Section 3.10: Site Plans and Technical Data - Rick Neufeld Comments

Northern Gateway Pipelines Inc.
Section 3.10: Site Plans and Technical Data
Table of Contents
2.6.3.2 Clay Deposits
Although the soil characteristics are not directly applicable to the design of the marine foundations, which
will be exclusively founded on rock, they are important when considering the possibility of a near shore
slope failure above the berth structures. These soils consist of relatively weak clays that can be
characterized as firm to stiff with a low to medium plasticity. These clays were originally deposited as
marine sediments and then later emerged above sea level as part of an overall terrain uplift which
occurred during the last glacial receding event. Because the soils are of a marine origin, they typically
have low shear strength, high compressibility, and low bulk permeability. In certain areas the local clays
may be potentially sensitive and can possibly exhibit abrupt loss of strength due to minor disturbances
such as construction activity or seismic events, making them highly susceptible to sliding failure. The
clay deposits are not considered suitable as a foundation material for structures that cannot tolerate
substantial settlements.
2.6.3.3 Alluvial Fan
An alluvial fan exists at the shoreline near the middle of terminal site. Because the material within the
alluvial fan was likely deposited during high peak flows of the associated streams, it may contain large
volumes of debris including trees, mud, rocks and boulders of various sizes. The presence of these
materials can be problematic for the installation of structural foundations and increase the potential for
large settlements.
2.6.4 Interpretation of Geotechnical Data
2.6.4.1 Marine Foundations in Bedrock
In general, the bedrock is very strong. However, the competency of the rock will vary throughout the
project site and certain areas may have localized fragmentation. Despite the possibility of periodic faults
and localized areas that are heavily jointed, the bedrock is suitable for pile, footing, and raft foundations.
Due to its high strength, the bedrock cannot be machine-excavated and preparation of foundations will
typically require drill and blast techniques.
When excavating or blasting rock, care will be taken to select a blast pattern that reduces the amount of
damage to the back walls and bottoms of the excavated surfaces. The blast pattern will limit the amount
of rock damage and rock overbreak past the cut lines. Final walls will be blasted using pre-split or
cushion blasting methods to improve the long term stability of the cuts and the wall slope will not exceed
a slope ratios recommended by the geotechnical engineer of record. As mentioned previously, to mitigate
potential rock slope instability, a detailed study of the rock structure including possible joints and faults
will be carried out in the vicinity of the marine structures.
The majority of the marine structure foundations will consist of either rock doweled steel piles grouted
into the rock or steel piles with rock socketed cast-in-place concrete plugs. Preliminary results indicate the
piles may be designed for an end bearing resistance of 6 MPa. Since the piles will likely be drilled for
some depth into the rock, a combination of shaft friction and end bearing resistance may be used. Specific
shaft and end bearing resistances will be determined from the geotechnical investigation conducted during
the detailed design stage.
Page 2-20 FINAL - Rev. 0 January 20, 2010