Standard Test Methods for Deep Foundation Elements Under Static Axial Compressive Load

Importancia y uso:

5.1 Field tests provide the most reliable relationship between the axial load applied to a deep foundation and the resulting axial movement. Test results may also provide information used to assess the distribution of side shear resistance along the element, the amount of end bearing developed at the element toe, and the long-term load-deflection behavior. The engineer may evaluate the test results to determine if, after applying appropriate factors, the element or group of elements has a static capacity, load response and a deflection at service load satisfactory to support the foundation. When performed as part of a multiple-element test program, the engineer may also use the results to assess the viability of different sizes and types of foundation elements and the variability of the test site.

5.2 If feasible, and without exceeding the safe structural load on the element or element cap (hereinafter unless otherwise indicated, “element” and “element group” are interchangeable as appropriate), the maximum load applied should reach a failure load from which the engineer may determine the axial static compressive load capacity of the element. Tests that achieve a failure load may help the engineer improve the efficiency of the foundation design by reducing the foundation element length, quantity, or size.

5.3 If deemed impractical to apply axial test loads to an inclined element, the engineer may elect to use axial test results from a nearby vertical element to evaluate the axial capacity of the inclined element. Or, the engineer may elect to use a bi-directional axial test on an inclined element (Test Methods D8169).

Note 1: The quality of the result produced by this test method 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/and the like. 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.

5.4 Different loading test procedures may result in different load-displacement curves. The Quick Test (10.1.2) and Constant Rate of Penetration Test (10.1.4) typically can be completed in a few hours. Both are simple in concept, loading the element relatively quickly as load is increased. The Maintained Test (10.1.3) loads the element in larger increments and for longer intervals which could cause the test duration to be significantly longer. Because of the larger load increments the determination of the failure load can be less precise, but the Maintained Test is thought to give more information on creep settlements (settlement due to consolidation is beyond the capability of the test procedures described in this standard). Although control of the Constant Rate of Penetration Test is somewhat more complicated (and uncommon for large diameter or capacity elements), the test may produce the smoothest curve and thus the best possible definition of capacity. The engineer must weigh the complexity of the procedure and other limitations against any perceived benefit of a smoother curve.

5.5 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 mobilized axial static capacity are properly documented. These factors may include, but are not limited to the following:

5.5.1 Potential residual loads in the element which could influence the interpreted distribution of load at the element tip and along the element shaft.

5.5.2 Possible interaction of friction loads from test element with upward friction transferred to the soil from anchor elements obtaining part or all of their support in soil at levels above the tip level of the test element.

5.5.3 Changes in pore water pressure in the soil caused by element driving, construction fill, and other construction operations which may influence the test results for frictional support in relatively impervious soils such as clay and silt.

5.5.4 Differences between conditions at time of testing and after final construction such as changes in grade or groundwater level.

5.5.5 Potential loss of soil supporting the test element from such activities as excavation and scour.

5.5.6 Possible differences in the performance of an element in a group or of an element group from that of a single isolated element.

5.5.7 Effect on long-term element performance of factors such as creep, environmental effects on element material, negative friction loads not previously accounted for, and strength losses.

5.5.8 Type of structure to be supported, including sensitivity of structure to settlements and relation between live and dead loads.

5.5.9 Special testing procedures which may be required for the application of certain acceptance criteria or methods of interpretation.

5.5.10 Requirement that non-tested element(s) have essentially identical conditions to those for tested element(s) including, but not limited to, subsurface conditions, element type, length, size and stiffness, and element installation methods and equipment so that application or extrapolation of the test results to such other elements is valid.

Subcomité:

D18.11

Referida por:

D7383-19, D3966_D3966M-22, D4945-17, D8169_D8169M-18

Volúmen:

04.08

Número ICS:

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

Palabras clave:

axial load test; deep foundation capacity; field testing; jack; load cell; loading procedure; reference beam ; static load test; top load test;