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SLURRY WALLS FOR SEEPAGE CUTOFF IN LEVEE APPLICATIONS – RECENT EXPERIENCE AND

CONSTRUCTION CHALLENGES IN THE NORTHERN

1Three Rivers Levee Improvement Authority

CONSTRUCTION CHALLENGES IN THE NORTHERN CENTRAL VALLEY OF CALIFORNIA

Deep Foundation InstituteSlurry Wall Committee

July 22, 2010

2Three Rivers Levee Improvement Authority

TRLIA Cutoff Walls Designed by GEI

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Bear River

Setback Levee

Feather River

Setback Levee

Feather River Levee

Segments 1 and 3 Total

Soil‐Bentonite Cutoff WallSoil Bentonite Cutoff Wall

Length (LF) 9,390 25,800 2,600 37,790

Max Depth (FT) 70 78 68 78

Area (SF) 439,000 1,668,000 176,000 2,283,000

Soil‐Cement‐Bentonite Cutoff Wall

Length (LF) 11,100 11,100

Max Depth (FT) 65 65

Area (SF) 620,000 620,000

3Three Rivers Levee Improvement Authority

Summary of TRLIA Cutoff Walls Designed by GEI

SOIL-BENTONITE CUTOFF WALL

4Three Rivers Levee Improvement Authority

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TYPICAL SOIL-BENTONITE CUTOFF WALL SPECIFICATION:

WALL WIDTH: 3 FT

BACKFILL PERMEABILITY: LESS THAN 5 X 10-7 CM/SEC

CONTENT OF DRY BENTONITE IN THE BACKFILL: NOT LESS THAN

1.5% BY WEIGHT

DEPTH OF KEY INTO PREVIOUSLY EXPLORED FINE-GRAINED

STRATUM: NOT LESS THAN 3 FT

5Three Rivers Levee Improvement Authority

BACKFILL FINES CONTENT: NOT MORE THAN 50%

6Three Rivers Levee Improvement Authority

Soil-Bentonite Cutoff Wall Under Setback Levee

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7Three Rivers Levee Improvement Authority

Soil-Bentonite Cutoff Wall Under Setback Levee

Heading Overlaps

POTHOLE TO CONFIRM LOCATION OF EXISTING WALL

MONITOR TRENCH EXCAVATION CUTTINGS TO CONFIRM

EXCAVATION INTO EXISTING WALL

4(H):1(V) SLOPE OF CUT INTO EXISTING WALL

MINIMUM 10-FOOT OVERLAP AT THE BOTTOM

8Three Rivers Levee Improvement Authority

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CUTOFF WALL ADJACENT TO CULTURAL SITE

9Three Rivers Levee Improvement Authority

10Three Rivers Levee Improvement Authority

Wall Construction Adjacent to Sensitive Cultural Site

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11Three Rivers Levee Improvement Authority

Wall Construction Adjacent to Sensitive Cultural Site

PREVENTIVE MEASURES TO AVOID TRENCH CAVE-IN

RAISED SLURRY LEVEL

INCREASED WORK HOURS

ALLOWED TOE OF BACKFILL CLOSER TO EXCAVATION FACE

ATTEMPTED TO INCREASE SLURRY UNIT WEIGHT

ATTEMPTED TO STIFFEN BACKFILL TO STEEPEN THE BACKFILL

SLOPE WITHIN TRENCH

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13Three Rivers Levee Improvement Authority

Wall Construction Adjacent to Sensitive Cultural Site

CUTOFF WALL AT TOE OF EXISTING LEVEE

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15Three Rivers Levee Improvement Authority

Soil-Bentonite Cutoff Wall at Toe of Levee

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Soil-Bentonite Cutoff Wall at Toe of Levee

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17Three Rivers Levee Improvement Authority

Longitudinal Crack Along Landside Levee Slope

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Inclinometer Plot – Levee with Longitudinal Crack

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19Three Rivers Levee Improvement Authority

Foundation Shear Strength Characterization

20Three Rivers Levee Improvement Authority

Field Vane Shear Strength of Cutoff Wall Backfill

(6 months after construction of cutoff wall)

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21Three Rivers Levee Improvement Authority

Repair Section – Levee with Longitudinal Crack

SOIL-CEMENT-BENTONITE

CUTOFF WALL

22Three Rivers Levee Improvement Authority

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23Three Rivers Levee Improvement Authority

Soil-Cement-Bentonite Cutoff Wall Through Levee

TYPICAL SOIL-CEMENT-BENTONITE CUTOFF WALL SPECIFICATION:

WALL WIDTH: 2.5 FT

BACKFILL PERMEABILITY: LESS THAN 5 X 10-7 CM/SEC

BACKFILL UNCONFINED COMPRESSIVE STRENGTH: 30 TO 300 PSI

DEPTH OF KEY INTO PREVIOUSLY EXPLORED FINE-GRAINED STRATUM:

INCREASED TO NOT LESS THAN 8 FT AFTER CONCERNS RAISED AS

PART OF SAFCA WORK ABOUT CONTINUITY OF BACKFILL AT THE

BOTTOM OF THE WALL

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25Three Rivers Levee Improvement Authority

Soil-Cement-Bentonite Cutoff Wall Through Levee

26Three Rivers Levee Improvement Authority

Exposed Recently Constructed Cutoff Wall

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CONSTRUCTION ISSUES WE ENCOUNTERED

TRENCH CAVE-IN

LARGE OBSTRUCTION

BACKFILL WITH HIGHER-THAN-SPECIFIED PERMEABILITY

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CUTOFF WALL TRENCH CAVE-IN

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29Three Rivers Levee Improvement Authority

Cutoff Wall Trench Cave-in – Levee Profile

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Cutoff Wall Trench Cave-in - Plan

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31Three Rivers Levee Improvement Authority

Cutoff Wall Trench Cave-in – Cross Section

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Cutoff Wall Trench Cave-in – Temporary Berm

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Cutoff Wall Trench Cave-in

Final Repair Plan and Profile

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Cutoff Wall Trench Cave-in

Final Repair Seepage Berm

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CUTOFF WALL TRENCH

OBSTRUCTION

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Obstruction in Levee Foundation

Abandoned Pump Station Sump

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Obstruction in Levee Foundation

Backfilled Excavation

CUTOFF WALL REACH WITH HIGHER-

THAN-SPECIFIED PERMEABILITY

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39Three Rivers Levee Improvement Authority

Cutoff Wall with Higher Permeability – Permeability Data

CUTOFF WALL REACH WITH HIGHER-THAN-SPECIFIED PERMEABILITY

Permeability Data:

Average of 44 QC Tests: 9.1x10-7 cm/sec

Maximum Value of QC Permeability Tests: 2.2x10-6 cm/sec

Average of 4 QA Tests: 5.8x10-7 cm/sec

Maximum Value of QA Permeability Tests: 7.1x10-6 cm/sec

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41Three Rivers Levee Improvement Authority

Cutoff Wall with Higher Permeability

Unconfined Strength Data

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Cutoff Wall with Higher Permeability – Piezometers

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QUESTIONS?QUESTIONS?

43Three Rivers Levee Improvement Authority

Deep Foundation InstituteSlurry Wall Committee

July 22, 2010