Measuring while drilling in Florida limestone for geotechnical site investigation

Abstract

Florida limestone can be challenging to recover during coring operations, as the rock generally is soft, porous, and often highly weathered. Low recoveries coupled with poor rock quality are common in Florida, which limits the data available for geotechnical design. However, the low recoveries and poor rock quality may be attributable to coring techniques and not the rock’s in situ condition. This paper explores integrating measuring while drilling (MWD) into standard coring procedures to provide in situ strength assessment and optimize core recoveries and rock quality to improve rock mass characterization. Six drilling parameters were monitored during the research, and a controlled drilling environment was developed to investigate each monitored parameter’s effects. Variable drill bit configurations were also explored to investigate the effects of bit geometry. Interdependent relationships between the drilling parameters were discovered and a new concept of operating within optimal drilling parameter ranges based on these relationships is introduced. The coring practices developed in the controlled environment were then tested in natural Florida limestone. It was concluded that operating within the optimal ranges allows in situ strength assessment and improves core recoveries and rock quality.