Tricky Blasting For Park & Ride

By Paul Fournier | September 28, 2010

Motorists unfamiliar with New Hampshire's Interstate 93 widening project might have been puzzled recently as they were forced to cut their speed in half for no apparent reason. Five minutes later they resumed their normal speed, unaware they had participated in a "rolling road block" while blasting took place for a new Park & Ride.

Led by New Hampshire State Police cruisers and Continental Paving trucks, the rolling road blocks are taking place once or twice a day as Precision Drilling and Blasting shatters tons of rock for the new Park & Ride off I-93's Exit 2 in Salem, N.H.

Rather than stop traffic altogether during blasting at highway projects, the DOT has been using the rolling road blocks successfully for some time, according to Richard Keegan, P.E., project engineer for the agency's Bureau of Construction.

Continental Paving of Londonderry, N.H., has the $6.4-million contract with NHDOT for all site work at the Park & Ride, which will provide parking for 472 vehicles and a full-service bus terminal, with Precision Drilling & Blasting of Lowell, Mass., subcontracted for blasting. Another contractor, Turnstone Corp. of Milford, N.H., is constructing the terminal building.

The Park & Ride is part of a $718-million project to widen I-93 from Salem, N.H., at the Massachusetts line to Manchester. Said to be one of the most ambitious projects ever undertaken by NHDOT, the widening involves constructing two additional travel lanes in each direction over the 20-mile section of interstate, making improvements at the interchanges at each of five exits, and replacing or rehabilitating 43 bridges. New Park & Ride facilities at exits 2, 3 and 5 will be built, and space within the highway median will be reserved to accommodate future commuter rail trains.

According to Peter Stamnas, project manager, the project will eventually encompass about 20 construction contracts. At the time of this report, it was approximately 5-percent complete, said Stamnas.

At the Exit 2 Park & Ride, one of the biggest construction challenges is the extensive amount of blasting that has to take place on a site hemmed in by I-93 and a number of industrial buildings, including one containing exotic automobiles.

"This used to be a dimensional stone quarry," said Bruce Eaton, blasting foreman for Precision Drilling and Blasting. "The rock is hard granite, it's full of vertical, horizontal and diagonal seams, and it's wet," said Eaton. The character of the rock, its proximity to industrial buildings — and even some large propane fuel tanks — plus the need to clear traffic from I-93 when shooting mandate extreme care, he said.

His crews are using Tamrock Tiger Super CHA700 and Atlas Copco D3 drills to bore the 3-1/2-inch holes for explosives. Drilling needs to penetrate rock at least 3 feet below subgrade for utility trenches and the building pad, resulting in holes usually between 9 feet and 10 feet deep. They're using dynamite and packaged emulsion explosives from Dyno Nobel and shooting anywhere from 300 pounds to 500 pounds per blast. The closer the buildings, the smaller the shots, he said.

Eaton noted they're controlling breakage by careful spacing of drill holes, amount of explosives and pounds of explosives per delay.

Specifications call for noise levels to be less than 128 decibels, while blast wave velocity has to be under 2 inches per second. He said they hadn't exceeded 0.6 seconds, according to seismograph readings taken by Bedford, N.H., geologist Mike Nutting, who was hired to conduct pre-blast surveys and monitor the blasting.

Blasting has to take place during non-rush hours — 9 a.m. to 3 p.m. — on weekdays. Coordination and cooperation among the contractors, NHDOT personnel, fire department, and State Troopers is closely maintained. And Continental Paving responds quickly to remove shattered rock from the scene.

"Continental has been really good about keeping up with us, quickly placing blankets before we blast and cleaning up right after," said Eaton.

Early estimates place the amount of rock to be blasted at about 10,000 cubic yards, but this could change as work progresses.

Work is also under way on other Park & Ride facilities. At Exit 4 Goguen Construction Company is nearly finished with its $1.4-million contract to build a bus terminal, while R.S. Audley has a $7.4-million contract to build a 443-space Park & Ride at Exit 5. The latter includes reconstructing a section of Route 28. Future plans for this area involve construction of a bus maintenance facility next to the Park & Ride.

The Park & Ride and bus facilities are an important component of the I-93 widening, and are geared to help reduce the bumper-to-bumper traffic that plagues this two-lane section of highway by taking a significant number of vehicles off the road.

Overall, the I-93 improvements are meant to address three main issues: safety, capacity/congestion, and condition of aging infrastructure, according to NHDOT.

Built in the 1960s, I-93 passes through five communities and includes sections of five state highways, as well as several other municipally owned and maintained roadways. It was designed to carry up to 70,000 vehicles per day but now has to accommodate 115,000 vehicles, leading to regular congestion and backups, and numerous accidents, many involving multiple vehicles. Safety is further compromised by substandard ramp and highway geometry at most of the interchanges, says NHDOT.

Each interchange (exit) has ramps with less than desirable grades and acceleration/deceleration lanes with less than desirable lengths. Furthermore, mainline grades are also greater than the desirable maximum at several locations. As traffic grows, notes the agency, the existing deficiencies will become more of a problem. Rebuilding I-93 will address these deficiencies by reconstructing each of the five interchanges, improving grades along the mainline and increasing capacity.

The condition of the highway and its bridges is also a main concern. Roadway, bridges and interchanges are at least 40 years old and need major rehabilitation and modernization. Fourteen of the 43 bridges within the Salem to Manchester corridor are on the state's "Red List."

Prepared by NHDOT's Bureau of Bridge Design, the Red List includes those structures that have low Federal Sufficiency Ratings and require two inspections each year because of poor conditions, weight restrictions or type of construction. FSR values run from 0 to 100 — the lower the number the poorer the condition of the structure.

So regardless of improving capacity by adding lanes, says NHDOT, major work needs to be done along the I-93 corridor anyhow just to improve existing infrastructure.

Citing the fact that I-93 is one of New Hampshire's principal arterials, transportation planners believe this huge, complex project will make the highway safer and improve its citizens' mobility.

And that is critical to the economic vitality of the state, the region and local communities.