January 24, 2006: Drilling the base of T4
Here is the worksite - with the drilling rig just to the left of T3 root.
On January 18th, T4 was dropped
and cleanup finished on January 21.
Now to finish the job the base will be pulverized explosively.
Here is the vertical drill in place - boring a hole down into the base of T4
Phillip and the drill
An array of 20 holes are marked - each will be 7' 9" deep and will be
loaded with explosives. This
depth is just above the mud-concrete interface at the base of the pier.
There were two columns for T4 - and here is the red marks indicating the
pattern for blast holes for each column of T4s.
Another view of the drill and its relationship to the Grace supports
When drilling through concrete, air, forced through the center of the drill
bit assembly forces concrete dust up and then a large vacuum cleaner sucks
the dust and deposits in a small mound to the side
Here is a short (10 Mb)
video showing continuous
drilling and the column of concrete dust being drawn up the hole.
When Mickey and I got there, Phillip had encountered some rebar
as he was drilling - and here, you can see the drill shaft and no dust.
Here is another short (10 Mb)
video segment showing the drilling
process interrupted when the bit encounters rebar - and no column of
concrete dust coming up the hole.
Looking down the hole, you can see that the rebar was cut by the carbide tipped
bit - but was bending and preventing the bit from turning
So Mickey and Phillip changed the bit - here is the new one
and here is the old bit - rather dull - at about $200/pop
The new bit is attached to the end of the drill shaft
and drilling resumes
But - even a new bit cannot pass beyond the mangled rebar
So Phillip starts a new hole
No problems this time and Mickey checks the depth.
Here is the incomplete hole (foreground) and the completed hole (background)
The bad hole is filled with concrete dust
and the finished product
Again - good drilling (note the column of concrete debris being forced
vertically up the drilled hole)
and a short episode of getting stuck - no debris
Time to leave Phillip to complete the array of holes