Location: North Vancouver, British Columbia, Canada
Client: Hatch Mott MacDonald
The Allison project is an expansion of the coal export facilities at the Neptune Bulk Terminals in North Vancouver, BC to increase the capacity of existing coal exports. The expansion work consists of a new railcar dumper building and conveyor system, a new shiploader at Berth 1, and an additional rail alignment around the existing facility (Track 0). M+EG was retained by Hatch Mott MacDonald to provide geotechnical design services for the project. M+EG was also involved in the previous feasibility study which considered an adjacent site a Neptune Terminals.
The major analyses were required for the dumper building that was to be founded some 20+ m below ground level. Advanced 2-dimensional FLAC modeling was used to evaluate the foundation response and soil-structure interaction under the seismic design loading cases. Foundations were also analyzed for the new shiploader and the towers for the conveyor system.
The estimated project value is about $240 million.
M+EG was responsible for the following activities:
- Site investigation (sonic coring, mud rotary drilling, Becker density test, CPT and shear wave velocity measurements).
- Laboratory testing on recovered soil samples, including advanced cyclic simple shear.
- Dynamic engineering analyses.
- Geotechnical input for the design of the dumper building and conveyor tunnel;
- Pile and spread footing design for the conveyor structures.
- Foundation design for the shiploader replacement at Berth 1.
- Perform risk assessment for the existing sheet pile wall along the berth;
- Review various ground improvement options.
- Advanced 2-dimensional modeling with (FLAC) to consider soil-structure interaction at the dumper building.
The principal aims of the FLAC analyses were as follows:
- To model the construction of the buried structure as practically as possible;
- Assess/confirm the magnitude and distribution of the static and dynamic soil and pore water pressures on the buried structures and compare with predictions from simplified approaches;
- Assess/confirm the potential for liquefaction under 2D conditions and compare with the simplified 1D results based on fully-coupled analyses;
- Evaluate the impact of the unloading conditions on the seismic response of the foundation soils - to consider the removal of soil within the building footprint and the impact of the stress reduction on the foundation response;
- Assess the magnitude of the dynamic pore pressures over the base of the structures and the potential impact due to the properties/dimensions of the jet-grout soil plug;
- Assess the impact of adjacent structures on the soil loads on the buried structures as well as the dynamic pore pressures and lateral ground displacements, as well as the estimation of buoyancy effects as a result of pore pressure build-up/liquefaction.
- The Becker penetration values were corrected using a site-specific correlation that was developed based on PDA measurements. The equivalent N values interpreted from Becker density test were compared with the SPT data, and show reasonable agreement.
- 2D non-linear dynamic analyses were performed using the program FLAC, which can simulate a full range of static and dynamic conditions with coupled fluid flow and soil-structure interaction. The UBCSand constitutive model was used to simulate the dynamic pore pressure generation under earthquake loading.
- The structural components of the dumper pit and conveyor tunnel were modeled using beam elements with interfaces connected to the surrounding soils. The interfaces are important for correctly modeling the soil-structure interactions.
- The FLAC analyses were performed based on effective stresses with fully-coupled flow. Hence, pore pressure redistribution was allowed during earthquake loading. The interaction of the mechanical behavior of the soil particles with the pore fluid and soil-structure interaction have been considered in this advanced analytical modeling.
- The results of the FLAC analyses will be used to finalize the design of both the dumper building and the conveyor access tunnel.