Manholes rethought : the Institute for Research in Construction's new manhole design is so simple and so effective that it's a wonder no-one thought of it before

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Canadian Consulting Engineer, 41, Mar/Apr. 2, p. 56, 58, 2000-03-01

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Manholes rethought : the Institute for Research in Construction's new

manhole design is so simple and so effective that it's a wonder no-one

thought of it before

Gallagher, J. F.; Baer, N.

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M a nhole s re t hought : t he I nst it ut e for Re se a rc h in Const ruc t ion's ne w

m a nhole de sign is so sim ple a nd so e ffe c t ive t ha t it 's a w onde r

no-one t hought of it be fore

N R C C - 4 3 9 5 6

G a l l a g h e r , J . F . ; B a e r , N .

M a r c h 2 0 0 0

A version of this document is published in / Une version de ce document se trouve dans:

Canadian Consulting Engineer, 41, (2), Mar/Apr., pp. 56, 58, March 01, 2000

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Manholes Rethought

The Institute for Research in Construction's new manhole design is so simple

and so effective that it's awonder no-one thought of it before.

By Nicole Baer and

J.F.

Gallagher

air is enhanced by the use ofa "radiator bag" placed around the crushed stone. This bag consists oftwogeotextile blan-. kets, spread atop and beneath the stone layer, which together work to keep the

wannair where it's needed - closeto the pavement surface.

A galvanized steel mesh, wrapped around the cylindrical manhole struc-ture during installation, prevents the crushed stones from dropping through the slots in the cement ring.

Above: Pre-cest concrete ring with slots for heat to escape.

Left: Warm air from the sewer dissipates through aggregate surrounding the man-hole, but is kept close to the surface by a geotextile bag.

Proof in:the field

With any 'proposed innovatibn such as this, lIIunicipaiities andutilitv

,en"n-the manhole are replaced with a ring ventilated with eight narrow slots. The holes in the manhole cover are plugged and the steel manhole cover is insulat-ed from below, causing the wanner air to flow out through the slots.

ModifYing the ground beyond the slots enables the wann air to dissipate beneath the pavement one or two metres inall directions. This is accom-plished by placing a layer of large,

clean, crushed stones around the

manhole. air through the is

58 CanadianConsult!ng Engineer MarchiApril2000

T

he National Research Council's Institute for Research in Con-. struction (IRC) has developed an innovation that will prevent heav-ing and crackheav-ing of pavement around manholes.

Frost damage around manholes is a common sight in many parts of the world, from the northern United States to Canada to Europe and north-ern Asia. When one considers the number of municipalities plagued by frost damage and the number of man-holes in each, the cost of the problem can readily be seen.

IRC's solution, developed by researcher Otto Svec, P.Eng., is so simple that one could say it has been staring us in the fuceall

these years. The simplicity lies in harnessing and using the natur-al wannth of the water flowing through storm and sanitary

sew-ers. The technique promotes convection,

which

causeswann

air to rise upwards in the manhole. Near the surface, the wannth is encouraged to radiate horizontally out-wards where it can protect the soil around the' manhole from frost The pavement immediately above suffers less stress, and thuswillnot heave.

Temperature differences between the bottom and the top of a manhole 200C. Rather than let

this

effecl it makes

INFRASTRUCTURE

continued from page 56

t:he p&Va,...t around1;het8It; new manhole design concept in a

real-life setting, IRC carried out a field test with. engineers in the city of Nepean, next door to Ottawa. Wayne· Newell, general manager of design and construc-tion in Nepean's Puhlic Works Department, paved the way for the test in the winter of 1998-99.

Nepean's enthusiasm for new technology was amply rewarded. Good results flowed along with the warm air rising in the test manhole. Despite fluctuating temperatures dur-ing the winter, de-icdur-ing salt applied to city streets, and wear and tear from vehicles, the IRe innovation worked like a charm. At winter's end, the pavement around the test manhole remained flat and free of cracks. This was in sharp contrast to pavement

around standard manholes, some

of which heaved by five centimetres.

At:

wint:er'e end,

The news on cost is also good: the slotted cement rings can easily be manufactured, and the entire installa-tion procedure costs little more than conventional manhole construction. Indications are that by extending the life of pavement by just one year, municipalities can recoup their invest-ment. The protected pavement is expected to last as long as pavement

where frost is not a concern.

Widespread adoption of the inno-vation could mean great potential for savings because of the sharply

lower incidence of road repairs.

Sec-ondary benefits include less traffic disruption, savings in energy and

environmental advantages. IRC has applied for an interna-tional patent on its innovation. Meanwhile, research will turn to making the technology as cost-effective as possible by developing a heat bag of smaller diameter and thickness, especially for road

rehabili-tation projects. CCI!

For infurmation on tlu!new manhole tech-nowgy, contactDr. Otto

J

Svec, Ph.D, P.Eng., senior research officer in the Urban Infrastructure Rehabilitation Pr0-gram of tlu! National Research Council's Institute for Research in Construction.

E-mail address: otto.suec@nrc.ca.

Nicole Baer is an Ottawa-based freelance writer. Jim Gallagher is manager ofpuIr lication services, Institute for Research in Construction, National Research Council of Canada.

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HIGHWAYS

continued from page 54

detects rollover by measuring the lateral forces (using the anti-lock braking system electronic control unit and accelerome-ters) and individnal wheel speeds (using sensors). Field studies in British Columbia have shown these systems give a return on investment of 2: I within five to 10 years.

Road safety is something that should be prev'l!ent and considered in all business decisions, especially those made by governments. We expect governments to provide leadership to promote a safe highway system. They should ensure, for example, that the enormous competitive pressures in the trucking industry resulting from just-in-time inventory and globalization do not compromise public safety.

The cost of traffic collisions is rising both in human and economic terms. As. a result, highway safety is starting to become an issue of worldwide concern, something like the groWth of environmental awareness in the early 1990s. Such rising public interest demands that road authorities and consulting engineers face the challenge of improving

safety on our roads. CCE

Said Easa is professor at Laluilu!ad University'and author oftwo

chapters on "GemneIrU;Design" and "Automated Highways, "puIr lislu!d, respectively, in Civil Engineering Handbook,CRC Press, 1995 and tlu! Encyclopaedia of Electrical and Electronics Engineering,John Wilry, 1999.He is al50 editor ofUrban Plan-ning and Development Applications of GIS,

just

publisluid

by

tJw

American Society ofCivil Engineers.