8/10/2019 Void Ratio and Void Ratio and Shear StrengthShear Strength of Two Compacted Crushed Stones-1966
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Engineering
Experiinent
Station
TO
IOWA
STATE
HIGHWAY COMMISSION
V061f}
RAYHO
ANID
S H I E ~
S1 RIENG1M OIF
TWO
by
Fernando H. Tinoco Graduate
Assistant
Richard L. Handy Professor of Civil
Engineering
James M Hoover
Assistant Professor
of Civil Engineering
Contribution
No.
66-6
from the Soil
Research
Laboratory Project 516-S
Iowa Highway Research Board Project HR-99
Iowa
State
University
Ames
Iowa
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1
VOID RATIO
ND
SHEAR STRENGTH OF
TWO COMPACTED
CRUSHED
STONESl
by
2
Fernando
H.
Tinoco Richard
L. Handy and James
M.
Hoover
ABSTRACT
Triaxial
compression
tests of two crushed
limestones
of
differ ing
highway
service records
indicate a
fundamental
difference
in their shear
strength
--
void
rat io
relat ionship.
Analyses
were
based
on
stress
C
.
C
:
J
C
C
.
C
I
-
>
.
C
l
>
:
J
.
.
I
>
0
I
>
C
C
c
.
c
.
0
I
I
)
Q
.
E
C
t
J
:
J
>
0
E
:
0
I
>
I
I
(
C
c
0
-
0
-
u
~
U
0
CJ
CJ
UJ
a::
a
UJ
>
I -
u
UJ
u..
u..
UJ
\
300
200
100
0
0.15
\
0.16 0.17
17
GARNER SAMPLES
Standard compaction
a Consolidation pressure
o Effective
pressure
0.18 0.19 0 20 0 21
0 22
VOID R TIO
Fig
6
Garner stone: effective
pressure
and consolida-
t ion
pressure
as
related
to
void
ra t io
0 23
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- -
2
/)
0 750
18
GARNER SAMPLES
Standard compaction
w
w
a
49 C
w
0
a
47
45
0 700
____ ____ ..i........ J _ _ _ _ _ _ __ ___
0.15 0.16 0.17
0.18 0.19 0 20 0.21
MINIMUM VOID RATIO
Fig
7 Garner stone:
values
of s i n ~ ,
and
as
re la ted
to
minimum
void
r a t io
0 22
0 23
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19
A similar extrapolation can be made for the Bedford
crushed
stone,
as
shown
in Table 3.
Table 3. Shear strength components of the Bedford
crushed
stone calculated
at e . = 0.
min
Degree of Compaction Cohesion, psi
Angle of
Frict ion,
deg.
Standard
Proctor
1171
36.5
Modified Proctor
1116
39.9
Calcite i s
also
the
predominant mineral of the
Bedford crushed
stone.
Von Karman
(1911)
performed t r iaxia l tes ts
on marbl.e at
very
high
cel l pressure,
up to 36,000 ps i and Bridgman (1936) and
Griggs
(1942)
performed high pressure
tes ts
on
calcite .
The envelopes
ob-
tained are
sl ight ly curved
and
the
mean
resul ts are
sunnnarized
in
Table 4.
Table
4 also shows the resul ts obtained
for
the
Bedford
material on
the
assumption that
the
fr ict ion angle
was
34.0, in
order
that
a
comparison could
be
drawn
with
the
above
quoted
authors
resul ts .
Table
4.
Shear strength
components of
calci te
for
a 80,000 psi .
Author
Von Karman
Bridgman
Griggs
Tinoco, e t . a l .
Tinoco,
e t . al .
Rock
Marble
Calcite
Bedford
(Std.
Comp.)
Bedford
Mod
.
Comp
. )
Cohesion, psi .
Angle
of
Frict ion,
deg.
4980 34
2990 34
1315
34
3868
34
The
implication
of
the
above
comparisons is
that
the
behavior
of
the
Bedford and Garner
stones
belongs in two
different
systems; the
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2
Garner
extrapolates
to
pure sl iding f r ic t ion whereas the Bedford
extrapolates to
s l id ing
fr ict ion
plus
a cohesion comparable to values
found
in solid
rock.
he exponential shear stress-void ra t io
function
for the Bedford
would appear
to indicate
increased
cohesion
caused by increased
grain
contact
areas under
higher
pressures.
This
implies a compressibil i ty
of the
Bedford
stone par t ic les . Under repeated
loading,
sl ight in ter-
granular
shear
movements could perhaps cause
the
loss in cohesion,
since grains
would
rio
longer
be properly arranged
or
interlocked to
cause an
increase
in
contact areas
with
loading.
That
i s
repeated
compressions resu l t in densif icat ion
and
a
mass
action ra ther
than
a
point-contact building-block action of individual grains .
In
the case
of the Garner mater ia l ,
the shear stress-void rat io
function is l inear and
therefore
ref lec ts the state
of
packing
within
the granular system. he
fr ict ion
parameter i s therefore a measure of
the
in terpart icle
in teract ion ra ther than
the f r ic t iona l characteris t ics
of
the par t ic les . Thus most crushed stones,
unlike
the Bedford, tend
to maintain strength under repeated
loading.
ON LUSIONS
he
shear-stress-void
ra t io
function
is
an
index
to
the
behavior
of compacted
crushed stone
materials under shear. Two different
types
of
behavior
are
inferred: a) compression of par t ic le contacts under
loading,
increasing
cohesion
and
giving an exponential
re la t ionship
between
shear
strength and
void r a t io
and
b)
sl iding a t point
contacts
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2
between
par t ic les
giving a
l inear
re la t ionship between
shear
strength
and void r a t io .
Behavior
(a)
apparently
is
not
stable
under
repeated loading,
since
shear
strength
is
gradually
los t . This
suggests a s tructura l
rearrangement of the
grains which
reduces grain- to-grain
contact
under
pressure,
and
therefore cohesion.
That is
the benefic ia l effect of
consolidating pressures
is
gradually
los t .
Thus
under repeated loading
the behavior
i s similar to that of a clay.
In
contras t ,
behavior
(b)
should
be
stable
under
repeated loading.
The difference in behavior
of
the two stones thus may re la te
to
the compression
and shear
character
of
the individual grain- to-grain
surface
contacts,
which
in
turn
should re la te
to
some
petrographic
characteris t ics of the rock.
ACKNOWLEDGEMENTS
The research reported herein
is
a portion
of
a project on ' 'Factors
Influencing
Stabi l i ty
of Granular Base
Course
Mixes under contract
with
the Iowa Highway Research Board, Iowa State Highway Commission and
Bureau of Public Roads, U.S . Department of Commerce
Appreciation i s extended
to the
following
organizations and per
sonnel:
to the
Iowa
Highway Research Board
and
Bureau of Public
Roads
for the i r
continuing support of th i s project; to
Mr.
Steve
Roberts,
Director
of Research, Mr.
Tom McElherne, Materials Engineer, and Mr. Ted
Welp, Geologist ,
Iowa
State
Highway
Commission, for their
valuable as
sistance and counseling;
and
to Dr. Turgut Demirel, Iowa State Universi ty,
for
his
advice,
in teres t and cri t ic isms.
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REFERENCES
1.
Anderson,
A. A.
and Welp,
T. L. (1960).
An
engineering
report
on the
soi ls ,
geology, terrain
and
climate of Iowa.
Iowa
State
Highway Connnission. Ames, Iowa pp. 3-12.
2. Best , T. (1966). Private communication. Ames, Iowa.
3. Bishop,
A.
W. and
Henkel, D.
J .
0957,) . The measurement of soil
properties in
the
t r iaxia l tes t . 190 pages. Edward Arnold
Ltd,
London.
4. Bridgman, P. W.
(1936). Shearing
phenomena
a t
high pressures.
Proc.
Amer.
Acad.
Arts. Sci . , 71, pp.
387-469. In
Skempton,
A.
W.
(1960). Effective Stress in soils., concrete
and
rocks. Proc. of
Cpnference on Pore
Pressure
and
Suction:in Soi ls . Butterworths,
London, pp.
4-16.
5.
Handy, R. L. (1965). Quanti tat ive X-ray dif f rac t ion measure
ments
by fast scanning. Analytical
Techniques for
Hydraulic
Cements and Concrete, ASTM STP
395,
Am.
Soc. Testing
Matl ' s . ,
pp.
30-44.
6. Henkel, D. J . (1959) , The relat ionships between shear
s t rength ,
pore water
pressure and volume-change character is t ics of saturated
clays . Geotechhique, Vol. 9, pp. 119-135.
7.
(1960).
The
relat ionship
between
the
effect ive
stresses and water
content in
saturated
clays. Geotechnique,
Vol. 10, pp. 41-54.
8. Horn, H. M.
(1961)
. An investigation
of
the fr ict ional character is t ics
of minerals. Ph.D. Thesis. Department of Civil Engineering,
Universi ty
of I l l ino i s ,
Urbana.
9. Hvorslev,
M. J .
(1937). ueber
die
Fest igkei t
seigenschaften
gest8rter
bindiger B8den . (On the
strength
properties of
re-
molded cohesive soi ls) .
Ingeniorvidenskabelige
Skrif ter A. No.
45, 159 pages. Reviewed in Hvorslev, M. J . (1960) .
Physical
components of the shear strength of saturated clays. Research
conference on Shear
Strength
of Cohesive Soi ls .
Am.
Soc. Civ.
Engr. Boulder, Colorado,
pp.
169-273.
10. (1960) .
Physical
components of the shear strength
of
saturated
clays . Research Conference
on Shear Strength of
Cohesive Soils . Am. Soc. Civ. Engr.
Boulder, Colorado,
pp. 169-273.
11. Griggs, D.
T. (1942).
Strength
and plas t ic i ty .
Handbook
of
Physical Constants ,
Geol.
Soc.
America.
Special Paper,
No.
36,
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23
pp. 107-130. In
Skempton,
A.
W.
(1960).
Effective Stress in
Soils , Concrete and Rocks. Proc.
of Conference
on Pore Pressure
and
Suction in Soi ls . Butterworths,-London, pp.
4-16.
12.
Karman,
Th.
Von
(1911). Festigkeitsversuche unter
allseit igen
Druck .
Ziet. Vereines Deutsch.
Ing. ,
55,
pp.
1749-57.
In
Skempton, A.
W.
(1960). Effective stress
in
soi l s concrete
and rocks.
Proc.
of
Conference
on Pore
Pressure
and
Suction
in
Soils. Butterworths, London, pp. 4-16.
13. Lambe, T.
W.
( 1958) . The
structure
of compacted clay .
Proc.
Am.
Soc. Civ. Engr. SMF
Div., Vol.
84, No.
SM2 Paper
No. 1654,
34 pages.
14.
Rutledge, P.
C.
(1947).
Review
of cooperative t r iax ial
research
program of the Corps
of
Engineers . Progress
Report
on
Soil
Mechanics Fact Finding
Survey. Waterways Experiment
Station,
Vicksburg,
Mississippi,
pp. 1-178.
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a
3c
al
a l
I
a
I
2
I
+
a
I
1
2
I
e
c
I
r
cp I
r
c
1
Cz
s1
Sz
24
PPENDIX A
Symbols used
in th is paper
Effective consolidation
pressure;
i . e .
applied consolida-
t ion pressure less pore pressure.
Effective
major principal st ress
Maximum shear st ress
Effective
mean pressure or effect ive pressure
Equivalent consolidation
pressure
which gives void ra t io
e under conditions of normal consolidation.
Effective cohesion
Effective
angle of internal
f r ic t ion
Q I
3
Intercept
of
fa i lure l ine
for
CJ
e
0
a +a
1 3
Intercept
of
fa i lure l ine for ~ a _ . . . ~
e
0
I
3
Angle that the fa i lure l ine makes with
hor izontal
axis 0: V
Angle that the fa i lure
l ine
makes
with
horizontal
axis
+a
1 3
2
I
e
e