636
Proceedings of the 18
th
International Conference on Soil Mechanics and Geotechnical Engineering, Paris 2013
The data capture frequency of the CPT soundings (2 cm/sec)
also allows for the identification of the thinner seams of sandy
and silty sand layers as well as the increases in the organic
content. For example, the soil classification of the B-28 data set
between 8.0 and 12.0 meters shows thin layers of clayey
materials. At these layers, the organic content appears to be
higher that the surrounding silty sand.
4 CONCLUSION
Although there are several CPT-based soil classification models
effectively used in subsurface investigations, accurate
identification of organic materials using CPT soundings
provides a challenge. The organic content indicator (
V-U
)
proposed in this study offers a continuous profile for the organic
content based on the soil classification and in-situ behavior
indexes as defined by the Zhang and Tumay’s probabilistic
method.
For the examples provided in this paper, the organic content
indicator shows a strong agreement with the test results and [(
V
-
U
) > 3.0] indicates an approximate level of 5% organic
material. The CPT-based indicator may provide a useful tool
considering the importance of identifying organic materials
which could lead to problems concerning stability, compaction,
compressibility and usability.
Soil classification effectiveness and accuracy of the Zhang
Tumay (1999) method has been evaluated with several data sets
under different conditions and test sites, and compared with
other classification charts, for subsoil stratigraphy (Tümay et.
al., 2011), multi model comparison (Hatipkarasulu and Tümay,
2011(1)), tip resistance value correction (Tümay and
Hatipkarasulu, 2011), effective area ratio assumption
(Hatipkarasulu and Tümay, 2011(2)), and data reduction effects
(Tümay and Hatipkarasulu, 2012). The method uses a non-
traditional approach which takes into account the probability of
having each soil type with depth. The use of soil classification
(
U
) and in-situ behavior (
V
) indexes for organic profiling
extends the same concept of accounting for the chance of
having organic material at any given depth. The organic content
indicator (
V-U
) profiling shows reliable performance in clayey
materials and its further evaluation is imperative for non-clay
organic soils.
5 ACKNOWLEDGEMENTS
This study rests on the interpretations of the field and laboratory
investigations conducted for the Mississippi River Long
Distance Sediment Pipeline Project designed and undertaken by
the Louisiana Department of Transportation and Development
(LADOTD). The contents of this paper reflect the views of the
authors, who are responsible for the facts and the accuracy of
the data presented herein, and do not necessarily indicate
official assessments of the agencies, firms and institutions with
which the authors are affiliated.
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