Figure F25. Illustration of the procedure for deployment of the penetration probes. A, B. The drill string pushes the probe into the formation. After penetration, the drill string is raised. C. The probe should stay in the ground and the bottom-hole assembly should slide upward as the drill string is raised a few meters. D. In many penetrometer deployments, when the drill string was raised it appears there was partial coupling between the drill string and tool. As a result, the tool was partially pulled out of its hole. E. During a successful penetration, there is an abrupt increase in pressure during penetration and then there is a slow dissipation of pressure after the tool is left in the ground. F. During unsuccessful deployments, the pore pressure record sharply drops during pullout. The result is a subhydrostatic pressure that gradually builds back to the formation pressure.