Geotechnical Desktop Study Borings >100 feet deep Water Well - - PowerPoint PPT Presentation

Geotechnical Desktop Study

Geotechnical Desktop Study

Borings >100 feet deep Water Well Logs Regional Geology Fault Mapping & Behavior

Borings Identified >100 Feet Deep

Faulting

Grain Size Distribution Comparison

Inverted Siphon Hydraulic Analysis

Comparison Projects

Mill Creek Drainage Relief Tunnel

• Dallas, Texas
• Diameter: 30’ and 35’
• Length: 26,385’ (~5 mi)
• Discharge: ~20,000 cfs

Waller Creek Tunnel

• Austin, Texas
• Diameter: 20’, 22’ & 26’
• Length: 5600’ (~1 mi)
• Discharge: ~8,500 cfs

San Antonio River Tunnel

• San Antonio, Texas
• Diameter: ~24’
• Length: ~16356’ (~3 mi)
• 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 (ks) = 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 (ks; ft) 0.001 San Antonio River Tunnel (SART) – San Antonio, TX Roughness coefficient (ks; 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 ft2/s
• Sediment Deposition Depth = 5% of Tunnel Diameter

Scenarios Analyzed

Diameter (ft) Differential Head (ft) Tunnel Length (mi) 5 30 5 10 40 10 15 50 15 20 60 20 25 70 25 30 80 30 35 90

• 40

100

• Diameter: 5’ intervals
• Heads : 10’ intervals
• Length: 5 mi intervals

Validation

Project Actual Rated Capacities (cfs) Spreadsheet (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 (ft) Head (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

Results

5 10 15 20 25 30 35 40 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Tunnel Diameter (ft) Flow (cfs)

FLOW RATE AT 50' HEAD

L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi 5 10 15 20 25 30 35 40 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Tunnel Diameter (ft) Flow (cfs)

FLOW RATE AT 60' HEAD

L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi 5 10 15 20 25 30 35 40 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Tunnel Diameter (ft) Flow (cfs)

FLOW RATE AT 30' HEAD

L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi 5 10 15 20 25 30 35 40 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000 Tunnel Diameter (ft) Flow (cfs)

FLOW RATE AT 40' HEAD

L = 5 mi L = 10 mi L = 15 mi L = 20 mi L = 25 mi L = 30 mi

Sensitivity Analysis

Parameter Range Minimum Design Maximum Roughness coefficient (ft) 0.0005 0.001 0.002 Minor loss (Entrance & Exit Losses) 0.2 +1.0 = 1.2 1.0+1.0 = 2.0 Bend Loss 0.006 (smooth bend) 0.02 (mitered bend)

• No. of Bends per mile (1,000-ft radius)

2.5 5 Kinematic Viscosity (x 10-5, ft2/s) 0.93 1.023 1.86 Sediment Deposition (% of Tunnel Diameter) 5 10

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.

Tunnel Applicability

Face Support Methods for Shields and TBMs

Pre-cast Concrete Segmental Lining Schematic

TBM Launch Site

• Site size > 5 acres
• Shaft size = 2 to 2.5 OD
• Haul routes considered
• Power = 20 MW +/-
• Noise screening

Fencing with Noise Barrier

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

Don, Wotring, PE, Brierley Associates Brian Gettinger, PE

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

AACE Class 5 Cost Estimate

Accuracy Range Includes Contingency Contingency = 50%

Estimate Class Maturity Level1 Typical Estimate Purpose Typical Estimating Method Expected Accuracy Range2 Class 5 0% to 2% Concept screening SF factoring, parametric models, judgement, or analogy L: -20% to -30% H: +30% to +50%

Cost Estimate

Shafts and In/Outlet Structures Mobilization and Bonding Other Allowances Contingency

Tunnel 44% 32% 13.5% 6% 3%

1.5%

Payment Items 25-ft Diameter (2019 millions USD) 40-ft Diameter (2019 millions USD) Project Subtotal $678.1 (65%) $1,005 (66%) Contingency (50%) $332.1 (32%) $492.7 (32%) Allowances $31.7 (3%) $31.7 (2%) Total $1,041 $1,530

Appendix B – 25-ft Diameter Tunnel Appendix C – 40-ft Diameter Tunnel Appendix D – Payment Items (32)

Historical Project Comparison

Northeast Boundary Tunnel

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