Acta Polytechnica CTU Proceedings


doi:10.14311/APP.2017.10.0061
Acta Polytechnica CTU Proceedings 10:61–64, 2017 © Czech Technical University in Prague, 2017

available online at http://ojs.cvut.cz/ojs/index.php/app

STABILIZATION AND SPECIFICATION OF CHARACTERISTIC
VALUE OF GEOTECHNICAL PARAMETERS

Ivan Vaníček

Czech Technical University in Prague, Faculty of Civil Engineering, Thákurova 7, Prague 6, Czech Republic
correspondence: ivan.vanicek@cvut.cz

Abstract. Soil stabilization, process, by which the soil properties are improved, is getting growing
attention during last periods. Paper is focused on application for earth structures. Methods of soil
stabilization together with their applicability for different soils are discussed firstly. The sensitivity of
the process of the cautious estimation of the characteristic values of geotechnical parameters which are
subsequently used for the design, is shown on the base of the logical scheme of the geotechnical design
report for earth structures. Finally the need of the laboratory tests for the closer specification of the
soil stabilization technology and also for the determination of the geotechnical data are discussed.

Keywords: Stabilization, Earth structure, Eurocode 7, characteristic value.

1. Introduction
Soil stabilization is one of the techniques of soil im-
provement. Together with soil reinforcement it is the
most applied techniques. Soil improvement methods
can be divided with respect to the characteristic values
specification into two basic subgroups [1]:

• Diffusive soil improvement;
• Discrete soil improvement.

In the first case, typical for soil stabilization, the
design counts with new properties for geological en-
vironment in general, better speaking for individual
quasi-homogeneous layers of the environment. In the
second case soil properties remain the same (on the
previous values), as well the parameters of the reinforc-
ing element (most often geosynthetics). The behaviour
of the composite therefore depends on the interaction
of these two basic materials and limit states of fail-
ures should be determined also for this reinforcing
element. For earth structures the improvement of in-
dividual soil layers of fill or surface of ground (subsoil)
has dominant application role. It is typical for earth
structures of transport engineering including airports.
However it is connected also with subsoil improvement
of large halls, especially when they are founded partly
in cut and partly on fill. Soil stabilization, mixing
soil particles with different additives, can be realized
either on site or in mixing centre situated of-site with
subsequent transport on the place of application. Ad-
ditives are different, either according to the soil type
or with respect of certain demands. The following
additives can be applied [2]:

• Lime, cement, plaster;
• Industrial by products as fly ash, energy-gypsum,
slag (cinder) [3];

• Additional soil - mechanically stabilized soil;
• Several chemical additives (resins, bitumen).

The paper is for the simplicity focused on the
first possibility, on the application of lime or cement,
whereas cement is typical for coarse soil and lime for
fine grained soils. The recommendation in this direc-
tion are often connected with index plasticity. For
cement application, the higher strength is reached,
however the strength is rising up relatively slowly.
The final result is more typical for road base or sub-
base or for layers just below floor (e.g. for above
mentioned halls), where higher strength is typically
demanded. Subsequently more attention is focused
on lime application, which is more suitable for fine
soils and where quicker effect of application is needed.

2. Lime stabilization
Quick lime is preferred for soil stabilization as it hy-
drates with water and calcium hydroxide develops.
This reaction is exothermic. Heat is created as the
result of quick lime reaction with wet soil having quick
impact on soil compaction which is after that for dryer
soil better. Therefore generally two impacts are dis-
tinguished, short term (having positive impact on soil
compaction) and long term (having positive impact
on strength increase). While short term effect occurs
for any quick lime application, long term effect need
a certain percentage of quick lime. Broadly speaking
this boundary is close to 2 % of added lime to dry
soil. Particle flocculation starts for higher content
of lime, changing grain size distribution curve with
lower content of fine particles. Soil creates clods and
change the structure. Therefore for fine grain soils
the stabilization process with lime leads to:

• Better soil workability;
• Strength increase.

From this point of view the long term effect is
more important for increase of characteristic values of
geotechnical parameters, however requires higher lime

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Ivan Vaníček Acta Polytechnica CTU Proceedings

content, usually in the range of 2 to 6 %. Stabilization
effect connected with long term effect is therefore
connected with reaction of lime with clay particles,
subsequently leading to:

• Growth in strength and the subsoil bearing ca-
pacity in general - due to the creation of cement-
ing bonds resulting from soil-lime pozzolanic reac-
tion, which, however, develop in time and therefore
strength tests are performed with a time lag of
mostly 28 days;

• Reduction in the susceptibility to swelling and
shrinkage;

• Reduction in moisture content is caused both by
absorption, extraction of moisture from the sur-
rounding soil after the lime type is changed into
slake lime, and by hydration heat as was mentioned
above.

At the same time, however, the new reaction of lime
with clay minerals leads to a change in plasticity thus
affecting another factor relevant for workability.

• Two additional notes are needed [4];
• For higher content of quick lime (above 4-6 %) there
is no another reduction of plasticity;

• For the development of cementing bonds clay parti-
cles are needed, at least 10 %.

3. Technology effect
The application of lime stabilization on site prevails
at the present days. After areal spreading of the
demanded content of lime the soil and lime are mixed
with the help of cutter or another machineries to the
required depth. Such modified layer is levelled by
grader or bulldozer and subsequently compacted by
roller. A great attention is devoted to the moisture
content at the time of compaction, to guarantee that
soil after compaction will not have more than 5 percent
of air in pores.

Therefore some specialists devote a great attention
to the mellowing - maturing, to the time between
soil and lime mixing and final compaction. Therefore
after mixing only light compaction is recommended
and after about 24 to 72 hours, followed by second
mixing supplemented by additional increase of water
the final compaction is applied. It is consistent that
this recommendation has some limits, as for example
for improvement of railway tract subsoil during rail
heave [5].

From this technology point of view the application
of lime stabilization is not recommended during late
autumn, as stabilized soil can freeze. For such case
addition of cement is recommended after short delay
after lime. Nevertheless this recommendation has
general character, as lime can prepare soil for cement
application. This effect can be reached by some special
mixed additives, e.g. for the Czech Republic it is
Dorosol, which contains a certain percentage of lime

and the rest are hydraulic ingredients. In this case a
special attention is devoted to dusting lowering.

4. Logical scheme of the earth
structure design

Contemporary version of the Eurocode 7 Geotechnical
design contains four important steps of the geotechni-
cal structure design and performance as specification
of geological model, geotechnical model, calculation
model and ending with structure realization, perfor-
mance connected with structure control. These four
phases can be used for the specification of the risk
with which the design and performance is connected,
first of all from the point of view of uncertainties and
indeterminateness. For earth structures this scheme
is presented in Fig. 1 in the form of the Geotechnical
design report - GDR.

Geological model should be specified not only for the
ground but also for the borrow pit, from which fill will
be constructed. Geotechnical investigation report or
Ground investigation report - GIR - includes not only
geological model but also results of the laboratory and
field tests of the ground and theirs presentation in the
form of measured or derived geotechnical parameters.
From the borrow pit technological samples are taken
and subsequently tested in the laboratory. Firstly it
is compaction test - most often Proctor standard test.

Range of the geotechnical investigation as well the
range of performed tests is connected with risk, with
which the design and performance is connected. Eu-
rocode 7 recommends three degrees for this specifi-
cation - with the help of so called Geotechnical cate-
gories (GC), when into:

• 1 GC belongs simple structures in modest geological
and geotechnical conditions. These structures are
designed with the help of up to day experiences -
calculation of limit states is not needed. Generally
into first GC belongs fills with high up to 3 m with
good ground conditions. However this is not the
case for the ground of fill which need improvement
- soil stabilization.

• 3 GC belongs very demanding structures, or struc-
tures with complicated ground - from the geological
and geotechnical point of view or structures con-
nected with extreme risk for surrounding environ-
ment in the case of failure.

• 2 GC belongs all other structures.

For the structures falling into 3 GC it is necessary
always determine mechanical-physical properties - ei-
ther for ground or for fill. For material of fill the test
are performed on samples compacted in laboratory
and for which moisture content and dry density are
falling into the accepted (recommended) range. The
same procedure is recommended for structure which
belongs to the second GC, however with one excep-
tion. In the case of 2 GC connected with lower risk the
mechanical-physical properties can be selected from

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vol. 10/2017 Specification of Characteristic Value of Geotechnical Parameters

Figure 1. GDR scheme for earth structures.

standard tables, based on the correlation of index
properties and mechanical-physical properties. Such
correlation for compacted fill is e.g. used in codes for
small dams, (in the CR it is e.g. code ČSN 75 2410
Small water reservoirs).
However for stabilized soils, firstly where the

strength increase is needed, such tables can be hardly
used, as there is a shortage or correlations, and there-
fore lab tests are needed. In this case very good
cooperation between project designer and specialist
on the lab tests is preferred, namely with respect to
the tests performed on samples which were prepared
by the nearly same way as is proposed stabilization
on the site.

5. Sensitivity of the
characteristic values
determination

As stated already lab tests of the mechanical-physical
properties are needed for structures belonging into 3
GC and 2 GC with moderate and high risk. After
that the results are statistically evaluated and after
subsequently they are used for the determination of
the characteristic values of the geotechnical parame-
ters. Here EC 7 defines the characteristic values as
“selected as a cautious estimate of the value affecting
the occurrence of the limit state”. This expression
should be taken very carefully, as:

• “selected” emphasizes the engineering judgement;

• “cautious estimate” emphasizes that a certain con-
servatism should be applied;

• “limit state” emphasizes that selected values should
have close relation to the given limit state.

Nevertheless also other aspects are playing signifi-
cant role during the process of selection:

• Amount of information and a degree of confidence
to these information;

• Volume of ground affected by expected limit state
of failure (e.g. slip surface) or an ability of the
structure to transfer loads - when both aspects are
connected with an ability to compensate weaker
zones by stronger ones [6].

Therefore for slip surface of failure with significant
length it is possible to select characteristic values
closer to the average ones, while for shorter slip sur-
face the cautious estimate will be more conservative.
For all that it can be specified that the characteristic
values selection is one of the most sensitive task of
the project designer. Probability of verification of
the selected values is very low. Quality of ground
is usually not controlled, only of the fill. But even
for the fill the control is going mostly via quality of
compaction, whether the moisture content and dry
density are falling into prescribed range. Direct tests
of mechanical-physical properties are rather excep-
tional, e.g. permeability control for sealing system of
landfills.

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Ivan Vaníček Acta Polytechnica CTU Proceedings

6. Laboratory measurement
Laboratory tests are needed for soil stabilisation where
the main aim is strength increase. Optimal content
of the additives should be determined as well with
mechanical-physical properties, from which the de-
signer selects characteristic values presented some in-
teresting results performed within her diploma theses,
devoted to the additives research [7]. For given soil,
characterized as clay with low plasticity (CL) she con-
cluded, that it is material unsuitable or conditionally
suitable which is also sensitive to freezing. She tested
stabilization by quick lime, cement and Dorosol, and
she focused on:

• Impact of lime on change of consistency limits;
• Impact of additives amount on increase of bearing
capacity (controlled via CBR test);

• Impact of additives amount and time on the resis-
tivity of stabilized soils to freezing cycles.

Follow-up diploma and PhD thesis are focused not
only on classical soils, but also on alternative ag-
gregates as flying ash, when different additives are
tested [3]. Last attention is devoted to the combi-
nation of additives with randomly distributed short
synthetic fibres. The evaluation of these tests is mostly
via possibility of application of stabilized soils into
road foundation - road base or sub-base layers, e.g.
according to the Czech code ČSN 73 6125. Up to now
lower attention is devoted to the additives application
for the own fill of the earth structure. There the prop-
erties as shear parameters and deformation modulus
have more informative impact, as they are needed for
the solution of the limit states - ULS - ultimate limit
state or SLS - serviceability limit state. The problem
is very sensitive, as a stiffness increase is function of
time and the designer should solve the limit states
not only for short term conditions, but also for long
term conditions.

7. Conclusion
The application of different additives for improvement
of soil properties has growing tendency. From the view
of lime application on fine grained soils it is neces-
sary to distinguished between improvement from the
workability view with short term effect and improve-
ment with long term effect, when strength increase has
permanent character. In the course of additives ap-
plication for earth structures of transport engineering
the designer should firstly specify his/her intention,
whether the process of improvement is focussed on the
ground and own fill or on the construction layers, as

the applications (and conditions) are different. Time
effect is playing important role as properties are time
dependant, mostly from the view of long term bonds
having decisive impact on the mechanical-physical
properties. Therefore the lab tests are needed pro for
demanding structures with moderate and high risk
and should be focused not only on the specification
of additive amount but also on the determination of
soil properties reported as characteristic values. From
the view of safety the designer of earth structures has
to face many uncertainties with respect to the soil
properties, (compared to the designer dealing with
man-made construction materials) as subsequent con-
trol of the compacted soil is limited and therefore the
transfer of experiences from one site to the another
one is limited.

Acknowledgements
The paper was prepared with financial support from the
research project TE0 120168 of the Technology Agency
of the CR: CESTI - Centre of effective and sustainable
transport infrastructure.

References
[1] I. Vaníček. Significance of geotechnical investigation
for geotechnical structure design. In Proceedings of 43rd
Conference with international participation: Foundation
Engineering. Brno, CGtS CICE, pp. 27–40. Brno, 2015.

[2] M. Vaníček, I. Vaníček. Earth Structures in Transport,
Water and Environmental Engineering. Springer,
Dordrecht, 2008.

[3] V. Mráz. Research of stabilized fly ash properties and
its application for earth structures of transport
engineering (in Czech). Ph.d. thesis, Czech Technical
University in Prague, Faculty of Civil Engineering, 2016.

[4] H. M. Greaves. An introduction to lime stabilization.
In Lime Stabilisation. Proceedings of the Seminar Held
at Loughborough University, Civil ans Building
Engineering Dept on 25 September 1996.

[5] J. H. Smith. Construction of lime or lime plus cement
stabilized cohesive soils. In Lime Stabilisation.
Proceedings of the Seminar Held at Loughborough
University, Civil ans Building Engineering Dept on 25
September 1996.

[6] I. Vaníček. Jubilee volume: Andreas Anagnostopoulos
50 years of service at the National Technical University
of Athens, chap. Earth Structures - sensitivity of the
design to the characteristic geotechnical parameters
values determination., pp. 543–552. Tsotras, 2015.

[7] Vrbová. Soil stabilization. Master’s thesis, Czech
Technical Universiti in Prague, Faculty of Civil
Engineering, 2008.

64


	Acta Polytechnica CTU Proceedings 10:61–64, 2017
	1 Introduction
	2 Lime stabilization
	3 Technology effect
	4 Logical scheme of the earth structure design
	5 Sensitivity of the characteristic values determination
	6 Laboratory measurement
	7 Conclusion
	Acknowledgements
	References