Micropiles Counter Unbalanced Loading During Partial Building Demolition-Paper

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The VCU Children’s Hospital of Richmond Pavilion was redeveloped while the existing hospital remained operational. The project demolished the southern half of the original building and excavated a new four-level basement, extending roughly 35 feet below the existing building’s lowest level. This created unbalanced soil pressures, threatened the remaining structure’s stability, and required underpinning and protection from lateral movement. Tight access, nearby utilities, and the need to limit disruption further constrained the work.<br /><br />Structural and geotechnical engineers developed a coordinated stabilization system. Seven large concrete buttresses and perpendicular shear walls along the demolition line provided lateral bracing for the retained building. A continuous grade beam connected these elements. Because the deep excavation would remove soil support beneath the beam, 95 vertical micropiles carried its vertical loads below the excavation.<br /><br />Vertical micropiles alone could not resist the required lateral forces. Instead, 34 A-frame assemblies paired vertical and battered micropiles, positioned about 30 feet from the building cut line. Post-tensioned horizontal ties connected the assemblies to the building-side grade beam, transferring lateral loads while avoiding conflicts with the excavation support tiebacks. Engineers iteratively analyzed beam stiffness, micropile capacity, and load distribution to refine the design. Load tests informed the micropile bond lengths and design bond strength.<br /><br />Installation sequencing was critical: micropiles were installed first, followed by grade beams, shear walls, buttresses, and horizontal ties. After the concrete reached the specified strength, the ties were tensioned; structural connections were completed, the battered piles were tensioned, and only then was demolition undertaken.<br /><br />The system allowed hospital operations to continue safely during construction. Monitoring showed approximately 10 mm (3/8 inch) of total horizontal movement after installation of the excavation support system. The project enabled redevelopment of an existing urban site while consolidating pediatric outpatient services in a new facility.

Keywords

VCU Children's Hospital of Richmond

pavilion redevelopment

existing hospital operational

deep excavation

micropiles

underpinning

lateral bracing

shear walls

grade beams

structural stabilization