Thin-Walled Tube sampling in accordance with AASHTO T207 or ASTM D1587 is critical to retrieving undisturbed, in-situ samples used for laboratory testing for obtaining useful soil parameters for use in AASHTO design methodologies. Use undisturbed in-situ samples retrieved in accordance with AASHTO T 207 or ASTM D1587 for lab testing. Where fine-grained, or cohesive soils are observed collect ThinWalled Tube samples at intermediate locations between the SPT. Use 3 inch diameter Thin-Walled Tubes unless deviations are requested in investigation and approved by the Bridge Division Geotechnical Branch. Indicate on logs length of sample collected (recovery) and if tube was unable to push the full 24” of undisturbed sample as specified by procedure.

Typically, samples can be extruded in the field and wrapped to prevent moisture loss or sealed in plastic bags immediately after measuring recovery length and obtaining pocket penetrometer and/or torvane measurements. Project specific guidelines may dictate that tube samples be capped or waxed at the ends and cut open in the lab.

Careful handling, transportation and storage of all samples is required to minimize sample disturbance and ensure accurate results of lab work. Exercise the following general precautions, in handling, transportation, and storage of samples. Perform lab tests as soon as possible after drilling is completed.

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.

Exercise the following when caring, handing, storing, and transporting rock samples:

The pocket penetrometer test is useful for estimating consistency and approximate measurements of unconfined compressive strength. It yields approximate information which is not suitable for foundation design. However, comparison of pocket penetrometer measurements at the time of sampling on the field and in the laboratory prior to laboratory strength testing may be useful for comparing consistency. Perform pocket penetrometer testing and record values on any and all cohesive or fine-grain samples collected from Thin-Walled /(Shelby) tube sampling and adhere to the following guidance:

Use the in-place vane shear test to determine the in-place shearing strength of fine-grained soil, which does not lend itself to undisturbed sampling and triaxial testing. Use this test when encountering organic silty clay (muck) or very soft clay. Ensure these materials are free of gravel or large shell particles because pushing the vanes through these obstructions would disturb the sample and probably cause physical damage to the vanes. Use the test with extreme caution in soil that has Standard Penetration Test values harder than 15 blows/12 in. Correct the vane shear results to the soil index properties.

This test is useful for index and classification purposes as it yields approximate information which is not suitable for foundation design. Adhere to the following when performing this test: