This code establishes the standard procedure and equipment requirements for obtaining undisturbed samples of soft to firm cohesive soils and sensitive clays using thin-walled tubes and stationary piston samplers.
Provides procedures for obtaining undisturbed soil samples using a thin-walled stationary piston sampler for geotechnical investigations.
Quick Reference Values
recommended area ratio max10%
maximum tolerable area ratio15%
inside clearance ratio1% to 3%
outside clearance ratio max2%
standard tube diameters38, 50, 75, and 100 mm
acceptable recovery ratio96% to 104%
Key Formulas
Area Ratio (Ar) = [(Dw^2 - De^2) / De^2] * 100
Inside Clearance (Ci) = [(Ds - De) / De] * 100
Outside Clearance (Co) = [(Dw - Dt) / Dt] * 100
Recovery Ratio = L / H (Length of sample / Depth of penetration)
Practical Notes
Tubes must be pushed continuously and steadily into the soil without impact hammering or rotation to minimize sample disturbance.
A low area ratio (ideally < 10%) and proper inside clearance (1-3%) are critical for obtaining high-quality undisturbed samples.
End sealing with microcrystalline wax should be done immediately upon extraction to prevent loss of natural moisture content.
Stationary piston samplers are highly recommended for very soft or sensitive clays to prevent sample drop-out and minimize disturbance.