Nothing left standing

By: Rodney Garrett, Contributing Author

At last, construction at the “Big Dig” (the Central Artery/Tunnel Project) is about to end with the completion date targeted for 2005. News about Boston’s Big Dig is no longer big. For the last 10 years, the public has been inundated with the happenings of this project covered by the news media and by the numerous documentaries broadcast on cable television. It was indeed well-covered, as it should have been, because of the project’s magnitude. It is arguably “the single largest, most complex highway [tunnel] project on the planet,” according to Matthew J. Amorello, chairman, Massachusetts Turnpike Authority (MTA).

MTA is the manager and operator of the project. Started in 1991, the newly constructed tunnel complex is an eight-lane leading to a 10-lane expressway, which links at the north end to recently built viaducts and the new Leonard P. Zakim Bunker Hill Bridge that crosses the Charles River. There also is a link to the Massachusetts Turnpike that heads west through the state. Another segment of the tunnel complex will lead I-90 beneath South Boston and Boston Harbor to the Logan Airport. Amorello said the new highway system will virtually eliminate the daily downtown 10-hour traffic jams. Once the outdated Central Artery, which runs above the new tunnel alignment, has been razed, there will be 27 acres freed up for building parks and plazas.

Careful where you drop it

The Central Artery is currently being demolished. The reason to construct the new tunnel system in the first place was to eliminate the outmoded artery that was grossly under capacity for accommodating 190,000 vehicles that use it daily. If there ever was a bottleneck in Boston’s highway system, this was it. The Central Artery was directly responsible for virtually all traffic snarls experienced downtown.

Demolishing the 1.4-mile-long viaduct presents a challenge because it is necessary to change daily the flow patterns of the traffic and the pedestrian walks to ensure both can safely move about in the downtown area. The risk of falling steel or concrete from the elevated highway, while dismantling it, would be a safety issue if the traffic patterns were not altered to correspond to the frequently changed active demolition sites.

Separate demolition contracts were awarded to Modern Continental Construction Co. and J.F. White Co., both headquartered in the Boston area, who in turn subcontracted the demolition work to the Testa Corp., Lynnfield, Mass. Testa is a diversified contractor with activities in site development projects, marine construction, crane rental services and demolition. The latter is one of its leading activities.

Testa’s contracts with Modern Continental and J.F. White have a combined valued of $40 million. Both contracts call for the demolition of not only the elevated highway (including a truss bridge) but all its access ramps. The artery is built of structural steel with steel-reinforced concrete roadways.

A contract description of Testa’s work responsibility, as outlined by the MTA, is as follows: demolish the two-level viaduct approaching and including the double-deck truss bridge spanning over the Charles River and the same viaduct extending south (including the temporary one) that totals 1.4 miles in length. Testa is responsible for not only the demolition but the removal of all demolished construction materials, which must be disposed of in accordance with all government regulatory agencies. This includes lead abatement procedures, which has been subcontracted to the Aulson Co. of Boston.

While some of the demolition work was accomplished last year, the main project did not get started until last December. Testa mobilized 50-plus major pieces of equipment to the project site between the Christmas and New Year’s holidays. The big equipment includes Caterpillar and Komatsu hydraulic excavators (including the largest Komatsu construction excavator marketed in North America), a special model Gradall excavator, Manitowoc, Mantis and Grove cranes and Vermeer track machines.

Shears that wag the excavators

While the equipment mentioned is of necessity for demolishing the viaduct and truss bridge, most of the excavators could not function effectively here without their fitted mobile shears and grapples. Shears and grapples are essential to cutting the concrete roadway into portable slabs and placing them on trucks. Likewise, they are used to cut up the structural steel in sizes that fit onto tractor flat-bed trailers. Testa’s choices of shears are models manufactured by Stanley LaBounty.

There are two main reasons Testa chose the shear-and-grab method for demolishing the viaduct. One is for the sake of its inherent safety. It means workers need not be positioned precariously at high places on the viaduct for cutting the structural steel by burning it with an acetylene torch. The other reason is one of “shear” economics. Shearing is the most productive way to cut up in situ structural steel. The grapples work in concert with the shears by grabbing the cut steel pieces and loading them onto the trucks. If an I-beam is too heavy for the grapples to lift, a crane lifts and loads it onto the truck. Another function for the grapples is to load the pre-cut concrete paving slabs onto trucks.

The jaw capacities of the shears are wide with a deep throat for taking big bites into any type construction materials. There are three different models of shears owned by Testa. Seven are model MSD 100, two are MSD 175 and three are MSD 200. Besides the 12 shears, the company owns 20 Stanley LaBounty grapples, one UP 90 universal processor, two CP 80 concrete pulverizers and seven CP 100 concrete pulverizers. The model MSD 200 is the largest mobile shears commercially available in North America.

Over 100,000 tons of structural steel will be dismantled and hauled to an off-site scrap yard for cutting into ship-transport sizes for export. Additionally, 100,000 cu yd of concrete are to be broken up and removed from the project for recycling by crushing and screening.

Breaking it down

The truss bridge to be demolished is a 376-ft-long (880 ft including the approaches) double-deck type that runs very close by the Leonard P. Zakim Bunker Hill Bridge. Two Manitowoc model 2250 lattice-boom crawler cranes (300-ton lift capacities) are being use for dismantling all the structural steel. One crane is on a barge so it is closer to the middle of the bridge for making short-radius lifts of structural steel pieces as they are cut. Many of the cut pieces are 50,000 lb each.

Demolishing the bridge’s double-deck concrete roadway (each level has six lanes) presented a special challenge to Testa because the outside lanes have massive parapets. The parapets were constructed with heavy-gauge rebar embedded profusely in a monolithic cast-in-place concrete. Using shears was not considered to demolish the parapet because it does not have the capacity to cut through such thick concrete.

A hydraulic hammer mounted on a hydraulic excavator also was not considered because the concrete is certain to spall with the pieces landing on railroad tracks (or trains) below. One section of the bridge is in close proximity to the Leonard P. Zakim Bridge where there is a constant flow of traffic. Safety would thus be an issue if a hammer were to be used.

To address this quandary, Testa is using two new Vermeer model T555 Commander II track trenchers mounted with 9-ft-diam. Vermeer Rockwheels. The Rockwheels are circular saw blades designed to cut steel-reinforced concrete. Crosscuts into the parapet are made every 6 ft with the track trencher. This crosscut procedure creates only harmless pebbles, sand and dust at the kerf as it is cutting the concrete. Once the parapet is cut into the 6-ft sections, they are picked up with the grapples and loaded onto trucks.

Next, 7-ft-wide longitudinal cuts are made in the bridge’s concrete paved roadways using the same track trenchers. Once the longitudinal cuts in the paving are completed, Stanley-LaBounty model MSD 100 shears attached to 100,000-lb Caterpillar excavators are used for transverse-cutting the steel-reinforced paving into 10-ft x 7-ft panels. These panels are loaded onto trucks using grapples and hauled from the demolition site to the portable crushing/screening plants located nearby in Boston.

All the crushing/screening activities are carried out by third parties. Here, the rebar is segregated from the crushed concrete. Crushed and screened to suitable aggregate sizes, the concrete is sold to road-building contractors and the steel to scrap handlers. Virtually all demolition materials coming from the demolition project are recycled. All the steel is being exported. To that end, the dismantled structural steel is cut into suitable shipping sizes at the scrap yard and loaded into the hold of a nearby harbored ship. Cutting the steel to shipping sizes is accomplished using six big hydraulic excavators fitted with two Stanley LaBounty MSD 200, two MSD 100 shears and two Stanley LaBounty 200 HDR grapples. One of the shears is an MSD 200 R rotator, which is mounted on a big Komatsu 1100 excavator. The function of the rotation is so the shears’ jaws can be indexed to bite into the steel no matter how the steel is oriented.

Specialized equipment on parade

The company’s vice president and chief field operations manager, Eric Johnson, made a complete equipment-requirement evaluation for carrying out the artery demolition project at the outset. By determining what demolition procedures would be taken, he and Steve Testa, owner, decided what equipment to use. Besides many pieces of equipment already in the fleet prior to this project, over $12 million in additional equipment was purchased to carry out the work.

Specialized mobile/portable equipment (i.e., shears, grapples and track trenchers) are playing a major role on this project. Fortunately, the specialized equipment lends itself to demolishing not only roads and bridges but also buildings of all kinds. This specialized equipment is versatile, albeit for demolition work, and is why Testa can justify the latest and best of the equipment for this project. When the project is completed, the equipment will be moved to other demolition jobs involving the demolition of buildings, roads or bridges. However, many roads and bridges contractors who are not involved directly with demolition work will find it more cost-effective to contract a demolition specialist, such as Testa, rather than attempt it on their own.

Testa’s vice president and CFO, John Ruffo, said choosing the most efficient equipment for a demolition job is important for assuring its financial success. Ruffo’s responsibility is to monitor the cost-effectiveness of all equipment in the fleet, including the specialized equipment. He said, “I keep close track as to the cost of equipment, which includes unscheduled down time and productivity. I see equipment in the fleet as either an asset when it is working or a liability when it is not. If any equipment is not utilized at a high rate for any reason, I quickly sell it.”