Standard Test Methods for Axial Rapid Load (Compressive Force Pulse) Testing of Deep Foundations

Importancia y uso:

4.1 Based on the measurements of force and displacement at the pile top, possibly combined with those from accelerometers 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 resistance and dynamic resistance at all points along the length of the pile for that portion of the test.

4.2 The compressive axial static resistance is derived from the test data and is therefore an indirect result. Test Method D1143/D1143M provides a direct and therefore more reliable measurement of static resistance.

4.3 The Engineer should ensure that the test as specified will generate the required peak force to meet the purpose of the test. In case that purpose is to establish geotechnical failure, the Engineer should also ensure that peak force results in significant permanent axial movement during the axial force pulse event.

4.4 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. This analysis typically includes a reduction factor to account for the loading rate effect, that is, additional load resistance that occurs as a result of a faster rate of loading than used during a static test. Test results from piles installed in cohesive soils generally require a greater reduction. 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 resistance by eliminating the dynamic component of the response.

4.5 The scope of this standard does not include analysis for foundation capacity, but in order to analyze the test data appropriately it is important that information on factors that affect the derived axial static capacity is properly documented. These factors may 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, and (6) final foundation settlement.

4.6 The accuracy of the derived results may improve when using additional strain transducers embedded in the pile. 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 resistance of the pile, or to infer the relative contribution of certain soil layers to the overall mobilized axial compressive resistance of the pile.

Note 1: 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 D3740 are generally considered capable of competent and objective testing and inspection. Users of these test methods 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.

Subcomité:

D18.11

Volúmen:

04.09

Número ICS:

93.020 (Earth works. Excavations. Foundation construction. Underground works)

Palabras clave:

axial compressive force pulse; displacement response; inertial reaction mass; rapid load test; ultimate axial pile capacity;