4.1 Various driven in situ penetrometers are used to evaluate the engineering behavior of soils. The Standard Penetration Test is the most common type. Engineering properties can be estimated on the basis of empirical correlations between N-values and soil density, strength or stiffness. Alternatively, the N-value can be used directly in foundation design using correlations to design parameters such as allowable bearing pressure or pile capacity. The N-value depends on the soil properties but also on the mass, geometry, stroke, anvil, and operating efficiency of the hammer. This energy measurement procedure can evaluate variations of N-value resulting from differences in the hammer system. See also Refs (1-6).3

4.2 There is an approximate, linear relationship between the incremental penetration of a penetrometer and the energy from the hammer that enters the drill rods, and therefore an approximate inverse relationship between the N-value and the energy delivered to the drill rods.

Note 1: Since the measured energy includes the extra potential energy effect due to the set per blow, tests for energy evaluation of the hammer systems should be limited to moderate N-value ranges between 10 and 50 (Ref (7)).

4.3 Stress wave energy measurements on penetrometers may evaluate both operator-dependent cathead and rope hammer systems and relatively operator-independent automatic systems.

4.4 The energy measurement has direct application for liquefaction evaluation for sands as referenced in Practice D6066.

4.5 This test method is useful for comparing the N-values produced by different equipment or operators performing SPT testing at the same site, aiding the design of penetrometer systems, training of dynamic penetrometer system operators, and developing conversion factors between different types of dynamic penetration tests.

Note 2: 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 D3740 are generally considered capable of competent and objective testing/sampling/inspection/etc. Users of this standard are cautioned that compliance with Practice D3740 does not in itself assure reliable results. Reliable results depend on many factors: Practice D3740 provides a means of evaluating some of those factors.

1.1 This test method describes procedures for measuring the energy that enters the penetrometer drill rod string during dynamic penetrometer testing of soil due to the hammer impact.

1.2 This test has particular application to the comparative evaluation of N-values obtained from the Standard Penetration Tests (SPT) of soils in an open hole as in Test Method D1586 and Practice D6066. This procedure may also be applicable to other dynamic penetrometer tests.

1.3 The values stated in SI units are to be regarded as standard. The inch-pound units given in parentheses are mathematical conversions which are provided for information purposes only and are not considered standard. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method.

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

1.4 Limitations—This test method applies to penetrometers driven from above the ground surface. It is not intended for use with down-hole hammers.

1.5 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.

1.5.1 The procedures used to specify how data are collected/recorded or calculated, in this standard are regarded as the industry standard. In addition, they are representative of the significant digits that generally should 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 be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analytical methods for engineering design.

1.6 The text of this standard references notes and footnotes which provide explanatory material. These notes and footnotes (excluding those in tables and figures) shall not be considered as requirements of the standard.

1.7 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 limitations prior to use.