Analytical and Probabilistic Correlations Between In-Situ Tests and Instantaneous Logging-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines how measured-while-drilling (MWD) data can support geotechnical investigations and correlate with in-situ test results. Sensors on hydraulic drilling machines continuously record parameters such as penetration rate, torque, return flow and hold pressure, alongside operator-controlled settings such as thrust, rotation speed and injection pressure.<br /><br />Individual parameters can indicate changes in soil resistance, density and clay content, and help identify layer boundaries or cavities. However, they must be interpreted using machine calibration, and primarily through trends rather than absolute values.<br /><br />The study focuses on two composite parameters defined in the relevant standard: penetration resistance, associated with dynamic cone penetrometer results, and the modified Somerton Index, associated with pressuremeter limit pressure. Across about 30 sites and 100 boreholes, the Somerton Index generally followed similar curve shapes across soil types, but its numerical values varied with the drilling machine, drilling method and tool.<br /><br />To address these differences, the presenters propose an empirical correction factor based on calibration logs. Reliable correction requires calibration under the same drilling settings as the investigation, including the same applied thrust. Corrected results show promising agreement between the Somerton Index and pressuremeter limit pressure, as well as between penetration resistance and dynamic cone results.<br /><br />The approach is affected by very heterogeneous coarse soils and by drilling very hard ground with low-power equipment. Overall, calibrated and corrected MWD parameters offer useful continuous information about subsurface conditions and can correlate well with conventional in-situ tests.

Keywords

measured-while-drilling

MWD data

geotechnical investigations

in-situ tests

penetration resistance

Somerton Index

drilling calibration

pressuremeter

dynamic cone penetrometer

subsurface conditions