Authors:
David Fletcher (dfletcher@vms1.uop.edu)
John Borns
David Veshosky
Suggested Courses:
Soils & Capstone Design
Level:
Junior & Senior
I. Situation
In 1986 the City of Pitcher, Wyoming, formed the Wyoming Woolies
Stadium Authority to build, own and operate a new stadium to accommodate
professional football games and other major events. Ostensibly
an independent body, the authority was known to be controlled
by the Pitcher City Council. Later that year the authority retained
the engineering consulting firm Matrix Engineering Associates
to design the site and structure. The consulting contract with
Matrix included geotechnical engineering and on-site inspection.
Matrix retained sub-consultant SoilTest Geotechnical Engineers
to research subsurface conditions, develop a soil boring program,
supervise borings, analyze data, and make design criteria recommendations.
Early in 1987 Benson-Marquardt Construction Company (BMCO) negotiated
a construction management contract with the Stadium Authority
to manage the project. In closing their deal, BMCO's primary
selling point was their guarentee to achieve substantial completion
prior to the first home game of the 1988-89 season. The Stadium
Authority accepted the BMCO proposal, but required a contractural
provision for liquidated damages in the amount of $10,000 per
calendar day. Weather in Wyoming is often a major impediment
to continuous winter construction work. The contractural provision
for liquidated damages allowed no relief for weather except for
catastrophic events beyond BMCO's control. Additionallly, design
work by Matrix was at that time only in the preliminary stages.
From the outset it was clear that each and every work day would
be a precious resource.
When Matrix retained SoilTest, the testing firm already had a
heavy backlog of work for Pitcher and several other governmental
clients. Under persistent pressure from Matrix, on behalf of
BMCO, SoilTest management sent a crew of two technicians and an
old, borrwed drill rig to the site with a quickly-developed hand
sketch of the boring location and instructions to complete the
borings in one day. By mid-afternoon, when the rain began, all
but two borings were completed; the crew then returned to the
shop with good intentions of returning later in the week. The
missing borings were never obtained or requested.
Dennis Snead was on-site Project Engineer for Matrix and was responsible
for most day-to-day engineering decisions to provide direction
and support for the fast-track project. The project was especially
challenging for Dennis, since this was his most responsible field
assignment to date on a project of such large magnitude. At various
times throughout the project, Dennis found himself intimidated
by Hardnose, BMCO's veteran construction superintendent, and uncertain
about the extent of his authority as a consulting engineer to
delay "progress" when technical and quality issues arose.
More than once BMCO's management "advised" Matrix principals
that any liquidated damages costs assessed against BMCO should
be shared by Matrix if Matrix delayed construction progress without
sufficient reason. Not the least of Dennis' challenges was the
marginal soil conditions across the site, and the tendency of
the native clay to resist compaction and impede construction during
and after rains. Dennis was puzzled by his firm's selection of
SoilTest to perform the geotechnical work because their reports
appeared to be incomplete and inconsistent in their recommendations.
Only much later was Dennis to discover that the President of
SoilTest was the chairman of the political party controlling city
hall and played a pivotal role in the city's selection of Matrix.
Due to the configuration of the stadium the four external stair
towers were constructed after the main mass of the stadium superstructure
was erected. During the course of site cut and fill Hardnose
noticed water ponding in the area of the west stair tower one
morning after a half-inch rainfall. He mentioned the condition
to Dennis, but it didn't seem very serious to Dennis at the time.
In the afternoon of Thursday, April 24, 1988, during his normal
inspection walk of the site, Dennis notes that Hardnose has directed
the excavation crew to "hog out" the area of the west
stair tower in preparation for digging, forming and pouring of
the tower foundation. As he approaches the hole, Dennis can see
Hardnose closely scrutinizing the soil material in the exposed
bank, which is clearly different in color and texture from that
in all other excavations on the site. Knowing that the Matrix
structural design was based on SoilTest reports of reasonably
uniform conditions across the site, Dennis returns to his office
trailer to check the portion of the SoilTest geotechnical report,
which Dennis hasn't yet found time to study thoroughly, pertaining
to the area of the west stair tower. To his dismay, Dennis discovers
the SoilTest report indicates their nearest boring fifty-five
feet southeast of the center of the west stair tower.
Dennis returns to the excavation and discusses the situation with
Hardnose, whom Dennis has gotten to know better during their occaissional
fishing weekends at the BMCO cabin in northern Wyoming. Dennis
wonders out loud whether he should issue a "Stop Work Order"
on the stair tower area and request his office to require SoilTest
to perform emergency investigation and analysis prior to allowing
construction to proceed. Hardnose notes the non-native material
appears to be mostly granular and well-compacted, and reminds
Dennis that the Wyoming Woolies' first home game is "73 work
days from today". Dennis tries to call his boss at the Matrix
office, but is unable to reach him. By this time it is 4:15 P.M.;
the excavation crew has completed digging the footing trench,
carpenters have set the edge forms, and the rod-busters are just
completing tying-up the footing steel. Dennis can't locate Hardnose,
but the assistant superintendent tells Dennis that Hardnose instructed
him to schedule ready mix trucks to begin arriving at 8:00 A.M.
tomorrow to pour the footing. On his way to his car Dennis hears
a carpenter foreman (who has long lived nearby) talking to someone
else about the gas station that once was located where the west
stair tower is now being built. Dennis spends the night worrying
about a decision he is reluctant to make.
Arriving at the project site at 8:00 Friday morning, he finds
the situation has only become more difficult since the site has
received a moderate overnight rain. Hardnose has had the footing
trench pumped dry, and has his pouring crew standing ready for
the trucks to arrive. When the first truck rumbles up the stone
drive, Dennis stays in his office trailer pretending to do yesterday's
paperwork.
The evening of the Woolies' home opener Ivan Civil, Dennis' boss,
arrives at the completed stadium to attend the game. On his way
to the Matrix suite via the west stair tower Ivan notices the
top-of-slab elevations at the stair landings are consistantly
lower than the corresponding elevations of the stadium floor slabs.
The next day he and Dennis Snead have a meeting.
II. Numerical and Design Problems
The following problems assume the stair tower has a total weight
of 200 tons and that the foundation is a spread footing with a
radius of 12 ft.
1. Assume the surface soil was classified as CL by the Unified
Classification system and that it had a plastic limit of 32 and
a liquid limit of 79. What sort of compaction equipment would
you recommend for the site preparation?
2. Over most of the site the clay extends 60 ft below the surface
and is underlain by dense sand and gravel. It is normally consolidated
with Poisson's ratio of 0.33. A plate load test gives an undrained
modulus of 200 ksf. Estimate the initial elastic settlement of
the stair tower.
3. After four months has passed, some vertical separation is noted
between the stair tower and the stadium amounting to about 0.6".
If the coefficient of consolidation is reported as 36 ft2/yr,
use Terzaghi's one-dimensional consolidation theory to estimate
the total ultimate separation.
III.
Solutions to Numerical Problems
1. Since soil is primarily clay with a high plasticity index (Unified
CL-lean clay), a sheepsfoot roller will likely be the most effective
compactor.
2. Since foundation diameter is 24' and layer depth is 60', H/B = 60/24 = 2.5. Thus the shape factor Cs is 0.605 (see pp 170-2, Fang, Foundation Engineering Handbook, Van Nostrand, 1991)
The settlement can be computed from:
Substituting the appropriate values gives:
3. Since cv is 18 ft2/yr, the time factor, T, is given
by:
where t is the elapsed time, and Hdr is the longest
drainage path. Substituting values gives:
This time factor corresponds to about 13% complete consolidation,
therefore the ultimate settlement will be about 0.6/.13 = 4.6".
4. The initial stress at the center of the clay is (30)(105) = 3.15 ksf. From the chart 5.24 in Fang, the stress increase is 400/(p 122)*0.5 = 0.44 ksf. Thus since the settlement is 4.6" from problem 3, the value of Cc is given by:
Substituting valus gives:
IV. Ethical Questions and Solutions
1. List the professional obligations of Matrix's principals, and
identify two aspects in which they failed to satisfy these obligations.
Matrix's principals had professional obligations to the general
public (taxpayers, as well as users of the stadium), their client
(City of Pitcher), and Dennis. As stated in the Code of Ethics
for Engineers of the National Society of Professional Engineers
(NSPE), their obligations required them to "hold paramount
the safety, health and welfare of the public". Their obligations
to the City of Pitcher required them to provide a safe design
at minimal cost, while meeting the schedule to allow the stadium
to be ready on time. Their obligation to Dennis involved providing
the necessary support/supervision to effectively do his job.
They failed to satisfy these obligations by hiring SoilTest as
a subcontractor, in order for Matrix to get the contract from
the City. When SoilTest performed inadequately, Matrix's ability
to compel them to do so was limited. In addition, this violates
provisions in sections II.1.d., II.5.a., II.5.b. and III.5.b.
of the NSPE Code of Ethics, prohibiting acceptance of a contract
awarded in return for financial or political considerations.
They also failed to satisfy these obligations by assigning a relatively
inexperienced engineer (Dennis) to a project with such a critical
schedule, then failing to provide adequate support/supervision.
This assumes that, due to Matrix's workload and resources, they
decided implicitly or explicitly that Dennis was the best they
could do on this project, but then did not adequately support/supervise
him.
2. List the professional obligations of SoilTest, assuming that
their principals were engineers, and identify two aspects in which
they failed to satisfy these obligations.
SoilTest had professional obligations to the general public and
their client (Matrix). These obligations involved protecting
the public health and welfare and meeting the specifications of
the contract. They appear to have violated provisions of the
NSPE Code of Ethics prohibiting accceptance of contracts in return
for financial or political considerations.
They failed to satisfy these obligations by undertaking a project
which they did not have adequate resources to complete and by
not performing the work they were contracted to do. Given their
heavy workload, they should have notified Matrix that they were
likely to be unable to complete the drilling prgram (NSPE Code
of Ethics section III.1.b.).
3. List Dennis Snead's professional obligations, and determine
to what extent he satisfied these obligations.
Dennis had professional obligations to the general public, the
client (City of Pitcher), and his employer. He failed to satisfy
these obligationsin several ways. He undertook a project which
may have been beyond his capabilities. This is prohibited by
NSPE Code of Ethics section II.2. He failed to review the soils
report at an early stage in the project, then did not require
SoilTest to complete the specified boring program. He used the
BMCO fishing cabin in violation of NSPE Code of Ethics section
II.4.c.. He failed to issue a Stop Work Order when he was faced
with a decision in which his professional judgment was required.
4. What uncertainties did Dennis face in dealing with the situation
described in the case? How could he have resolved them? Why didn't
he?
Dennis was uncertain about soil conditions at the site, the implications
of poor soil, and the extent of his authority to stop work.
He could have resolved the uncertainties by requiring SoilTest
to perform drawings in the area of the stairway. Given the delay
which that would have caused, he might have delayed pouring the
stairway foundations until he could analyze the sensitivity of
the design to soil that was of lower quality than had been assumed.
He could have resolved the uncertainty over his authority by discussing
it with a more experienced engineer at Matrix, suggesting some
hypothetical situations. His authority would have been stronger
had he not gone on fishing trips to BMCO's cabin.
He didn't resolve the uncertainties because:
1) He didn't review the soil report at an early stage, so was unaware of SoilTest's failure to complete the boring program.
2) He may not have consulted with a senior engineer because he did not want to appear uncertain or too inexperienced to have been assigned to a project such as this;
3) He didn't want to delay the pour because of the cost and potential
liability involved.
5. How does the presence of uncertainty affect professional and
ethical issues
If Dennis had been certain that soil conditions would result in
unacceptable settlement of the stairway, his professional obligation
would have been to delay the pour until borings could be performed
and the stairway could be redesigned. Allowing the pour to proceed
would have been unethical, since he would be violating his obligations
to the general public and his client.
If Dennis had been certain that soil conditions would not result
in unacceptable settlement, his professional obligation was to
allow the pour to proceed so that the project could be completed
on time.
Without being able to resolve the uncertainty, Dennis needs to
consider the severity of the implications of decision alternatives.
If the soil is good and the pour proceeds, everything is fine.
If the soil is good and Dennis delays the pour, the stadium will
not open on time and Matrix will incur damage to its professional
reputation. Matrix and SoilTest will likely disagree about the
cause of the delay and incur costs for delays and litigation.
If the soil is poor and the pour proceeds, the stadium will open
on time but additional repairs and costs will be involved and
the professional reputation of Matrix will suffer. Matrix and
SoilTest will likely disagree about the cause of the delay and
incur costs for delays and litigation. If the soil is poor and
Dennis delays the pour, the stadium will not open on time.