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ASTM D8169/D8169M-26
Standard Test Methods for Deep Foundation Elements Under Bi-Directional Static Axial Compressive Load
Standard Test Methods for Deep Foundation Elements Under Bi-Directional Static Axial Compressive Load
D8169_D8169M-26
ASTM|D8169_D8169M-26|en-US
Standard Test Methods for Deep Foundation Elements Under Bi-Directional Static Axial Compressive Load
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D8169/D8169M Standard Test Methods for Deep Foundation Elements Under Bi-Directional Static Axial Compressive Load>
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Significance and Use
4.1 The bi-directional axial compressive load test provides separate, direct measurements of the axial capacity mobilized above an embedded jack assembly and element end bearing plus any axial capacity mobilized below the jack assembly. The maximum mobilized axial capacity equals two times the maximum jack assembly load. Test results may also provide information used to assess side shear resistance distribution along the element, mobilized end bearing, and long-term load-displacement behavior. Tests that attempt to fully mobilize the axial compressive resistance may allow the Engineer to improve element design efficiency by reducing element length, quantity, or size.
4.2 The specified maximum test load should be consistent with the Engineer’s desired test outcome. For production elements (permanent, working, elements), the Engineer may require that test load magnitude be limited in order to measure element movement at a predetermined proof load as part of a quality control or quality assurance program.
4.3 The Engineer or other interested parties may analyze bi-directional axial compressive load test results to estimate load versus movement behavior that would occur for axial static compressive or tensile loading applied at the element top (see Note 1, Note 2, and Note 3). Factors that may affect the element response to axial static loading during a static test include, but are not limited to:
(1) element installation equipment and procedures,
(2) elapsed time since initial installation,
(3) element material properties and dimensions,
(4) type, density, strength, stratification, and groundwater conditions both adjacent to and beneath the element,
(5) test procedure,
(6) prior load cycles,
(7) ground surface elevation during the test,
(8) groundwater level during the test.
Note 1: To estimate the load-displacement curve for the element as if it were loaded in compression at the top (as in Test Methods D1143/D1143M), the Engineer or other interested parties may use strain and movement compatibility to sum element capacity mobilized above and below the embedded jack assembly for a given element-top movement. This “equivalent 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 element, resulting in internal element stresses and displacements that differ from those developed when a load is applied at the element top. Bi-directional testing will generally not test the structural capacity of the element top. Structural defects near the element top may go undetected unless separate integrity tests are performed prior to or after bi-directional testing (see Note 8). Test Methods D1143/D1143M can be used to apply static axial compressive load directly to the element top.
Note 3: Analysis of bi-directional load test results to estimate element displacements that would be measured by applying a tensile (uplift) load at the element top should consider strain and movement compatibility. Users of this standard are cautioned to interpret conservatively tensile capacity estimated from analysis of a compressive load. Test Methods D3689/D3689M can be used to apply static axial tensile load directly to the element top.
4.4 The Engineer will usually locate the jack assembly where resistance above the assembly equals resistance below it. A poorly chosen assembly location may reduce the maximum available resistance and the value of the test. Assembly location determination requires suitable site characterization, consideration of construction methods, and proper application of engineering principles and judgment.
4.5 The axial capacity of elements can change as time elapses after element installation, possibly increasing (set-up) or decreasing (relaxation), depending on soil or rock properties and on pore-water pressure and soil structure disturbance caused by element installation. This behavior may affect both driven elements and cast-in-place elements. The Engineer may specify a waiting period between element installation and static testing based on field testing or prior experience.
4.6 Multi-level testing using two or more jack assembly levels may increase the probability of fully mobilizing the axial capacity of the element. This standard does not provide details for multi-level testing (see Note 4), but a conceptual discussion is included here for completeness. Typically, bi-directional jack assemblies are installed at two levels within the element (lower and upper), thus separating the element into three segments (upper, middle, and lower). Ideally the upper and middle segments together have greater capacity than the lower segment, the upper segment has greater capacity than the middle segment, and the lower and middle segments together have greater capacity than the upper segment. Sufficient instrumentation must be furnished to simultaneously monitor the expansion and pressure in both assemblies. Testing may take place in three stages:
Stage 1: The lower assembly is pressurized. The upper assembly is closed and unpressurized. The greater available axial resistance above the lower assembly is used to fully mobilize the resistance below it. This stage ends when the lower assembly is sufficiently expanded, typically to more than half of its maximum stroke. The lower assembly is then depressurized.
Stage 2: The upper jack assembly is pressurized while the lower assembly is left open to passively drain as it closes. This stage mobilizes the capacity of the middle section as it moves downwards while closing the lower assembly.
Stage 3: The lower jack assembly is closed to mobilize the capacity below it. Pressurization of the upper assembly continues from Stage 2 using the combined resistance of the lower and middle segments to mobilize the resistance of the top upper segment.
Note 4: Multi-level testing has many possible variations. Jack assembly locations, element instrumentation, and the order of assembly loading can be altered as dictated by site conditions and project goals. Successful testing requires greater expertise and understanding by both the design and testing engineers.
Note 5: Any bi-directional load test may not fully mobilize axial compressive element resistance in all element sections. Practical, economical, or code considerations may also result in bi-directional load tests that are not intended to fully mobilize axial resistance in some or all element sections. In these cases, bi-directional test interpretation may under-predict total axial compressive element capacity.
Note 6: 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 facility used. Agencies that meet the criteria of Practice D3740 are generally considered capable of competent and objective testing/sampling/inspection. Reliable results depend on many factors; Practice D3740 provides a means of evaluating some, but not all, of those factors.
Scope
1.1 The test methods described in this standard measure axial displacements of a single, deep foundation element when loaded in bi-directional static axial compression using a non-retractable embedded jack assembly. These methods apply to all deep foundation elements, referred to herein as “elements,” which function in a manner similar to driven piles, cast-in-place piles, drilled shafts, caissons, or barrettes (LBEs) regardless of their installation method. 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:
Procedure A | Quick Test | 9.2.1 |
Procedure B | Extended Test (optional) | 9.2.2 |
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 deep foundation elements used in the constructed foundation. See Appendix X1 for comments regarding some factors, which influence test results and their interpretation.
1.6 A qualified engineer (specialty engineer, not to be confused with the 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 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 load unit (weight), while the mass unit 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 Procedures in this standard used to specify how data are collected, recorded and calculated are regarded as industry standard. In addition, they are representative of the significant digits that should generally be retained. 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.