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CPT/PCPT- Based Organic Material Profiling
Matière organique - Le profilage basé sur le CPT/PCPT
Tümay M.T.
Louisiana State University, Baton Rouge, LA, USA and Boğaziçi University, İstanbul, Turkey
Hatipkarasulu Y.
The University of Texas at San Antonio, San Antonio, TX, USA
Marx E.R.
Fugro Consultants, Inc., Baton Rouge, LA, USA
Cotton B.
Fugro Consultants, Inc., Kenner, LA, USA
ABSTRACT: Cone and Piezocone Penetration Test (CPT and PCPT) based analysis and modeling is a popular and handy tool for
geotechnical engineers for subsurface investigations and soil characterization. However, effective identification and extent of organic
content proves to be a challenge based on traditional CPT and PCPT data and methodologies. This paper presents a comprehensive
CPT/PCPT-based organic content identification method using Zhang and Tumay (1999) probabilistic soil classification method. The
probabilistic method employs a non-traditional modeling approach that takes the uncertainty of correlation between the soil
composition and soil behavior into account. The method is based the conformal mapping of the Douglas and Olsen (1981)
classification chart which results in the soil classification index (U) and in-situ behavior index (V). The organic content identification
method proposed in this paper uses the in-situ behavior index (V) in combination with the compositional soil classification index (U)
to estimate the organic content. A detailed description of the proposed methodology and a discussion of effective applications are
included in the paper.
RÉSUMÉ : Le pénétromètre quasi-statique et le piézocône (CPT et PCPT) constituent des outils d’analyse populaires et pratiques
pour la reconnaissance géotechnique des sites et la caractérisation des sols. Cependant, l’identification des sols organiques ainsi que
l’évaluation de la teneur en matière organique à partir des données classiques obtenues au CPT et au PCPT
se sont révélées être un
challenge. Cet article présente une méthode d’évaluation complète de la teneur en matière organique basée sur le CPT et la méthode
de classification des sols probabiliste de Zhang et Tumay (1999). Cette méthode probabiliste utilise une approche de modélisation non
conventionnelle qui prend en compte l’aléa sur la corrélation entre la composition du sol et son comportement mécanique. La
méthode est basée sur l’abaque de classification des sols de Douglas et Olsen (1981) qui permet de définir l’indice de classification
des sols (U) et l’indice de comportement in situ (V). La méthode d’évaluation du contenu en matière organique proposée dans l’article
utilise l’indice de comportement in situ (V) combiné à l’indice de classification (U) pour estimer la teneur en matière organique du
sol. Une description détaillée de la méthodologie proposée et une discussion de ses applications sont aussi présentées dans l’article.
KEYWORDS: CPT, PCPT, Cone Penetration, Soil Classification ,Organic Soils
1 INTRODUCTION
Cone and Piezocone Penetration Test (CPT and PCPT) (ASTM
D5778-12) based analysis and modeling is a popular and handy
tool for geotechnical engineers for subsurface investigations and
soil characterization. Since the 1960s, several modeling
approaches have been developed for soil classification and
evaluation of different soil properties such as the strength and
consolidation characteristics of geomedia. However, effective
identification and extent of organic content has proved to be a
challenge based on traditional CPT and PCPT data and
methodologies. Although some models identify organic
materials as a separate soil class, they do not provide a
continuous profile (for example, Schmertmann, 1978;
Robertson et al, 1986; Robertson, 1990). Considering the
likelihood of having different levels of organic content in any
soil type, a continuous profile will provide additional
understanding and evaluation of the subsurface.
This paper presents a comprehensive CPT/PCPT-based
organic content identification method using Zhang and Tumay
(1999) probabilistic soil classification method. The organic
content identification method proposed in this paper uses the
Zhang and Tumay method’s in-situ behavior index (
V
) in
combination with the compositional soil classification index (
U
)
to estimate the organic content. A detailed description of the
proposed methodology and a discussion of effective
applications are included in the paper. The paper also presents
analyses of two well-documented test sites to illustrate the
effectiveness of CPT/PCPT-based profiling and their correlation
to laboratory test results.
2 CPT-BASED PROBABILISTIC SOIL CLASSIFICATION
Unlike
the
traditional
chart-based
two-dimensional
classification methods, the Zhang and Tumay method uses a
probabilistic region estimation method to address the
uncertainty in misclassifying the soil layers. This statistical
based method provides a profile of the probability or the chance
of having each soil type (clayey, silty, and sandy) with depth.
This method is similar to the classic soil classification methods
which are based on soil composition. The probability of
incorrectly identifying soil type using the tradition CPT
classification charts, especially in transition zones, motivated
the development of the probabilistic region estimation method.
This CPT classification method addresses the uncertainty of
correlation between the soil composition and soil mechanical
behavior.
In the Zhang and Tumay probabilistic method, conformal
mapping was performed on the Douglas and Olsen (1981) chart
to transfer the chart axis from the CPT data (
q
c
, R
f
) to the soil
classification index (
U
) and in-situ behavior index (
V
). The
conformal transformation is accomplished using the following
equations:
