Foundation solutions combining Ductile Iron Piles with Ground Improvement

Ground improvement systems like aggregate piers and rigid inclusions can provide a low-cost option for many projects. However, ground improvement projects often have challenges that require a deep foundation approach on a part of the job. Some examples challenges include:

• Most commonly, low-vibration Ductile Iron Piles (DIPs) are used for new foundation support near existing structures that can’t tolerate the higher-vibrations associated with some ground improvement techniques.
• Logistical constraints on a job site that won’t allow larger ground improvement equipment to access certain parts of the required work area. This includes areas with limited overhead or tight access areas.
• Perimeter wall foundations that abut existing structures, requiring deep foundations to transfer building loads below the zone of influence of older foundations.
• Structures with specific features like large mat foundations, equipment pits, interior tanks, or other building components that are too heavy to be supported on ground-improvement.
• Unexpected subsurface conditions, like urban fill, that can’t be penetrated with ground improvement techniques.
• Subsurface conditions where unsuitable soils extend to depths beyond the treatment depth for ground improvement systems.

Foundation design (i.e. shallow foundations vs. pile caps) and settlement compatibility are often two technical aspects that need to be considered when combining systems. The deflection characteristics for Ductile Iron Piles are often compatible with typical settlement performance of foundation supported by ground improvement. Where the potential for differential settlement does exist, this risk can be addressed by incorporating a transition zone between the different support conditions. In addition, Ductile Iron Piles can also be designed as rigid inclusions with an engineered aggregate pad to support shallow foundations, further enhancing foundation compatibility.

Many ground improvement contractors have the experience and equipment to install Ductile Iron Piles, making the addition of DIPs to their ground improvement projects a simple task. Requiring only a medium-sized excavator and a percussion hammer, some of the largest ground improvement contractors in the US are quick to implement this FAST. SIMPLE. SAFE.® solution to provide comprehensive geotechnical solutions to their customers.

DuroTerra has worked with many geotechnical specialty contractors to provide a combination of Ductile Iron Piles (DIPs) at select foundation locations while ground improvement is used for support of other foundations. Below are a couple of examples of projects that combined Ductile Iron Piles with ground improvement.

PROJECT EXPERIENCE – BUILDING 89

Construction of a new 6-story residential building was planned immediately adjacent to an existing 4-story residential brick building. With fill and organics extending up to 18 feet below grade, the majority of the building was designed for shallow foundations supported by rigid inclusions penetrating the fill, organics and glacial outwash deposits to terminate in glacial till. Because of concerns about access and vibrations generated during ground improvement installation, the perimeter foundations adjacent to the existing building were designed as pile caps / grade beams supported by Ductile Iron Piles. Series 118/9.0 Ductile Iron Piles were designed for 50 Ton working capacity. Piles were driven through upper weaker soils and terminate by achieving “set” on glacial till or rock at depths of up to 88 feet. Full-scale load testing verified the working capacity of the piles. Following load testing, a total of 38 piles were installed in only 3 working days. For more information, check out the project summary.

PROJECT EXPERIENCE – CHRISTIAN BROTHERS HIGH SCHOOL

A new 33,000 square foot gymnasium addition was designed for support using aggregate piers. However, the perimeter wall foundations were planned immediately adjacent to the existing school. There was a concern about access of ground improvement equipment and also the potential that the new foundations supported on ground improvement may transfer loads to the existing pile-supported school building. With loads of up to 8 kips/foot along grade beams, the design team originally specified drilled micropiles with a 50 ton (compression) capacity. The ground improvement contractor proposed the use of Ductile Iron Piles as a cost-effective foundation alternative to the specified micropiles. In addition to being a much faster installation process, the Ductile Iron Piles provided a lower vibration solution than the ground improvement system to address that concern. An exterior grouted Series 118/9.0 Ductile Iron Pile solution was designed to match the 50 ton capacity on a 1:1 basis. Capacity was verified with a full-scale load test. Installation then proceeded at rates of more than 500 LF/day to accelerate the piling scope of work. For more information, check out the project summary.