A Review of Micropiles Beneficial Aspects through a Case History near False Creek, Canada-Paper

Paper

Pdf Summary

The paper presents a case history of micropile underpinning used during construction of a 15 m-deep excavation for a residential tower near False Creek in Vancouver. The excavation was less than 1 m from pilecaps supporting two Georgia Viaduct piers, making control of settlement and rotation essential.<br /><br />The viaduct foundations consisted of pilecaps supported by cast-in-place concrete piles whose tips were above the planned excavation grades. Excavation-related soil movement could therefore have caused excessive movement of the existing foundations. Space around the pilecaps was limited, so twelve drilled micropiles were installed around each cap and structurally connected by enlarging the caps. The micropiles transferred loads to the deeper, competent glacial till, below the excavation. Each 200 mm-diameter micropile was designed for an 850 kN service load and tested before excavation.<br /><br />Micropiles were particularly suitable because they could be installed in the congested work area and resist both compression and tension. This capacity allowed the micropile groups to act as coupled forces, helping control pilecap rotation as well as settlement. Internal bracing separately helped limit horizontal movement.<br /><br />Automated laser displacement meters and tilt meters continuously tracked three-dimensional movement and rotation during approximately 12 months of excavation and construction. Manual surveys periodically checked the automated readings. Monitoring thresholds were adjusted for seasonal temperature effects.<br /><br />Results showed that the viaduct foundations remained within the displacement and rotation limits set by the bridge engineer. The authors conclude that properly designed micropiles can effectively underpin sensitive structures beside deep excavations, particularly where access is restricted, and can provide reliable control of both vertical movement and rotation.

Keywords

micropile underpinning

deep excavation

settlement control

rotation control

existing foundations

bridge piers

glacial till

construction monitoring

structural support

Vancouver excavation