beacon hill voids update_compressed
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Voids Investigation andRemedial Work
Capital Committee
May 12, 2011
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1. Background Information2. Voids Identification, Exploration and Filling
3. Bulking of Soils
4. Conclusions
5. Actions Taken for University Link
Presentation Outline
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Background Information
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Tunnel Work Earth pressure balance tunnel
boring machine[1 TBM for both tunnels]
Southbound tunnel drive:February 2006 to May 2007
Northbound tunnel drive:July 2007 to March 2008
Background Information
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Beacon Hill Station
Findings : Excess spoil removed => conveyor weight scale data Nine target areas located in zone ( ~300-feet long ) Identified potential voids volume of 3,296 cy based on
weight
Background Information
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Excess Belt Scale Weight Gradation Scale
Voids Identification, Exploration and Filling
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PHASE 1 [Void Identification & Filling]
April & May 2009 Performed investigation utilizing
Subsurface explorations andprobes along tunnel centerline
Used targeted approach based onweight-scale data
Microgravity measurements trialto delineate disturbed zones andvoids
Drilled 38 probe holes
Filled voids with CDF
Voids Identification, Exploration and Filling
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Beacon Hill Station
Voids discovered in each of the 9 zones Voids coincided with over-excavation identified by weigh-scale
data Phase 1 found and filled 2,544 of 3,296 cy ( 78% fill factor )
Voids Identification, Exploration and Filling
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PHASE 2 [Compaction Grouting]
June and July 2009 Developed a program to compact
loose zones
Pumped cement grout through patternof holes
Grout pressures 300 to 600 psi tocompact loose zones
Drilled 61 holes Placed another 293 cy of grout
Voids Identification, Exploration and Filling
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Beacon Hill Station
Phase 1 & 2 => found and filled 2,837 of 3,296 cy
Fill Factor = 87% Six of nine areas filled within 10% of total theoretical volume
(blue ovals ) Potential for approximately 430 cubic yards of subsurface
ground loss distributed in three areas ( purple ovals )
Voids Identification, Exploration and Filling
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Beacon Hill Station
Phase 3
Step 1 Step 3 Step 5 CompactionGrout
Step 2 Step 4 Throughout
Voids Identification, Exploration and Filling
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PHASE 3 [Verification Explorations]
July 2010 December 2010
Delineate the extent/nature ofdisturbed zones
Backfill any remaining loose zones
Drilled 108 holes ( steps 1 thru 4 )
Placed another 115 cy of grout
Voids Identification, Exploration and Filling
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Voids Identification, Exploration and Filling
Total fill placed (Phases 1, 2 & 3) = 2,952 cy of 3,269 cy Fill factor = 90% No need for Step 5: Compaction grouting throughout
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NB NB
Total
SB SB
Total
Phase
Total
Cum
Total
Cum
%
#holes
VolPlaced
#holes
VolPlaced
VolPlaced
VolPlaced
FillFactor
EstimateLoss 1,939 1,330 3,296
Ph 1 Fill 21 1,632 17 912 2,544 2,544 78%
Ph 2 Fill 26 87 34 206 293 2,837 87%
Ph 3 Fill 47 71 61 44 115 2,952 90%
Bulking
Total Fill 94 1,790 112 1,162 2,952
% Fill 92.3% 87.4% 90.3%
Bulking of Soils
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Bulking
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3D Interpreted View of Voids (westerly area)
NB SB
Bulking of Soils
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3D Interpreted View of Disturbed Zones and Voids
NB SB
Bulking of Soils
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NB NB
Total
SB SB
Total
Phase
Total
Cum
Total
Cum
%
#holes
VolPlaced
#holes
VolPlaced
VolPlaced
VolPlaced
FillFactor
Estimate
Loss 1,957 1,339 3,296Ph 1 Fill 21 1,632 38 17 912 2,544 2,544 78%
Ph 2 Fill 26 87 60 34 206 293 2,837 87%
Ph 3 Fill 47 71 108 61 44 115 2,952 90%
Bulking 167 177 344 3,269 100%
Total Fill 94 1,957 206 112 1,339 3,296
% Fill 100.0% 100.0% 100.0%
Bulking of Soils
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The voids were caused by over-excavation
The over-excavation: failure to operate in closedmode with full excavation face support asrequired by the Contract
The belt scales measured over-excavation (e.g.high excavated material weights)
Conclusions
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Reviewed data and identified other potential voids
Developed phased plan with integrated team (CM,Engineers-of-Record, Contractor, Tunnel Experts)
Executed and completed our phased plan
Accomplished program objectives (filledvoids/compacted loose zones) within budget
Actions Taken
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TBM Control System: Display 8 hours of face pressure sensor data
Confirm TBM is consistently operating as required
(e.g. above ambient pressure)
Actions Taken for University Link
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TBM Data Logger: Obtain/plot data routinely
Confirm operating parameters are being maintained
TBM Belt Weigh-Scale Gather data after each ring advance
Compare to theoretical weight calculation
Take immediate remedial action, asnecessary
TBM Conditioning Materials Sufficient/proper materials available
Used according to soil profile
Actions Taken for University Link
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Construction management team is being trainedto read and interpret the measured data
CM team will have a trained inspector in the
tunnel heading at all times
Real time data will be displayed on a computer inthe CM office
Actions Taken for University Link
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IF any critical parameters (e.g. face pressure, beltscale weights, etc.) are not as required/expected
THEN Immediately investigate and havecontractor take corrective action
Actions Taken for University Link