Environmental Engineering Reference
In-Depth Information
3.2
Control of field compaction: Criteria and tests
Field compaction trials were performed in both
experimental road sections, using the same com-
paction equipment and only varying the number
of vibratory roller passes. in Figure 5 is repre-
sented the evolution of relative compaction with
the compactive effort, showing a substantial differ-
ence depending upon the granular base foundation
conditions.
The minimum allowable field relative compac-
tion (98% of M.P. maximum dry unit weight),
according to ePe-98) has not been achieved when
the unbound aggregate is compacted directly on
the existing pavement. consequently, experimental
results demonstrate that the same volcanic mate-
rial responds differently, and that the efficiency of
the densification process is determined by a new
factor affecting field compaction: the mechanical
properties of the layer foundation.
as previously mentioned, the regional road
administration had raised objections, based on its
previous experience, to the utilization of the gen-
eralized laboratory compaction tests as specified
tests to control field compaction of volcanic aggre-
gates due to their greater insensitivity to moisture
content variation, obtaining quasi-horizontal
compaction curves. This finding is attributable to
high permeability of volcanic crushed aggregates,
and therefore moisture content directly measured
on the compacted lift underestimates the effectively
participant water in the compaction process.
nevertheless, Modified Proctor compaction test
curves on aggregate samples recovered from stock-
pile and from each test road section after densifi-
cation reveal that the volcanic cGa employed for
base course responds to moisture variations, as can
be seen in Figure 6. This figure compares water
content-dry density curves from all-in aggregates
of different petrographic natures (volcanic and
non-volcanic), suggesting that the basaltic aggre-
gates from azores even achieve higher maximum
dry unit weights than the others represented on the
graphic.
These volcanic crushed mineral aggregates are
habitually lacking in fine-grained sizes (even from
continental regions), have high porosity and mean
water absorption values around 3%.
on the same Figure 6, compaction curves for
other basaltic crushed granular materials from
some recently built roads in the canaries and cape
Verde have been plotted. as it can be seen, all of
them provide evidence of a normal performance in
compaction tests.
The observation of this result not only has pro-
vided some support to the assumption that Proctor
tests can be applied to volcanic materials, but also is
consistent with the european standard en 13285
Rate of compaction vs. compactive energy
100
99
98
97
96
95
94
93
92
91
90
89
88
0
10
20
30
40
50
Number of roller passes
Ex perimental trial road section comp acted on existing pavement
Ex perimental trial road section comp acted on new lapilli subgrade
Figure 5. Variation of relative compaction with com-
paction effort depending on foundation conditions.
which specifies the Modified Proctor laboratory
test as relative compaction test for unbound mix-
tures, independently of the petrologic nature of the
soil or aggregate.
3.2.1
Control methodology in the Canary Islands
Volcanic granular materials utilized in the canaries
for unbound road bases are obtained from crushing
basaltic and phonolitic rocks, since at the present
time sedimentary deposits of gravels present a very
restricted quarrying due to environmental reasons,
and low density pyroclastic aggregates (lapilli)
are only employed to form subgrades as they do
not observe spanish road standard specifications
(PG-3) as for fracture strength, gradation and
sand equivalent.
in spain, the general employment require-
ments for unbound continuous grading aggregates
(cGa) used in bases and subbases are founded
on road construction standard PG-3 (article 510.
“
Zahorras
”). This granular material has to observe
some general conditions with respect to reduced
plasticity, particle fracture strength, shape and
angularity, being spread with compacted lift thick-
ness not greater than 30 cm. end-product control
criteria are based upon:
- Rate of compaction control: for heavy traic
flow >200 heavy-vehicles/day, a level of rela-
tive compaction of 100% (of P.M. maximum
dry unit weight) in the construction is required.
For lower traffic categories and on road shoul-
ders, a relative compaction not less than 98% is
accepted.
- Bearing capacity control by means of in-situ
plate loading tests: The modulus of vertical
reaction measured in the second cycle of plate
load test (e
V2
) is specified to be over 80 to 180
MPa depending on the heavy traffic conditions,
and not to be lesser than the modulus of the
