T.
FIN C H
B.Sc ., D.I.C., M.Sc ., Research Fellow, School of Civil Engineering , University of Sydney
REPORT ON A TEST TO EVALUATE A BRECCIA
AS A ROAD BASE COURSE MATERIAL
( Paper No. A6 8)
This paper describes an experiment with a laboratory test track. A
length of road, 4.88 m (16 ft) long by 0.91 m (3 ft) wide by 0.15 m
(6 in) deep was subjected to 45,000 passes of a rolling wheel load.
The materials tested, stabilised and unstabilised breccia and
dolerite, are currently being used as base course materials. The
materials behaved satisfactorily when dry, but when tested wet the
unstabilised breccia and the dolerite suffered considerable deformations as compared to the deformations of the stabilised breccia.
The unstabilised breccia in particular showed typical features of a
failed pavement.
Horizontal movements equal to vertical movements were
recorded. There was little agreement between the deflection bowl
shape predicted by isotropic elastic theory and the as-measured
shape. Due to hysteresis and permanent deformations, the deflection bowl formed by a rolling wheel was unsymmetrical about the
wheel. It is suggested that a pavement may experience considerably
higher deformations under a single pass of a wheel load than would
be expected from the average deformation per load.
INTRODUCTION
1.
The Australian Road Research Board (ARRB) and the University of
Sydney have developed a model test track (Sparks 1970 and Sparks and Davis
1970). The material testing policy is to alternate between tests of an ad hoc character
to investigate the behaviour of materials which are being used, or proposed to be
used, in actual road construction, and tests of a more fundamental nature to attempt
to gain an understanding of the behaviour of materials subjected to a moving load.
2.
The test described in this report is an ad hoc test performed at the request
and in collaboration with the Department of Main Roads (DMR) , N.S.W. The
purpose of the test was to evaluate the performance of stabilised and un stabilised
breccia when subjected to a repeated rolling load. The breccia has only recently
been used as base course material in highways in the Sydney region. A second
material, a dolerite which had been used for some years in roads constructed by
the DMR, was also tested as a control.
ARRB ROAD MACHIN E
3.
The machine is essentially as described by Sparks and Davis (1970) with
modifications to the main drive and to the main ram as recommended by Sparks
(1970). The machine is capable of subjecting a 4.88 m (16 ft) long by 0.91 m (3 ft)
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wide by 0.30 (12 in) deep length of model road to a rolling wheel load of up to
2360N (530 lb) at a speed of up to 3 m/s (10 ft/s) . The transverse position of the
wheel may be set to follow any pattern. For this experiment the wheel was a 230 mm
(9 in) diameter, 50 mm (2 in) wide pneumatic tyre with the tread ground off to
give a continuous contact pattern on the road surface. The tyre pressure was 620 kPa
(90 psi), the vertical thrust 530 lb, and the trolley speed 1.5 m/s (5 ft/s). The
transverse position of the wheel was set to fO'llow a pattern which formed a normal
distribution between + 228 mm (+9 in) and - 228 mm (-9 in) of the road
centreline, with a maximum at the centreline. This pattern repeated itself every
100 passes of the wheel, and trafficking of the test material is in terms of these
'patterns' or 'cycles', each cycle being 100 individual passes of the wheel.
4.
Some trouble with the machine was experienced in the early stages of the
test, mainly because of the modifications to the main drive and main ram, but by
the completion of the test the machine was operating satisfactorily.
5.
The length of the test track itself was divided into four 1.22 m (4 ft) bays,
three containing breccia and the fourth dolerite. A fifth 0.46 m (18 in) long bay of
surface course material only was also laid as a control; it received the same
trafficking as the other bays.
INSTALLATION OF MATERIAL
SUBGRADE
6.
It was considered that deflection in the subgrade might have some effect on
the behaviour of the breccias. Deflections would give rise to relative movement
between particles, which might accelerate degradation of the material. The specified
maximum deflection was to be between 0.25 to 1.0 mm (0.010 and 0.040), and
after investigation, a 12.5 mm (} in) layer of soft sponge rubber was used. This
produced deflections of 0.25 to 0.65 mm (0.010 to 0.025 in). A layer of polythene
was laid between the sponge rubber and the base course, and up the sides of
each bay.
BASE COURSE
7.
The material was compacted to simulate as closely as possible field conditions. All four bays were compaoted at optimum moisture content to 100 per cent
Proctor dry density using a 750 w Kango vibrating hammer acting O'n a 150 mm
x 150 mm (6 in x 6 in) square base. Each bay was compacted in three layers to a
final depth of 152 mm (6 in), and the surface smoothed with a steel billet. Polythene
was used to prevent the material sticking to the compacting equipment. The
materials were tested and mixed at the DMR North Sydney Laboratory, and
transported to the road machine laboratory one bay at a time.
8.
Bay 1 was untreated breccia, its behaviour being used as a reference for the
behaviour of the stabilised breccias. Bay 2 was breccia treated with lime and bay 3,
breccia treated with lime and blast furnace pozzolan (bfp). These stabilising agents
are being used in current road construction. Bay 4 was dolerite, to act as a control.
This dolerite has been used as a base course for some years. See TABLE I for details
of the material and placement conditions.
Volume 7) Part 7, 1974
107
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
TABLE I
MATERIAL AND PLACEMENT CONDITIONS OF BAYS
Bay 1
Material
Installed water content per cent
Water content prior to wetting
per cent
Final water content per cent
Breccia
Bay 2
Bay 4
Dolerite
1.2
4.8
9.0
9.5
Breccia
3/4 per cent
lime +
2% per cent bfp
9.0
2.5
6.3
2.8
7.6
3.6
8.0
+
Breccia
2 per cent
lime
Bay 3
+
7.5
SURFACE COURSE
9.
The purpose of the course was to provide:
(a) a wearing surface for the wheel and a more realistic cross-section, and
(b) a suitable medium for embedding the measuring targets.
10.
After compaction each bay was immediately sealed with a 'RSK' cationic
emulsion. After all four bays were complete, a nominal 6 mm U- in) thick sandasphalt surface course was applied hot. The sand was fine Roseville sand and the
mixture contained seven per cent bitumen (by weight). Problems were encountered
as the mixture cooled, and the resulting surface contained some irregularities.
11.
A fifth bay, consisting of the sand-asphalt laid on primed 25.4 mm (1 in)
thick boards, was constructed. This bay was to act as a control section. It was
hoped that the deformations of this bay could be deducted from those of the other
bays to obtain the net deformation of the base course.
MEASURING TARGETS
12.
The targets were 11 mm (7/16 in) diameter discs with three legs around the
periphery to enable them to be pressed into the sand-asphalt. Their vertical movement was recorded by placing a ball bearing in a 4 mm (5/32 in) diameter hole
cut in the centre of the disc and measuring the position of the ball with a dial gauge.
The horizontal movements were measured by focusing a travelling microscope onto
a 0.5 mm (0.020 in) diameter hole in the disc. The system is as described by Sparks
(1970).
13.
Six rows each of 15 targets were laid in each bay. The 15 targets were on
the centreline, and 25 mm (1 in), 50 mm (2 in), 75 rom (3 in) , 125 mm (5 in),
180 mm (7 in) , 250 mm (10 in) and 355 rom (14 in) left and right of the centreline. Bay 5 had only two rows each with 13 targets.
14.
The targets were installed by pressing the three legs of the disc into the
sand-asphalt. No difficulty was experienced, even when the asphalt was cold.
'Araldite' was used between the disc and the asphalt, the holes in the disc being
covered with tape.
15.
It was realised that these targets would be measuring the surface settlement,
and not the settlement of the base course. It was found impossible to embed the
targets directly in the base course material because of the large particle size, but
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as an experiment, the targets of bay 4-row five, and bay 5- row one- right were
installed by coring out a plug to the full depth of the sand-asphalt, and backfilling
with 'Araldite'. This technique worked well for small displacements, and the movements measured appeared to be those of the base material rather than the surface.
However, after larger flexures and distortions had taken place in bay 4 during the
latter part of the test, the 'Araldite' plugs tended to work loose. (See Fig. 13- bay
4-row five) .
16.
The notation used for identifying an individual target is as follows:
bay no./row no. / target distance from centreline
e.g., 2/ 3/ 7R (bay 2, tow 3, 7 in right of centre).
Bay numbers have been omitted when the information is not required .
J7. Deflections and deformations are based on an orthogonal co-ordinate system:
Z vertical (positive downwards), X lateral (positive to the right of the wheel
direction) , and Y longitudinal (positive in the wheel direction) .
TRANSDUCERS
18.
To gain experience in their use, five displacement transducers were installed,
three in bay 4 and one each in bays 2 and 3. They were Hewlett-Packard
7DCDTlOO, with a linear stroke lehgth of 5 mm (0.2 in). One transducer in each
of bays 2, 3 and 4 was installed to measure the vertical deflection of the base
course/subgrade interface, and two more transducers measured the vertical deflection of the surface course/ base course interface of bay 4. The transducers themselves were clamped below the road bed, and the cores were extended with 1.6 mm
(1/16 in) diameter steel rod. When passing through the base course material, the
rods were protected with nylon tube, the annular space being filled with petroleum
jelly. 12 mm (t in) diameter discs were silver soldered to the tops of the rod.
No mechanical or electrical problems were encountered with the installation.
TEST PROCEDURE
19.
To 'bed-down' the sand asphalt surface course, the wheel was run with a
tyre pressure of 620 kPa (90 psi), a total load of 400 N (90 lb) and at a speed of
1.5 m / s (5 ft /s) for 16 passes of the wheel over each section of the track. The
position of each target was then measured, this set of readings being used as
the datum.
20.
With a constant temperature of 20 degrees C (68 degrees F), the road was
subjected to 150 cycles of load over the period July 1971 to November 1971.
Measurements of the surface profile and the dynamic behaviour of the road under
'Benkelman beam' and 'plate bearing' type tests were taken after one, five, ten, 50
and 150 cycles.
21.
Water content samples were then taken and in spite of the bitumen seal it
was found that the material in each bay had dried from seven to eight per cent, to
one to two per cent (see TABLE I).
22.
The next stage of the test consisted of wetting the bays sufficiently to keep
the material damp, but not so much that the pore pressures became positive. The
method devised was perforce somewhat arbitrary. A 25 mm (1 in) wide strip of
Volume 7, Part 7, 1974
109
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
the sand asphalt was cut out down the extreme side of each bay (this strip was not
subject to trafficking) , and the surface of the road and the 25 mm (l in) channels
so formed were kept covered with water. Polythene sheets were laid over the road
surface to stop evaporation of the water while the road was being trafficked.
23 .
The immediate swelling of the bays was recorded and the road trafficked
from December 1971 to May 1972 for a further 300 cycles. Measurements being
taken after 50, 94, 150 and 300 cycles (200, 244, 300 and 450 cycles total) .
Throughout this stage of the test the road was kept wet while trafficking was taking
place, but ,the road tended to dry out while measurements were being taken.
The vertical position of every target, and the horizontal position of targets
24.
0, 3R, 3L, 14R, 14L were recorded on every occasion.
The 'Benkelman beam' type test consisted of measuring the transient vertical
25.
deflection of targets If3R, 3/3R, 3/3L, 4/3R, 4/3L and 6/3R in each bay. (Targets
75 mm (3 in) left and right were just clear of the rubber tyre as the loaded wheel
travelled along the centreline of the bay. These tests are referred to as rolling
wheel tests.)
26.
Because of difficulty in reading six dial gauges simultaneously, and because
it was found that the sand-asphalt suffered considerable creep distortion, the wheel
was stopped between rows of targets while the dial gauges were read. The wheel was
then moved manually approximately 230 mm (9 in) to halfway between the next
two rows of targets, and the dial gauges read again. The equipment to dynamically
record 'the pavement behaviour was not available, and it was later found that there
was a considerable difference between the static deflection measurements and
measurements taken with the wheel moving at 1.5 m/s (5 ft/s).
27.
The 'plate bearing' test consisted of locating the wheel at the centre of each
bay and cycling the load three times from 0 - 2360 N (530 lb). The vertical deflections of the six targets 75 mm (3 in) to the right of the centreline were recorded
on dial gauges. These targets measured the deflections at approximately 130 mm
(5 in) , 280 mm (11 in) and 500 mm (20 in) radius from the wheel. These tests
are referred to as static wheel tests.
BEHAVIOUR OF TEST MATERIALS -
GENERAL
28.
This section will report the general behaviour of the four test materials.
Paras 50 to 66 will discuss the results in detail with more concern for their value
in a fundamental understanding of the behaviour of road bases.
0-150 CYCLES
29.
The average permanent settlement of the centre area of each bay (the average
of the 42 targets 3R to 3L in all six rows) is shown in Fig. 1, and the symmetrical
profile of each bay in Fig. 2. The symmetrical profile is derived by averaging the
deformation of all the 12 targets which are at the same distance from the centreline.
Vector movements in plan are shown in Fig. 3, and ,the longitudinal profile of the
centre area of the bays in Fig. 4. An error developed in the dial gauge measuring
the transverse eX') position of the targets, but because of the method of measuring
110
ARRB PROCEEDINGS
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EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
Total ~ ot Cycles
10
50
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Trafficking
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average of all torgets
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Fig . 1 -
Average permanent settlements (0 to 150+ cycles)
Fig . 2 -
Symmetrical lateral oroliles (0 to 150+ cyclea'
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Plan vector movements (X-Y) (0 to 150 cycles)
Volume 7, Part 7, 1974
Plan vector movements (X-V) during swelling
(150 to 150+ cycles)
111
FINCH -
EVALUATING 'B RECCIA AS ROAD BASE COURSE :MATERIAL
Whul
Boy 2
Boy 1
Bay 3
Boy 4
450
E
E 5·0
10·01---
- - - - - - - - - -- - - - - : : - - - - : - : - - -!::!21£. : A v ~rog~ sdttement of th~ 7targ£u within
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Fig . 4 -
Longitudinal profi l es (0 to 450 cycles)
the horizontal position it was possible to eliminate this error by averaging pairs
of targets in adjacent rows, i.e. row one and row two, row three and row four, row
five and row six. The plan vector movement diagrams are therefore shown with
only three rows of targets.
30.
During the first ten cycles of loading all bays showed volumetric compaction
or 'consolidation'. However, bays 2, 3 and 4 (breccia + lime, breccia + lime +
bfp, dolerite) all showed slight heave in the un trafficked areas, implying that shear
distortion had also taken place. Bay 1 (breccia) did not show heave in the
untrafficked area, but could nevertheless have experienced shear distortion.
3l.
After the initial 10 cycles, all four bays behaved in a similar manner, the
heave in the untrafficked areas giving way to settlements.
32.
The lesser settlement of the centre targets of the bays which was very
noticeable in the case of bays 2, 3 and 4 (see Fig. 2) has not been satisfactorily
explained. A similar effect was measured by Sparks and Davis (1970) in the
previous experiment on the machine (see their Figs 5, 8 and 9c) .
33.
From the rolling wheel tests (see Figs 18 to 24) bays 1, 3 and 4 behaved as
rigid slabs on a flexible subgrade, while bay 2 (breccia + lime) behaved as a flexible
base course.
34.
Fig. 1 shows the average settlement of the centre area of each bay. If the
settlement of bay 5 (the bay consisting of surface course only) is deducted from
the settlement of the other four bays, then bay 1 (pure breccia) would show zero
net settlement and bays 2, 3 and 4 a net settlement of about 0.25mm (0.01 in)
However, in <the early stage of the test (up to 5 cycles) bay 5 had in fact settled
more than bays 1 and 2. Together with the scatter in the results and the nonuniformity of the sand-asphalt, the conclusion reached at this stage of the test was
that no real distinction could be made between the four bays, but that their
behaviour could be described as satisfactory.
WETTING
35.
Measurements immediately after wetting, but before further trafficking have
been designated as 150+ cycles. The heave after wetting is shown in Figs 1 and 2
112
ARRB PROCEEDINGS
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EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
and the plan vector movements during swelling in Fig. 5. The swelling of all four
bays was extremely uniform, and gave some confidence in the measuring system.
Both in absolute terms and as a proportion of the previous settlement, bay 1
(untreated breccia) and bay 4 (dolerite) swelled the most, and bays 2 and 3
(stabilised breccias) the least. As might be expected, wetting had virtually no effect
on bay 5, the bay consisting of bitumen surface course material only.
36.
The direction and magnitude of the swelling movements may be associated
with two causes. The first is the reversal of shrinkages caused by the material
drying, and the second is that the strains are caused by the relief of stresses induced
by the rolling load. Bay 3 (breccia + lime + bfp) showed systematic and
symmetrical expansion, probably due to reversal of shrinkages due to drying. Bay I
(breccia), however, showed some swelling movements in the direction opposite to
that of the wheel, possibly due to relief of stresses induced by the rolling load.
37.
In the untrafficked areas bays 1, 3 and 4 showed an outward swelling movement, perhaps associated with shrinkage, but bay 2, which had been behaving as a
flexible base course and had sustained longitudinal horizontal deformations equal
to the vertical deformations, showed inward horizontal lateral movements on
wetting. These movements may be indicative of horizontal lateral compressive
stresses having been induced in this bay.
38.
Although the results are not completely consistent, a tentative conclusion
might be that horizontal lateral stresses were induced in the material that was
deforming as a flexible layer, but not in the materials that behaved as rigid slabs.
Boyl
10 ' 0
Not e ' ....",c rogc
-
01 1111
42
ta rge ts
.....'tn in75mmOlCCntrw:tirw Ol
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200
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1000
450
LaoOlng Pott erns
Fig. 6 -
Average permanent settlements (0 to 450 cycles)
9' 0
Note : Each point is the average settlement of 6 tar grl~
Fig. 7 -
Volume 7, Part 7, 1974
Latera l profiles -
bay 1 (0 to 450 cycles)
113
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
No te: : E actl p oin t is th e o v t:rog c. sc:tt l ement o r 6 t org ets .
Fig . 9 -
Lateral profiles -
bay 3 (0 to 450 cycles)
3 -0 ,
!:!£1!t: Eoch p oi nt is the ove rcgll H tt lcmcrnt
Fig. 8 -
Lateral profiles -
0 ,'
6 torget ..
Tr a ff ick ing
~
bay 2 (0 to 450 cycles)
01"-
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Fig . 11 -
114
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Fig. 10 -
LeQend
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------+: -----'
Plan vector movements (X-Y) (0 to 450 cycl es)
ARRB PROCEEDINGS
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
Fig . 12 -
Volume 7, Part 7, 1974
Bays 1 & 2 surface at 450 cycl es
05
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
39.
Rolling wheel tests conducted immediately after wetting but before further
trafficking showed a complete change in behaviour of bays 1 and 4 (breccia,
dolerite). Whereas previously these bays had rocked on the subgrade and behaved
essentially as rigid slabs, after wetting they deformed as flexible base courses in
the same manner as bay 2 (breccia + lime) - see Figs 18 and 23. Bay 2 (breccia
+ lime) showed virtually no change in behaviour after wetting, but this may have
been due Ito the high bulk permeability af this material allowing immediate drainage
of the bay. (Fig. 20.) Bay 3 (breccia + lime + bfp) showed a reduction in deflections, possibly due to the expansion af the material creating greater friction between
bays and between this bay and the side walls of the test track. (Fig. 22.)
150+-450 CYCLES
40.
The average settlement of the centre area of each bay is shown in Fig. 6,
lateral profiles in Figs 7 to 10, and plan vector movements in Fig. 11. Bay 1 (pure
breccia) deformed the most. The centre of the bay immediately settled about 6 mm
Ct in) and the untrafficked areas heaved. Part of the asphalt surface course appeared
to have impacted into the breccia and mud from this opening had covered the
centre of the bay. After 300 cycles total, the surface had deteriorated to such an
extent that it had to be resprayed with the 'RSK' emulsion to avaid complete
collapse, and a local pot hole that had developed at the junction with bay 2 had
to' be patched with asphalt. Hair line cracks could be seen over the trafficked area
of the asphalt (see Fig. 12) .
41.
Initially, bay 2 (breccia + lime) increased its rate of permanent settlement
and sustained some shear distortion. However, the maximum deflections in the
rolling wheel tests reduced as the bay was subjected to further trafficking. The
surface remained intact, but not quite as smooth as bay 3.
42.
Bay 3 (breccia + lime + bfp) showed almost no increase in its rate of
average settlement, but this was partly due to shear distortion taking place as well
as permanent settlement. The bay as a whole remained intact at 450 cycles,
showing its 'rocking' characteristic in the rolling wheel tests. The surface was hard
and smooth with no signs of degradation of the asphalt (see Fig. 13).
43.
Bay 4 (dolerite) settled at about half the rate of bay 1, with considerable
shear distortion. The surface remained generally intact, although small plugs of
asphalt broke away immediately above the transducers installed at the interface
between the dolerite and the asphalt (see Fig. 13).
44.
Bay 5 (asphalt surface course only) showed almost no change in behaviour
after wetting, and more confidence can now be placed in the difference in behaviour
between the other bays.
45.
The test was terminated when bay 3 (breccia + lime + bfp) had reached
the same rate of permanent settlement per log loading cycle as it had before
wetting. The settlements of bays 1, 2 and 4 were continuing, but it was felt that
more useful results on the behaviour of the materials when subject to wetting could
be obtained from more conventional laboratory testing. In addition, it was becoming
difficult for the wheel to folJow the large differential settlements between bays. The
hydraulic ram supplying the 2360 N (530Ib) load can only move through 20 mm
(i in).
116
ARRB PROCEEDINGS
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EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
Fig. 13 -
Volume 7, Part 7. 1974
Bays 3 & 4 surface at 450 cycles
117
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
46.
One area of doubt with the results is whether the fully stabilised breccia
(bay 3) would have behaved differently if the material had cracked, thus allowing
water to enter the main body of the test bay. After excavation it could be seen
that the water had not penetrated to the centre of the bay, but had run directly
from the sampling holes at each side of the bay to the porous rubber subgrade.
However, water should have penetrated down the polythene layers between bays
2 and 3 and 4, and there was no sign of degradation at these joints even though
there would have been large relative movements because of the 'rocking' action
of bay 3.
ROLLING WHEEL TESTS
47.
Bays 1 and 4 (breccia, dolerite) prior to wetting, and bay 3 (breccia + lime
+ bfp) at all times, rocked on the subgrade. These rolling wheel maximum readings
are ambiguous and will have no real relationship with the elastic response of the
intact material in these bays.
48.
Of interest in the present test is the degree of correlation between the
behaviour of the test bays and their deflection under load. At 200 cycles completed,
the maximum deflection of each bay ranked the bays in the same order as the
permanent deformation of the bays. However, the maximum deflection of bay 2
at 150 cycles was the same as bay 1 at 200 cycles, even though bay 1 was in a
far worse condition at this stage than bay 2 at 150 cycles. This is because the
deflections of bay 2 decreased even though it continued to suffer permanent
deformations under load. The qualitative behaviour of the fours bays is summarised
in TABLE II.
CONCLUSIONS
49.
All four materials behaved satisfactorily when tested dry. Pure breccia, and
perhaps dolerite, were uns atisfactory when tested wet. When tested in the road
machine under the conditions of this test, the breccia stabilised with lime and blast
furnace pozzolan behaved as a rigid slab, and interpretation of deflections using
elastic flexible layer theory is invalid.
DISCUSSION
50.
The vector movements in the three planes X-Y, Y-Z, X-Yare shown in
Figs 11 and 14 to 16. Y is the longitudinal direction, X the lateral, and Z the
vertical. When trafficked dry, bays 1, 3 and 4 sustained essentially vertical movements only. There were some longitudinal movements in the trafficked areas,
TABLE II
QUALITATIVE BEHAVIOUR OF THE FOUR BAYS
Bay 1
(breccia)
o cycles
118
Bay 2
(breccia
lime)
+
Bay 3
(breccia
lime
bfp)
Bay 4
(dolerite)
+.
' Dry'
150 cycles
slab
flexible
slab
slab
'Wet'
450 cycles
flexible
flexible
slab
flexible
ARRB
PROCEEDINGS
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
'4 L
Lc ft
. . --I
3.
~
\
o
3L
,W
<
-:~,""
\
200\244
\.
j
'3 00
1450CYC'U
~
IIXMI&IR:S'II
r
)
150'·
200'
l244
!
Mh,AW)
~
1300
'4 50
IrMII&lX'M
III&IW#Wd
150·..
° 4 50
Boy'
~45 0
450
\ 300
\200
T
\.150·
.
Scale:
0 ·, 0-2
l( m~) 1L~;"O'
0"
0'2
IIM/kilAi»
"\y",,
.=.!!.
1S0cycl u
"0 2'0
E : x (m m)
lcgcnd
2·0
/
lateral
,,0
Y Vcrrt icQ'
(m m )
( rnm) Z Vc.rt icol
IIMmmtJ
150"·
.- .,... , Boy 5
i
"
2J\
!~ !
\i
20~
" 50·
Bay 4
\
!:::!.Q!£ : Ava-oge: 01 s ix tc rgets ot each position
Fi g. 14 -
Lateral vector movements (X-Z) (0 to 150 cyc les)
Fig . 15 -
Lateral vector movements (X-Z) (0 to 450 cycles)
and some lateral movements in the untrafficked areas, but these are probably due
to shrinkage of the base course material. The vertical deformations that were
measured, especially in the case of bay 1, were mainly in the surface course. These
bays were behaving as rigid slabs on the flexible subgrade.
51.
When trafficked wet, bays 1 and 4 sustained considerable distortion. The
untrafficked areas moved upwards and outwards at about 45 degrees (Fig. 15),
and the trafficked areas moved downwards and forwards at about 45 degrees (Fig.
16b). The bays started to behave as a flexible base course and in the case of bay 1
the deflection bowl became narrower as the maximum increased. After considerable
trafficking, as the permanent deformations being induced into the test bays by the
wheel decreased, the forward movements decreased even faster. That is, as the
materials approached a state of equilibrium with the applied loading the longitudinal
deformation vectors (Fig. 16) became steeper.
52.
Bay 2 was much less affected by the wetting than bays 1 and 4, but its
behaviour when dry had the same qualitative pattern as bays 1 and 4 when wet.
That is, flexible behaviour and longitudinal vectors at about 45 degrees steepening
as the rate of settlement reduced. However, there was little lateral shoving of the
untrafficked areas in this bay.
Volume 7, Part 7, 1974
119
FINCH _ . EVALUATING BRECCIA AS ROAD BASE COURSE MATERIA:L
Y Horizontal longitudinal Oqlermotion (mm)
0·5
1·0
1- 5
·450 cyclCls
Boy 3
Y Horizontal lo ng it ud inal detormation (mm)
Boy 2
0-5
1' 0
0·5
2·0
1· 0
!:!2.1s.:
Each boy consisted o f U\c.
same materiol installed
at a d ittcrc.nt density ~ t
somc wotcr content .
Fig . 16 -
Longitudinal vector movements (Y-Z)
(0 to 450 cycles)
1·5
Y Horizontal longitudinal deformation
0r-____r-~~----~--(-m-mr)--~5;.~0----r_--~
2 ·0
Fig . 17 -
Longitudinal vector movements In Dolerite
experiment
.H21! :V.rtical movements from avc.ragc of -42 torgds !75nYn
of whccl L Horizontal movements 'rom overag,_ of
18 torgds.( 3R .0. 3l in cach row.)
10'.0
120
ARRB PROCEEDINGS
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
53.
Bay 3 behaved erratically because of its rocking slab action on the subgrade.
There were no systematic longitudinal vector movements other than shrinkage and
swelling.
It appears that the horizontal movements occur when the material deforms
54.
as a flexible base course with an appreciable deflection bowl. Similar movements
were measured by Sparks (1970), and are shown replotted as vector movements
in Fig. 17. In this case, the vector direction is at about 30 degrees to the vertical,
but the shape of the deflection bowl was not recorded. The horizontal movements
cannot be justified by linear elasticity. Non-linear elasticity without recoverability
would appear at first to be inappropriate for a material which is being subjected to
repeated loading. Other theoretical analyses might be visco-elasticity, elasto-plasticity,
hysteresis (caused either by visco-elasticity, plasticity or some other mechanism), and
non-homogeneity.
55.
A visco-elastic approach would entail the wheel continually climbing out of
its own deflection bowl, and this would involve the time dependent behaviour of the
road materials. :Another approach is that the material ahead of the wheel on its
'Nth' pass is responding differently from the material behind the wheel because
it has suffered only 'N-}' passes of the wheel. Either the materials response to
load is being altered, or the state of stress in the material is changing.
56.
Both hysteresis and permanent deformations were measured in the static
wheel tests, but it is difficult to draw definite conclusions as most of the deflections
took place in the sponge rubber, and the time-dependence of the deflections
was not investigated. There is a possibility that the permanent deformations may
be due to mechanical friction in the dial gauges used to measure the deflections.
stort I
toblCl
50
0'5
E
E
Start
table
I.
Bay 1
I Bo y 2
I'
Cycl~s
Boy 1
E
E.
0 '5
" 0
, Position of wh(l(ll
150·Cyclu
(Immediately after
wetting but no extra
trafficking)
"0
Fig . 18 -
Longitudinal deflection profiles during rolling
wheel tests - Bay 1
'Position of wheel
Volume 7. Part 7, 1974
121
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
f.I'- -- - Boy
Whu.1
O - !5m
-L..
2
- -- - ----i
0·5
150cyclu
0 ·5
200 eyelets
0'5
ROil in g Wheel Test
7.
O£flections tro m thcr.
four torgds in centre.
.
'-
S tat ic Whul Test.
(mm )
at bay ()/)R • 3/3L, 4 /3R
4/ 3L) normalised t o a
co mm on c.:ntrc:line .
Finol unload
1
1st lood
3rd lOad
,,
I
I
I
I
0 '5
No rmalised d eflection profiles - Bay 1.
\
I
'..._t.' ' . . .
Fig . 19 -
Normalised deflection profiles -
200 cyclc:s
J..-/
Bay 1
'-0
Fig. 20 -
,
/
, Whul postion
Longitud inal deflection profiles during rolling
whe el te st - Bay 2
57.
The measurable permanent deformations induced by the static and rolling
tests were unexpected, especially as all the measuring targets were not directly
loaded. In this particular test they may be associated with the soft subgrade but
if they are representative of prototype road behaviour then it suggests that during
a single pass of the wheel much larger permanent deformations are induced than
would be expected from the average rate of permanent deformation per load cyele.
58.
Because the wheel is tracking along different paths, it is possible that the
vector sum of the deformations induced by all the loading paths is less than the
deformations induced by anyone individual pass. For example, a material
deforming at constant volume and repeatedly loaded by a statistically uniform
pattern of loads will show zero net deformation, even though deformations will be
induced by anyone individual load.
59.
This aspect of the problem of obtaining a theoretical solution to road base
course behaviour is further brought out by attempts to test materials in the laboratory. The usual repeated load tri-axial test, a regular variation of the major
principal stress, is an approximate simulation of the conditions experienced ,by a
point vertically beneath a load being applied to the surface of a road. The true
stress path will not only be traced in three-dimensional stress space with all principal
stresses varying, but also with rotation of the principal stresses. In addition, because
122
ARRB PROCEEDINGS
FINCH ~ EVALUATING " BRECCIA AS ROAD BASE COURSE MATERIAL
a wheel may pass at any distance from the point considered, the direction and
magnitude of the applied stress path wBl vary with each load application. In the
field of metal fatigue such variations in applied stress path direction change the
cumulative damage to the metal to a considerable extent. The simple repeated
load tri-axial test is therefore only an index test of the behaviour of materials when
used in roads.
60.
The horizontal deformations and their justification will be investigated
further with the test track. Of interest would be the path traced by a point in
the base course as the wheel passes overhead. By ideal elastic theory, this path
should be a closed loop symmetrical about a vertical line passing through the
point considered. It is possible that this deflection loop is skewed in a forward
direction. It is hoped to record its path in the next experiment. In addition, load
cells installed in the base course to measure the horizontal stresses, both transient
and permanent, will be installed.
61.
Horizontal loads transmitted by the wheel to the road surface are obviously
of great importance. It has unfortunately been found to be too costly to conveniently
measure this load directly. However, the frictional resistance of the wheel bearing is
extremely low and it does not appear to be possible for the wheel to transmit a
significant horizontal force to the road.
62.
In order to compare the deflections under a static load with those under
a rolling load, the deflection profiles from the rolling wheel tests have been
normalised to a common centreline. Only the four targets 3/3R, 3/3L, 4/3R, 4/3L
have been used, and the points shown in Figs 19, 21 and 24 are the average of the
0 ·5
O ',~ m
0" 1
150
cyc ~ :Io
0· 3
Bcy2
\
lo'r
\'
' 5 0· cycles
'-
( mm)
200 cycles
'Po~ iti on or wheeL
Su
Fig . 21 -
I.g . 2'2 lo r symbols
Normal ised defl ection profil es -
Volume 7, P art 7, 1974
Bay 2
Fig . 22 -
Longitud inal deflection profiles duri ng rolling
wheel test - Bay 3
123
FINCH Boy
31
EVALUATING BRECCIA AS lWAD BASE COURSE MATERIAL
Bay 4
I
End
Tobit
_J~.
E
,.
.5
200c),c ln
,,
0·5
Su
fi g.
19
lor ~ymboI ~
'.1-
\L
Cmm )
150·cyclcs
Fig . 23 -
Fig. 24 -
longitudinal deflection profiles during roiling
wheel test - Bay 4
Normalised deflection profiles -
Bay 4
Wheel
+
0'5
- - - Bay 1
Bay 2
Bay 3
Note: Deflections along a
line tangential to a 75mm
radius circle: cllntrtld on
th .. load .
Finit~ ele.rT'Ient
solution.
1'0
D"fl<,etion
(mm)
6mm
, Surface course} E : E1
152mm
, Base eourse
==,*==1 Sub grod"
12'5mm
Fig . 25 -
124
V, 0 ·33
- E,159kPa from laboratory
tests. V , 0
Isotropic elastic deflection profiles at 200 cycles
ARRB PROCEEDINGS
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
"
left and right pairs of targets. The average deflection profile drawn through these
points is therefore both the instantaneous average deflected profile and also the
reversed influence line for the settlement of the centre of the bay. The deflections
at different radii in the static wheel loading tests are also shown on the diagrams.
63.
Both the static and the rolling tests showed permanent deformations induced
in the road surface, even though the wheel had not passed directly over the
measuring points. It is therefore to be expected that there will not be perfect
agreement between the two profiles. However, in general there is a good agreement
on the right hand side of the diagrams (,the loading side), with discrepancies on
the left hand side due to the hysteresis and permanent settlements.
64.
Any material that shows hysteresis on cyclic loading (even though the
strains are fully recoverable) will have an unsymmetrical 'Benkelman beam'
profile, and different methods of field testing will, if used to interpret the full road
structure, give results dependent on whether the test is loading or unloading.
65.
A point of interest is the heave measured about 0.5 m (20 in) behind and
0.5 m in front of the wheel-see especially bay 1 at 200 cycles and bay 2 at
150 and 200 cycles (Figs 19 and 21). From the corresponding deflection profiles,
it can be seen that this heave is possibly associated with interference from the
adjacent bay. If however this heave is representative of the behaviour of a
continuous layer then it would show a significant difference in behaviour between
static and rolling loads.
66.
Deflections from finite element isotropic elastic solutions for an axi-symmetric
structure the same area as the test bays (i.e., 584 mm (23 in) radius) are shown in
Fig. 25. They are compared with the deflections of bays 1, 2 and 3 at 200 cycles.
A major source of error is the boundary condition at the sides of the bay. The
theoretical solution assumes smooth vertical interfaces, whereas in practice there
will have been some shear stress on this boundary. Better agreement may also be
possible with anisotropic or 'no-tension" elastic solutions. As can be seen from
Fig. 25, the discrepancy between the theoretical deflections and the measured
deflection are so large that meaningful isotropic parameters are difficult to estimate.
However, very approximate values of Young's modulus, based on the deflections
at 100-125 mm (4 to 5 in) radius and a Poisson's ratio of 0.33 would be 35 MPa
(5000 psi) for bay 1 (breccia), 90 MPa (13,000 psi) for bay 2 (breccia + lime),
and 70 MPa (10,000 psi) for bay 4 (dolerite). Bay 3 could not be evaluated
because of its rigid behaviour.
CONCLUSIONS
67.
Horizontal movements which are a constant proportion of vertical movements
are ·induced in a flexible pavement when subjected to a rolling load .
68.
Rolling loads and cycled static loads show hysteresis and appreciable
permanent settlements, indicating departures from elasticity.
69.
Because of hysteresis and permanent deformation, the transient longitudinal
deflection profile is not symmetrical about the wheel.
Vplume 7, Part 7, 1974
125
FINCH -
EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
DISCUSSIONS
70.
Because of the irrecoverable deformations induced by a load, it has not been
possible to obtain a simple comparison between static loading and a rolling load.
71.
Even when the road is sustaining very little average permanent deformation
per pass of the wheel, individual passes of the wheel at different lateral positions
may nevertheless induce large permanent deformations and therefore indicate
inelastic behaviour.
72.
There is very little agreement between the shape of the deflection bowls
predicted by isotropic elastic analysis and the shape of the measured deflections
bowl.
REFERENCES
SPARKS, G. H. (1970) . Development and use of a machine for examining the behaviour of
pavement structures under the action of moving wheel loads. 'M . Eng. Sc. Thesis, University
of Sydney.
SPARKS, G. H . and DAVIS, E. H . (1970) . First road base experiment with a laboratory test
track. Proc. 5th ARRB Conf., Vol. 5, pt 4.
DISCUSSIONS
E. C. BROW N
Principal Engineer (Aerodromes), Australian Government Department of Housing and Construction
72.
What was the significance of the horizontal strain versus vertical strain plot
presented in your initial address?
W. O. Y AND ELL
Lecturer, School of Highway Engineering , University of New South Wales
73.
This paper is a fine piece of work. However every work of art has its imperfections. In para. 61 the author was wrong in assuming that the sole source of
horizontal force was friction in the road wheel axle. The rolling resistance of the
deforming tyre can also be considerable, depending on its inflation pressure.
74.
I think it is misleading to associate asymmetry in the deflection bowl, mentioned in para. 55, with visco-elasticity. All road materials are energy absorbing;
few are visco-elastic. Does the author know of any methods for predicting horizontal movements in his repeatedly traversed track?
75.
Does the author believe that the Kanga hammer compaction of the scaled
test pavement adequately simulates roller compaction? Does he intend to plot the
progressive deformation taking place in the body of the pavement?
76.
Since the author's test rig is of small scale it is most suited to either pure
comparison studies or for investigating phenomenological behaviour. For the latter
to be successful, a technique for analysing a realistic mathematical model must
be developed. So far, original analyses have not appeared from Sydney University
and existing ones have been ignored. How long will this continue?
126
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EVALUATING BRECCIA AS ROAD BASE COURSE MATERIAL
DlSCUSSIONS / AUTHOR 'S CLOSURE
A. K. PA R KIN
Lecturer, Department of Civil Engineering , Monash University, Victoria
77.
The author has noted significant permanent longitudinal deformations
during trafficking of test pavements (Figs 16 and 17), and has offered two possible
explanations for this behaviour in para. 55.
78.
It is also possible, however, that these deformations may result from the
fact that the test wheel is drawn, rather than driven, over the test track. Real
traffic loading consists of both free-wheeling axles and driving axles, but their effects
on residual pavement deformations may well be different, resulting from the
different directions of the pavement reaction force. It would, therefore, seem fruitful
to examine this matter at some time, using the road test machine.
J . N. HAN K S
Research Scientific Officer. Country Roads Board. Victoria
79.
The author states that dynamic and static stresses must differ and that a
longitudinally non-symmetrical distribution of deformation is very likely. I concur
on both points and indeed would say that asymmetry simply must occur because
'behind' and 'in front of' the rolling load are intrinsically different conditions when
any relative particle movement can occur. The only real question is at what stiffness would the effects become negligible in practice?
80.
This experiment and many others show the intense difficulty in formulating
a theoretical model for behaviour which even approximates what actually happens.
Compounding this are the problems of satisfactory parameter determination and
of non-uniformity in all dimensions of a road material. Thus design on a theoretical
basis (so called rational methods) must be decades away, at best.
81.
In particular, I express my full agreement with para. 59 wherein the author
points out that the usual triaxial test is only an index test of the behaviour of road
materials. No doubt it is of a superior nature compared to highly simplified index
tests but an index test it remains. Far too often one reads claims that triaxial type
tests provide fundamental values which can be used in design. As the author shows,
the reality is that the triaxial test is just another type of empirical test. This conclusion can be reinforced by consideration of the fact that, if selection of an appropriate density and moisture condition for the specimens is difficult enougb, the
attainment of a representative material structure and stress history must be thought
impossible.
AUTHOR'S
CLOSURE
82.
The significance of the horizontal versus vertical strain plot is not fully
understood; it is hoped that further studies in the road machine will help to clarify
the situation. The plot was presented as an observed feature of the behaviour of
the material when trafficked under the particular loading conditions of the machine.
It is appreciated that braking and driving wheels are likely to cause different responses in material behaviour and it would be possible to simulate these types of
Volume 7, Part 7, 1974
127
FINCH -
EVALUATING BRECCIA AS ROAD BASE COU RSE MATERIAL
AUTHOR'S CLOSURE
loading with the machine, but at present only loads transmitted by a towed wheel
are being considered in the comparison tests on base materials.
83.
The compaction of material in the machine by means of an electric vibrating
hammer was not intended to simulate the type of compaction which occurs in the
field under a roller. The hammer was used because it was a practical method of
achieving a particular controlled level of density, and it is thought to be a valid
method of compaction for the type of comparative test being carried out.
It is hoped to carry out more fundamental studies with the machine in84.
cluding an examination of horizontal movements, but a full treatment on these
lines must await the availability of research workers at the University. Meanwhile
the machine is being used mainly for comparative studies on road base materials.
85.
I agree with the point made by Dr Yandell that the deformation of the
pneumatic tyre will impose some horizontal forces on the pavement.
86.
The results of the test confirm the exper:ience of the Department of Main
Roads, in that the performance of the materials is rated in the same order.
12Sl
ARRB PROCE EDINGS