Undisturbed block samples are suitable for laboratory tests where large-sized samples of undisturbed material are required or where such sampling is more practical than conventional tube sampling (Practices D 1587 and D 6519), or both.

This method of sampling is advantageous where the soil to be sampled is near the ground surface. This is the best available method for obtaining large undisturbed samples of very stiff and brittle soils, partially cemented soils, and some soils containing coarse gravel.

Excavating a column of soil may relieve stresses in the soil and may result in some expansion of the soil and a corresponding decrease in its unit weight (density) or increase in sampling disturbance, or both. Usually the expansion is small in magnitude because of the shallow depth. Stress changes alone can cause enough disturbances in some soils to significantly alter their engineering properties.

The chain saw has proved advantageous in sampling difficult soils, which are blocky, slickensided, or gravelly, or materials containing alternating layers of hard and soft material.³ The chain saw uses a special carbide-tipped chain.⁴

Note 1—The quality of the result produced by this standard is dependent on the competence of the personnel performing it, and the suitability of the equipment and facilities used. Agencies that meet the criteria of Practice D 3740 are generally considered capable of competent and objective sampling. Users of this practice are cautioned that compliance with Practice D 3740 does not in itself assure reliable results. Reliable results depend on many factors; Practice D 3740 provides a means of evaluating some of those factors.

1.1 This designation outlines the procedures for obtaining undisturbed block (cubical and cylindrical) soil samples.

1.2 Undisturbed block samples are obtained for laboratory tests to determine the strength, consolidation, permeability, and other geotechnical engineering or physical properties of the undisturbed soil.

1.3 Two sampling practices are presented. Practice A covers cubical block sampling, while Practice B covers cylindrical block sampling.

1.4 These practices usually involve test pit excavation and are limited to relatively shallow depths. Except in the case of large diameter (that is, >0.75 m) bored shafts of circular cross-section in unsaturated soils, for depths greater than about 1 to 11/2 meters or depths below the water table, the cost and difficulties of excavating, cribbing, and dewatering generally make block sampling impractical and uneconomical. For these conditions, use of a thin-walled push tube soil sampler (Practice D 1587), a piston-type soil sampler (Practice D 6519), or Hollow-Stem Auger (D 6151), Dennison, or Pitcher-type soil core samplers, or freezing the soil and coring may be required. This practice does not address environmental sampling; consult Guides D 6169 and D 6232 for information on sampling for environmental investigations.

1.5 Successful sampling of granular materials requires sufficient cohesion, cementation, or apparent cohesion (due to moisture tension (suction)) of the soil for it to be isolated in a column shape without undergoing excessive deformations. Additionally, care must be exercised in the excavation, preservation and transportation of undisturbed samples (see Practice D 4220, Group D).

1.6 The values stated in SI units are to be regarded as the standard. No other units are included in this standard.

This practice offers a set of instructions for performing one or more specific operations. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this practice may be applicable in all circumstances. This ASTM standard is not intended to represent or replace the standard of care by which the adequacy of a given professional service must be judged, nor should this document be applied without consideration of a project's many unique aspects. The word "Standard" in the title of this document means only that the document has been approved through the ASTM consensus process.

1.8 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory requirements prior to use. For specific hazard statements, see Section 6.