NM 44: 長期供用性保証のある経緯
Richard W. May , W. Allen Palmer , and Max E. Valerio
NM44:ニューメキシコ 44号はこれまで国内でも最も危険な道路といわれてきた。全域にわたって国内4位の人口を有し、水資源、天然資源に恵まれているが、9番目に失業率が高い。ニューメキシコ州の道路輸送局(NMSHTO)は、この地域を適切な道路ができてアルバカーキー、サンタ・フェ、ラス・クルチェスなどの都市間の物と人の移動が容易になれば、優れて経済成長できると考えている。しかしながらNMにおける通常のやり方では、この地域を結ぶ道路の残り118マイルを改良するには27年かかるであろう。NMSHTDはまた、改良した道路を将来 20年にわたって良好な状態に保つための維持修繕には車線1マイルにつき年間 1万6000ドルを要すると見ている。
Mesa工事開発コントラクタ (PDC)とNMSHTDは、すべての事項について、オープンな対話を続ける。これは、誰にとっても学ぶところのおおい経験である。NMSHTDは、いくつかの斬新な方法を見ることとなり、供用性に関する責任を負っていれば関心もなかったような構造の供用性を見るまたとない機会を得た。私的な主体としての Mesa PDCは、州当局の見通しを通じて開発と落札のプロセスに関わることができ、そのような新手法の限界に関する新しい知見を得た。
この Abstractだけでは全容が分かりにくいのですが、最近、言われているアセットマネージメントなどともまったく違う新しい契約方法のようです。20年間の供用性を保証する請負主体は、Mesa PDCという維持管理公社ともいうべき一応は私的な管理主体で、工事請負は従来型の最低落札方式で、請負者は品質管理で合格すれば供用性に関しては責任を負わないというものです。供用性の保証のために、州当局と仕様について綿密に協議し、道路設計を行う、つまり工事の入札以前にMesa PDCとは契約が成立しているようです。州はこの維持管理公社に対して20年間の維持費の支払うわけです。維持管理公社は、予期しない修繕などに関するリスクを負っています。工事はコントラクタと州の間で従来どおり行われます。ただ、仕様が維持管理公社独特のものになっているようです。維持管理公社と言っても維持管理の手を持っているわけではなく、実際の維持を州が直轄でやれば、維持管理公社が弁済する仕組みになっています。そうしたリスクを負うため、設計についても独自の基準できめ細かくやっているようで、こまかく、現地条件に合わせて設計するようです。
入札の前に、何回かコントラクタに公聴会を行って起こりえるリスクなどを明確にして設計、仕様を手直しするといったこともやっているようです。そして入札の結果、予定価格を下回る応札がないと、さらに見直しをするという手順を踏みます。維持管理公社は州当局と協力して業者の間の調整にあたることになります。 品質管理の仕様のPWLというのも珍しいものです。舗装に関してのpay factor（支払い係数）というのがあって下の表のようになっています。個々の管理項目に合格していれば、表のpercent Weightingの欄の得点が与えられ、合格していなければ0点で、全項目合計して100％で100％支払われるわけです。100％を切っても支払いはあるわけですが、60％を切ってはならないということにしているようです。ところが60％を切ってももう一つ救いがあって、試験室で試験して供用性が証明されれば、合格ということになる仕組みがあるようです。
DR. MANSOUR SOLAIMANIAN ﾐ Good presentation. This
sulfate reaction heaving you were talking about, how sure are you
that it was due to the sulfate reaction and not coming from
expansion of the clay from the bottom? The reason I bring this up
is because we have observed something very similar on a 12 mile
stretch of a Superpave Highway in PA, the construction was over
in October and the ride quality was very good at the time and then
right after the winter and the ground freeze, the ride quality really
deteriorated. Now we are seeing that it is smoothening out again.
So I was wondering what your experiences has been in this regard.
DR. RICHARD MAY ﾐ To the ordinary layman looking at this
heaving; it does look very much similar to plastic clays swelling
up. There are a number of reasons why we are pretty sure about
what we observed. One, with swelling clay all over, one would
expect to have a wide extent of affected area with differential up
and down swelling with any kind of moisture change. These
particular swells occurred in very narrow locations in areas where
you could see that there was some kind of concentrated water flow
carrying sulfate ions. We also knew that there was gypsum mining
near the southern part of this project with calcium sulfate white
deposits all over the place. So we were fairly certain it was soil
sulfate related and luckily, the swelling that occurs under these
conditions is a permanent swell; they donﾕt shrink back down like
plastic clays. We did not do any testing or anything because we
were fairly sure it was sulfate related. I donﾕt know if I answered
your question, but I hope I did.
DR. JAMES WINFORD ﾐ Nice and timely presentation. Two
quick questions. Number one, from a cash stream analysis what
does your payment schedule look like for the total $215 million
contract? Secondly, what kind of participation, in terms of an
extended warranty, did your HMA paving subcontractors offer in
addition to just supplying and installing the HMA materials.
DR. MAY ﾐ The $215 million was the cost of initial construction.
This project had a unique feature where the state actually was still
paying for the initial construction out of a separate pocket separate
from the warranty and professional services contract. So the
payoff for that money is just like any other state job using the low
bid process; we were acting as an agent for the state and the
contractors were paid by the state the same way, just like any other
job. The other question regarding warranty ﾐ the only thing we
required from the contractors was the same one-year material and
workmanship that NMSHTD required, just basically the same as
they have on any other job.
DR. GEOFFREY ROWE ﾐ Very nice presentation and very nice
road to drive on. I drove it last year, beautiful scenery and very
nice pavement. My question is, do you, what are your planned
maintenance activities. Do you have some money set aside over
the next few years if you run into bigger expenses planned. How
you intend to limit spending the project life. Do you have a plan,
for resurfacing in say year ﾒXﾓ and what other maintenance
activities are being planned?
DR. MAY ﾐ First, I need to clear up a major misrepresentation
here; we donﾕt have $110 million set aside. Remember, we got
paid $60 million for the pavement warranty. We could lose up to
an additional $50 million. To answer your question, we do have
some planned maintenance set up. We have several scenarios that
we envision; but, again it comes down to ﾒhow good is our crystal
ball versus reality?ﾓ. The beauty of this project for the state is that
if the crystal ball is not very good, it is not a problem for them, it is
a problem for us. But we do have some scenarios that we think are
going to happen. So, does that answer your question?
DR. ROWE ﾐ I certainly am interested in what some of the
scenarios might be.
DR. MAY ﾐ I cannot give you the details on our scenarios, Geoff,
but it would be something like what you have suggested, including
some planned resurfacing.
MR. WENG ON TAMﾐ We are embarking on a fairly large project
in central Texas also and isolated pockets of sulfates are a potential
issue we are going to be dealing with. I was wondering if there is
any innovative technologies or methodologies that you used to try
to locate these.
DR. MAY ﾐ First of all, God bless you. I donﾕt know if I can share
any innovative technologies; however, there is one suggestion that
I can offer to you - control the water. Water is the driving feature
on this reaction. You can have a low sulfate content in certain
areas, but if the water can transport sulfate ions and they collect,
the result will be a fairly good reaction even though the measured
sulfate content was fairly low. So the best piece of advice I have is
to control the water, especially during construction - watch your
MR. JAMES SCHEROCMAN ﾐ If the contractors didnﾕt have any
other warranty requirements other than one year, what did they do
different to assure you that you were getting a better job that was
going to last 20 years?
DR. MAY - I donﾕt know that it was their job to reassure us, Jim.
That is why we were out there to see that we hopefully got what
we designed. The contractor had no extra duties to reassure us; it
was a matter of us watching what was going on, taking samples,
cores, and measuring what was happening. The risk and
responsibility is all ours.
MR. SCHEROCMAN ﾐ So were you in essence then just a super
talented inspection force? Iﾕm asking it for a particular reason,
because it really makes a big difference. What you are doing is
paying attention to what somebody else is doing and you are
relying upon your eyes, ears and inspection and people to get the
job that you were supposed to get, correct?
DR. MAY ﾐ That is correct.
MR. SCHEROCMAN ﾐ So you basically guaranteed performance
based upon inspection of the construction work.
DR. MAY ﾐ Actually, Jim, we had to guarantee performance
before we could see the inspection work.
MR. DALE S. DECKER ﾐ Rich, itﾕs scary but Jim and I were
thinking along, somewhat along the same line. I guess my question
was more philosophical approach. If you, realizing the constraints
that you had to work with, above the low bid environment, in a
perfect world if you had it to do over again, would you not prefer
to have the contractor both absorbing part of the risk and part of
the potential gain, in being more of a partner rather than just a low
bid guy out there thatﾕs brought in materials. Donﾕt you think you
would have gotten a better product, or do you think you would
have gotten a better product?
DR. MAY - I guess the answer to that kind of depends on the
contractor, Dale. Some contractors would like to get involved in
more of that and we are working on that aspect on other projects.
Yes, some contractors do want to get a piece of that risk and
reward; but other contractors donﾕt want to have any part of it.
From personal experience, I think if youﾕre in more of a design-build
relationship and you do establish that partnership like we
have on our Virginia project, I think you can get a better product.
MR. W. ALLEN PALMER ﾐ Iﾕd like to comment on Jim
Scherocmanﾕs question. Whatﾕs going to guarantee or give us more
reassurance that we are going to get what we ask for and that our
warranties really will work out? The first conversation that I had
with a contractor on the road that involved one of the six lots that
ultimately ended up being removed and replaced was a very
interesting conversation. The question came up, ﾔYou know weﾕve
got 2400 tons of material in the lot and you are asking us to
remove it and you are assuming that its got zero value, and we
know that it has some valueﾕ; this was the argument on the other
side. Being an agent for the state, we did have an interesting
relationship with the contractor. If, for example, we left that
material in place and the contractor took a substantial pay
reduction on that material, that money did not go back to Koch
Performance Roads or Mesa PDC to help us manage our risk in
that area over a long period of time. The money went back to the
state. So there was no relationship between the contractor, the
state, the district office or whatever to address issues that might
develop over a long period of time. In effect, we were given all the
authority out on the roadway to enforce the specifications that we
saw fit to enforce. In some cases, if we determined in our
judgment that this material in fact would perform to our
satisfaction, we made a decision to leave it in place. But in a very
few instances where it made sense from a performance-related
perspective to have the materials cut out, we went ahead and made
that decision. So the state gave us some leeway to enforce the
specification the way we saw fit.
MR. SCHEROCMAN ﾐ If what Iﾕm hearing is correct, and I
believe it is, then are we saying we can build better roadways that
are much more durable and long lasting just by doing enough
testing and enough QA work during construction to make sure the
contractor does what he is supposed to do?
DR. MAY ﾐ I believe so. The answer is yes.
MR. SCHEROCMAN ﾐ So do I, because highways donﾕt fall apart
uniformly from end to end. They fall apart in particular areas
because we paved in the rain or there was a soft spot in the grade
we didnﾕt fix and all the rest of that. So I like what happened here,
only because what you did was get a good job because you
basically paid attention to what you were buying.
DR. MAY ﾐ We had a lot of help with that - the contractors, as
well as our subcontractors.
PROFESSOR HUSSAIN BAHAI ﾐ Again a conceptual the
question. In your analysis, did you use any prediction models or
did you rely totally on performance related properties.
DR. MAY ﾐ We used a lot of prediction models. The Asphalt
Institute models as well as others were evaluated and we did
analyses with various elastic layered and temperature dependent
modeling and stress dependent modeling. But to answer your
question, Hussain, we did use a lot of prediction models.
HUSSAIN BAHAI ﾐ Can you tell us your level of confidence or
your feeling about the models that you used? I mean you are
probably one of the very few people that use these models for such
a long time. Are you satisfied with the level of performance
models that we have now?
DR. MAY ﾐ I donﾕt know that Iﾕm satisfied. Much could be done
toward improving those models, particularly in characterizing the
new materials, as you well know with NCHRP 9-10. The Asphalt
Institute models are more than just a little old now - more than 20
years. So we have developed some adjustments for polymer-modified
materials or refined materials that we prefer in certain
layers. So the answer to your question, Hussain, is that I donﾕt
think we are satisfied at all. We would love to have some new
models and we were really hopeful for the AASHTO 2002 project
to provide us with some help in that regard.
PROF. BAHAI ﾐ If you had, do you feel like if you had better
models you would have, could reduce the risk or accept lower bids
for these contractors? And if that is so, you are holding the
warranty. Do you feel that we have really cut down on the cost of
the improve our performance models?
DR. MAY ﾐ Absolutely. But the question is, getting to that point
where you have confidence in your models, so that there is
opportunity for time and performance data to back that up. But
absolutely, if we had better models we could sharpen our pencils
on the proposal ﾐ this is very true.
DR. HAROLD VON QUINTUS ﾐ One quick question. In setting
up the acceptance testing plan, did you say you used the standard
acceptance plan that New Mexico typically uses on their project, or
did you use a different confidence level there so in deciding the
number of tests and when to take the tests?
DR. MAY ﾐ Iﾕll give you my answer, Harold, and Al Palmer can
correct me if Iﾕm wrong; but the state is using moving averages
and we use a percent within limits. So it was a major shift from
the normal operation of the State.
MR. GALE PAGE (Submitted Discussion) Suppliers and
contractors have encouraged agencies to see their point of view in
the development of specifications. I believe the experience of Koch
on this project indicates that suppliers and contractors can benefit
in experiencing the agency point of view.
Koch as a binder supplier encourages agencies to use uniform
national specs for binder, but as an agent for New Mexico
specified additions to a binder spec such as elastic recovery and
ring and ball.
Koch as a contractor would not unexpectedly encourage agencies
to use incentives and payment in tons, but as an agent for New
Mexico focused on contractor disincentives and payment in square
My point is that it is only when we (agency, supplier, and
contractor) see, understand, and appreciate each others point of
view that we will have a basis for making real meaningful
improvements to specifications.
AUTHORSﾕ CLOSURE: The Mesa, PDC plan for the 20-year
warranty period includes a wide range of activities that are defined
as Capital Renewal in the Agreement with NMSHTD. This
includes Pavement Reconstruction, such as structural overlays, and
Preventive Maintenance, such as crack filling. Some of the various
alternative scenarios evaluated on this project are summarized in
the Life Cycle Cost Analysis, shown in Table 4 of this paper.
Within the $70,122,000 of the Mesa, PDC future non-discounted
maintenance costs are various planned maintenance and structural
improvements, including crack filling, fog sealing, partial and full
depth patching, and resurfacing overlays of various types and
timing for the mainline and shoulders.
Mesa, PDC and NMSHTD agreed on the terms and conditions of
the Pavement Warranty prior to final design and prior to NMSHTD
awarding any construction contracts. The terms and conditions of
the Pavement Warranty remained unchanged throughout the
bidding and construction period, although significant value
engineering and change orders did occur. The pavement warranty
responsibilities of Mesa, PDC, officially began at substantial
completion of each of the four construction contracts. At those
times, Mesa, PDC provided NMSHTD with performance bonding
which totaled $110 million for the pavement warranty. NMSHTD
required the contractors to provide a one year ﾒmaterial and
workmanshipﾓ warranty for all of their work, including the