Geotechnical Desktop Study
Borings >100 feet deep Water Well Logs Regional Geology Fault Mapping & Behavior Geotechnical Desktop Study
Borings Identified >100 Feet Deep
Faulting
Grain Size Distribution Comparison
Inverted Siphon Hydraulic Analysis
Comparison Projects Mill Creek Drainage Relief Tunnel Waller Creek Tunnel San Antonio River Tunnel • • • Dallas, Texas Austin, Texas San Antonio, Texas Diameter: ~ 24’ • • • Diameter: 30’ and 35’ Diameter: 20’, 22’ & 26’ • Length: 26,385’ ( ~ 5 mi) • Length: 5600’ ( ~ 1 mi) • Length: ~16356’ ( ~ 3 mi) Discharge: ~20,000 cfs Discharge: ~8,500 cfs Discharge: ~6,700 cfs • • •
Regional Topography
HCFCD Inverted Siphon Concept
Methodology • Spreadsheet solves for two parameters • Darcy-Weisbach equation – Head loss equation • Swamee-Jain equation – Darcy friction coefficient ( f ) • Approximation of implicit Colebrook-White equation • VB programming used in excel for iteration
Design Parameters • Roughness coefficient (k s ) = 0.001 ft Project Parameter Value Mill Creek Drainage Relief Tunnel (MCDRT) – Dallas, TX Manning’s Roughness Coefficient 0.011 Waller Creek Tunnel (WCT) – Austin, TX Roughness coefficient (k s; ft) 0.001 San Antonio River Tunnel (SART) – San Antonio, TX Roughness coefficient (k s; ft) 0.002 • Minor (Inlet & Outlet Losses) = 0.2 + 1.0 = 1.2 ft • Bend Loss = 0.006 per bend • No. of Bends per mile (1,000-ft radius) = 2.5 Kinematic Viscosity = 1.023 x 10 -5 ft 2 /s • • Sediment Deposition Depth = 5% of Tunnel Diameter
Scenarios Analyzed Differential • Diameter: 5’ intervals Diameter Tunnel Length Head (ft) (mi) • Heads : 10’ intervals (ft) • Length: 5 mi intervals 5 30 5 10 40 10 15 50 15 20 60 20 25 70 25 30 80 30 35 90 - 40 100 -
Validation Actual Rated Spreadsheet Project Capacities (cfs) (cfs) Mill Creek, Dallas 20,000 (approx.) 19,831 Waller Creek, Austin 8,500 (approx.) 8,486 San Antonio River Tunnel 6,700 (approx.) 6,720
Flow Rates for 10-mile Tunnel Flow rate (cfs) Diameter Head (ft) (ft) 30 40 50 5 70 81 90 10 423 489 547 15 1,205 1,394 1,560 20 2,527 2,922 3,270 25 4,477 5,176 5,792 30 7,132 8,244 9,224 35 10,557 12,202 13,651 40 14,810 17,117 19,149 *Additional results in Appendix B
FLOW RATE AT 30' HEAD FLOW RATE AT 40' HEAD 40 40 35 35 Tunnel Diameter (ft) Tunnel Diameter (ft) 30 30 25 25 20 20 15 15 10 10 5 5 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Flow (cfs) Flow (cfs) L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi FLOW RATE AT 50' HEAD FLOW RATE AT 60' HEAD 40 40 35 35 Tunnel Diameter (ft) 30 Tunnel Diameter (ft) 30 25 25 20 20 15 15 10 10 5 5 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Flow (cfs) Flow (cfs) L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi Results
Range Parameter Minimum Design Maximum 0.0005 0.001 0.002 Roughness coefficient (ft) 0 0.2 +1.0 = 1.2 1.0+1.0 = 2.0 Minor loss (Entrance & Exit Losses) 0 0.006 (smooth bend) 0.02 (mitered bend) Bend Loss 0 2.5 5 No. of Bends per mile (1,000-ft radius) 0.93 1.023 1.86 Kinematic Viscosity (x 10 -5 , ft 2 /s) 0 5 10 Sediment Deposition (% of Tunnel Diameter) Takeaways: • Surface roughness has the highest influence on the tunnel flow rate. • Sediment depth has the second most influence on the tunnel flow rate. • Other parameters interchangeably rank higher to lower depending on the differential head, tunnel diameter, and length. Sensitivity Analysis
Tunnel Applicability
Face Support Methods for Shields and TBMs
Pre-cast Concrete Segmental Lining Schematic
• Site size > 5 acres • Shaft size = 2 to 2.5 OD Fencing with Noise Barrier • Haul routes considered • Power = 20 MW +/- • Noise screening TBM Launch Site
Third-party Impacts • The construction of large diameter flood control tunnel(s) will have a significant impact on traffic and noise in the area surrounding the shaft sites Truck traffic for a 40-foot diameter tunnel construction will require hundreds of truck trips each work day. • Time of day restrictions are sometimes placed at shaft site locations that are in a residential area. • Typical time of day restrictions may be 7:00 AM to 7:00 PM. • Tunnel construction below ground is pursued essentially 24 hours a day, 7 days a week. Above the tunnel it will be difficult to to even notice that tunnel construction is taking place
Typical TBM Progress Rates • For this planned flood control tunnel, we would recommend assumed progress rates for initial planning purposes as follows: 25-foot Diameter Tunnel 75 ft/day 40-foot Diameter Tunnel 50 ft/day • The Anacostia River Tunnel which is a 23 -foot diameter soft ground tunnel was constructed with an average daily progress rate of 80 ft/day and a maximum daily progress of 120 ft/day.
Construction Packaging and Schedule • A planned flood control tunnel may exceed 10 miles in length and 40 foot in diameter. • A tunnel project of this size is often broken up into several construction contracts. • Each contract would have one or more TBMs with individual TBM runs typically being a few miles in length. • From discussions with tunnel contractors for planning purposes, an upper limit on mining length with a single TBM before major mechanical rehabilitation is required is between 5 and 7 miles. This distance may be appropriate for breaking up longer tunnels into segments.
Cost Analysis F O R C O N C E P T U A L T U N N E L A U G U S T 2 9 , 2 0 1 9 presented by Don, Wotring, PE, Brierley Associates Brian Gettinger, PE
Estimate Maturity Typical Estimate Expected Accuracy Typical Estimating Method Level 1 Range 2 Class Purpose SF factoring, parametric Concept L: -20% to -30% Class 5 0% to 2% models, judgement, or screening H: +30% to +50% analogy Accuracy Range Includes Contingency Contingency = 50% AACE Class 5 Cost Estimate
25-ft Diameter 40-ft Diameter Payment (2019 millions (2019 millions Items Contingency USD) USD) Project $678.1 (65%) $1,005 (66%) 32% Tunnel Subtotal Contingency 44% $332.1 (32%) $492.7 (32%) (50%) Allowances $31.7 (3%) $31.7 (2%) 3% Allowances Total $1,041 $1,530 6% Other 1.5% 13.5% Mobilization and Appendix B – 25-ft Diameter Tunnel Bonding Shafts and In/Outlet Appendix C – 40-ft Diameter Tunnel Structures Appendix D – Payment Items (32) Cost Estimate
Northeast Boundary Tunnel Historical Project Comparison
Phase 1 Conclusions
1. Tunneling in Harris County is feasible based on the geotechnical conditions and project experience in similar soils 2. Tunnels can move a significant rate of stormwater operating entirely by gravity as an inverted siphon 3. Tunnel cost including a 50% contingency for a representative 10-mile- long, 25- and 40-foot diameter tunnel are $1 billion and $1.5 billion respectively Phase 1 Outcomes
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