Slurry MTBM in Alluvial Soils and 25k Rock Chris L. Windley, P.E. McKim & Creed Inc. Stephen D. Leitch, P.E. Hazen and Sawyer, P.C. Joshua P.

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1 Slurry MTBM in Alluvial Soils and 25k Rock Chris L. Windley, P.E. McKim & Creed Inc. Stephen D. Leitch, P.E. Hazen and Sawyer, P.C. Joshua P. Farmer, P.E. Hazen and Sawyer, P.C.

2 Project Background City of Raleigh System-Wide Capacity Study 10-year Storm Basis Generated Detailed CIP Crabtree Parallel Interceptor Required to: Correct Identified Hydraulic Restrictions Accommodate Future Flows up to 2030 Minimize SSO s

3 Phase I Interceptor Specifics 16,000 LF of 72 and 4,000 LF of 60 Gravity Sewer 3 Crossings Requiring Trenchless Installation Consistent Deep Cuts (20-30 ) Highly Variable Soil Conditions Nearly all Excavations below Water Table

4 Regional Geology - Triassic/Mesazoic Basins Project Location

5 Regional Geology - Triassic/Mesazoic Basins Project Location

Regional Geology - Triassic/Mesazoic Basins Geologic Conditions formed 200 250 million years ago Eroded Sediment created Alluvial Fans Formed Sedimentary Rock Structure Seafloor Spread = Tectonic

6 Regional Geology - Triassic/Mesazoic Basins Geologic Conditions formed million years ago Eroded Sediment created Alluvial Fans Formed Sedimentary Rock Structure Seafloor Spread = Tectonic Shift Stress Cracks Form Magma intrudes Extremely Hard Igneous Rock Intrusions dikes (vertical)p sills (horizontal) known as Diabase. Pangaea Result in Extremely Variable & Difficult Tunneling Conditions.

7 Regional Geology - Triassic/Mesazoic Basins

Phase I Sewer Interceptor Critical Factors Corrosion Resistance Critical (High Peaking Factor) Large Pipe ID Required (60 & 72 ) Combination = Reduced Carrier Pipe Material

8 Phase I Sewer Interceptor Critical Factors Corrosion Resistance Critical (High Peaking Factor) Large Pipe ID Required (60 & 72 ) Combination = Reduced Carrier Pipe Material Options Creek Crossings Deep Installation Proximity to Recharge Source Precise Line and Grade (0.008%) Alluvial - Loose, Granular Soil Materials Underlain by Fractured and Hard Rock

9 Phase I Sewer Interceptor Critical Factors

Segmental Excavation Shield Support Pneumatic/Backacter

10 Trenchless Excavation Methods Evaluated Categories of Excavation Methods Considered Hand Mining/Traditional Segmental Excavation Shield Support Pneumatic/Backacter Drill & Blasting Open-Face Mechanized Closed Face Mechanized

11 Trenchless Excavation Methods Evaluated Fixed Point Tunnel Profile = Highly Variable Soil Conditions Structures Potentially Impacted + High Profile Corridor + Flat, Tight Hydraulic Design = Line & Grade Accuracy Required High Groundwater + Loose Granular Material = Closed Face Methods or Compressed Air & Segmental Excavation

Reinforced Concrete Jacking Pipe Carbon Steel Jacking Pipe

12 Trenchless Tunnel Support Methods Evaluated Categories of Tunnel Support Methods Considered Pipe Jacking Reinforced Fiberglass Jacking Pipe Reinforced Concrete Jacking Pipe Carbon Steel Jacking Pipe Assembled-in-Place Support Steel Liner Plate Ribs & Lagging Shotcrete Rock Anchors/Bolts & Wire Mesh

Support = One Integrated System Single-Pass

13 Trenchless Tunnel Support Methods Evaluated Single- Pass vs Two-Pass Two-Pass Excavation Support Carrier Pipe/System Conveyance Single-Pass System Conveyance + Excavation Support = One Integrated System Single-Pass Pipe Jacking Two-Pass Pipe Jacking Assembled-in-Place Systems

14 Tunneling with Pipe Jacking Methods What is Pipe Jacking? Tunnel Lining: Jacking Pipe or Casing Thrust/Advancement: Hydraulic Jacking Frame One-pass or Two-pass is an option Types of Pipe Jacking Jack and Bore (Horizontal Auger Boring) Compressed Air Hand Tunneling 1 Slurry Microtunneling (MTBM) 1 Can also be installed similar to the TBM process using internal jacks to advance off the built in place liner plate or ribs and lagging.

15 Tunneling with Assembled-in-Place Methods Assembled-in-Place Tunnel Support Many Types of Tunnel Lining Thrust/Advancement: Hydraulic from Support or Rock Two-pass only Requires Consistent Man-entry Types of Excavation Systems using Assembled-in- Place Tunnel Support TBMs Hard Rock - Open-Faced Single Shield, Gripper, & Double Shield Soft Earth - Closed-Face EPBM & Slurry Shield Compressed Air Hand Tunneling 1

(400 + Crossing) Two-Pass Only Single Shield TBM Inability to Control Fluidized Material Worker

16 Trenchless Methods Eliminated Jack and Bore (Horizontal Auger Boring) Limited Availability at Size Required Inability to Control Fluidized Material Line and Grade Control Length of Drive (400 + Crossing) Two-Pass Only Single Shield TBM Inability to Control Fluidized Material Worker Safety (workers in the tunnel) Two-Pass Only Slurry Shield TBM Eliminated due to equipment availability

17 Final Trenchless Method Decision Compressed Air Hand Tunneling vs Earth Pressure Balance Machine vs Slurry Microtunneling

Advantages Inexpensive Over Short Distances

Smaller Footprint Can Handle Mixed Face Conditions

Obstructions Capability to Install One-Pass Tunnel

Worker Safety Risk Not Widely Available/Reduced

18 Advantages Inexpensive Over Short Distances Dewatering not Required High Line and Grade Accuracy Smaller Footprint Can Handle Mixed Face Conditions Capability to Easily Identify and Clear Larger Obstructions Capability to Install One-Pass Tunnel Option Disadvantages Compressed Air Hand Mining Worker Safety Risk Not Widely Available/Reduced Contractor Availability Not Cost Effective Over Long Distances Uncontained Spoil Removal

Conditions Disadvantages Safety Concerns/Worker Entry Required Expensive Reduced Equipment

19 Earth Pressure Balance Machine (EPBM) Advantages Dewatering Not Required Potential for Subsidence and Surface Heave is Lowered High Line and Grade Accuracy Can Handle Mixed Face Conditions Disadvantages Safety Concerns/Worker Entry Required Expensive Reduced Equipment Availability Largest Operational Footprint Spoil Removal Limits Production One-Pass Option Not Available

High Line and Grade Accuracy Medium-sized Footprint/Flexible Can Handle Mixed Face Conditions

20 Advantages Remote Controlled/ no Worker Entry Required Dewatering not Required Potential for Subsidence and Surface Heave Minimized Reduced Skin Friction by Lubrication Contained Spoil Removal High Line and Grade Accuracy Medium-sized Footprint/Flexible Can Handle Mixed Face Conditions Capability to Install One-Pass Disadvantages Slurry Microtunneling Expensive Can Have Issues with Large Cobbles and Boulders

21 Slurry Microtunneling Selected Key Decision Criteria for Selection of Slurry Microtunneling Remote Controlled/ No Worker Entry Required Capability to Install One-Pass Tunnel Option Medium-sized Footprint/Flexible Contained Spoil Removal

22 Microtunnel Design Horizontal Positioning and Vertical Limitations Launch Shaft Location Pipe Material Selection for Single-pass Tunneling Design Calculations Regulatory (NCDOT) Approval

Microtunnel Design Horizontal Positioning and Vertical Limitations Horizontal Positioning Maximize separation with existing utilities, structures & creek

23 Microtunnel Design Horizontal Positioning and Vertical Limitations Horizontal Positioning Maximize separation with existing utilities, structures & creek Allow room for shafts/pits Vertical Limitations Maintain design grade in inconsistent material Achieve vertical clearances with existing utilities and creeks

24 Launch Shaft Location Microtunnel Design Work with spatial constraints Minimize location in hard rock Shaft in rock vs. extended tunnel Accessibility

25 Microtunnel Design Pipe Material Selection for Single-pass Tunneling Consistency with overall pipe material for project Water-tight joint system Pipe stiffness Corrosion resistant Regulatory requirements

26 Design Calculations Microtunnel Design Jacking forces vs. allowable Thrust blocking Pipe deflection (Long-term) Buckling

27 Microtunnel Design Regulatory (NCDOT) Approval FRP for Pipe Jacking Microtunneling Single-pass Installation Launch and receiving shafts near embankments Solution: Comprehensive submittal packet and close coordination w/ncdot

28 Is Microtunneling the Best Option For You? Project Conditions that May Warrant Slurry MTBM Limited / No Ability to Effectively Dewater Tunnel Area in High Groundwater Areas Dewatering in Areas with High Conductivity and/or Cohesionless Soils Near Roadways Or Railroads Subsidence or Heave is Critical Gravity Sewer with Critical Line and Grade and Minimal Allowance for Variation Tunnel Installations with Varying Subsurface Conditions Mixed Face Conditions

29 Is Microtunneling the Best Option For You? Slurry Microtunneling has proven to be a good choice for the City of Raleigh Crabtree Project NCDOT Approved Single-pass Tunnels All Three MTBM Installations are Complete No Subsidence, Settlement or Heave Reported Ability to Handle Unexpected Subsurface Conditions

30 Questions?

MICRO-TUNNELING LARGE DIAMETER SEWER MAY BE THE BEST OPTION FOR YOU

ABSTRACT MICRO-TUNNELING LARGE DIAMETER SEWER MAY BE THE BEST OPTION FOR YOU Christopher L. Windley, PE (McKim & Creed, Inc.)* Joshua P. Farmer, PE and Stephen D. Leitch, PE (Hazen & Sawyer, PC) *McKim