Changing the face of Charleston : The unbuilding of the Grace and Pearman Bridges
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(Jul 10 2006)
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(Feb 17)
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(Mar 27)
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(Feb 28)

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

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Attribution: C. Frank Starmer and Sparky Witte from