Looking east toward Knightdale. This is the route of
the 64 bypass. That's Crabtree Creek in the foreground and the distant
bridge is access to Anderson Point Park on the right. Workers have begun
driving piles for the east bridge abutment. |
|
Large planks are being laid on the left to give the
heavy equipment access to the creek bank. |
Once the equipment can get to the site, things get
busy. Cranes converge to prepare the bridge support pilings. |
The east abutment starts to take shape and work
continues in the creek to build temporary platforms so the equipment can
get into position to construct the bridge pilings in the water. |
Pilings construction begins by using a pile driver to
hammer very large steel pipe or caissons into the ground to reach bedrock - 40 to 60
feet down. |
Besides
a pile driver, a vibratory hammer
can be used to sink pilings and it's also effective in
removing them. The smaller caissons supporting the work platforms
are all removed at jobs end. The hammer is supported by a crane. Hydraulic
clamps in the foreground pinch onto the caisson while hydraulic motors
spin eccentrics to produce massive vertical vibrations that drive the
caisson into the ground.
|
This is the power pack. A diesel engine turns a large
hydraulic pump. The hammer and power pack are linked through several high
pressure hydraulic hoses. |
Various drill equipment is used to clean out the caissons in
preparation for receiving re-bar and then concrete. |
To spin the tools, you need a really big drill rig. |
Now let's see......
Is that a 3/8" or 1/2"chuck? Whose
got the chuck key for this sucker? |
This winch and seat is used to lower an inspector into the caisson.
Claustrophobia is a disqualification for this job! |
This is a re-bar cage that will be lowered into a caisson. Notice the
lengths of steel pipe tied in with the rebar. These are inspection pipes.
Voids and other defects in the pile can be detected using an ultrasonic
transmitter in one pipe and a receiver in another pipe. The method,
referred to as Crosshole Sonic
Logging (CSL) measures the density of the pile throughout its length.
Another description of CSL can be found here.
|
Once the rebar cage is in place, the caisson is
filled with concrete. This concrete pump
is used to move the concrete from a delivery truck and pump it to a
caisson that the truck can't reach. |
A finished pile |
In
the foreground temporary steel forms are being used to extend the piles
above ground. In the background a horizontal form rests on 'I' beams
across four piles. More rebar and concrete is added to produce the caps. |
Once the caps are sufficiently cured, the forms are
removed. The combination of columns and cap is called a bent. Concrete
beams span the bents. |
