Pitt River Bridge
Location: Port Coquitlam, British Columbia, Canada
Client: MMM Group / Peter Kiewit Sons.
In 2007, MEG Consulting Limited (M+EG) was sub-contracted to MMM Group, (design lead for Peter Kiewit Sons design-build team), to perform geotechnical earthquake engineering analyses for the Pitt River Bridge and Mary Hill Interchange (PRB/MHI) project. The project included construction of a new 380-m cable stay bridge structure across the Pitt River and the highway approaches on both sides of the river. On the west side this included a new interchange at the intersection of Lougheed Highway with the Mary Hill Bypass.
The scope of work provided by M+EG for the design-build considered the following:
- Supervision of drilling, sampling and in-situ testing at selected onshore and in-river locations;
- Laboratory testing (including static and advanced dynamic testing for samples at river location - resonant column and cyclic direct simple shear test);
- 1D site response analyses using both equivalent linear and non-linear programs (SHAKE & DESRA);
- Analysis of the susceptibility of the granular soils to initial liquefaction under the design earthquake conditions;
- Analysis of ground deformations resulting from earthquake loading and design of remedial measures based on 2D FLAC models;
- Determination of soil-pile kinematic interaction.
M+EG also provided field testing and inspection services during the construction of the bridge abutments, which included on-site supervision for stone column ground improvement and dynamic pile testing using Pile Driving Analyzer (PDA) and CAPWAP analyses.
- Prior to performing any testing on the recovered Shelby tube samples, the tubes selected for testing were sent to be gamma-rayed. The results of the gamma-rays provide details on sample quality and allowed selection of the best quality samples for the execution of dynamic testing.
- Dynamic laboratory tests were performed to define the shear modulus degradation and damping curves for the representative undisturbed soil samples to be used for the site response analyses. In addition, the liquefaction resistances of the sand and silt layers were determined using the cyclic direct simple shear (CycDSS) tests. Cyclic DSS results were used to estimate pore pressure generation during seismic loading and to evaluate the potential of liquefaction.
- Layout of the ground improvement was designed using dynamic FLAC 2D analyses for the bridge abutments. Lateral ground movements and the resulting forces acting on the piles were calculated (based on MCEER/ATC-49) to check the structural response of the foundations under the design earthquake levels.
- Ground improvement by stone columns was proposed to increase the resistance of the granular foundation layers for earthquake design. Detailed ground improvement specifications were defined prior to installation of the stone columns. An initial verification trial was performed by the ground improvement contractor. Cone penetration testing was defined as the method for assessing the acceptability of the ground improvement work at the trial location in order to ensure that densification was achieved according to the specifications. The results from the trial area were used to verify the methodology of densification for the stone column installation.