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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

1. Introduction

Pursuant to RFP Section 1-04.5(1), Disputes, WSDOT submits this position paper to the Dispute Review Board (DRB) for the hearing on PCO 123 — DSC 006 Clay Layer ESU 2C.

This dispute concerns whether 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 differs materially from the contract baseline and was not reasonably foreseeable. WSDOT has twice denied the claim (SL 9727-162, Sep 18, 2025; SL 9727-242, Jan 16, 2026).

The central question: whether the observed settlement constitutes a DSC under Section 1-04.7, or falls within the Design-Builder’s contractual risk allocation under Section 1-02.4(2) and GBR Section 3.2.7.

2. Project Summary

The I-405/Brickyard to SR 527 Improvement Project enhances four and a half miles of the corridor, primarily in Bothell. The DSC 006 dispute involves structures in the Sammamish River Valley Area (MP 23.59–24.00). The Design-Builder’s ground improvement program at these structures included stone column installation and surcharging. The dispute centers on whether the settlement behavior observed constitutes a DSC.

3. Relevant Contractual Requirements

3.1 RFP Section 1-02.1 — Responsibility for Design

“the Design-Builder undertakes full responsibility for delivery of the Project”

“If the Contract Documents omit or misdescribe the Work necessary to be performed … the Design-Builder shall not be excused from performing such omitted Work (no matter how extensive) … without entitlement to a Change Order hereunder except as specifically allowed by the Contract Documents.”

3.2 RFP Section 1-02.2 — Reference Documents

“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.”

“… 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 per Appendix A1.

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

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

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

“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 … shall not relieve the Design-Builder from responsibility … without additional expense to WSDOT.”

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

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 … 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.”

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

“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 … and shall obtain specific instructions in writing … before proceeding with the Work affected thereby.”

3.7 RFP Section 1-04.7 — Differing Site Conditions

“Differing Site Conditions shall mean (a) actual subsurface or latent physical conditions … 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 …”

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

“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.”

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

Section 2.6.5.2:

“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.”

Section 2.6.2.1 (Design-Build Modifications to the GDM):

“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 Ch.22 from this Design-Build contract. The GDR is a Reference Document per Appendix A1.

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

“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.”

The GBR is a Contract Document. 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. Footnote 3 applies only to portions of the Brickyard Area (MP 21.40–22.74) and Canyon Park (MP 25.50–26.10), not the Sammamish River Valley.

4. Discussion of Settlement and Clay Layer Conditions

Background for the Board’s reference. WSDOT’s arguments are presented in Section 6.

4.1 Background on ESU 2C

ESU 2C is a clay layer beneath the affected structures. The Design-Builder’s ground improvement program included stone column installation and surcharging. Settlement predictions indicated manageability within the design and construction timeline. Observed settlement exceeded those predictions.

4.2 GDR Overburden Value Discrepancy

GDR consolidation test results for two samples (NE-30vw-19 S-12 and NE-32p-19 S-10) used overburden values of 1060/1065 psf, implying a saturated unit weight of ~75 pcf. Laboratory-tested saturated unit weight averaged 113 pcf (SL 9727-162, Attachment 1 IED V4, pp.2–3). This produced overburden error factors of 2.39x and 2.00x, inflating GDR-reported OCR values from corrected values of ~1.49 and ~1.00 to the reported 3.57 and 1.99.

A higher OCR suggests less compressible clay; a lower OCR suggests more compressible. The inflated values would lead to less conservative settlement predictions. The discrepancy was apparent from comparing the Design-Builder’s own work products.

4.3 Settlement Predictions vs Observed Settlement

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, LTR 291, PDF pp.47–49) provides a construction timeline. Construction on Wall 23.80R began September 2, 2024. By October 18, 2024 (46 days), the fascia wall leveling pad was poured in the area that would exhibit excessive settlement. By October 31, 2024, wall panels were tilting 2–5 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 pre-award and post-award settlement predictions were virtually identical (both ~1 inch of post-construction settlement). This indicates the post-award investigation program did not cause the Design-Builder to revise or challenge the GDR-derived settlement parameters.

4.4 Stone Column Ground Improvement and CPT Evidence

The Design-Builder’s own pre- and post-stone-column CPT investigations (LTR 291, GeoEngineers Memo Figures 12–14, 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. The record spans 60 years:

• 1966 WSDOT Foundation Design Recommendation (R. V. LeClerc, P.E.): “Our calculations indicate a settlement of 3.2 ft is possible at this point, with 2 years required for 90 per cent” (G03 Vol 1, pp.563–570). Recommends sand drains “18 in. in diameter on 10-ft spacing” — a direct predecessor to stone column treatment.
• WSDOT 1959 and 1966 settlement calculations: consolidation settlements of 1.4–4.0 ft, time-settlement curves extending 40+ years (G03 Vol 1, pp.170–232, pp.661–694).
• Shannon & Wilson, Inc. Location Soils Survey (March 4, 1966): clay deposits of 10–30+ ft thickness, SPT N-values of 2–10 blows/ft (G03 Vol 1, pp.411–447).
• 1956 WSDOT inter-office communication: “settlements in the order of 0.5 ft. could be expected at the bridge ends” (G03 Vol 1, pp.60–62).
• 1967 highway commission communication: “an additional 1’ to 2’ of settlement” during overload (G03 Vol 1, pp.1062–1066).

4.6 Appendix N2 Deep Foundations

Appendix N2 Bridge As-Builts shows bridges in the vicinity bear on deep foundations, indicating the area was recognized as having challenging settlement and bearing capacity conditions.

5. Sequence of Events

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 data.

WSDOT’s Response:

The Contract establishes that the GBR, not the GDR, is the baseline for DSC comparison (Section 1-02.4(2)). 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” and “design performance” inherently encompass magnitude and behavior.

GBR Table 1 baselines poor ground in the Sammamish River Valley (MP 23.59–24.00) without Footnote 3’s 10-foot depth limit. Poor ground at all depths is a baseline condition at these locations. The conditions Skanska is complaining about were anticipated by the Contract and placed within the Design-Builder’s risk allocation.

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

Skanska’s Argument:

“Incorrect overburden values” in the GDR are factual numerical miscalculations stamped by WSDOT. Section 1-02.4(2).1 does not apply.

WSDOT’s Response:

Two separate obligations the Design-Builder has not satisfied:

First, Section 1-02.4(2) makes no warranty of Design-Builder interpretations. The GDR is a Reference Document at the Design-Builder’s risk (Section 1-02.2).

Second, Section 1-03.5 required prompt notification upon discovering apparent errors. The discrepancy between implied unit weights (~75 pcf) and laboratory-measured values (113 pcf) was apparent from the Design-Builder’s own work products. The GeoEngineers memo itself raises the overburden value issue (LTR 291, PDF p.14), confirming awareness. No Section 1-03.5 notification was filed.

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

Skanska’s Argument:

Section 2.6 states geotechnical analyses “shall be based on … information contained in the GDR.” The Design-Builder had a right to rely on GDR values. WSDOT directed reliance.

WSDOT’s Response:

Section 2.6 requires the Design-Builder to use GDR information as part of its geotechnical evaluation. “Use” is not “rely without question.” It does not convert the GDR into a warranty or shift the risk allocation in Section 1-02.4(2).

Section 2.6.2.1 explicitly excludes GDM Chapter 22 from design-build contracts. GDM Ch.22’s designation of the GDR as a “contract document” applies to traditional Design-Bid-Build projects. For this contract, the GDR is a Reference Document per Appendix A1, at the Design-Builder’s risk per Section 1-02.2.

6.4 “Reasonable Investigation” Requires Interpretation, Not Just Data Collection

Skanska’s Argument:

245+ additional explorations, SIPs, lab testing, and monitoring meet the “reasonable investigation” standard.

WSDOT’s Response:

“Reasonable investigation” under Section 1-02.4(1) requires the Design-Builder to “make interpretations and draw conclusions.” This encompasses analysis and interpretation, not merely data collection.

The Design-Builder selected median values from a variable dataset without demonstrating sensitivity analysis on key parameters. Evaluating sensitivity to reasonable parameter ranges is a component of the “interpretations and conclusions” required by Section 1-02.4(1). The Design-Builder did not reconcile discrepancies between unit weights used for other analyses and GDR-reported values.

The Design-Builder’s own Figure 21 (GeoEngineers Memo, LTR 291, PDF p.46) illustrates this point. Pre-award and post-award settlement predictions are virtually identical (both ~1 inch). Despite 245+ additional explorations, the Design-Builder did not revise the GDR-derived settlement 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 parameters demonstrate a material difference under Section 1-04.7(a) and unusual nature under Section 1-04.7(b).

WSDOT’s Response:

Even if a material difference could be demonstrated, the DSC definition requires conditions “not discoverable from a reasonable investigation.” The Design-Builder has not established this element.

Appendix G03 (at DB’s risk per Section 1-02.2) documents settlement magnitudes up to 4.0 ft, consolidation periods up to 2 years for 90% primary consolidation, and ground improvement techniques at this interchange. The 1966 Foundation Design Recommendation alone predicts 3.2 ft with “2 years required for 90 per cent” (G03 Vol 1, p.564). These conditions were discoverable.

Nearby bridges on deep foundations (Appendix N2) further indicate the area was recognized as having challenging settlement conditions.

The Design-Builder’s own construction timeline further supports discoverability. 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.” The settlement behavior became apparent during construction not because of unforeseeable subsurface conditions, but because the pre-construction analysis had not accounted for the full range of clay compressibility at these locations.

The Design-Builder’s own CPT investigations reflect disturbance to the clay layer from stone column installation. Section 1-02.4(2) provides that subsurface behavior may be influenced by the Design-Builder’s means and methods. Backcalculated OCR values may reflect combined effects of soil properties and construction-induced disturbance, not solely in-situ conditions.

6.6 Burden of Proof Not Met

Under Section 1-04.7(1), the Design-Builder bears the burden of proving a DSC exists. The supplemental materials do not address:

1. The GBR baseline. The Design-Builder compares observed conditions to GDR data rather than the GBR baseline established by Section 1-02.4(2).
2. Sensitivity analysis. No evidence of evaluating sensitivity of settlement predictions to reasonable ranges of key parameters.
3. Section 1-03.5 duty. No discussion of the duty to seek written instructions upon discovering apparent GDR errors.
4. Means and methods influence. No analysis of how stone column installation influenced settlement behavior. CPT data reflects disturbance, yet the supplemental materials do not discuss this influence.

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 GBR, not the GDR, is the baseline for DSC comparison under Section 1-02.4(2). GBR Section 3.2.7 baselined poor ground conditions and assigned the Design-Builder responsibility to assess “significance to the structure and the overall design performance to be achieved.” GBR Table 1 baselines poor ground in the Sammamish River Valley without the 10-foot depth limit that applies to other zones.

The conditions were foreseeable from reference information available during procurement. Historical settlement records document magnitudes up to 4.0 ft and consolidation periods up to 2 years at the same interchange.

The Design-Builder’s position has structural weaknesses: it compares to GDR rather than GBR baseline; has not demonstrated sensitivity analysis; did not file a Section 1-03.5 notification; has not addressed stone column disturbance influence; and has not carried its burden of proof under 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

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 — Potential DSC at Wall 23.80R (Apr 9, 2025)
16. WSDOT SL 9727-103 — Initial Response (Apr 23, 2025)
17. Skanska LTR 226 — Expanded DSC Notice (Sep 4, 2025)
18. WSDOT SL 9727-149 — Laboratory Testing Package 01 (Sep 4, 2025)
19. WSDOT SL 9727-162 — Written Determination Denying DSC 006 (Sep 18, 2025)
20. WSDOT SL 9727-162, Attachment 1 — Initial Engineering Decision V4
21. Skanska LTR 244 — Laboratory Testing Discrepancies (Sep 30, 2025)
22. Skanska LTR 246 — Notice of Protest 006 (Oct 1, 2025)
23. WSDOT SL 9727-175 — Acknowledged Protest, Granted Extension (Oct 10, 2025)
24. WSDOT SL 9727-180 — Corrected Lab Data (Oct 17, 2025)
25. Skanska LTR 291 — Supplement to Notice of Protest 006 (Dec 8, 2025)
26. WSDOT SL 9727-242 — Response to Supplement, Denial Reaffirmed (Jan 16, 2026)
27. Skanska LTR 336 — Notice of Dispute (Jan 30, 2026)
28. WSDOT SL 9727-257 — Acknowledged Dispute (Feb 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 & Wilson Location Soils Survey
32. Appendix G03, Vol 1, pp.563–570 — 1966 Foundation Design Recommendations
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 N2 — Bridge As-Builts (Vicinity Deep Foundations)

WSDOT Position Paper — DRB Hearing, Protest 006 — DSC 006 Clay Layer ESU 2C (PCO 123)