ASTM D1587 governs the extraction of undisturbed samples using thin-walled Shelby tubes, a standard that directly applies to Charlotte's Piedmont geology. The city's profile of residual soils derived from granitic and metamorphic bedrock requires careful handling to preserve the natural fabric and moisture content. Without this technique, cohesion and void ratio estimates become unreliable, compromising foundation design. For projects in areas like South End or uptown, where historic grading has created variable fill depths, undisturbed sampling paired with a calicata exploratoria provides a dual picture of soil structure and stratigraphy.
In Charlotte's Piedmont soils, a properly extracted Shelby tube sample can mean the difference between a 30% overdesign and a foundation that fits the ground.
Scope of work
Area-specific notes
Charlotte sits on the eastern edge of the Piedmont Plateau, where residual soils can exceed 30 m in depth. The shallow bedrock in Dilworth contrasts sharply with the deep saprolite in Ballantyne. A common risk is using disturbed samples for settlement analysis — the void ratio gets altered, and the computed settlement may be half of reality. Another risk is tube collapse in loose sands during extraction, which ruins the sample. That is why experienced crews in Charlotte always check for caving conditions before pushing the tube. A bad sample leads to a bad foundation, and that is not a gamble worth taking.
Standards used
ASTM D1587-15 (Standard Practice for Thin-Walled Tube Sampling), ASTM D4220-19 (Standard Practices for Preserving and Transporting Soil Samples), IBC 2021 Chapter 18 (Soils and Foundations)
Linked services
Shelby Tube Extraction & Field Handling
Our crews use hydraulic push rigs to advance thin-walled tubes with controlled feed rates. Each sample is logged, sealed, and labeled on site. We follow ASTM D1587 to the letter, including tube cleaning and lubrication to reduce friction. This service covers up to 5 tubes per borehole, with vertical transport included.
Lab Testing on Undisturbed Specimens
Once the tubes arrive at the lab, we trim and test the material for triaxial compression (UU, CU, CD), one-dimensional consolidation, and unconfined compression. All tests follow ASTM standards. The results give you moduli, strength parameters, and consolidation curves that reflect real field conditions.
Typical parameters
Top questions
What is the difference between a Shelby tube sample and a split-spoon sample?
A split-spoon sample is disturbed — it tells you the blow count and a general soil type, but the structure is broken. A Shelby tube sample preserves the intact fabric, moisture, and voids. That makes it suitable for lab tests like consolidation and triaxial, where disturbance would skew the results.
How deep can a Shelby tube sample be taken in Charlotte?
In residual soils of the Piedmont, the practical limit is about 15 to 20 m, depending on soil density and rig capacity. Below that, the tube may buckle or the sample may plug. For deeper zones, we switch to coring or other methods. The key is knowing the local stratigraphy before deciding the depth.
How much does undisturbed sampling cost in Charlotte?
The typical range for Shelby tube sampling in Charlotte is between US$460 and US$1,200 per sample, including field extraction and basic sealing. Costs vary with depth, number of tubes, and site accessibility. Additional lab testing is billed separately. Contact us for a project-specific quote.
When should I request undisturbed sampling instead of SPT only?
If your design relies on settlement calculations, shear strength parameters, or consolidation behavior, you need undisturbed samples. SPT alone gives you blow counts and disturbance. For example, a mat foundation on clay in the Catawba floodplain would require consolidation tests from Shelby tubes to predict long-term settlement.
What precautions are taken to preserve the sample after extraction?
Immediately after extraction, the tube ends are cleaned, waxed, and capped. The tube is labeled with depth and orientation, then placed upright in a padded crate. Temperature is kept between 4 and 22 °C during transport. The lab receives the tube within 24 hours to trim and test before moisture loss occurs.