Building to Mother Nature’s specs
Time was, if one wanted to build a road, all that was needed were money, materials and manpower.
It was essentially a question of planning the road, gathering the materials and equipment and getting to work.
But in the last three decades, concern about the environment has increased dramatically to the point that a major construction project’s ramifications must be considered before the first spade of dirt is overturned.
“Engineers cannot only be involved with design,” says Herb Tateishi, a project manager in Hawaii for Parsons Brinckerhoff, headquartered in Glastonbury, Conn. “We must be sensitive to environmental issues and apply the latest in engineering technology to address these issues.”
Although the word “environment” conjures up images of air, water and woods, it also entails historical, cultural, social and economic matters as it as it pertains federal highway projects.
When preparing to embark on a major infrastructure project like construction of a highway through wilderness, wetlands or historic villages, today’s contractors and engineering firms must rely on experts from many disciplines, including archaeology, architecture, history, forestry, hydrology, biology and economics.
“You could easily have 30 different disciplines working on a project,” says Arvid Thomsen, national director of transportation planning and environmental services for HDR, an Omaha, Neb., engineering firm.
Often, contractors must hire outside specialists — a college professor who is an expert on a particular endangered species, for example — because their in-house staffs are not large enough. “We have alliances with a lot of different firms,” says Thomsen, adding that on some projects, his company finds itself temporarily allied with firms it normally regards as competitors.
Ever since the National Environmental Policy Act (NEPA) of 1969 mandated preparation of environmental impact statements (EIS) for major federal highway projects, new alliances between contractors, subcontractors and outside experts have become commonplace.
Daniel Van Petten, principal environmental planner for Kansas City, Mo.-based HNTB Corp., says contacting the state and federal natural resource agencies with jurisdiction in each affected area is the first step in putting together an EIS. Next, a literature search is conducted to obtain information on landscape features like caves, springs, archeological sites and wetlands, and a map is developed from that search.
Another map plots man-made structures like homes and historic buildings. “By overlaying those maps, we find corridors that are the least disruptive to the natural environment and the human environment,” Van Petten says. The early screening out of bad alternatives is a key objective.
In addition to avoiding historic buildings and the fragile components of various ecosystems, planners must also steer clear of hazardous waste. Over the years, computers, and now newer technologies such as GPS and GIS have helped speed the EIS process.
The EIS is a major undertaking in itself, but for some large projects — chiefly those involving urbanized areas or rail lines — it must also be combined with transit alternatives analyses and highway corridor studies into a single comprehensive “Major Investment Study.”
Legislation Prompts Diligence
NEPA’s passage was the watershed development that brought about today’s environmental diligence. The act requires that mitigation measures be taken during construction, and a rigorous assessment of environmental ramifications be conducted for projects involving federal funds. This means most of them, says Van Petten. “Very few highways or bridges are built without federal participation,” he says.
A patchwork of other legislation and regulations has been developed in the past quarter century, including the Environmental Quality Improvement Act of 1970, the Clean Water Act of 1972, the Endangered Species Act of 1973 and a 1977 executive order mandating protection of wetlands. Complicating matters is the fact that contractors must deal with a disparate collection of state and federal agencies in getting their plans approved — the EPA, the Army Corps of Engineers, the Department of the Interior and the Surface Transportation Board, to name a few. One does not necessarily take precedence over another, nor is there a pecking order. “It’s kind of a free-for-all,” Thomsen says.
Moreover, many of the government agencies charged with reviewing project plans or issuing permits are following the lead of the private sector by downsizing and streamlining, says Thomsen, resulting in overworked employees and a case backlog.
Contractors agree that coordination of the whole process is important, as is ensuring the public’s involvement and input. Thomsen says his company normally sets up an interagency coordination group charged with identifying any state or federal agencies that may have a role in a project, and keeping the lines of communication open between agencies. The project manager is responsible for getting the various agencies together for regular meetings to keep them apprised of developments.
Effective communication with regulatory agencies and environmental groups early in a project schedule enables a contractor to identify the public’s concerns, gauge regulators’ reactions and defuse potential conflicts, says Van Petten. Such steps will foster consensus-building.
In some cases, says Thomsen, it may be beneficial to involve local land-use firms that are familiar with the zoning, jurisdictions and politics of their locality.
Contractors have adopted numerous techniques and practices that minimize disruption to the environment, including top-to-bottom bridge construction, constructed wetlands, terracing, seeding, sodding and mulching.
A variety of materials is available to help in this regard, among them geosynthetics products like erosion control blankets and turf reinforcement mats, “hydromulch” (a spray made from seeds and other natural materials), silt fences and mechanically stabilized retaining walls. Erosion control blankets can be made of straw, coconut fibers, synthetic materials and biodegradable yarn.
Although contractors have a wide variety of products at their disposal to assist them in mitigation measures, it is not unusual for them to tailor materials to fit the circumstances — concrete additives that help the finished product blend into its surroundings, for example.
Top-to-bottom bridge construction, also called “top down” construction, solves the problem of bridge-building in areas that are inaccessible because of environmental restrictions or difficult site conditions.
The erection equipment is located on top of the structure, at the end portion of the bridge that has already been erected. Workers bring materials to the site over the completed portions of the bridge. After a span is completed, the erection equipment moves forward to the next span.
This construction method is ideal for wetlands and other environmentally sensitive areas because there is no need for an access road, dredged channel or construction trestle. New lanes can be added in the median or shoulders of existing transportation corridors to keep congested urban traffic flowing without purchasing new right-of-way.
Cantilever construction is a common top-to-bottom bridge-building method. Progressive cantilever construction involves the attachment of segments to the end of the bridge to form a cantilever extending toward the next support. A crane or winch system atop that cantilever is used to attach the next segment and hold it in place while post-tensioning cables are tightened. The lifting mechanism can then move onto the newly attached segment and repeat the process. Balanced cantilever construction, by contrast, proceeds outward from a pier in both directions.
Span-by-span construction is a third top-down method of erecting pre-cast segmental bridges. With this technique, pre-cast segments are placed on the trusses that span between two piers, then assembled and post-tensioned.
Top-to-bottom construction was used on viaducts leading to the Harano Tunnel, which runs through the Koolau Mountains on Route H-3 in Hawaii. The tunnel is part of a $1 billion Hawaii Department of Transportation project — a 16-mile interstate on the island of Oahu — that began in the 1960s and is slated to be completed late this year.
On the mountain’s windward side, pre-cast concrete segments, each 10 feet long and weighing about 75 tons, were joined together with high strength post-tensioning steel to form spans ranging from 260 to 300 feet. Cast-in-place segments — for which the concrete was poured high above the ground — were used on the opposite side of the mountain and post-tensioned with cables. Spans range from 160 to 360 feet, reducing the need for piers and minimizing disruption to the sensitive land. A color additive was included in the concrete mix for the tunnel portals to make them blend into the mountainsides. The contractor made extensive use of geosynthetics fabrics to control erosion.
Environmentally sensitive techniques and practices are crucial for refurbishments as well as construction of new infrastructure. “The trend will continue to be focused on rehabilitation and refurbishment of old (bridge) structures,” says Foster Beach, senior vice president for infrastructure operations with ICF Kaiser International, a Fairfax, Va.-based engineering and contracting firm. Beach says EPA is becoming increasingly concerned about harmful effects from removal of lead used in old bridge coatings.
Recycling of concrete and other materials from an old structure is also an important part of mitigation, says Ken Buck, chief of the Army Corps of Engineers’ construction branch for civil works.
Concrete can be broken up and hauled to a concrete plant for use as an aggregate in new batches. It can also be pulverized and placed on a slope underneath a bridge to prevent erosion where growing grass would be difficult.
Plant and Animal Life
Mitigation measures involve more than just techniques used in the actual infrastructure construction. Steps taken to alleviate disruption to the surrounding wildlife, vegetation and aesthetics are all equally important.
When the Arizona Department of Transportation undertook the reconstruction of State Route 87, experts went to great lengths to preserve plant and wildlife. “On other projects, we have often tried to work around wildlife,” says Ed Corral, ADOT’s environmental expert on the project. “On this one, because the roadway was already in place, we had to move a great deal of cacti.”
SR 87 winds through the fragile Sonoran Desert, a portion of the Tonto National Forest. The reconstruction project involved widening the stretch between Fountain Hills and Payson into a four-lane highway and building three bridges to carry the new lanes over creeks and washes.
More than 4,000 cacti — including saguaro, ocotillo, barrel, prickly pear and cholla — were transplanted during the earth-moving phase. The contractor marked and documented each plant’s directional orientation and root depth as it was dug up so that replanting conditions could mimic original conditions as closely as possible. The plants were placed in a nursery until the excavation and blasting work was completed and then replanted on embankment slopes which were left rough-cut to appear more natural. Each plant was tagged to facilitate monitoring after replanting.
Wildlife, too, received a great deal of attention. Because native bats play an important role in the desert ecosystem by feeding on insects and pollinating the saguaro cactus, biologists suggested roughening the underside of some concrete box culverts installed along the roadway. That makes it easier for bats to attach themselves, encouraging their continued habitation on the site.
Additionally, blasting work in the desert hills exposed un-weathered, pale gray granite that clashed with its darker surroundings. The contractor addressed that issue by staining the granite with an environmentally benign, photosensitive material that will quickly darken to the color of the undisturbed landscape.
Some 450 boulders ranging from three to five feet in diameter were also salvaged and placed on the embankment slopes, to mimic natural conditions. The cacti were then replanted on the slopes to complete their rehabilitation.
Despite the relatively new-found environmental sensitivity, however, the question remains: Would top-to-bottom construction and the numerous other mitigation practices be used if it were not for the environmental laws and regulations in place? “Probably not,” concedes Van Petten. But he argues that public sentiment favors preservation of the environment, and that in itself would carry weight even without the laws on the books. “Sometimes a project doesn’t get built if there’s too much opposition to it. This formalized process allows people to have a say in what happens in their communities, neighborhoods and rural areas.”
ICF Kaiser’s Beach says contractors do not object to the mitigation measures as much as they do the protracted process of getting project approval. Demands on transportation systems — including airports and railroads as well as roads and bridges — continue to grow, and projects must be expedited, he says. Congress will focus on that this year when the ISTEA legislation is up for reauthorization.
County reduces cost of pothole patching
Like many of its counterparts, the Cass County Road Commission in Cassopolis, Mich., has tackled the vexing problem of maintaining road quality with the constraints of budget cuts.
The commission considered a full range of available patching methods and technologies in its efforts to reduce costs while adequately maintaining the county’s 752 miles of paved road.
Goals included extending repair patch life, increasing the speed of patch application, increasing emergency response times and having the capability to patch in extremely cold weather.
To meet those goals, in January 1996, the commission acquired a pothole patcher built by Sweeprite Manufacturing, Regina, Saskatchewan.
The fully automated patching unit has allowed the commission to reallocate labor to more productive and pressing tasks because it has surpassed projected productivity increases and cost reductions, says says Rick Senger, managing director of the road commission.
A single operator can now apply 12 to 15 tons of patching material per day, 300 percent more than the two-man crews used in the past.
From June through September 1996, one person laid down nearly 800 tons of patch — something that would have required eight people using other equipment, says Senger. Additionally, unlike many alternative models that only lay down cold asphalt, the new patcher lays down both hot and cold as well as a variety of new polymer asphalts. Less sophisticated models would have required the road commission to store oil and emulsifiers in tanks to tailor the patch mixes, according to Senger.
The concept of self-contained mobile patching enables a single operator to travel at high speeds to problem road surfaces with loads of up to five tons, allowing small holes to be patched before they become major problems. “It’s made a safer road system for our people to drive on,” Senger says.
In addition, the commission has now found other repair and rehabilitation uses for the patcher including repair of shoulder breaks, road cuts and wheel ruts. Increased safety, particularly during night operations and rapid emergency responses, has been another benefit to the county.
New bridge retains look of the past
The Depot Road Bridge over the Mill Brook in Coventry, Conn., in use for over 150 years, was an historical structure eligible for inclusion on the National Register of Historic Places.
However, the bridge, a dry laid stone arch with an 11.5-foot clear span and 7-foot rise, began showing signs of impending failure, including loss of stones from the arch and deformed retaining walls.
Additionally, the existing bridge did not meet current criteria for hydraulic capacity or scour protection. An underground stone arch tailrace tunnel beneath the bridge and roadway further complicated the rehabilitation alternatives.
Limited information was available on the tailrace, which once served a water-powered industrial site located immediately upstream of the bridge. To bolster this information, officials conducted interviews with abutting property owners and made field investigations consisting of ground penetrating radar studies, probes and test pit excavations.
Because of its condition, traffic across the two-lane bridge had to be reduced to one-lane, and the structure was load- posted. An inspection by the Connecticut Department of Transportation indicated the bridge was structurally deficient and no longer wide enough to handle modern day vehicular traffic. These findings made the repair or replacement of the bridge eligible for funding under the state Local Bridge Program. Coventry subsequently sought recommendations from its consulting engineer, Nathan L. Jacobson & Associates, Chester, Conn.
The consulting engineer studied a number of alternatives for structural rehabilitation that would meet current design criteria from the state DOT and AASHTO while maintaining the aesthetic appearance of the bridge. After considering the current condition of the bridge, safety issues associated with the tailrace and current design criteria, the town engineer recommended a complete bridge replacement and removal of the tailrace tunnel within the limits of the new bridge construction.
A memorandum of agreement between the town, the state Historic Preservation Office, and DOT, the U.S. Army Corps of Engineers and the Advisory Council on Historic Preservation provided for documentation of the existing bridge prior to its removal, in accordance with the standards of the Historic American Engineering Record, as well as archaeological monitoring and documentation of the bridge foundations and tailrace tunnel sections removed during construction.
The town requested that the replacement structure be designed to retain the old bridge’s historic look while meeting the current AASHTO and state DOT design criteria. After considering several bridge types, the engineer selected a pre-cast reinforced concrete rigid frame structure with a clear span of 20 feet, a rise of 10 feet and a traveled width of 24 feet. Cast-in-place reinforced concrete was selected for the parapets and wingwalls. A cast-in-place concrete footing supported on timber pilings was included in the design to prevent undermining of the bridge foundation caused by scouring of the stream bed during high stream flows.
A simulated stone masonry form lining and color staining process were specified for the exposed faces of the cast-in-place parapets and wingwalls to retain the bridge’s original appearance. Steel backed timber guide railing, designed to meet AASHTO criteria, was specified for the bridge and roadway approaches.
The contract for construction of the bridge was awarded to Milton C. Beebe & Sons, Storrs, Conn., and was completed within five months. Concrete Systems, Hudson, N.H., provided the pre-cast rigid frame under license from CON/SPAN Bridge Systems, Dayton, Ohio.
The simulated stone masonry and color staining process were supplied by Connecticut Bomanite Systems, Newtown, Conn., under license from Custom Rock International, St. Paul, Minn.
Once the cast-in-place concrete parapets and wingwalls were cured and form markings removed, the exposed faces were color-stained to create the appearance of natural stone masonry. Weathering steel was used for the steel backing plates of the guide railing, and the timber posts and rails were treated with an oil-borne preservative to minimize future maintenance. A new granular base and bituminous concrete pavement were placed on the bridge and its roadway approaches, and stone riprap was placed along the stream embankments to prevent erosion.
Construction of the bridge was completed on time and under budget for about $348,000. DOT and other officials have given it rave reviews, and the Portland Cement Association honored the bridge with an Award of Excellence.
Sophisticated technology clears tunnel gases
Recently, the Massachusetts Turnpike Authority had to find a more efficient air monitoring and filtration system for the increasingly crowded Prudential Tunnel.
Controls for huge ventilation fans on its aging 1960s era filtration system emanated from terminal boards loaded with electro-mechanical relays. Hundreds of miles of multi-colored wires led to the fans to respond to a gas sensor that measured the carbon monoxide (CO) in various sections of the tunnel, which runs under Boston’s famous Copley Square.
A malfunction would often require hours of hit-and-miss guesswork to locate the failed unit and replace it. To protect tunnel users, employees had to maintain a constant alert. Fans were often kept running more than necessary to make sure the CO was kept under control, a system neither energy- nor labor-efficient.
Turnpike engineers’ original request was for a microprocessor-based control system, but when Interscan Corp., Chatsworth, Calif., read the quote request, the company realized it had an opportunity to break new ground.
Rather than reinvent the wheel, the company decided to employ technology that has been around for years — the programmable logic controller (PLC) — to fulfill the requirements for automation.
For the Prudential Tunnel, the PLC helps perform a much wider variety of tasks than would have been possible with the microprocessor by itself. Through a touch screen, an operator can access any one of six different functions and make a variety of changes if necessary.
For instance, an operator can control ventilation at any time of day, check CO readings at high-traffic locations or focus on monitoring a single channel. If an accident causes an unanticipated traffic flow change, for example, the CO samples can be accelerated to ascertain whether fan speed adjustments are needed.
The automatic controls have enabled turnpike employees to spend less time in the tunnel, releasing them for other duties. A substantial energy savings also is realized since fans are turned on only as directed by the amount of CO in the air.