This document discusses correlations between the Standard Penetration Test (SPT) and Cone Penetration Test (CPT). It notes that while SPT is widely used, CPT provides more reliable and repeatable results. The document reviews research on expressing the relationship between SPT N-values and CPT cone resistance (qc) through ratios of qc/N. It presents Robertson and Campanella's method which uses the relationship (qc/pa)/N60 to determine soil behavior type from CPT and SPT data. While this is a simple method, it can cause confusion at boundary zones between soil types. Developing a CPT-SPT correlation provides additional geotechnical data based on the more common

1. Made by
Aman Varshney
SPT-CPT Correlation
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2. Introduction of SPT-CPT
Correlation
 The Standard Penetration Test (SPT) is widely
employed in-situ test. Even though there have
been continuous attempts to standardize the SPT
process, it is still hard to have the reliability and
repeatability of the SPT. A significant experience
related to the design methods from the local SPT
correlation has been built. However, with time
passed, direct CPT design interactions will be
grown as well on the basis of local experience
and field examination. Therefore, it is necessary
to make correlation between SPT and CPT
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3. The Correlation between qc and
N
 There have been a lot of researches in order to
express the relation between SPT N and CPT
cone penetration resistance qc as a number. The
ratios of qc/N have broad ranges and the ratios
were released causing plenty of confusions. The
change in released qc/N ratio can be theoretically
explained to some extent reconsidering between
qc/N ratios and mean grain size (D50). It is
obvious that the values of qc/N ratios rise with
rising mean grain size.
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5. Robertson and Campanella:
 This method for correlating SPT and CPT data
uses the following relationship between
SPT N60 data and CPT tip resistance:
 (qc/pa)/N60
 qc = tip resistance (psi)
pa = atmospheric pressure (psi)
 Soil behavior type can be determined from this
equation based on the following table:
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7. Conclusion
 This is perhaps the simplest method for relating
the results of these two tests, but it can cause
some confusion when the results fall on the
border of two soil behavior type zones, or in
situations where the ratio of CPT to SPT data
could indicate one of several different soil types.
 It is useful to develop the correlation between
CPT and SPT, because after correlating we will
obtain plentiful data based on SPT.
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8. Thank You
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