Beacon Hill Voids Update_compressed

8/6/2019 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


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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


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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


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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 )


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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


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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 )


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Beacon Hill Station

Phase 3

Step 1 Step 3 Step 5 CompactionGrout

Step 2 Step 4 Throughout


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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


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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


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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


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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


Documents

Beacon Hill Voids Update_compressed