Concrete Cutting Helps Prevent Environmental Disaster

Tue September 15, 2009 - Northeast Edition
CEG

The cut pieces were removed so that leaking fuel tanks could be fixed.
The cut pieces were removed so that leaking fuel tanks could be fixed.



North America’s largest transportation network, the New York City Metropolitan Transportation Authority (MTA), spans a 5,000-sq.-mi. area fanning out from New York City through Long Island, southeastern New York State and Connecticut. Since the first New York subway opened in 1904, the transport network in the metropolitan area has grown exponentially. Today, the MTA handles on average over 8.5 million passengers a week.

With 422 bus routes, rail and subway lines, measuring almost 6,000 mi. combined, the MTA has a massive undertaking in ensuring that the subways, buses and railroads provide New Yorkers with 2.6 billion scheduled trips each year in a safe and timely fashion. Any potential or actual problems have to be dealt with efficiently and safely, causing minimal disruption.

In September of 2008, the New York City MTA faced a unique environmental challenge at the Spring Creek Depot in Brooklyn. They needed to reach through 30 in. (76 cm) of reinforced concrete — not the expected eight — to fix six leaking underground diesel fuel storage tanks.

Seemingly out of reach, diesel fuel was leaking underground and mixing with seawater. Typically, MTA’s general contractor, The Franklin Company of College Point, N.Y., would have considered traditional demolition methods to gain access — a widely-accepted solution. However, this was not a typical concrete cutting job. MTA policy prohibited such action above active piping and tanks out of concern potential damage and rupture. Complicating matters further, the diesel fuel tanks were not only needed for this still-active bus depot, they were in a very public area of Brooklyn. The contractor and MTA realized that complexities like these demanded specialized skills and tools.

Precision saws capable of cutting through 30 in. (76 cm) of concrete and rebar were required. The task also demanded the problem-solving skills of experienced craftsmen who could operate the saws and avoid creating dangerous vibrations, which could further damage the tanks. Existing electrical wiring and piping surrounding the tanks further complicated matters and required a careful approach.

MTA and the general contractor decided to call Indiana-based CSDA member WF Meyers Company Inc. to carry out this complex cutting task. Project manager Gary Hall explained that there were three key prerequisites for successful project completion: special cutting equipment, delicacy and project management skills.

“First, we felt our diamond belt saw would work extremely well in this application. While saw cutting, we had to minimize noise and keep the site environmentally safe, containing the slurry by sandbagging the work area. Essentially the team created a canal that moved the runoff so that they could pump the water and slurry into a frac tank,” Hall explained. “Don’t forget,” he said, “the work had to be performed while the bus garage still operated.” The company used its own diamond belt saw to cut approximately 700 lineal ft. (213 m) at a depth of 30 in. without having the luxury of drilling holes because of the delicate nature of the oil tanks.

The 8,000-lb., (3,629 kg) track-mounted diamond belt saw was chosen because it can cut deep concrete without overcutting. In addition, the saw causes little disruption by cutting with minimal noise and vibration, helping to maintain the structural integrity of surrounding buildings and structures. The saw can produce fast cutting speeds of up to 200 sq. ft. (18.6 sq m) per hour, and cuts to depths of up to 16 ft. (4.8 m). Water is used to flush out the cut, ensuring dust-free operation. Only one person is required to operate the saw, and this person is responsible for programming the cutting parameters and monitoring the progress of the cut. The machine stands 6 ft. (1.8 m) tall, measuring 7 ft. (2 m) in length and 34 ft. (10 m) in width, and is capable of cutting 2 to 3 in. (5 to 7.6 cm) of concrete per minute and .075 to 1 in. (1.9 to 2.5 cm) of steel rebar per minute, depending on the depths of both materials.

Using a blueprint to avoid damaging the maze of electrical wires and pipes, the cutting crew guided the saw through the two layers of concrete as it cut an area above each tank. The cut concrete now allowed access to expose the piping and tank sumps. WF Meyer used the diamond belt saw in delicate balance with a frac tank and mud pump to dispose of the water and remove the remaining concrete. They then used a vacuum to detach pea gravel and stone from the site. This process exposed the complete tanks for repair and new seals and led to the replacement of all faulty and compromised piping.

The biggest challenge faced by the WF Meyers crew was the cutting of the rebar. Furthermore, the varied size of the rebar, typically measuring 0.625 or 0.75-in. (1.6 or 1.9 cm) in diameter, forced the crew to adjust the pressure of the cutting and perform the task manually. Although difficult, the problem was handled by the constant monitoring by the crew. The only other delay encountered by the crew was when cutting needed to stop to replace worn saw belts. The crews always carried spare diamond cutting belts for such occurrences, so the cutting process was never shut down for an extended period of time.

The saw used by the diamond belt saw for the cutting was powered by a 75-hp (56 kW) motor, working off three-phase electricity. The highly-advanced saw used for performing the cuts can be powered automatically or manually. However, in this application the saw was predominantly used manually by the operator. As cutting commenced, it was noted that the saw cut faster when used manually, so the operator was able to make quick adjustments when encountering thicker concrete or rebar. The saw is typically slower when set automatically because its parameters will not allow it to over-amp.

In terms of usage, the saw required approximately 50 to 75 gal. (189 to 284 L) of water per-minute at 50 to 80 lbs. of pressure. The crew ensured a constant water supply to cool and guard against premature wear of the diamond belt. As water feeds underneath the side of the belt through the hollow core guide bar, the diamond belt hydroplanes on the guide bar and avoids contact with any metal surface.

“WF Meyers came in with the tools that were necessary to cut the thickest of concrete,” said Franklin Company engineer, Robert Laga. “We would work with WF Meyers again in a heartbeat. There was no other way the job could have been completed as effectively and creatively.”

Over the two-month period of the project, a total of 700 ft. (213 m) of concrete was cut. The crew performed cuts of 15 and 50 ft. (4.6 and 15 m) in length through 30-in.-thick concrete. Cutting speeds varied due to the location and thickness of embedded rebar. On average, it took approximately 2.5 hours to complete each 15-ft. cut.

CEO Ken Barnes said, “The Spring Creek job is a clear example of how versatile we are and how our capabilities continue to extend further and further across industries.”

Reprinted courtesy of the Concrete Sawing & Drilling Association, Concrete Openings magazine, June 2009.