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The Grouted Helical Micropile:
As I have noted in the past, one of Danbro’s (and our installer network’s) unrivaled strengths is our accumulated knowledge and experience with the Grouted Helical Micropile, easily surpassing that of any other distributor/dealer group in the country. Initially, we got in on the ground (pun intended) floor when Chance, our original supplier, registered their patent, giving us a seven-year head start on the competition. In addition, there were other circumstances which accelerated the learning curve for Team Danbro.
In New Jersey, during the 1990s, helicals became the product of choice for structural support in the environmental remediation business. Generally, environmental remediation involves the removal of spoils, created when old, rusted-out oil tanks leech contaminants into the soil, from beneath residences and businesses. During the process, the structures were supported on deep foundations while the soil spoils were removed. The helicals needed to be grouted since the piles were ultimately exposed and unsupported after the contaminated soil was removed. This application accounted for more than twenty-five percent of the helicals our dealers installed during that period. Click here for Remediation Case Studies
Super Storm Sandy also generated demand for grouted helicals since the structures needed to be cribbed-up out of the flood zone and supported on piles. Because driven piles require moving the structure in order to drive the piles, thereby creating expensive logistical and safety dilemmas, helicals were both a cost-and-time-saving safe alternative. Again, the helicals needed to be sleeved and grouted to compensate for buckling concerns. Both New Jersey’s and New York’s programs accepted the concept as did the “Build Back Better” program on Long Island. Over the years, we have installed Grouted Helical Micropiles throughout the Northeast and Mid-Atlantic States. Click here for When In Doubt, Grout Article
Finally, the nature of the unstable soils in our territory lends itself to grouted piles. This pile eliminates buckling, lateral, and corrosion concerns. The uncased version also provides increased capacity from skin friction from the grout column, which can be a cost-saving alternative to other piling systems.
Danbro’s hashtag, “Been There Built There”, broadcasts that, in the helical realm, we have seen it all and done it all. As it relates to Grouted Helical Micropiles, nothing could be truer… until the Kay Drive project in Cherry Hill, New Jersey!
Every aspect of this remediation project, including mobilization, access, and depth of excavation, presented extreme and unique challenges. Borings from the delineation survey indicated a soft silty clay and, instead of a typical spread-out, umbrella-like contaminated zone, the oil stayed within the footprint of the structure, but went extraordinarily deep. This prompted a very deep excavation, which, in turn, required sheeting and shoring in the deep pit, in addition to the normal grouted underpinning piles supporting the house in compression. The home is architecturally significant with an original heat-radiating floor system and natural cooling stone roof, both of which were major innovations in their day. These considerations and the higher-than-normal loads eliminated the possibility of relocating the structure during the remediation process.
The project took 16 months as the job proceeded cautiously and slowly in sections. First, IDEAL 5.5 (schedule 80) pipe piles were installed 35’ with 28’ of grout-filled steel casing (27’ exposed) to meet the 40-kip ultimate load. Both underpinning brackets and modified beam seat brackets were used in termination. The beam seat brackets (2”X2”X12”) added a perpendicular 2”X 8” on top to accommodate shims to support the heavy concrete radiant floor. Cross-bracing was also utilized for added stability due to the unusual length of exposed pilings.
After the spoils were removed, lagging and tiebacks were installed. Due to the height of exposed piles, fragile soil conditions, and the length of the project, an innovative lagging system was also employed. It used welded angles on the steel piles (3”X 8”) and slid the lagging between the angles, since the traditional approach was deemed unsteady and unstable. The tiebacks (IDEAL 1 ½” Square Shaft) were installed in three rows. The first row of nineteen tiebacks was 6’ below grade and went 35’. The second row of nineteen was 15’ below grade and went 25’. The third row employed ten tiebacks, went 20’ below grade, and were 20’ in length. All forty-eight tieback anchors were preloaded to 1.3 design load with a 40 ton center hole jack and hydraulic pump.
Mobilization involved multiple machines to speed or accommodate various tasks. Over excavation was required, not only for the unusually deep dig, but also for the long gradual approach that was required to safely accommodate the transport of men, equipment, and material down into the hole. A 312 Excavator did the heavy lifting in removing the contaminated soil with smaller machines in the tight confines underneath the structure. A Dingo was used to drive piles under the house as it had to maneuver between vertical support piles. A Kubota 121 was used for the tieback work and perimeter foundation piles. Click here for Kay Drive Case Study
The significance of the Grouted Helical Micropile (cased or uncased) is that it eliminates or mitigates the concerns for buckling, lateral, or corrosion below grade, while also allowing for the use of helicals above ground. This significant innovation has greatly reduced design concerns with helicals providing design professionals with more tools for problem-solving. Art Koziol, the Installer on this challenging project, is not only one of the most experienced helical hands in the country, but he may also have installed more grouted helicals than anyone else. He is one of our longest serving installers and among a dozen or so with both extensive house-raising and remediation work. Danbro is fortunate to have a network of well-trained, experienced installers who have mastered the Art (pun intended) of the Grouted Helical Micropile. Click here for Grouted Helical Micropile Product Information
by Pat Haffert
Danbro Vice President