Spun out with helical piles?

Helical piles can be a good tool for underpinning existing structures and supporting new boardwalks and lightly-loaded buildings. However, like any piling system, there are limitations that impact the use of the system. We often hear of these common limitations and concerns from both design professionals as well as the geotechnical contractors who install them. In fact, many of our geotechnical contracting customers install both Ductile Iron Piles and helical piles and are very skilled at selecting the most appropriate tool for the job.

Have you had this conversation with your project team?

• The helical piles are getting hung up and can’t penetrate the urban fill.
• We can’t reach the torque requirements specified for the job and now the pile capacity is reduced.
• What’s the capacity when the piles are “spinning out” on rock or dense ground?
• We need greater pile capacity to optimize my foundations, but we don’t think the helical piles can get the higher capacity in these soil conditions.
• We couldn’t achieve the torque and now the piles are going much deeper. Now what?

Where do you turn in these cases? Many of our customers will tell you that they’ve turned to Ductile Iron Piles to solve these specific issues in construction. And both design teams and contractors are frequently turning to DIPs in the design phase to pre-emptively avoid these potential issues.

Ductile Iron Piles – A Helical Pile Alternative

Ductile Iron Piles have become a go-to alternative for many projects to provide a reliable, higher-capacity alternative to helical piles for new construction, building additions and interior renovations. The modular, low-vibration Ductile Iron Pile system is installed using an excavator-mounted, medium-sized percussion hammer to drive the pile using high-frequency percussive energy. This method produces low vibrations, allowing the system to effectively work on wide open sites, immediately adjacent to or even inside existing buildings. The modular piles and medium-sized equipment allow the system to be easily used on tight sites where limited access solutions (like helical piles) might be required. In addition, TRM’s Plug and Drive connection system results in rapid installations with production rates of 400 to more than 1,200 linear feet per crew day.

A Ductile Iron Pile driven through an unexpected, buried grade beam

Ductile Iron Piles (DIPs) offer compression capacities of 25 to 100 tons in a variety of geotechnical conditions. The high capacity can often result in fewer piles and a more cost-effective foundation. DIPs are typically successful at driving through challenging urban fill sites (see picture). Piles can be driven to rock to generate high capacity in end-bearing. When reaching bedrock is not practical, an exterior grouted approach can be used to generate exceptional frictional capacity through grout-to-ground bonding, which reduces the concern of achieving torque requirements. This versatility in developing geotechnical resistance provides confidence that you will develop high capacities in a variety of ground conditions and lowers your risk for project delays and change orders resulting from unexpected helical pile performance.

If you are considering helical piles on your project, reach out to us for a feasibility assessment to know your options.

PROJECT EXPERIENCE – 112 NEEDHAM STREET

Design of the 2.5-story office building included 85 helical piles with a compression capacity of 15 tons. During pile installation, the helical piles weren’t achieving the designed torque in a sand and gravel layer prior to “spinning out” on very dense underlying soils. To avoid costly project delays, the design team elected to utilize a low vibration, higher-capacity exterior grouted Ductile Iron Pile to develop frictional capacity in the sand and gravel and provide foundation support. Designing the piles for twice the capacity as the helical piles allowed the quantity to be reduced to only 56 piles. A Series 118/7.5 pile with a 220 mm grout shoe was installed to penetrate the fill and organic soils and bond in the underlying sand and gravel. Tension load testing was performed up to 250% of the design (150 kips) to confirm the design. Vibration monitoring during installation showed levels between 0.3 and 1.0 in/s. Check out the project summary for more information about the project. For more information, check out the project summary.

PROJECT EXPERIENCE – RHODE ISLAND NATIONAL GUARD – ADAL FUEL CELL BUILDING 8

Renovations and improvements to the Rhode Island Air National Guard (RIANG) 143rd Airlift Wing’s ADAL Fuel Cell Building 8 project included two separate building additions. Foundation support was designed for helical piles with a working capacity of 40 kips. During installation of the helical piles, substantially lower torque levels were recorded in the loose sand, resulting in significantly reduced capacities. After consideration of the alternatives, the design team decided to switch to a low vibration, exterior grouted Ductile Iron Pile to meet the original pile capacity requirements for foundation support. A Series 118/7.5 (118 mm diameter with 7.5 mm wall thickness) pile with a 220 mm oversized conical grout shoe was selected for the re-design. The DIP design was based on penetrating the fill and developing friction capacity with a 17-foot bond length in the underlying sand layer.

Two pre-production compression load tests were performed at the site; one in each building addition area. Each pile moved less than 0.05 inches at the design load of 40 kips (100%) and less than 0.12 inches at 80 kips (200%). Test results confirmed the working capacity. The installation of 73 production piles to depths of 35 feet were achieved in only 3 working days, averaging more than 850 linear feet per day. As a result of this successful project, DIPs have now been used on four other successful projects at the base. For more information, check out the project summary.