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Chain of events,
cause and effect, we analyze what went
right and what went wrong as we
discover that many outcomes can be
predicted,
planned for, and even prevented. I'm John
Chidgey
and this is Causality. Causality is
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Thank you! "Big Dig"
This incident is often referred to as
the "Big Dig"
collapse or the "Big Dig" tunnel ceiling
collapse
despite the fact it had nothing directly
to do with the Big Dig in its entirety
but rather the incident related more to
a single
exit portal. The Big Dig itself was a
large civilian construction project
that took 15 years from start to finish,
though the project was technically
referred to
as the C.A.T. Project or the Central Artery
Tunnel Project.
The project took twice as long as the
original estimate. Cost
$14.6B US Dollars which was more
than double the 1996 $1B dollar
estimate and 5
times the $3B original
project estimate in 1983.
Traffic congestion in Boston had long
been a problem as the city had grown
from a time before cars existed
with some studies in the 80s suggesting
that by 2010 Bostons rush hour could
last approximately 16 hours every single
day.
To address this a new bridge and two key
tunnels were proposed to be built
as a concerted set of projects which
were collectively referred to
as the "Big Dig". The first tunnel was
named the Ted Williams tunnel
and goes beneath Boston harbour taking
interstate 90 (the I90)
traffic from South Boston to Boston
Logan International Airport. Construction
began in 1991 and was completed
in 1995. The second tunnel was located
below the Fort Point Channel and formed
part of an I90 connector with the I93
interchange.
It would effectively replace the
elevated I93 Central Artery which had
become deteriorated with age;
extend the I90 also called the
Massachusetts Turnpike or "Mass-Pike"
to the Logan International Airport
providing an interchange for the I90
and the I93
and also replace the I93 bridge over
the Charles River.
In 1985 the department of public works
entered into an agreement with Bechtel
Parsons Bricknehoff
hence referred to as BPB, a joint venture
formed between Bechtel Corporation and
Parsons Bricknerhoff, Quade and Douglas
to prepare a preliminary project
management plan. In 1990
congress allocated $755M US
dollars to the massive highway
improvement project,
and a year later the Federal Highway
Administration gave its approval to move
ahead.
A massive civil construction project
required significant and expensive
traffic sequencing during construction.
Traffic sequencing is a term sometimes
used in road construction where traffic
is directed via various detours,
temporary roads, road direction
reassignments and so on in accordance
with a traffic management plan
for the road construction project. In
order to coordinate the construction
sequence
the approved traffic plan required a
temporary above ground ramp
to carry traffic from D Street to the
entrance of the Ted Williams Tunnel
in order to provide access under Boston
Harbour to the airport
before work was finished on the
remainder of the I90 connector.
This would be achieved by constructing a
portal under D Street
that would eventually connect through
but was completed first
in 1993 well before the completion of
either the Ted Williams Tunnel
or the remainder of the I90 connector.
For those not familiar
a portal is the name used for tunnel
entries and
exits. The D Street portal...
(yes Boston has a series of streets that
are just an alphabetical letter...
A, B, C, D Street and so on so there's that...)
The D
Street portal had a heavily reinforced
concrete roof
slab varying between 1.5 meters to 2
meters (that's 5 to 7ft)
thick in order to accommodate the
weight
of a parking deck that was originally
intended to be built
over the portal. With that background
let's talk about the incident itself. At
approximately 11pm
local Daylight Savings Time on Monday
the 10th of July, 2006
an entire row consisting of 20 anchor
bolts pulled free from a suspended
ceiling segment
in the D Street portal. The ceiling
consisted of a series of four
3.6m (that's 12ft) wide by 2.4m
(that's 8ft) long
by 100mm or 4" thick
3 tonnes
or 4,700lbs of reinforced concrete
and steel panels.
They provided segregation between the
roadway and the ventilation system above
that roadway.
With an entire row no longer supporting
that side of the ceiling panels they
began to rotate
downwards with the additional load of
the rotated panels causing rapid
fracturing of the concrete.
One minute later a 1991 black Buick
sedan
driven by Mr Angel Del Valle, aged 46
with the sole passenger his wife Melina
aged 38,
was traveling eastbound in the
I90 connector, en route to the
Logan International airport to pick up
Angel's brother and sister-in-law
who returning from a trip to Puerto Rico.
As the vehicle approached the exit
portal
four panels of the suspended concrete
ceiling detached from the tunnel roof
and fell onto the vehicle. The panels
crushed
the right-hand side of the vehicle's
roof as the car came to rest against the
Northern tunnel wall.
Approximately 26 tonnes of concrete and
steel
had fallen onto both the vehicle and the
roadway.
Mr Del Valle was able to escape through the
driver's side window sustaining only
minor injuries.
Melina was crushed and died instantly.
Following the incident Mr Del Valle
stated that although he saw the concrete
panels starting to come down from the
roof,
he was unable to avoid them in time.
Immediately following the incident
the underground sections were closed to
all traffic pending a complete
inspection.
The first ramp to fully reopen was on
the 9th of August, but the entirety of
all of the underground sections weren't
fully reopened
until nearly 12 months after the
incident occurred.
So what went wrong? The work scopes
were split between many companies with
the primary oversight being Bechtel
Parsons Bricknerhoff and the
Massachusetts Turnpike Authority, that's
the MTA,
who took an increasing oversight role
towards the end of the project,
as each component was gradually handed
over.
Bechtel Parsons Bricknerhoff were
essentially the secondary approver for
the design
of the project as a whole as well as its
constituent components.
The D Street portal itself was
constructed by Kiewit/Perini/Atkinson/
Cashman,
a joint venture based in Boston, which
was contracted by the Massachusetts
department of public works to construct
the land-side West tunnel approach to
the Ted Williams Tunnel.
The tunnel consisted of approximately
800 meters that's 2600ft
of cut and cover and one section of
depressed open highway
as well as the D Street portal and a
temporary ramp
required for traffic sequencing during
construction of the larger tunnels.
The section design consultant for this
was HDR Engineering Incorporated
headquartered in Omaha, Nebraska. The
roadway in the Eastbound
D Street portal tunnel at the accident
site consisted of two
12 foot or 3.6 meter wide travel lanes
and along the South side of the tunnel
an 18 foot or 5.4 meter wide
acceleration lane.
All tunnels beyond a set length require
ventilation to ensure air quality is
maintained and to correctly handle
airflow during a fire emergency.
During the original letting of the
portal section
no allowance had been made for
ventilation as this component of the
design was intended to be added in a
later work scope.
The portal design was, therefore, done in
two
parts and was executed by two different
companies.
The aforementioned joint venture
constructed the cut and cover tunnel
but the I90 connector tunnel
"finishes" section design consultant
which included the D Street portal
finishing
which included the ventilation system,
was Gannett Fleming Incorporated
headquartered in Camp Hill, Pennsylvania.
For the suspended ceiling Gannett
Fleming engineers followed the
directions set
in the design policy memorandum number
107 by Fay,
Spofford and Throndike, Inc
(that's FST for short)
Howard, Needles, Tammen & Bergendoff
(HNTB
for short) using the embedded steel
channel inserts
instead of roof girders for the roof
attachments.
The D Street portal slab was not
constructed in the same way as the rest
of the tunnel, with additional slab
thickness and reinforcing intended for a
different
goal and did not have any embedded steel
channel inserts or anchor points
embedded into it in its initial design.
Hence the design was adjusted to use
adhesive anchors with an epoxy resin.
This technique was also used in other
sections of the I90 Connector tunnel
and on the HOV
ramp, that's High Occupancy Vehicle or
HOV. The ceiling
in the D Street portal was installed by
Modern Continental Construction Company
Incorporated
(Modern Continental for short) of
Cambridge, Massachusetts.
It was constructed between 1999 and
April of 2000.
The ceiling module that collapsed in
this incident was installed in November
1999.
Modern Continental installed the last
ceiling module of the I90 Connector
Tunnel in July 2002.
Whilst the use of epoxy resins for
anchoring applications was not unheard
of
it was unusual for a suspended load in a
long-term application.
Investigators used Fourier Transform
Infrared Spectroscopy Headspace Gas
Chromatography and Mass Spectroscopy of
epoxy samples
from the majority of the anchors that
failed in the incident, as well as other
randomly selected anchors to determine
their chemical composition.
In all cases it was found to be
consistent with a fast
set epoxy. Installation of the anchors in
the D
Street portal began in July 1999 using
epoxy purchased from Newman Renner Colony.
The investigations confirmed that the
invoices indicate
that Modern Continental purchased Power-
fast, Fast Set NRC1000
Gold Epoxy during the period when the D
Street portal ceiling was being
installed.
Further testing of this epoxy showed
that anchors installed using best
practices,
and I quote, "...exhibited significant and
continued displacement (aka creep) when
subjected to loads as low as one
thousand pounds.
Anchors loaded to four thousand pounds
completely separated from their anchor
holes before the end of the 82-day test
period..."
end quote. The portal ceiling segment
anchors had an expected maximum
load of 2,600 pounds and based on the
above tests,
due to its susceptibility to creep was
not a suitable epoxy for use in any
long-term tension load application.
The above tests however suggest that the
ceiling should have failed sooner than
it did.
The likely reason it did not fail sooner
is that the ventilation system was not
in operation for some time
after the physical installation. Until
the ventilation system was operating
the ceiling tiles would have presented
their own independent gravitational load
on the support anchors,
their so-called dead weight or dead load.
Once the ventilation system became
operational the air pressure would
increase and decrease cyclically
due to changes in flow direction and
pressure and would also have induced
vibration into the material which would
have then
accelerated the creep. The investigators
also tested standard set epoxy
under the same conditions and found that
in the 82 day test
under a 2,000 pound load, Standard Set
did creep
at about 1/10th of the rate of Fast
Set,
and it did so in a flat linear increment.
The Fast Set during that time exhibited
a non-linear,
with increasing rate of creep, after just
55 days.
So let's talk about the epoxy. Epoxies
are basic components that when combined
and cured create an epoxy resin and are
sometimes called
Polyepoxides hence epoxy for short.
Epoxy resin is combined with a hardener
also
sometimes called a curative or a
co-reactant and when they are mixed the
amine groups on the hardener molecules
begin to link with the epoxide groups on
the resin molecules releasing heat in
the process.
The reaction is therefore exothermic and
creates a thermosetting polymer
and unlike thermoplastic it resists
reforming under applied heat and
chemicals.
Most resin molecules have an epoxide
ring at each end and the harder
molecules have an amine group
at each end hence they both link in an
alternating pattern to form long polymer
chains
and cross-link between polymer chains.
The more cross-links that exist between
the polymer chains the more
resin resists significant rearrangement
of the polymer molecules
so the polymer cannot be melted and
reformed. This type of polymer is called
a Thermoset.
As the crosslink polymer network forms
the viscosity of the material increases
and eventually the reaction slows and
finally stops,
although any unbonded reactants may not
have been free to migrate through the
solution
if not well enough mixed beforehand
leading to some
unbonded reactive groups. Hence the
faster the setting of the epoxy,
the more likely uncured sections will
exist and there will be
less cross-linked polymers. So
what is creep? Creep refers to a gradual
continuing deformation
of a material under a sustained load.
It's similar to dislocations we
discussed on Episode 35 about the San
Bruno Gas Pipeline explosion.
As a polymer, the stiffness of an epoxy
is time and temperature dependent, hence
if the load is applied suddenly the
epoxy responds like a hard
glassy solid. If a load is static, meaning
it's held constantly against the plastic,
the long chain polymer molecules have
time to rearrange and slide past one
another and the stiffness of the epoxy
decreases to a range where it can be
described as
"rubbery." I know. Technical terms like
"rubbery."
Anyway. Polymer materials with an
instantaneous elastic response followed
by a slowly increasing deformation
are referred to as Viscoelastic. The time
needed for the glassy to rubbery
transition
depends on the molecular structure and
the lengths of the polymer chains
between
crosslinks and also as the temperature
increases
the rate of rearrangement increases
allowing the glassy-to-rubbery transition
to occur more rapidly. In a well-formed
cross-linked network of a Thermoset,
the polymer molecules are prevented from
moving very far,
and once the rubbery state is reached, no
further softening occurs.
The design for the anchor resin provided
by Gannett Fleming to Modern Continental
specified the following, and I quote:
"...Provide adhesive
consisting of two component plastic
resin and catalyst hardener mixture,
resin material shall remain unaffected
by continuous humidity and by chemicals
present in a vehicle exhaust type
of air duct environment..." (end quote) The
specification goes on to include minimum
design service loads, minimum factors of
safety,
and installation requirements that had
to be met. The epoxy selected
by Modern Continental used a two-part
epoxy material,
resin and hardener formulated by Sika
Corporation of Lyndhurst, New Jersey
packaged by Powers Fasteners
Incorporated (formerly the Rawlplug
Company Incorporated)
of New Rochelle, New York and distributed
by Newman Renner
Colony LLC of Westwood, Massachusetts.
Sika Corporation supplied the epoxy
resin and hardener in bulk to Powers,
which packaged, marketed and distributed
it for Newman Renner Colony as
NRC1000 a gold epoxy, which was used by
Modern Continental on this project.
In order to begin installation the
construction contractor needed their
final design to be approved by the
consultants
and Modern Continental submitted a total
of four individual submissions
for their anchor design. The first three
anchor design submissions were rejected
by Gannett Fleming, with Gannet Fleming
requesting additional information
each time. On the 30th of December, 1999
Modern Continental submitted the fourth
anchor adequacy submittal.
The anchor service load data in that
submittal
were the values calculated and specified
by Gannett Fleming originally in their
initial design.
The anchor load capacity data was
extracted from the powers design manual
(second edition)
and powers indicated the adhesive
anchors were capable of supporting up to
6,350
pounds each in
4,000 psi concrete,
while maintaining a safety factor of
4 against the ultimate load which in
this case was
25,400 pounds.
None of the four submissions included
any specific reference to exactly
which epoxy formulation was going to be
used
for the anchor. The fourth submission
included a copy of a draft revision of
ICBO ER-4514 dated October 1999
in response to a specific request by the
Gannett Fleming engineer based on his
review of a previous submission.
ICBO is the International Conference of
Building Officials,
and ER-4514 was the ICBO's independent
evaluation report
for the Power-Fast adhesive anchor
system from Powers.
The draft report revision limited the
use of the Power-Fast fast set epoxy to
short-term loads such as those resulting
from wind or earthquake forces.
On the 17th of December, 1999 the anchor
capacity structural calculations were
certified
by a registered professional engineer
employed by Sigma Engineering
International Incorporated of Lincoln,
Rhode Island,
noting that, and i quote: "...the calculations
were performed to compare the anchor
minimum design service loads per
project specification with the allowable
loads provided by the anchor bolt
manufacturer only..."
(end quote) In other words no accounting
for creep
and long-term use in this application
was made.
On the 7th of January, 2000 Gannett
Fleming authorized the contract to
proceed with the anchor installation per
their design
and this was later secondarily approved
by B/PB
in February 2000. Having said that, due
to schedule pressures the contractor had
already been installing the anchors
prior to formal approval
since July, 1999 as previously mentioned
some
5 months before that formal approval
came through.
But hang on a minute! They found problems
in 1999.
On the 7th of October, 1999 Modern
Continental's project manager contacted
B/PB
via a formal letter that they had become
aware of problems involving
"...a small percentage of adhesive anchors
in the HOV ceiling mock-up."
The ceiling module had been built in
August that year and by October the
hanger plates had displaced from the
roof
by about 1/2 an inch or 12mm
prompting their letter.
B/PB responded on the 12th of October
suggesting that the turnbuckles in the
ceiling module
may have been causing excessive load on
some supports,
leading to creep. They also suggested
incorrect fitting of the bolts and the
epoxy
by the constructor as another potential
cause.
Several meetings with Powers and Modern
Continental ensued and were followed by
a letter from Powers to Modern
Continental on the 29th of October, 1999
reminding of the correct installation
procedures but
ultimately stating that since the design
of the ceiling plate
module and anchors were not done by
Powers they could not address,
and I quote: "...the different loads that may
be acting on these anchors..."
(end quote). On the 8th of November, 1999
Modern Continental wrote back to B/PB
attaching Power's formal response and
concluded amongst
other comments with, and I quote: "...it is
improbable that the anchors were
overstressed as a result
of erection loads or the erection
procedures..." (end quote)
So let's time out for a second. It's a "he
said," "she said,"
kind of situation. Prove that these
anchors were all installed correctly
despite the fact that some of the
anchors were installed in the presence
of a B/PB
engineer, unless every single one was
that's not enough proof that the anchors
weren't installed correctly.
During retesting several failed but
evidence was found where
incorrect hole cleaning was applied and
insufficient epoxy was used
leading B/PB to issue Deficiency Report
001,
and after many letters and emails
back and forth with allegations of
incorrect installation procedures being
followed and in an email
from the B/PB design manager to the
project engineer and structural engineer
internally to B/PB stating the following
and I quote:
"...we are not trying to hold up
construction, we are trying to make a
determination
that the installation is safe and
functional..."
(end quote). Sensing frustration? It gets
worse.
The tension between the two companies
escalated to the suggestion
of completely pulling and reinstalling
every single anchor
in the HOV ramp area with no clear
agreement of who should pay
until the overarching CAT Project agreed
in February, 2000 to pay to retest all
anchors to a higher proof test
and split the cost of any that required
replacement.
To that end: 187 anchors were tested.
19 of them failed! Deficiency Report 001
was considered to be closed and it was
closed on the 26th of January, 2001.
On the 17th of December, 2001
a Modern Continental QA inspector filed
a non-compliance report
to B/PB after finding multiple anchor
displacements in the I90 connector
tunnel.
The action directed by bpb was the same
as it had been undertaken
in the HOV tunnel, 2 years previously.
These were executed
and the non-compliance was closed out.
During the investigation
two other incidents of anchor slippage
were found.
In several B/PB field engineering reports
in 2001 and once again
in 2002, however neither were formally
flagged
as non-compliances or defects and no
deficiency reports were created.
Despite the discovery of these damaged
anchor bolts,
over a four year period, project
officials did not begin
any inspection program. So
what are the key findings? The NTSB
investigation delivered its report on
the 10th of July, 2007 on the anniversary
of the incident
and there were 20 findings in their
report. I'm going to focus on 4
that I think are key. Finding #5:
Gannet Fleming and Bechtel
Parsons Bricknerhoff failed to account
for the fact that polymer adhesives are
susceptible to deformation
(creep) under sustained load with the
result that they made no provision for
ensuring the long-term safe performance
of the ceiling support anchoring system.
Finding #10: Gannet Fleming approved the D
Street portal anchors without
identifying which epoxy formulation was
being used.
Finding #13: After unexplained anchor
displacement was found in the interstate
90 connector tunnel in 1999 and 2001,
Bechtel Parsons Bricknerhoff and Modern
Continental Construction Company
Incorporated should have instituted a
program to monitor anchor performance to
ensure that the actions taken in
response to the displacement
were effective. Finding #15: Had the
Massachusetts Turnpike Authority
at regular intervals between November
2003 and July 2006
inspected the area above the suspended
ceilings in the D Street portal tunnels
the anchor creep that led to this
accident would likely have been detected
and action could have been taken that
would have prevented this accident.
The report also noted that there was no
evidence found
that Modern Continental had any
information at that time to suggest that
the epoxy it was using was susceptible
to creep. The National Transportation and
Safety Board (or NTSB)
determined that and I quote: "...the probable
cause of the July 10,
2006 ceiling collapse in the D Street
portal of the I90 connector
tunnel in Boston Massachusetts
was the use of an epoxy anchor adhesive
with poor creep resistance.
That is an epoxy formulation that was
not capable of sustaining long-term
loads.
Over time the epoxy deformed and
fractured until several ceiling support
anchors pulled free and allowed a
portion of the ceiling to collapse."
(end quote). Let's talk about the fallout.
In late 2008 the family of Melina Del
Valle
reached a $28.09M USD
settlement with 15 parties named in
their wrongful death lawsuit.
Bechtel Parsons Bricknerhoff and Modern
Continental paid the largest share of
the settlement
with Powers Fasteners and Gannett
Fleming Incorporated the next largest
following that.
The supplier of the epoxy compound,
Powers Fasteners, was charged
with one count of involuntary
manslaughter. Action
against Powers Fasteners Incorporated
was the first criminal indictment
following the July, 2006 incident.
The suspended ceiling structure in the D
Street portal was removed.
During subsequent tunnel evaluations, it
was determined that
because of the short length of that
tunnel section and its proximity to a
tunnel opening,
the suspended ceiling was not necessary
for adequate tunnel ventilation.
The ceiling structure was never replaced.
So what do we learn from all of this?
Certainly don't start installing things
until the design is approved.
That's always a good one, but it's clear
that neither of the reviewing companies
looked beyond the static load strengths
which showed that people reviewing
within those companies didn't fully
understand
the nature of epoxies. Firstly though
inspections. People don't seem to
see that inspections are a form of
protection; a layer of protection if you
will.
Beyond the basic quality assurance
aspects during a project (which were
lacking),
the operational company or organization
should be performing appropriate
inspections regularly.
Whether that's for concrete cracking,
corrosion of metals, warping,
bulging or in this case epoxy creeping,
regular maintenance inspections are a
catch-all for many types of premature
failures.
No tunnel inspections were performed to
determine the physical and functional
condition of the ceiling system
from the time the I90 Eastbound
connected tunnel was open to traffic on
the 18th of January, 2003
until the day of the incident. Had the
MTA
been inspecting post handover they would
have seen the epoxy
creep. No question. No doubt. Fundamentally
though
the evolution of the suspended ceiling
design during the course of the project
led to a poor choice and although
it is possible to find adhesives that
will hold that amount of load
over a long period of time the design
choice was probably still not the best.
Had the original portal ceiling slab
design incorporated anchor points,
embedded in the concrete, it wouldn't
have been an issue,
but the way the design was split across
different companies over a long period
of time
allowed this kind of oversight or gap to
creep in
which then necessitated a sub-optimal
solution.
The NTSB report also states and I quote:
"In civil projects adhesive anchors are
typically used in short-term or sheer
load applications.
Under these conditions even if the
adhesive is susceptible to creep the
displacement will likely never reveal
itself
and those responsible for specifying
approving installing and testing the
anchors will not be aware of it."
If you're specifying something to be
used, you really need to understand it
since clearly most of the people
involved in this project didn't
really understand epoxy creep they
shouldn't have been specifying
it; and when you're a registered
professional engineer and approving a
document
it's doing half the job to say "it meets
the load requirements"
but to not consider the application it
was used for?
That's important too. Ultimately there
was enough blame
to share around in this incident. There
were multiple engineers that could have
challenged the results of the HOV ramp
test anchors.
The engineers that cited problems in
2001 and 2002
should have raised those as formal
defects to the project to be
investigated and rectified.
The MTA should have been conducting
regular inspections too.
Ultimately though the design, review,
construct and assurance process on this
project
failed. The design was not specific
enough on a crucial point. The review of
the design
was not detailed enough on that crucial
point.
When the warning signs came to light, the
construction and assurance process
incorrectly blamed the installation, when
the true cause
was not properly determined. Were the
wrong people
involved in these stages of the project?
Most likely? Were the right people
ignored
due to cost and time pressure?
Potentially.
Could a simple visual inspection have
found the problem and prevented this
incident
from occurring? Most definitely. Those
engineering companies were held to some
account but what about
the MTA? My observation is that
operations companies like the MTA can
look at inspections as an operational
expense
and when nothing obvious is going wrong
over a long time period
they tend to become the lowest priority
task and
get pushed off repeatedly. Another
suggestion I've heard
is that because it's brand new, why would
you need to inspect it?
But inspections are critical! They are
the layer of protection against the
unforeseen
and they aren't about what you expect to
see...they're about finding what you don't
expect,
and acting on it. Had the MTA developed
and performed those inspections as part
of and following the project handover
this could have been avoided.
I'm not excusing the design errors at
all
but I am saying that a relatively
inexpensive walk down
would have detected this well before
anything ever happened.
So the next time you're thinking you can
put off that overdue inspection
a few more days...make the time...
and just do it! If you're enjoying
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A big thank you to all of our Patrons
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Mitch Bielger, John Whitlow, Kevin Koch,
Oliver Steele, Hafthor
and Shane O'Neill with an extra special
thank you to our Gold Producer known
only as
'r'. Causality is heavily researched and
links to all materials used for the
creation of this episode
are contained in the show notes. You can
find them in the text of the episode
description of your podcast player or
on our website. You can follow me on the
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@johnchidgey (all one word), or the network
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This was Causality. I'm John Chidgey.
Once again, thanks so much for listening...
[Music]