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Denver, CO

Park View Office Tower Deep Foundation

Deep foundation · new construction

MODERATE fit$2.10M – $2.45M (alternate path)

Why bid: Drilled shafts are the primary spec — outside our core specialty. Micropile alternate is viable but requires a value engineering submission and a redesign cycle. Worth bidding the alternate only if the schedule float exists for VE review.

Executive summary

Twelve-story Class-A office tower in downtown Denver with a 3-level below-grade parking podium. Spec-specified foundation is 16-inch drilled shafts socketed 8 ft into the Pierre Shale at approximately 65 ft depth — well outside our typical equipment envelope. A 4-pile micropile group alternate would deliver equivalent capacity (320 kip per group) using our standard 9-7/8 in. cased rigs already mobilized for the adjacent retaining wall scope on the project. The alternate path requires owner approval and a 4-6 week design submission. Worth bidding the alternate only if schedule float exists; the as-specified scope is a pass.

Key findings
Spec calls for 16-in. drilled shafts — outside our envelope

We don't run >12 in. shaft rigs. The as-specified scope would require sub'ing 100% of the foundation work; margins after sub markup are below our threshold.

Cited · Spec 31 63 16, Section 2.1
Micropile alternate viable at equivalent capacity

4-pile groups of 9-7/8 in. cased micropiles deliver 320 kips per group — matches the 12 drilled-shaft schedule. Group efficiency factor of 0.85 confirmed against DFI 8th Edition guidance.

Cited · Internal: DFI 8th Ed., Ch. 7
Pierre Shale bond zone is forgiving but slow

Hard plastic shale provides bond, but bit wear is the production driver. Expect 50% production reduction in the bond zone vs. overburden drilling.

Cited · Geotech Report, Section 5.4
Recommended design
Primary system

16-inch drilled shafts to bedrock (alternate: 9-7/8 in. cased micropile group)

Loading320 kips per shaft / per micropile group
Shaft count (spec)48 shafts × 65 ft
Micropile alt (group)192 piles in 48 groups of 4
Bond zone depth8 ft into Pierre Shale
Pile diameter (alt)9-7/8 in. cased permanent
Test program (alt)2 verification + 8 proof tests
Risk assessment

Owner rejects VE alternate, forcing as-specified scope

HIGH
Contractual

Mitigation: Submit a both-base bid + alternate. If alternate rejected, we no-bid the base.

Pierre Shale bit wear higher than estimate

MEDIUM
Cost

Mitigation: Carry premium tooling allowance. Pre-bid call with vendor to validate bit life on this formation.

Coordination with retaining wall scope on same site

MEDIUM
Schedule

Mitigation: Sequence shaft drilling after wall completion to avoid rig conflict on tight site.

Clarifications needed

Will the owner consider a value-engineered micropile alternate?

HIGH priority

Cost delta is $400-600K in our favor with the alternate. Without confirmation, bidding the base is uneconomical.

Is the published axial design load (320 kips) factored or unfactored?

HIGH priority

Spec text is ambiguous. ASD vs LRFD changes group sizing by ~15%.

Confirm Pierre Shale unconfined compressive strength range

MEDIUM priority

Geotech narrative says 'hard plastic shale' but reports no UCS data. Bond stress assumption sensitive to actual strength.

Cost drivers
Order-of-magnitude estimate$2.10M – $2.45M (alternate path)
  • Permanent casing — 192 piles × 65 ft × 9-7/8 in.
  • Tooling consumption in Pierre Shale bond zone
  • VE design submission and owner review cycle
  • Site logistics on a constrained downtown footprint

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