Protest 006 - Executive Summary

Protest 006 - Differing Site Condition, ESU 2C clay deposit beneath Walls 23.80R, 23.72R, 23.73R and 23.74R and I-405 Mainline Bridge Abutment 10. Contract No. 9727, I-405 Brickyard to SR 527 Improvement Project. PCO 123. Draft for internal review.

• April 9, 2025. The Design-Builder gave first notice of a potential Differing Site Condition at Wall 23.80R (Skanska LTR 171 dated April 9, 2025), acknowledged in WSDOT Serial Letter (SL) No. 9727-103 dated April 23, 2025.
• April 26 to May 13, 2025. Three deep borings were drilled at GeoEngineers' recommendation to evaluate ESU 2C, reaching 246.5, 250 and 239.25 feet. Holocene Drilling, Inc. drilled B-1-25 and WSDOT drilled B-2-25 and B-3-25.
• May 1 to November 25, 2025. Laboratory testing by three laboratories, WSDOT, GeoEngineers and Haley & Aldrich. WSDOT transmitted its results as Laboratory Testing Package 01 (WSDOT SL No. 9727-149 dated September 4, 2025) and issued a corrected consolidation report (WSDOT SL No. 9727-180 dated October 17, 2025) after the Design-Builder raised a density discrepancy (Skanska LTR 244 dated September 30, 2025).
• August 27, 2025. GeoEngineers issued the memorandum reporting the investigation, including the overburden error and the corrected overconsolidation ratios.
• September 4, 2025. The Design-Builder expanded the notice to five structures (Skanska LTR 226).
• September 18, 2025. WSDOT issued its written determination denying the Differing Site Condition across all five structures under RFP Section 1-04.7 Differing Site Conditions (WSDOT SL No. 9727-162), transmitting the Internal Engineering Decision that carries the supporting analysis.
• October 1, 2025. The Design-Builder filed its Notice of Protest 006 within the fourteen-day window (Skanska LTR 246).
• October 10, 2025. WSDOT granted a 59-day extension for the supplement (WSDOT SL No. 9727-175), setting the deadline at December 8, 2025.
• December 8, 2025. The Design-Builder filed its supplement (Skanska LTR 291).
• January 16, 2026. WSDOT reaffirmed the denial, addressing all four arguments and adding the historical settlement record at Appendix G03 (WSDOT SL No. 9727-242).
• January 30, 2026. The Design-Builder filed a Notice of Dispute on behalf of AECOM and GeoEngineers (Skanska LTR 336), acknowledged in WSDOT SL No. 9727-257 dated February 6, 2026.
• March 13 to May 1, 2026. The parties arranged an executive meeting (Skanska LTR 374, WSDOT SL No. 9727-307, Skanska LTR 416, WSDOT SL No. 9727-335). WSDOT noted that this work becomes critical path in March 2027.
• May 8, 2026. The parties met and agreed to resolve the matter by Change Order rather than refer it to the Dispute Review Board.
• April 2026. The redesign basis was submitted as NDC 145 Segment 2 Geotechnical Report Addendum 5 and NDC 146 Addendum 6.
• August 25, 2026. The justification narrative went to the Project Engineer. Derek Case returned a review markup on September 2, 2026, and responses are threaded into it.

1. The Matter

The ESU 2C clay deposit beneath the northbound approach to the I-405 Mainline Bridge behaved under load in a way that neither the Design-Builder's designers nor WSDOT expected. Wall 23.80R settled far beyond the approximately 1.12 inches the Released for Construction design predicted, portions of the wall were torn down and rebuilt, and the subgrade beneath the leveling pad was overexcavated three feet and replaced. The subsequent investigation recalculated settlement at approximately 8 to 9 inches.

The Design-Builder asserted that this was a Differing Site Condition, resting principally on an overburden error in two consolidation test reports furnished in the Geotechnical Data Report, which inflated the reported overconsolidation ratios. The question WSDOT answered was whether the condition met the contractual definition of a Differing Site Condition, and whether the Geotechnical Data Report carried a WSDOT representation the Design-Builder was entitled to rely on.

2. WSDOT's Position

WSDOT denied the Differing Site Condition twice, and both determinations stand.

The Geotechnical Data Report is furnished as a Reference Document at the Design-Builder's risk under RFP Section 1-02.2, and RFP Section 1-02.4(2) makes no representation or warranty that the Design-Builder's interpretations of it are correct. It is the Geotechnical Baseline Report, not the Geotechnical Data Report, that establishes the baseline against which a Differing Site Condition is measured, and GBR Section 3.2.7 baselined poor ground in this area and assigned the Design-Builder responsibility to assess it. RFP Section 1-02.4(1) required a reasonable effort to verify the geotechnical assumptions on which the design depended, and the record did not demonstrate one. No physical site condition was identified that met the contractual definition.

The overburden discrepancy is recorded in the narrative and is not disturbed by the Change Order. This Change Order does not correct the Geotechnical Data Report.

3. The Resolution

The Change Order is not a Differing Site Condition. It is a WSDOT-Initiated Change under RFP Section 1-04.4(1) WSDOT-Initiated Changes. WSDOT requires a foundation and approach embankment at Abutment 10 that place the structure below the ESU 2C deposit and remove load from it, in place of the spread footings on stone-column improved ground shown in the Released for Construction documents.

Three consequences follow from that basis, and each matters:

1. The two written determinations stand. WSDOT SL No. 9727-162 and WSDOT SL No. 9727-242 are not superseded, and the risk allocation they describe continues to govern subsurface risk on this Contract.
2. The RFP Section 1-04.7 aggregate deductible is not consumed. Because the adjustment is not made under RFP Section 1-04.7, the aggregate is untouched by an amount that would otherwise have exhausted it.
3. Entitlement is not conceded. The finding is confined to the engineered solution WSDOT requires at these structures.

Amount. The agreed equitable adjustment is $36,394,776, comprising $24,353,812 in direct costs and $12,040,964 in indirect costs, less a negotiated reduction of $394,776, for $36,000,000 payable.

Time. The Change Order carries a total time extension of 129 calendar days. The allocation between this issue and the Sound Transit directed change, PCO 010B Platform Change, is a WSDOT determination and is open. The allocation moves the two time impact lines and the negotiated reduction. It does not move the $36,000,000 payable.

Protests resolved. The Change Order also closes eight protests, each at no cost, with WSDOT's determinations on them unaffected and no part of the amount payable allocated to any of them: Protest 002 BRT Station Design, 011 SR 522 Transit Hub Power, 012 CCTV Pole, 013 KCM Power Vault, 015 Contaminated Soil in the Old BNSF Right of Way, 016 Bridge 405/70N-W Deck Thickness, 018 Juanita Creek West Wetland, and 023 77R Pedestrian Railing at 17th Avenue.

Change Order Narrative, PCO 123

Description of Change

This is a WSDOT-initiated Change Order in accordance with RFP Section 1-04.4 Changes. It compensates the Design-Builder for the redesign and reconstruction of the I-405 Mainline Bridge north abutment, Abutment 10, and Retaining Walls 23.72R, 23.73R, 23.74R and 23.80R, resolves Protest 006, and closes at no cost the protests listed in the Cost and Time Extension section.

Evolution and Summary

The structures at issue stand at the north end of the I-405 Mainline Bridge crossing of the Sammamish River valley, near the SR 522 interchange. They are the mainline bridge north abutment, identified in the design documents as Abutment 10 and referred to in the Design-Builder's geotechnical reports as Pier 10, the adjacent approach wing walls, and Retaining Walls 23.72R, 23.73R, 23.74R, and 23.80R. Wall 23.80R supports a portion of the westbound SR 522 to northbound I-405 ramp alignment. Beneath all of them lies a deep, soft clay deposit designated Engineering Soil Unit 2C, or ESU 2C. The observed behavior of this clay layer and how that differed from the expectations of the Design-Builder’s designers and WSDOT is the circumstance that initiated this Change Order.

On October 6, 2023, the Design-Builder issued the Released for Construction (RFC) version of its Subsurface Investigation Plan (SIP), Phase 1, prepared by GeoEngineers. That plan covered the explorations for the structures now at issue, including the area around the mainline bridge north abutment, the approach wing walls, and Wall 23.80R. WSDOT reviewed and commented on the plan before it was issued.

On April 19, 2024, the Design-Builder issued the RFC version of the Segment 2, Early Design Package 1B Geotechnical Report, which covers this area. For ESU 2C the report adopted a design overconsolidation ratio (OCR) of 2.0. Working from that value, the Design-Builder elected to carry the abutment and adjacent walls on spread footings over stone-column improved ground, supplemented by wick drains and staged construction. WSDOT project office staff and subject matter experts reviewed and commented on the submittal through the design review process.

Construction began on Wall 23.80R at the north end, near wall Station 20+00, on September 2, 2024. On October 18, 2024, the Design-Builder poured the fascia wall leveling pad south of wall Station 15+50. That is where the wall would go on to settle far beyond the predicted amount. Thirteen days later, on October 31, 2024, the Design-Builder found several fascia panels in that same station range tilting outward 2 to 5 inches.

The wall came apart from there. Between November 6 and November 15, 2024, the Design-Builder tore down the affected portions of Wall 23.80R and began surveying the leveling pad. Survey results on December 10, 2024 showed settlement continuing, worst between wall Station 12+00 and 14+00 and present at most locations south of Station 15+50. GeoEngineers went to the site on December 13, 2024 to examine the subgrade beneath the leveling pad between wall Station 12+00 and 14+00. Between January 7 and January 15, 2025, at the direction of GeoEngineers, the Design-Builder overexcavated that subgrade to a depth of three feet and replaced it with geosynthetics and imported gravel, in accordance with GeoEngineers' response to RFI #0265, and between January 7 and February 6, 2025 rebuilt the torn-down wall sections on a new load transfer pad.

The settlement along this section of Wall 23.80 did not stop after the rebuild. On March 19, 2025, the Design-Builder sent the latest survey of the rebuilt wall to its geotechnical engineer, GeoEngineers, which evaluated the data over the following week. On March 22, 2025, GeoEngineers recommended to the Design-Builder that work be stopped on Abutment 10 and in the vicinity of Walls 23.72R and 23.73R, out of concern that ESU 2C was settling more than expected and that the neighboring structures faced the same behavior. GeoEngineers issued a Corrective Action Plan on April 1, 2025 recommending a gravel surcharge on top of the wall to drive the remaining settlement early. The Design-Builder notified WSDOT of the atypical settlement by email that same day. A three-foot gravel surcharge, sized to mimic the future load of pavement and traffic, was placed on top of Wall 23.80R between April 8 and June 13, 2025.

On April 9, 2025, the Design-Builder issued Skanska LTR 171 dated April 9, 2025, its first notice of a potential Differing Site Condition, covering Wall 23.80R alone. WSDOT acknowledged the notice in WSDOT Serial Letter (SL) No. 9727-103 dated April 23, 2025. WSDOT did not issue a determination at that point. It stated instead that it would continue to partner with the Design-Builder to determine a path forward as additional information was gathered.

That partnering produced the investigation that followed. Three new deep borings were drilled to gather additional data on ESU 2C at depths that extended well below the depths of the earlier explorations, which in this area had generally stopped between roughly 80 and 130 feet. In a collaborative effort, WSDOT assisted Skanska/GeoEngineers by performing some of the borings. Boring B-1-25 was drilled by Holocene Drilling, Inc. as directed by GeoEngineers, between April 25 and April 29, 2025 to a total depth of 246.5 feet. WSDOT drilled B-2-25 between April 30 and May 7, 2025 to 250 feet, and B-3-25 between May 7 and May 13, 2025 to 239.25 feet. WSDOT also performed the in-situ vane shear testing in B-2-25 and B-3-25, with In-Situ Engineering performing the vane shear testing in B-1-25.

Laboratory testing on the recovered samples ran from May 1 to November 25, 2025, when the boring logs were finalized with the results. The testing was conducted by three independent laboratories: WSDOT, GeoEngineers, and Haley & Aldrich. WSDOT transmitted its consolidation and triaxial results for Borings B-1-25, B-2-25, and B-3-25 to the Design-Builder as WSDOT Laboratory Testing Package 01 under WSDOT SL No. 9727-149 dated September 4, 2025. The Design-Builder raised a density discrepancy in one sample in Skanska LTR 244 dated September 30, 2025, and WSDOT issued a corrected consolidation test report in WSDOT SL No. 9727-180 dated October 17, 2025. Running alongside the borings, a separate and larger instrumented gravel preload test was built near Wall 23.72R between May 21 and December 4, 2025 to obtain a larger scale test of settlement performance. Settlement under the Wall 23.80R surcharge appeared to stabilize between June 13 and June 20, 2025, and the surcharge was removed.

On August 27, 2025, GeoEngineers issued a memorandum reporting what the investigation had found. The GDR consolidation test results for two samples had used overburden values of approximately 1,060 pounds per square foot, which imply a saturated unit weight near 75 pounds per cubic foot. Laboratory testing measured the saturated unit weight at an average of 113 pounds per cubic foot. GeoEngineers put the resulting error in the overburden at factors of approximately 2.39 and 2.00, and the corrected overconsolidation ratios at approximately 1.6 and 1.0 against the 3.57 and 1.99 calculated from the GDR. Separately, using a new design overconsolidation ratio of 1.3, GeoEngineers recalculated settlement at Wall 23.80R at approximately 8 to 9 inches against the approximately 1.12 inches produced by the design value of 2.0.

On September 4, 2025, the Design-Builder issued Skanska LTR 226, expanding the notice from Wall 23.80R alone to Walls 23.80R, 23.72R, 23.73R, and 23.74R together with Abutment 10, and attaching the GeoEngineers memorandum and an AECOM supplemental notice dated September 2, 2025.

WSDOT issued its written determination in WSDOT SL No. 9727-162 dated September 18, 2025, denying the Differing Site Condition across all five structures under RFP Section 1-04.7 Differing Site Conditions. The letter transmitted WSDOT's Internal Engineering Decision, which carried the supporting analysis, including the overburden and OCR discrepancy, and concluded on four findings. First, the Design-Builder had relied on the Geotechnical Data Report (GDR), which is furnished as a Reference Document at the Design-Builder's risk under RFP Section 1-02.2 Disclaimer Regarding Documentation. Second, the record did not demonstrate a reasonable effort to verify the geotechnical assumptions on which the design depended, as RFP Section 1-02.4(1) General requires. Third, no physical site condition had been identified that met the contractual definition of a Differing Site Condition. Fourth, the Geotechnical Baseline Report (GBR) had baselined poor ground in this area, and GBR Section 3.2.7 assigns to the Design-Builder the responsibility to assess poor ground conditions and their significance to the structure and to overall design performance. Under RFP Section 1-02.4(2) Subsurface Information, it is the GBR rather than the GDR that establishes the baseline against which a Differing Site Condition is measured.

That determination started the protest clock. The Design-Builder filed its Notice of Protest 006 in Skanska LTR 246 dated October 1, 2025, thirteen days later and within the fourteen-day window in RFP Section 1-04.5 Procedure, Protest, and Dispute by the Design-Builder. In WSDOT SL No. 9727-175 dated October 10, 2025, WSDOT granted a 59-day extension for the supplement, setting the deadline at December 8, 2025 and reserving 39 calendar days for the WSDOT response. That letter also asked the Design-Builder to share any information that would help the parties agree on the proper engineering solution rather than hold it for the final dispute package.

The Design-Builder filed the supplement, Skanska LTR 291 dated December 8, 2025. It advanced four arguments: that the GDR overburden values were factual errors rather than matters of professional judgment, that more than 245 post-award explorations satisfied the reasonable investigation standard, that the observed settlement met the Differing Site Condition definition under both parts (a) and (b), and that the GBR's poor ground classification addressed the kind of ground but not the magnitude of its behavior. The supplement carried an estimate of $25,407,284 and a preliminary schedule position of approximately seven months, tied to an Abutment 10 design package then expected in November 2026.

WSDOT reaffirmed the denial in WSDOT SL No. 9727-242 dated January 16, 2026, addressing all four arguments and adding the historical settlement record in Appendix G03 and the deep foundations shown in the Appendix N2 bridge as-builts. The Design-Builder filed a Notice of Dispute in Skanska LTR 336 dated January 30, 2026, on behalf of AECOM and GeoEngineers, and WSDOT acknowledged it in WSDOT SL No. 9727-257 dated February 6, 2026.

Before proceeding to the Dispute Review Board (DRB), the Design-Builder requested an escalation meeting to review the issue with executive level authorities and experts from both parties. Skanska LTR 374 dated March 13, 2026 proposed the week of April 6, 2026. WSDOT accepted in WSDOT SL No. 9727-307 dated March 27, 2026, noted that this work becomes critical path in March 2027, and asked for the design, geotechnical, structural, and embankment details in advance. The Design-Builder presented its proposed solution on April 22, 2026 and submitted the supporting geotechnical basis shortly after. Notice of Design Change (NDC) 145, Segment 2 Geotechnical Report Addendum 5, was finalized April 27, 2026 and carries the Abutment 10 deep foundation and the ESU 2C strength re-characterization. NDC 146, Addendum 6, was finalized April 29, 2026 and carries Walls 23.72R and 23.73R and the northbound approach embankment. The meeting was confirmed for May 8, 2026 in Skanska LTR 416 dated April 28, 2026 and WSDOT SL No. 9727-335 dated May 1, 2026.

The May 8, 2026 meeting brought together the WSDOT project office, WSDOT I-405 Program leadership, the WSDOT Headquarters Construction Office, the WSDOT State Geotechnical Engineer, the Skanska project office, Skanska leadership, AECOM, and GeoEngineers. The Design-Builder presented the geotechnical basis for its original design, the additional investigation it had carried out, and the solution it proposed for Walls 23.80R, 23.72R, 23.73R, and 23.74R and Abutment 10.

The Engineered Solution

The solution was developed by the Design-Builder and its engineers, AECOM and GeoEngineers, and was reviewed collaboratively by WSDOT subject matter experts through the design review process. It replaces the original scheme of spread footings on stone-column improved ground with a deep foundation at the abutment and a lightweight embankment behind it.

Abutment 10 deep foundation. Abutment 10 is redesigned onto three fully cased drilled shafts, 10 feet in diameter and approximately 275 feet deep, founded well below ESU 2C. A full-depth 1.5-inch steel casing is left in place and acts as a structural element rather than as temporary support. Tip grouting is used at each of the three shafts to induce a substantial portion of the elastic settlement at the shaft tips before the bridge loads are applied. The shafts carry a new shaft cap in place of the original spread footing, and crosshole sonic logging is used to verify shaft integrity.

Geofoam approach embankment. The northbound approach embankment is converted from granular fill to geofoam. The purpose is to take weight off the underlying clay, which limits further consolidation settlement and reduces downdrag on the adjacent existing fills that carry live traffic. The geofoam is fully encapsulated in a liner, above, below, and at the sides, to protect it against hydrocarbon degradation. The embankment also requires soil mass removal, a reinforced load distribution pad, a precast and cast-in-place fascia wall, slope paving, and custom interfaces where the existing drainage system meets the foam and liner.

Approach walls. Walls 23.72R and 23.73R and the associated wing walls are redesigned to suit the revised approach embankment and abutment configuration. Wall 23.74R receives a design modification. Wall 23.80R is disassembled and re-assembled, with monitoring and surcharge, and a temporary northbound on-ramp is required during that work.

Credits. The change deletes the original Abutment 10 spread footing and the original MSE wall, landscape, and fill scope in the embankment area. Both are credited against the change.

Conclusion

WSDOT has decided to compensate the Design-Builder for this added work. The settlement measured in ESU 2C exceeded what could reasonably have been expected at these structures, and the additional investigation required to understand it went well beyond what a Design-Builder would ordinarily perform. That combination does not represent a level of risk WSDOT intended to transfer to the Design-Builder under this Contract. Resolving the matter by Change Order rather than through the Dispute Review Board keeps the mainline bridge work moving ahead of the March 2027 critical path date, secures an acceptable foundation solution that WSDOT subject matter experts have reviewed, and settles the related open items in a single agreement. WSDOT has concluded that this resolution is in the best interest of the Project and of the agency.

Basis for the Change

Under RFP Section 1-04.4(1) WSDOT-Initiated Changes, WSDOT will make an equitable adjustment by agreement with the Design-Builder. This Change Order is that agreed adjustment.

In the light of the additional information and analysis performed by the DB and their EOR (with support from WSDOT), their original design for Abutment 10 and surrounding retaining walls is no longer appropriate. This requires a complete redesign of the work in that area. The new engineering solution requires a foundation and approach embankment at Abutment 10 that place the structure below the ESU 2C clay deposit and remove load from it, in place of the spread footings on stone-column improved ground shown in the Released for Construction documents. This Change Order compensates the Design-Builder for the difference between the two configurations, net of the credits identified below. The price also includes payment for supplemental schedule recovery efforts by the DB to recover a portion of the project critical path delay caused by this issue. In addition, there is compensation for extended overhead associated delay to the project critical path that could not be recovered.

The circumstances supporting this Change Order are as follows:

1. The settlement measured at Wall 23.80R exceeded the predicted range under normal construction loading, and the behavior could not be reproduced from the laboratory-derived parameters available at the time of design. It was also recognized that the issue extended beyond Wall 23.80 to encompass Abutment 10 and its’ associated retaining walls.

2. The exploration and analysis program required to characterize that behavior of the deeper soil unit went beyond the exploration and testing ordinarily performed for structures of this type. It took three borings to depths between 239.25 and 250 feet, in-situ vane shear testing, a full-scale gravel surcharge, an instrumented preload test running more than six months, and laboratory testing by three laboratories over seven months to finalize the data and reach conclusions.

3. The conditions caused a material increase in the cost and the time required for the Work. The original spread footings on stone-column improved ground are replaced by a deep foundation at Abutment 10 and a lightweight embankment behind it.

Cost and Time Extension

The agreed equitable adjustment for this Change Order is $36,000,000, made up of the following elements.

Direct costs

Indirect costs

Total

Of the amount payable, $1,000,000 is attributable to the time impact of the Sound Transit directed change, PCO 010B Platform Change. The balance of $35,000,000 is WSDOT's.

Protests resolved by this Change Order

This Change Order also resolves the protests listed below. Each is closed at no cost. No part of the amount payable is allocated to any of them, and WSDOT's determinations on those protests are unaffected.

The total time extension for this Change Order is 129 calendar days. 113 calendar days are attributable to Protest 006, the ESU 2C clay layer condition, and 16 calendar days are attributable to the Sound Transit directed change, PCO 010B Platform Change.

The milestones change as follows

• A. Substantial Completion: from 1884 calendar days to 2013 calendar days (March 23, 2029)
• C. BRT and Transit Vehicle Access: from 1505 calendar days to XXXX calendar days (XX/XX/XXXX)
• D. Ready for BRT Service: from 1655 calendar days to XXXX calendar days (XX/XX/XXXX)
• E. Toll Infrastructure Completion: from 1525 calendar days to 1654 calendar days (March 29, 2028)
• F. Toll Commencement: from 1655 calendar days to 1784 calendar days (August 3, 2028)

INTERNAL / PRIVILEGED

WSDOT POSITION PAPER

DRB Hearing - Protest 006 - DSC 006 Clay Layer ESU 2C (PCO 123)

Contract 9727 - I-405, Brickyard to SR 527 Improvement Project

Submitted by: Washington State Department of Transportation Date: {{DATE}}

1. Introduction

Pursuant to Request for Proposal (RFP) Chapter 1 General Provisions Section 1-04.5(1), Disputes, WSDOT hereby submits this position paper and supporting documents to the Dispute Review Board (DRB) for the upcoming DRB hearing on PCO 123 - DSC 006 Clay Layer ESU 2C.

This dispute concerns whether an unanticipated clay layer (Engineering Soil Unit 2C) beneath retaining walls (23.80R, 23.72R, 23.73R, 23.74R) and I-405 Mainline Bridge Abutment 10 in the Sammamish River Valley constitutes a Differing Site Condition (DSC) under RFP Section 1-04.7. The Design-Builder claims the settlement behavior observed at these structures differs materially from the contract baseline and was not reasonably foreseeable. WSDOT has twice denied the claim as without merit (WSDOT SL 9727-162, September 18, 2025, and WSDOT SL 9727-242, January 16, 2026).

The procedural history is as follows. Skanska first notified WSDOT of a potential DSC at Wall 23.80R in Skanska LTR 171 (April 9, 2025). Skanska expanded the DSC notice to all affected structures in Skanska LTR 226 (September 4, 2025). WSDOT denied the DSC in WSDOT SL 9727-162 (September 18, 2025). Skanska filed a Notice of Protest in Skanska LTR 246 (October 1, 2025) and submitted supplemental information in Skanska LTR 291 (December 8, 2025). WSDOT reaffirmed its denial in WSDOT SL 9727-242 (January 16, 2026). Skanska filed a Notice of Dispute in Skanska LTR 336 (January 30, 2026), filed on behalf of AECOM and GeoEngineers. WSDOT acknowledged the dispute in WSDOT SL 9727-257 (February 6, 2026).

The central question is whether the observed settlement constitutes a DSC under RFP Section 1-04.7, or whether those conditions fall within the Design-Builder's contractual risk allocation under RFP Section 1-02.4(2) and GBR Section 3.2.7. This paper summarizes the relevant contract requirements, the technical issues, the sequence of events, and WSDOT's position on Protest 006.

2. Project Summary

The I-405/Brickyard to SR 527 Improvement Project enhances four and a half miles of the corridor, primarily in Bothell, from just south of the State Route 522 interchange and ending at the SR 527 interchange. WSDOT, Sound Transit and design-build contractor Skanska USA Inc. will deliver improvements that benefit all users, while addressing aging infrastructure, opening upstream fish habitat, and connecting communities, freight and Regional Growth Centers throughout the corridor.

Since implemented in 2015, express toll lanes (ETL) have helped improve reliability of trips on the north end of the I-405 corridor. However, the single-lane section still experiences heavy congestion, especially for people traveling south during the morning commute. The project will extend the dual-express toll lane system on the north end of I-405 and improve access to the voter-approved Stride bus rapid transit service to address congestion and help keep all vehicles moving efficiently.

The DSC 006 dispute involves structures located in the Sammamish River Valley Area, approximately MP 23.59-24.00 along the I-405 corridor. This area encompasses retaining walls 23.80R, 23.72R, 23.73R, and 23.74R, and the I-405 Mainline Bridge Abutment 10. The Design-Builder's ground improvement program at these structures included stone column installation and surcharging to manage settlement in the soft soils underlying the Sammamish River Valley. The dispute centers on whether the settlement behavior observed during and after construction at these locations constitutes a DSC.

3. Relevant Contractual Requirements

3.1 RFP Section 1-02.1 - Responsibility for Design

RFP Section 1-02.1 establishes that:

"the Design-Builder undertakes full responsibility for delivery of the Project"

The provision further states:

"If the Contract Documents omit or misdescribe the Work necessary to be performed in order to deliver the Project in accordance with the intent of the Contract Documents, the Design-Builder shall not be excused from performing such omitted Work (no matter how extensive) or misdescribed details of the Work, and such Work shall be performed as if fully and correctly set forth and described in the Contract Documents, without entitlement to a Change Order hereunder except as specifically allowed by the Contract Documents."

This provision assigns comprehensive design responsibility to the Design-Builder.

3.2 RFP Section 1-02.2 - Reference Documents

RFP Section 1-02.2 provides:

"The Design-Builder is not entitled to rely on any document or information provided by WSDOT, except to the extent expressly provided otherwise in the Contract Documents. ... Unless stated otherwise in the Contract, the Design-Builder is not entitled to rely on the Reference Documents."

"The Design-Builder further acknowledges and agrees that (a) if and to the extent the Design-Builder or anyone on the Design-Builder's behalf uses any of said information in any way, such use is made on the basis that the Design-Builder, not WSDOT, has approved and is responsible for said information, and (b) the Design-Builder is capable of conducting and is obligated hereunder to conduct any and all studies, analyses and investigations as it deems advisable to verify or supplement said information, and that any use of said information is entirely at the Design-Builder's own risk and at its own discretion."

The GDR is classified as a Reference Document for this Design-Build contract per Appendix A1.

3.3 RFP Section 1-02.4 - Examination of Site of Work

RFP Section 1-02.4 provides:

"The Design-Builder has, prior to submitting its Proposal, in accordance with prudent and generally accepted engineering and construction practices, reviewed all Contract and Reference Documents provided by WSDOT; inspected and examined the Site and surrounding locations; and undertaken other appropriate activities sufficient to familiarize itself with surface and subsurface conditions discernible from the surface affecting the Project, to the extent necessary for submittal of a Proposal."

"The Design-Builder is solely responsible for all Site conditions discoverable from a reasonable Site examination."

This provision establishes a broad investigation obligation encompassing the full range of geotechnical evaluation activities.

3.4 RFP Section 1-02.4(1) - General (Investigation Obligation)

RFP Section 1-02.4(1) provides:

"It is the Design-Builder's responsibility to make interpretations and draw conclusions with respect to the character of the geotechnical materials encountered and their impact upon its Work, and perform additional explorations and testing, both prior to bid and post-award, to supplement the GBR and GDR data to design the Project elements."

"Any failure of the Design-Builder to take the actions described and acknowledged in this clause shall not relieve the Design-Builder from responsibility for estimating properly the difficulty and cost of successfully performing the Work, or from performance of the Work without additional expense to WSDOT."

3.5 RFP Section 1-02.4(2) - Subsurface Information

RFP Section 1-02.4(2) provides three critical rules:

"WSDOT makes no representation or warranty expressed or implied that: 1. The Design-Builder's interpretations from the GBR or GDR are correct."

"Whenever there is an inconsistency between geotechnical conditions described in the GBR and the information in the GDR, then the geotechnical conditions described in the GBR shall take precedence and shall be the geotechnical conditions against which actual geotechnical conditions encountered are compared for the purpose of determining if a Differing Site Condition exists."

"The behavior of such conditions may be dependent upon and influenced by the means and methods selected by the Design-Builder to perform the Work."

These three rules are central to the DSC analysis in this dispute.

3.6 RFP Section 1-03.5 - Ambiguities (Duty to Report)

RFP Section 1-03.5 provides:

"The Design-Builder shall not take advantage of any apparent error, omission, inconsistency, or other defect in the Contract Documents. The Design-Builder shall promptly notify WSDOT of any error, omission, inconsistency, or other defect that the Design-Builder may discover in the Contract Documents, and shall obtain specific instructions in writing from the WSDOT Engineer regarding any such error, omission, inconsistency, or other defect before proceeding with the Work affected thereby."

This provision establishes the Design-Builder's duty to report apparent errors or inconsistencies before proceeding with affected Work.

3.7 RFP Section 1-04.7 - Differing Site Conditions

RFP Section 1-04.7 provides:

"For Work unrelated to an ATC, Differing Site Conditions shall mean (a) actual subsurface or latent physical conditions encountered at the Site that are substantially or materially different from the baseline conditions identified in the GBR and the data in the GDR as set forth in Section 1-02.4(2) and which are not discoverable from a reasonable investigation and analysis of the Site, or (b) physical conditions of an unusual nature, differing materially from those ordinarily encountered and generally recognized as inherent in the type of Work provided for in the Contract and the Work Site characteristics ... provided in all cases that the Design-Builder had no actual or constructive knowledge of such conditions as of the Proposal Due Date."

Both elements must be satisfied: a material difference from baseline, and that the conditions were not discoverable through reasonable investigation.

3.8 RFP Section 1-04.7(1) - Burden of Proof

RFP Section 1-04.7(1) provides:

"The Design-Builder shall bear the burden of proving that a Differing Site Condition exists and that it could not reasonably have worked around the Differing Site Condition so as to avoid additional cost."

The burden falls on the Design-Builder to prove both elements.

3.9 RFP Section 2.6 and Section 2.6.2.1 - Geotechnical and GDM Modifications

RFP Section 2.6.5.2 provides:

"Geotechnical engineering and analyses shall be based on the findings from subsurface field investigation explorations and laboratory tests performed by the Design-Builder and information contained in the GDR."

RFP Section 2.6.2.1 (Design-Build Modifications to the GDM) identifies provisions that do not apply to this Design-Build contract:

"WSDOT has identified the following provisions of the WSDOT Geotechnical Design Manual that do not apply to design-build contracts: ... Chapter 22, Geotechnical Project Development, Reports, and Support for Design-Build Projects"

GDM Chapter 22 defines the GDR as a "contract document," but that designation applies to traditional Design-Bid-Build projects. Section 2.6.2.1 excludes GDM Chapter 22 from this Design-Build contract. For this contract, the GDR is classified as a Reference Document per Appendix A1.

3.10 GBR Section 3.2.7 and Table 1 - Poor Ground and Sammamish Valley Baseline

The GBR is a Contract Document (not a Reference Document). GBR Section 3.2.7 defines poor ground conditions in full as follows:

"Variable and poor ground conditions will be encountered within the Project limits. Poor ground conditions are defined as loose granular soil, soft cohesive soil, and organic soil (i.e., including but not limited to peat) that can create the likelihood of immediate and long-term settlement, inadequate bearing strength, and instability during or following the completion of construction. Baselined areas where poor ground conditions are likely to be encountered are identified in Table 1."

"Poor ground conditions are defined to occur where uncorrected standard penetration resistance (SPT) blow counts are less than or equal to 10 for non-cohesive soils and less than or equal to four for cohesive soils and all organic soils. Where these physical conditions are encountered, the ground behavior will be controlled by the design and construction decisions of the Design-Builder. Therefore, it shall be the Design-Builder's responsibility to assess these poor ground conditions and their related significance to the structure and the overall design performance to be achieved."

(GBR p.9, lines 5-18.)

GBR Table 1 (p.11) identifies baselined areas where poor ground conditions are likely to be encountered. The DSC 006 structures (Walls 23.72R-23.80R and Abutment 10) are located in the Sammamish River Valley Area (MP 23.59-24.00). The Sammamish River Valley row in Table 1 carries a plain checkmark in the Poor Ground column without Footnote 3's superscript. This means poor ground at all depths is a baseline condition at these wall locations. Footnote 3 ("As a baseline condition, poor ground is not present deeper than 10 feet below the existing ground surface") applies to portions of the Brickyard Area and Canyon Park, not the Sammamish River Valley. This is verified from GBR Table 1 (p.11) and Figure 3, Sheet 6.

GBR Section 4 (p.12) further states: "No design recommendations or interpretive information is provided herein." The GBR provides baselines, not design parameters. The Design-Builder must determine settlement magnitudes, consolidation timeframes, clay thicknesses, and engineering parameters through its own investigation and analysis, using the GDR and the reference information compiled in Appendix G03.

GBR Section 2.1 (p.5) describes the reference information: "a reference document has been compiled to include data and information sources from past projects. The reference document contains geological, geotechnical, and regional geology information for the Project area." This reference document is Appendix G03, which contains the 60-year historical record described in Section 4.5.

4. Discussion of Settlement and Clay Layer Conditions

This section provides a plain-language explanation of the technical issues for the Board's reference. It is intended as background. WSDOT's arguments are presented in Section 6.

4.1 Background on ESU 2C and Affected Structures

Engineering Soil Unit 2C (ESU 2C) is a clay layer encountered beneath retaining walls 23.80R, 23.72R, 23.73R, 23.74R, and I-405 Mainline Bridge Abutment 10 in the Sammamish River Valley. The Design-Builder's ground improvement program at these structures included stone column installation and surcharging. The Design-Builder's settlement predictions indicated the settlement would be manageable within the design and construction timeline. Observed settlement exceeded those predictions.

4.2 GDR Overburden Value Discrepancy

The GDR consolidation test results for two samples (NE-30vw-19 S-12 and NE-32p-19 S-10) used overburden values of 1060 psf and 1065 psf, which imply a saturated unit weight of approximately 75 pcf. Laboratory-tested saturated unit weight averaged 113 pcf (WSDOT SL 9727-162, Attachment 1 IED V4, pp.2-3). This discrepancy produced overburden error factors of 2.39x and 2.00x, inflating the GDR-reported overconsolidation ratio (OCR) values from the corrected values GeoEngineers reported of approximately 1.6 and 1.0 to the 3.57 and 1.99 calculated from the GDR.

A higher OCR suggests the clay has been preloaded by historical stresses and would be less compressible under new loading. A lower OCR suggests the clay is normally consolidated or only lightly overconsolidated, making it more compressible. The inflated OCR values in the GDR would lead to less conservative (more optimistic) settlement predictions.

The discrepancy between the unit weights implied by the GDR consolidation test overburden values and the laboratory-measured saturated unit weights was apparent from comparing the Design-Builder's own work products. The GeoEngineers memo attached to Skanska LTR 291 (Section 2.0, item 1, PDF p.14) identifies the same overburden value issue.

4.3 Design-Builder's Settlement Predictions vs Observed Settlement

The Design-Builder's settlement predictions relied on parameters selected from the GDR consolidation test data. The Design-Builder selected median values from a variable dataset. Observed settlement exceeded the predictions. The Design-Builder contends this demonstrates a material difference from baseline.

The GeoEngineers Appendix A (Timeline of Activities, Skanska LTR 291, PDF pp.47-49) provides a construction timeline relevant to the sequence of observations. Construction on Wall 23.80R began September 2, 2024. By October 18, 2024 (46 days later), the fascia wall leveling pad was poured in the area that would exhibit excessive settlement. By October 31, 2024, wall panels were tilting 2 to 5 inches. Skanska LTR 171 reports that after panels were reset on November 6, 2024, Skanska observed the next day (November 7) that reset panels had gained 1 to 2 inches of positive batter overnight, indicating active and ongoing settlement under normal construction loading. The affected wall sections were torn down November 6-15, 2024 and rebuilt January-February 2025. The Design-Builder's own Figure 21 (GeoEngineers Memo, PDF p.46) shows the pre-award and post-award settlement predictions were virtually identical (both approximately 1 inch of post-construction settlement). This indicates the Design-Builder's post-award investigation program did not cause it to revise or challenge the GDR-derived settlement parameters.

4.4 Stone Column Ground Improvement and CPT Evidence

The Design-Builder installed stone columns as part of its ground improvement program. The Design-Builder's own pre- and post-stone-column CPT (Cone Penetration Test) investigations (Skanska LTR 291, GeoEngineers Memo Figures 1A-1B for locations, PDF pp.23-24, and Figures 12-14 for CPT tip resistance profiles, PDF pp.37-39) show reduced tip resistance within the ESU 2C clay layer following stone column installation. Reduced tip resistance is consistent with construction-induced disturbance to the clay structure.

4.5 Historical Settlement Record (Appendix G03)

Appendix G03 is Reference Information available during procurement. It includes extensive historical settlement analyses from the Woodinville Interchange vicinity. The record spans 60 years and includes:

• A December 28, 1966 WSDOT Foundation Design Recommendation by R. V. LeClerc, P.E., Materials Engineer, stating: "Our calculations indicate a settlement of 3.2 ft is possible at this point, with 2 years required for 90 per cent. Therefore it is our opinion that some other form of foundation treatment should be specified" (Appendix G03 Vol 1, p.564). The accompanying Foundation Design Recommendations sheets (pp.567-570) specify "2 yr" preload durations at multiple stations across the Woodinville Interchange.

• WSDOT 1959 and 1966 settlement calculations predicting consolidation settlements of 1.4 to 4.0 feet at various interchange locations, with time-settlement curves extending 40+ years (Appendix G03 Vol 1, pp.170-232, pp.661-694).

• A Shannon and Wilson, Inc. Location Soils Survey dated March 4, 1966, independently documenting clay deposits of 10-30+ feet thickness with SPT N-values of 2-10 blows/ft and recommending preloading and surcharging (Appendix G03 Vol 1, pp.411-447).

• A November 15, 1956 WSDOT inter-office communication confirming: "settlements in the order of 0.5 ft. could be expected at the bridge ends ... from loads imposed by the approach fills" (Appendix G03 Vol 1, pp.60-62).

• A January 3, 1967 highway commission communication recommending scheduling a resurfacing project "1 or 2 years after traffic opening" due to anticipated long-term settlement and predicting "an additional 1' to 2' of settlement" during a recommended overload period of "a minimum 4 month period" (Appendix G03 Vol 1, pp.1062-1066).

These documents collectively record settlement magnitudes (up to 4.0 ft), multi-year consolidation timeframes (up to 2 years for 90% primary consolidation), and ground improvement techniques (preloading, sand drains, staged construction) at this interchange. These records were available as Reference Information during procurement.

Appendix G03 Vol 2 includes additional evidence from multiple independent sources:

• A 1994 geotechnical report by Hong West & Associates (HWA) for the Bothell-Swamp Creek project (MP 23.78-30.32) documented a 40-foot-thick layer of very soft lean clay (CL) at BH-1 (Sta L 866+52) with SPT N=0/0/0 (push) from 25-30 ft depth. Four consolidation tests yielded Cc values of 0.19-0.77 and estimation equations Cc=0.007(Wn-10) and Cc=0.009(LL-10). Organic silt at BH-7 had e0=3.3 (very high compressibility) and dry density of 34.3 pcf (Appendix G03 Vol 2, pp.635-876).

• A 1994 bridge widening report by Landau Associates Inc. (LAI) independently confirmed AASHTO Soil Profile Type III ("soft to medium stiff clay 30 ft or more in thickness") at the SR 522 interchange. Boring L-6 recorded the sampler "advanced under weight of hammer and rods" at 25 ft depth. LAI provided design parameters of Su=200 psf for organic silt/peat and Su=500 psf for soft clay, and warned that "compressible organic silt and peat near the existing ground surface north of the river may lead to unacceptable overall and differential falsework settlement." This report was included in the Bothell Toll Lanes RFP as reference G7 (Appendix G03 Vol 2, pp.1218-1426).

• A 1996 geotechnical report by Hong West & Associates for the North Creek Diversion Project, a King County sewer pipeline that crossed the same Sammamish River Valley, documented very soft lean clay with SPT blow counts of 0-0-0 at valley-floor elevations identical to the DSC 006 wall corridor. Peat with moisture content up to 228% overlay the clay. This was a completely separate project by a different agency and consultant (Appendix G03 Vol 2, North Creek Diversion extract).

• A 1996 WSDOT bridge widening geotechnical report for the SR 522 interchange area compiled boring data from three investigation eras (1966 Shannon & Wilson, 1966 WSDOT, and 1996 WSDOT). Lab testing revealed organic silt (OH) with moisture content of 136% and liquid limit of 155 at 26 ft depth. P-Y curve foundation design data documented an organic silt layer with unit weight of only 43 pcf at the North Creek Bridge. The report's bibliography listed the HWA 1994 report as covering "M.P. 23.78 to M.P. 30.32," the exact milepost of Wall 23.80R (Appendix G03 Vol 2, pp.2099-2239).

• A February 1996 WSDOT geotechnical constructability review for the same bridge widening identified a "compressible layer" at Piers NB-10, NB-11, NB-12, and SB-12 at the SR 522 interchange. Shaft tip elevations had to be located below this layer. This review was authored by T.M. Allen and J.G. Cuthbertson of the WSDOT Geotechnical Branch (Appendix G03 Vol 2, pp.2240-2242).

The GBR directed the Design-Builder to assess poor ground conditions at the DSC 006 wall locations (GBR Section 3.2.7). Appendix G03 provided the data to do so. The record spans 60 years (1956-1996), encompasses 11+ independent firms and agencies, and documents settlement magnitudes up to 4-5 ft, consolidation periods of 2+ years, clay thicknesses of 40-63+ ft, and engineering parameters (Cc=0.19-0.77, Cv=0.005-0.012 ft2/day, OCR near 1.0) at the same interchange. A reasonably competent Design-Builder reviewing G03 in response to the GBR's directive would have identified these conditions before bid.

4.6 Appendix N2 Deep Foundations in the Vicinity

Appendix N2 Bridge As-Builts includes drawings showing that bridges in the vicinity bear on deep foundations. The use of deep foundations at nearby structures indicates the area was recognized as having challenging settlement and bearing capacity conditions.

5. Sequence of Events and Chronology

6. WSDOT Position

6.1 The GBR Baseline Is Dispositive

Skanska's Argument: The GBR may have baselined "poor ground" generally, but it did not baseline OCR values as low as 1.0-1.3 or compressibility characteristics inconsistent with the GDR consolidation test data. The clay layer behavior observed during construction differs materially from the contract baseline.

WSDOT's Response: The Contract establishes that the GBR, not the GDR, is the baseline for DSC comparison. Under RFP Section 1-02.4(2), when there is an inconsistency between geotechnical conditions described in the GBR and information in the GDR, the GBR takes precedence. The Design-Builder's arguments repeatedly compare observed conditions to GDR data rather than the GBR baseline. This comparison is inconsistent with the contractual framework.

GBR Section 3.2.7 does not merely "classify" ground as poor. It expressly assigns the Design-Builder responsibility to "assess these poor ground conditions and their related significance to the structure and the overall design performance to be achieved" (GBR p.9). "Significance to the structure" and "design performance" inherently encompass magnitude and behavior. The Design-Builder's argument that the GBR only classifies ground without addressing magnitude misreads the provision. The GBR's language requires the Design-Builder to assess the full range of settlement characteristics, not merely acknowledge that poor ground exists.

As described in Section 3.10, GBR Table 1 baselines poor ground in the Sammamish River Valley Area (MP 23.59-24.00) without Footnote 3's 10-foot depth limit. Poor ground at all depths is a baseline condition at the DSC 006 structure locations.

The very conditions Skanska is complaining about were anticipated by the Contract and placed within the Design-Builder's risk allocation. The Contract assigned that responsibility to the Design-Builder.

6.2 GDR Overburden Values: Section 1-03.5 Duty, Not WSDOT Warranty

Skanska's Argument: The "incorrect overburden values" in the GDR are factual numerical miscalculations in consolidation test results stamped by WSDOT, not matters of professional judgment. RFP Section 1-02.4(2).1 therefore does not apply. WSDOT cannot avoid responsibility for factual misrepresentations by re-labeling the document. (Skanska LTR 291, GeoEngineers Memo Section 2.0, item 1, PDF p.14.)

WSDOT's Response: Even if GDR values contain errors, the Contract establishes two separate obligations that the Design-Builder has not satisfied.

First, RFP Section 1-02.4(2) makes no representation or warranty that the Design-Builder's interpretations from the GBR or GDR are correct. The GDR is a Reference Document provided at the Design-Builder's risk per RFP Section 1-02.2.

Second, RFP Section 1-03.5 required the Design-Builder to promptly notify WSDOT and obtain written instructions upon discovering apparent errors, omissions, or inconsistencies. As described in Section 4.2, the discrepancy between the implied unit weights (approximately 75 pcf) and laboratory-measured values (113 pcf) was apparent from comparing the Design-Builder's own work products. The GeoEngineers memo itself raises the overburden value issue (Skanska LTR 291, GeoEngineers Memo Section 2.0, item 1, PDF p.14), confirming the Design-Builder was aware of the discrepancy. However, no Section 1-03.5 notification was filed. The Design-Builder did not seek written instructions from WSDOT before proceeding with affected Work.

6.3 Section 2.6 Does Not Create a Warranty or Override Risk Allocation

Skanska's Argument: RFP Section 2.6 states that "geotechnical engineering and analyses shall be based on ... information contained in the GDR." The Design-Builder therefore had a contractual right to rely on GDR values without independent verification. WSDOT directed reliance on GDR data.

WSDOT's Response: RFP Section 2.6 requires the Design-Builder to review and use available GDR information as part of its overall geotechnical evaluation. The requirement to "use" information is not the same as a right to "rely" on it without question. Section 2.6 does not convert the GDR into a warranty by WSDOT of Design-Builder interpretations. It does not shift the risk allocation established by RFP Section 1-02.4(2). The Design-Builder retains the obligation to reconcile inconsistencies and exercise engineering judgment in selecting design parameters.

RFP Section 2.6.2.1 (Design-Build Modifications to the GDM) explicitly lists "Chapter 22, Geotechnical Project Development, Reports, and Support for Design-Build Projects" among provisions that "do not apply to design-build contracts." GDM Chapter 22 defines the GDR as a "contract document," but that designation applies to traditional Design-Bid-Build projects. For this Design-Build contract, the GDR is classified as a Reference Document per Appendix A1. RFP Section 1-02.2 provides that Reference Information is at the Design-Builder's risk.

The Design-Builder's reliance on GDR data without independent verification remains at the Design-Builder's risk. Section 2.6 does not alter this allocation.

6.4 "Reasonable Investigation" Requires Interpretation, Not Just Data Collection

Skanska's Argument: The Design-Builder performed 245+ additional explorations, SIPs, extensive laboratory testing, and a long-term monitoring program. This volume of post-award testing meets or exceeds the "reasonable investigation" standard in RFP Section 1-02.4(1).

WSDOT's Response: "Reasonable investigation" under RFP Section 1-02.4(1) requires the Design-Builder to "make interpretations and draw conclusions with respect to the character of the geotechnical materials encountered and their impact upon its Work." This is a contractual obligation that encompasses analysis and interpretation, not merely data collection. The Design-Builder's obligation extends beyond gathering data to evaluating, reconciling, and interpreting that data in the context of all available information.

The question is whether the Design-Builder's investigation, interpretation, and resulting design assumptions were reasonable and appropriately conservative given the variability and information available. WSDOT notes the following:

The Design-Builder selected median values from a variable dataset without demonstrating that it evaluated the sensitivity of settlement predictions to reasonable ranges of key parameters. In variable soil conditions, evaluating sensitivity to reasonable parameter ranges informs design values and risk management during design development. This is a component of the "interpretations and conclusions" required by RFP Section 1-02.4(1), not merely a professional standard of practice. The absence of demonstrated sensitivity analysis undermines the Design-Builder's claim that settlement behavior was unforeseeable.

The Design-Builder did not reconcile discrepancies between unit weights used for other design analyses and values reported in the GDR. This reconciliation is part of the interpretation obligation under RFP Section 1-02.4(1).

The Design-Builder's own Figure 21 (GeoEngineers Memo, Skanska LTR 291, PDF p.46) illustrates this point. The figure compares post-construction settlement estimates at Abutment 10 across four analysis phases. The pre-award analysis and the post-award analysis produce virtually identical predictions (both approximately 1 inch). The post-award line does not diverge from the pre-award line despite 245+ additional explorations. This indicates the Design-Builder's post-award investigation program did not prompt it to revisit, challenge, or independently verify the GDR consolidation parameters. The volume of explorations is not at issue. The adequacy of interpretation is.

WSDOT further notes that the Design-Builder controlled the laboratory testing program. WSDOT SL 9727-149 (September 4, 2025) transmitted laboratory results for Borings B-1-25, B-2-25, and B-3-25. The cover letter states that a GeoEngineers representative "personally delivered the soil samples to the State Materials laboratory for testing. They identified the specific portions of each sample to be tested and supplied all necessary parameters for the advanced testing procedures." The Design-Builder's consultant selected which samples to test, at what depths, and specified the confining pressures for the triaxial tests. WSDOT's laboratory executed the testing protocol GeoEngineers designed. The investigation was the Design-Builder's investigation throughout.

6.5 Settlement Behavior Was Foreseeable and Discoverable

Skanska's Argument: Surcharge settlement data and backcalculated soil parameters demonstrate a material difference from the GDR/GBR baseline under RFP Section 1-04.7(a) and unusual nature under RFP Section 1-04.7(b). The encountered conditions satisfy both DSC prongs and were not reasonably anticipated.

WSDOT's Response: Even if the Design-Builder could demonstrate a material difference from baseline under RFP Section 1-04.7(a) or (b), the DSC definition requires that the conditions were "not discoverable from a reasonable investigation and analysis of the Site." The Design-Builder has not established this element.

The GBR directed the assessment. G03 provided the data.

GBR Section 3.2.7 (p.9) explicitly warned of "soft cohesive soil, and organic soil" causing "immediate and long-term settlement, inadequate bearing strength, and instability" in the Sammamish River Valley. GBR Table 1 (p.11) baselines poor ground at the DSC 006 wall locations at all depths, without Footnote 3's 10-foot depth limit that applies to other areas. The GBR then assigns the Design-Builder responsibility to "assess these poor ground conditions and their related significance to the structure and the overall design performance to be achieved." The GBR provides no settlement magnitudes, no consolidation timeframes, no clay thicknesses, and no engineering parameters for this area. GBR Section 4 (p.12) states: "No design recommendations or interpretive information is provided herein."

The GBR did not need to provide those parameters. Appendix G03 provided them. As described in Section 4.5, G03 contains 60 years of subsurface investigations at the SR 522 interchange from 11+ independent firms and agencies (1956-1996). A Design-Builder performing the assessment required by Section 3.2.7 would have found:

• Settlement magnitudes of 0.5 to 4-5 ft, both predicted and measured, across eight or more independent analyses. The 1966 Foundation Design Recommendation states "a settlement of 3.2 ft is possible at this point, with 2 years required for 90 per cent" (Appendix G03 Vol 1, p.564). The 1968 field data confirms settlements of 1-3+ ft were measured and were still continuing after 2-3 years of loading (Appendix G03 Vol 1, pp.1127-1140).

• Clay thicknesses of 40-63+ ft at the interchange. HWA BH-1 at MP 23.78 documented 40 ft of very soft CL with SPT N=0/0/0 from 25-70 ft depth (Appendix G03 Vol 2, pp.635-876). WSDOT boring H-2-14 found continuous gray clay from 27 to 90+ ft (Appendix G03 Vol 1, pp.530-557). These thicknesses far exceed the GBR's SPT N<=4 threshold for poor ground in cohesive soils.

• Consolidation parameters including Cc=0.19-0.77 from 11+ tests across three decades of work, Cv=0.005-0.012 ft2/day in the soft clay, and OCR near 1.0 indicating normally consolidated conditions (Appendix G03 Vol 2, pp.870-883, HWA 1994 Appendix E).

• Ground improvement precedent including sand drains "18 in. in diameter on 10-ft spacing" (LeClerc, 1966, Appendix G03 Vol 1, p.565), wick drains (HWA, 1996, Appendix G03 Vol 2, pp.2099-2118), surcharge loading, and staged construction at this exact interchange over a 40-year period. The 1966 sand drain recommendation is a direct predecessor to the stone column treatment used in the current project.

• Foundation type precedent showing that every bridge pier at the SR 522 interchange has required pile foundations since the 1960s ("All piers to be on pile foundations," Appendix G03 Vol 1, p.~890). A February 1996 WSDOT constructability review identified a "compressible layer" at Piers NB-10, NB-11, NB-12, and SB-12 that constrained drilled shaft design (Appendix G03 Vol 2, pp.2240-2242).

These conditions were discoverable through the reasonable investigation and analysis required by RFP Section 1-02.4(1). The "not discoverable" element of RFP Section 1-04.7 is not met.

Independent confirmation from multiple sources.

The foreseeability record is not limited to WSDOT investigations. G03 includes reports from at least 11 independent firms and agencies, all documenting the same soft clay at the same location:

• Landau Associates Inc. (1994) independently classified the SR 522 interchange subsurface as AASHTO Soil Profile Type III ("soft to medium stiff clay 30 ft or more in thickness") and warned that "compressible organic silt and peat near the existing ground surface north of the river may lead to unacceptable overall and differential falsework settlement" (Appendix G03 Vol 2, pp.1218-1426). This report was included as reference G7 in the prior Bothell Toll Lanes RFP.

• Hong West & Associates (1996) documented SPT N=0-0-0 in very soft lean clay at valley-floor elevations identical to the DSC 006 wall corridor, in a King County sewer pipeline project unrelated to WSDOT (Appendix G03 Vol 2, North Creek Diversion extract).

• Metropolitan Engineers (1970), Earth Consultants (1980), GeoEngineers (1993), and Converse Consultants (1987) all documented soft to very soft clay at nearby locations in the Sammamish River Valley (Appendix G03 Vol 2, HWA 1996 Appendix C).

As described in Section 4.6, nearby bridges bear on deep foundations (Appendix N2), further indicating the area was recognized as having challenging settlement conditions. Where deep foundations were selected for nearby bridges, a prudent Design-Builder would evaluate whether shallow-supported structures and ground improvement programs at the same location would encounter similar settlement challenges.

The Design-Builder's own timeline confirms discoverability.

The GeoEngineers Appendix A (Skanska LTR 291, PDF pp.47-49) shows that GeoEngineers recommended stopping work on Abutment 10 and Walls 23.72R/23.73R on March 22, 2025, ten days before the April 1 email to WSDOT. GeoEngineers' concern was that "the ESU 2C may be settling more than expected and the issue could affect those other design elements also." This stop-work recommendation confirms that the Design-Builder's own geotechnical consultant recognized the settlement risk was broader than the initial Wall 23.80R observation. The settlement behavior became apparent during construction, not because of unforeseeable subsurface conditions, but because the Design-Builder's pre-construction analysis had not accounted for the full range of clay compressibility at these locations.

As described in Section 4.4, the Design-Builder's own pre- and post-stone-column CPT investigations reflect disturbance to the clay layer from stone column installation. RFP Section 1-02.4(2) provides that subsurface behavior may be influenced by the Design-Builder's means and methods. The backcalculated OCR values on which the Design-Builder's settlement predictions rely may reflect the combined effects of soil properties and construction-induced disturbance, not solely in-situ conditions.

6.6 Burden of Proof Not Met

Under RFP Section 1-04.7(1), the Design-Builder bears the burden of proving that a DSC exists and that it could not reasonably have worked around the condition to avoid additional cost. The Design-Builder has not met this burden. The Design-Builder's supplemental materials do not address:

1. The GBR baseline. The Design-Builder does not acknowledge that under RFP Section 1-02.4(2), the GBR (not the GDR) establishes the geotechnical baseline for DSC comparison. The Design-Builder's arguments compare observed conditions to GDR data rather than the GBR baseline.

2. Sensitivity analysis. The Design-Builder has not provided evidence that it evaluated the sensitivity of settlement predictions to reasonable ranges of key parameters in variable soil conditions.

3. Section 1-03.5 duty. The Design-Builder does not address its duty under RFP Section 1-03.5 to seek written instructions upon discovering apparent errors or inconsistencies. If the Design-Builder believed the GDR overburden values were erroneous, Section 1-03.5 required prompt notification.

4. Means and methods influence. The Design-Builder does not analyze how stone column installation influenced settlement behavior. The Design-Builder's own CPT data reflects disturbance from stone column installation, yet the supplemental materials do not discuss this influence. The choice of ground improvement method, installation sequence, and spacing are means-and-methods decisions within the Design-Builder's risk framework per RFP Section 1-02.4(2).

6.7 WSDOT's Procedural Response

WSDOT has engaged collaboratively throughout this dispute. Upon receiving the initial DSC notice (Skanska LTR 171, April 9, 2025), WSDOT did not immediately deny the claim. WSDOT SL 9727-103 (April 23, 2025) stated that WSDOT "will continue to partner with Skanska to determine a path forward as additional information is gathered." WSDOT then participated in the subsequent investigation period, including performing laboratory testing at the State Materials Laboratory on samples provided by GeoEngineers (WSDOT SL 9727-149, September 4, 2025). WSDOT issued its formal determination only after the Design-Builder expanded the claim scope (Skanska LTR 226, September 4, 2025) and five months of collaborative investigation.

The protest procedural timeline proceeded as follows. Skanska LTR 246 (October 1, 2025) filed the Notice of Protest and requested a 75-day extension to provide supplemental information per RFP Section 1-04.5.2. WSDOT SL 9727-175 (October 10, 2025) responded by granting a 59-day extension (supplement due December 8, 2025) and stating that WSDOT would require 39 calendar days to review and respond after receipt of the supplement. In that same letter, WSDOT requested early information sharing, stating: "If there is any important piece of information that would help us all reach agreement on the proper engineering solution, please provide it now rather than hold until the final dispute package." Skanska LTR 291 (December 8, 2025) filed the supplement within the 59-day window. WSDOT SL 9727-242 (January 16, 2026) issued the response 39 days after receipt of LTR 291, consistent with the timeline established in SL 9727-175. The Design-Builder timely filed its Notice of Dispute (Skanska LTR 336, January 30, 2026) within 14 days of receiving the determination.

7. Conclusion

The contract framework is clear. The GBR, not the GDR, is the baseline for DSC comparison under RFP Section 1-02.4(2). GBR Section 3.2.7 baselined poor ground conditions at the DSC 006 structure locations and assigned the Design-Builder responsibility to assess those conditions and their "significance to the structure and the overall design performance to be achieved." GBR Table 1 baselines poor ground in the Sammamish River Valley Area without the 10-foot depth limit that applies to other zones.

The conditions at issue were foreseeable from reference information available during procurement. The GBR told bidders to assess poor ground. Appendix G03 provided 60 years of data (1956-1996) from 11+ independent firms and agencies answering that directive, documenting settlement magnitudes up to 4-5 feet, consolidation periods of 2+ years, clay thicknesses of 40-63+ feet, and engineering parameters (Cc=0.19-0.77, Cv=0.005-0.012 ft2/day) at the same interchange. Nearby bridges on deep foundations (Appendix N2) further indicate the area was recognized as having challenging settlement conditions. The GBR provided no quantitative parameters for this area because it did not need to. G03 provided them. These conditions were discoverable through the reasonable investigation and analysis required by RFP Section 1-02.4(1).

The Design-Builder's position has structural weaknesses. The Design-Builder compares observed conditions to the GDR rather than the GBR baseline. The Design-Builder has not demonstrated sensitivity analysis on variable soil parameters. The Design-Builder did not file a Section 1-03.5 notification regarding the GDR overburden discrepancy. The Design-Builder has not addressed the influence of stone column installation on settlement behavior. And the Design-Builder has not carried its burden of proof under RFP Section 1-04.7(1).

WSDOT maintains that the outcomes observed are a result of design and investigation decisions made by the Design-Builder within the Contract's risk framework and do not constitute a Differing Site Condition under RFP Section 1-04.7.

8. Recommendations Sought From the DRB

WSDOT respectfully requests that the Board provide a recommendation on the following question:

Whether the subsurface conditions encountered at Walls 23.80R, 23.72R, 23.73R, 23.74R, and I-405 Mainline Bridge Abutment 10 constitute a Differing Site Condition under RFP Section 1-04.7, or whether those conditions fall within the Design-Builder's contractual risk allocation under RFP Section 1-02.4(2) and GBR Section 3.2.7.

9. List of Attachments

1. RFP Appendix A1 - Contract and Reference Document Classification
2. RFP Section 1-02.1 - Responsibility for Design
3. RFP Section 1-02.2 - Reference Documents
4. RFP Section 1-02.4 - Examination of Site of Work
5. RFP Section 1-02.4(1) - General (Investigation Obligation)
6. RFP Section 1-02.4(2) - Subsurface Information
7. RFP Section 1-03.5 - Ambiguities
8. RFP Section 1-04.7 - Differing Site Conditions
9. RFP Section 1-04.7(1) - Burden of Proof
10. RFP Section 2.6 - Geotechnical
11. RFP Section 2.6.2.1 - Design-Build Modifications to the GDM
12. GBR Section 3.2.7 - Poor Ground (extract)
13. GBR Table 1 - Baseline Conditions (extract)
14. GBR Figure 3, Sheet 6 - Sammamish River Valley Area
15. Skanska LTR 171 - DSC 006 Potential DSC at Wall 23.80R (April 9, 2025)
16. WSDOT SL 9727-103 - Initial Response to DSC 006 (April 23, 2025)
17. Skanska LTR 226 - Expanded DSC Notice (September 4, 2025)
18. WSDOT SL 9727-149 - WSDOT Laboratory Testing Package 01 (September 4, 2025)
19. WSDOT SL 9727-162 - Written Determination Denying DSC 006 (September 18, 2025)
20. WSDOT SL 9727-162, Attachment 1 - Initial Engineering Decision V4
21. Skanska LTR 244 - Laboratory Testing Discrepancies (September 30, 2025)
22. Skanska LTR 246 - Notice of Protest 006 (October 1, 2025)
23. WSDOT SL 9727-175 - Acknowledged Protest, Granted Extension (October 10, 2025)
24. WSDOT SL 9727-180 - Corrected Lab Data, No-Warranty Reaffirmed (October 17, 2025)
25. Skanska LTR 291 - Supplement to Notice of Protest 006 (December 8, 2025)
26. WSDOT SL 9727-242 - Response to Supplement, Denial Reaffirmed (January 16, 2026)
27. Skanska LTR 336 - Notice of Dispute (January 30, 2026)
28. WSDOT SL 9727-257 - Acknowledged Dispute (February 6, 2026)
29. Appendix G03, Vol 1, pp.60-62 - 1956 WSDOT Inter-Office Communication
30. Appendix G03, Vol 1, pp.170-232 - 1959 Settlement Calculations
31. Appendix G03, Vol 1, pp.411-447 - 1966 Shannon and Wilson Location Soils Survey
32. Appendix G03, Vol 1, pp.563-570 - 1966 Foundation Design Recommendations (LeClerc, "2 years required for 90 per cent")
33. Appendix G03, Vol 1, pp.661-694 - 1966 Settlement Calculations
34. Appendix G03, Vol 1, pp.1062-1066 - 1967 Highway Commission Communication
35. Appendix G03, Vol 1, pp.524-562 - 1966 Foundation Recs ES & WS Ramps (LeClerc, 17 borings, "4 to 5 ft" subsidence)
36. Appendix G03, Vol 1, pp.643-651 - 1966 Slope Stability Analyses (F.S. as low as 0.589)
37. Appendix G03, Vol 1, pp.714-931 - 1966 Woodinville IC Plans and Boring Logs (25+ borings, "IN PRACTICALLY LIQUID STATE")
38. Appendix G03, Vol 1, pp.1127-1140 - 1968 Settlement and Pore Pressure Measurements (field data)
39. Appendix G03, Vol 2, pp.635-876 - 1994 HWA Bothell-Swamp Creek GeoRep (BH-1 at MP 23.78, N=0/0/0, 40 ft CL)
40. Appendix G03, Vol 2, pp.1218-1426 - 1994 LAI SR 522 Bridge Widening (Soil Profile Type III, Su=200/500 psf)
41. Appendix G03, Vol 2, pp.2099-2239 - 1996 Bridge Widening GeoRep (OH MC=136%, 15+ borings, 3 investigation eras)
42. Appendix G03, Vol 2, pp.2240-2242 - 1996 Geotech Constructability Review ("compressible layer" at SR 522 piers)
43. GBR vs G03 Comparison Summary (WSDOT work product)
44. Appendix N2 - Bridge As-Builts (Vicinity Deep Foundations)

Respectfully submitted,

Washington State Department of Transportation Evelyn Pao, P.E., Project Director