603
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
1
Correlation between cone penetration rate and measured cone penetration
parameters in silty soils
Corrélation entre le taux de pénétration d‘un cône et des mesures de paramètres de pénétration au
cône dans les sols limoneux.
Poulsen R., Nielsen B.N., Ibsen L.B.
Aalborg University, Department of Civil Engineering, Aalborg, Denmark
ABSTRACT: This paper shows, how a change in cone penetration rate affects the cone penetration measurements, hence the cone
resistance, pore pressure, and sleeve friction in silty soil. The standard rate of penetration is 20 mm/s, and it is generally accepted that
undrained penetration occurs in clay while drained penetration occurs in sand. When lowering the penetration rate, the soil pore water
starts to dissipate and a change in the drainage condition is seen. In intermediate soils such as silty soils, the standard cone penetration
rate may result in a drainage condition that could be undrained, partially or fully drained. However, lowering the penetration rate in
silty soils has a great significance because of the soil permeability, and only a small change in penetration rate will result in changed
cone penetration measurements. In this paper, analyses will be done on data from 15 field cone penetration tests with varying
penetration rates conducted at a test site where the subsoil primary consists of sandy silt. It is shown how a reduced penetration rate
influences the cone penetration measurements e.g. the cone resistance, pore pressure, and sleeve friction.
RÉSUMÉ: Dans cet article, on montre comment un changement dans le taux de pénétration d’un cône affecte les mesures de
pénétration de cône, d'où la résistance du cône, la pression interstitielle et la friction manche en sol limoneux. Le taux normal de
pénétration est de 20 mm/s, et il est généralement admis que la pénétration se produit dans de l'argile non drainée alors que la
pénétration se produit dans le sable drainé. Lors de l'abaissement du taux de pénétration, l'eau interstitielle du sol commence à se
dissiper et un changement de l'état de drainage est vu. Dans les sols intermédiaires, tels que les sols limoneux, le taux de pénétration
de cône standard peut conduire à un drainage des conditions qui pourraient être non drainées, partiellement ou totalement déchargée.
Cependant, l'abaissement du taux de pénétration dans les sols limoneux a une grande importance en raison de la perméabilité du sol et
seulement un petit changement dans le taux de pénétration se traduira par des mesures de pénétration au cône changé. Dans ce
document, les données de 15 essais sur le terrain de pénétration au cône, avec différents taux de pénétration menées sur un site d'essai
où le premier sous-sol se compose de limon sableux, sont analysés. L’influence d’une réduction du taux de pénétration sur les
mesures de pénétration d’un cône, par exemple la résistance du cône, la pression de pore, et la friction manchon, est démontrée
.
KEYWORDS: Silt, CPT, penetration rate, cone resistance, pore pressure, sleeve friction, drainage, in situ testing.
1 INTRODUCTION
The Cone Penetration Test (CPT) is an in situ testing method
that today’s geotechnical engineers often make use of when
determining soil parameters, and classifying soil type. The
standard rate of penetration is 20 ± 5 mm/s, (ASTM 2007), and
while the cone is pushed into the ground the cone resistance,
(
q
c
), pore pressure (
u
2
), sleeve friction (
f
s
), and depth (
d
) are
measured.
During the penetration, the pore water starts to dissipate, and
the dissipation for sands occurs so quickly that the penetration
appears as fully drained, whereas the dissipation happens over
time for clays, for which reason the penetration is undrained in
clays. For intermediate soil, such as silty soils, the penetration is
somewhat in between; that is partially drained.
According to several researchers (Silva and Bolton 2005,
Lehane et al. 2009, Kim et al. 2008, Schneider et al. 2008,
Chung et al. 2006, House et al. 2001), the drainage is dependent
on the soil permeability, compressibility and penetration rate.
The soil permeability and compressibility are both connected to
the soil type. However, the penetration rate is regardless of soil
type 20 mm/s.
When the penetration rate is lowered, the pore water
dissipates (change in drainage condition) which results in an
increased cone resistance (Lehane et al. 2009, Kim et al. 2008,
Chung et al 2006, House et al. 2001). For this reason, the largest
cone resistance that could be obtained corresponds to a fully
drained penetration. This effect has been shown by several
researchers (Chung et al. 2006, House et al. 2001 and Randolph
and Hope 2004) from laboratory tests in clay. Kim et al. (2008)
also conducted laboratory as well as field cone penetration tests
in cohesive soil and found that the soil behaves undrained for a
penetration rate of 20 mm/s and partially drained for a
penetration rate of 0.05 mm/s.
According to Poulsen et al. (2011a), the change in
penetration rate and hence drainage condition has a greater
impact in silty soils where the standard rate of penetration often
induces a partially drained penetration.
This paper analyses data from 15 field cone penetration tests
conducted with a penetration rate varying from 60 to 0.5 mm/s.
Only a short description of the method for the cone penetrations
tests will be given. The results and the interpretation of how a
change in the penetration rate affect the measured parameters,
hence the cone resistance, pore pressure, and sleeve friction will
be given.
2 DESCRIOTION OF EXEPERIMENTAL PROGRAM
The aim of the research is to examine how a change in the cone
penetration rate affects the measured cone penetration
parameters when conducting cone penetration tests (CPT). The
research was carried out at a test site located in the northern
Jutland in Denmark, more specifically at a field near the town
Dronninglund.
