CMC installation at Essington Market The CMCs are typically installed using a displacement auger or a driven pipe man- drel that laterally compresses the soil mass while generating virtually no spoils. The CMC displacement auger is hollow, allowing placement of the cement based grout column, as the auger is withdrawn. The grout is injected under moderate pressure, typi- cally less than 150 psi (10 bars). The uncon- fined compressive strength of the grout is adapted to the requirements of the design and varies between 1,000 and 3,000 psi (6.8 and 20.6 MPa) for typical applications. CMCs are installed without generating spoils or creating vibrations. The grout for the CMC element is placed with enough back pressure to avoid collapse of the displaced soils during auger withdrawal. The installation process allows for the creation of a column with the diameter that is at least as large as that of the auger. CMC are installed with drilling equipment that has large torque capacity and high-static down thrust to efficiently displace and compress the surrounding soil laterally. Advantages Many potential users are not aware of the benefits of this relatively new technology. From a financial perspective, using CMC reduces project costs when compared to more traditional pile foundations or excavation and replacement of unsuitable soils. This is because fewer construction materials are required, installing CMCs is faster than installing piles and spoil disposal is eliminated. In addition, the method has the following benefits: • Promotes development of brownfield sites underlain by poor quality soils • Avoids excavation and replacement of poor quality soils and limits spoil, reducing waste generation • Provides a cost-effective solution com- pared to conventional foundation systems 74 • DEEP FOUNDATIONS • MAY/JUNE 2012 • The lengths of CMC can be adjusted in the field without splicing or cutting • Reduces schedule for installation in many instances • Reduces the cost of the structure by substituting pile caps, grade beams and structural slabs with spread footings and slabs-on-grade • Improves the performance of the methane barrier system when required on hazardous sites by eliminating complex detailing around pile caps • Eliminates the need to hang utilities under structural slabs as utilities are installed directly within the LTP • Improves the overall slab quality by allowing construction under the roof after the shell of the structure has been erected where applicable • Eliminates the cracking often found in structural slabs due to constrained shrinkage along lines of piles • Reduces the carbon footprint associ- ated with foundations by significantly reducing concrete and steel quantities Design-Build Solution CMC were patented and introduced to the U.S. market in 2004. After eight years of demonstration and acceptance, the unique knowledge of CMC lies with Menard, therefore projects are traditionally developed using a design-build approach. Menard routinely teams with local engineers that represent their clients and apply fundamental knowledge about the local soil conditions to review and verify the CMC design. CMC have been successfully used to support large storage tanks in ports, major highway embankments and retaining walls on soft ground near waterways, runway extensions on filled ground, large warehouses on brownfield landfill sites and numerous commercial and residential multi-family buildings. Alternative to Piling Menard, in a joint venture with sister com- pany Nicholson Construction Company, performed the largest CMC project to date in the U.S. at the Essington Avenue Market in Philadelphia, Pa. Because CMCs are well adapted to high surface loading conditions and strict settlement requirements, they (51,100 m ) regional produce market and distribution center, which is a 34 ft (10.4 m) tall, single-story structure with a 425 ft x 1,295 ft (130 m x 395 m) footprint and a continuous full perimeter loading apron. The Essington Avenue Market houses were an ideal solution for the 550,000 sq ft 2 retail and wholesale produce sellers, and is conveniently located minutes from the Philadelphia International Airport. However, the 63 acre (25 hectare) former brownfield was originally an uncontrolled municipal solid waste (MSW) landfill, and for almost 15 years the site remained undeveloped. The existing MSW fill and the under- lying organic silts were considered unsuit- able to support up to 10 ft (3 m) of new fill to raise the floor grade, and the building structure and floor slab loads, due to their susceptibility to long-term consolidation settlement and degradation of the MSW. The foundation system was originally designed for driven piles and structural concrete floors, supported on pile caps, above driven piles. Menard and Nicholson proposed a value engineered re-design alternative using CMC to support the facility. The CMC inclusions were spaced under the slab in a grid pattern (providing an indirect support mechanism) that is dependent on the magnitude of the new load. The value engineering proposal specified CMCs in more concentrated arrangements under the footings (providing a direct
