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Behavior of fine-grained soils compacted with high shear stresses
Comportement des sols fins compactés avec des niveaux de cisaillement élevés
Perez N., Garnica P., Mendoza I., Reyes M.A.
Mexican Transportation Institute
ABSTRACT: One of the parameters used to carry out the quality control of unbound compacted fine-grained materials is the
maximum dry unit weight obtained from a Proctor standard or modified test. However, these tests are far from simulating the field
compaction mechanism produced by the sheep foot roller equipment. Lately, the gyratory compactor has been put forward as a new
laboratory equipment to determine the compaction curves. This paper shows results of Proctor and modified compaction curves as
well as the ones obtained from the gyratory compactor. The new method of compaction was evaluated for three soils classified as CH,
ML and SM. The controlled variables in the gyratory compactor were the gyration angle, the vertical pressure, and the number of
gyrations. The results showed that the optimum water content is reduced as the vertical pressure increases and the opposite happens
with the dry unit weight. In addition, it was observed that the Proctor compaction curve is obtained with a vertical pressure of 200 kPa
and around 200 gyrations regardless the soil type. On the other hand, it seems that the compaction curves are similar disregarding the
rate of gyration and gyration angle.
RÉSUMÉ : Un des paramètres classiques utilisés pour le contrôle de qualité des sols fins compactés non traités est le poids volumique
sec obtenu dans l’essai Proctor, standard ou modifié. Cet essai est cependant loin de simuler les mécanismes de compactage in situ
produits par des équipements tels que les rouleaux à pieds dameurs. Récemment, le dispositif de compactage giratoire a été mis en
avant, en tant que nouveau dispositif de laboratoire pour la détermination des courbes de compactage. Cette communication présente
une comparaison des courbes de compactage obtenues aussi bien avec les essais Proctor qu’av
ec le dispositif giratoire, pour lequel les
influences de paramètres tels que la pression verticale, l’angle de giration et le nombre de girations ont été évaluées pour des sols de
classe CH, ML et SM. Une discussion est ensuite proposée, montrant que la
teneur en eau optimale diminue avec l’augmentation de
la pression verticale, une tendance opposée apparaissant pour le poids volumique sec. On a aussi observé que la courbe Proctor
classique est obtenue pour une pression verticale de 200 kPa et environ 200 girations, quel que soit le type de sol. Les courbes de
compactage obtenues ne semblent cependant pas dépendre de la vitesse ni de l’angle de giration.
KEYWORDS: gyratory compactor, soil compaction, quality control, Proctor test, compaction curves, pavements, unbound materials.
MOTS-CLÉS : compacteur giratoire, compactage des sols, contrôle de qualité, essai Proctor, courbes de compactage, revêtement
routier, matériau non traité
1 INTRODUCTION
Soil compaction is a process which is often used in the
construction of almost every single engineering structure.
Examples such structures are dams, the approaches of bridges,
mats for buildings, airports, pavements, etc.
To carry out the quality control of the compacted materials it
is necessary to count with two parameters, that is to say, the
field dry unit weight and the maximum dry unit weight obtained
in a laboratory test which can be Proctor standard or modified
(this paper is focused in the evaluation of lab maximum dry unit
weight).
To evaluate laboratory properties (i.e. the dry unit weight,
resilient modulus, unconfined compression, etc), it is paramount
that the test specimens possess as far as possible the same
structure that the soil will have in field. The evaluation of the
maximum dry unit weight and optimum water content of fine-
grained soils with test as the Proctor standard and modified test
is an example of an inconsistency between field and lab
structure. The field equipment for these cases are the sheepfoot
roller which compacts the soil from bottom to top while in the
Proctor standard test the soil is compacted by impacts, thus, it is
expected to obtain different soil structures. On the other hand,
Ping et al. (2003) have found that the field and laboratory
compaction curves are completely different. Thus, as a
consequence, some researchers (Ping et al., 2003;Milberger y
Dunlap, 1996; Mokwa et al., 2008, etc.) have put forward the
gyratory compactor as a new equipment to determine the
laboratory compaction curves.
In this paper, the compaction curves were obtained with the
gyratory compactor and then they were compared with the
standard and modified compaction curves. In addition, it was
studied the effect on the compaction curve of variables as the
vertical pressure, the angle of gyration and the number of
gyrations. The procedures, equipments and results are described
in the following paragraphs.
2 GYRATORY COMPACTOR
Compaction in this equipment is achieved by the application of
vertical stress to a known mass within a mold of 100 or 150 mm
internal diameter. The longitudinal axis of the mould is rorated
(gyrated) at a fixed angle to the vertical while the platens are
kept parallel and horizontal. During the compaction the height
of the sample is automatically measured and the mixture density
is calculated. The operator can choose whether to compact to a
certain number of gyrations, a certain height or until a target
density(http://www.cooper.co.uk).It is important to mention that
even this equipment was designed to compact specimens of
asphalt mix, lately it has been utilized to compact fine-grained
and granular soils.
3 TEST SOILS
During this research it was collected a series of samples
classified as clay (CH), silt (ML) and sand (SM) (Figure 1).
