Abstract:
Measurement While Drilling MWD is an emerging technology where several sensors are installed on drill rigs to continuously measure the operational and ground response parameters of the drilling operation. Penetration rate, crowd (down pressure), torque, rotation speed, fluid injection pressure, and flow rate (the last two are only measured if mud rotary drilling is used) are the main parameters typically measured during MWD. Although Cone Penetration Test (CPT) produces continuous information about the subsurface conditions, MWD has several advantages. Unlike CPT, soil is brought to surface during the MWD operations where they can be investigated for engineering and index properties (soil classification). Furthermore, MWD can penetrate through hard soil and rocks while CPT is unable to penetrate into rocks. Finally, additional in-situ tests (e.g., Standard Penetration Test, SPT) and sampling (e.g., Shelby tubes) can be used during MWD. This new technology, therefore, has the potential to significantly improve the geotechnical site investigation and the design of deep foundations. However, foundation design based on MWD data has not been developed yet. In this study, MWD data from five boreholes drilled in the State of Nebraska are compared with the CPT test data collected next the each drill hole. The soils encountered during these tests are mostly high and low plasticity silt and clay. During the drilling process, Shelby tubes were pushed to collect soil samples for laboratory tests. Unconsolidated Undrained (UU) triaxial compression tests were conducted on the collected samples. Some in-situ Shear Vane tests were also conducted at some locations during the drilling process. Both MWD and CPT data were compared and correlated to the shear strength of soil layers. Both CPT data and undrained shear strength data from UU tests were used to calculate unit side resistance and unit toe bearing of different layers encountered. Finally, the MWD data was correlated to the calculated unit side resistance and unit toe bearing of different layers in an attempt to develop a criteria for designing foundations based on the MWD data.