Case Study: Retaining Structure to Support Deep Excavation and a Temporary Bridge-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines how existing structures were retained and supported during deep cut-and-cover excavation and construction of a temporary bridge for Ottawa Stage 2 LRT. The project includes extensive rail, station, tunnel, bridge, and retaining-wall works across the east, west, and southwest corridors.<br /><br />A key geotechnical concern is Champlain Sea clay (“Leda clay”), which can settle differentially under loading and lose much of its strength if disturbed. The cut-and-cover works therefore required site-specific support-of-excavation (SOE) systems. Depending on ground conditions and location, these included soldier piles, secant or slurry walls, braced systems, soil nails and shotcrete, rock bolts, and open cuts.<br /><br />The case study focuses on excavation near Richmond Road, including a temporary bridge and its interaction with the SOE. Subsurface conditions ranged from fill and till to sandstone. Finite-element analysis in PLAXIS 2D assessed staged construction, ground settlement, and structural response under highway and construction loads. Bridge and strut connections to the SOE were modeled as pinned. Building performance criteria included limits on total settlement and angular distortion, alongside damage-risk assessment based on angular distortion and horizontal strain.<br /><br />A geotechnical instrumentation and monitoring plan tracked ground, utilities, structures, groundwater, and excavation support. It comprised 1,415 instruments and monitoring points across the project areas. The presentation documents the design approach, construction sequence, analytical assessments, and monitoring program, but the supplied text does not report specific final performance results.

Keywords

Ottawa Stage 2 LRT

cut-and-cover excavation

temporary bridge

support of excavation

Leda clay

geotechnical instrumentation

PLAXIS 2D

settlement monitoring

retaining walls

staged construction