Pile swap and custom tooling saves money for contractor
Challenging contract calls for shift in piling type and support from Bauer rigs
Linde-Griffith Construction Company was called on to assist when the original contractor on a condo project was unable to reach bearing capacity on a test pile program. The end result was a cost-saving switch to Full Displacement Piles (FDP) using a Bauer BG 36 H Drilling Rig and custom tooling.
Linde-Griffith – founded in 1909 – was primarily a pile driving contractor until about 20 years ago when it expanded into foundation drilling. "We've seen more and more engineers seeking techniques that offer greater capacity with less noise and vibration," says Linde-Griffith's Senior Executive Vice President Mike Shannon.
In the midst of apartment buildings and businesses, the yellow mast of a Bauer BG 36 H Drilling Rig towered more than 90 feet over the landscape. The Linde-Griffith field crew braved 30-plus-mph winds and single-digit windchills as the linchpin machine of its FDP operation bored through the frosty soil.
The Hackensack project started out as a driven pile project. The previous contractor had run a Pile Driving Analyzer (PDA) Test and was unable to reach the design capacity despite installing various pile types to depths of up to 175 feet.
The owner and engineer reached out to Linde-Griffith's John Shannon looking for ideas.
Linde-Griffith suggested using FDP piles. Mike Shannon summarizes the FDP technique: "The piles don't rest on rock here, you get your load bearing because the displacement and compaction of the soil, and grout column build up enough friction to meet capacity."
"The results were impressive when we Static Load Tested the piles," recalls Shannon. "We were able to achieve the loads they needed with a 55-foot FDP pile."
The switch to FDP piles was also the most environmentally sound choice, according to Shannon. "They did all the remediation but still didn't want any material to be exported," he says. "FDP allowed us to keep all soils in the ground where they belong."
BG 36 H the centrepiece drill
The FDP operation revolved around the BG 36 H Drilling Rig. Linde-Griffith owns a fleet of drilling rigs, including two Bauers acquired from Equipment Corporation of America's (ECA) New York/New Jersey branch.
It was January 2018 when the BG 36 H executed test piles at Hackensack. The original plan was to have two rigs driving the FDP operation. The other was to be a BG 28 H.
By the time permitting and environmental delays had been cleared, Linde-Griffith's BG 28 H was tied up on other projects. It was agreed that the BG 36 H would be the only drilling rig on site.
Linde-Griffith worked with ECA to equip the BG 36 H with 510-mm (20-inch) FDP Tooling to drill 1,322 FDP piles from 52 to 57 feet. Each pile consisted of a 20-inch grout column with a 10-inch-by-1/4-inch hollow pipe in the centre to provide additional shaft friction. The FDP piles created enough shear and base resistance so landing the pile on competent rock was unnecessary.
Linde-Griffith executed each FDP pile in a sequence. First, the displacement tool bored down to the desired depth to loosen and densify the surrounding soil, leaving an open excavation. 4 1/2 to 5 1/2 cubic yards of 5,000-psi grout was then pumped into each hole under pressure through a hollow drill stem as the BG 36 H extracted the displacement tool.
The rotation of the tool densified any loose material. The reinforcement cage was then dropped, and in some cases vibrated, into the fresh concrete to finish off the pile.
"On an auger cast pile you're relieving the pressure of the ground as you're drilling down and the spoils are coming out," Shannon explains. "Here, you're actually creating more pressure because the soil is staying in the ground and pushing against the sides."
The FDP piles were laid out in a grid pattern with single piles around the perimeter for grade beams and caps containing up to six piles for areas supporting the heaviest column loads.
Drilling was not especially challenging in these soil conditions, but the grid pattern and FDP process itself caused increasing resistance with each pile. "In these clusters," Shannon explains, "the first couple are always a lot easier because you don't have any resistance. But the more piles and concrete you put in, the more you're displacing and densifying the soil around the existing piles and it gets tighter and tighter."
Another challenge was that Linde-Griffith had to maintain a 10-foot distance from piles with uncured concrete.
"It's based on how your layout is with the spacing of your piles, and how you plan," says Shannon. "With this type of pile (FDP), you need to really project two to three days ahead to maintain production."
FDP tooling critical to operation
Bauer tooling was critical to the FDP operation, according to Shannon. "It's all Bauer displacement tooling designed specifically for this project," he says. "It was engineered to achieve the required loads with these soil conditions."
Friction was an issue. The soil conditions and grout acted like sandpaper on the tooling, especially the displacement bulb above the auger flight and the cutting teeth on the wear plates.
"Quality control is very important out here so we change the tooling out once a week," says Shannon, noting that extras are on hand at all times. "Then we just refurbish, re-weld, hardface, and bring them out when we need them."
"The main concern on this job was that a driven pile couldn't achieve the load required," says Shannon. "Our decision to bring in the larger 20-inch full displacement tooling combined with the quality control this machine offers made this project. The amount of information you get from that machine is unique and very impressive."
The quality control Shannon speaks of is driven by the patented Bauer B-Tronic System. Both Linde-Griffith and the project's third-party engineer have access to such data as stroke count, grout pressure, and drilling depth via a desktop computer or mobile device. There is no second-guessing whether a pile is driven to the proper depth and contains the right amount of concrete. There was also a safety benefit since the engineer was able to monitor drilling from a safe distance because B-Tronic transferred the operator's view to an iPad.
The B-Tronic System doesn't simply provide data. It also has a feature called B-Drive, which automates monotonous operations. Linde-Griffith's operator, for example, was able to program the BG 36 H to drill to a specific depth by simply typing in parameters. During concrete placement, he plugged in the targeted grout volume and pressure. B-Drive automatically extracted the tooling once those numbers were achieved. Not only did this ensure a consistently grouted column, but it also allowed Linde-Griffith to share the exact amounts of concrete consumed with the owner.
"We have it set up where I can view it from anywhere," says Shannon, noting that he travels between sites all day. "I keep a laptop in my car so if I'm not here, I can see what's going on."
Linde-Griffith was installing up to 25 FDP piles in less than 10 hours each day, which could have been even higher. Productivity was hampered by shorter days, muddy site conditions, and up to 45 minutes spent cleaning the BG 36 H and tooling at the end of each day.
Linde-Griffith started drilling the first week of October 2019 and finished by February 2020. Strong production and smart planning resulted in the project being completed on schedule.
Brian M. Fraley is owner of Fraley Construction Marketing.
The article originally appeared in the May 2020 issue of Heavy Equipment Guide.