ASTM D2166 / D2166M - 13

    Standard Test Method for Unconfined Compressive Strength of Cohesive Soil

    Active Standard ASTM D2166 / D2166M | Developed by Subcommittee: D18.05

    Book of Standards Volume: 04.08


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    Significance and Use

    5.1 The primary purpose of the unconfined compression test is to quickly obtain a measure of compressive strength for those soils that possess sufficient cohesion to permit testing in the unconfined state.

    5.2 Samples of soils having slickensided or fissured structure, samples of some types of loess, very soft clays, dry and crumbly soils and varved materials, or samples containing significant portions of silt or sand, or both (all of which usually exhibit cohesive properties), frequently display higher shear strengths when tested in accordance with Test Method D2850. Also, unsaturated soils will usually exhibit different shear strengths when tested in accordance with Test Method D2850.

    5.3 If tests on the same sample in both its intact and remolded states are performed, the sensitivity of the material can be determined. This method of determining sensitivity is suitable only for soils that can retain a stable specimen shape in the remolded state.

    Note 2For soils that will not retain a stable shape, a vane shear test or Test Method D2850 can be used to determine sensitivity.
    Note 3The 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 D3740 are generally considered capable of competent and objective testing/sampling/inspection. Users of this standard are cautioned that compliance with Practice D3740 does not in itself ensure reliable results. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some of those factors.

    1. Scope

    1.1 This test method covers the determination of the unconfined compressive strength of cohesive soil in the intact, remolded, or reconstituted condition, using strain-controlled application of the axial load.

    1.2 This test method provides an approximate value of the strength of cohesive soils in terms of total stresses.

    1.3 This test method is applicable only to cohesive materials which will not expel or bleed water (water expelled from the soil due to deformation or compaction) during the loading portion of the test and which will retain intrinsic strength after removal of confining pressures, such as clays or cemented soils. Dry and crumbly soils, fissured or varved materials, silts, peats, and sands cannot be tested with this method to obtain valid unconfined compression strength values.

    Note 1The determination of the unconsolidated, undrained strength of cohesive soils with lateral confinement is covered by Test Method D2850.

    1.4 This test method is not a substitute for Test Method D2850.

    1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026, unless superseded by this standard.

    1.5.1 The procedures used to specify how data are collected/recorded and calculated in this test method are regarded as the industry standard. In addition, they are representative of the significant digits that should generally be retained. The procedures used do not consider material variation, purpose for obtaining the data, special purpose studies, or any considerations for the user's objectives; and it is common practice to increase or reduce significant digits of reported data to commensurate with these considerations. It is beyond the scope of this test method to consider significant digits used in analysis methods for engineering design.

    1.6 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

    1.6.1 The gravitational system of inch-pound units is used when dealing with inch-pound units. In this system, the pound (lbf) represents a unit of force (weight), while the unit for mass is slugs. The rationalized slug unit is not given, unless dynamic (F = ma) calculations are involved.

    1.6.2 It is common practice in the engineering/construction profession to concurrently use pounds to represent both a unit of mass (lbm) and of force (lbf). This implicitly combines two separate systems of units; that is, the absolute system and the gravitational system. It is scientifically undesirable to combine the use of two separate sets of inch-pound units within a single standard. As stated, this standard includes the gravitational system of inch-pound units and does not use/present the slug unit for mass. However, the use of balances or scales recording pounds of mass (lbm) or recording density in lbm/ft3 shall not be regarded as nonconformance with this standard.

    1.7 This standard does not purport to address all of the safety problems, 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 limitations prior to use.


    2. Referenced Documents (purchase separately) The documents listed below are referenced within the subject standard but are not provided as part of the standard.

    ASTM Standards

    D653 Terminology Relating to Soil, Rock, and Contained Fluids

    D854 Test Methods for Specific Gravity of Soil Solids by Water Pycnometer

    D1587 Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes

    D2216 Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass

    D2488 Practice for Description and Identification of Soils (Visual-Manual Procedure)

    D2850 Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils

    D3740 Practice for Minimum Requirements for Agencies Engaged in Testing and/or Inspection of Soil and Rock as Used in Engineering Design and Construction

    D4220 Practices for Preserving and Transporting Soil Samples

    D4318 Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils

    D6026 Practice for Using Significant Digits in Geotechnical Data

    D6913 Test Methods for Particle-Size Distribution (Gradation) of Soils Using Sieve Analysis

    D7263 Test Methods for Laboratory Determination of Density (Unit Weight) of Soil Specimens

    E177 Practice for Use of the Terms Precision and Bias in ASTM Test Methods

    E691 Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method


    ICS Code

    ICS Number Code 93.020 (Earth works. Excavations. Foundation construction. Underground works)

    UNSPSC Code

    UNSPSC Code 11111501(Soil)


    Referencing This Standard

    DOI: 10.1520/D2166_D2166M

    ASTM International is a member of CrossRef.

    Citation Format

    ASTM D2166 / D2166M-13, Standard Test Method for Unconfined Compressive Strength of Cohesive Soil, ASTM International, West Conshohocken, PA, 2013, www.astm.org

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