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OCR for page 23
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Horizontal deflection (in) A steel reinforcing cage was installed at the top of each test
-1.0 0.0 1.0 2.0 3.0 4.0 pile to connect the test piles to the pile cap. The reinforcing
-5 cage consisted of six #8 reinforcing bars that were confined
within a #4 bar spiral with a diameter of 8 in. and a pitch of
6 in. The test piles typically extended about 2 ft above the
base of the pile cap and the reinforcing cage extended 2.25 ft
0
above the base of the cap and 8.75 ft below the base. The steel
Depth from Ground Surface (ft)
pipe pile was filled with concrete that had an average uncon-
fined compressive strength of 5000 psi.
5 A pile cap was constructed by excavating 2.5 ft below the
0.5 in
surface of the surface clay layer. The concrete was poured
0.75 in directly against vertical soil faces on the front and back sides of
1.0 in
1.5 in
each pile cap. This procedure made it possible to evaluate pas-
10
2.0 in sive force against the front and back faces of the pile caps. In
2.5 in
contrast, plywood forms were used along the sides of each cap
String Pot Above Load Pt.
String Pot At Load Pt. and were braced laterally against the adjacent soil faces. This
15 construction procedure created a gap between the cap side-
wall and the soil so that side friction would be eliminated.
Steel reinforcing mats were placed in the top and bottom of
each cap.
20
Figure 3-12. Deflection vs depth curves at
several deflection increments for single pile 3.5 Pile Group Testing Procedure
lateral load test.
Lateral load was applied using MTS actuators with the load
centered at a height of 11 in. above the top of the pile cap. Each
of deflection increments. The shape array provides horizon- actuator could produce 600 kips in compression and 450 kips
tal deflection values at 1 ft intervals from the top of the pile, in tension. Another pile group or groups provided a reaction for
which was approximately 40 in. above the load point. the applied load. In all cases, the reaction pile group or groups
Without any corrections, the computed deflection curves were located 32 ft away from the test pile group to minimize
obtained from the shape arrays are consistent with the max- interference between the two pile groups during lateral load-
imum pile head deflections measured by the string poten- ing. Each actuator was fitted with two 8.67-ft extension pieces
tiometers at the load point. The deflected shape curves also to span the 32.1-ft gap between the pile groups. The actuator
are consistent with the free-head (zero-moment) boundary was attached to a concrete corbel atop each pile cap using steel
condition. tie-rods that extended through PVC sleeves in the corbel and
were bolted to the back face of the corbel. This allowed load to
be applied without affecting the soil around the pile group. The
3.4 Pile Group Properties
tie-rods were prestressed to minimize displacement of the steel
A total of 16 lateral load tests were performed on the 4 pile during the load tests. A three-dimensional swivel head was
groups. Schematic drawings of the pile group layout and the located at each end of the actuator to provide a zero moment
soil improvement geometries are provided in Appendix A. All or "pinned" connection. Each swivel could accommodate ± 5°
pile groups consisted of nine test piles, which were driven in of pile cap rotation about a horizontal line and ± 15° of pile cap
a 3 × 3 arrangement with a nominal center to center spacing rotation about a vertical line.
of 3 ft. The tests piles were 12.75-in. outside diameter pipe The lateral load tests were carried out with a displacement
piles with a 0.375-in. wall thickness and they were driven control approach with target pile cap displacement increments
closed-ended with a hydraulic hammer to a depth of approx- of 0.25, 0.5, 0.75, 1.0, and 1.5 in. During this process, the actu-
imately 44 ft below the excavated ground surface. The steel ator extended or contracted at a rate of about 40 mm/min.
conformed to ASTM A252 Grade 3 specifications and had a Additionally, at each increment, 10 cycles with a peak pile cap
yield strength of 58.6 ksi based on the 0.2% offset criteria. The amplitude of ±0.1 in. were applied with a frequency of approx-
moment of inertia of the pile itself was 279 in.4; however, angle imately 1 Hz to evaluate dynamic response of the pile cap. After
irons were welded on opposite sides of two to three test piles this cyclic loading at each increment, the pile group was pulled
within each group, which increased the moment of inertia back to the initial starting point prior to loading to the next
to 324 in.4. higher displacement increment.
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Load Test Instrumentation the length of each pile cap to evaluate pile cap rotation. On
both caps, string potentiometers were located 2 in. from the
Applied load was measured directly by the load cell on the north and south edges of the corbel, with a distance of 44.72 in.
actuator, which was calibrated in the laboratory prior to test- between the potentiometers on Cap 1 and a distance of 108 in.
ing in the field. Lateral pile cap displacement was measured (9 ft) for Cap 2 as shown in Figure 3-13. Each potentiometer
using two string potentiometers attached to the pile cap at the was attached to an independent reference beam supported at a
elevation of the loading point (0.92 ft above the top of the cap) distance of about 6 ft from the side of the pile cap. The pile
on the east and west sides of the actuator attachment point as rotation, , was determined using the following equation:
shown in Figure 3-13. Lateral pile cap displacement also was
measured on the back side of each corbel with two string - 2
= tan -1 1
H
(4)
potentiometers attached 1.75 ft (21 in.) and 0.375 ft (4.5 in.)
above the top of the pile cap directly in line with the load direc-
tion. Therefore, the vertical distance between these two string where 1 and 2 are the vertical pile cap deflection at two
pots was 1.375 ft (16.5 in.) as shown in Figure 3-13. Finally, ver- points on the pile cap and H is the distance between the
tical pile cap displacement was measured at two points along measurements.
Figure 3-13. Typical instrumentation layout for piles caps with a partial-length corbel
(Caps 1 and 4) and a full-length corbel (Caps 2 and 3).
