641
Dynamic
CBR
as a method of embankment compaction assessment
Dynamique
CBR
comme une méthode d'évaluation de compactage du remblai
Zabielska-Adamska K., Sulewska M.J.
Bialystok University of Technology, Bialystok, Poland
ABSTRACT: In engineering practice, earth construction requires suitable soil compaction, usually relating to the Proctor methods.
Materials of the built-in embankment and the subgrade have their own specifications, dependant on the kind of earth structure and soil
plasticity characteristics. Care should be taken not to use compaction degree (% of maximum compaction) as the only parameter to
assess soil compaction. This applies to both cohesive soil and to fly ash whose permeability and mechanical properties dependent on
moisture content at compaction. Therefore, for these types of soils California Bearing Ratio could be used as a method of compaction
assessment being an indicator of soil bearing capacity. The
CBR
research was done for both static (classic) and dynamic methods on
fly ash samples without soaking them to replicate field conditions. A load of 2.44 kPa was applied to all the samples subjected to
penetrations. The dynamic
CBR
tests were conducted by using Light Weight Deflectometer consisting of a falling weight to produce a
defined load pulse of the
CBR
piston. The
CBR
test could be used for running compaction control during embankment erection, which
specially refers to dynamic
CBR
test due to the speed of research execution.
RÉSUMÉ: Dans la pratique d’ingénierie, la construction en terre nécessite un compactage du sol adapté, concernant en général les
méthodes Proctor. Les matériels encastrés du remblai et de la plate-forme ont leurs propres spécifications, dépendant du genre de la
construction en terre et de caractéristiques de plasticité du sol. Il faut prendre soin de ne pas utiliser le degré de compactage (% de
compactage maximum) comme le seul paramètre pour évaluer la compactage du sol. Cela s’applique aux sols cohésifs et à cendres
volantes dont la perméabilité et des propriétés mécaniques dépendent de la teneur en humidité au compactage. Donc, pour ceux types
de sol l'indice portant californien pourrait être utilisé comme une méthode d’évaluation du compactage étant un indicateur de la
capacité portante. Les recherches
CBR
ont été effectuées pour les méthodes statiques (classiques) et dynamiques sur les échantillons
de cendres voltantes sans les faire tremper à reproduire les conditions de terrain. Une charge de 2,44 kPa a été appliqué à toutes
échantillons soumis à des pénétrations. Les tests de dynamique
CBR
ont été effectués a l’aide de déflectomètre constitué par la masse
tombante pour produire une impulsion de charge définie du piston
CBR
. Le test
CBR
pourrait être utilisé pour exécuter le contrôle du
compactange lors de l’érection de remblai, qui se réfère en particulier à l'essai dynamique de
CBR
en raison de la rapidité d'exécution
de la recherche.
KEYWORDS: compaction, California Bearing Ratio (
CBR
), dynamic
CBR
(
CBR
d
), fly ash, compaction assessment.
1 INTRODUCTION
In engineering practice, earth construction requires suitable soil
compaction, usually relating to the Standard and Modified
Proctor methods. Materials of the built-in road embankment and
the subgrade have their own specifications, dependant on the
kind of earth structure and soil plasticity characteristics. Care
should be taken not to use compaction degree (% of maximum
compaction) as the only parameter to assess compaction of
material in embankments. This applies to both cohesive soil and
fly ash. The permeability and mechanical properties of
compacted fly ash are dependent on moisture content present
during compaction, as are properties of cohesive mineral soils
(Turnbull and Foster 1956, Mitchell et al. 1965, Zabielska-
Adamska 2006 and 2011). Consequently different values of
geotechnical parameters are obtained for water content on either
side of the optimum water content on the compaction curve, for
the same dry densities. Thus for these types of soils California
Bearing Ratio,
CBR
, may be used as a method of compaction
assessment, since it is an indicator of ground bearing capacity
broadly used in the design of civil engineering.
The laboratory
CBR
tests by means of both static (classic)
and dynamic methods were carried out to establish relationship
between bearing ratio and fly ash compaction. Samples,
compacted by the Standard or Modified Proctor methods, were
prepared without soaking them to replicate field conditions
during earth structure erection. The dynamic
CBR
,
CBR
d
, tests
were done by using impact generator and guide rod, which are
the parts of Light Weight Deflectometer (LWD), and additional
equipment in a
CBR
piston. A falling weight is to produce a
defined load pulse of the
CBR
piston that can be used both in
laboratory and field tests. The aim of this study was to prove
that
CBR
tests could be used as the methods of road
embankment or subgrade compaction assessment. This refers
especially to
CBR
d
test which may be used for running
compaction control during embankment erection due to the
speed of research execution, as well as Light Weight
Deflectometer (Sulewska 2012).
1 LITERATURE REVIEW
California Bearing Ratio,
CBR
, is expressed as the percentage
ratio of unit load,
p
, which has to be applied so that a
standardized circular piston may be pressed in a soil sample to a
definite depth with a rate of 1.25 mm/min and standard load,
corresponding to unit load,
p
s
, necessary to press the piston at
the same rate into the same depth of a standard compacted
crushed rock.
(1)
%100
s
p
p
CBR
CBR value is used for evaluation of the subgrade or subbase
strength, and may be applied to assess the resistance to failure
