Ross Park Mall
- Location: Pittsburgh, PA
- Owner: Simon Property Group
- General Contractor: G & C Contracting
- Technique(s) Utilized: Micropiles
Background
The owners of Ross Park Mall in Pittsburgh were planning an expansion to include high-end
retail stores. However, prior to construction, the existing structure was experiencing unacceptable floor slab heaving due to the expansion of the underlying pyritic siltstone present below the slab. Structural damage to the slab was observed in areas of the proposed construction. Pyrite expansion in bedrock results from a chemical reaction between pyritic sulfur and oxygen. This process typically occurs after the materials are exposed to air or water.
In order to repair the floor, the project’s design team recommended that the floor slab and underlying pyritic siltstone be removed to a depth of approximately 12 inches below the bottom of the existing floor slab elevation. A new structural floor slab system was planned and to be supported by micropiles. Nicholson was contracted to design and install 123 micropiles inside the operational mall. It was extremely important to debond the micropile steel from the expansive ground to eliminate the risk of pile heave due to the pyritic condition.
The piles were installed with a Davey Kent DK 515 drill using rotary percussive drilling methods in congested areas with as little as 14 feet of headroom. The piles were designed to support compression loads of 50 kips and drilled to depths of approximately 17 feet. The pile installation was completed at night in order to reduce disturbance to the operating mall.
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