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11/13/2012
PAGE 1
UNCONVENTIONAL SUBSURFACE INVESTIGATION METHODS FOR SOIL TUNNEL/TRENCHLESS PROJECTS
Tracy Lyman – Brierley AssociatesNate Soule – Brierley Associates
• CONVENTIONAL SUBSURFACE EXPLORATION METHODS
• EXAMPLES AND HEARTACHES
• ALTERNATIVE EXPLORATION METHODS
• ADVANTAGES AND EXAMPLES
INTRODUCTION
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• AUGER BORING
• ROTARY WASH BORING
• SPLIT SPOON SAMPLES @ 5 FT (N‐VALUES)
• UNDISTURBED SAMPLES
• CONE PENETROMETER/VANE SHEAR
• LAB TESTING
STANDARDIZED, REPEATABLE,
WELL‐UNDERSTOOD
CONVENTIONAL METHODS
• BORING SPACING/SCOPE
• 200 ‐500 FT
• USNCT/T AND INDUSTRY PRACTICE
• LARGE/COMPLEX – 1.5 TO 2.25 % PROJECT COST
• SMALL/ROUTINE – 1 TO 1.5% OF PROJECT COST
CONVENTIONAL METHODS ‐ SCOPE
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• GROUND TYPES
• COARSE GRAVEL, COBBLES, BOULDERS
• ARTIFICIAL FILL/HARD OBSTRUCTIONS
• MIXED FACE
• HIGH GROUNDWATER IN SILT/SILTY SAND
• PROBLEMS
• VERTICAL VARIABILITY
• HARD OBSTRUCTIONS
• LOW PERMEABILITY IN SILT AND SILTY SAND
LIMITATIONS/PROBLEMS
• DENVER 72‐IN STORM DRAIN
• SEATTLE WATER LINE
• DENVER INTERCEPTOR SEWER
PROJECT EXAMPLES/HEARTACHES
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• 300 FT HIGHWAY CROSSING
• SAND/SILTY SAND NEAR CREEK
• AUGER BORINGS AT EACH SHAFT (NO CENTER BORING IN HIGHWAY)
• WHEELED TBM WITH SAND SHELVES PLANNED AND DEWATERING
• CONTRACTOR SHAFT EXCAVATION = THIN SILT AT 2 ‐3 FT INTERVALS
• DEWATERING VERY PROBLEMATIC
• SWITCHED TO MICROTUNNEL = CHANGE ORDER $$
• TEST PITS – BETTER OBSERVATION OF SILT
• CONTINUOUS SAMPLING AT TUNNEL HORIZON
DENVER 72‐IN STORM DRAIN
• LARGE WATERLINE PROJECT
• AUGER BORINGS/SPLIT SPOON
• GBR USED – SILT, SAND, GRAVEL, OCCASIONAL COBBLES
MANY COBBLES
VERY HIGH UCS
CONFIRMED COBBLES WITH
BUCKET AUGER HOLES
MTBM RESCUE SHAFTS
• TEST PITS /
LARGE DIAMETER BORINGS
SEATTLE WATERLINE
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• 36 – IN PIPE
• SAND, GRAVEL, WEAK BEDROCK (SILTSTONE, CLAYSTONE, SANDSTONE)
• OPEN SPACE PARK CROSSING
CONTRACTOR ENCOUNTERED LIMESTONE (HIGH UCS)
DESTROYED SOIL CUTTING TOOLS
RESCUE SHAFTS NOT ALLOWED IN OPEN SPACE
OPEN SPACE LIMESTONE – SEISMIC REFRACTION, CORE BORING
GEOPHYSICS TO AUGMENT BORINGS
DENVER INTERCEPTOR SEWER
• TEST PITS
• LARGE DIAMETER BORINGS
• GEOPHYSICS
• PILOT BORE
• VACUUM BORE
UNCONVENTIONAL EXPLORATION METHODS
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• METHOD
• OPEN EXCAVATION
• DEWATERING
• ADVANTAGES
• LARGE “SAMPLE SIZE”
• OBSERVE PIT WALL
• OBSERVE SOIL BEHAVIOR
• DEWATERING VOLUME
• CONTINUOUS SAMPLING
• COST
• $125 ‐ $175/HR BACKHOE OPERATOR/EQUIPMENT
• DEWATERING EXTRA
TEST PITS
• METHOD
• 18 TO 30‐IN AUGER/BUCKET AUGER
• DIRECTLY OBSERVE SOIL
• CONTINUOUS SAMPLING
• ADVANTAGES
• LARGE “SAMPLE SIZE”
• OBSERVE SOIL BEHAVIOR
• OBSERVE GROUNDWATER
• COST
• $200 ‐ $250/HR
• LOGISTICAL SUPPORT EXTRA
LARGE DIAMETER BORINGS
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• METHOD
• SEISMIC REFRACTION
• CROSS‐HOLE SEISMIC
• GROUND PENETRATING RADAR
• ELECTRICAL SURVEY
• ADVANTAGES
• FILL IN BETWEEN BORINGS
• MAP BEDROCK SURFACE
• FIND BURIED OBSTRUCTIONS
• COST
• $5,000 TO $7,000/DAY
GEOPHYSICS
• METHOD
• HDD OR PILOT TUBE BORE
• BORE TUNNEL HORIZON
• ADVANTAGES
• DIRECT OBSERVATION OF TUNNEL HORIZON
• FIND OBSTRUCTIONS
• FIND COBBLES/BOULDERS
• COST
• $500/HR HDD RIG & CREW
PILOT BORE
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• METHOD
• VACUUM EXCAVATION/TRUCK
• LOOK FOR UTILITIES
• LOOK FOR OBSTRUCTIONS
• ADVANTAGES
• DIRECT OBSERVATION OF UTILITY OR OBSTRUCTION
• OBSERVE BORE WALL
• OBSERVE SOIL BEHAVIOR
• COST
• $200/HR VAC TRUCK AND CREW
• DEWATERING EXTRA
VACUUM BORE
• DENVER URBAN DRAINAGE STORM DRAIN
• FORT COLLINS STORM DRAIN
• DENVER WATER STORM DRAIN
CASE EXAMPLES
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DENVER URBAN DRAINAGE
Proposed 48” Steel Pipe4 to 17-ft Deep to Invert240-ft Long
48” Storm Sewer
Parallel with Tunnel
8” WaterlineInterfered with Tunneling PitNeeded to be Raised
Restricted AccessCDOT Access LinesCDOT Barrier LinesFHWA PermitFRICO Ditch RoadPrivate Property to the West
Cobbles & Boulders
Groundwater
Test Pits
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HDD TRIAL BORE
GUIDED RAMMING OR MICROTUNNELING?
• VERY LOW COVER/BELOW DIVIDED HIGHWAY
• SAND, SILT, GRAVEL BELOW GROUNDWATER
• SOME C0BBLES
QUESTION: GUIDED RAMMING OR MICROTUNNELING??
USE TEST PITS AND HDD BORE
• COBBLES AND GROUNDWATER/DEWATERING
• FEASIBILITY OF PILOT TUBE PUSH
DENVER URBAN DRAINAGE ‐ SUMMARY
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FORT COLLINS STORM DRAIN
RAISED VERTICAL ALIGNMENT
TEST PITS:
CONFIRMED HIGH GROUNDWATER
CONFIRMED FLOWING GROUND
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Back in the day – 1800’s
Another view from 1916 on the other side of the tracks. Note the bridge and the pipe foundation
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DIFFICULT!
PIPE RAMMING BEST CHANCE OF SUCCESS
AVOID KNOWN CONCRETE OBSTRUCTIONS
SUMMARY
TRADITIONAL EXPLORATIONS – STANDARDIZED, REPEATABLE, WELL‐UNDERSTOOD
OTHER METHODS PROVIDE: DIRECT OBSERVATION OF SOIL/SOIL BEHAVIOR
LARGER SAMPLE SIZE
COBBLES, BOULDERS, OBSTRUCTIONS
CONSIDER ALL OPTIONS – PROJECT SUCCESS
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