SR 520 Project Montlake Cut Tunnel Expert Review Panel Report EXPERT REVIEW PANEL MEMBERS: John Reilly, P.E., C.P.Eng. John Reilly Associates International Brenda Böhlke, Ph.D., P.G.. Myers Böhlke Enterprise Vojtech Gall, Ph.D., P.E. Gall Zeidler Consultants Lars Christian Ingerslev, P.E. PB Red Robinson, C.E.G., R.G. Shannon and Wilson Gregg Korbin, Ph.D. Geotechnical Consultant John Townsend, C.Eng. Hatch-Mott MacDonald José Carrasquero-Verde, Principal Scientist Herrera Environmental Consultants Submitted to the Washington State Department of Transportation July 17, 2008 SR520, Montlake Cut, Tunnel Alternatives, Expert Review Panel Report July 17h, 2008 Page 2 TABLE OF CONTENTS 1. EXECUTIVE SUMMARY......................................................................................................................5 1.1. INTRODUCTION .......................................................................................................................................5 1.2. ENVIRONMENTAL CONSIDERATIONS ......................................................................................................5 1.3. TUNNELING METHODS CONSIDERED......................................................................................................5 Figure 1 - Immersed Tunnel Construction (General) ......................................................................................6 Figure 2 - Tunnel Boring Machine (Elbe River, Hamburg) ............................................................................6 Figure 3 – Sequential Excavation Method (Beacon Hill Tunnel, Seattle).......................................................7 1.4. GEOTECHNICAL CONSIDERATIONS .........................................................................................................7 1.5. ALIGNMENTS CONSIDERED.....................................................................................................................8 Figure 4 - Plan of tunnel alignments A, B, C and D considered .....................................................................8 1.6. METHODS, LENGTHS, GRADES AND MINIMUM SOIL COVER..................................................................9 Table A – Alignments, Lengths, Road Grades and Minimum Cover..............................................................9 Alignment B - Modified........................................................................................................................9 Table A-1 – Alignment B Modified................................................................................................................9 Plan of Alignment B Modified......................................................................................................................10 1.7. ACCEPTABLE RAMP GRADES ................................................................................................................10 Table B – WSDOT Design Manual, Maximum Grades for Ramps ..............................................................10 1.8. FINDINGS REGARDING THE TUNNELING METHODS CONSIDERED..........................................................11 2. REPORT, SR520 EXPERT PANEL, MONTLAKE CUT TUNNELS .............................................12 2.1. INTRODUCTION AND BACKGROUND, THE COWI REPORT....................................................................12 Figure 5 – General arrangement of the COWI Immersed Tunnel Proposal ..................................................12 This Document...................................................................................................................................12 Project Context..................................................................................................................................12 Expert Review Panel, convening and objectives ...............................................................................13 Input from the Project and Mediation Panel Members .....................................................................13 Cost of the alternatives not addressed...............................................................................................14 2.2. EXPERT REVIEW PANEL - WORKSHOP ..................................................................................................14 Considerations...................................................................................................................................14 2.3. PROPOSED MONTLAKE CUT TUNNEL – PROJECT CONSIDERATIONS ....................................................14 Tunnel - configuration, coordination and considerations.................................................................14 SR 520 Project Schedule....................................................................................................................15 2.4. INITIAL DELIBERATIONS AND CONSIDERATIONS..................................................................................15 3. ENVIRONMENTAL CONSIDERATIONS........................................................................................16 3.1. BACKGROUND.......................................................................................................................................16 3.2. ENVIRONMENTAL ELEMENTS ...............................................................................................................17 Fisheries and Fish Habitat ................................................................................................................17 Chinook Salmon.............................................................................................................................18 Steelhead ........................................................................................................................................18 Coastal/Puget Sound Bull Trout.....................................................................................................19 Wetlands and Riparian Vegetation....................................................................................................19 Parks and Recreation ........................................................................................................................20 Historic and Cultural Resources .......................................................................................................20 3.3. ENVIRONMENTAL EFFECTS...................................................................................................................21 Table C - Comparative Environmental Effects of Tunnel Construction Methods ........................................21 Table D – Salmonoids Migration Timing for ESA Listed Species in Montlake Cut ....................................24 4. GEOTECHNICAL CONDITIONS NEAR MONTLAKE CUT........................................................24 Background........................................................................................................................................24 Ground conditions .............................................................................................................................24 Subsurface Data - Cautions...............................................................................................................25 Alignment and depth considerations .................................................................................................25 5. ALIGNMENT ALTERNATIVES ........................................................................................................25 SR520, Montlake Cut, Tunnel Alternatives, Expert Review Panel Report July 17h, 2008 Page 3 5.1. ALIGNMENTS CONSIDERED ..................................................................................................................26 Figure 6 - Plan of tunnel alignments considered...........................................................................................27 Considerations regarding the Alignments .........................................................................................28 5.2. METHODS, LENGTHS, GRADES AND MINIMUM SOIL COVER................................................................28 Table E – Alignment, Method, Lengths, Road Grades and Minimum Cover ...............................................28 Table E-1 – Alignment B Modified ..............................................................................................................29 5.3. ACCEPTABLE RAMP GRADES ................................................................................................................29 Table F – WSDOT Design Manual, Maximum Grades for Ramps...............................................................29 6. TUNNELING METHODS CONSIDERED.........................................................................................30 Figure 7, Immersed Tunnel Construction (General) .....................................................................................30 Figure 8 - Tunnel Boring Machine (Elbe River, Hamburg) ..........................................................................30 Figure 9 – Sequential Excavation Method (Beacon Hill Tunnel, Seattle).....................................................31 Discussion..........................................................................................................................................31 7. SPECIFICS OF EACH CONSTRUCTION METHOD .....................................................................32 7.1. SEQUENTIAL EXCAVATION METHOD (SEM) TUNNELING....................................................................32 General