The use of rock coring for foundation design is necessary to obtain useful design data for design methodologies in AASHTO. Observation of drill rig performance, identifying bedrock or rock mass layer, and switching to rock coring shall be at the driller and field logger discretion. Typically, this depth will be evident by drill rig performance, but also can be detected by SPT refusal or resistance when pushing for a Shelby tube sample. Cemented soil and shale can often be difficult to identify and collect core sample. Air, water, or water based, or combination of geotechnical coring media as appropriate to the geological conditions are acceptable for retrieving samples in 5-ft core runs through bit types of driller selection. Conduct coring operations in accordance with AASHTO T225.