A new geotechnical investigation tool called the CPT Stinger has recently been developed to acquire geotechnical information cost effectively at deepwater sites. Combining jumbo piston core (JPC) sampling with the CPT Stinger (deployed using the same rigging as the JPC) provides a full geotechnical profile at a given location, down to a depth of 35m below mudline. Cone penetration test (CPT) data are collected during initial free-fall insertion of the CPT Stinger apparatus. These data could be used to provide a continuous stratigraphic profile from mudline down to the depth where conventional CPT data (push rate of 2cm/s) are acquired, if a reliable and repeatable method for correcting the free-fall insertion data could be developed. Several methods have previously been proposed to correct soil shear strength for rate of loading effects. These methods are evaluated in this paper by comparing their results to data acquired in 2011 at a deepwater site in the Gulf of Mexico. The paper gives an operator''s perspective on the potential of different methodologies in correcting free-fall CPT Stinger data for deepwater site investigations.
Deepwater geotechnical acquisition is a cost intensive activity that causes operators to evaluate tradeoffs between project economics and the relative value of the information being gathered. Operators are continuously evaluating more economical options for acquiring high quality data that can be used for design. A new system has been recently developed called the CPT Stinger, and it proposes to reduce geotechnical data acquisition costs by combining the traditional jumbo piston core (JPC) sampling technique with a CPT system that is deployed with the same equipment. The CPT Stinger essentially replaces the JPC core barrel and liner with the CPT cone, data logger, rod assembly and power and control modules (Young et al., 2011).