psi_report_322-95001_-_volume_ii.pdf

GEOTECHNICAL ENGINEERING SERVICES REPORT

UNITED STATES SECTION, INTERNATIONAL BOUNDARY & WATER COMMISSION

LOWER RIO GRANDE PROJECT – INTERIOR LEVEES

REHABILITATION OF MAIN FLOODWAY, FROM 23RD STREET TO FM 1015

HIDALGO COUNTY, TEXAS

PSI REPORT NO. 322-95001 - VOLUME II (NORTH LEVEE)

PREPARED FOR S&B INFRASTRUCTURE, LTD.

MAY 2009

PSI REPORT 322-95001

VOLUME II (NORTH LEVEE)

MAIN FLOODWAY NORTH LEVEE

Levee Section Station Limits Soil Borings Critical Section Location

Section 1 255+31 to 302+50 MFN1-1 to MFN1-5 287+41.93

Section 2 302+50 to 353+50 MFN1-6 to MFN1-10 338+97.05

Section 3 353+50 to 405+00 MFN1-11 to MFN1-15 400+81.88

Section 4 405+00 to 456+00 MFN1-16 to MFN1-20 452+05.46

Section 5 456+00 to 508+00 MFN1-21 to MFN1-25 483+39.89

Section 6 508+00 to 550+50 MFN1-26 to MFN1-30 524+37.34

Section 7 550+50 to 592+08 MFN1-31 to MFN1-35 567+12.85

Section 8 711+00 to 758+00 MFN1-36 to MFN1-40 742+83.63

Section 9 758+00 to 810+50 MFN1-41 to MFN1-45 784+68.61

Section 10 810+50 to 863+00 MFN1-46 to MFN1-50 816+04.36

Section 11 863+00 to 914+50 MFN1-51 to MFN1-55 909+41.57

Section 12 914+50 to 965+00 MFN1-56 to MFN1-60 950+50.57

Section 13 965+00 to 1018+50 MFN1-61 to MFN1-65 1002+75.07

Section 14 1018+50 to 1060+50 MFN1-66 to MFN1-70 1044+85.25

Section 15 1060+50 to 1112+50 MFN1-71 to MFN1-75 1096+77.17

Section 16 1112+50 to 1163+00 MFN1-76 to MFN1-80 1157+58.29

Section 17 1163+00 to 1214+00 MFN1-81 to MFN1-85 1198+65.59

Section 18 1214+00 to 1266+00 MFN1-86 to MFN1-90 1229+65.37

Section 19 1266+00 to 1328+50 MFN1-91 to MFN1-96 1302+53.92

Section 20 1328+50 to 1366+00 MFN1-97 to MFN1-101 1360+29.15

Section 21 1366+00 to 1406+84 MFN1-102 to MFN1-106 1401+54.11

VOLUME II, SECTION 1 - PAGE NO. 1

SECTION 1.0: STA. 255+31 TO STA. 302+50.00 (MFN1-1 TO MFN1-5)

This section describes the subsurface conditions and the geotechnical engineering analyses for the Main Floodway North levee extending between Sta. 255+31 and Sta.

302+50.00. The subsurface conditions in this area of the project site were explored with five (5) soil borings (i.e., MFN1-1 through MFN1-5).

1.1 CROSS-SECTIONAL INFORMATION

The revised cross-sectional drawings of the levee system were provided by S & B Infrastructure, LTD on May 6, 2009. The existing cross-sectional information, in conjunction with the proposed levee crown elevations was reviewed to identify the maximum height (most critical) for the proposed levee geometry and a design levee cross-section was selected. The cross-section at Sta. 287+41.93 was used for the analyses. Please note that the dimensions are rounded to the nearest foot for calculation purposes.

Key information pertaining to the design cross-section for this segment of levee includes the following:

1. Proposed Crown Width: 16 feet

2. Proposed Enlargement Side Slope Inclination: 3H:1V on both sides

3. Flood Water Elevation: Three (3) feet below crown (freeboard)

4. Existing Levee Height: 20.5 feet

5. Maximum final Levee Height: 23 feet

6. Maximum Additional Fill to Raise the Levee: 2.5 feet

1.2 SUBSURFACE CONDITIONS

The subsurface conditions within this portion of the levee were explored with five soil borings (i.e., Borings MFN1-1 through MFN1-5) drilled to a depth of 50 feet below the existing ground surface.

Laboratory test data along with detailed descriptions of the soils found within this portion of the levee system can be found on the logs of Borings MFN1-1 through MFN1-5 include in Appendix 1.1 of this Chapter. Appendix 1.1 also contains portions of the laboratory test data including the results of the consolidated undrained triaxial tests with pore pressure measurements (CU test), consolidation tests and permeability tests.

Existing levee materials consisted predominantly of firm to very stiff lean to fat clay.

Native soils beneath the levee generally consist of firm to very stiff sandy lean clay, and medium dense poorly graded sand and silty sand. The range of the laboratory test results is presented below in Table 1.1:

VOLUME II, SECTION 1 - PAGE NO. 2

Table 1.1: Range of Laboratory Test Results (Borings MFN1-1 through MFN1-5)

Soil Type Moisture Content (%)

Atterberg Limits

Shear Strength (tsf)

Percent Passing No.

200 (%)

SPT – N

Values

(blows/ft)

Levee (CL, CH) 3 to 30 LL = 42 to 63

PI = 23 to 44 0.2 to 4.5 81 to 98 -

Lean Clay (CL) 17 to 30 LL = 48

PI = 29 0.5 to 2.5 96 -

Fat Clay (CH) 17 to 31 LL = 54 to 67 PI = 31 to 44 0.25 to 1.75 56 to 99 -

Silty Sand (SM) 24 to 33 - - 9 to 13 20 to 22

Notes: LL: Liquid Limit; PI: Plasticity Index

1.3 DESIGN SOIL STRENGTH PROFILE

The soil strength parameters selected for the design profile are based on: 1) the results of our field and laboratory test data on selected soil samples, 2) prudent engineering judgment based on experience with similar soils, and 3) published correlations.

The selection process for obtaining soil strength parameters used in the stability analyses for the 1) Short-Term Condition, 2) Long-Term Condition, and 3) Rapid Draw- Down Condition (upstream slope) are described below:

• As previously mentioned, average undrained strength of the soil as measured by the Unconfined Compression tests and Unconsolidated Undrained tests were used to analyze the slopes in “short-term” conditions. For a clay layer (at a given cross-sectional location), the strength test results obtained on the soils of the nearest boring locations were averaged to obtain the undrained shear strength parameters.

For a sand layer, the blow counts obtained from the field Standard Penetration Test (N-Values) were used to obtain the angle of internal friction. The values were obtained utilizing various correlations available in the geotechnical literature, our engineering judgment and well-established local experience.

• To analyze the slopes in “long-term and rapid draw-down conditions” (for a clay layer), the effective cohesion (c’) value and the effective angle of internal friction (φ’) were utilized. These parameters were obtained from the CU tests performed, as well as published correlations. The phreatic surface developed during a theoretical steady-state seepage condition was utilized for both of these stability scenarios.

VOLUME II, SECTION 1 - PAGE NO. 3

The design soil strength parameters used in the slope stability analyses for this section are presented below in Table 1.2:

Table 1.2 Design Soil Strength Parameters

Soil Strength Parameter(s) Stratum

(Elev. Range, feet) Undrained (Short-Term)

Effective (Long-Term & Rapid Draw-down) Levee

(+114 to +94 ft.) Su = 1,000 psf c’ = 250 psf φ’= 27o

Fat Clay (CH) (+94 to +82 ft.) Su = 2,000 psf c’ = 200 psf φ’= 20o

Lean Clay (CL) (+82 to +73 ft.) Su = 1,500 psf c’ = 150 psf φ’= 25o

Silty Sand (SM) (Below +73 ft.) φ’ = 34o c’ = 0 psf φ’ = 34o

Notes: Su - Undrained Shear Strength, c’ - effective cohesion, φ’ - effective angle of internal friction

1.4 DISCUSSION OF RESULTS AND RECOMMENDATIONS

Using the soil strength parameters shown in Table 1.2, slope stability analyses were performed for the design (critical) cross-section previously mentioned in this section. The proposed side slopes of the levee enlargement at this location are 3H:1V with a maximum slope height of about 23 feet. The results of the stability analyses are shown graphically in Appendix 1.2.

• Based on the results of the slope stability analyses for the levee slopes, the minimum calculated factor-of-safety for the short-term condition is 3.33 (see Figure 1.1), thereby indicating stable slopes. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.3, as recommended in the USACE publication Slope Stability Manual (EM 1110-2-1902), and USACE publication Design & Construction of Levees Manual (EM 1110-2-1913).

• Based on the stability analysis for the long-term condition, the minimum calculated factor-of-safety is 1.56 (see Figure 1.2), thereby indicating stable slopes. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.5, as recommended in the USACE publication Slope Stability Manual (EM 1110- 2-1902), and USACE publication Design & Construction of Levees Manual (EM 1110-2-1913).

• For the rapid draw-down condition using effective soil strength parameters, the minimum calculated factor-of-safety is 1.73 (see Figure 1.3) and the levee slopes are considered to be stable. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.0, as recommended in the USACE publication Slope Stability Manual (EM 1110-2-1902), and USACE publication Design & Construction of Levees Manual (EM 1110-2-1913).

In addition, the near-surface clay soils along the project alignment are subject to

VOLUME II, SECTION 1 - PAGE NO. 4

weathering (aging) in response to wetting and drying cycles, thereby resulting in a decrease in soil strength over time. A rapid draw-down condition in conjunction with soil weathering may result in sloughing of the flood-side levee slope following a flood event.

These shallow failures should be regarded as a maintenance issue and it is recommended that they be repaired soon after they occur to maintain the integrity of the levee.

1.5 LEVEE SETTLEMENT ANALYSIS

Within this segment of the levee (i.e., between Sta. 255+31 and Sta. 302+50.00), the levee is planned to be raised by approximately 2.5 feet. Based on our analyses, the long-term settlement induced by the proposed levee enlargement is estimated to be less than one (1) inch.

1.6 SEEPAGE ANALYSIS

A steady-state seepage analysis was performed in accordance with USACE EM 1110-2- 1901 using the finite-element computer program SEEP/W (see Figure 1.4). Hydraulic gradients were calculated for the design cross-section and compared to established criteria. Based on this analysis, the exit gradient at the landside toe was calculated to be less than 0.5. The ratio of the critical gradient (the gradient at which piping can occur) to the calculated gradient results in a factor-of-safety against piping. Based on a critical gradient of 0.8, the resulting factor-of-safety exceeds the minimum value of 1.6, as recommended by the USACE. In addition, the steady-stage seepage rate for this section of levee is estimated to be approximately three (3) gallons per day, which is considered to be low. Therefore, mitigation measures for seepage control are not warranted. Results of the seepage analysis are presented on Figure 1.4.

1.7 CONSTRUCTION RECOMMENDATIONS

As previously mentioned, the levee will be raised by a maximum of about 2.5 feet in this section (Sta. 255+31 to Sta. 302+50.00). Borrow materials for levee construction can be clays, sandy clays classified as CL, and fat clays (CH). Silts, sands and organic soils are unsuitable for levee construction. The borrow materials must be selected and placed in strict accordance with Section 4 of USACE Publication EM 1110-2-1913.

The borrow materials should be placed in maximum lifts of 12 inches of loose material and should be compacted to at least 95 percent of standard Proctor maximum dry density as determined by ASTM D 698 with the range of three percentage (-1% to +3%) points of the optimum moisture content value. The first layer of fill should be placed in a relatively uniform horizontal lift and be adequately keyed into the existing levee soils.

Please refer to Volume 1 of this report for additional recommendations.

Any structures or other special features within the levee (such as pipe penetrations) should be designed and constructed in accordance with Section 8 of USACE Publication

EM 1110-2-1913.

VOLUME II, SECTION 1 - PAGE NO. 5

1.8 CONCLUSIONS

Based on our analyses of this section (Sta. 255+31 to Sta. 302+50.00), the levee can be raised by a maximum of about 2.5 feet with a side slope inclination of 3H:1V or flatter.

The slope stability, seepage and settlement of the new levee system are acceptable and satisfy prudent and well-accepted USACE engineering criteria for the stability of levees.

VOLUME II, SECTION 1 - PAGE NO. 6

APPENDIX 1.1

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Lean Clay (CL), Very Stiff, Dark Brown, Moist

Sand Lense at 13 Feet

APPROXIMATE BOTTOM OF LEVEE

FAT CLAY (CH), Very Stiff, Brown, Moist

Clayey Sand Layer at 30 feet

SAND WITH SILT (SP-SM), Poorly Graded, Fine Grained, Medium Dense, Brown, Moist, Wet

CL

CH

SP-SM

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-1

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/13/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 256+99.32

INITIAL GROUND WATER (FT) 26

GROUND WATER

FINAL GROUND WATER (FT): 21

TYPE OF BORING: HOLLOW STEM AUGER/WET ROTARY

APPROXIMATE SURFACE ELEVATION: 111.16 feet

COORODINATE (X) OR EASTING: 1064994

COORDINATE (Y) OR NORTHING: 16578595

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:2

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-5

\M F

N

-5 R

E V

1.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

47.5

50.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Firm to Very Stiff, Dark Brown, Moist

Shear Strength = 2.3 tsf

APPROXIMATE BOTTOM OF LEVEE

FAT CLAY (CH), Firm to Very Stiff, Brown, Moist

CH

CH

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-2

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/14/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 266+84.09

INITIAL GROUND WATER (FT) not encountered during dry augering

GROUND WATER

FINAL GROUND WATER (FT): not encountered

TYPE OF BORING: HOLLOW STEM AUGER/WET ROTARY

APPROXIMATE SURFACE ELEVATION: 110.38 feet

COORODINATE (X) OR EASTING: 1065968

COORDINATE (Y) OR NORTHING: 16578451

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:2

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-5

\M F

N

-5 R

E V

1.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Very Stiff, Dark Brown, Moist

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Soft to Very Stiff, Brown, Moist

Shear Strength = 1.33 tsf

Soft at 25 to 30 Feet

Firm at 35 Feet

Very Stiff at 50 Feet

CH

CL

31 2

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-3

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/15/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 276+98.50

INITIAL GROUND WATER (FT) not encountered during dry augering

GROUND WATER

FINAL GROUND WATER (FT): not encountered

TYPE OF BORING: HOLLOW STEM AUGER/WET ROTARY

APPROXIMATE SURFACE ELEVATION: 110.43 feet

COORODINATE (X) OR EASTING: 1066964

COORDINATE (Y) OR NORTHING: 16578264

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:2

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-5

\M F

N

-5 R

E V

1.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Lean Clay (CL), Firm to Very Stiff, Dark Brown, Moist

Shear Strength = 0.93 tsf

APPROXIMATE BOTTOM OF LEVEE

FAT CLAY (CH), Firm to Very Stiff, Brown, Moist

Shear Strength = 0.84 tsf

Firm at 35 Feet

Very Stiff Below 40 Feet

CL

CH

30 13

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-4

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/16/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 287+41.93

INITIAL GROUND WATER (FT) not encountered during dry augering

GROUND WATER

FINAL GROUND WATER (FT): not encountered

TYPE OF BORING: HOLLOW STEM AUGER/WET ROTARY

APPROXIMATE SURFACE ELEVATION: 109.95 feet

COORODINATE (X) OR EASTING: 1067977

COORDINATE (Y) OR NORTHING: 16578015

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:2

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-5

\M F

N

-5 R

E V

1.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Firm to Very Stiff, Dark Brown, Moist

Shear Strength = 2.76 tsf

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Stiff to Very Stiff, Brown, Moist

FAT CLAY (CH), Stiff to Very Stiff, Brown, Moist

Very Stiff at 35 Feet

Stiff at 40 Feet

Very Stiff at 45 Feet

CH

CL

CH

26 12

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-5

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/17/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 297+89.72

INITIAL GROUND WATER (FT) not encountered during dry augering

GROUND WATER

FINAL GROUND WATER (FT): not encountered

TYPE OF BORING: HOLLOW STEM AUGER/WET ROTARY

APPROXIMATE SURFACE ELEVATION: 109.26 feet

COORODINATE (X) OR EASTING: 1068995

COORDINATE (Y) OR NORTHING: 16577763

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:2

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-5

\M F

N

-5 R

E V

1.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000 4,500

CL

CH

SP

SM

MFN1-1

CH

CH

MFN1-2

CH

CL

MFN1-3

CL

CH

MFN1-4

CH

CL

CH

MFN1-5

E le va tio n

1064994 1065968 1066964 1067977 1068995

111.2 110.4 110.4 110.0 109.3

50.0 50.0 50.0 50.0 50.0

Varying soil deposits, including fill materials may exist between the sampling intervals and between boring locations.

PROJECT #

Borehole North East Elev. Depth

MFN1-1

MFN1-2

MFN1-3

MFN1-4

MFN1-5

16578595 16578451 16578264 16578015 16577763

Distance Along Baseline

DATE PLATE

322-95001 1

SUBSURFACE FENCE DIAGRAM

MFN1-1 through MFN1-5

IBWC North Levee

Hidalgo County

May 2009

F E

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3/4" #4 #10 #40 #200

2.0 0.075

US IBWC Levee mm mm

Boring No.: MFN-1 mm mm

Sample Depth: 38 to 40

GRADATION CURVE

Cc: 2.13 Cu: 0.74

D50: 0.15 D60: 0.17

D10: 0.08 D30: 0.10

SERIES NO. SAMPLE IDENTIFICATION GRADATION INFORMATION

152 76.2 19.1 4.75 0.42 0.002

PARTICLE SIZE IN MM

COARSE FINE COARSE MEDIUM

US STANDARD SIEVE SIZE

6" 3"

BOULDERS COBBLES

GRAVEL SAND

SILT OR CLAY CLAY

FINE

# ##3

SILT

OR

CLAY

0.0010.010.1110100 Grain Size, mm

Pe rc en t P as si ng

US IBWC Levee mm mm

Boring No.: MFN-1 mm mm

Sample Depth: 48 to 50

GRADATION CURVE

US STANDARD SIEVE SIZE

6" 3"

BOULDERS COBBLES

GRAVEL SAND

SILT OR CLAY CLAY

FINECOARSE FINE COARSE MEDIUM

SERIES NO. SAMPLE IDENTIFICATION GRADATION INFORMATION

152 76.2 19.1 4.75 0.42 0.002

PARTICLE SIZE IN MM

D10: 0.07 D30: 0.13 D50: 0.18 D60: 0.19 Cc: 2.71 Cu: 1.27

# ##3

SILT

OR

CLAY

0.0010.010.1110100 Grain Size, mm

Pe rc en t P as

US IBWC Levee mm mm

Boring No.: MFN-1 mm mm

Sample Depth: 98 to 100

GRADATION CURVE

Cc: 0.00 Cu: 0.00

D50: 3.50 D60: 6.30

D10: 0.00 D30: 0.22

SERIES NO. SAMPLE IDENTIFICATION GRADATION INFORMATION

152 76.2 19.1 4.75 0.42 0.002

PARTICLE SIZE IN MM

COARSE FINE COARSE MEDIUM

US STANDARD SIEVE SIZE

6" 3"

BOULDERS COBBLES

GRAVEL SAND

SILT OR CLAY CLAY

FINE

# ##3

SILT

OR

CLAY

0.0010.010.1110100 Grain Size, mm

Pe rc en t P as

US IBWC Levee mm mm

Boring No.: MFN-2 mm mm

Sample Depth: 43 to 45

GRADATION CURVE

US STANDARD SIEVE SIZE

6" 3"

BOULDERS COBBLES

GRAVEL SAND

SILT OR CLAY CLAY

FINECOARSE FINE COARSE MEDIUM

SERIES NO. SAMPLE IDENTIFICATION GRADATION INFORMATION

152 76.2 19.1 4.75 0.42 0.002

PARTICLE SIZE IN MM

D10: 0.00 D30: 0.00 D50: 0.00 D60: 0.08 Cc: 0.00 Cu: 0.00

# ##3

SILT

OR

CLAY

0.0010.010.1110100 Grain Size, mm

Pe rc en t P as g

1 of 10MFN-2, 4-8 ft.xls

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: See Remarks Sample No./ID: NA

Liquid Limit: NA Plastic Limit: NA Plasticity Index: NA Percent Passing No. 200: NA

Specimen/Stage Data Before Test After Consolidation & Shear Description Saturation/Consolidation Specimen/Stage No. 1 2 3 1 2 3 Specimen/Stage No. 1 2 3

Diameter (D),in.: 2.85 2.86 2.85 - - - Method Wet Mounting Method Height (H), in.: 5.61 5.71 5.69 - - - Cell Pressure, lbs/in2 70.1 79.3 89.4 Volume (Vo, Vf = Vo -Δ 3:V), cm 585.2 599.8 596.8 579.3 583.6 577.8 Back Pressure, lbs/in2 60.4 58.6 59.6 Moisture, {Wo, Wf} %: 23.9% 18.3% 19.6% 23.2% 22.2% 19.7% B-Parameter 0.96 0.97 0.99 Wet Soil Wt. {Mo, Mf}, ,gm: 1179.17 1214.90 1238.81 1190.96 1226.72 1245.85 Consolidation Pressure, lbs/in2 9.8 20.7 29.7 Wet Unit Weight, pcf: 125.7 126.40 129.5 127.0 127.63 130.3 Volume Change After (Δ 3V), cm 5.9 16.2 19 Dry Unit Weight, pcf: 101.4 106.9 108.3 103.1 104.5 108.8 Time for Consolidation, min. 1108 4013 4038 Specific Gravity (Assumed): 2.7 2.7 2.7 2.7 2.7 2.7 Failure Type: Bulge-Fractures Void Ratio, eo, ef: 0.63 0.61 0.55 0.62 0.57 0.50 Bulge-Fractures Degree of Saturation, So, Sf: 1.02 1.02 1.02 1.01 1.05 1.07 Bulge-Fractures

Shear Data Specimen/Stage

1 2 3 Strain Rate, %/hr 0.5 0.5 0.5 Axial Strain at Failure, % 11.67 11.45 11.37 Deviator Stress, lbs/in2 (Δσ) 18.80 34.78 50.19 Excess Pore Pressure, lbs/in2 (u) 5.26 10.33 14.22 A-Parameter, (u/Δσ) 0.28 0.30 0.28 Total Major Pincipal Stress, lbs/in2 (σ1 = σ3 + Δσ) 28.45 55.28 79.80 Total Minor Pincipal Stress, lbs/in2 (σ3) 9.64 20.50 29.61 Effectivel Major Pincipal Stress, lbs/in2 (⎯σ⎯1 = σ1 − u) 23.18 44.95 65.58 Effectivel Minor Pincipal Stress, lbs/in2 (⎯σ⎯3 = σ3 − u) 4.38 10.17 15.39

Remarks: 1st point 4-5 ft., 2nd point 5-6 ft., 3rd point, 6-7 ft.

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Boring Number: MFN-2 Depth, feet: See Remarks Sample No./ID:

Cohesion (C T ), ksf: 0.21 Friction Angle( φ T ), deg: 25.1 Cohesion (C d ), ksf: 0.25 Friction Angle( φ d ), deg: 35.4

Remarks: 1st point 4-5 ft., 2nd point 5-6 ft., 3rd point, 6-7 ft.

PLA

TE A

-11

0 10 20 30 40 50 60 70 80 90 100 Normal Stress,psi

Sh ea r S tr es s, p si

Specimen 1 - Total Stress Circle Specimen 1 - Effective Stress Circle Specimen 2 - Total Stress Circle Specimen 2 - Effective Stress Circle Specimen 3 - Total Stress Circle Specimen 3 - Effective Stress Circle Total Stress Envelope Effective Stress Envelope

MFN-2, 4-8 ft.xls 2 of 10

(n

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Boring Number: MFN-2 Depth, feet: See Remarks Sample No./ID:

Cohesion (C d ), ksf: 0.19 Friction Angle( φ d ), deg: 25.1

Remarks: 1st point 4-5 ft., 2nd point 5-6 ft., 3rd point, 6-7 ft.

0 10 20 30 40 50 60 p' = {Sig 1' + Sig 3'/2}, psi q'

{S ig

S ig

2, p si

Specimen 1 Specimen 2 Specimen 3

MFN-2, 4-8 ft.xls 3 of 10

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Boring Number: MFN-2 Depth, feet: See Remarks Sample No./ID:

Remarks: 1st point 4-5 ft., 2nd point 5-6 ft., 3rd point, 6-7 ft.

0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 Axial Strain, %

St re ss /P re ss ur e, p si

Delta Sigma of 1 Delta Sigma of 2 Delta Sigma of 3 Pore Pressure of 1 Pore Pressure of 2 Pore Pressure of 3

MFN-2, 4-8 ft.xls 4 of 10

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 4-5 feet Sample No./ID:

Specimen/Stage: Stage 1 gEffective Confinin Pressure, psi: 9.8 Failure Type: Bulge-Fractures Remarks:

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

Axial Strain (%)

St re ss o r P re ss ur e (p si σ 1 σ 3

⎯σ⎯1 ⎯σ⎯3

Cell Pressure Back Pressure

Δσ Pore Pressure

MFN-2, 4-8 ft.xls 5 of 10

MFN-2, 4-8 ft.xls 6 of 10

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 4-5 feet Sample No./ID:

Specimen/Stage: Stage 1 gEffective Confinin Pressure, psi: 9.8 Remarks:

Clock Elaspsed Burrette Volume Date Time Time, min. Readings cm3

4/19/2009 2:17:00 PM 0.0 24.5 0.0

4/19/2009 2:17:06 PM 0.1 23.7 0.8

4/19/2009 2:17:15 PM 0.3 23.6 0.9

4/19/2009 2:17:30 PM 0.5 23.5 1.0

4/19/2009 2:18:00 PM 1.0 23.4 1.1

4/19/2009 2:19:00 PM 2.0 23.2 1.3

4/19/2009 2:21:00 PM 4.0 23.0 1.5

4/19/2009 2:25:00 PM 8.0 22.7 1.8

4/19/2009 2:32:00 PM 15.0 22.4 2.1

4/19/2009 2:47:00 PM 30.0 21.7 2.8

4/19/2009 3:17:00 PM 60.0 21.1 3.4

4/19/2009 7:22:00 PM 305.0 19.0 5.5

4/20/2009 8:45:00 AM 1108.0 18.6 5.9

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

0.01 0.1 1 10 100 1000 10000 Elapsed Time, min.

C ha ng e in V ol um e, c m 3 .

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 5-6 feet Sample No./ID:

Specimen/Stage: Stage 2 gEffective Confinin Pressure, psi: 20.7 Failure Type: Bulge-Fractures

Remarks:

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

Axial Strain (%)

St re ss o r P re ss ur e (p si σ 1 σ 3 ⎯σ⎯1 ⎯σ⎯3 Cell Pressure Back Pressure

MFN-2, 4-8 ft.xls 7 of 10

MFN-2, 4-8 ft.xls 8 of 10

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 5-6 feet Sample No./ID:

Specimen/Stage: Stage 2 gEffective Confinin Pressure, psi: 20.7 Remarks:

Clock Elaspsed Burrette Volume Date Time Time, min. Readings Cm3

4/19/2009 2:22:00 PM 0.0 24.5 0.0

4/19/2009 2:22:06 PM 0.1 22.5 2.0

4/19/2009 2:22:15 PM 0.3 22.1 2.4

4/19/2009 2:22:30 PM 0.5 21.6 2.9

4/19/2009 2:23:00 PM 1.0 21.2 3.3

4/19/2009 2:24:00 PM 2.0 20.6 3.9

4/19/2009 2:26:00 PM 4.0 19.6 4.9

4/19/2009 2:30:00 PM 8.0 18.8 5.7

4/19/2009 2:37:00 PM 15.0 17.9 6.6

4/19/2009 2:52:00 PM 30.0 16.7 7.8

4/19/2009 3:22:00 PM 60.0 15.3 9.2

4/19/2009 7:22:00 PM 300.0 11.3 13.2

4/20/2009 7:00:00 AM 998.0 8.7 15.8

4/20/2009 3:30:00 PM 1508.0 8.6 15.9

4/22/2009 9:15:00 AM 4013.0 8.3 16.2

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

20.0

0.01 0.1 1 10 100 1000 10000 Elapsed Time, min.

C ha ng e in V ol um e, c

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 6-7 feet Sample No./ID:

Specimen/Stage: Stage 3 gEffective Confinin Pressure, psi: 29.7 Failure Type: Bulge-Fractures

Remarks:

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0 11.0 12.0 13.0 14.0 15.0

Axial Strain (%)

St re ss o r P re ss ur e (p si σ 1 σ 3

⎯σ⎯1 ⎯σ⎯3

Cell Pressure Back Pressure

MFN-2, 4-8 ft.xls 9 of 10

MFN-2, 4-8 ft.xls 10 of 10

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IBWC - Main Floodway e North Leve Classification: Fat Clay

Project Number: 322-95001 Borin Number: MFN-2 Depth, feet: 6-7 feet Sample No./ID:

Specimen/Stage: Stage 3 gEffective Confinin Pressure, psi: 75.0 Remarks:

Clock Elaspsed Burrette Volume Date Time Time, min. Readings cm3

4/19/2009 2:27:00 PM 0.0 24.5 0.0

4/19/2009 2:27:06 PM 0.1 22.2 2.3

4/19/2009 2:27:15 PM 0.3 21.9 2.6

4/19/2009 2:27:30 PM 0.5 21.7 2.8

4/19/2009 2:28:00 PM 1.0 21.5 3.0

4/19/2009 2:29:00 PM 2.0 21.1 3.4

4/19/2009 2:31:00 PM 4.0 20.8 3.7

4/19/2009 2:35:00 PM 8.0 20.5 4.0

4/19/2009 2:42:00 PM 15.0 20.0 4.5

4/19/2009 2:57:00 PM 30.0 19.2 5.3

4/19/2009 3:27:00 PM 60.0 17.8 6.7

4/19/2009 7:22:00 PM 295.0 12.8 11.7

4/20/2009 7:00:00 AM 993.0 7.7 16.8

4/20/2009 3:30:00 PM 1503.0 6.7 17.8

4/22/2009 9:45:00 AM 4038.0 5.5 19.0

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

16.00

18.00

20.00

0.01 0.1 1 10 100 1000 10000 Elapsed Time, min.

C ha ng e in V ol um e, c

1 of 10MFNI-5, 8-10, 13-15, 18-20

Consolidated Undrained Triaxial Test with Pore Pressure Measurements (ASTM D 4767)

Project Name: IDWC-Main Floodway South Classification: Sandy Clay, Brown

Project Number: 322-95001 Borin Number: MFS-5 Depth, feet: See Remarks Sample No./ID: NA

Liquid Limit: NA Plastic Limit: NA Plasticity Index: NA Percent Passing No. 200: NA

Specimen/Stage Data Before Test After Consolidation & Shear Description Saturation/Consolidation Specimen/Stage No. 1 2 3 1 2 3 Specimen/Stage No. 1 2 3

Diameter (D),in.: 2.84 2.86 2.84 - - - Method Wet Mounting Method Height (H), in.: 5.61 5.55 5.55 - - - Cell Pressure, lbs/in2 50.2 60.3 80.1 Volume (Vo, Vf = Vo -Δ 3:V), cm 583.2 585.5 574.9 568.9 563.0 547.8 Back Pressure, lbs/in2 40.1 40.1 40.3 Moisture, {Wo, Wf} %: 20.7% 21.7% 24.1% 24.7% 22.9% 23.7% B-Parameter 0.95 0.95 0.96 Wet Soil Wt. {Mo, Mf}, ,gm: 1177.10 1145.33 1150.27 1206.80 1171.65 1149.21 Consolidation Pressure, lbs/in2 10.1 20.1 39.8 Wet Unit Weight, pcf: 125.9 122.06 124.8 129.1 124.87 124.7 Volume Change After (Δ 3V), cm 14.3 22.5 27.1 Dry Unit Weight, pcf: 104.4 100.3 100.6 103.6 101.6 100.8 Time for Consolidation, min. 2830 2815 2825 Specific Gravity (Assumed): 2.7 2.7 2.7 2.7 2.7 2.7 Failure Type: Bulge-Fractures Void Ratio, eo, ef: 0.63 0.66 0.67 0.59 0.59 0.59 Bulge-Fractures Degree of Saturation, So, Sf: 0.89 0.89 0.89 1.14 1.04 1.08 Bulge-Fractures

Shear Data Specimen/Stage

1 2 3 Strain Rate, %/hr 0.5 0.5 0.5 Axial Strain at Failure, % 11.11 14.12 9.84 Deviator Stress, lbs/in2 (Δσ) 23.16 28.96 38.71 Excess Pore Pressure, lbs/in2 (u) 6.33 9.64 23.87 A-Parameter, (u/Δσ) 0.27 0.33 0.62 Total Major Pincipal Stress, lbs/in2 (σ1 = σ3 + Δσ) 33.23 49.03 78.43 Total Minor Pincipal Stress, lbs/in2 (σ3) 10.07 20.07 39.73 Effectivel Major Pincipal Stress, lbs/in2 (⎯σ⎯1 = σ1 − u) 26.89 39.39 54.57 Effectivel Minor Pincipal Stress, lbs/in2 (⎯σ⎯3 = σ3 − u) 3.73 10.43 15.86

Remarks: Speciment 1: MFS-5, 8-10 ft.; Specimen 2: MFS-5, 13-15 ft.; Specimen 3: MFS-5, 18-20 ft.

Project Name: IDWC-Main Floodway South Classification: Sandy Clay, Brown

Project Number: 322-95001 Boring Number: MFSI-5 Depth, feet: See Remarks Sample No./ID: 0

Cohesion (C T ), ksf: 1.14 Friction Angle( φ T ), deg: 11.3 Cohesion (C d ), ksf: 0.51 Friction Angle( φ d ), deg: 27.4

Remarks: Speciment 1: MFS-5, 8-10 ft.; Specimen 2: MFS-5, 13-15 ft.; Specimen 3: MFS-5, 18-20 ft.

0 20 40 60 80 100 Normal Stress,psi

Sh ea r S tr es s, p si

Specimen 1 - Total Stress Circle Specimen 1 - Effective Stress Circle Specimen 2 - Total Stress Circle Specimen 2 - Effective Stress Circle Specimen 3 - Total Stress Circle Specimen 3 - Effective Stress Circle Total Stress Envelope Effective Stress Envelope

MFNI-5, 8-10, 13-15, 18-20 2 of 10

VOLUME II, SECTION 1 - PAGE NO. 7

APPENDIX 1.2

North Levee - Section 1 (Sta. 255+00 to Sta. 302+50) Borings MFN 1-1 to MFN 1-5 Crown Width: 16 ft; Enlargement Side Slopes: 3H:1V Crown Elevation: 114 ft; Flood Elevation: 111 ft

Soil Properties Name: Levee (Undrained) Unit Weight: 125 pcf Cohesion: 1000 psf Name: Fat Clay (CH) (Undrained) Unit Weight: 125 pcf Cohesion: 2000 psf Name: Lean Clay (CL) (Undrained) Unit Weight: 125 pcf Cohesion: 1500 psf Name: Silty Sand (SM) Unit Weight: 120 pcf Cohesion: 0 psf Phi: 34 °

Levee

Fat Clay (CH)

Lean Clay (CL)

Silty Sand (SM)

Short Term Condition Method: Spencer Minimum Factor-of-Safety: 3.33 Center: (-53.225, 130.948) ft Radius: 64.162 ft

FIGURE 1.1Distance (ft) -150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

E le va tio n (ft

Crown Width: 16 ft; Enlargement Side Slopes: 3H:1V Crown Elevation: 114 ft; Flood Elevation: 111 ft

Soil Properties Name: Levee (Effective) Unit Weight: 125 pcf Cohesion: 250 psf Phi: 27 ° Name: Fat Clay (CH) (Effective) Unit Weight: 125 pcf Cohesion: 200 psf Phi: 20 ° Name: Lean Clay (CL) (Effective) Unit Weight: 125 pcf Cohesion: 150 psf Phi: 25 ° Name: Silty Sand (SM) Unit Weight: 120 pcf Cohesion: 0 psf Phi: 34 °

Levee

Fat Clay (CH)

Lean Clay (CL)

Silty Sand (SM)

Long Term Condition Method: Spencer Minimum Factor-of-Safety: 1.56 Center: (-53.247, 141.64) ft Radius: 57.343 ft

FIGURE 1.2

Distance (ft)

-150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

E le va tio n (ft

Crown Width: 16 ft; Enlargement Side Slopes: 3H:1V Crown Elevation: 114 ft; Flood Elevation: 111 ft

Soil Properties Name: Levee (Effective) Unit Weight: 125 pcf Cohesion: 250 psf Phi: 27 ° Name: Fat Clay (CH) (Effective) Unit Weight: 125 pcf Cohesion: 200 psf Phi: 20 ° Name: Lean Clay (CL) (Effective) Unit Weight: 125 pcf Cohesion: 150 psf Phi: 25 ° Name: Silty Sand (SM) Unit Weight: 120 pcf Cohesion: 0 psf Phi: 34 °

Levee

Fat Clay (CH)

Lean Clay (CL)

Silty Sand (SM)

Rapid Draw-Down Condition Method: Spencer Minimum Factor-of-Safety: 1.73 Center: (41.3, 130.038) ft Radius: 42.543 ft

FIGURE 1.3

Distance (ft)

-150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

E le va tio n (ft

Crown Width: 16 ft; Enlargement Side Slopes: 3H:1V Crown Elevation: 114 ft; Flood Elevation: 111 ft

Exit Gradient = 0.5

Soil Properties Name: Levee K-Sat: 1.18e-005 ft/hr Name: Fat Clay (CH) K-Sat: 1.18e-005 ft/hr Name: Lean Clay (CL) K-Sat: 1.18e-005 ft/hr Name: Silty Sand (SM) K-Sat: 0.0118 ft/hr

FIGURE 1.4

Levee

Fat Clay (CH)

Lean Clay (CL)

Silty Sand (SM)

Steady-State Seepage Analysis Contours of Hydraulic Gradient

.6 e-ft³ /h r

Distance (ft) -150 -140 -130 -120 -110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150

E le va tio n (ft

VOLUME II, SECTION 2 - PAGE NO. 1

SECTION 2.0: STA. 302+50.00 TO STA. 353+50.00 (MFN1- 6 TO MFN1-10)

analyses for the Main Floodway North levee extending between Sta. 302+50.00 and Sta.

353+50.00. The subsurface conditions in this area of the project site were explored with five (5) soil borings (i.e., MFN1-6 through MFN1-10).

2.1 CROSS-SECTIONAL INFORMATION

The revised cross-sectional drawings of the levee system were provided by S & B Infrastructure, LTD on May 6, 2009. The existing cross-sectional information, in conjunction with the proposed levee crown elevations was reviewed to identify the maximum height (most critical) for the proposed levee geometry and a design levee cross-section was selected. The cross-section at Sta. 338+97.05 was used for the analyses. Please note that the dimensions are rounded to the nearest foot for calculation purposes.

3. Flood Water Elevation: Three (3) feet below crown (freeboard)

4. Existing Levee Height: 22.5 feet

5. Maximum final Levee Height: 25 feet

6. Maximum Additional Fill to Raise the Levee: 2.5 feet

2.2 SUBSURFACE CONDITIONS

borings (i.e., Borings MFN1-6 through MFN1-10) drilled to depths between 50 feet and 100 feet below the existing ground surface.

Laboratory test data along with detailed descriptions of the soils found within this portion of the levee system can be found on the logs of Borings MFN1-6 through MFN1-10 include in Appendix 2.1 of this Chapter. Appendix 2.1 also contains portions of the laboratory test data including the results of the consolidated undrained triaxial tests with pore pressure measurements (CU test), consolidation tests and permeability tests.

Existing levee materials consisted predominantly of firm to hard lean clay and fat clay.

Native soils beneath the levee generally consist of firm to very stiff lean clay and sandy lean clay, soft to firm fat clay, and loose to very dense silty sand. The range of the laboratory test results is presented below in Table 2.1:

VOLUME II, SECTION 2 - PAGE NO. 2

Table 2.1: Summary of Laboratory Test Results (Borings MFN1-6 through MFN1-10)

Soil Type Moisture Content (%)

Atterberg Limits

Shear Strength (tsf)

Percent Passing No.

200 (%)

SPT – N

Values

(blows/ft)

Levee (CL, CH) 7 to 22 LL = 45 to 61

PI = 23 to 37 0.65 to 2.58 92 to 99 19 to 59

Lean Clay, Sandy Lean

Clay (CL) 18 to 39 LL = 28 to 42

PI = 8 to 24 0.25 to 1.5 56 to 91 -

Fat Clay (CH) 11 to 30 LL = 50 PI = 27 0.25 to 1.72 - -

Clayey Sand (SC), Silty

Sand (SM), Sand (SP)

14 to 31 - - 8 to 85 3 to 52

Notes: LL: Liquid Limit; PI: Plasticity Index

2.3 DESIGN SOIL STRENGTH PROFILE

The soil strength parameters selected for the design profile are based on: 1) the results of our field and laboratory test data on selected soil samples, 2) prudent engineering judgment based on experience with similar soils, and 3) published correlations.

The selection process for obtaining soil strength parameters used in the stability analyses for the 1) Short-Term Condition, 2) Long-Term Condition, and 3) Rapid Draw- Down Condition (upstream slope) are described below:

• As previously mentioned, average undrained strength of the soil as measured by the Unconfined Compression tests and Unconsolidated Undrained tests were used to analyze the slopes in “short-term” conditions. For a clay layer (at a given cross-sectional location), the strength test results obtained on the soils of the nearest boring locations were averaged to obtain the undrained shear strength parameters.

For a sand layer, the blow counts obtained from the field Standard Penetration Test (N-Values) were used to obtain the angle of internal friction. The values were were utilized. These parameters were obtained from the CU tests performed, as

VOLUME II, SECTION 2 - PAGE NO. 3

are presented below in Table 2.2:

Table 2.2 Design Soil Strength Parameters

Stratum

(Elev. Range, feet) Undrained (Short-Term)

Effective (Long-Term & Rapid Draw-down) Levee

(+112 to +88) Su = 1,000 psf c’ = 250 psf φ’= 27o

Fat Clay 1 (CH) (+88 to +77) Su = 1,500 psf c’ = 150 psf φ’= 23o

Silty Sand 1(SM) (+77 to 50) φ’ = 29o c’ = 0 psf φ’ = 29o

Fat Clay 2 (CH) (+50 to +35) Su = 2,000 psf c’ = 200 psf φ’= 20o

Lean Clay (CL) (+35 to +25) Su = 1,600 psf c’ = 160 psf φ’= 25o

Silty Sand 2 (SM) (Below +25) φ’ = 34o c’ = 0 psf φ’ = 34o

Notes: Su - Undrained Shear Strength, c’ - effective cohesion, φ’ - effective angle of internal friction

2.4 DISCUSSION OF RESULTS AND RECOMMENDATIONS

Using the soil strength parameters shown in Table 2.2, slope stability analyses were performed for the design (critical) cross-section previously mentioned in this section. The proposed side slopes of the levee enlargement at this location are 3H:1V with a maximum slope height of about 25 feet. The results of the stability analyses are shown graphically in Appendix 2.2.

• Based on the results of the slope stability analyses for the levee slopes, the minimum calculated factor-of-safety for the short-term condition is 2.42 (see Figure 2.1), thereby indicating stable slopes. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.3, as recommended in the USACE factor-of- safety is 1.52 (see Figure 2.2), thereby indicating stable slopes. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.5, as recommended in the USACE publication Slope Stability Manual (EM 1110-minimum calculated factor-of-safety is 1.72 (see Figure 2.3) and the levee slopes are considered to be stable. The computed factor-of-safety for this condition exceeds the minimum acceptable value of 1.3, as recommended in the USACE publication

VOLUME II, SECTION 2 - PAGE NO. 4

decrease in soil strength over time. A rapid draw-down condition in conjunction with soil weathering may result in sloughing of the riverside levee slope following a flood event.

These shallow failures should be regarded as a maintenance issue and it is recommended that they be repaired soon after they occur to maintain the integrity of the levee.

2.5 LEVEE SETTLEMENT ANALYSIS

Within this segment of the levee (i.e., between Sta. 302+50.00 and Sta. 353+50.00), the levee is planned to be raised by a maximum of approximately 2.5 feet. Based on our analyses, the long-term settlement induced by the proposed levee enlargement is estimated to be less than one (1) inch.

2.6 SEEPAGE ANALYSIS

A steady-state seepage analysis was performed in accordance with USACE EM 1110-2- 1901 using the finite-element computer program SEEP/W (see Figure 2.4). Hydraulic gradients were calculated for the design cross-section and compared to established criteria. Based on this analysis, the exit gradient at the landside toe was calculated to be approximately 0.47. The ratio of the critical gradient (the gradient at which piping can occur) to the calculated gradient results in a factor-of-safety against piping. Based on a critical gradient of 0.8, the resulting factor-of-safety exceeds the minimum value of 1.6, as recommended by the USACE. In addition, the steady-stage seepage rate for this section of levee is estimated to be less than 4 gallons per day, which is considered to be low. Therefore, mitigation measures for seepage control are not warranted. Results of the seepage analysis are presented on Figure 2.4.

2.7 CONSTRUCTION RECOMMENDATIONS

As previously mentioned, the levee will be raised by a maximum of about 2.5 feet in this section (Sta. 302+50.00 and Sta. 353+50.00). Borrow materials for levee construction shall be clays, sandy clays classified as CL, and fat clays (CH). Silts, sands and organic soils are unsuitable for levee construction. The borrow materials must be selected and placed in strict accordance with Section 4 of USACE Publication EM 1110-2-1913.

The borrow materials shall be placed in maximum lifts of 12 inches of loose material and shall be compacted to at least 95 percent of standard Proctor maximum dry density as determined by ASTM D 698 with the range of two (2) percentage (+1% to +3%) points of the optimum moisture content value. The first layer of fill shall be placed in a relatively uniform horizontal lift and be adequately keyed into the existing levee soils. Please refer to Volume 1 of this report for additional recommendations.

VOLUME II, SECTION 2 - PAGE NO. 5

2.8 CONCLUSIONS

Based on our analyses of this section (Sta. 302+50.00 and Sta. 353+50.00), the levee can be raised by a maximum of about two and one half (2½) feet with a side slope inclination of 3H:1V or flatter. The slope stability, seepage and settlement of the new levee system are acceptable and satisfy prudent and well-accepted USACE engineering criteria for the stability of levees.

VOLUME II, SECTION 2 - PAGE NO. 6

APPENDIX 2.1

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Very Stiff, Dark Brown, Moist

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Firm to Very Stiff, Brown, Moist

SILTY SAND (SM), Poorly Graded, Fine Grained, Loose to Dense, Brown, Wet

CH

CL

SM

10357

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-10

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/14/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 349+37.95

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 24

TYPE OF BORING: WET ROTARY

APPROXIMATE SURFACE ELEVATION: 107.63 feet

COORODINATE (X) OR EASTING: 1073811

COORDINATE (Y) OR NORTHING: 16578829

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Firm to Very Stiff, Dark Brown, Moist

Shear Strength = 1.23 tsf

APPROXIMATE BOTTOM OF LEVEE

FAT CLAY (CH), Soft to Firm, Brown, Moist

Shear Strength = 0.11 tsf

SILTY SAND (SM), Poorly Graded, Fine Grained, Medium Dense to Dense, Brown, Wet

CH

CH

SM

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-6

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/17/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 307+85.40

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 23

TYPE OF BORING: WET ROTARY

APPROXIMATE SURFACE ELEVATION: 108.83 feet

COORODINATE (X) OR EASTING: 1069946

COORDINATE (Y) OR NORTHING: 16577814

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Very Stiff, Dark Brown, Moist

Shear Strength = 2.58 tsf

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Very Soft to Stiff, Brown, Moist Shear Strength = 1.30 tsf

Very Soft at 25 Feet

Shear Strength = 0.93 tsf

SILTY SAND (SM), Poorly Graded, Medium Dense, Brown, Moist to Wet

FAT CLAY (CH), Very Stiff, Brown, Moist

CH

CL

SM

CH

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 100 FEET

LOG OF BORING MFN1-7

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/24/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 317+02.55

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 22

TYPE OF BORING: WET ROTARY

APPROXIMATE SURFACE ELEVATION: 108.48 feet

COORODINATE (X) OR EASTING: 1070730

COORDINATE (Y) OR NORTHING: 16578101

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

FAT CLAY (CH), Very Stiff, Brown, Moist

Shear Strength = 1.72 tsf

LEAN CLAY (CL), Firm to Very Stiff, Brown, Moist

Sandy and Firm at 70 Feet

SILTY SAND (SM), Poorly Graded, Fine Grained, Medium Dense to Dense, Brown, Wet

Medium Dense Below 80 Feet

Well Graded with Gravel Below 85 Feet

CL

SM

20 22

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 100 FEET

LOG OF BORING MFN1-7

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/24/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 317+02.55

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 22

TYPE OF BORING: WET ROTARY

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

52.5

55.0

57.5

60.0

62.5

65.0

67.5

70.0

72.5

75.0

77.5

80.0

82.5

85.0

87.5

90.0

92.5

95.0

97.5

100.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Very Stiff to Hard, Dark Brown, Moist

LEVEE MATERIAL: Lean Clay (CL), Firm, Dark Brown, Moist

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Very Stiff, Dark Brown, Moist Shear Strength = 1.46 tsf

CLAYEY SAND (SC), Poorly Graded, Fine Grained, Loose to Medium Dense, Brown, Moist

Silt layer at 35 feet

SAND WITH SILT (SP-SM), Poorly Graded, Fine Grained, Medium Dense, Brown, Wet

CH

CL

CL

SC

SP-SM

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-8

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/13/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 328+75.02

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 21.2

TYPE OF BORING: WET ROTARY

APPROXIMATE SURFACE ELEVATION: 108.35 feet

COORODINATE (X) OR EASTING: 1071970

COORDINATE (Y) OR NORTHING: 16578227

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

4'' to 6'' GRAVEL BASE LEVEE MATERIAL: Fat Clay (CH), Very Stiff, Dark Brown, Moist

Shear Strength = 1.88 tsf

Shear Strength = 0.79 tsf

APPROXIMATE BOTTOM OF LEVEE

LEAN CLAY (CL), Very Stiff, Brown, Moist

SAND WITH SILT (SP-SM), Poorly Graded, Fine Grained, Loose to Very Dense, Brown, Wet

CH

CL

SP-SM

PL PI

P

LA

S T

IC

IT

Y

IN

D E

X

P

A S

S

IN

G N o.

S

IE

V

E

SHEAR STRENGTH

(tons/square foot)

0.0 0.5 1.0 1.5 2.0 2.5

S O

IL

T

Y P

E

HP UC TV

DEPTH OF BORING: 50 FEET

LOG OF BORING MFN1-9

Hidalgo County

D E

P T

H , F

T

IBWC North Levee

LL

M O

IS

T

U R

E C

O N

T E

N T

LI

Q

U

ID

LI

M

IT

P

LA

S T

IC

LI

M

IT

N -B

LO

W

S /F

T

S A

M P

LE

S

U N

IT

W

E

IG

H T

(p cf

U S

C S

S Y

M B

O L

UU

PSI Project No.: 322-95001

SOIL DESCRIPTION

DATE DRILLED: 4/14/09

NOTES:

Geotechnical Consulting Services 2020 North Loop 499, Suite 302 Harlingen, Texas 76548

STATION NO.: 335+97.05

INITIAL GROUND WATER (FT) Could not be determined due to drilling fluid

GROUND WATER

FINAL GROUND WATER (FT): 23

TYPE OF BORING: WET ROTARY

APPROXIMATE SURFACE ELEVATION: 108.13 feet

COORODINATE (X) OR EASTING: 1072923

COORDINATE (Y) OR NORTHING: 16578318

B L_

A U

S T

IN

G

IN

T S

T D

U S

L A

B .G

D T

/1 0/

:4

P

U S

I B

W C

L E

V E

E \0

N

O R

T H

L O

G S

\F

IN

A L

LO

G

S \M

F N

-1

0\ M

F N

-1

R

E V

2.

G

P J

2.5

5.0

7.5

10.0

12.5

15.0

17.5

20.0

22.5

25.0

27.5

30.0

32.5

35.0

37.5

40.0

42.5

45.0

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

0 500 1,000 1,500 2,000 2,500 3,000 3,500 4,000

CH

CL

SM

MFN1-10

CH

CH

SM

MFN1-6

CH

CL

SM

CH

CL

SM

MFN1-7

CH

CL

CL

SC

SP

SM

MFN1-8

CH

CL

SP

SM

MFN1-9

E le va tio n

1073811 1069946 1070730 1071970 1072923

107.6 108.8 108.5 108.4 108.1

50.0 50.0

100.0 50.0 50.0

Varying soil deposits, including fill materials may exist between the sampling…