Slope Stability and Pipeline Foundation Assessment:

Engineer of company was engaged to perform a geotechnical investigation and slope stability analysis for a proposed natural gas pipeline section near Chetwynd, BC, as part of a TC Energy infrastructure upgrade. The scope included foundation assessment for pipeline support, slope hazard evaluation, and recommendations for ground improvement or mitigation where required.

Test Pits: Excavated in accessible locations to assess shallow soil properties and verify stratigraphy.

Groundwater Monitoring: Standpipes installed to observe water table fluctuation and seepage patterns.

Topographic Survey: Conducted to develop accurate slope profiles and cross-sections for analysis.

Slope Stability Analysis

  • Software Used: SLOPE/W (GeoStudio), LimitEquilibrium and Finite Element models

  • Methods:

    • Bishop’s Simplified Method

    • Spencer Method for cross-check

  • Slope Configurations: Natural slopes, cut slopes (pipeline ROW), and fill embankments were evaluated

  • Soil Parameters: Cohesion (c), Friction angle (ϕ), and unit weight (γ) obtained from lab and empirical correlations

  • Seismic Loading: Seismic coefficient based on NBCC 2020 hazard values for Zone 6

  • Water Conditions: Both dry and saturated (worst-case) conditions were modeled

  • Factor of Safety (FoS): Targeted FoS > 1.5 (static), >1.1 (seismic)

Pipeline Foundation and Settlement Evaluation

  • Pipe Load and Support: Evaluated allowable bearing capacity using Terzaghi and Meyerhof methods

  • Subgrade Modulus (k-value): Used for stress-distribution modeling under pipeline bedding

  • Differential Settlement: Analyzed using elastic and consolidation settlement theories

  • Frost Susceptibility: Assessed potential for frost heave in fine-grained soils, recommended non-frost-susceptible backfill

  • Anchor Block Stability: For steep slopes and expansion loops, lateral resistance was calculated using p-y curves

Recommendations

  • Use of reinforced geogrid layers or geotextiles in fill areas with low shear strength

  • Installation of French drains or subsurface drainage systems on slopes with high water content

  • Minimum pipe embedment depths and select granular bedding to reduce differential movement

  • Avoidance of highly plastic clays and zones of active slope creep

  • Erosion protection measures: riprap placement or hydroseeding for slope faces

  • Ongoing instrumentation (inclinometers, piezometers) for long-term performance monitoring.

  • Sometimes designed MSE rockery wall

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