Geotechnical Risk for Underground Construction · 3. Abrasivity 4. TBM Performance 5. Friction 6....

Greg Raines, [email protected]

Geotechnical Risk for Underground Construction

Agenda1. Obstructions2. Mixed Ground / Mixed Face 3. Abrasivity4. TBM Performance 5. Friction6. Thrust Restraint7. Stickiness8. Sensitive Soils9. Fines in Slurry10. Slaking, Raveling, & Invert

Degradation

11. Groundwater Control12. Faults 13. Heavy Ground14. Squeezing Ground 15. Rock Burst16. Hydrothermal Conditions17. Hazardous Gas18. Settlement19. Flowing Ground

Obstructions:Risk

Abandoned Ground Support Systems

Steel Pipe Obstruction

BouldersWells and Casings

Piles and Building FoundationsOld Foundation Block

Photo Credit:TunnelTalk

Photo Credit: Stantec

Photo Credit: Stantec Photo Credit: The Seattle Times

Photo Credit: Stantec Photo Credit: Stantec

Obstructions: Characterization

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Photo Credit: Tunnel Geophysics Image Search

Obstructions:Mitigation

Photo Credit: Akkerman

Photo Credit: AkkermanPhoto Credit: Stantec

Photo Credit: Herrenknecht

Mixed Ground:Risk

VS

Photo Credit: Soumagne Tunnel


Photo Credit: GeoHazards

Mixed Face:Risk

STATION

ELEVATION

MTBM PIPELINE CROSSINGAT .25% SLOPE

Photo Credit: Portland Water Bureau

Mixed Face: Characterization


Mixed Face: Mitigation

Photo Credit: Hayward Baaker

Photo Credit: StantecPhoto Credit: Daegu Metropolitan


Abrasivity: Risk




Abrasivity: Characterization

Granitic Porphyry Thin SectionPhoto Credit: Colorado School of Mines

Photo Credit: St. Cloud Granite

Photo Credit: Colorado School of Mines


Millers Drilling Index (ASTM G75-01)

RAR:Relative Abrasion Resistance

Abrasivity: Characterization

Photo Credit: Norwegian University of Science and Technology

Photo Credit: ASTM

Abrasivity: Mitigation

TBM/Disc Cutter Mechanic Shop

Photo Credit: Alimineti Madhava Reddy Tunnel ProjectPhoto Credit: Trakkom

Abrasivity: Mitigation

Photo Credit: MecTunnelPhoto Credit: PressureWorx

Photo Credit: Levent OzdemirPhoto Credit: Herrenknecht

TBM Performance:

Risk


Unconfined Compressive Strength

TBM Performance:

CharacterizationBrazilian Tensile Strength

Resiliency (Toughness)

Photo Credit: Colorado School of MinesPhoto Credit: Colorado Scool of MinesPhoto Credit: Colorado School of Mines

TBM Performance:

Mitigation


General Description Grain Shape Loose, φ (deg) Dense, φ (deg)

Ottawa Standard Sand Well Rounded 28 35

Sand from St. Peter sandstone Rounded 31 37

Silty sand from Franklin Falls Dam site, NH

Subrounded 33 37

Silty sand from vicinity of John Martin Dam, CO

Subangular to Subrounded

36 40

Sand from Great Salt Lake Angular 38 47

Well-graded, compacted crushed rock

Angular - 60

Friction:Risk

Photo Credit: Holtz & Kovacs, 1981

Friction: Characterization


Photo Credit: Retsch


Interjack Installation

Intermediate Jacking

Pin Lube System

Friction:Mitigation





Automated Pipe Lubrication

Photo Credit: Tunneling and Underground Space Technology

Concrete Thrust Block

Thrust Restraint




𝑃𝑃𝑢𝑢𝑢𝑢𝑢𝑢 = ℎ +𝐻𝐻2 𝛾𝛾 tan2 45 +

𝜑𝜑2 + 2𝑐𝑐 tan2 45 +

𝜑𝜑2 𝐻𝐻𝐻𝐻

Pult = Passive resistance of thrust blockγ = Soil unit weightH = Height of thrust blockh = Depth to top of thrust blockB = Width of thrust blockφ = Soil friction anglec = Soil cohesion

𝛿𝛿 =𝑞𝑞𝐻𝐻 1 − 𝑢𝑢2

𝐸𝐸𝑠𝑠

THRUST BLOCK DEFORMATIONFor a square thrust block of B, it is

q = Bearing pressure on thrust blockυ = Poisson’s RatioEs = Young’s Modulus of the soil

Thrust Restraint: Mitigation


Photo Credit: Collucio Construction

Photo Credit: Collucio Construction

Stickiness: Risk




Stickiness: Characterization


Different Conditioners• Dispersants• Polymer • Limited amounts of water• Jetting or hand removal

Stickiness: Mitigation



Photo Credit: Jaybee Fluids

Sensitive Soils: Risk

GRANBY STREET SEWERHartford, CT

• Encountered very sensitive varved clays.

• Three tunnels constructed via microtunneling for 2,500 linear feet total.



Ratio of Unconfined Compressive Strength of an undisturbed soil specimen to its unconfined strength after remolding

Sensitive Soils: Characterization

Photo Credit: Soil Mechanics – Soil Classification and Compaction

Sensitive Soils: Mitigation

Photo Credit: Mitchell, 1981


Fines in Slurry: Risk

Photo Credit: Slurry Separation Image Search



Hydrometer Test

Fines in Slurry: Characterization

Photo Credit: International Journal of Geosciences

Fines in Slurry: Mitigation

Photo Credit: GN Solids Control

Photo Credit: GN Solids ControlPhoto Credit: GN Solids Control

Slaking, Raveling, & Invert Degradation:

Risk

Photo Credit: Underground Raveling Image Search

Photo Credit: StantecPhoto Credit: Seismic Performance of Rock Block Structures


Characterization




Mitigation

Photo Credit: Potenza Photo Credit: Tekflex – Minova

Photo Credit: East End Bridge Tunnel

Groundwater Control:

Risk




Characterization



Characterization

Multi-level Single

Typical stand-pipe piezometer Multi-level vibrating wire piezometer

Fully Grouted Multi-level vibrating wire piezometer

Photo Credit: Stantec Photo Credit: StantecPhoto Credit: Geokon


Characterization • Packer Testing (Single & Double)• Constant Head• Falling Head• Pump Test

Tunnel Alignment



Mitigation

Photo Credit: Newman Dewatering


Photo Credit: Robbins

Photo Credit: TunnelTalk

Faults: Risk

2+44

Fault “A”

Fault “B”

Fault “B” right side Chamber

High Angle Normal Fault


Faults: Characterization

Fault exposed in tunnel & discontinuitydata collected to document it

Aerial Photo Lineation MapFault/Lineation MapPhoto Credit: Stantec

Photo Credit:

Probe Drill/Grout

Faults: Mitigation

Grouting Array

High Groundwater Inflows


Photo Credit: TunnelTalk Photo Credit: Trevor Carter

• Unable to advance TBM due to immense pressures

• Encountered in deep, fault zones

Heavy Ground: Risk

Photo Credit: McMillen Jacobs Associates


Heavy Ground: Characterization

• Drill hole through faults from surface • RQD values• Probe drilling in tunnel

RQD %= 50%= 50%= 14%= 92%= 43%= 100%


Photo Credit: Pula Subbaiah Veligonda Tunnel

• Heavy support• Pre-support• Spiling• Thicker shield• Don’t stop progress

Heavy Ground: Mitigation

Photo Credit: J.F. Shea – 2012 NAT

Photo Credit: J F Shea – 2012 NAT Photo Credit: J F Shea – 2012 NAT

Heavy Ground: Mitigation

Photo Credit: McMillen Jacobs Associates

Squeezing Ground:

Risk

Photo Credit: Squeezing Soil Image SearchPhoto Credit: Stantec

• Rule of thumb—UCS vs overburden stress

• Strength/stress ratio• Modeling • Linear into plastic

Squeezing Ground:

Characterization

Photo Credit: Trevor Carter


Photo Credit: Tunneling in Squeezing Ground

Squeezing Ground:

Mitigation

Hand mining over the TBM shield

• Yielding support • Ribs w/ slides • American commercial • TBM shield is tapered • Shotcrete—jacks between

shotcrete panels

Photo Credit: StantecPhoto Credit: DSI Underground / Jennmar

Photo Credit: Giovanni & Marco Barla

• In-situ Stress• Brittleness• Stored Energy• Released Energy

Rock Burst:Risk




2nd Video Rock Burst:

Risk

Video Credit: McNally Support System - Robbins

Rock Burst:Characterization

Photo Credit: Goodman Jack - DGSI


Photo Credit: StantecPhoto Credit: Hydrofrac

Rock Burst: Mitigation

Drilling of horizontal and vertical relief holes, and shotcrete application

Photo Credit: Journal of the Southern African Institute of Mining and Metallurgy

Photo Credit: StantecPhoto Credit: Mirarco

Hydrothermal Conditions:

Risk

Photo Credit: Tunneltalk

Geothermal Inflow, Iceland



• Pictures from Simon?

Hydrothermal Conditions:

Characterization

Geothermal Gradient Map, CO

Upper Colorado River Hot Spring

Temperature Gradient w/ Depth

Mapped Hot Springs





Hydrothermal Conditions:Mitigation

Increased ventilation

Ice VestMandatory Breaks & Limited Working Hours Photo Credit: Utrop

Photo Credit: SRK Consulting

Photo Credit: Glaciertek

Hazardous Gas: Risk


Photo Credit: Ashley Pon/Getty Images

Petroleum fields: CH4

Hazardous Gas: Characterization

Bacteria Geothermal fields: CO2

Aerobes: CO2Sulfate reducers: H2SMethanogens: CH4

Photo Credit: MicrobeWiki – Kenyon College Photo Credit: Geothermal Education Office

Photo Credit: KQED Science Photo Credit: flickr

Gas station: gasoline vapors

Hydrothermal Alteration: H2SPhoto Credit: James Maynard

Hazardous Gas:Characterization

Groundwater samplingPore gas sampling

Sample ScreeningPhoto Credit: Stantec


Hazardous Gas: Mitigation

Mechanical Controls

System Monitoring

Crew TrainingPhoto Credit: Stantec Photo Credit: Stantec

Settlement: Risk

King Street in Seattle, above Bertha TBM Photo Credit: KIRO 7 News


Settlement: Characterization



Settlement:Mitigation

Photo Credit: Bft International

Photo Credit: Dogus

Photo Credit: Dragageshk

Settlement should be controlled by:• Designing construction methods to

prevent settlement• Continued monitoring of surface

and subsurface conditions for settlement or indicators

• Extensometers

Settlement: Mitigation

Photo Credit: Bor-ExPhoto Credit: Geokon

Settlement:Mitigation


wet sand

Sinkhole

Flowing, running ground

wet fine sand

clay

silt

Flowing Ground in TBM

Flowing Ground: Risk




Different Conditioners• Dispersants• Foam Injection Ratios• High Density Limestone Slurry• Bentonite • Polymer

Flowing Ground: Mitigation

Photo Credit: Tunnelling and Supported Deep Excavations in the Greater Cairo

Photo Credit: Hatch Mott MacDonald

Surprises Are Inevitable —There will always be unexpected ground conditions and neither the owner nor the design team can completely eliminate surprises from complex underground projects.

Gould, 1995


Thank you

Geotechnical Risk for Underground Construction · 3. Abrasivity 4. TBM Performance 5. Friction 6....

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