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Geotechnical characterization of carbonate marls for the
construction of impermeable dam cores
F. Lamas, C. Irigaray, J. Chacon*
Department of Civil Engineering, University of Granada, Polytechnic Building, Avda. Fuentenueva, s/n, 18071 Granada, Spain
Accepted 31 January 2002
Abstract
Fine-grained, more or less cohesive carbonate materials are extremely widespread in terms of surface area and are, therefore,
commonly used as materials to construct impermeable cores for dams. However, it has not been adequately documented
whether the carbonate content in fine-grained soils significantly affects their engineering behaviour. The present study shows
that the carbonate content substantially influences the engineering behaviour of clayey material. For this, we subjected 32
samples to different laboratory tests, such as the normal Proctor, the Atterberg limits, granulometric analysis, oedometric and
undrained triaxial tests. The resulting parameters were correlated with the carbonate content of the samples. The materials
studied in this work had been used in the construction of the impermeable core of the San Clemente Dam, belonging to the
hydrographic basin of the Guadalquivir River (southern Spain). These marls present, as their prime characteristic, a carbonate
content of the fine fraction consistently exceeding 50%, giving them special importance in the study of this phenomenon. In this
study, a direct relationship was found between the geotechnical properties of the soils studied and their degree of compaction,
with the carbonate content and the type of minerals in the clay being the main factors determining the behaviour of these soils.
Finally, we conclude that the percentage of carbonates should be used as a classification criterion for the soils used to construct
the cores of earth-filled dams. D 2002 Elsevier Science B.V. All rights reserved.
Keywords: Carbonate soils; Engineering behaviour; Classification systems; Impermeable core; Earth-filled dams; San Clemente Dam (Granada,
Spain)
1. Introduction
Marls are composed mainly of clay minerals and
carbonate in varying proportions, normally between
35% and 65% (Bellair and Pomerol, 1980). The index
properties ofmarls depend on the carbonate content and
on the type and content of minerals in the clay (El
Amrani Paaza et al., 1998). In the geotechnical classi-
fication of these materials, the methodology used is
usually the same as for fine soils (clays and silts)—that
is, according to the characteristics of consistency of the
clay fraction. However, the carbonate content is not
normally considered in the classification of these soils.
The present study examines the geotechnical proper-
ties of marls as a function of their carbonate content,
with the aim of using these materials in the construction
of impermeable cores of earth-filled dams. For this, we
have worked with the materials used in the construction
of the core of the San Clemente Dam (Delgado, 1983),
situated in the Guadalquivir River hydrographic basin
0013-7952/02/$ - see front matter D 2002 Elsevier Science B.V. All rights reserved.
PII: S0013 -7952 (02 )00048 -0
* Corresponding author. Tel.: +34-958249450; fax: +34-
958246138.
E-mail address: jchacon@ugr.es (J. Chacon).
www.elsevier.com/locate/enggeo
Engineering Geology 66 (2002) 283–294
(southern Spain; Fig. 1). This dam was constructed and
is managed by the Hydrographic Confederation of the
Guadalquivir, an independent office within the Spanish
Ministry of the Environment.
San Clemente Dam is situated over Jurassic lime-
stones on the left bank and in the centre of the river,
and limestone marls and marls on the right bank,
enclosing the valley in the form of a wide V. In terms
of construction materials, this dam of heterogeneous
gravity is a heterogeneous dam of gravity. It has a
height of 91.5 m and a crown length of 580 m, so that
the total volume of materials used was 2,100,000 m3.
The overflow channel is situated on the left bank,
comprised of three chutes closed by curved 8�4 m
Taintor gates. Also, there are bottom and irrigation
drains of 1.80 m in diameter all along the diversion
tunnel, mechanised upstream, with compound closure
by wagon gates activated from an intake tower and,
downstream by gate valves and Howell–Bunger reg-
ulation valves. The dam is stabilised hydraulically by
a core of cohesive impermeable marls of low plasti-
city and vertical disposition, with symmetrical 1:4
slopes upstream as well as downstream (Fig. 2), these
materials being the object of the present study. The
characteristics of the dam and of its impermeable core
are presented in Table 1.
2. Study method
In this work, we selected 32 samples which we
considered representative of the study material, given
the lithological homogeneity of the marly series.
The samples were extracted by a backhoe to a
maximum depth of 4 m, discounting the previous brush
clearing. In all the borings, for the preparation of the
samples, we followed the ASTM D 421 regulation
(ASTM, 1986). The characteristics were studied from
remoulded samples, since marls to be used as a con-
struction material for a dam core must previously be
moulded and, therefore, this is the final state of the
material used in construction. The moulding was car-
ried out with the samples from the intermediate stock
(Fig. 2), which were moistened to the moisture level of
the soils used in the dam (Table 1). From these samples,
by quartering while avoiding moisture losses, we
obtained the different representative fractions needed
for the tests. In the cases requiring sample preparation
Fig. 1. Geographic location.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294284
these were made by compacting to placement moisture,
with a 20-lb mini Harvard compactor for oedometric
pellets and normal Army sledge hammer for 1.5-in.
sample used in the triaxial tests. In both cases, the
compaction was performed in five layers, 12 blows per
layer, thereby simulating the result of the Normal
Proctor used in the compaction of impermeable dam
cores. The moulding technique followed technical
constructions guidelines for the building of the imper-
meable dam core (Delgado, 1983).
For the geotechnical identification and character-
ization of the samples selected, normalized tests from
Fig. 2. San Clemente Dam. (A) Drainage basin. (B) Location of the quarries. (C) Type section.
Table 1
Characteristics of San Clemente Dam
General characteristics Mandatory characteristics of the impermeable core
Characteristic Value Characteristic Value
Type Rock-filled dam
with a clay core
Maximum size 15 cm
Height from the foundation 91.5 m Maximum Proctor density (dmax) 1.7 g/cm3
Width of the crown 11 m Optimal Proctor moisture (wop) 15–24%
Length of the crown 580 m Moisture of compacted soil
during placement at the site
wop+1.5%
Volume of the rock fill 1,347,302 m3 Plasticity index 12–30%
Volume of the core 412,536 m3 Permeability constant <10�6 cm/s
Volume of the filters 197,220 m3 Internal effective friction angle z20jVolume of concrete 55,942 m3 Effective cohesion > 2 kPa
Overflow type Lateral Organic matter content <3%
Drain volume of the overflow 620 m3/s Soluble salt content <4%
Type and dimensions of the gates Taintor 8�4 m Sulphate content <2%
Number and diameter of drains 2�1.8 m Dispersability Not dispersive
Gate type Wagon Compaction equipment Roller
Valves type and drainage capacity Howell–Bunger, 90 m3/s Percentage of compaction >95% of dmax
F. Lamas et al. / Engineering Geology 66 (2002) 283–294 285
different countries were performed (FAA, 1957;
ASTM, 1986; MOPU, 1986, 1991; AASHTO, 1986;
ISSMFE, 1987). Carbonate content was determined
by Bernard’s calcimetric method (Chaney and Slonim,
1982).
The choice of the triaxial test was justified given
the impermeability of the marl treated and the impor-
tance of ascertaining the interstitial pressures in this
test. The consolidation tests were performed with
samples submerged in water in which drainage was
regulated to simulate as closely as possible the phe-
nomena that occur within the dam, extending the time
of each step to 48 h in order to ensure that the primary
consolidation was finalized. According to the condi-
tions governing the dam design, we deemed it
unlikely to reach pressures of 100 kPa and, thus, we
used this pressure as the maximum value in the
triaxial (maximum cell pressure) and oedometric
(maximum step pressure) tests.
The potential expansivity of the laboratory samples
was estimated by evaluating the swelling pressure of
expansive soils, defined as the pressure that must be
exerted on a soil for it not to expand (ISSMFE, 1987).
The test was made on a moulded sample under
optimal moisture conditions under three different
pressures (0, 10 and 30 kPa), verifying for each the
percentage of expansion when equilibrium is reached.
The results for the expansion percentages for each
pressure are presented in a semilogarithmic graph
(pressure on the x-axis in logarithmic scale and the
percentage of expansion on the y-axis in arithmetic
scale). The pressure of expansion is the value corre-
sponding to the intersection of the straight line bearing
the results found with the x-axis.
3. Results
The results of the different tests are summarized in
Tables 2 and 3.
Table 3
Summary of the principal mean results for the marls studied
Mineralogical properties
Carbonate content: 53.5%
Mineralogy of the clays:
Smectite content: 45%
Illite content: 45%
Kaolinite content: 10%
Index properties
Content in sand fraction: 11.1%
Content in silt fraction: 49.4%
Content in clay fraction: 39.5%
Liquid limit: 44%
Plasticity index: 25%
Proctor maximum density: 1.71 Tn/m3
CBR index: 1.57
Content in organic matter: 0%
Classification according to different systems
USC: Low-plasticity inorganic silty clay (CL)
PG3: Tolerable soil
AASHTO: Clayey soil [A-6(15)]
AAFSTC: Silty clay
USC: unified soil classification. PG3: soil classification for the
construction of roads and bridges in Spain. AASHTO: classification
of the American Association of State Highway and Transportation
Officials. AAFSTC: American Air Force Soil Texture Classifica-
tion.
Table 2
Experimental values of the variables studied in the 32 samples
selected
Variable Units Values
Highest Mean Lowest S.D.
Natural moisture
content
% 22.5 15.8 10.9 3.1
Largest size Mm 20.0 10.0 2.0 7.1
Fraction <0.08 mm % 98.9 90.8 71.0 6.4
Greatest density Tn/m3 1.82 1.71 1.62 0.05
Optimum moisture
content
% 22.2 18.3 15.2 1.6
Liquid limit % 57.6 43.8 31.0 5.0
Plastic limit % 25.5 18.9 15.8 2.3
Plasticity index % 34.5 25.0 15.2 3.9
Carbonates % 72.3 53.5 32.2 8.68
Quart % 25.3 20.3 0.0 10.26
Sulphates % 3.55 0.92 0.01 1.00
Dispersability �10�6 m3/s 3.77 2.42 1.58 0.89
Permeability �10�9 m/s 54 1.94 0.025 9.83
Specific gravity Tn/m3 2.75 2.68 2.52 0.05
Cohesion kPa 4.6 1.9 1.0 0.9
Angle of friction Degrees 35.0 24.8 15.5 3.9
Preconsolidation
pressure
kPa 21 13 8 3
Vertical
consolidation
constant
�10�8 m2/s 8 2.89 0.12 1.67
Clay fraction % 45.3 39.5 30.1 6.6
Activity 0.74 0.60 0.30 0.10
Void ratio 0.650 0.522 0.420 0.048
F. Lamas et al. / Engineering Geology 66 (2002) 283–294286
3.1. Mineralogical composition
The mineralogical composition was determined by
X-ray diffraction analysis following the method of
oriented aggregates (Voinovitch, 1971).
The fractions greater than 0.08 mm were composed
primarily of carbonate (>90%), quartz and gypsum in
proportions of less than 1%. The silty fraction was
composed of carbonate (>80%) and quartz, with
traces of iron (limonite group). The carbonate content,
in the overall samples, had a mean value of 53.5%.
The clayey fraction was comprised fundamentally
of smectite and illite in equal and quite substantial
proportions (45%), with a much lower proportion of
kaolin clays (10%).
3.2. Granulometry and Atterberg limits
The fine-particle content (particles of less than 0.08
mm) had a mean value of 88.9%, sands constituting
11.1%. The clay content varied between 30.1% and
45.3%, with a mean value of 39.5%. The liquid limit
fluctuated between 31.6% and 57%, with a mean
value of 43.8% and a standard deviation of 5%,
reflecting strong homogeneity. The plasticity index
also presented quite uniform values, ranging from a
high of 34.5% to a low of 15.2%, with a mean of 25%.
In general, plasticity increased with the clayey frac-
tion. Fig. 3 shows the direct correlation between these
two parameters.
Consistency is a fundamental parameter in the
construction of impermeable cores and their subse-
quent performance over the life of the dam. To
determine the relationship between consistency and
carbonate content, we used the Atterberg limits (Arkin
and Michaeli, 1989). An inverse relationship was
found, with high correlation coefficients between
these limits and the carbonate content (Fig. 4).
3.3. Activity
The activity index values present a high of 0.74
and a low of 0.3, with a mean of 0.6 and a standard
deviation of 0.1. In general, the higher the index, the
more clayey and, therefore, plastic the corresponding
soil is. Fig. 5 shows the relationship between the
activity and the carbonate content—at a higher pro-
portion of carbonates the activity index proved to be
lower.
3.4. Expansivity
According to the ‘‘Technical Committee on Expan-
sive Soils’’ (ISSMFE, 1987), the soils studied pre-
sented a weak (<15 kPa) and moderate (15–20 kPa)
expansion potential (Alimi-Ichola, 1991). The expan-
Fig. 3. Relationship between the plasticity index and the clay content.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294 287
sivity was measured by calculating the maximum
variation of the void ratio with respect to the initial
void ratio in a one-dimensional consolidation test.
Therefore, samples were moulded to 98% of the
normal Proctor density and optimal moisture, to
reproduce the compaction characteristics of the mate-
rial making up the dam core studied. The data for this
variation in the void ratio reached a high of 0.65, with
a mean value of 0.52. Fig. 6 indicates a clear influ-
ence of the carbonate concentration in the expansivity
mechanism.
The variation of the void ratio was determined at
the end of the primary consolidation, enabling the
measurement of the compactness of the material, as
well as its alterability by water, which is related to the
texture of the samples (Jevremovic, 1994)—that is,
the textural properties of soil depend directly on their
carbonate content.
Fig. 5. Relationship between the activity and the carbonate content.
Fig. 4. Consistency limits according to the carbonate content.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294288
3.5. Effective cohesion and internal effective friction
angle
Triaxial tests were made without drainage, with
prior consolidation and with interstitial pressure meas-
urements (CU test). The results (Table 2) show that
the effective cohesion varied within a narrow range of
values, between 1 and 4.6 kPa, with a mean value of
1.9 kPa and a standard deviation of 0.09. According to
the internal effective friction angle, the range was
broader, from 15.5j to 34.9j, with a mean of 24.8jand a standard deviation of 3.4j. Fig. 7 shows a good
correlation between the effective cohesion and the
carbonate content.
3.6. Permeability
A total of 36 permeability tests were conducted in a
triaxial cell with a head-to-tail pressure gradient
(Bureau of Reclamation, 1974). The values of the
Fig. 7. Variation of effective cohesion with the carbonate content.
Fig. 6. Variation in the void ratio with the carbonate content.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294 289
permeability constant ranged from 2.45�10�9 to
8.1�10�8, a vast majority of the results falling within
a narrow band (8.0�10�9 to 1.6�10�8). The uni-
formity of the data was owed basically to two factors:
first, the nature of the marly–clayey fraction, which
gave strong cohesion as well as very fine grain size
(more than 90% of the material was finer than 0.008
mm); and second, the homogenisation during the
moulding of the samples, which become flocculated
structures and, therefore, substantially more ordered
and homogenized than in the unaltered state. Never-
theless, permeability augmented with greater carbo-
nate content (Fig. 8).
3.7. Compaction and dispersability
The density of compaction (standard Proctor test)
varied from a high of 1.77 g/cm3 to a low of 1.62
g/cm3, with a mean value of 1.71 g/cm3 with a
standard deviation of F0.075. Internal dispersability
tests were performed on the samples, invariably
revealing a greater vulnerability to tubification the
higher the carbonate content. This test was made
using the ‘‘Pinhole method’’ (Sherard 1982), meas-
uring the flow rate up to a constant value caused
by the pressure of 1020 mm of a water column
(Table 2).
3.8. Unified soil classification (USC)
Fig. 9 shows the samples studied in the plasticity
chart. All the soils belonging to the group ‘‘low-
plasticity clays’’ have acceptable uniformity (although
they belong to the same group symbol, CL, their
carbonate contents substantially differ).
3.9. Soil-texture classification of the Federal Ameri-
can Agency
The texture classification of the Federal Aviation
Agency of the USA (FAA, 1957) divides soils (except
for gravels) into 12 groups according to their content
(%) of sand, silt and clay (Fig. 10). In this system, the
samples studied belong to groups E-3 (muddy sandy
clay) or E-4 (muddy clay)— that is, they are all
included in the generic group of clay soils. However,
this classification proves inadequate to define their
geotechnical behaviour, and it fails to take into consid-
eration the carbonate nature of the different samples.
3.10. Soil classification for the construction of roads
and bridges in Spain (PG3 classification)
In Spanish civil engineering projects, the PG3 stand-
ard for road and bridge construction (MOPU, 1991) is
Fig. 8. Permeability constant versus carbonate content.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294290
an official classification system defining four levels of
soil quality, according to values of maximum particle
size, percentage <0.08 mm, Atterberg limits, dry den-
sity (standard Proctor test), CBR index and organic
matter content. These four groups from lower to higher
quality are as follows: inadequate soils, tolerable soils,
adequate soils and selected soils. Our samples, accord-
ing to the results (Table 3), correspond to ‘‘tolerable
soils’’ in all cases. However, this classification does not
take into account the carbonate nature, so that it does not
differentiate the samples, despite that, as discussed
above, the varying carbonate contents of each sample
confer a different geotechnical behaviour.
3.11. Soil classification for highway construction in
USA (AASHTO classification)
This classification is based on granulometry (frac-
tions less than 2, 0.4 and 0.08 mm), liquid limit and
plasticity index. All the samples studied are classi-
fied within the A-6 group, these corresponding to
clayey soil, which are inappropriate for use in
cements. As in the foregoing systems, this classi-
fication also fails to consider the varying geotech-
nical behaviour of these soils as a consequence of
their respective carbonate contents (Datta et al.,
1982).
Fig. 10. Textural classification of the Federal Aviation Agency (USA).
Fig. 9. Projection of the samples studied in the Casagrande plasticity chart.
F. Lamas et al. / Engineering Geology 66 (2002) 283–294 291
4. Discussion of the results
For the construction of dam cores and subsequent
safety, a study of the consistency of the material is
vital, being indicative of the degree of soil workability
at the time of execution (Chen et al., 1992). In the
present study, the correlation coefficient between the
liquid limit and the carbonate content was 0.89, the
equation determining this relationship being (Fig. 4):
ll ¼ �0:514� ½%ðCaCO3Þ� þ 71:11
The fact that this straight line has a slightly
shallower slope than that found in the literature
(Khamehchiyan et al., 1994) explains the susceptibil-
ity of these remoulded samples. The plastic limit
presents less variability with respect to the carbonate
content, so that the slope of the straight line relating
these variables is shallower, with greater scattering of
the data (Fig. 4):
lp ¼ �0:28� ½%ðCaCO3Þ� þ 34:02
As the moisture content diminished, the mobility of
the different fractions, including carbonate content,
declined; therefore, the influence that the carbonate
content exerted over the consistency of the material
was less in the case of the plastic limit than in the
liquid limit.
The plasticity index, as well as the clay percentage
fell as the carbonate content rose (Usselmann, 1971),
so that the influence of the carbonate was determined
fundamentally by the silty–sandy fraction. Of course,
in marly soils, the carbonate content increases usually
at the expense of clayey material. Nevertheless, the
variability ranges both in the quantity and type of clay
as well as in plasticity are rather narrow, implying a
certain independence between the carbonate and clay
contents.
According to Dumbleton and West (1966), the
soil activity is a function of the charge and exchange
capacity and is determined by the relative proportion
of the different minerals in the clay, this decrease
being in the direction montmorillonite>illite>kaolin-
ite, regardless of the carbonate content. Other authors
(Skempton and Vaughan, 1993) have mentioned the
clay–carbonate equilibrium, but without giving it
much importance. However, in the marls studied
here, constant values were not found in the activity
index, which instead proved to be related to the
carbonate content according to the following expres-
sion (Fig. 5):
A ¼ �0:01� ½%ðCaCO3Þ� þ 1:09
Although the correlation index was in general high
(0.88), the concentration zone of the carbonates
between 45% and 60% presented a better correlation.
The void ratio varied less the higher the carbonate
content, showing a good correlation for the values
within the range 50–60% carbonate (Fig. 6). For
carbonate samples of similar plasticity, other authors
(Datta et al., 1982; Khamehchiyan et al., 1994) re-
ported more uniform values for expansivity, this being
less influenced by the carbonate concentration. Never-
theless, the carbonate content of the samples used in
these studies was much lower than in ours. In the
samples where the smectite content of the clay fraction
exceeded the mean (45%), we found a lower correla-
tion between the void ratio and the carbonate content.
Thus, for these cases, the expansivity depended more
on the composition of the clay fraction than on the
textural characteristics.
The influence of the carbonates on the variability
of effective cohesion was determined by the expres-
sion (Fig. 7):
c V ¼ 1807:4� ½%ðCaCO3Þ��1:749
The increase in the carbonate content, at constant
density and moisture, clearly diminished the effective
cohesion, as observed by other authors (Khameh-
chiyan et al., 1994). The stress–strain behaviour of
the samples clearly varied between clayey types when
the carbonate content was low, and the sandy types
with high carbonate contents. The zone of strongest
influence appeared for carbonate contents of between
48% and 60%. For concentrations higher than 60%,
the decline in effective cohesion began to be regulated
by other variables, especially the clay content (Conrad,
1993).
Given that the total content in clay and especially
the type of clay minerals of the samples remained
nearly constant, the greater permeability noted is
better explained by the alteration of inner texture,
which changed the drainage network of the sample
F. Lamas et al. / Engineering Geology 66 (2002) 283–294292
tested, as a consequence of the varying carbonate
content. Mckown and Ladd (1982) demonstrated that
carbonate content reduced by HCl treatment increased
permeability, due not only to greater CO2 and con-
sequent dissolution of the carbonate but also to
tubification. In the case of an impermeable core, this
phenomenon can result from the relative acidity of the
dammed waters (these being from the high-mountain
and thus of great purity) and in the sample by
dissolution or leaching of the carbonate in the
amassed water. Locally, the contrary effect is possi-
ble—that is, precipitation of carbonates and/or the
residual plugging of interstices, causing rigidity and
eventual loss of the elasticity crucial to an imperme-
able core. The increased hollowing by tubification as
well as possible cementing and crushing alter the
characteristics both of the permeability and of the
tenso-deformation characteristics. These effects grow
in importance as the contents in biogenic carbonates
augment (Datta et al., 1982).
According to the above, the geotechnical proper-
ties studied change notably with the variation of the
carbonate content. Therefore, construction, stability
and durability of a dam core is related to this
content.
5. Conclusions
The results of the different tests show a clear
relationship between expansion, plasticity, activity
and carrying capacity of the soils studied and their
degree of compactness, determined by the carbonate
content. The intrinsic factor determining the geotech-
nical behaviour of these soils is, in addition to the type
and quantity of clay minerals, the percentage of
carbonate in the silt fraction.
Existing engineering classifications fail to provide
an adequate response to these factors (clay minerals
and, especially, carbonate content) and, thus, none of
these systems satisfactorily explains the different
behaviour of the marls studied. In fact, none of the
classifications mentioned takes into account or even
refers to carbonate content.
In the present work, we show the need to incorpo-
rate the percentage of carbonate as a classification
criterion of the soils used to construct dam cores from
loose material.
Acknowledgements
This research has been supported by ‘‘Grupo de
Investigaciones Medioambientales: Riesgos Geologi-
cos e Ingenierıa del Terreno,’’ Code RNM 121 of the
Andalusian Research Planning. The authors wish to
express their gratitude for the words and encourage-
ment of Dr. Ing. D. Joaquın Delgado Garcıa, Director
of the Granada branch of the Confederacion Hidrog-
rafica de Guadalquivir, and the author of the dam
project which served as the basis for this study.
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