|
Canada's “Rock to Road” Magazine
Buyers'
Guide 2004 Issue
For a copy of the issue
that contains these articles with colour photos, click
here.
Value
engineering pays off on roadbuilding contract
By Andy Bateman, Engineering
Editor
A
value engineering proposal on an Ontario roadbuilding contract has saved
more than 20 per cent in direct project costs, as well as slicing nearly
a year off the contract schedule for the general contractor Aecon Construction
and Materials Ltd.
Ministry of Transportation of Ontario (MTO)
contract 2002-4001 extends Highway 417 west of Ottawa, near the village
of Antrim by 7.2 km from Regional Road 20 easterly to 1.6 km west of
Panmure Rd. The job involves the construction of new four-lane highway
and one intersection in an area of Leda clay, a natural deposit well
known in the Ottawa area for its instability. For road engineers, Leda
clay presents several challenges, not least of which are structural
weakness, large settlements under load and extreme sensitivity to disturbance.
Here, for instance, the estimated total settlement is projected to be
as much as 1.2 m. Recognising these properties, the original design
incorporated polystyrene and blast furnace slag as lightweight fill
materials, together with vertical wick drains to facilitate drainage
of the underlying clay soils. (See sidebar on Leda clay).
After reviewing the original design, Aecon
Construction and Materials Ltd. developed and submitted a change proposal
in partnership with Ottawa based consulting engineers Urkkada Technology.
Under the proposal, most of the expensive lightweight materials would
be replaced by locally available rock borrow and the drainage process
would be accelerated by additional wick drains together with a thicker
surface drainage layer. Such proposals are encouraged by the MTO and
allow identified cost savings to be shared equally between the ministry
(as owner) and the contractor. The proposal was accepted, with the result
that the quantity of polystyrene fill was reduced from 26 000 to 6 000
m3 while the quantity of lightweight blast furnace slag fill was reduced
from 65 000 to just 2 000 tonnes. Quantities for rock borrow and Granular
B surface drainage layer were increased accordingly, while wick drain
quantities jumped from 37 800 to over 200 000 linear metres. Andrew
Weltz, Aecon's project coordinator, reports that these changes are expected
to result in both significant cost savings and earlier job completion.
The job started in October 2002 and is now scheduled to wrap up in summer
2004, nearly twelve months ahead of its original summer 2005 completion
date.
On site, wick drain installation is concentrated
near the new intersection of Highway 417 and Regional Road 20, with
some of the wick drains here up to 35 m long. In section, individual
wick drains consist of fibre wrapped plastic sections 102 mm x 6 m and
were installed by mandrels mounted on Caterpillar 365 and Hitachi 550LC
excavator units. Once the drains have penetrated through the surface
crust, insertion into the underlying soft Leda clay is straightforward.
The surface settles as the clay then dewaters, with the rate of settlement
accelerated by the weight of fill materials, supplemented by the weight
of some 60 000 tonnes of rock borrow, placed as a 2 m thick surcharge
lift on bridge approaches and ramps. Once monitoring has confirmed the
settlement process is complete, construction of the bridge structures
will begin, with the bridge abutments, wing walls and piers founded
on piles driven down to bedrock.
Granular base materials and rock borrow for
the contracts are being supplied from the Kinburn quarry of Ottawa-based
Thomas Cavanagh Construction Ltd.
Aecon Construction and Materials Ltd. is based
in Brampton, Ont.
|
Leda
Clay - the roadbuilder's challenge
The
Ottawa area is known for its weak, sensitive and compressible
marine clay soils. These clay deposits were originally laid down
after the last glaciation, when the Champlain Sea flooded the
area and then eventually receded as the land rebounded. Sediments
from the Champlain Sea created clay plains including areas of
'Leda' clay. In some locations the resulting clay beds are up
to 70 metres thick, with innumerable small tracts of shallower
clay elsewhere. These are marine clays from which the salt has
been leached, and their very high values for sensitivity (comparing
undisturbed to remoulded strength) indicates a potentially severe
loss of strength if disturbed. Design challenges associated with
the sensitivity of Leda clay include, among others, limitations
on embankment heights to address settlement and stability, difficult
handling, grading, excavation and disposal operations, limitation
on cut depths, extreme frost susceptibility and induced long term
settlements resulting from dewatering. A number of major failures
in the past are attributable to Leda clay.
As recently as 1993, an area some 50
km east of Ottawa, failed and slid into the South Nation River.
Settlement of older buildings and highway embankments is also
evident in the area. On previous road construction projects, such
as Highway 416, large settlements due to compression of clay subsoils
was a major design consideration in areas of high bridge approach
fills, resulting in innovative construction techniques such as
lightweight fill materials to reduce the magnitude of settlements
and vertical wick drains to accelerate the rate of settlement.
Wick drains provide a route by which water can escape upwards
from the loaded clay. On reaching the surface, this water can
be contained within a drainage layer and directed to the site's
surface drainage system. "Freeway Construction Techniques in
Areas of Sensitive Clay Soils - Highway 416 Case Study," by Darwyn
G. Sproule; P. Eng and Brent Loken; P. Eng, both of the MTO. Paper
prepared for presentation at the 1998 Annual Conference of the
Transportation Association of Canada.
|
Back to
top
Loader
demonstrates value of strict maintenance in tough quarry application
By Andy Bateman,
Engineering Editor
An aggregate
producer's approach to maintenance delivers long equipment service life
in tough applications.
Primary
load and carry in a quarry is one of the most arduous duties for a wheeled
loader and its operator. The machine is repeatedly digging into unsorted
shot rock and then travelling loaded for some distance, often over uneven
surfaces and in dusty or wet conditions. Some owners do not expect long
machine life in this application, while others believe that a well-maintained
machine, in the hands of a good operator, can deliver extended service
life even in these punishing conditions. Aggregates and Roadbuilding
recently visited the Burlington quarry of Nelson Aggregates where two
loaders owned by crushing contractor Trent Valley Sand and Stone Ltd.
were loading and hauling shot rock to a portable crushing spread.
At first glance the loaders, both Komatsu WA600's,
appeared to be of similar vintage, but in fact nearly fifteen years
separated their respective delivery dates. Trent Valley purchased the
older machine, a WA600-1, in March 1988 while the company's WA600-3LK
was purchased just last year. The WA600-1 was fitted with a Komatsu
5.73 m3 bucket and the WA600 3LK was fitted with a Hensley 6.87 m3 bucket.
Trent Valley's Peter Lloyd reports that the
WA600-1 has been on primary load and carry duty for most of its service
life, now 15,000 hours and counting, and has delivered 100 per cent
operating availability to date. All routine maintenance on this loader
has been completed in-house, including engine oil changes every 200-250
hours and transmission oil changes every 500 hours. Under the hood,
the engine looked dry with no visible leaks and appeared clean burning
when running, with minimal visible emissions even under heavy load.
Still on routine maintenance, Lloyd reports that the oil in the loader's
front and rear differentials is changed every 1000 hours rather than
the specified interval of 2000 hours in recognition of the constant
travelling inherent in load and carry duty.
Lloyd also underlines the importance keeping
the loader's radiator clean for efficient cooling and gives the radiator
on this unit a full pressure wash every two weeks to remove any dust
build up. Preventive maintenance measures, completed after 9000 hours,
included an engine bearing roll-in and head overhaul, as well as flushing
of the transmission cooler and resealing of the hydraulic pumps. The
bearings on the original alternator, still going strong, were replaced
last winter. The loader was repainted five years ago and is now on its
second set of tires.
As Lloyd says, "Not everyone will agree with
the way we look after our machines, but we believe our approach pays
off in the long run. With proper maintenance, the older loader should
continue in service for some time. Not only that, when the time does
come to replace it, we should realise its maximum resale value."
Trent Valley Sand and Stone Ltd. is based in
Scarborough, Ont.
Back to
top
2004
Buyers' Guide issue
Aggregates
and Roadbuilding Magazine
4999 St Catherine Street West. Suite 315
Westmount, Quebec H3Z 1T3
Tel: (514) 487-9868 Fax: (514) 487-9276
EMail: rocktoroad@sympatico.ca
|
