ASTM International - ASTM D7383-08
Standard Test Methods for Axial Compressive Force Pulse (Rapid) Testing of Deep Foundations
|Publication Date:||1 October 2008|
|ICS Code (Earthworks. Excavations. Foundation construction. Underground works):||93.020|
significance And Use:
Based on the measurements of force and displacement at the pile top, possibly combined with those from acceleration or strain transducers located further down the pile, these test methods measure... View More
Based on the measurements of force and displacement at the pile top, possibly combined with those from acceleration or strain transducers located further down the pile, these test methods measure the pile top deflection in response to an axial compressive force pulse. The relatively long duration of the force pulse compared to the natural period of the test pile causes the pile to compress and translate approximately as a unit during a portion of the pulse, simultaneously mobilizing compressive axial static capacity and dynamic resistance at all points along the length of the pile for that portion of the test. The Engineer may analyze the acquired data using engineering principles and judgment to evaluate the performance of the force pulse apparatus, and the characteristics of the pile's response to the force pulse loading.
If significant permanent axial movement occurs during the axial force pulse event, the Engineer may analyze the results of the test to estimate, after assessing inertial effects and the dynamic soil and rock response along the side and bottom of the pile, the ultimate axial static compression capacity (see Note 2). The scope of this standard does not include analysis for either ultimate or design foundation capacity. Factors that may affect the axial static capacity estimated from force pulse tests 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 saturation of the soil, or rock, or both adjacent to and beneath the pile, (5) quality of force pulse test data, (6) foundation settlement, (7) analysis method, and (8) engineering judgment and experience. If the Engineer does not have adequate previous experience with these factors, and with the analysis of force pulse test data, then a static load test carried out according to Test Method D 1143 should be used to verify estimates of static capacity and its distribution along the pile length. Test Method D 1143 provides a direct and more reliable measurement of static capacity.
Note 2-If a force pulse test produces insufficient axial movement, subsequent analysis may overestimate the static capacity because of difficulty in separating the static and dynamic components of the response. The analysis of a force pulse test to estimate static capacity also typically includes a reduction factor to account for the additional load resistance that occurs as a result of a faster rate of loading than used during a static test. Force pulse test results from cohesive soils generally require a greater reduction factor due to the rate of loading effect, chosen conservatively to produce a lower static capacity estimate. The Engineer should determine how the type, size, and shape of the pile, and the properties of the soil or rock beneath and adjacent to the pile, affect the rate-of-loading reduction factors and the amount of movement required to mobilize and accurately assess the static capacity. Correlations between actual measurements and force pulse estimates of the ultimate axial static compression capacity generally improve when using additional transducers embedded in the pile. Static capacity may also change over time after the pile installation, especially for driven piles. Both static and force pulse tests represent the capacity at the time of the respective test, and correlation attempts should provide results for a similar time of testing after pile installation or include analysis to account for changes in the soil strength during the time between the two tests.
When used in conjunction with additional transducers embedded in the pile, these test methods may also be used to measure the pile response to the axial force pulse along the pile length. When combined with an appropriate method of analysis, the Engineer may use data from these optional transducers to estimate the relative contribution of side shear and end bearing to the mobilized axial static compressive capacity of the pile, or to infer the relative contribution of certain soil layers to the overall axial compressive capacity of the pile.
Note 3-When used in conjunction with additional transducers embedded in the pile the force pulse test analysis may provide an estimate of the pile's tension (uplift) capacity. Users of this standard are cautioned to interpret the estimated side resistance conservatively. If the Engineer does not have adequate previous experience for the specific site and pile type with the analysis of force pulse test data for tension capacity, then a static load test carried out according to Test Method D 3689 should be used to verify tension capacity estimates. Test Method D 3689 provides a direct and more reliable measurement of static tension capacity.
Note 4-The quality of the result produced by these test methods 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 testing and inspection. Users of these test methods 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.View Less
1.1 These test methods cover procedures for testing an individual vertical or inclined deep foundation to determine the displacement response to an axial compressive force pulse applied at its top. These test methods apply to all deep foundation units, referred to herein as "piles," that function in a manner similar to driven or cast-in-place piles, regardless of their method of installation.
1.2 Two alternative procedures are provided:
1.2.1 Procedure A uses a combustion gas pressure apparatus to produce the required axial compressive force pulse.
1.2.2 Procedure B uses a cushioned drop mass apparatus to produce the required axial compressive force pulse.
1.3 This standard provides minimum requirements for testing deep foundations under an axial compressive force pulse. Plans, specifications, provisions (or combinations thereof) prepared by a qualified engineer, may provide additional requirements and procedures as needed to satisfy the objectives of a particular deep foundation test program. The engineer in responsible charge of the foundation design, referred to herein as the "Engineer", shall approve any deviations, deletions, or additions to the requirements of this standard.
1.4 The proper conduct and evaluation of force pulse testing requires special knowledge and experience. A qualified engineer should directly supervise the acquisition of field data and the interpretation of the test results so as to predict the actual performance and adequacy of deep foundations used in the constructed foundation. A qualified engineer shall approve the apparatus used for applying the force pulse, rigging and hoisting equipment, support frames, templates, and test procedures.
1.5 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. The word "shall" indicates a mandatory provision, and the word "should" indicates a recommended or advisory provision. Imperative sentences indicate mandatory provisions.
1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.7 All observed and calculated values shall conform to the guidelines for significant digits and rounding established in Practice D 6026.
1.8 The method used to specify how data are collected, calculated or recorded in this standard is not directly related to the accuracy to which the data can be applied in the design or other uses, or both. How one uses the results obtained using this standard is beyond its scope.
1.9 ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentioned in this standard. Users of this standard are expressly advised that determination of the validity of any such patent rights, and the risk of infringement of such rights, are entirely their own responsibility.
1.10 This standard may involve hazardous materials, operations, and equipment. 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. Section 7 provides a partial list of specific hazards and precautions.