Pile Load Tests.

Pile load tests have been previously discussed. As shown in Fig. 6.19, the pile load test can take a considerable amount of time and effort to properly set-up. Thus only one or two load tests are often recommended for a particular site.

The location of the pile load tests should be at the most critical area of the site, such as where the bearing stratum is deepest or weakest. The first step involves driving or installing the pile to the desired depth. In Fig. 16.32, the small arrows point to the prestressed concrete piles that have been installed and are founded on the bearing strata. The next step is to install the anchor piles, which are used to hold the reaction frame in place and provide resistance to the load applied to the test piles. The most common type of pile load test to determine its vertical load capacity is the simple compression load test (i.e., see “Standard Test Method for Piles Under Static Axial Compressive Load,” ASTM D 1143-94, 2004). A schematic set-up for this test is shown in Fig. 16.33 and includes the test pile, anchor piles, test beam, hydraulic jack, load cell, and dial gauges. Figure 16.34 shows an actual load test where the reaction frame has been installed on top of the anchor piles and the hydraulic loading jack is in place. A load cell is used to measure the force applied to the top of the pile. Dial gauges, such as shown in Fig. 16.35, are used to record the vertical displacement of the piles during testing.

Pile load test. The small arrows point to the prestressed concrete piles that will be subjected to a load test. The large arrow points to one of the six anchor piles.
FIGURE 16.32 Pile load test. The small arrows point to the prestressed concrete piles that will
be subjected to a load test. The large arrow points to one of the six anchor piles.


Schematic setup for applying vertical load to the test pile using a hydraulic jack acting against an anchored reaction frame.
FIGURE 16.33 Schematic setup for applying vertical load to the test pile using a hydraulic jack acting
against an anchored reaction frame.


Pile load tests. The reaction frame has been set up and the hydraulic jack and load cell are in place.
FIGURE 16.34 Pile load tests. The reaction frame has been set up and the hydraulic jack and
load cell are in place.


Pile load tests. This photograph shows one of the dial gauges that are used to record the vertical displacement of the top of the pile during testing.
FIGURE 16.35 Pile load tests. This photograph shows one of the dial gauges that are used to
record the vertical displacement of the top of the pile during testing.

As the load is applied to the pile, the deformation behavior of the pile is measured. The pile is often subjected to a vertical load that is at least two times the design value. In most cases, the objec- tive is not to break the pile or load the pile until a bearing capacity failure occurs, but rather to confirm that the design end-bearing parameters used for the design of the piles are adequate. The advantage of this type of approach is that the piles that are load-tested can be left in-place and used as part of the foundation. Figure 16.36 presents the actual load test data for the pile load test shown in Figs. 16.34 and 16.35. For this project, the prestressed concrete piles were founded on solid bedrock and thus the data in Fig. 16.36 show very little compression of the pile. In fact, the recorded displacement of the pile was almost entirely due to elastic compression of the pile itself, instead of deformation of the bearing strata.
Figure 16.37 shows a commonly used method of analysis for static axially compressive or tension load testing of piles.

Pile load test data.
FIGURE 16.36 Pile load test data. This plot shows the actual data recorded from the pile load test shown
in Figs. 16.34 and 16.35. The vertical deformation is the average displacement recorded by the dial gauges.
The axial load is determined from a load cell.

Method of analysis for static axially compressive or tension load testing of piles.
FIGURE 16.37 Method of analysis for static axially compressive or tension load testing
of piles. (Reproduced from NAVFAC DM-7.2, 1982.)

0 comentarios:

Post a Comment