The Burke Mountain Community Centre in Coquitlam, BC required a permanent anchored soil-nail shotcrete retaining wall standing up to 11.3 m tall with a 100-year service life. I was the lead structural engineer for the wall’s concrete and anchor-connection components, working alongside the geotechnical engineer of record, the general contractor, and the City of Coquitlam as owner - all on a compressed, bid-driven schedule.

My Role

Lead structural engineer of record for the structural components: the shotcrete facing, the anchor-head-to-concrete connections, the general notes and specifications, and the construction-phase reviews.

What I Designed

Permanent anchor-head connection

  • Carried a 350 kN factored lock-off load - a 35% increase over the reference-project precedent
  • 350 mm two-mat facing, 500 x 500 x 38.1 mm bearing plate, eight headed studs at 19 mm diameter x 270 mm
  • Full verification of plate bending, stud shear, punching shear, reinforcement demand, and nail-head capacity to CSA A23.3

Two-stage, non-composite design philosophy

  • Stage 1 and Stage 2 facings each independently resist 100% of earth pressure and anchor loads
  • Deliberately concedes interface bond over the design life, building redundancy into a structure that cannot be inspected once buried

Shoring alternative analysis

  • Structural analysis of a soldier-pile and secant-pile alternative for the north and west sections
  • W610x270 H-piles in 914 mm drilled shafts, single-row anchors, and a galvanized-versus-secant corrosion assessment for a 75-to-100-year service life

The Mid-Bid Facing Change

Every bidding contractor flagged the cast-in-place Stage 2 facing as a cost and schedule risk. I authored the engineering review that resolved the change to shotcrete within four working days of the RFI:

  • Redesigned the anchor connection for the shotcrete substrate and increased the final facing from 300 mm to 350 mm, placed in two 175 mm lifts for constructability on a vertical face
  • Closed specification gaps across CSA A23.1/A23.2/A23.3, the ACI 506 series, and ASTM C1583 - including striking a counterproductive bonding-agent clause that introduced a debond-plane risk
  • Mandated two-mat rebar segregation control, Face 1 / Face 2 surface preparation, an anchor-head shooting sequence for void-free encapsulation, and CSA exposure class C-1
  • Rejected a proposal to locally thicken shotcrete over the anchor heads, citing shotcrete shadowing at the three-layer rebar geometry, a stiffness discontinuity requiring transition reinforcing, and CSA cone-breakout edge-distance limits
  • Ran preliminary numbers on the spot during negotiation, confirmed 200 mm was not achievable, and proposed 250 mm with revised anchor hardware as the minimum viable configuration - accepted the same afternoon

The full technical dispute was resolved within one week of the original RFI, across three organizations, with no impact to project schedule.

Quality and Constructability Reviews

  • Reviewed the geotechnical consultant’s drafted drawings against structural markups, catching a soil-nail inclination discrepancy, 49 missing structural notes, and a revision-status contradiction before issue
  • Resolved a contractor query on anchor stressing strength with a punching-shear-versus-sqrt(f’c) capacity analysis - 53% capacity at 10 MPa, 85% at 25 MPa, 93% at 30 MPa - and proposed a high-early-strength mix that cut anchor testing from 7 days to 3
  • Wrote the pre-construction shotcrete qualification-panel specification: two 1800 x 1800 x 350 mm panels with embedded anchor heads, ACI-certified nozzleman with 5+ years at similar scale, ACI 506.6T core grading, destructive cross-section through the anchor head, and defined re-qualification triggers
  • Produced a 27-note structural general-notes package and a 24-item consolidated specification redline against the geotechnical special provision
  • Reviewed a cellular-concrete gap-fill proposal and flagged a reversed fresh-pour fluid-pressure load case of roughly 53 kPa over a 9 m lift that the one-way face was never designed for, plus a drainage-continuity failure mode
  • Rejected a cold-galvanizing spray substitution on the encased anchor hardware, holding hot-dip galvanizing after fabrication per CSA G164 against the 75-to-100-year durability requirement

Outcome

The detailed calculation package passed third-party peer review at the client’s request. Two scope-change submissions were authored and accepted, and structural effort was held near the original lump-sum base fee despite multiple wall configurations and two facing-system changes. The client and contractor adopted the shotcrete Stage 2 change, the two-lift facing sequence, and hot-dip galvanized anchor hardware.

Codes and Standards

CSA A23.1, CSA A23.2, CSA A23.3, CSA G30.18M, CSA G40.21, CSA G164, CSA W59, ACI 506.2, ACI 506R, ACI 506.5, ACI 506.6T, ASTM A108, ASTM A780, ASTM A1064, ASTM C1583, FHWA GEC-7 (Soil Nail Walls Reference Manual).