Augercast (CFA) Report - SAMPLE

EXECUTIVE SUMMARY
Click here for Augercast/CFA Report

A 762 mm diameter dedicated test pile constructed to a depth of 37.03 m was tested by LOADTEST. Sub-surface conditions at the test pile location consist primarily of medium dense sand and coquina limestone of varying degree of cementation.

The maximum sustained bi-directional load applied to the pile was 11.85 MN. At the maximum load, the displacements above and below the O-cell were 4.47 mm and 51.46 mm, respectively. Unit shear data indicated an average maximum net unit side shear of 788 kPa below the O-cell as calculated using data collected from Strain Gage Level 1. We also calculated a maximum applied end bearing pressure of 13,390 kPa after correcting for the aforementioned unit side shear value.

Using the procedures described in the report text and in Appendix C, we constructed an equivalent top load curve for the test pile. For a top loading of 5.6 MN, the adjusted test data indicate this pile would settle approximately 11.8 mm essentially all of which is estimated elastic compression.

LIMITATIONS OF EXECUTIVE SUMMARY

We include this executive summary to provide a very brief presentation of some of the key elements of this O-cell test. It is by no means intended to be a comprehensive or stand-alone representation of the test results. The full text of the report and the attached appendices contain important information which the engineer can use to come to more informed conclusions about the data presented herein.


TEST RESULTS AND ANALYSES

General: The loads applied by the O-cell act in two opposing directions, resisted by the capacity of the pile above and below. Theoretically, the O-cell does not impose an additional upward load until its expansion force exceeds the buoyant weight of the pile above the O-cell. Therefore, net load, which is defined as gross O-cell load minus the buoyant weight of the pile above, is used to determine side shear resistance above the O-cell and to construct the equivalent top-loaded load-settlement curve. For this test we calculated a buoyant weight of pile of 0.23 MN above the O-cell.

Upper Side Shear Resistance: The maximum upward applied net load to the upper side shear was 11.62 MN which occurred at load interval 1L-13. At this loading, the upward movement of the O-cell top was 4.47 mm (Appendix A, Page 2).

In order to assess the side shear resistance of the test pile, loads are calculated based on the strain gage data (Appendix A, Page 3) and an estimate of pile stiffness (AE) which is presented below. We used the ACI formula (Ec=57000f´c) to calculate an elastic modulus for the concrete, where f’c was reported to be 40.96 MPa at the 28-day break. This, combined with the area of reinforcing steel and nominal pile diameter, provided an average pile stiffness (AE) of 14,500 MN for the length of pile. Net unit shear curves are presented in Appendix F. Net unit shear values for loading increment 1L-13 follow in Table A:

TABLE A: Average Net Unit Side Shear Values for 1L-13

Load Transfer Zone Displacement Net Unit Side Shear
Top of Pile to Strain Gage Level 6 0.000 mm 0 kPa
Strain Gage Level 6 to Strain Gage Level 5 0.025 mm 3 kPa
Strain Gage Level 5 to Strain Gage Level 4 0.175 mm 20 kPa
Strain Gage Level 4 to Strain Gage Level 3 0.525 mm 21 kPa
Strain Gage Level 3 to Strain Gage Level 2 1.95 mm 616 kPa
Strain Gage Level 2 to O-cell 3.8 mm 487 kPa
O-cell to Strain Gage Level 1 50.65 mm" 788 kPa

Combined End Bearing And Lower Side Shear Resistance: The maximum O-cell load applied to the combined end bearing and lower side shear was 11.85 MN which occurred at load interval 1L-13 (Appendix A, Page 2, Figure 1). At this loading, the average downward movement of the O-cell base was 51.46 mm. The load taken in shear by the 3.05 m pile section below the O-cell is calculated to be 15.75 MN assuming an estimated unit side shear value of 788 kPa and a nominal 762 mm pile diameter. The applied load to end bearing is then 6.11 MN and the unit end bearing at the base of the pile is calculated to be 279.7 ksf (13390 kPa) at the above noted displacement. A unit end bearing curve is presented in Appendix F. Creep Limit: See Appendix D for our O-cell method for determining creep limit. The combined end bearing and lower side shear creep data (Appendix A, Page 2) indicate that a creep limit of 8.2 MN was reached at a movement of 5.2 mm (Figure 4). The upper side shear creep data (Appendix A, Page 2) indicate that no apparent creep limit was reached at a maximum measured movement of 4.5 mm (Figure 5). A top-loaded pile will not begin significant creep until both components begin creep movement. This will occur at the maximum of the movements required to reach the creep limit for each component. We believe that significant creep for this pile will not begin until a top loading exceeds 19.8 MN by some unknown amount.

Equivalent Top Load: Figure 2 presents the equivalent top-loaded load-settlement curves. The lighter curve, described in Procedure Part I of Appendix C, was generated by using the measured upward top of O-cell and downward base of O-cell data. Because it is often an important component of the settlements involved, the equivalent top load curve requires an adjustment for the additional elastic compression that would occur in a top-load test. The darker curve as described in Procedure Part II of Appendix C includes this adjustment.

The test pile was loaded to a combined side shear and end-bearing load of 23.5 MN. For a top loading of 5.6 MN, the adjusted test data indicate this pile would settle approximately 11.8 mm essentially all of which is estimated elastic compression.

Note that, as explained previously, the equivalent top load curve applies to incremental loading durations of eight minutes. Creep effects will reduce the ultimate resistance of both components and increase pile top movement for a given loading over longer times. The Engineer can estimate such additional creep effects by suitable extrapolation of time effects using the creep data presented herein. However, our experience suggests that such corrections are small and perhaps negligible for top loadings below the creep limit indicated in Figure 2.


Pile Compression Comparison: The measured maximum pile compression, averaged from two telltales, is 4.47 mm at 1L-13 (Appendix A, Page 1). Using an average pile stiffness of 14,500 MN and the load distribution in Figure 3 at 1L-13, we calculated an elastic compression of 4.23 mm over the length of the compression telltales. We believe this agreement provides good evidence that the value of the estimated pile stiffness is reasonable and that the O-cell loaded the pile in accord with its calibration.

Back

Project Profiles:

Upcoming Conferences:

News: