SLURRY WALLS FOR SEEPAGE CUTOFF IN LEVEE APPLICATIONS RECENT EXPERIENCE AND CONSTRUCTION CHALLENGES IN THE NORTHERN CENTRAL VALLEY OF CALIFORNIA

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1 SLURRY WALLS FOR SEEPAGE CUTOFF IN LEVEE APPLICATIONS RECENT EXPERIENCE AND CONSTRUCTION CHALLENGES IN THE NORTHERN CENTRAL VALLEY OF CALIFORNIA Deep Foundation Institute Slurry Wall Committee July 22, TRLIA Cutoff Walls Designed by GEI 2 1

2 Bear River Setback Levee Feather River Setback Levee Feather River Levee Segments 1 and 3 Soil Bentonite CutoffWall Length (LF) 9,390 25,800 2,600 37,790 Max Depth (FT) Area (SF) 439,000 1,668, ,000 2,283,000 Soil Cement Bentonite Cutoff Wall Length (LF) 11,100 11,100 Max Depth (FT) Area (SF) 620, ,000 Total Summary of TRLIA Cutoff Walls Designed by GEI 3 SOIL-BENTONITE CUTOFF WALL 4 2

3 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 BACKFILL FINES CONTENT: NOT MORE THAN 50% 5 Soil-Bentonite Cutoff Wall Under Setback Levee 6 3

Soil-Bentonite Cutoff Wall Under Setback

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

4 Soil-Bentonite Cutoff Wall Under Setback Levee 7 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 8 4

5 CUTOFF WALL ADJACENT TO CULTURAL SITE 9 Wall Construction Adjacent to Sensitive Cultural Site 10 5

RAISED SLURRY LEVEL INCREASED WORK HOURS ALLOWED

TO INCREASE SLURRY UNIT WEIGHT ATTEMPTED TO STIFFEN

6 Wall Construction Adjacent to Sensitive Cultural Site 11 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 12 6

7 Wall Construction Adjacent to Sensitive Cultural Site 13 CUTOFF WALL AT TOE OF EXISTING LEVEE 14 7

8 Soil-Bentonite Cutoff Wall at Toe of Levee 15 Soil-Bentonite Cutoff Wall at Toe of Levee 16 8

9 Longitudinal Crack Along Landside Levee Slope 17 Inclinometer Plot Levee with Longitudinal Crack 18 9

10 Foundation Shear Strength Characterization 19 Field Vane Shear Strength of Cutoff Wall Backfill (6 months after construction of cutoff wall) 20 10

11 Repair Section Levee with Longitudinal Crack 21 SOIL-CEMENT-BENTONITE CUTOFF WALL 22 11

12 Soil-Cement-Bentonite Cutoff Wall Through Levee 23 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 24 12

13 Soil-Cement-Bentonite Cutoff Wall Through Levee 25 Exposed Recently Constructed Cutoff Wall 26 13

14 CONSTRUCTION ISSUES WE ENCOUNTERED TRENCH CAVE-IN LARGE OBSTRUCTION BACKFILL WITH HIGHER-THAN-SPECIFIED PERMEABILITY 27 CUTOFF WALL TRENCH CAVE-IN 28 14

15 Cutoff Wall Trench Cave-in Levee Profile 29 Cutoff Wall Trench Cave-in - Plan 30 15

16 Cutoff Wall Trench Cave-in Cross Section 31 Cutoff Wall Trench Cave-in Temporary Berm 32 16

17 Cutoff Wall Trench Cave-in Final Repair Plan and Profile 33 Cutoff Wall Trench Cave-in Final Repair Seepage Berm 34 17

18 CUTOFF WALL TRENCH OBSTRUCTION 35 Obstruction in Levee Foundation Abandoned Pump Station Sump 36 18

19 Obstruction in Levee Foundation Backfilled Excavation 37 CUTOFF WALL REACH WITH HIGHER- THAN-SPECIFIED PERMEABILITY 38 19

Cutoff Wall with Higher Permeability Permeability Data

PERMEABILITY Permeability Data: Average of 44 QC Tests:

2.2x10-6 cm/sec Average of 4 QA Tests: 5.

20 Cutoff Wall with Higher Permeability Permeability Data 39 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 40 20

21 Cutoff Wall with Higher Permeability Unconfined Strength Data 41 Cutoff Wall with Higher Permeability Piezometers 42 21

22 QUESTIONS? Deep Foundation Institute Slurry Wall Committee July 22,

GEOTECHNICAL INVESTIGATION PROPOSED OUTFALL LOCATION CITY OF MORGAN S POINT DRAINAGE HARRIS COUNTY, TEXAS REPORT NO

GEOTECHNICAL INVESTIGATION PROPOSED OUTFALL LOCATION CITY OF MORGAN S POINT DRAINAGE HARRIS COUNTY, TEXAS REPORT NO. 1140198001 Reported to: SIRRUS ENGINEERS, INC. Houston, Texas Submitted by: GEOTEST