Attachment 07. IOI Rehab Geotechnical Report_20150121.pdf

Geotechnical Baseline Report Rehabilitation of International Outfall Interceptor

Nogales and Rio Rico, Arizona January 21, 2015

Terracon Project No. 63145034

Prepared for:

URS Group, Inc.

San Antonio, TX

Prepared by:

Terracon Consultants, Inc.

Tucson, Arizona ldbraun Stamp

Terracon Consul tants, Inc. 355 S. Eucl id Avenue, Suite 107, Tucson, Arizona 85719 P [520] 770-1789 F [520]-792-2539 terracon.com

January 21, 2015

URS Group, Inc.

9901 IH-10 West, Suite 350 San Antonio, TX 78230-2252

Attn: Mr. Ted Stawasz, P.E.

Re: Geotechnical Baseline Report Rehabilitation of International Outfall Interceptor Nogales and Rio Rico, Arizona Terracon Project No. 63145034

Dear Mr. Stawasz:

Terracon Consultants, Inc. (Terracon) has completed the geotechnical engineering services for the above referenced project. These services were performed in general accordance with your subcontract agreement number 311584.US signed June 26, 2014. Terracon issued a Geotechnical Data Report for this project dated January 21, 2014. This geotechnical baseline report builds on the data presented in the data report and provides the geotechnical engineering recommendations concerning excavation, bedding and backfilling for utilities, design recommendations for manhole construction and general earthwork recommendations for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

Louis D. Braun, E.I.T. Donald R. Clark, P.E.

Geotechnical Engineer Senior Principal ldbraun Stamp

Rehabilitation of IOI ■ Nogales and Rio Rico, Arizona January 21, 2015 ■ Terracon Project No. 63145034

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TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY .......................................................................................................................... i

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

3.0 SUBSURFACE CONDITIONS

3.1 Regional and Site Geology

3.2 Subsurface Soil Conditions

3.3 Groundwater Conditions

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Excavation Considerations

4.2 Trench Bedding

4.3 Trench Backfill

4.4 Manhole Design and Construction

4.5 Seismic Considerations

4.6 General Earthwork Recommendations

4.6.1 Site Preparation

4.6.2 Compaction Requirements

4.7 Corrosion Considerations

5.0 GENERAL COMMENTS

APPENDIX A – FIELD EXPLORATION

Exhibits A-1a to A-1i Site Plan and Boring Location Diagram Exhibit A-2 Field Exploration Description Exhibit A-3 General Notes Exhibit A-4 Unified Soil Classification Exhibits A-5 to A-39 Boring Logs

APPENDIX B – LABORATORY TESTING

Exhibit B-1 Laboratory Testing Exhibits B-2 to B-4 Atterberg Limits Results Exhibits B-5 to B-16 Grain Size Distribution Exhibits B-17 to B-19 Moisture Density Relationship Exhibits B-20 to B-35 Direct Shear Tests Exhibits B-36 to B-44 Summary of Laboratory Results

APPENDIX C – FENCE DIAGRAMS

Exhibits C-1 to C-9 Subsurface Profiles

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EXECUTIVE SUMMARY

A geotechnical engineering exploration has been performed for the proposed Rehabilitation of the International Outfall Interceptor project located along the Nogales Wash and the Union Pacific Railroad (UPRR) from the northwest corner of North Morley Avenue and East Madison Street to the Nogales International Wastewater Treatment Plant from Nogales to Rio Rico, Arizona.

Terracon’s geotechnical scope of work included the advancement of 35 test borings to depths of approximately 12.5 to 51.5 feet below existing site grades, laboratory testing on representative samples of the subsurface materials, engineering analyses, and development of engineering recommendations for design and construction.

Based on the information obtained from our engineering analyses of the field and laboratory data, the following geotechnical considerations were identified:

n In general, the near surface on-site soils consist of sand with variable amounts of clay, silt and gravel, sandy lean clay, silt and gravel with variable amounts of clay, and silt.

Groundwater was encountered in 11 of the 35 borings with depths ranging from 9.5 to 32 feet below ground surface. Fill was encountered in 16 borings to depths of approximately 6 to 20 feet. For purposes of this report and the recommendations, the subsurface conditions have been grouped into four boring groups (i.e. Groups 1 through 4).

n No unusual difficulties are expected for excavation of the trenches for the proposed pipeline. However, some cobble sized materials were encountered within the Group 3 test borings and refusal to auger drilling was encountered in Boring B-33 in this test boring group at a depth of 12.5 feet (presumably on cobbles). Some additional effort may be necessary to extract cobble or boulder sized materials, particularly in deep narrow excavations such as utility trenches. Consideration should be given to obtaining a unit price for difficult excavation in the contract documents for the project.

n All trench excavations should be sloped or shored in accordance with OSHA excavation regulations during construction. A detailed discussion of the open trench excavations and safety considerations are presented in the report.

n Groundwater seepage should be anticipated for excavations at the planned invert elevation of construction at certain locations on the alignment of the project. At a minimum the contractor should be expected to utilize temporary sump and pumping systems to control water within the excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth.

n For a Type 1 Standard Installation, ACPA recommends the use of clean coarse grained sand, pea gravel or crushed rock as pipe bedding. However, for this project, we recommend the use of coarse well graded gravel based on the depth of the pipeline and

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n We anticipate that the pressures exerted at the base of proposed manholes from vertical loading will approximately equal to or less than the in-situ stresses and will be fully compensated by the removal of the existing overburden soils to accommodate manhole construction. The use of precast base sections for manhole support is considered acceptable for use on the project. If necessary, cast-in-place reinforced concrete mat foundations of appropriate size and dimensions could also be utilized.

n Buoyancy will become a factor for manhole design where groundwater will be located above the base elevation of these structures. Two types of manhole structures should be considered and analyzed for resistance to the upward buoyant forces. One type of structure is the traditional smooth-wall manhole that utilizes its own weight and the friction resistance with the adjacent backfill soils to resist the upward buoyant force. In the instance where the weight of the manhole and friction cannot resist the buoyant forces consideration should be given to an extended base manhole installation which will increase the size of the base beyond the walls of the manhole.

n Based on the site soil properties, the site is classified as Site Class D in accordance with Chapter 20 of ASCE 7 as required by the 2012 International Building Code.

This executive summary should be used in conjunction with the entire report for design and/or construction purposes. It should be recognized that specific details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled General Comments should be read for an understanding of the report limitations.

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GEOTECHNICAL BASELINE REPORT

REHABILITATION OF INTERNATIONAL OUTFALL INTERCEPTOR

NOGALES AND RIO RICO, ARIZONA

Terracon Project No. 63145034 January 21, 2015

1.0 INTRODUCTION

This report presents the results of our geotechnical engineering services performed for the proposed Rehabilitation of International Outfall Interceptor (IOI) project located along the Nogales Wash and the Union Pacific Railroad (UPRR) from the northwest corner of North Morley Avenue and East Madison Street to the Nogales International Wastewater Treatment Plant from Nogales to Rio Rico, Arizona. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

n Subsurface soil and groundwater conditions n Recommendations for utility installation by open-cut excavation techniques;

n Recommendations for bedding and backfilling of utilities;

n Foundation design backfilling, lateral earth pressures and buoyancy recommendations for manholes; and, n Site preparation and structural fill requirements and general earthwork recommendations.

Our geotechnical engineering scope of work for this project included drilling 35 test borings to depths of approximately 12.5 to 51.5 feet for subsurface exploration, laboratory testing, preparation of this report, and a geotechnical data report submitted under a separate cover.

Logs of the borings along with Site Plan and Boring Locations diagrams (Exhibits A-1a through A- 1i) are included in Appendix A of this report. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included in Appendix B of this report.

Descriptions of the field exploration and laboratory testing are included in their respective appendices.

2.0 PROJECT INFORMATION

Information regarding this project was derived from our review of the as-built drawings of the Nogales International Sanitation Project Outfall Pipeline, prepared by International Boundary and Water Commission dated May 1, 1971. We understand the entire alignment of the International Outfall Interceptor extends from Mexico to the Nogales International Wastewater Treatment Plant. The proposed rehabilitation project will focus on the portion of the alignment that is located along the Nogales Wash and the UPRR from the northwest corner of North

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Morley Avenue and East Madison Street to the Nogales International Wastewater Treatment Plant (NIWTP) from Nogales to Rio Rico, Arizona. The rehabilitation of the existing pipeline will include possible reconstruction and point repairs of the RCP pipeline, including replacing or repairing select manholes. The top of the pipeline varies in depth from approximately 3 to 28 feet below existing grade along this portion of the alignment. The pipeline varies in diameter, the majority of the pipeline is 30 inches in diameter along the project alignment and increases to 36 inches and finally 42 inches in diameter before in reaches the NIWTP.

The total length of the project is approximately 7½ miles. The beginning point of the alignment of the IOI extends beneath the Nogales Wash. The Nogales Wash at this location flows through a concrete lined open floodway near the northwest corner of North Morley Avenue and East Madison Street, Sta. 54+00 of the IOI alignment. The remainder of the alignment extends along either the west or the east side of the wash, mainly along the shoulder of different roadway alignments, until it reaches the Nogales International Wastewater Treatment Plant, Station 460+00 of the IOI alignment. The site layout can be seen on the Site and Boring Locations Diagrams, Exhibits A-1a through A-1i in Appendix A.

3.0 SUBSURFACE CONDITIONS

3.1 Regional and Site Geology

The project area is located in the Basin and Range physiographic province (1Cooley, 1967) of the North American Cordillera (2Stern, et al, 1979) of the southwestern United States. The southern portion of the Basin and Range province is situated along the southwestern flank of the Colorado Plateau and is bounded by the Sierra Nevada Mountains to the west. Formed during middle and late Tertiary time (100 to 15 m.y. ago), the Basin and Range province is dominated by fault controlled topography. The topography consists of mountain ranges and relatively flat alluviated valleys. These mountain ranges and valleys have evolved from generally complex movements and associated erosional and depositional processes.

Structurally, the site lies within the Santa Cruz River Basin. Drainage flows to the Santa Cruz River during late Tertiary time, coupled with structural activity discussed above, are generally responsible for the present day topography within the basin.

Typically, the ranges in this area are of small areal extent, but protrude significantly above adjacent wide alluviated plains and valleys. The basin rims are formed by the mountain ranges which consist of sedimentary, igneous and metamorphic materials which have been subjected

1Cooley, M.E., 1967, Arizona Highway Geologic Map, Arizona Geological Society.

2Stern, C.W., et al, 1979, Geological Evolution of North America, John Wiley & Sons, Santa Barbara, California.

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Surficial geologic conditions mapped at the site (3Wilson, et al, 1960) consist of alluvium of Quaternary age (10,000 to 1 m.y. ago). The alluvial materials have been described as deposits consisting of sand, silt and gravel. Locally, the alluvium can include clay deposits commonly referred to as playas. Playas are typically formed in shallow temporary lake beds on the valley floor.

3.2 Subsurface Soil Conditions

Specific conditions encountered at each boring location are indicated on the individual boring logs.

Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in-situ, the transition between materials may be gradual. Details for each of the borings can be found on the boring logs included in Appendix A of this report. Fence diagrams showing the relationship of the proposed pipeline to the subsurface profile at the boring locations is shown on Exhibits C-1 through C-9, in Appendix C. The profile of the pipeline on the fence diagrams has been developed on the basis of our review of the as-built plans previously referenced in this report.

Based on conditions encountered in the borings, subsurface conditions on the project site can be generalized as follows:

Group 1: Boring Locations B-1 to B-6

Description Approximate

Depth to Bottom of Stratum (feet)

Material Encountered Consistency/ Relative Density

Stratum 1 7 to 14 Fill: Sand soils with variable amounts of clay, silt and gravel Very loose to very dense

Stratum 2 51.5 Sand soils with variable amounts of clay, silt and gravel Very loose to very dense Notes:

1. Asphalt concrete pavement was encountered at the surface at the location of Borings B-4 and B-6.

2. Groundwater was encountered in Borings B-1 through B-4 at depths of 13 to 17.5 feet at the time of the field exploration.

3Wilson, E.D., Moore, R.T., and O'Haire, R.T.; 1960, Geologic Map of Pima and Santa Cruz Counties, Arizona, Arizona Bureau of Mines, University of Arizona.

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Group 2: Boring Locations B-7 to B-14, B-18 to B-20, B-29 to B-31, B-35

Description Approximate

Depth to Bottom of Stratum (feet)

Material Encountered Consistency/ Relative Density

Stratum 1 51.5

Interbedded Sand soils with variable amounts of clay, silt and gravel /Lean

Clay with variable amounts of sand /Silt with variable amounts of sand

Very soft to very stiff /Very loose to very dense

Notes:

1. Asphalt concrete pavement was encountered at the surface at the location of Borings B-7, B-18 and B-19.

2. Groundwater was encountered in Borings B-10, B-20, B-29 through B-31 and B-35 at depths of 9.5 to 32 feet at the time of the field exploration.

Group 3: Boring Locations B-15 and B-16, B-21, B-33 and B-34

Description Approximate

Depth to Bottom of Stratum (feet)

Material Encountered Consistency/ Relative Density

Stratum 1 (Borings B- 16, B-21, B- 33 and B-34)

6 to 10 Gravel soils variable amounts of clay, silt and sand/Silty Clayey Sand with gravel

Loose to very dense

Stratum 1 (Boring B-15)

Fill: Clayey Sand with gravel /Poorly

Graded Gravel with Clay and Sand/Silty Sand

Loose

Stratum 2 26 Sand soils with variable amounts of clay, silt and gravel Medium dense to Very

Dense Notes:

1. Groundwater was not encountered in these borings at the time of the field exploration.

2. The Stratum 2 soils contain variable amounts of cobbles at different depths in the test borings.

3. Refusal to auger drilling was encountered at a depth of 12.5 in Boring B-33.

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Group 4: Boring Locations B-17, B-22 to B-28, B-32

Description Approximate

Depth to Bottom of Stratum (feet)

Material Encountered Consistency/ Relative Density

Stratum 1 6 to 20 Fill: Sand soils with variable amounts of clay, silt and gravel Very loose to very dense

Stratum 2 26.5 Interbedded Sand soils with variable amounts of clay, silt and gravel / Lean Clay with variable amounts of sand

Soft to very stiff /Very loose to very dense

Notes:

1. Asphalt concrete pavement was encountered at the surface at the location of Boring B-32.

2. Groundwater was encountered in Boring B-28 at a depth of 21.5 feet at the time of the field exploration.

Laboratory tests were conducted on selected soil samples and the test results are presented in Appendix B.

3.3 Groundwater Conditions

Groundwater was observed in 11 of the 35 test borings at the time of field exploration. The depth where groundwater was initially encountered in the test borings varied from approximately

9.5 to 32 feet below the ground surface. This included test borings B-1 through B-4, B-10, B-20, B-28 through B-31 and B-35. These observations represent groundwater conditions at the time of the field exploration and may not be indicative of other times, or at other locations.

Groundwater conditions can change with varying seasonal and weather conditions, and other factors.

Five of the borings (i.e. Borings B-1, B-10, B-20, B-31 and B-35 were completed with the installation of open well piezometers for delayed groundwater measurements. The remainder of the test borings were either backfilled with soil cuttings or cement-bentonite grout (where groundwater was encountered) upon completion of the field exploration.

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

For purposes of developing the engineering recommendations contained in this report, we have grouped the subsurface conditions by test boring into four groups (i.e. Groups 1 through 4) as outlined in Section 3.2. These groupings were determined on the basis of similar subsurface and groundwater conditions as well as the relative density and/or consistency of the soils as evidenced by the field penetration testing.

Geotechnical engineering recommendations have been developed for the project to address the following:

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Resourceful ■ Responsive ■ Reliable 6 n Recommendations for utility installation by open-cut excavation techniques;

n Recommendations for bedding and backfilling of utilities;

n Foundation design backfilling, lateral earth pressures and buoyancy recommendations for manholes; and, n Site preparation and structural fill requirements and general earthwork recommendations.

Our geotechnical engineering recommendations are contained in the following sections of this report.

4.1 Excavation Considerations

Planned excavation depths will vary across the alignment of the project. In general, excavation depths are anticipated to vary from approximately 3 to as great as 24 feet.

No unusual difficulties are expected for open-cut excavation of trenches on the project. Bedrock was not encountered in any of the test borings to the maximum depth of exploration along the alignment of the project. However, some cobble sized materials were encountered within the Group 3 test borings and refusal to auger drilling was encountered in Boring B-33 in this test boring group at a depth of 12.5 feet (presumably on cobbles). Some additional effort may be necessary to extract cobble or boulder sized materials, particularly in deep narrow excavations such as utility trenches. Consideration should be given to obtaining a unit price for difficult excavation in the contract documents for the project.

Groundwater seepage should be anticipated for excavations at the planned invert elevation of construction at least at the locations of Borings B-1 through B-4, B-20, and B-28 through B-31.

Groundwater conditions can change with varying seasonal and weather conditions, and other factors. Therefore groundwater could be encountered in trench excavations at other locations and depths on the project. At a minimum the contractor should be expected to utilize temporary sump and pumping systems to control water within the excavations. Well points may be required for significant groundwater flow, or where excavations penetrate groundwater to a significant depth.

The individual contractor(s) is responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottoms.

Excavations should be sloped or shored in the interest of safety following local, state and federal regulations, including current OSHA excavation and trench safety standards. Instability in the form of caving, sloughing, and raveling should be expected in deeper excavations which extend into the granular soil deposits (Groups 2 and 3) or where fill soils were encountered (Groups 1 and 4). The contractor should be advised that slope height, slope inclination, and excavation depth should in no instance exceed those specified by these safety regulations.

Flatter slopes than those dictated by these regulations may be required depending upon the soil

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OSHA Health and Safety Standards for Excavations classify soils into three basic types (i.e., Type A, B, and C). Depending upon the soil type, OSHA required excavation slopes range from 3/4H:1V (horizontal:vertical) for Type A soils, 1H:1V for Type B soils, and 1-1/2H:1V for Type C soils. OSHA dictates that any excavation extending to a depth of more than 20 feet shall be designed by a Registered Professional Engineer. Based upon the subsurface conditions encountered at the boring locations, it appears the excavations will extend primarily into granular soils with variable amounts of clay, silt and gravel. However, at some locations, the excavation will penetrate substantial thicknesses of cohesive clay soils. The granular soils and interbedded granular and cohesive soils will classify as Type C soils according to OSHA. Where there is a substantial thickness of cohesive soils, these will classify as Type B according to OSHA. For planning purposes we recommend assuming a Type C soils for the majority of the project alignment in all four groupings of the test borings. For excavations encountering layered materials, the slope must be based on the most stringent slope requirements of any underlying layer penetrated based on OSHA requirements.

In lieu of trench slopes as defined by OSHA, trench shoring or shields (trench boxes) may be utilized to increase excavation slopes. We anticipate that trench boxes will be utilized where the pipeline alignment lies adjacent to existing roadways or structures. The contractor would be responsible for the design of the temporary shoring in accordance with applicable regulatory requirements.

Care should be taken during excavation to protect the structural integrity of any existing structures, pavements, or adjacent underground utilities. Depending upon factors such as the depth of excavation, the location of the existing improvements, groundwater and soil conditions, temporary sheeting and/or shoring may be required. For preliminary designs, excavations should not be performed within a surface defined as 5 feet horizontal from the nearest edge of existing foundations or other settlement sensitive structures and then downward at 2 horizontal to 1 vertical slope. Flatter slopes may be required, and the contractor should be advised to consult with a registered professional engineer to provide specific recommendations regarding measures to protect existing improvements.

Particular caution should be exercised when excavations are performed in existing fill or near existing utility lines. The OSHA trench safety guidelines for adequate side slopes based on soil types may not apply in these situations. Existing underground utilities should be shored and

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All vehicles and soil piles should be kept a sufficient lateral distance from the crest of the trench slope to maintain safe working conditions. Vehicles and soil piles located adjacent to trenches would significantly influence the stability of the slopes as outlined by the OSHA regulations. A more detailed stability analysis would be required for these conditions. Additionally, vibrations from traffic, construction equipment, pile driving, or similar sources can influence slope stability.

The exposed slope faces should be protected from the elements. Surface water should be diverted from all excavations. If water enters an excavation it should be removed along with any loosened or softened soil. The length of open trench should be held to a minimum.

The materials which may be encountered along the excavation of the proposed pipeline alignment will and should be expected to vary significantly. The borings represent soil conditions at discrete locations and are not necessarily representative of conditions along the entire alignment. Thus, the stability of the excavation slope should be reviewed continuously by qualified personnel during construction. The generalized guidelines provided above are based solely upon the materials encountered in the widely spaced exploratory borings.

4.2 Trench Bedding

We recommend that determination of pipe loads and supporting strengths be completed on the basis of the design procedures outlined in the Concrete Pipe Design Manual, American Concrete Pipe Association (ACPA), 2011. The design procedure, based on the ACPA Manual requires:

n Determination of the Earth load n Determination of the Live Load n Selection of Bedding n Determination of Bedding Factor n Application of an Appropriate Factor of Safety n Selection of Pipe Strength

The ACPA Manual provides for four types of pipe installations in Illustration 4.4 of the manual.

As outlined in the manual, the selection of the installation type should be based on an evaluation of the quality of construction and the amount of inspection anticipated for the project.

For purposes of this project, we anticipate that a Type 1 Standard Installation will be utilized.

For a Type 1 Standard Installation the bedding thickness should be determined on the basis of the following equation:

n Db= Do/24, where

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Db is the depth of the bedding (in inches), and Do is the outer diameter of the pipe (in inches)

However, a minimum depth of bedding (Db) of 3 inches is recommended. Additionally, the bedding and the haunch bedding should extend laterally beyond the sides of the pipe a minimum distance in inches of Do/6, but not less than 9 inches is recommended for a pipe diameter of 30 inches, and 12 inches is recommended for a pipe diameter of 42 inches.

Another consideration in the determination of an appropriate bedding depth for this project is consideration of the relative density and consistency of the subgrade soils that will be found at invert elevation of the pipeline. For Boring Groups 1, 3 and 4, granular soils or granular fill soils of very loose to loose relative density can be anticipated. In these instances, the minimum bedding depth determined in accordance with the ACPA Manual is recommended provided that the granular soils found at invert elevation of the proposed pipeline, are scarified, moisture conditioned and compacted to a minimum depth of 10 inches below the level of the bedding materials. Compaction of these types of soils to a minimum of 95% of the maximum density determined in accordance with ASTM D 698 (Standard Proctor) is recommended. Moisture content should be maintained in a range of +/- 2% from optimum moisture content.

In the event that very soft or soft subgrade or otherwise unstable soils are encountered at pipe invert elevation (generally associated with Boring Group 2), we recommend that the depth of the bedding be increased to a minimum of 24 inches. Deeper sections of bedding may be required depending of the stability that can be attained with the bedding for construction or the instability of the subgrade soils. Consideration should be given to obtaining a unit price and for a contract allowance for variable thicknesses and amounts of bedding that may be required to deal with these situations during construction.

The bedding is provided to distribute the vertical loads around the lower exterior surface of the pipe and reduce stress concentration in the pipe wall. The most ideal bedding material is one that will maintain positive contact with the pipe as the pipe settles under the applied load of the backfill soils and the live load of any traffic. For a Type 1 Standard Installation, ACPA recommends the use of clean coarse grained sand, pea gravel or crushed rock. However, for this project, we recommend the use of coarse well graded gravel based on the depth of the pipeline and the anticipated subgrade soil conditions at invert elevation. The trench bedding materials are recommended for backfill to the haunch level (spring line) of the pipe.

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The following material specifications for bedding materials are recommended:

Percent Finer by Weight Gradation (ASTM C 136)

1-1/2" 1” .................................................................................................... 90-100 No. 8 Sieve ....................................................................................... 35-80 No. 200 Sieve ....................................................................................... 0-8 n Plasticity Index ................................................................... 8 (max) n Minimum Resistivity ..................................................2,000 ohm-cm n pH ................................................................................. 6.0 to 12.0

The bedding should be placed in lifts not exceeding 10 inches in loose thickness and should be compacted to a minimum of 95% of the maximum density determined in accordance with ASTM D 698 (Standard Proctor). Moisture content should be maintained in a range of +/- 2% from optimum moisture content.

4.3 Trench Backfill

Spoil materials derived from the excavation of the pipeline will be used for the trench backfill during construction. All of the materials represented by Boring Groups 1 through 4 are considered suitable for use as trench backfill. However, very soft to soft and wet cohesive (clay soils) may require additional handling and efforts on the part of the contractor prior to using these material as backfill. Processing of these materials by means of aeration or some form of chemical stabilization may be required in order to achieve moisture contents that will meet the requirements for proper compaction during the backfill construction.

Recommended compaction and moisture content criteria for trench backfill materials are as follows:

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Material Type and Location

Per the Standard Proctor Test (ASTM D 698)

Minimum Compaction

Requirement (%)

Range of Moisture Contents for Compaction (referenced from optimum moisture content) Minimum Maximum

Beneath any structural feature including proposed pavements, curb, gutter or where the trench excavation is within 2 feet of these elements:

From Surface To 2 feet Below Surface 100 for granular 95 for cohesive

-3% +3%

From 2 feet Below Surface To 1 foot Above Top of Pipe*

95 -3% +3%

From 1 foot Above Top of Pipe to Bottom of Trench

90 -3% +3%

On any utility easement street outside limits of structural features as outlined above:

From Surface To 2 feet Below Surface 90 -3% +3%

From 2 feet Below Surface To 1 foot Above Top of Pipe

90 -3% +3%

From 1 foot Above Top of Pipe to Bottom of Trench

90 -3% +3%

*Note: For intervals where the distance from 2 feet below the surface to 1 foot above the top of the pipe exceeds 5 feet, the recommended level of compaction should be increased to a minimum of 98%

4.4 Manhole Design and Construction

We anticipate the manholes for the project will be constructed of precast concrete riser sections supported on a precast concrete base section. Manhole riser sections of 36 to 72 inches in diameter are anticipated for the project.

We anticipate that the pressures exerted at the base of proposed manholes from vertical loading will be approximately equal to or less than the in-situ stresses and will be fully compensated by the removal of the existing overburden soils to accommodate manhole construction. The use of precast base sections for manhole support is considered acceptable for use on the project. If necessary, cast-in-place reinforced concrete mat foundations of appropriate size and dimensions could also be utilized.

Variable subgrade conditions should be expected at the planned depth of the manholes along the alignment. For Boring Groups 1, 3 and 4, granular soils or granular fill soils of very loose to loose relative density should be anticipated. In these instances, we recommend that the base of

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Resourceful ■ Responsive ■ Reliable 12 the proposed manholes be supported on properly prepared subgrade soils. At a minimum the granular soils found at invert elevation of the proposed pipeline should be scarified, moisture conditioned and compacted to a minimum depth of 10 inches below the level of the manhole base or foundation system. Compaction of these types of soils to a minimum of 95% of the maximum density determined in accordance with ASTM D698 (Standard Proctor) is recommended. Moisture content should be maintained in a range of +/- 2% from optimum moisture content.

In the event that very soft or soft subgrade or otherwise unstable soils are encountered at the base or foundation elevation of a manhole (generally associated with Boring Group 2), we recommend that the unstable material be over-excavated to a minimum depth of 2 feet and be replaced with compacted granular bedding materials. Deeper sections of bedding may be required depending of the stability that can be attained with the bedding for construction or the instability of the subgrade soils. The bedding should be placed in lifts not exceeding 10 inches in loose thickness and should be compacted to a minimum of 95% of the maximum density determined in accordance with ASTM D 698 (Standard Proctor). Moisture content should be maintained in a range of +/- 2% from optimum moisture content.

Buoyancy will become a factor for manhole design where groundwater will be located above the base elevation of these structures. Two types of manhole structures should be considered and analyzed for resistance to the upward buoyant forces. One type of structure is the traditional smooth-wall manhole that utilizes its own weight and the friction resistance with the adjacent backfill soils to resist the upward buoyant force. In the instance where the weight of the manhole and friction cannot resist the buoyant forces consideration should be given to an extended base manhole installation which will increase the size of the base beyond the walls of the manhole. With this type of structure, additional resistance will include the added weight of the base section as well as the additional weight of the soil above the base to create more resistance to the upward force developed by the displaced groundwater.

For purposes of determining the unit skin friction against the sides of the manholes, we recommend use of the following equation:

n fs= K s’v tan d, where fs= unit skin friction is psf K = lateral earth pressure coefficient s’v = the effective overburden pressure (gz, where g= the effective soil unit weight and z is the depth along the side of the manhole), and, d = angle of friction between the soil and the side of the manhole

For the soils encountered in the Boring Groups outlined in this report, the recommended design parameters to be used in the preceding equation are as follows:

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Boring Group K, Earth Pressure Coefficient g, Unit Weight (pcf)1,2 D, Angle of Friction

(degrees) 1, 3 and 4 0.5 125 27

2 0.7 120 17 Notes:

1. Unit weights assume that the backfill materials placed against the sides of the manholes are compacted to the densities outlined in Section 4.3 of this report

2. Buoyant unit weights should be used in the analyses foe soils below the level of groundwater at the manhole.

The unit skin friction values computed on the basis of the preceding parameters are ultimate values. Appropriate factors of safety should be included in the analyses.

Shallow groundwater levels should be anticipated for excavations at the planned invert elevation of construction at least at the locations of Borings B-1 through B-4, B-20, and B-28 through B-

31. Groundwater conditions can change with varying seasonal and weather conditions, and other factors. Therefore groundwater could be encountered in manhole excavations at other locations and depths on the project. Based on our review of the as-built plans of the existing outfall line, the location of existing manholes that require consideration of groundwater impact within the project alignment include MH Nos. 18 to 36, MH Nos. 59 to 68, MH Nos. 83 to 95.

The maximum allowable depth of a typical precast concrete manhole with regard to lateral earth pressures is in excess of 300 feet, consequently lateral earth pressures are not considered a critical element of the design. However, for any other structures subject to differential lateral loading conditions from soils on the project, the following lateral earth pressure parameters are recommended for use in the design. For soils above any free water surface, recommended equivalent fluid pressures are:

Design Case Design Recommendation1

Active Case 40 psf/ft

Passive Case 360 psf/ft

At-Rest Case 60 psf/ft

These values listed in the preceding table are based on using the on-site granular soils typical from Boring Groups 1, 3 and 4. Cohesive (clay) soils, typically from Boring Group 2 are not recommended for backfill against any structure (other than manholes) where lateral earth pressures will be a consideration in the design and construction.

The lateral earth pressures listed in the preceding table do not include any factor of safety, they assume drained conditions, and they are not applicable for submerged soils/hydrostatic loading.

Additional recommendations may be necessary if submerged conditions are to be included in the design of any structure (other than manholes) where lateral earth pressures will be a consideration in the design and construction.

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Backfill placed against the proposed manholes should be compacted to the minimum densities outlined in Section 4.3

4.5 Seismic Considerations

4.6 General Earthwork Recommendations

The following presents recommendations for general earthwork operations on the project, including site preparation, subgrade preparation and placement of engineered fills. Earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, and other geotechnical conditions exposed during the construction of the project.

4.6.1 Site Preparation

Strip and remove existing vegetation, debris, and other deleterious materials from proposed structural and pavement areas. Exposed surfaces should be free of mounds and depressions which could prevent uniform compaction.

Stripped materials consisting of vegetation and organic materials should be wasted from the site, or used to revegetate landscaped areas or exposed slopes after completion of grading operations. If it is necessary to dispose of organic materials on-site, they should be placed in non-structural areas, and in fill sections not exceeding 5 feet in height.

Description Value 2012 ASCE 7 Site Classification 1 D2

Site Latitude N 31.3773°

Site Longitude W 110.9385° Ss Spectral Acceleration for a Short Period 0.202

S1 Spectral Acceleration for a 1-Second Period 0.062 Fa Site Coefficient for a Short Period 1.60

Fv Site Coefficient for a 1-Second Period 2.40 1 Note: The site is classified in accordance with Chapter 20 of ASCE 7 as required by the 2012 International Building Code.

2 Note: ASCE 7 requires a site soil profile determination extending to a depth of 100 feet for seismic site classification. The current scope does not include the required 100 foot soil profile determination. Borings extended to a maximum depth of 51.5 feet, and this seismic site class definition considers that very dense soil continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths would be required to confirm the conditions below the current depth of exploration.

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If fill is placed in areas of the site where existing slopes are steeper than 5:1 (horizontal:vertical), the area should be benched to reduce the potential for slippage between existing slopes and fills. Benches should be wide enough to accommodate compaction and earth moving equipment, and to allow placement of horizontal lifts of fill.

Exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of ten inches, conditioned to near optimum moisture content, and compacted.

4.6.2 Compaction Requirements

Recommended compaction and moisture content criteria for engineered fill materials are as follows:

Material Type and Location

Per the Standard Proctor Test (ASTM D 698)

Minimum Compaction

Requirement (%)

Range of Moisture Contents for Compaction

Minimum Maximum

On-site granular or approved imported fill soils:

95 -3% +3%

Aggregate base (beneath pavements) 100 -3% +3%

Miscellaneous backfill 95 -3% +3%

4.7 Corrosion Considerations

Laboratory test results indicate that tested on-site soils have a minimum resistivity values ranging from 360 to 3300 ohm-centimeters, and pH values ranging from 7.3 to 9.4. The tested on-site soils indicated the soluble sulfates values ranged from <50 to 200 ppm and the soluble chlorides ranged from <10 to 59 ppm. These values should be used to determine potential corrosive characteristics of the on-site soils with respect to contact with the various underground materials which will be used for project construction.

Results of soluble sulfate testing indicate that ASTM Type II portland cement is suitable for all project concrete on and below grade. Concrete should be designed for negligible sulfate exposure in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4.

Refer to Summary of Laboratory Results contained in Appendix B for the complete results of the various corrosivity testing conducted on the site soils in conjunction with this geotechnical exploration.

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5.0 GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, pipeline construction and other earth-related construction phases of the project.

The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between borings, across the site, or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided.

The scope of services for this project does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing.

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APPENDIX A

FIELD EXPLORATION

N

Drawn By:

Checked By:

Approved By:

Project Mngr:

File No.

Date:

Scale:

Project No. EXHIBIT

Consulting Engineers and Scientists

355 SOUTH EUCLID, SUITE 107 TUCSON, ARIZONA 85719

FAX. (520) 792-2539PH. (520) 770-1789

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LDB

BMB

BMB

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63145034.DWG

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SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1a

URS GROUP, INC.

REHABILITATION OF INTERNATIONAL

APPROXIMATE BORING LOCATION

B-1

B-2

B-3

NO

RT

H M

O

RL

EY

A

VE

NU

E

TU

CS

O N-

NO

G

AL

ES

H

IG

HW

AY

OUTFALL INTERCEPTOR

NO

G

AL

ES

W

AS

H

UP

RR

Checked By:

Approved By:

Project Mngr:

File No.

Date:

Scale:

Project No. EXHIBIT

Consulting Engineers and Scientists

355 SOUTH EUCLID, SUITE 107 TUCSON, ARIZONA 85719

FAX. (520) 792-2539PH. (520) 770-1789

BMB

LDB

BMB

BMB

63145034

NA

63145034.DWG

10/14

SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1b

URS GROUP, INC.

APPROXIMATE BORING LOCATION

N B-4

B-5

B-6

B-7

NORTH HOHO

KAM

DRIVE

TUCSON-NO

G

ALES HIGHW

AY

EAST DOE STREET

REHABILITATION OF INTERNATIONAL

OUTFALL INTERCEPTOR

U P

R R

N O

G A

LE

S

W A

S H

Approved By:

Project Mngr:

File No.

Date:

Scale:

Project No. EXHIBIT

Consulting Engineers and Scientists

355 SOUTH EUCLID, SUITE 107 TUCSON, ARIZONA 85719

FAX. (520) 792-2539PH. (520) 770-1789

BMB

LDB

BMB

BMB

63145034

NA

63145034.DWG

10/14

SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1c

URS GROUP, INC.

APPROXIMATE BORING LOCATION

N B-8

B-9

B-10

N O

R

TH

S M

O K

E Y

L A

N E

TU

C S

O N

-N O

G

ALE

S H

IG

H

W A

Y

EAST CALLE SONORA

EAST BAFFERT DRIVE

REHABILITATION OF INTERNATIONAL

OUTFALL INTERCEPTOR

U P

R R

N O

G A

LES

W

AS

H

Project Mngr:

Approved By:

Checked By:

Drawn By:

Project No.

Scale:

Date:

File No. Consulting Engineers and Scientists

EXHIBIT

355 S EUCLID, SUITE 107 TUCSON, AZ 85719

FAX. (520) 792-3549PH. (520) 770-1789

BMB

LDB

BMB

BMB

63145034

N/A

63145034.DWG

10/2014

SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1d

N

URS GROUP, INC.

TUCSON-NOGALES HIGHWAY

APPROXIMATE BORING LOCATION

B-11

W

ES

T

ES

CO

ND

ID

O

C

RO

SS

IN

G

B-12

B-13

B-14

W

ES

T

PR

ODU

CE

R

OW

REHABILITATION OF INTERNATIONAL

OUTFALL INTERCEPTOR

UPRR

NOGALES WASH

Project Mngr:

Approved By:

Checked By:

Drawn By:

Project No.

Scale:

Date:

File No. Consulting Engineers and Scientists

EXHIBIT

355 S EUCLID, SUITE 107 TUCSON, AZ 85719

FAX. (520) 792-3549PH. (520) 770-1789

BMB

LDB

BMB

BMB

63145034

N/A

63145034.DWG

10/2014

SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1e

N

URS GROUP, INC.

TUCSO

N-NO

GALES HIGHW

AY

APPROXIMATE BORING LOCATION

B-15

W

ES

T

GOLD

H

ILL

R

OAD

B-16

B-17

B-18

N O

R

TH

O

LD

T U

C

SO

N H

IG

HW

AY

NO

RTH SILVER HILL DRIVE

REHABILITATION OF INTERNATIONAL

OUTFALL INTERCEPTOR

UPRR

N O

G

ALES W

ASH

Approved By:

Project Mngr:

File No.

Date:

Scale:

Project No. EXHIBIT

Consulting Engineers and Scientists

355 SOUTH EUCLID, SUITE 107 TUCSON, ARIZONA 85719

FAX. (520) 792-2539PH. (520) 770-1789

BMB

LDB

BMB

BMB

63145034

NA

63145034.DWG

10/14

SITE PLAN & BORING LOCATIONS DIAGRAM

NOGALES ARIZONA

A-1f

URS GROUP, INC.

APPROXIMATE…