Field Test Evaluation of Effect on Cone Resistance Caused by Change in Penetration Rate

This paper presents how a change in cone penetration rate affects the measured cone resistance during cone penetration testing in silty soils. Regardless of soil, type the standard rate of penetration is 20 mm/s and it is generally accepted that undrained penetration occurs in clay while drained penetration occurs in sand. In intermediate soils such as silty soils, the standard cone penetration rate may result in drainage conditions varying from undrained to partially or fully drained conditions. Field cone penetrations tests have been conducted with different penetration rates on a test site in Dronninglund where the subsoil primary consists of sandy silt. A total of 15 cone penetration tests with penetration rates varying from 60 to 0.5 mm/s and two geotechnical borings were conducted at the test site. Large soil samples were also collected from the test site in order to determine soil properties in the laboratory. A change in the measured cone resistance occurs by lowering the penetration rate. This is caused by the changes in drainage conditions. Compared to the normal penetration rate of 20 mm/s, this paper illustrates that lowering the penetration rate leads to an increase in the cone resistance from 1.0 – 1.7 depending on the initial drainage condition. This can be important if a project requires knowledge of the drained soil parameters in silt.