Those familiar with the Philadelphia construction market tend to associate JJA with the region’s most established companies. JJA only dates back to 1981 when founded by Jim Anderson. Since then, the company has expanded its expertise into nearly every aspect of heavy civil construction. Expansion into new areas is in JJA’s DNA.
JJA’s rectangular 700-foot-long jobsite – just inside the main gate of the Navy Yard – is a straight shot connecting Crescent Drive to Intrepid Lane. To the right, towering ships anchored in the square-shaped pocket of the Delaware River dwarf most of the construction equipment on site.
From an engineering standpoint, this project was necessary to abate the subsidence of Broad Street due to hydraulic erosion. “The old seawall was cracked and leaking, allowing water underneath Broad Street,” explains JJA’s Chief Engineer Bob Crawford, P.E. “This area undergoes a 6-foot tide, so the water goes up and down in the Reserve Basin 6 feet twice each day. The tidal ebb and flow getting through the seawall was undermining the roadway to the extent that they had to shut down a portion of Broad Street.”
The joints in the existing cast-in-place concrete wall – located 20 feet apart – had widened over time. Every time the tide rolled out, small amounts of soil were removed.
JJA has been at work on this project since June 2022, according to Crawford. “There was an existing concrete seawall sitting on a timber deck,” he says. “Our overall scope was first to drive a line of NZ 38 sheet piles to create a new 700-foot steel seawall behind the existing concrete wall, then remove the old seawall and timber deck on which it sat, and drive 12-inch epoxy-coated piles in front to support a new concrete pedestrian walkway.”
“The new steel seawall had to be anchored to a concrete tieback sitting on batter piles,” says Crawford. “The tieback sits 50 feet behind the seawall. The 3-inch diameter galvanized tendons go from the steel seawall back to the concrete tieback. Once that system and the utilities are all in, we reconstruct the Broad Street roadway, new sidewalk, bike path, and pedestrian plaza.”
To construct the concrete tieback anchor, JJA drove 79 18-inch and 79 16-inch pipe piles, which were designed to be 80 feet long and driven on a 2V:1H batter. During test pile installation, it was determined that there were locations on the project where the tieback piles would need to be spliced and driven more than 100 feet to achieve design capacity due to changing soil conditions.
“None of the pipe piles on the project are seated in rock,” Crawford says. “The 16-inch compression piles and 18-inch tension piles both derive their capacity from predominantly skin friction with only a minor contribution from end bearing for the compression piles.”
“We’ve seldom done friction piles so this was an experience to go through the test pile program and all the dynamic analysis iterations with Urban Engineers to determine that the production piles will attain the design capacity,” says Crawford.
Since past work was performed with a crane-mounted hammer, JJA was first-time customer for Junttan USA. Junttan USA rented JJA a PMx28 Pile Driving Rig with HHK5S Hydraulic Impact Hammer to drive the pipe piles in October 2022, while the contractor simultaneously scheduled a rig from another vendor to vibrate in the sheet piles. When that rig became unavailable due to an emergency project, Junttan USA’s Sales Engineer Matt Eastburn saw an opportunity to expand the role of its rig.
Junttan USA had never rented a rig with a vibro package and leaned on its partners in Canada to supply the package to be installed on the PMx28. The cross-continental partnership paid off.
“For the sheet piles, we had the rig equipped with a PTC variable moment hammer, so we had to mount the power pack on the back,” Eastburn explains. “We took off the counterweight and essentially used the power pack in its place.”
Junttan USA had Junttan Canada ship the vibro and power pack to the Navy Yard where the PMx28 was waiting. JJA provided crane support on the assembly. The transition between vibratory and standard pile driving was seamless.
When the time came to drive the 16- and 18-inch-diameter piles, the vibro components were removed, and the counterweight and HHK5S hammer were re-installed. Aside from a small portion where a Philadelphia Water Department culvert pokes through the seawall, all pile driving was ultimately done using the Junttan PMx28.
“We did all the engineering in house,” explains Eastburn. “Junttan USA installed the vibro kit, which was supplied by Junttan Canada. They had retrofitted it to a PMx28 they had in stock. Junttan Oy is always supportive of our companies, but their main role here was engineering work for the batter piles.”
“The most challenging part of the engineering we had to do was the stability analysis to ensure that the rig wasn’t going to tip over while holding the 2V:1H batter and the 8,000-pound pile and 23,500-pound hammer,” says Eastburn. “With the elimination of a portion of the counterweight, we were able to lay the leader back with a full length pile.”
“Junttan was amazing,” says Crawford. “Matt did a balancing act with the weight of the hammer. I don’t know if it’s near the limits of the PMx28’s capability, but it’s probably pretty close to get 26 degrees of incline and hold all that weight in place.”
“We’ve done batter piles before, but not quite this extreme,” Crawford says. “At this angle, we would have needed significant anchored false work to maintain the pile angle at such an extreme batter.”
Crawford also believes its conventional equipment would have faced other challenges in this application. “We’ve had problems in the past with diesel hammers on significant batters. Diesel hammers tend to misfire when tilted. We don’t have that issue with the Junttan hydraulic hammer.”
Although JJA has experience installing batter piles of lesser degrees, 26 degrees was a batter it had never encountered. This angle was necessary due to the heavy loads such as large trucks and transports that will enter the Navy Yard on Broad Street. Because these live loads will exert high lateral pressure on the new steel sheet pile Seawall, they had to be counteracted by the batter piles in the tieback anchor.
Due to the extreme batter, JJA required a follower to drive the batter piles the final few feet to grade. Junttan USA suggested the idea, but did not supply the follower itself.
Steve was accustomed to operating JJA’s standard setup – a crane with diesel hammer. Junttan USA sent in a tech and provided on-site training, which included an in-depth assessment of the rig’s components and how to operate it. In addition to being a quick study, Steve had studied the manual prior to training.
“Steve had quite the learning curve at the beginning, but once he got to know the machine, he was off to the races,” says Eastburn.
Since JJA had never used a Junttan rig in the past, production was a serious concern, especially considering that the piles were to be driven with a 26-degree batter. JJA was ultimately able to meet or exceed estimated production for the installation of the sheeting as well as the batter pipe piles.
Although Crawford acknowledges that the PMx28’s ability to hoist and drive piles without falsework was the main factor for choosing Junttan, the operator’s ability was also factor. He says, “There’s a learning curve, of course. But once it has been overcome, production reaches where it needs to be.”
The narrow 700-foot-long site also made using a crane-mounted diesel hammer with leads and bottom falsework prohibitive, according to Crawford. “The crane would have
to be positioned to control the top end of the leads where a majority of the pre-driving weight is located,” he says. This would then require falsework at the bottom of the pile to maintain orientation and position. After completing one pile, we’d have to move the entire set up ahead every time. With the Junttan, it’s self-contained. It holds the pile and moves it ahead without expending time to disassemble and reset falsework.”
The sheet piles were driven straight and accurately as well also without the need for alignment falsework. At the completion of driving the steel sheet pile seawall, JJA had to connect a double channel waler to the back of the sheet pile to accept the tieback tendon connections. The adjustments needed to attain proper bearing for the waler attachment were all less than 1 inch.
Junttan USA’s Eastburn adds that having a single rig offered JJA easier setup, better site access, and less equipment to maintain. He says, “Our PMx28 setup is transported in three loads – one lowboy for the rig itself and two falloff loads on standard flatbeds for the hammer and counterweights. It requires a little bit of machine support to assemble, but once it’s set up, you can track back and forth to each pile on site.”
During installation of the 16-inch pipe piles for the tieback anchors, JJA encountered the remains of a 700-foot-long timber bridge from the 1800s about 11 feet down. The bridge had once connected Broad Street with this area of the Navy Yard, which was once known as League Island.
The Pennsylvania Historic Museum Commission determined that the underground structure had low historical significance, so JJA was permitted to put points on the 16-inch pipe piles to penetrate the bridge wall, which was comprised of 6- and 12-inch timbers. The tips allowed the contractor to drive 16-inch piles through roughly 2 feet of wood using the PMx28.
“If you’re driving a pile on a batter with a crane and leads and a timber wall is there, the pile will slide down the wall trying to find a weak spot and then penetrate there,” says Crawford. “This pushes the pile off of its design location and orientation. The Junttan held it where it had to be, so we were able to keep the pile on its designed line while penetrating the wall. The point penetrated and the hammer held up well under this added stress.”
The pile driving challenges were not just under the ground. The Navy Yard is densely populated with buildings connected by a labyrinth of narrow streets and 90-degree turns. Transporting 80-foot-long piles on a 100-foot-long trailer was a logistical challenge, especially with the historic sycamore trees that bordered the site.
PIDC agreed to prune the fronts of the trees to provide access for the piles and the Junttan rig. “PIDC needed a good reason just to prune them,” says Crawford. “To get approval to take them down would require an act of Congress.”
He continues, “If we’d have done this pile driving conventionally with a crane boomed over those trees, it never would have happened. We don’t have the space or clearance to fit a rig holding a 26-degree batter through the tree canopies. Booming back just the mast of the Junttan rig where the trees had been pruned in the front worked for us, and more importantly, worked for PIDC.”
JJA finished its pile driving work with the Junttan setup in July 2023, but continued marching toward the timely completion of the project in December. As drivers and pedestrians enter the Navy Yard, they will see freshly paved roads, newly constructed granite clad wall with recreated stone piers, a new pedestrian walkway with extensive landscaping, but will never realize the complex geotechnical challenges below that were overcome by a forward-thinking project team and a willingness to break out of the comfort zone and engage with new equipment technologies.