the follow ing c rite r ia : (1) sh e a r stren g th v a lu e s

p lo tting betw een se c tio n s 8 and 15 are in agreem ent with b ack a n a ly s is

re s u lts ; (2) va lues p lo ttin g h igher th an se c tio n 8 o v erestim ate rock m ass

streng th and imply th a t the P illa r Slide would not have fa iled ; and (3)

57

O Large # Medium

# Large

200" O Medium

-vse c tio n o x F a iled slope

S ec tion la S table Slo

S ection 1 1 \ S table Slope

F ric tion Angle (degrees)

E xplanation

Laboratory D irec t Shear In S itu D irec t Shear T rlax ial C om pression

V Cp Qr ♦ Cp Qp • Cp Qp• Cp Qp .■ Cr Or

Cp = peak co h esio n ; C r = re s id u a l cohesion ; Qp = p eak fric tio n ang le ; Q r = re s id u a l fric tio n an g le ; open sym bols = sa tu ra ted te s te d sam ples

Figure 24 . R elationsh ip be tw een rock su b s tan ce streng th v a lu es and back a n a ly s is

58

Section 18 ' F a iled Slope

S ection 15 S table Slope

CpOp /

S ec tion 11 S tab le Slope

F ric tion Angle (degrees)

E xplanation

Cp = peak co h esio n Cr = re s id u a l co h esio n Qp = peak fric tio n angle Qr = re s id u a l fric tio n ang le

O tr ia x ia l sam ples O in s itu d ire c t sh ea r 0 one stan d ard d ev ia tio n for

laboratory d irec t sh e a r sam ples — sa tu ra ted te s te d sam ples

Figure 25 . R ela tionsh ip betw een the average rock su b s tan ce streng th and b ack a n a ly s is

va lues p lo tting be low se c tio n 15 underestim ate rock m ass stren g th and

imply th a t the s tab le slope rep re sen ted by se c tio n 15 should have fa i le d .

If th e se c rite r ia are u sed the b e s t e s tim ato rs of rock m ass

streng th are: (1) peak c o h e s io n -re s id u a l fric tio n angle v a lu es ob tained

from sa tu ra ted sam ples te s te d by labora to ry d irec t sh e a r and (2) peak

c o h es io n -p e ak fric tio n angle v a lu e s ob ta ined from sm all-g ra in ed sam ples

te s te d sa tu ra ted (Fig. 25). Shear s tren g th param eters th a t overestim ate

rock m ass s treng th are peak c o h e s io n -re s id u a l fric tio n ang le v a lu es ob ­

ta ined from laboratory d irec t sh e a r sam ples te s te d a t the in s itu m oisture

con ten t and a ll peak c o h e s io n -p e a k fric tio n angle v a lu e s . Shear s treng th

param eters defined by re s id u a l cohesion and re s id u a l fric tion angle tend

to s lig h tly underestim ate rock m ass s tre n g th . In s itu d irec t sh e a r te s te d

sam ples tend to underestim ate rock m ass s tre n g th . H ow ever, th is re su lt

is not conclu sive b ecau se o f the lim ited number of sam ples te s te d and

the d iffic u ltie s a s so c ia te d w ith the te s tin g p ro ce d u re . The tr ia x ia l

sm all-g ra ined sam ple te s te d dry o v e res tim a tes rock m ass s tre n g th .

C om parison betw een rock su b s tan ce sh ear streng th v a lu e s and

back a n a ly s is v a lu es has show n th a t the d isc o n tin u itie s th a t d iffe ren ­

tia te the rock m ass s treng th from the rock su b s ta n c e stren g th are not

s ig n ifican t for the G ila C onglom erate . For slope d es ig n work the sh e a r

streng th p a ra m e te rs , p eak co h esio n and re s id u a l fric tio n ang le derivedIfrom laboratory d irec t sh e a r te s t in g , are considered appropriate desig n

p a ra m e te rs .

59

60

E ngineering C la s s if ic a tio n s

Engineering c la s s if ic a tio n s of so ils are g en era lly su ited to the

requirem ents of the various a g en c ie s proposing them . For so il eng ineers

engaged in e a r th - f i l l work the m ost w idely u sed system of c la s s if ic a tio n

is the U nified Soil C la s s if ic a tio n . This system is b a sed on the grading

of so il p a rtic le s i z e . C la s s if ic a tio n of G ila s i te s by the U nified Soil

C la s s if ic a tio n is show n in Table 1 .

A second method of c la s s if ic a tio n favored by rock m echanics

eng ineers is b a sed on rock s tre n g th . Two w idely accep ted c la s s i f ic a ­

tions b a sed on rock su b s tan ce stren g th are th o se by D eere and M iller

(D eere , 1968) and P iteau (1970). The D eere and M ille r c la s s if ic a tio n

does not give adequate rep re se n ta tio n for G ila Conglom erate m ateria l

b ecause the low est ca tego ry of c la s s if ic a tio n is very low stren g th (maxi­

mum 4 ,000 p s i com pressive s tre n g th ) . The maximum com pressive stren g th

for G ila sm a ll-g ra in ed sam ples w as 296 p s i . The c la s s if ic a tio n by

P iteau is b a sed on the c o n s is te n c y of cohesive so ils and rocks and a

minimum streng th envelope derived from experim ental d a ta . P ite a u 's

c la s s if ic a tio n is show n in Figure 26 along w ith G ila Conglom erate

streng th v a lu e s . This c la s s if ic a tio n p lac es the G ila Conglom erate b e ­

tw een a very s tif f so il and a very so ft ro ck , which ad eq u a te ly d e sc rib e s

the G ila rock s tre n g th .

61

Very so ft so il

Soft so il

Firm so il

S tiff so il

Very s tiff so il G ila C onglom erate

Very so ft rock

Soft rock

Hard rockMinimum Strength

Envelope

Very hard rock

C ohesion (psi)

Figure 26 . C la s s if ic a tio n o f G ila Conglom erate accord ing to the P iteau sy s tem —Redrawn from P iteau (1970)

CONCLUSIONS

The G ila C onglom erate a t Bagdad v a rie s be tw een a s i l ty sand"

th a t is m oderately to w ell cem ented and a w e ll-g rad ed sandy gravel

th a t is m oderately to poorly cem en ted . The g ra v e l-s iz e frac tio n m akes

up 5 to 75 p e rcen t of the conglom erate and the fine frac tion 2 to 62 p e r­

c e n t. The average in s itu m oisture con ten t for specim ens lo ca ted a t the

p it face is 7 p e rcen t w ith a range of 5 to 10 p e rc e n t. U nit w eights range

betw een 128 and 152 lb /f t^ w ith a m ean of 138 lb / f t ^ .

On the b a s is of rock stren g th the G ila is c la s s if ie d be tw een a

very s tif f so il and a very so ft ro ck . The b e s t te s tin g procedure for d e ­

term ining rock su b s tan ce streng th w as laboratory d irec t sh e a r . T riax ial

com pression te s tin g w as a cc ep tab le if the maximum fragm ent s iz e does

not exceed 15 to 20 p e rcen t of the specim en d iam eter (Dvorak and P e te r,

1961). In s itu d irec t sh e a r te s t s are expensive and d ifficu lt to perform .

Peak c o h e s io n -re s id u a l fric tio n angle v a lu e s more c lo se ly approxim ated

the G ila Conglom erate rock m ass stren g th th an did peak co h es io n -p e ak

fric tio n angle and re s id u a l c o h e s io n -re s id u a l fric tio n angle v a lu e s . Re­

su lts from laboratory d irec t sh e a r te s tin g of five sam ples te s te d a t the

in s itu m oisture con ten t in d ica ted th a t the average p eak co h esio n is 56

p s i w ith a range of 18 to 93 p s i . The re s id u a l fric tio n an g les ranged b e ­

tw een 30 and 33 deg rees w ith a mean of 32 d e g re e s . For sa tu ra ted

sam ples the mean p eak c o h esio n w as 61 p ercen t low er th an th a t for

sam ples te s te d a t the in s itu m oisture c o n te n t. R esidual fric tio n an g les

were 2 deg rees low er for sa tu ra te d s a m p le s .

62

63

A com parison betw een the eng ineering p roperties of g rain s i z e ,

un it w eight, and m oisture con ten t in d ica ted th a t peak co h esio n is a

function of (1) g ra in s iz e d is tr ib u tio n , (2) un it w e igh t, and (3) m oisture

co n ten t. R esidual fric tio n ang le is a function of (1) g ra in s iz e d is tr ib u ­

tio n , (2) m oisture c o n ten t, and (3) u n it w e ig h t. These functional re la ­

tio n sh ip s are not a l l in c lu siv e b ecau se the sh ear streng th param eters

a lso depend on o ther p roperties th a t were not m easured a s p art of th is

s tudy .

Back a n a ly s is was perform ed on fa iled and s ta b le s lo p es to d e ­

lineate a region of v a lu es for rock m ass s tre n g th . For a 32 -deg ree m ean

fric tion ang le the average rock m ass cohesive streng th w as 33 p s i w ith a

range betw een 14 and 52 p s i . Back a n a ly s is o f s ta b le s lo p es in d ica ted a

lower accep tab le lim it for rock m ass s tre n g th . Back a n a ly s is can be

used a s a check on the v a lid ity of rock te s tin g re s u lts or rock streng th

re su lts ob ta ined from d e s ig n c h a r t s . An upper lim it for rock m ass

streng th can be determ ined from a fa iled s lo p e . If one is not p re sen t in

the mine area a sea rch o f the surrounding a re a s for fa iled s lo p es in

sim ila r rock ty p es can be m ad e .

APPENDIX A

GRAIN SIZE DISTRIBUTION GRAPHS AND DATA

64

65

SANDSILTCLAY

GRAVELCOARSE FINE COARSE

SIEVE 200 100

> 6 0

u_

lu 3 0

PARTICLE DIAMETER (MM)

Figure A - l . G rain s iz e d is trib u tio n graph for in s itu d irec t sh ear site

Table A - l . Grain size data for In situ direct shear site

SieveSize

Sample

IDS 1 IDS 2 IDS 3 X s

1" 7 8 .87 9 2 .34 96 .43 89.21 9 .1 9

3 /4 " 61 .55 83 .43 94 .85 79 .94 16 .92

1 /2 " 3 1 .86 75 .44 87 .86 65.05 29.41

#4 2 8 .55 73 .99 86 .45 63 .00 3 0 .48

#10 22.13 70 .26 80 .75 57.71 3 1 .2 6

#20 19.43 67.99 7 1 .99 53.14 2 9 .26

#40 17 .06 66 .16 59.81 47 .68 26 .70

#70 14.58 64 .28 4 4 .6 0 4 1 .15 25 .03

#100 13 .40 63 .36 3 7 .60 38 .12 24 .98

#200 10 .89 60 .87 27 .92 33.23 25.41

67

SANDSILTCLAY

GRAVELCOARSE COARSE

SIEVE 200 100

>- 6 0

ui 3 0

2 0

PARTICLE DIAMETER (MM)

m eanlim it for one e stim ated s tandard dev ia tio n

Figure A-2. Grain size distribution graph for site 1

Table A-2. Grain size data for site 1

Sample

Size 1A IB 1C ID IE IF 1G X s

1" 95 .93 9 8 .89 99 .25 98 .74 98 .17 9 5 .17 97 .41 97 .65 1 .57

3 /4 " 92 .80 9 7 .97 98 .49 98 .38 97 .43 9 4 .2 4 9 4 .9 8 96 .33 2 .29

1 /2 " 83 .39 9 1 .3 8 93 .73 9 6 .86 95 .44 9 1 .74 0 9 .87 91 .92 4 .3 6

1 /4 " 62 .70 67 .15 72 .88 91.21 89 .22 82 .67 8 1 .9 8 78 .26 10.92

#4 55.61 57 .87 62 .76 88 .49 85 .23 7 9 .10 77 .73 72 .40 13.43

#10 34 .85 33 .42 34 .57 65 .52 63 .88 59 .78 57 .14 49 .88 14.85

#20 2 2 .98 20 .12 19.50 3 3 .76 42 .79 4 0 .67 39 .32 31.31 10.20

#40 17.01 14 .09 13.53 15 .52 30 .29 27 .82 27 .39 20.81 7 .34

#70 12.93 10 .48 10.29 11 .78 24 .18 21 .60 21 .25 16.07 6 .00

#100 11 .58 9 .3 7 9 .3 0 10.11 22.31 19 .78 19.51 14.57 5 .7 0

#200 8 .9 3 7 .31 7 .42 7 .2 9 19.63 17.01 17 .12 12.10 5 .54

69

SANDSILTCLAY

GRAVELMEDIUM COARSE COARSE

SIEVE 200 100 i/2" r

> - 6 0

ui 3 0

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a ted standard dev ia tio n

Figure A -3. Grain size distribution graph for site 2

Table A -3. Grain size data for site 2

SampleSieveSize 2A 2B 2C 2D X s

1" 99 .37 99 .37 9 9 .5 6 100.00 99 .58 0 .3 0

3 /4 " 9 8 .99 9 8 .79 9 9 .0 0 100.00 9 9 .20 .55

1 /2 " 9 8 .4 0 9 8 .2 4 9 8 .8 3 9 9 .65 98 .78 .63

1 /4 " 9 4 .4 0 9 4 .45 9 6 .1 0 95 .39 9 5 .09 .82

#4 8 9 .5 8 8 9 .24 91 .21 88 .72 89 .69 1 .07

#10 64 .97 62 .38 62 .72 57.51 61 .90 3 .1 4

#20 4 6 .1 3 4 4 .0 7 4 4 .4 8 38 .29 4 3 .2 4 3 .4 2

#40 33.91 32 .87 3 4 .13 27 .59 3 2 .13 3 .0 7

#70 26 .16 25 .03 2 6 .90 20 .87 24 .74 2 .69

#100 22 .57 2 2 .70 24 .62 18.98 22 .22 2 .3 5

#200 18.33 18 .75 20 .80 15.63 18 .38 2 .13

71

SANDSILTCLAY

GRAVELFINE | COARSECOARSE

SIEVE 200 100

>. 6 0

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a te d standard d ev ia tio n

Figure A-4. Grain size distribution graph for site 3

Table A-4. Grain size data for site 3

SampleSieveSize 3A 3B 3C 3D 3E 3F 3G 3H 31 X s

1" 100 .00 100.00 9 9 .8 5 100 .00 9 5 .4 5 9 8 .83 94 .25 87.91 99 .11 9 7 .2 6 4 .1 3

3 /4 " 100 .00 9 9 .54 9 9 .7 4 9 9 .64 95 .33 9 7 .44 .9 4 .1 1 86 .98 99.11 9 6 .88 4 .2 7

1 /2 " 9 9 .0 7 9 8 .8 7 9 9 .0 7 99 .09 9 3 .9 4 95 .52 93 .45 84 .62 9 7 .69 9 5 .70 4 .7 3

1 /4 " 9 7 .9 0 9 7 .0 0 9 6 .9 0 97 .73 8 9 .46 9 1 .10 90 .25 80 .41 9 2 .85 92 .62 5 .68

#4 9 6 .7 8 9 4 .5 2 9 5 .4 7 9 6 .06 86 .54 87 .80 88 .75 78 .42 9 0 .75 90 .57 5 .9 5

#10 82 .02 7 8 .82 8 1 .25 81 .40 68 .68 66 .83 73.13 63 .60 7 2 .56 74 .25 6 .94

#20 61 .13 5 8 .7 2 60.51 59 .68 4 9 .2 8 48 .99 57 .39 49 .13 55 .00 55 .54 5 .12

#40 47.41 4 5 .4 2 46 .81 4 5 .6 0 36 .41 37.61 4 5 .6 8 40 .33 4 2 .60 4 3 .1 0 4 .0 8

#70 3 7 .8 6 3 6 .6 0 3 7 .46 3 6 .2 5 28 .10 30 .14 37.91 34 .37 34 .19 3 4 .76 3.51

#100 3 6 .46 3 3 .77 3 4 .44 3 3 .1 8 25 .44 27 .45 35.01 32.01 30 .97 3 1 .88 3 .3 8

#200 26 .50 2 6 .4 8 2 6 .58 25 .65 19.23 23.21 29.21 27.73 24 .58 25 .46 2 .90

73

SANDSILTCLAY

GRAVELCOARSE COARSE

SIEVE 200 100 40

> 6 0

PARTICLE DIAMETER (MM)

Figure A -5. Grain size distribution graph for site 4 .

Table A -5. Grain size data for site 4

SampleSieveSize 4C 4E 4F X s

1" 93 .77 9 5 .6 0 95 .22 94 .86 0 .9 7

3 /4 " 84 .05 9 1 .3 5 89 .00 88 .13 3 .73

1 /2 " 83 .19 8 0 .2 4 81 .44 81 .62 1 .48

1 /4 " 4 7 .95 5 4 .00 70 .47 57 .47 11 .65

#4 4 0 .9 6 4 5 .8 2 63 .30 50 .03 11.75

#10 26 .19 3 0 .60 35 .76 30 .85 4 .7 9

#20 18 .37 2 2 .15 24.41 21 .64 3 .0 5

#40 13 .59 16 .70 18 .80 16 .36 2 .62

#70 10.03 12 .90 14.99 12 .64 2 .49

#100 8 .8 3 11 .66 13.64 11 .38 2 .42

#200 6 .53 9 .1 8 11.05 8 .9 2 2 .2 7

75

SANDSILTCLAY

GRAVELCOARSECOARSE

SIEVE 200 100 40 20

> 60

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a te d s tandard dev ia tio n

Figure A-6. Grain size distribution graph for site 7

Table A -6. Grain size data for site 7

SampleSieve ---------------------------------------------------------------------------------------------------------------------------------S ize 7A 7B 7C 7D 7E 7F 7G 7H 71 x s

1" 9 4 .69 9 9 .40

3 /4 " 9 3 .9 8 9 9 .05

1 /2 " 92 .62 9 8 .2 6

1 /4 " 86 .63 85 .14

#4 8 5 .12 82 .05

#10 7 8 .60 70 .77

#20 68 .67 6 0 .56

#40 56 .77 5 0 .46

#70 4 3 .7 5 3 9 .02

#100 3 9 .1 6 35 .91

#200 28.91 2 6 .6 6

9 5 .3 4 100 .00 9 3 .27

9 3 .4 4 9 9 .7 6 91 .52

9 1 .4 8 98 .93 89 .77

8 5 .6 8 91 .30 88 .29

8 3 .53 8 7 .88 86 .94

7 5 .4 0 77 .23 73 .23

65 .54 67 .56 60 .84

5 4 .13 56.11 50 .34

4 1 .5 8 43 .11 40 .72

3 7 .0 0 3 7 .92 36 .40

2 6 .34 36 .52 28 .63

96 .03 99 .74 96 .80

95 .15 98 .89 96 .01

94 .36 9 8 .16 94 .91

92 .47 96 .23 9 1 .03

91 .87 9 5 .47 8 8 .78

80 .47 77 .22 7 6 .97

61 .37 61 .19 6 1 .56

48 .35 4 8 .67 46 .21

37 .35 37 .52 32 .38

32 .62 32 .63 27 .40

24.84 24 .26 19 .65

9 9 .08 9 7 .15 2 .4 8

9 8 .53 9 6 .28 2 .9 4

9 6 .98 9 5 .05 3 .2 7

90 .57 8 9 .82 3 .4 6

88 .00 87 .74 4 .1 2

77 .77 76.41 2.91

67 .37 63 .85 3 .3 7

54 .56 51 .73 3 .7 6

4 1 .4 8 39 .66 3 .5 4

36 .28 35 .04 3 .5 9

28 .10 25 .99 2 .86

77

SANDSILTCLAY

GRAVELCOARSE • FINE

SIEVE 200 100

> 60

ui 3 0

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a te d standard d ev ia tio n

Figure A-7. Grain size distribution for sm all-grained triaxialspecimens

Table A-7. Grain size data for sm all-grained triaxial specimens

SampleSieve ----------------------------------------------------------------------------S ize QTG 1 QTG 2 QTG 3 QTG 4 QTG 5 QTG 6 QTG 7 X s

1" 100 .00 100 .00 100 .00 100.00 100 .00 . 100 .00 .1 0 0 .0 0 100.00 0 .0

3 /4 " 9 5 .5 5 100.00 100 .00 9 2 .5 4 100 .00 100.00 97 .01 9 7 .87 2 .96

1 /2 " 9 2 .79 9 8 .29 100.00 86 .39 100 .00 100 .00 96.11 9 6 .23 5 .09

1 /4 " 84 .09 92 .42 9 8 .04 7 7 .55 97 .32 9 5 .07 89.51 9 0 .5 7 7 .5 0

#4 7 9 .70 90 .52 9 7 .62 7 4 .87 95 .64 9 3 .24 87 .25 88.41 8 .4 2

#10 63 .64 79 .57 9 2 .29 61 .04 85 .17 76 .15 7 5 .86 76 .25 11 .09

#20 50.61 60 .92 81 .51 4 9 .04 66 .04 5 5 .18 63 .28 60 .94 11 .08

#40 4 0 .5 2 4 4 .0 7 68 .64 4 1 .77 45 .81 3 8 .63 55.91 47 .91 10.73

#70 3 1 .42 30 .15 53.41 35 .77 31.31 24 .35 4 5 .09 35 .93 9 .9 9

#100 2 7 .0 0 2 4 .40 45 .31 32 .54 25 .47 18 .02 39 .22 3 0 .28 9 .4 0

#200 18 .82 16 .15 32 .15 25 .58 17.15 8 .31 28 .66 2 0 .97 8 .25

79

SANDSILTCLAY

GRAVELMEDIUM | COARSE COARSE

SIEVE 200 100

> 6 0

iiJ 3 0

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a ted stan d ard d ev ia tio n

Figure A-8. Grain size distribution graph for medium-grainedtriaxial specimens

Table A -8. Grain size data for medium-grained triaxial specimens

SampleSieveSize 8 9 10 11 12 13 14 15 16 17 18 X s

1" 89.73 82.97 100.00 100.00 95.00 85.62 92 .38 100.00 91.33 100.00 100.00 94.28 6.32

3 /4 " 84.23 82.97 92 .38 96 .82 95 .00 79.51 64.24 100.00 88.29 87.18 100.00 88.24 10.54

1 /2" 78.56 72.08 81.14 82.73 90.99 72.23 47.34 86.75 74 .84 67.42 91 .95 76.91 12.61

1 /4" 61.35 58.76 59 .92 60.64 71.79 48.24 39.52 51.37 56.38 44 .47 74.41 56.99 10.66

#4 56.31 • 54.94 54 .76 54.70 65.00 43.41 35.56 43.07 51.07 38.22 66.60 51.24 10.16

#10 39.90 41.71 43 .68 35.58 47.31 27.83 23.26 24.25 32.73 26.79 46 .58 35.42 8 .98

#20 27.77 32.76 35 .68 24.50 36.58 20.60 17.17 15.57 20.68 20.49 33 .82 25.97 7 .70

#40 20.17 26.73 28.43 19.75 29.08 16.03 12.91 10.71 13.76 15.92 25.39 19,90 6.60

#70 14.71 21 .87 22.41 16.05 22.88 11.82 9.72 7 .78 9 .49 12.75 19.36 15.35 5.56

#100 12.65 19.69 20.08 14.67 20.26 9 .57 8.35 6 .67 7 .92 11.43 16.77 13.46 5.14

#200 9 .65 15.34 16.95 12.46 16.08 5.23 5.74 4 .79 5.54 9.11 11.70 10.24 4 .59

81

SANDSILTCLAY

GRAVELFINE MEDIUM COARSE FINE COARSE

SIEVE 200 100

> 6 0

uj 3 0

PARTICLE DIAMETER (MM)

m eanlim it for one e s tim a ted standard dev ia tio n

Figure A -9. Grain size distribution graph for large-grainedtriax ial specimens

Table A -9. Grain size data for large-grained triax ial specimens

SampleSieveSize 19 20 21 22 23 24 25 26 27 28 X s

1" 100.00 100 .00 93 .92 9 4 .2 7 86 .02 100 .00 100.00 66.11 100 .00 100 .00 9 4 .03 10 .84

3 /4 " 9 0 .0 0 92 .81 82 .58 76 .11 80 .57 82 .42 94.01 55 .20 9 6 .7 6 9 3 .56 84 .40 12 .36

1 /2 " 68 .95 65 .79 67 .99 63 .22 75 .52 70 .67 84 .63 7 8 .56 7 8 .5 6 86.49 74 .04 7 .9 5

1 /4 " 3 4 .1 6 4 .121 5 7 .80 4 9 .4 4 70 .14 51 .66 66 .20 30 .63 62 .20 70.41 53 .39 14 .48

#4 29 .43 3 7 .6 8 5 4 .86 4 5 .5 0 65.73 4 7 .54 61 .49 26 .17 57 .55 65.13 52.11 19 .45

#10 18.14 2 7 .8 6 4 2 .8 3 3 2 .4 2 4 5 .1 6 30 .73 42 .90 15 .28 4 3 .0 0 4 7 .09 34 .54 11 .47

#20 13.56 2 2 .65 3 3 .02 24 .32 30 .39 22 .14 30 .05 9 .9 0 3 1 .6 6 36 .87 25 .46 8 .6 6

#40 10.97 18 .99 2 5 .05 19 .04 22 .48 17 .00 22.29 6 .9 2 23.51 30 .53 19.68 6 .85

#70 9 .0 7 15 .52 18 .62 15 .08 17.52 13 .28 16.63 4 .8 8 17 .30 25 .39 15.33 5 .53

#100 8 .1 6 13 .76 16.04 1 3 .40 15.50 11.64 14.22 4 .0 5 14.73 3 2 .1 0 14 .36 7 .24

#200 6 .6 7 10.31 11 .72 10 .38 11.93 8 .7 7 10.09 2 .70 10 .77 19 .16 10.25 4 .1 7

APPENDIX B

LABORATORY SHEAR-DISPLACEMENT GRAPHS

83

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2 0 0 NORMAL STRESS ( P S D

FORWARD SHEARING DIRECTION REVERSE SHEARING DIRECTION

RESIDUAL

PEAK

1 . 0 INCH

DISPLACEMENT (INCHES)

Figure B - l. Key for shear-displacem ent graphs OD

SH

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S280

Figure B-2. Shear-displacement graphs for specimens 1A (upper) and IB (lower)

00cn

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25 5 0

DISPLACEMENT (INCHES)

Figure B-3. Shear-displacement graphs for specimens 1C (upper) and ID (lower)

SH

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200

DISPLACEMENT (INCHES)

Figure B-4. Shear-displacement graphs for specimens IE (upper) and IF (lower)

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200

DISPLACEMENT CINCHES)

Figure B-5. Shear-displacement graphs for specimens 1G (upper) and 2A (lower)0000

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DISPLACEMENT (INCHES)

Figure B-6. Shear-displacem ent graphs for specimens 2B (upper) and 2C (lower)00CO

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200

DISPLACEMENT (INCHES)

Figure B-7. Shear-displacem ent graphs for specimens 2D (upper) and 2E (lower)

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400

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18 -

DISPLACEMENT (INCHES)

Figure B -8. Shear-displacem ent graphs for specimens 3A (upper) and 3B (lower)

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(X

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10012 -

5 0 1

DISPLACEMENT ( INCHES)

Figure B-9. Shear-displacem ent graphs for specimens 3C (upper) and 3D (lower)

toM

SH

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DISPLACEMENT (INCHES)

Figure B-10. Shear-displacem ent graphs for specimens 3E (upper) and 3F (lower)

iOW

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S200

6 -

4 -

2 -

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50 100

DISPLACEMENT ( INCHES)

Figure B - l l . Shear-displacem ent graphs for specimens 3G (upper) and 3H (lower)

CO

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(X

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100 200200

200

DISPLACEMENT (INCHES)

Figure B -12 . S h ea r-d isp lacem en t graphs for specim ens 4A (upper), 4B (lower le f t ) , and 31 (lower right)

CO

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(X

1

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3 0 0

3 0 0

DISPLACEMENT (INCHES)

Figure B-13. Shear-displacem ent graphs for specimens 4C (upper) and 4E (lower)

too>

SH

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18

DISPLACEMENT CINCHES)

Figure B-14. Shear-displacem ent graphs for specimens 7A (upper) and 7B (lower)

to

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2002 00

DISPLACEMENT (INCHES)

Figure B-15. Shear-displacem ent graphs for specimens 7C (upper) and 7D (lower)

tooo

SH

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(X

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18

200

DISPLACEMENT (INCHES)

Figure B -16 . S h ea r-d isp lacem en t graph for specim ens 7E (upper) and 7F (lower)

<oCO

REFERENCES

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B ishop, A. W . , 1955, The u se of the s lip c irc le in the s ta b ili ty a n a ly ­s is of earth s lo p e s : G eo tech n iq u e , Vol. 5 , p . 7 -1 7 .

D eere , D . N . , 1968, G eo log ica l c o n s id e ra tio n s , in Z len k iew icz ,O . C . , and S tagg , D . , e d s . , Rock M echan ics in Engineering P rac tice : New York, John W iley & S o n s , p . 1 -2 0 .

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G ilb e rt, G . K ., 1875, Report on the geology o f portions of New M exico and Arizona: U .S . G eog. and G eo l. S u rveys, W . 100th M e r .: Vol. 3 , p . 501 -567 .

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_________ , and Bray, John, 1974, Rock slope eng ineering : London,In s titu tio n of M ining and M eta llu rgy , 309 p .

Ja in , S . P . , and G u p ta , R. C . , 1974, In -s i tu te s tin g for rock f i l ls :Jour. G eo tech n ica l Engineering D iv is io n , P roceedings of the American S oc ie ty of C iv il E n g in e e rs , Vol. 100, N o. GT9, p . 1031-1050 .

P itea u , D . R . , 1970, G eologic fac to rs s ig n if ic an t to s ta b ili ty of open p it s lo p es in rock: P lanning open p it m in es, Johannesburg , Sym posium , South A frican In s t , o f M ining and M eta llu rgy , p . 51.

S chrader, F . C . , 1915, M ineral d e p o s its o f the Santa Rita and P atagonia M o u n ta in s , A rizona: U .S . G eo l. Survey B ull. 582, 373 p .

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