Choice of
Technology and Construction Method
As in the development of appropriate alternatives
for facility design, choices of appropriate technology and methods for
construction are often ill-structured yet critical ingredients in the success
of the project. For example, a decision whether to pump or to transport
concrete in buckets will directly affect the cost and duration of tasks
involved in building construction. A decision between these two alternatives
should consider the relative costs, reliabilities, and availability of
equipment for the two transport methods. Unfortunately, the exact implications
of different methods depend upon numerous considerations for which information
may be sketchy during the planning phase, such as the experience and expertise
of workers or the particular underground condition at a site.
In selecting among alternative methods and
technologies, it may be necessary to formulate a number of construction plans
based on alternative methods or assumptions. Once the full plan is available,
then the cost, time and reliability impacts of the alternative approaches can
be reviewed. This examination of several alternatives is often made explicit in
bidding competitions in which several alternative designs may be proposed or
value engineering for alternative construction methods may be permitted. In
this case, potential constructors may wish to prepare plans for each
alternative design using the suggested construction method as well as to
prepare plans for alternative construction methods which would be proposed as
part of the value engineering process.
In
forming a construction plan, a useful approach is to simulate the construction
process either in the imagination of the planner or with a formal computer
based simulation technique. By observing the result, comparisons among different
plans or problems with the existing plan can be identified. For example, a
decision to use a particular piece of equipment for an operation immediately
leads to the question of whether or not there is sufficient access space for
the equipment. Three dimensional geometric models in a computer aided design
(CAD) system may be helpful in simulating space requirements for operations and
for identifying any interference. Similarly, problems in resource availability
identified during the simulation of the construction process might be
effectively forestalled by providing additional resources as part of the
construction plan.
Example
1-1: Roadway rehabilitation
An example from a roadway rehabilitation project
in Pittsburgh, PA can serve to illustrate the importance of good construction
planning and the effect of technology choice. In this project, the decks on
overpass bridges as well as the pavement on the highway itself were to be
replaced. The initial construction plan was to work outward from each end of
the overpass bridges while the highway surface was replaced below the bridges.
As a result, access of equipment and concrete trucks to the overpass bridges was
a considerable problem. However, the highway work could be staged so that each
Overpass Bridge was accessible from below at prescribed times. By pumping
concrete up to the overpass bridge deck from the highway below, costs were
reduced and the work was accomplished much more quickly.
Example
1-2: Laser Leveling
An example of technology choice is the use of
laser leveling equipment to improve the productivity of excavation and grading.
In these systems, laser surveying equipment is erected on a site so that the
relative height of mobile equipment is known exactly. This height measurement
is accomplished by flashing a rotating laser light on a level plane across the
construction site and observing exactly where the light shines on receptors on
mobile equipment such as graders. Since laser light does not disperse
appreciably, the height at which the laser shines anywhere on the construction
site gives an accurate indication of the height of a receptor on a piece of
mobile equipment. In turn, the receptor height can be used to measure the
height of a blade, excavator bucket or other piece of equipment. Combined with
electro-hydraulic control systems mounted on mobile equipment such as
bulldozers, graders and scrapers, the height of excavation and grading blades
can be precisely and automatically controlled in these systems. This automation
of blade heights has reduced costs in some cases by over 80% and improved
quality in the finished product, as measured by the desired amount of
excavation or the extent to which a final grade achieves the desired angle.
These systems also
Permit the use of smaller machines and less skilled operators.
However, the use of these semi-automated systems requires investments in the
laser surveying equipment as well as modification to equipment to permit
electronic feedback control units. Still, laser leveling appears to be an
excellent technological choice in many instances.
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