Inside Dirt - Vol. 3
Stories from the Big Dig they don't want you to hear.
My commentary on this Boston Herald article was going to be just another stand-alone post on the ongoing controversy surrounding the Big Dig, but I figured I might as well include it in my Inside Dirt series. Chalk it up to it being a slow news day on the local front, I guess.
Again, these posts are based of my personal experience and observations from my time spent on the Project. Agree? Disagree? Think I'm full of crap? Let me know. Comments section below is open 24 hours a day.
Patchwork early fix failed in Big Dig tunnel
And people blame the rising cost of HOUSING on the recent decline in the state's population? Yeah, right. I'm sure it has nothing whatsoever to do with people choosing not to participate in the taxpayer-funded Big Dig bailout program coming down the pike.
Hmmm...I wonder.
That's the ONLY answer you have, Keith?
As much as I respect Keith Sibley, and consider him one of the "good guys" in this fiasco, I can't help but feel that his answer here is rather disingenuous.
As Keith Sibley and project construction managers well know, there are several ways in which defective material or voids in the concrete can get trapped in the concrete slurry walls. The most common, and easily detectable (and avoidable) of these are as follows:
Substandard slurry mix used to support the walls of the excavation prior to and during concrete placement: If the slurry fails in this regard, the walls of the excavation can break up, sending chunks of soils and clay into the concrete as it's being placed. Field testing for the quality of the slurry is easily performed on-site with a minimal amount of effort on the part of B/PB Material Technicians working in conjunction with the B/PB Field Engineering staff.
Failure to confirm clean bottom of excavation prior to concrete placement: Before any concrete can be placed for a slurry wall panel, it is the responsibility of the B/PB Field Engineer to test the soundness of the bottom of the excavation. This is done by lowering a line with a metal weight on the end down into the hole and bouncing it off the bottom. If the bottom of the hole is "clean", you will feel the "thud" of the weight on the hard surface. If there is material on the bottom that would require additional effort by the contractor to remove, the softness of the clay or soil can be felt as well. This is something I've done on numerous occasions. It's not rocket science, but it requires the experience to know what you're doing and what you're looking for.
Failure to properly monitor the elevation of the top of concrete and bottom of tremmy pipe during placement: Concrete is placed in the wall panels via a tremmy pipe, which consists of several sections of pipe connected together and extended down to the bottom of the excavation. The concrete flows down the pipe and displaces the slurry upward as the placement progresses. When there is sufficient concrete in the hole, the pipe is raised and a section is removed, and the placement continues. It is critical that there be sufficient concrete in the hole to ensure that as the pipe is raised, the bottom end remains submerged in the fresh concrete. Should the pipe come out of the concrete at any time then the fresh concrete will mix with the slurry, creating a void of structurally unsuitable material. Again, this is not rocket science, but the process requires close monitoring by a competent Field Engineer to guarantee a quality end product.
If at any phase of the construction, these three activities are not closely and competently monitored, it should come as no surprise if the resulting end product proves to deficient.
The FIRST thing that should be looked as these investigations start to pick up steam are these field inspection reports. Was the work properly inspected and documented? Was the person signing off on these inspection reports qualified to do so? Were corrective actions taken if deficiencies in the work were noted?
These are the questions officials SHOULD be focusing on. Let's put an end to the finger pointing, pull these inspection records, and get some friggin' answers already. The taxpayers deserve nothing less that complete disclosure of all project records pertaining to this defective work.
See these previous posts for more "Inside Dirt":
Introduction
Volume 1
Volume 2
My commentary on this Boston Herald article was going to be just another stand-alone post on the ongoing controversy surrounding the Big Dig, but I figured I might as well include it in my Inside Dirt series. Chalk it up to it being a slow news day on the local front, I guess.
Again, these posts are based of my personal experience and observations from my time spent on the Project. Agree? Disagree? Think I'm full of crap? Let me know. Comments section below is open 24 hours a day.
Patchwork early fix failed in Big Dig tunnel
Big Dig managers failed in their attempts to fix defective tunnel walls a few years ago, raising questions about maintenance costs and the likelihood of a permanent repair.
[snip]
The failure of those efforts is significant because the ability to implement lasting repairs will determine whether taxpayers end up shelling out more money to maintain Interstate 93 tunnels after contractors leave town.
And people blame the rising cost of HOUSING on the recent decline in the state's population? Yeah, right. I'm sure it has nothing whatsoever to do with people choosing not to participate in the taxpayer-funded Big Dig bailout program coming down the pike.
While project officials prepare repair plans, state and federal investigators are asking how inspectors for Bechtel and Modern Continental failed to identify and correct the problems in the first place.
Hmmm...I wonder.
(Bechtel Project Manager Keith) Sibley said yesterday he does not know why inspectors missed the defects. "The only answer I have is that the defective material is more readily distinguishable at this age of the tunnels," he said, explaining that unsound clay and other trapped materials may have been mistaken for concrete.
That's the ONLY answer you have, Keith?
As much as I respect Keith Sibley, and consider him one of the "good guys" in this fiasco, I can't help but feel that his answer here is rather disingenuous.
As Keith Sibley and project construction managers well know, there are several ways in which defective material or voids in the concrete can get trapped in the concrete slurry walls. The most common, and easily detectable (and avoidable) of these are as follows:
Substandard slurry mix used to support the walls of the excavation prior to and during concrete placement: If the slurry fails in this regard, the walls of the excavation can break up, sending chunks of soils and clay into the concrete as it's being placed. Field testing for the quality of the slurry is easily performed on-site with a minimal amount of effort on the part of B/PB Material Technicians working in conjunction with the B/PB Field Engineering staff.
Failure to confirm clean bottom of excavation prior to concrete placement: Before any concrete can be placed for a slurry wall panel, it is the responsibility of the B/PB Field Engineer to test the soundness of the bottom of the excavation. This is done by lowering a line with a metal weight on the end down into the hole and bouncing it off the bottom. If the bottom of the hole is "clean", you will feel the "thud" of the weight on the hard surface. If there is material on the bottom that would require additional effort by the contractor to remove, the softness of the clay or soil can be felt as well. This is something I've done on numerous occasions. It's not rocket science, but it requires the experience to know what you're doing and what you're looking for.
Failure to properly monitor the elevation of the top of concrete and bottom of tremmy pipe during placement: Concrete is placed in the wall panels via a tremmy pipe, which consists of several sections of pipe connected together and extended down to the bottom of the excavation. The concrete flows down the pipe and displaces the slurry upward as the placement progresses. When there is sufficient concrete in the hole, the pipe is raised and a section is removed, and the placement continues. It is critical that there be sufficient concrete in the hole to ensure that as the pipe is raised, the bottom end remains submerged in the fresh concrete. Should the pipe come out of the concrete at any time then the fresh concrete will mix with the slurry, creating a void of structurally unsuitable material. Again, this is not rocket science, but the process requires close monitoring by a competent Field Engineer to guarantee a quality end product.
If at any phase of the construction, these three activities are not closely and competently monitored, it should come as no surprise if the resulting end product proves to deficient.
The FIRST thing that should be looked as these investigations start to pick up steam are these field inspection reports. Was the work properly inspected and documented? Was the person signing off on these inspection reports qualified to do so? Were corrective actions taken if deficiencies in the work were noted?
These are the questions officials SHOULD be focusing on. Let's put an end to the finger pointing, pull these inspection records, and get some friggin' answers already. The taxpayers deserve nothing less that complete disclosure of all project records pertaining to this defective work.
See these previous posts for more "Inside Dirt":
Introduction
Volume 1
Volume 2
