Enhanced Access Penetration System for Cone Penetration at Difficult Sites

Cone Penetration Testing (CPT) is one of the most flexible geotechnical and environmental in situ characterization techniques. Test methods and probing systems have been developed to determine a wide array of geotechnical properties and, more recently, to investigate environmental sites. Despite its many advantages, a major limitation has been refusal of the CPT probe in geologic layers shallower than the desired sounding depth. These layers can be cemented soils, such as caliche that is typically found in arid regions, coarse-grained formations (i.e., gravel and boulders), or volcanic flow fields. Refusal in these layers has historically resulted in the need to mobilize a drill rig to penetrate the refusal layer and continuation of the investigation through a cased borehole. This increases cost and the detailed CPT profile of the site stratigraphy is lost. To address this limitation, we are developing the Enhanced Access Penetration System (EAPS). This paper describes our investigation of laser and overburden drilling as potential techniques to integrate with CPT for penetrating hard layers. We conclude that laser drilling is not currently feasible and that air rotary drilling is the preferred overburden drilling method. A prototype EAPS incorporating air rotary drilling is described. The system allows characterization, sampling, and drilling tools to be exchanged down-hole, without removal of the rod string. Field test results from EAPS deployments at the Department of Energy's Hanford Site and at Umatilla Chemical Depot are also presented.