The standard penetration test (SPT) is one of the most widely used in-situ penetration tests for subsurface exploration. Its suitability for assessing and predicting the design parameters of granular materials has been well appreciated by the geotechnical engineering community over several decades. However, in the case of soft to very soft clays, the correlation between the standard penetration number (N) and the undrained shear strength is poor. In the recent past, tests conducted at a constant rate of penetration, such as the cone penetration test (CPT), ball penetration test, and T-bar penetration test, have become popular in soft clay regions. These tests also have a distinct advantage over SPT in terms of test setup because, in the case of SPT, the entire weight of the sampler and the rod assembly is directly applied on the subsoil, whereas in the case of CPT, the weight of the assembly is supported externally prior to the penetration. This can cause significant operational advantage in case of soft clay deposits. Despite the shortcomings, SPT is still one of the most widely available site investigation tools in the field, as samples are available for inspection and index tests. The operational disadvantages in the case of soft clay deposits can be overcome by altering the penetration process of SPT. A quasi-static penetration at a constant rate rather than a dynamic penetration will help establish a relationship between the penetration resistance and the strength parameters of soft soils. In this article, a quasi-static penetration test using the standard SPT sampler is conducted on reconstituted clay samples in order to develop an empirical correlation with the laboratory vane shear strength. The particle image velocimetry technique is used for detecting the influence zone and plugging during penetration. Copyright © 2018 by ASTM International.