Final Report - NFW2 NFE2.pdf

iii

Executive Summary

The existing subsurface conditions of the 2009 USIBWC Rio Grande Flood Control System Projects - North Floodway West & East Levees (Segments NFW2 and NFE2) were investigated and analyzed in this Final Geotechnical Engineering Report. The limits of Segment NFW2 are from FM 491 to FM 1425 - Sta. 456+00 to 557+75 & 0+99 to 528+00. The limits of Segment NFE2 are from FM 491 to FM 1425 - Sta. 307+00 to 923+50. Segment NFW2 was originally slated to be investigated by 127 exploratory borings (BH-01 – BH-127) and Segment NFE2 by 123 exploratory borings (BH-01 – BH-123) drilled on top of the existing levee to a minimum depth of approximately two times the maximum proposed levee height; typically 60 feet below the existing top of levee. In addition approximately every fourth boring was to be advanced to a depth of 120’ below the existing top of levee to perform a detailed underseepage analysis.

During the course of our field exploration, we began to notice areas of consistency between adjacent borings. Through due diligence, with respect to cost effectiveness, we reevaluated our strategic plan and eliminated borings in these areas, providing larger spacing between borings.

This reevaluation resulted in a reduction of 57 borings along Segment NFW2 and 51 borings along Segment NFE2. All exploratory borings were drilled along the approximate centerline of the existing levee at the time of our study. Final borings were drilled at the approximate locations shown on the Boring Location Maps located in Appendix A.

Laboratory tests were performed on selected specimens obtained from the exploratory borings to evaluate the engineering characteristics of the various soil strata encountered during the field exploration activities. The soil profile within the limits of the North Floodway Levee (NFW2 & NFE2) can be generally characterized as a top layer of low to moderately plastic sandy/silty clay “CL/CH” (identified as the existing levee embankment) followed by a strata of lean to fat clays “CL to CH” with an underlying layer of hard clay “CL/CH” and mostly stiff clayey/silty sands and poorly graded sands “SC”, SM” and “SP”. All areas of the existing levee within these segments consisted of suitable material which can be left in place. A summary of the generalized soil profiles utilized in our analysis can be found in Appendix A.

We performed a detailed engineering analysis to assess the condition of the existing levee and underlying soils within this project. Our main focus was to quantify the engineering properties of the in-situ soils and their ability to withstand the additional loads imposed by the proposed embankment in areas of deficiency. The scope of this analysis is explained in detail in the body of this report.

The calculated global stability factors of safety are higher than the minimum factors of safety required by the USACE Manual EM 1110-2-1902 ‘Slope Stability’. Levee slopes were analyzed utilizing station specific existing and proposed cross-sections provided to us by S&B Infrastructure. These cross-sections generally reflected a 3.0:1.0 (horizontal:vertical) slope and a 16 ft access road top width (minimum traffic loading was incorporated into analysis).

Analysis and summary of results can be found in Appendix B.

A settlement analysis was performed, based on consolidation tests performed on samples retrieved from the field operations of the underlying native soils. Using methods and guidelines in the USACE Manual EM 1110-1-1904 ‘Settlement Analysis’, we estimated a total anticipated settlement 1.5 inches in Segment NFW2 and 2.0 inches for Segment NFE2 iv in the areas of anticipated levee raise. These values incorporate a 1% consolidation of the newly placed fill material (assuming density control measures are followed during construction).

Analysis is described in further detail in the body of the report and consolidation reports can be found in Appendix G.

The ultimate bearing capacity of the underlying soils were established and provided in this report to assist in the design of the proposed improvements. The factors of safety for these segments proved to be in compliance to the USACE guidelines required factor of safety of 2.0.

Analysis and computed factors of safety can be found in Appendix D.

We conducted a detailed through/underseepage analysis that adheres to both the USIBWC and USACE requirements along this stretch. The soil from the deeper borings was classified and “k” values for permeability were assigned to each of the varying strata. This allowed us to conduct a very detailed seepage analysis to ensure that Seepage Remediation Techniques were only specified in areas that truly warrant their implementation. The seepage analysis concluded that no seepage remediation techniques were needed for this stretch of levee. The analysis and findings can be found in detail in Appendix C.

It is our understanding that the subject project considers raising the existing levee a maximum of approximately 3.0 feet above the existing top of levee in both Segments NFW2 & NFE2 (including caliche for access road). Within both of these segments, there are areas of no-raise construction that will simply widen the levee crown to include a 16’ wide access road and re-graded to the recommended slopes.

For recommendations with regard to construction means and methods and/or new embankment specifications refer to the section of this report titled, “General Considerations During Construction”. This area provides the designer recommendations as it relates to Site Drainage, Site Preparation, Embankment Fill Placement Recommendations, and Embankment Construction Benching Recommendations.

The geotechnical engineer certifies that existing levee reaches, where no alterations are proposed, meet the requirements of the Federal Emergency Management Administration (FEMA) found in 44 CFR Section 65.10 (Code of Federal Regulations, Title 44 – Emergency Management Administration, Section 65.10 – Mapping of Areas Protected by Levee Systems). In alteration areas of the existing levees, the construction contractor must adhere to the construction methodology presented in this report for levee certification.

This summary is only intended to provide a brief overview of the findings and recommendations.

The following report discusses the results of this study in greater detail.

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INTRODUCTION............................................................................................... - 1 - GENERAL PROJECT OVERVIEW ............................................................... - 1 -

History & General Project Information .............................................................................- 1 - Project Description ...............................................................................................................- 2 - Proposed Improvements (North Floodway Levee – NFW2 & NFE2) .............................- 2 - Scope and Limitations of Investigation...............................................................................- 3 -

EXISTING LEVEE SURFACE & SUB-SURFACE CONDITIONS............ - 4 -

Site Location / Description ...................................................................................................- 4 - Previous Geotechnical Studies .............................................................................................- 4 - Subsurface Stratigraphy ......................................................................................................- 6 - Rainfall...................................................................................................................................- 6 -

LEVEE GEOTECHNICAL INVESTIGATION............................................. - 8 - Soil Borings and Laboratory Tests......................................................................................- 8 -

LABORATORY INDEX TESTING ................................................................. - 9 - Moisture Content ..................................................................................................................- 9 - Plasticity Index ....................................................................................................................- 10 - Minus 200 / Sieve Analysis / Hydrometer .........................................................................- 10 - Summary of Index Testing.................................................................................................- 11 -

LABORATORY STRENGTH & COMPRESSIBILITY TESTING .......... - 11 -

Unconfined Compression Test ...........................................................................................- 11 - Consolidation Test ..............................................................................................................- 12 -

SLOPE STABILITY ANALYSIS ................................................................... - 12 - Minimum Factors of Safety for Overall Stability Analysis..............................................- 16 - Soil Design Parameters.......................................................................................................- 16 - Levee Reaches Analyzed.....................................................................................................- 16 -

SETTLEMENT ANALYSIS............................................................................ - 19 - SEEPAGE ANALYSIS..................................................................................... - 20 - BEARING CAPACITY ANALYSIS .............................................................. - 21 -

GENERAL CONSIDERATIONS DURING CONSTRUCTION ................ - 23 -

Site Drainage Recommendations.......................................................................................- 23 - Site Preparation Recommendations..................................................................................- 23 - Embankment Fill Placement Recommendations .............................................................- 24 - Embankment Construction Benching Recommendations ..............................................- 24 -

REFERENCES.................................................................................................. - 25 -

APPENDIX A – BORING LOGS/LOCATION MAPS/PROFILES.................A

APPENDIX B – SLOPE STABILITY ANALYSIS.............................................B APPENDIX C – SEEPAGE ANALYSIS..............................................................C

APPENDIX D – BEARING CAPACITY ANALYSIS........................................D

APPENDIX E – GRADATIONS/HYDROMETERS..........................................E

APPENDIX F – UNCONFINED COMPRESSION TESTS............................... F

APPENDIX G – CONSOLIDATION REPORTS .............................................. G

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INTRODUCTION

L&G Engineering Laboratory, L.L.C. was contracted by S&B Infrastructure, Ltd. to perform a subsurface geotechnical investigation and engineering analysis on the section of the Rio Grande Flood Control System identified in Figure 1 of this report. This report covers the North Floodway West & East Levee segments (NFW2 & NFE2) of the rehabilitation and improvements project that extends from FM 491 to FM 1425 (Refer to Appendix A for a detailed location map). Contained in this report is a general project overview which includes; the techniques and testing procedures used to perform the subsurface exploration and testing, engineering analysis consisting of settlement, through/underseepage, slope stability, bearing capacity, and soil strength parameters derived from extensive laboratory testing.

GENERAL PROJECT OVERVIEW

History & General Project Information

In 1932 an agreement was reached between the United States and Mexico to develop a coordinated plan for an international project to protect the Lower Rio Grande Valley against flooding from the Rio Grande. This agreement, which later resulted in the Lower Rio Grande Flood Control Project (LRGFCP), was developed by the International Boundary and Water Commission (IBWC). The LRGFCP was designed to provide general flood protection of urban, suburban, and highly developed irrigated farm lands in the Rio Grande delta and is jointly operated by the USIBWC and MxIBWC (CILA). The LRGFCP facilities in the United States are located in Hidalgo, Cameron, and Willacy Counties, Texas, with the river levee beginning near the Town of Peñitas at the head of the delta, about 180 river miles from the Gulf of Mexico.

The United States interior floodway system is flanked by 168 miles of levees covering the natural channel of the Arroyo Colorado, and 102 miles of levees along the Rio Grande

(USIBWC 1980).

The design flood for the LRGFCP is based on a peak flow of 250,000 cubic feet per second (cfs) at Rio Grande City, which attenuates to 235,000 cfs at Peñitas. During the design flood, Anzalduas Diversion Dam and Retamal Diversion Dam would each allow for the flow to be diverted equally (105,000 cfs each) into the United States and Mexico, respectively. The Anzalduas Dam and Banker Weir divert floodwaters from the Rio Grande River into the U.S.

interior floodway system, located in Hidalgo, Cameron, and Willacy Counties. This interior system allows for the passage of 105,000 cfs in the Main Floodway and divides the flow to 84,000 cfs in the North Floodway, and 21,000 cfs in the Arroyo Colorado.

The Main Floodway Levee is approximately 43 levee miles long. The levee ROW runs primarily through agricultural areas, except in the upper and lower reaches where the levee runs through the Cites of McAllen, Weslaco, and Mercedes. The Main Floodway flows into Llano Grande Lake, a shallow depression located southwest of the City of Mercedes in southeast Hidalgo County, and disperses at a divider dike into the North Floodway and the Arroyo Colorado.

The North Floodway is approximately 46 levee miles long, extending from near the Town of Mercedes to the Laguna Madre northwest of Arroyo City. The levee ROW also runs primarily through agricultural areas, except in the upper reaches near the Main Floodway divider dike where the levee runs through the Cities of Weslaco and Mercedes. The North Floodway was

- 2 -constructed by the USIBWC in 1942 as part of the Lower Rio Grande Flood Control Project.

The North Floodway separates from the Llano Grande Lake at its northern end. The North Floodway drains the vast majority of Willacy County, a significant portion of northern and eastern Hidalgo County, and a small portion of northwestern Cameron County. The North Floodway empties into the Laguna Madre north of the dredged Arroyo Colorado mouth. The North Floodway has a high channel bottom and therefore does not receive any flow from Llano Grande except during flood conditions. The flood control features at this site are used to divert a significant portion of flood waters conveyed by the Main floodway to the North Floodway during flood events. (USIBWC 2007)

The existing levee system contains both new and old levees (pre and post Hurricane Beulah 1967). Older levees have since been upgraded and raised to meet the needs of IBWC and FEMA flood control requirements as a function of today’s rapid urban growth. In general, IBWC levees consist of 10 to 15 foot high earthen embankments (with regard to the surrounding ground surface) with typical 3.0:1.0 (horizontal : vertical) vegetated side slopes and 10 to 15 foot wide crests (mostly utilized as access roads for inspection). Most recently in 2007 and 2008, Hidalgo County in coordination with the USIBWC, Department of Homeland Security (DHS) and various local agencies began the DHS Flood Protection Levee Improvements Project which introduced the combination of a proposed levee raising with a vertical concrete flood protection structure in various areas of the LRGFCP along the Rio Grande river. The purpose of these improvements was to provide both adequate protection against a 100 year flood event and tactical support for our southern border protection initiative.

Project Description

The proposed 2009 USIBWC Rio Grande Flood Control System Projects has commenced to provide adequate safety and protection against a 100 year flood event and the loadings that an event of that magnitude would impose on the existing interior levee system of the Lower Rio Grande Flood Control Project. The improvements proposed for the existing levee include raising the top of levee elevation to appropriate heights designed by the USIBWC, detailed engineering analysis to evaluate the adequacy of existing levee material and possible seepage issues, evaluate the existing levee and proposed levee configurations for compliance with USACE requirements for levee certification, and using fill material to increase the top crown width of the levee embankment to accommodate a 16 ft. access road.

Proposed Improvements (North Floodway Levee – NFW2 & NFE2)

The project site NFW2 along the North Floodway West Levee Bank begins at FM 491 (Station 456+00), and concludes at FM 1425 (Station 528+00). The stationing on this project is a bit deceiving due to the fact that a station equation was utilized by S&B Infrastructure in an attempt to mirror the USIBWC existing stationing numbers. The actual stationing does start at station 456+00 and concludes at station 557+75; an equation is then used to convert the ending point back to station 0+99 through station 528+00. At the time this report was written, the scope of the proposed improvements included raising the existing top of levee elevations in areas not meeting the height requirements designed by USIBWC, widening the top of levee crown to 16 feet and placing an all-weather surface (caliche/gravel roadbed) to allow for an access road atop the levee. In addition, proposed levee slopes both landside and riverside (floodway side) were to be graded to 3.0:1.0 slopes recommended and 2.5:1.0 slopes maximum in areas of fill (only tie-

- 3 -ins to the existing slope required in areas flatter than 3.0:1.0). The areas of this segment which require levee raising were provided to us by S&B Infrastructure via cross-sections identifying existing and proposed levee heights. A detailed breakdown of the critical cross-sections in this segment used in our geotechnical analysis can be found on the “Typical Section Summary” sheet in Appendix A. All station numbers are references from a centerline file provided by S&B Infrastructure, Ltd.

The project site NFE2 along the North Floodway East Levee Bank begins FM 491 (Station 307+00), and concludes at FM 1425 (Station 923+50). At the time this report was written, the scope of the proposed improvements mirrored those identified in the previous paragraph for NFW2. A detailed breakdown of the critical cross-sections in this segment used in our geotechnical analysis can be found on the “Typical Section Summary” sheet in Appendix A. All station numbers are references from a centerline file provided by S&B Infrastructure, Ltd.

Scope and Limitations of Investigation

This report has been prepared in general accordance with requirements from both the USACE and FEMA. No specific warranty program or other standards, except acceptable industry standards, were followed during the course of this investigation. This report is intended for use by S&B Infrastructure, Ltd. and their representatives. This report may not contain sufficient information for purposes of other parties or agencies for uses in determining construction means and methods.

The stratigraphies shown on the boring logs (included in Appendix A) represent the conditions at the boring locations. These stratifications represent approximate boundaries between subsurface materials; their actual transition may be gradual. The purpose of this study is to identify and evaluate the existing soil composition and strength parameters of the current levee and underlying strata, and analyze proposed levee reconstruction and rehabilitation cross-sections for stability, settlement, seepage, and their ability to resist applied loads as a composite section. It should be noted that the borings were drilled within the limits of the proposed levee improvements as approved by S&B Infrastructure, Ltd. A Location Map of these borings can be found in Appendix A of this report. S&B Infrastructure, Ltd. also provided survey and tie down of the exact location of each boring. The location of each boring, along with the top of hole elevation and station/offset with respect to the centerline provided to us, is located on every boring in Appendix A. Boring depths are based on a minimum two times the maximum proposed levee height from the toe elevation of the levee.

The benchmarks for this study are to:

1. explore the existing subsurface conditions at the site and create a generalized soil profile that will be used for engineering analysis

2. evaluate the relevant engineering properties of the samples collected and create boring logs for representation of in-situ soils

3. calculate strength parameters for the existing levee soil and underlying strata to be used in structural evaluation

4. provide minimum factors of safety for overall stability and bearing capacity

5. provide a detailed seepage analysis

6. highlight potential constructability issues and state general considerations for the construction process

7. provide a settlement analysis, with maximum settlement for this stretch of levee

The scope of this geotechnical engineering study does not include an environmental assessment of the air, soil, rock, or water conditions on or adjacent to the existing levee system. No environmental options are presented in this report. No study was performed on any hazardous materials, or the effect that construction may have on the existing ecosystems at or nearby the proposed construction. If environmental assessments are needed to begin construction, please contact our office for further assistance.

EXISTING LEVEE SURFACE & SUB-SURFACE CONDITIONS

Site Location / Description

The North Floodway West & East Levees (NFW2 & NFE2) are located in the North/Eastern most quadrant of Hidalgo County and run along the North Floodway portion of the Lower Rio Grande Floodway System. Figure 1 illustrates the general location of the geotechnical investigation beginning from FM 491 and ending at FM 1425. Proposed construction for this area consists of raising the top of levee elevation in deficient areas and providing an all-weather levee access road. Typical 3.0:1.0 embankment slopes are being utilized throughout most of the re-design. Refer to Appendix A for a detailed break-down of the typical sections being used in our analysis.

Figure 1: General Location Map

Previous Geotechnical Studies

Through research and coordination with S&B Infrastructure, Ltd., we were able to utilize two existing geotechnical studies previously conducted in the area. The first was United States Army Corps of Engineers (USACE) Engineer Research and Development Center (ERDC) Condition Assessment of the U.S. International Boundary and Water Commission, Lower Rio Grande

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Valley Levees, South Texas (ERDC TR-03-4) dated October 2003. The scope of this document entailed assessing the condition of the levees to detect, identify and map potentially unstable levee reaches that require repair, replacement or remedial measures using a combination of airborne and surface geophysics, geologic studies, ground truth investigations and geographic information systems. In order to properly and justly assess the levees the ERDC and USIBWC devised a ten-point criteria system. The criteria and average results for the reaches were as follows:

NFW2 NFE2

Performance History under Flood Stage 4/4 4/4 Construction History 4/4 4/4 Visual Inspection 3.5/4 3.5/4 Material Type 2.5/4 2.5/4 Topographic Irregularity 2.5/4 2.5/4 Slope Stability 3.5/4 3.5/4 Man-Made Intrusions 3/4 2.5/4 Geology 3.5/4 3/4 Proximity to Borrow Areas 3.5/4 3.5/4 Anomalies 3/4 3/4

Overall 8.8 8.6

The overall values showed these reaches to be “Acceptable” with reference to the criteria listed above. Lower scores were exhibited in the areas of Material Type, Topographic Irregularity, Geology and Anomalies. These lower scores signified a more mixed soil composition in the existing levees of clays, silts and sands with underlying shallow sands through much of the reaches which could prove problematic with regard to underseepage. The general composition of the levee as stated here was somewhat contradictory to the findings of the other geotechnical study as well as our findings based on physical geotechnical explorations. See the “Subsurface Stratigraphy” section of this report for further information.

The other geotechnical study provided by S&B Infrastructure, Ltd., was the Technical Memorandum for Geotechnical Explorations of Levee System within the Lower Rio Grande Flood Control Project (Interior Floodway Levees) dated December 2007. This study serves as a Phase I preliminary exploration study of the Interior Levees (Main and North Floodway) conducted by S&B Infrastructure, Ltd. for the USIBWC. The scope of the study was to better define the geology of the area, model the soil types present and develop general ideas of soil strengths within and directly below the existing levee for the purposes of future rehabilitation (USACE EM 1110-2-1913). In this study exploratory borings were drilled at an average spacing of 500 linear feet to depths of approximately 5 feet below the average ground surface (12 to 25 feet below existing top of levee grades). Borings were taken only in locations USIBWC had previously called out as deficient with respect to safe containment of LRGFCP design flood flows (100 year flood flow). There were two sections, spanning approximately 2.1 miles and 2.8 miles, of Segment NFW2 investigated in the study as illustrated on the location maps in Appendix A. A similar section of NFE2, approximately 2.1 miles long was also examined across from NFW2. Borings in these areas showed predominantly moderate to highly plastic fat and lean clays with some areas of clayey sands and silts. Shear strengths for the existing levee soils based on hand penetrometer and unconfined compression tests were generally high averaging

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3,000 to 4,000 pounds per square foot. In general, the results from this study were consistent with the findings of our geotechnical analysis. See the “Subsurface Stratigraphy” section of this report for further information.

Subsurface Stratigraphy

On the basis of our soil borings, there are several generalized strata that possess similar physical and engineering characteristics at the boring locations. The soil profile within the limits of the North Floodway Levee (NFW2 & NFE2) can be generally characterized as a top layer of low to moderately plastic sandy/silty clay “CL/CH” (identified as the existing levee embankment) followed by a strata of lean to fat clays “CL to CH” with an underlying layer of hard clay “CL/CH” and mostly stiff clayey/silty sands and poorly graded sands “SC”, SM” and “SP”. The lines designating the interfaces between strata on the boring logs represent approximate boundaries. Transitions between strata may be gradual. Refer to Appendix A for a graphical representation of the subsurface profile.

Rainfall

The annual average precipitation for Hidalgo County is approximately 23.0 inches. Of this rainfall, 14 inches, or approximately 60 percent of annual rainfall occurs during the months of April thru September. According to the United States Department of Agriculture, Soil Survey of Hidalgo County, our geotechnical field investigation performed in April/May of 2009 was conducted during a relatively moderate to dry climatic period. According to the National Weather Service no uncommonly extreme amounts of rainfall occurred prior to or during our sub-surface exploration.

Waterstrike

Both dry auger and mud rotary drilling techniques were used to complete the soil borings.

During the drilling operations, a waterstrike was encountered in the majority of the borings. It should be noted that fluctuations in water levels are influenced by variations in rainfall and surface water run-off from season to season. The construction process itself may also cause variations in the water level. If the subsurface water elevation is critical to the construction process the contractor should check the subsurface water conditions just prior to construction excavation activities or contract L&G Engineering Laboratory to install and monitor piezometer wells for water level evaluation. Subsurface water and cave-in depths are based on measurements referenced from the top of existing levee elevation at the time of exploration.

Table 1 shows the waterstrike elevation with respect to top of hole elevation at each boring in tabular form for Segment NFW2 & NFE2.

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Segment NFW2

Boring No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

1 Hole Omitted 32 32.00 63 Hole Omitted 95 24.00

2 25.00 33 &

34 Hole Omitted 64 31.00 96 19.00

3 28.00 35 23.50 65 31.00 97 29.00

4 35.00 36 22.50 66 ~ 69 Hole Omitted 98 18.00

5 Hole Omitted 37 Hole Omitted 70 23.00 99 24.00

6 27.00 38 25.00 71 Hole Omitted 100 20.00

7 Hole Omitted 39 Hole Omitted 72 27.00 101 22.00

8 27.00 40 27.50 73 Hole Omitted 102 N/A

9 Hole Omitted 41 Hole Omitted 74 28.00 103 Hole Omitted

10 30.00 42 20.00 75 Hole Omitted 104 27.00

11 Hole Omitted 43 Hole Omitted 76 32.00 105 22.00

12 25.00 44 21.00 77 & 78 Hole Omitted 106 32.00

13 & 14 Hole Omitted 45 22.00 79 21.00 107 25.00

15 27.50 46 &

47 Hole Omitted 80 Hole Omitted 108 Hole Omitted

16 27.00 48 19.50 81 20.00 109 27.00

17 Hole Omitted 49 Hole Omitted 82 32.00 110 & 111 Hole Omitted

18 28.00 50 20.00 83 25.00 112 27.00

19 Hole Omitted 51 Hole Omitted 84 19.00 113 21.00

20 28.00 52 28.00 85 22.00 114 ~ 116 Hole Omitted

21 Hole Omitted 53 &

54 Hole Omitted 86 22.50 117 21.50

22 22.00 55 30.00 87 20.00 118 & 119 Hole Omitted

23 & 24 Hole Omitted 56 28.00 88 24.00 120 23.00

25 23.00 57 Hole Omitted 89 Hole Omitted 121 ~ 123 Hole Omitted

26 & 27 Hole Omitted 58 35.00 90 35.00 124 28.00

28 30.00 59 Hole Omitted 91 20.00 125 & 126 Hole Omitted

29 Hole Omitted 60 20.50 92 18.00 127 25.00

30 19.00 61 Hole Omitted 93 31.50

31 Hole Omitted 62 18.00 94 31.00

Table 1: Water Strike Elevation Summary

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Segment NFE2

Boring No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

Boring

No.

Water Strike Depth from Top of Hole

(ft.)

1 21.00 32 Hole Omitted 64 Hole Omitted 94 31.00 2 20.00 33 19.00 65 32.00 95 Hole Omitted

3 & 4 Hole Omitted 34 Hole Omitted 66 12.00 96 17.00 5 23.00 35 17.00 67 15.00 97 25.00 6 Hole Omitted 36 Hole Omitted 68 Hole Omitted 98 Hole Omitted 7 23.00 37 28.00 69 19.00 99 12.00 8 23.00 38 19.00 70 Hole Omitted 100 Hole Omitted 9 24.00 39 & 40 Hole Omitted 71 7.00 101 24.50

10 Hole Omitted 41 19.00 72 Hole Omitted 102 38.00 11 34.00 42 Hole Omitted 73 20.00 103 & 104 Hole Omitted 12 16.00 43 19.00 74 & 75 Hole Omitted 105 N/A 13 26.00 44 Hole Omitted 76 18.00 106 15.00 14 Hole Omitted 45 19.00 77 30.00 107 19.00 15 19.00 46 & 47 Hole Omitted 78 Hole Omitted 108 16.00 16 17.00 48 21.00 79 20.00 109 Hole Omitted 17 Hole Omitted 49 18.00 80 Hole Omitted 110 18.00 18 20.00 50 & 51 Hole Omitted 81 20.00 111 & 112 Hole Omitted

19 & 20 Hole Omitted 52 17.00 82 Hole Omitted 113 23.00 21 19.00 53 20.00 83 21.00 114 Hole Omitted 22 Hole Omitted 54 Hole Omitted 84 Hole Omitted 115 28.00 23 12.00 55 30.00 85 21.00 116 16.00 24 Hole Omitted 56 Hole Omitted 86 20.00 117 28.00 25 22.00 57 15.00 87 14.00 118 19.00

26 & 27 Hole Omitted 58 16.00 88 Hole Omitted 119 20.00 28 20.00 59 & 60 Hole Omitted 89 N/A 120 20.00 29 14.00 61 18.00 90 16.00 121 25.00 30 Hole Omitted 62 Hole Omitted 91 & 92 Hole Omitted 122 32.00 31 20.00 63 20.00 93 N/A 123 28.00

Table 1: Water Strike Elevation Summary

LEVEE GEOTECHNICAL INVESTIGATION

Soil Borings and Laboratory Tests

Subsurface conditions at the site were slated to be evaluated by one hundred and twenty seven

(127) and one hundred and twenty three (123) exploratory borings for Segments NFW2 and NFE2 respectively. The borings were advanced to 60 ft below the top of levee, and every fourth boring was advanced to 120 ft below the top of levee. During the course of our field exploration, we began to notice areas of consistency between adjacent borings. Through our internal due diligence process, we reevaluated our strategic plan and eliminated borings in these areas, providing larger spacing between borings. This reevaluation resulted in a reduction of fifty-seven (57) borings along Segment NFW2 and fifty-one (51) borings along Segment NFE2. All borings were drilled at the approximate locations shown on the Boring Location Maps located in Appendix A of this report. S&B Infrastructure, Ltd. provided survey and tie downs of the

- 9 -exact locations of the completed borings. In addition S&B Infrastructure, Ltd. provided Technical Memorandums and Location Maps for previously conducted geotechnical explorations in the area (as a result in these areas the existing levee was only sampled and tested every fourth hole for verification of existing soil conditions). All borings were drilled and logged by representatives of L&G Engineering Laboratory and our sub-contractors. All laboratory testing was performed by L&G Engineering Laboratory. The soil borings were drilled in general accordance with American Society of Testing Materials Procedure D 420 using a truck mounted drilling rig with dry auger and wet rotary techniques.

As part of the drilling procedures, Standard Penetration Tests (SPT) were performed at five foot intervals for use in determination of soil strength parameters. SPT tests were executed in compliance with American Society of Testing Materials procedures (ASTM D1586) and results for SPT are reported as blows per foot on the boring logs and on the test summary tables. A 140 pound hammer was used to drive the split barrel sampler through three six inch increments. The first six inch increment is referred to as the seating drive. The number of blows required to drive the sampler through the second and third increments is recorded as the SPT result. Where dense or hard material was encountered the SPT was terminated after one of the following occurrences:

a total of 50 blows was applied during any one of the 6 inch increments a total of 100 blows was applied no advancement of the sampler was observed during the execution of 10 consecutive blows

2,122 (1,087 ~ NFW2 & 1,035 ~ NFE2) split barrel samples and 397 (116 ~ NFW2 & 281 ~ NFE2) thin walled Shelby tube samples were collected during the drilling operations in general compliance with American Society of Testing Materials procedures (ASTM D3550). The Shelby tube samples were used for laboratory testing of both soil consolidation and unconfined compressive strength testing. Shelby tube samples were collected when cohesive clays were encountered, or when samples could successfully be extracted for testing.

In the laboratory, each sample was evaluated and visually classified by a member of our Geotechnical Engineering staff. The moisture content, Atterberg limits, and particle size analysis were evaluated, and a summary of the results and their corresponding depths are presented on the boring logs in Appendix A.

Samples will be retained in our laboratory for 30 days after submittal of this report. Other arrangements may be provided at the request of the Client.

LABORATORY INDEX TESTING

Moisture Content

The moisture content of a soil is defined as the ratio of the weight of the water in the sample to the dry weight of the soil sample. The moisture contents for the samples obtained as part of our geotechnical exploration of Segment NFW2 varied from 1 percent to 43 percent. The moisture contents for the samples obtained in Segment NFE2 varied from 2 percent to 60 percent. The

- 10 -variance in these percentages can be attributed to range in depth and distance between samples.

Another major factor could be the location of the sample relative to the encountered water table at that particular location. Lastly, the variation could be caused by the difference in soil classification, as some soils may inherently absorb more water than others. A list of all the moisture contents can be found on the boring logs in Appendix A.

Plasticity Index

The Plasticity Index is known as the difference between the liquid limit and the plastic limit of a soil. These limits are commonly referred to as the Atterberg limits, which describe the consistency of soils with respect to their varying moisture contents. The liquid limit is defined as the moisture content at which soil begins to transition from a plastic to a liquid state and begins to behave as a liquid material. The plastic limit refers to the water content at the point of transition from a semisolid to a plastic state where soil starts to exhibit plastic behavior. A soils behavior can be divided into four basic states: liquid, plastic, semisolid and solid. The plasticity index shows the range in which a soil acts in a plastic state. Experience has shown that the more plastic a soil is the more expansive and compressive it will act. PI values for the borings in Segment NFW2 performed range from less than 1 (non-plastic sands) to 61 (fat high plasticity clays). PI values for the borings in Segment NFE2 performed range from 4 (non-plastic sands) to 61 (fat high plasticity clays).

Minus 200 / Sieve Analysis / Hydrometer

The standard grain size analysis is used to determine the relative proportions of different grain sizes as they are distributed along a range of different sized sieves. The minus 200 sieve analysis is used commonly as a tool for soil classification and identification using the Unified Soils Classification System. Results for this test are reported as a percentage of soil passing the particular opening or sieve number. This test is also used to determine the suitability of soil for construction purposes. Generally a % -200 greater than 50% indicates a non-granular cohesive soil with large amounts of fines in the soil composition. The % -200 values for the samples collected in Segment NFW2 range from 5% (sands or sandy gravels with little to no fines) to 100% (high plasticity clays with little to no coarse grained material). The % -200 values for the samples collected in Segment NFE2 range from 0% (sands or sandy gravels with little to no fines) to 100% (high plasticity clays with little to no coarse grained material). Materials with extremely high or low percentages may present constructability problems due to runoff and difficulty maintaining proper moisture content.

Standard gradation analysis involves two parts, the sieve analysis and the hydrometer analysis.

The sieve analysis consists of stacking progressively finer sieves and passing a soil mass through. The sieve sizes correspond to different particle sizes within a soil and allow for the construction of a gradation curve. Hydrometer analyses are used primarily in fine grained soils but are also very useful in establishing the ‘tail-end’ of a gradation curve for soils having a mixture of coarse grained and fine grained soil constituents. Gradation curves based on sieve analyses and hydrometers analyses can be found in Appendix E.

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Summary of Index Testing

A summary of the index testing performed on the collected samples can be found on the boring logs in relation to their corresponding depths in Appendix A. Table 2 is a table representing the total number of index tests performed for the North Floodway Levee Segments NFW2 & NFE2.

Segment NFW2

Test Name & ASTM Designation Number of Tests

Performed

Moisture Content (ASTM D 2216-98) 1201

Plasticity Index (ASTM D 4318-00) 569

% Finer than No 200 (ASTM D 1140-00) 984 Hydrometer & Sieve Analysis (ASTM D 422 – 63) 248

Segment NFE2

Test Name & ASTM Designation Number of Tests

Performed

Moisture Content (ASTM D 2216-98) 1317

Plasticity Index (ASTM D 4318-00) 574

% Finer than No 200 (ASTM D 1140-00) 1091 Hydrometer & Sieve Analysis (ASTM D 422 – 63) 252

Table 2: Index Testing Summary

LABORATORY STRENGTH & COMPRESSIBILITY TESTING

Unconfined Compression Test

The unconfined compression test is a special type of unconsolidated undrained triaxial test that is commonly used for clay samples. In this test procedure, drainage of pore water from the soil sample is not permitted and the test sample is sheared to failure by the application of deviator (axial) stress. The axial load is applied rapidly to the sample and the resulting shear failure force is referred to as the unconfined compressive strength of the sample. This result is then divided by two to derive the undrained shear strength of saturated clays. Theoretically, the unconfined compression test and the unconsolidated undrained triaxial test should result in similar undrained shear strength for saturated clays; however, it has been proven that the unconfined compression test provides a more conservative result than the triaxial test.

Several unconfined compression tests were performed due to the high volume of stiff cohesive clay samples obtained from the field subsurface exploration (maximum 2 performed per boring).

The Shelby tube samples were extracted and cut to a length / diameter ratio of approximately two to one. Refer to Appendix F to see the sample depth and location, along with the corresponding unconfined compressive strength recorded from that test. The undrained cohesion values were

- 12 -used in the soil stratification and the calculation of the ultimate bearing capacity and overall slope stability (end of construction case).

Consolidation Test

The one dimensional consolidation tests were performed to determine the magnitude and rate of volume decrease that a laterally confined soil would undergo when subjected to different vertical pressures. The main purpose of this test is to obtain data that will be used to predict the rate and amount of approximate settlement of the levee structure. The test specimens were placed inside a metal ring with porous stones on both top and bottom. The loadings were then applied and settlement was recorded. From the measured data, the consolidation curve (pressure-void ratio relationship) was plotted in log format. This data is useful in determining the compression index, the recompression index and the pre-consolidation pressure (or maximum past pressure) of the soil. In addition, the data obtained can also be used to determine the coefficient of consolidation and the coefficient of secondary compression of the soil.

The consolidation properties determined from the consolidation test were used to estimate the magnitude of the total anticipated settlement. Estimates of this type are vital in the design of engineered structures and the evaluation of their performance. Consolidation input values and strain readings can be found in tabular form in Appendix G of this report.

SLOPE STABILITY ANALYSIS

For purposes of analyzing the stability of the levee in its final configuration, the method as outlined in USACE EM 1110-2-1902, “Slope Stability”, and USACE EM 1110-2-1913, “Design and Construction of Levees”, was used. The limit equilibrium method of analysis is the most commonly used method of analyzing the stability of both natural and man-made slopes. The fundamental principles behind this method are that the soil mass above a potential failure surface acts as a rigid body, and the shear strength of the material is fully engaged at all points along the surface at the moment of initial movement. A failure criterion is adopted through a comparison between forces, moments and stresses tending to cause instability of the mass versus those that resist instability and the conditions for static equilibrium are applied to analyze the problem.

Two-dimensional (2-D) sections are analyzed and plane strain conditions (no deformation of plane surfaces and no strain until failure condition is reached). The results of the analyses are expressed in terms of a safety factor in the form of a ratio of the available shear strength along the potential failure surface (the capacity) to the shear stress required to maintain equilibrium of the failure mass under the applied loads (the demand). This method is the most appropriate for this application and has traditionally been used in the analysis of man-made earth structures such as levees.

Two levee sections were investigated for this report; North Floodway Segment NFW2 & NFE2.

For Segment NFW2, the levee reach analyzed consisted of 2 typical sections. The first section covered station 456+00 to station 557+75 then is modified through the use of a station equation to reflect a new station of 0+99 to station 445+00. This section consisted of a raising of the existing top of levee a maximum of 3 feet and a reconstruction of the landside and riverside (floodway) slopes to proposed 3.0:1.0 grades (maximum 2.5:1.0 grades on the landside slopes).

The second section covered stations 445+00 through 528+00 within NFW2 and consists of a matching geometry to that of the first section with the inclusion of an irrigation canal running along the landside of the levee. The inclusion of this feature requires a modification of the analysis methods.

For Segment NFE2, the levee reach analyzed consisted of 2 typical sections. The first section covered station 415+00 through station 923+50 within NFE2. This section consisted of a raising of the existing top of levee a maximum of 3 feet and a reconstruction of the landside and riverside (floodway) slopes to proposed 3.0:1.0 grades (maximum 2.5:1.0 grades on the landside slopes). The second section consisted of station 307+00 through station 415+00 within NFE2 and consists of a matching geometry to that of the first section with the inclusion of an irrigation canal running along the landside of the levee. The inclusion of this feature requires a modification of the analysis methods.

The 3 cases that require analysis as per the USACE EM 1110-2-1902, “Slope Stability”, and USACE EM 1110-2-1913, “Design and Construction of Levees” are as follows (modified cases have been included as well due to the presence on an elevated irrigation canal on both Segment NFW2 and NFE2 ~ modeled conservatively as affecting the entire levee structure):

Case I: End of Construction (Figure 2) – This case generally reflects the condition of the levee directly following completion of the proposed construction. The riverside (floodway) of the raised levee is not subject to flooding under this condition.

Figure 2: End of Construction

Case I (MOD): End of Construction (Figure 2A) – This case generally reflects the condition of the levee directly following completion of the proposed construction. The riverside (floodway) of the raised levee is not subject to flooding under this condition although the presence of an irrigation canal is considered in our analysis (utilized in Segment NFW2 & NFE2).

- 13 -

Figure 2A: End of Construction (Modified for Irrigation Canal)

Case II: Long-Term Steady-State Seepage (Figure 3) – This case generally reflects a condition where a pool level reaching the maximum allowable height (3.0 feet below proposed top of levee elevation) has persisted for a long period of time on the riverside (floodway) of the levee, such that a steady-state seepage condition has developed through the existing and newly reconstructed levee.

Figure 3: Steady State Seepage

Case II (MOD): Long-Term Steady-State Seepage (Figure 3A) – This case generally reflects a condition where a pool level reaching the maximum allowable height (3.0 feet below proposed top of levee elevation) has persisted for a long period of time on the riverside (floodway) of the levee, such that a steady-state seepage condition has developed through the existing and newly reconstructed levee. The presence of an irrigation canal is considered in our analysis (utilized in Segment NFW2 & NFE2).

- 14 -

Figure 3A: Steady State Seepage (Modified for Irrigation Canal)

Case III: Rapid Drawdown (Figure 4) – This case generally reflects a condition where a pool level reaching the maximum allowable height (3.0 feet below proposed top of levee elevation) has persisted for a long period of time on the riverside (floodway) of the levee, resulting in a steady-state seepage condition through the existing and newly reconstructed levee prior to the occurrence of a rapid drawdown.

Figure 4: Rapid Drawdown

Case III (MOD): Rapid Drawdown (Figure 4A) – This case generally reflects a condition where a pool level reaching the maximum allowable height (3.0 feet below proposed top of levee elevation) has persisted for a long period of time on the riverside (floodway) of the levee, resulting in a steady-state seepage condition through the existing and newly reconstructed levee prior to the occurrence of a rapid drawdown. The presence of an irrigation canal is considered in our analysis (utilized in Segment NFW2 & NFE2).

- 15 -

Figure 4A: Rapid Drawdown (Modified for Irrigation Canal)

The stress-strain properties of the materials in both the existing fill and foundation govern the potential location of failure surfaces. Actual failure surfaces are very complex and can never be known in advance; however, research into the behavior of soils have yielded methods of analysis that can be applied to some general surfaces for the purpose of predicting actual field behavior of the materials. Using the Modified Bishop Method, circular failure surfaces were investigated using the slope stability program GSTABL7 with STEDwin analysis software version. 2.005.

Minimum Factors of Safety for Overall Stability Analysis

The current criteria listed in USACE EM 1110-2-1913 states that for the end of construction case, the minimum factor of safety for slope stability is 1.3. The minimum factor of safety for the steady state seepage case is 1.4, and 1.0 to 1.2 for the sudden drawdown case.