Drilled shaft resistance based on diameter, torque and crowd (drilling resistance vs. Rock strength) phase II : final report.

Final reportPDFTech ReportFDOT Contract No. BDV31-977-20UF Contract No. 00Compressive strengthEvaluationField testsLaboratory testsLimestoneLoad testsRock drillingTorqueUnited StatesFloridaFlorida. Dept. of Transportation. Research CenterMcVay, Michael C.Rodgers, Michael O.University of Florida. Dept. of Civil and Coastal EngineeringFlorida. Dept. of TransportationUS Transportation CollectionThe research focused on evaluation of Florida limestone\ue2\u20ac\u2122s unconfined compressive strength, qu, throughdrilling parameters \ue2\u20ac\u201c crowd, torque, penetration rate, rotational speed, and bit diameter \ue2\u20ac\u201c in both thelaboratory and field for assessing a shaft\ue2\u20ac\u2122s side shear. Synthetic homogeneous limestone blocks ofvarious strengths were cast in the laboratory and allowed to cure for 14 days; The blocks were thendrilled with rock augers of two different diameters at multiple penetration rates and drilling rotationalspeeds. Both crowd and torque were measured in real time. Estimation of rock strength, qu from drillingrelationships developed by Karasawa (2002a) and Teale (1965) were evaluated. It was found thatTeale\ue2\u20ac\u2122s specific energy approach could estimate rock strength, qu using the multiple diameter drill bitsexpected in field drilled shaft construction.In the field, shaft installation was monitored (crowd, torque, penetration rate, etc.) at three sites (LittleRiver, Overland, and Kanapaha) from which rock strength, qu was estimated along with shaft side shear.For side shear, FDOT\ue2\u20ac\u2122s design equation in limestone was used with split tension strength initiallyestimated from qt/qu ratio established by field cores; subsequently, Johnston\ue2\u20ac\u2122s qu vs. qt/qu relationshipwas used. The estimated unit skin friction in multiple rock formations and segments was compared byinstrumented segment during Osterberg, Statnamic, and top-down static load testing. The mean bias(measured/predicted) unit side shear in limestone was 1.00, and the coefficient of variation, CV, was0.07. The results suggest that estimating rock strength and shaft side shear using drilling parameters isviable, especially considering the currently available rig monitoring equipment (Jean Lutz, Bauer, etc.)