Sampling methods are generally governed by geological conditions and the geomaterials to be encountered in the field. Applicable sampling methods corresponding to soil types shall be employed to obtain appropriate samples for visual classification, and laboratory testing afterward. Perform Standard Penetration tests (SPT) in accordance with AASHTO T 206 or ASTM D1586 every 5-ft. interval beginning at 5-ft. depth from the surface. When a boring is proceeding in cohesionless materials, collect split-spoon samples along with the SPT every 5-ft interval. Where cohesive soils are encountered collect Thin-Walled (Shelby) Tube samples in accordance with AASHTO T 207 or ASTM D1587 at intermediate locations between the SPT. Continuous sampling within the top of 15 to 20 feet of borings may be necessary where soils are anticipated to vary at the top or when required for design for the proposed structure.

Borehole efforts should focus on SPT in overburden soils. Switch to coring when bedrock or a rock mass is identified. Where bedrock/rock are encountered, collect rock core samples in accordance with AASHTO T 225. Place the extracted rock cores into dedicated rock core boxes that are often constructed of wood or heavy-duty cardboard for laboratory testing. Determine the Rock Quality Designation (RQD), percent recovery, and any other rock observations noted in Chapter 4 soon after as the core extraction is completed and record the values in the field logs.