Significance and Use
4.1 The bi-directional axial compressive load test provides separate, direct measurements of the pile side shear mobilized above an embedded jack assembly and the pile end bearing plus any side shear mobilized below the jack assembly. The maximum mobilized pile resistance equals two times the maximum load applied by the jack assembly. Test results may also provide information used to assess the distribution of side shear resistance along the pile, the amount of end bearing mobilized at the pile bottom, and the long-term load-displacement behavior.
4.2 The specified maximum test load should be consistent with the engineer’s desired test outcome. For permanent (working) piles, the engineer may require that the magnitude of applied test load be limited in order to measure the pile movement at a predetermined proof load as part of a quality control or quality assurance program. Tests that attempt to fully mobilize the axial compressive resistance of the test pile may allow the engineer to improve the efficiency of the pile design by reducing the piling length, quantity, or size.
4.3 The engineer and other interested parties may analyze the results of a bi-directional axial compressive load test to estimate the load versus movement behavior and the pile capacity that would be measured during axial static compressive or tensile loading applied at the pile top (see Notes 1-3). Factors that may affect the pile response to axial static loading during a static test include, but are not limited to the:
(1) pile installation equipment and procedures,
(2) elapsed time since initial installation,
(3) pile material properties and dimensions,
(4) type, density, strength, stratification, and groundwater conditions both adjacent to and beneath the pile,
(5) test procedure,
(6) prior load cycles.
Note 1: To estimate the load displacement curve for the pile as if it were loaded in compression at the top (as in Test Methods D1143/D1143M), the engineer may use strain and movement compatibility to sum the pile capacity mobilized above and below the embedded jack assembly for a given pile-top movement. This “top-load” curve will be limited by the lesser of the displacement measured above or below the embedded jack assembly. To obtain adequate minimum displacement during the test, the engineer may wish to specify a maximum test load greater than the desired equivalent “top load”.
Note 2: A bi-directional load test applies the test load within the pile, resulting in internal pile stresses and pile displacements that differ from those developed during a load test applied at the pile top. Bi-directional testing will generally not test the structural suitability of a pile to support a load as typically placed at the pile top. Structural defects near the pile top may go undetected unless separate integrity tests are performed prior to or after bi-directional testing (see Note 8). The analysis of bi-directional load test results to estimate the pile-top movement that would be measured by applying a compressive load at the top of the pile should consider strain compatibility and load-displacement behavior. ASTM D1143/D1143M provides a standard test method for the direct measurement of pile top movement during an axial static compressive load applied at the pile top.
Note 3: The analysis of bi-directional load test results to estimate pile displacements that would be measured by applying a tensile (uplift) load at the top of the pile should consider strain and movement compatibility. Users of this standard are cautioned to interpret conservatively the tensile capacity estimated from the analysis of a compressive load. ASTM D3689/D3689M provides a standard test method for the direct measurement of axial static tensile capacity.
4.4 For the purpose of fully mobilizing the axial compressive capacity, the engineer will usually locate the jack assembly at a location within pile where the capacity above the assembly equals the capacity below it. A poorly chosen assembly location may result in excessive movement above or below the jack assembly, limiting the applied load and reducing the usefulness of the test result. Determination of the assembly’s location requires suitable site characterization, consideration of construction methods, and the proper application of engineering principles and judgement (see Note 4). More complex test configurations, using multiple levels of jack assemblies, may provide a higher probability that the full resistance of the pile along its entire length may be determined. Details regarding such complex arrangements are beyond the scope of this standard.
Note 4: The bi-directional load test may not fully mobilize the axial compressive pile resistance in all sections of the pile. Practical, economical, or code considerations may also result in bi-directional load tests that are not intended to fully mobilize the axial resistance in some or all sections of the pile. In these cases, interpretation of the bi-directional test may under-predict the total axial compressive capacity of the pile.
Note 5: The quality of the results produced by this test method are 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 test method 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 The test methods described in this standard measure the axial displacement of a single, deep foundation element when loaded in bi-directional static axial compression using an embedded bi-directional jack assembly. These methods apply to all deep foundations, referred to herein as “piles,” which function in a manner similar to driven piles, cast in place piles, or barrettes, regardless of their method of installation. The test results may not represent the long-term performance of a deep foundation.
1.2 This standard provides minimum requirements for testing deep foundations under bi-directional static axial compressive load. Plans, specifications, and/or provisions prepared by a qualified engineer may provide additional requirements and procedures as needed to satisfy the objectives of a particular test program. The engineer in charge of the foundation design, referred to herein as the engineer, shall approve any deviations, deletions, or additions to the requirements of this standard.
1.3 This standard provides the following test procedures:
Extended Test (optional)
1.4 Apparatus and procedures herein designated “optional” may produce different test results and may be used only when approved by the engineer. The word “shall” indicates a mandatory provision, and the word “should” indicates a recommended or advisory provision. Imperative sentences indicate mandatory provisions.
1.5 The engineer may use the results obtained from the test procedures in this standard to predict the actual performance and adequacy of piles used in the constructed foundation. See Appendix X1 for comments regarding some of the factors influencing the interpretation of test results.
1.6 A qualified engineer (specialty engineer, not to be confused with the foundation engineer as defined above) shall design and approve the load test configuration and test procedures. 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. This standard also includes illustrations and appendixes intended only for explanatory or advisory use.
1.7 Units—The values stated in either SI units or inch-pound units (presented in brackets) 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. Reporting of test results in units other than SI shall not be regarded as nonconformance with this test method.
1.8 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.
1.9 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D6026.
1.9.1 The procedures used to specify how data are collected, recorded and calculated in this standard 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 be commensurate with these considerations. It is beyond the scope of this standard to consider significant digits used in analysis methods for engineering design.
1.10 This standard offers an organized collection of information or a series of options and does not recommend a specific course of action. This document cannot replace education or experience and should be used in conjunction with professional judgment. Not all aspects of this guide 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.
1.11 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, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.12 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.