Cone penetrometer system for measuring cone index and stress relaxation

A portable computer-controlled cone penetrometer was designed for making cone index and relaxed cone index measurements. The new penetrometer is DC powered and was interfaced to an IBM personal computer. Software was used for controlling the penetrometer motor speed (penetration rate), and sampling cone depth, cone index and stress relaxation data at approximately 85 Hz. Cone insertion rate ranged from 2.6 to 6.7 mm/s. The stroke was 450 mm and up to three intervals could be programmed for collecting stress relaxation data (cone index with no cone movement for up to 1 min). The maximum measurable cone index was approximately 7.0 MPa. Penetrometer accuracy was verified using an Instron test machine.