Civil Engineering Reference
In-Depth Information
FIGURE 13.23
This prestressed concrete pile struck an underground obstruction, displaced laterally, and
broke near ground surface. The arrow points to the location of the breakage.
The pile is often subjected to a vertical load that is at least 2 times the design value. In
most cases, the objective is not to break the pile or load the pile until a bearing capacity fail-
ure 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 13.28 presents the
actual load test data for the pile load test shown in Figs. 13.26 and 13.27. For this project,
the prestressed concrete piles were founded on solid bedrock, and thus the data in Fig. 13.28
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.
Pile Cap, Grade Beams, and Floor Slab.
After the piles have been successfully installed,
the next step is to construct the remainder of the foundation:
1.
Cut-off top of piles:
Especially for the indicator piles, the portion of the pile
extending above ground surface may be much longer than needed. In this case, the pile can
be cut off or the concrete chipped off by using a jackhammer, such as shown in Fig. 13.29.
2.
Grade beam excavation:
The next step is to excavate the ground for the grade
beams that span between the piles. Figure 13.29 shows the excavation of a grade beam
between two piles. For the foundation shown in Fig. 13.29, there is only one pile per cap;
thus the pile caps are relatively small compared to the size of the grade beams.
Those prestressed piles that broke during installation should also be incorporated into
the foundation. For example, in Fig. 13.30, the pile located at the bottom of the picture
is the same broken pile shown in Fig. 13.23. The replacement pile, which was successfully
installed to the bearing strata, is located at a distance of 5 ft (1.5 m) from the broken pile
(i.e., the pile near the center of Fig. 13.30). As previously mentioned, replacement piles
