- 1229 - SPT Capability to Estimate Undrained Shear Strength of Fine-Grained Soils of Tehran, Iran Frazad Nassaji Department of Civil Engineering, University of Hormozgan, Iran Email: nassaji_farzad@yahoo.com Behzad Kalantari Assistant Professor, Department of Civil Engineering, University of Hormozgan, Iran Email: behzad996@yahoo.com ABSTRACT The SPT is considered one of the most common in-situ tests to evaluate the strength of coarse grained soil. In this study, it is tried to answer the question that, whether is possible to estimate undrained shear strength (S u ) of fine-grained soil from N (SPT) .To fulfil this objective, the ability of SPT to estimate S u of fine-grained soil in the southern as well as eastern of Tehran (Iran) using the multi linear regression analysis from SPSS software has been (evaluated) used for the study. Results have shown that considering other parameters such as natural water content (w n ), liquid limit (LL) and plasticity index (PI), to establish correlations in addition to N (SPT) , increases the correlation coefficient for estimation and also decreases the estimation error. Relationships are developed based on N and N 60 . Comparison between current proposed correlations and previous proposed correlations has shown that for fine- grained soil of the mentioned locations in Tehran, current proposed correlations have more carefully compared to previous correlations. (Standard Deviation = 0.28 for current correlations and Standard Deviation = 0.35, 0.48, 0.56 for previous correlations). KEYWORDS: Undrained shear strength, Standard penetration test, Correlation, Fine- grained soil I NTRODUCTI ON According to the unavailability of equipment and also financial and time limitations in a project, in many cases various types of relationships may be needed to estimate the geotechnical parameters from the values that are extracted from the in-situ tests. One of these important parameters is undrained shear strength that known with S u or C u . S u could be estimated from the in-situ tests such as pocket penetrometer, cone penetration test (CPT), standard penetration test