4-Exhibit C 004 Geotechnical Report NB.pdf

Geotechnical | Environmental | Construction Inspection & Testing | Forensic Engineering & Expert Witness

Geophysics | Engineering Geology | Laboratory Testing | Industrial Hygiene | Occupational Safety | Air Quality | GIS

Geotechnical Evaluation Cotton Lane Improvements

Goodyear, Arizona

AZTEC Engineering 501 North 44th Street, Suite 301 | Phoenix, Arizona 85008

June 13, 2023 | Project No. 607589001

Geotechnical | Environmental | Construction Inspection & Testing | Forensic Engineering & Expert Witness

Geophysics | Engineering Geology | Laboratory Testing | Industrial Hygiene | Occupational Safety | Air Quality | GIS

3202 East Harbour Drive | Phoenix, Arizona 85034 | p. 602.243.1600 | www.ninyoandmoore.com

Geotechnical Evaluation Cotton Lane Improvements Goodyear, Arizona

Mr. Jack Fleming, PE AZTEC Engineering 501 North 44th Street, Suite 301 | Phoenix, Arizona 85008

June 13, 2023 | Project No. 607589001

Kenneth Rush, III, PE Senior Engineer

Steven D. Nowaczyk, PE Managing Principal Engineer

KR/SDN/tlp

6/1 3/2

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CONTENTS

1 INTRODUCTION 1

2 SCOPE OF SERVICES 1

3 SITE DESCRIPTION 2

4 AERIAL PHOTOGRAPH REVIEW 2

5 PROPOSED CONSTRUCTION 3

6 FIELD EXPLORATION AND LABORATORY TESTING 3

6.1 Soil Borings 3

6.2 Laboratory Testing 5

6.3 Percolation Testing 5

7 GEOLOGIC CONDITIONS 5

8 SUBSURFACE CONDITIONS 6

8.1 Alluvium 6

8.2 Groundwater 7

8.3 Surface Water 7

9 GEOLOGIC HAZARDS 7

9.1 Land Subsidence and Earth Fissures 7

9.2 Faulting and Seismicity 8

10 GEOTECHNICAL CONSIDERATIONS 8

11 RECOMMENDATIONS 9

11.1 Earthwork 9

11.1.1 Preconstruction Survey 10

11.1.2 Excavation Characteristics 10

11.1.3 Temporary Slope Stability 10

11.1.4 Vertical Shoring and Trench Boxes 11

11.1.5 Bottom Stability 12

11.1.6 Construction Dewatering 12

11.1.7 Subgrade Preparation 12

11.1.8 Backfill Material and Re-use of On-site Soils 12

11.2 Pipe Bedding and Modulus of Soil Reaction (E’) 13

11.3 Engineered Fill Placement and Compaction 14

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11.4 Controlled Low Strength Material (CLSM) 15

11.5 New Pavement Design Summary 15

11.5.1 Design R-value 15

11.5.2 Traffic Volumes and Growth Rates 16

11.5.3 Resilient Modulus 17

11.5.4 Drainage Coefficient 17

11.5.5 Serviceability 17

11.5.6 Flexible Pavement – Standard Deviation and Level

of Reliability 17

11.5.7 Pavement Design Recommendations 17

11.5.8 Structural Number Check 18

11.6 Corrosion 18

11.7 Concrete 19

11.8 Site Drainage 20

11.9 Pre-Construction Conference 20

11.10 Construction Observation and Testing 20

12 LIMITATIONS 20

13 REFERENCES 22

TABLES

1 – Summary of Aerial Photograph Review 2

2 – Test Boring and Percolation Test Locations 4

3 – Summary of Percolation Test Results 5

4 – Modulus of Soil Reaction (E’) for Native Soils 14

5 – Compaction Recommendations 14

6 – Cotton Lane R-Value Summary 16

7 – Traffic Loading Information 16

8 – Recommended Pavement Section 17

9 – SN Summary 18

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FIGURES

1 – Site Location 2 – Exploration Locations 3 – Lateral Earth Pressures for Braced Excavation (Granular Soil) 4 – Pipe Bedding Guidelines

APPENDICES

A – Boring Logs B – Laboratory Testing C – Percolation Test Results

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1 INTRODUCTION

In accordance with scope of work dated November 29, 2022 and your authorization, we have performed a geotechnical evaluation for the Cotton Lane Improvements project in

Goodyear, Arizona. The purpose of our evaluation was to assess the subsurface conditions in order to provide geotechnical recommendations for design and construction. This report presents the results of our evaluation and our geotechnical conclusions and recommendations regarding the proposed construction.

2 SCOPE OF SERVICES

The scope of our services for this project generally included:

• Reviewing readily available geotechnical data, aerial photographs, and published geologic literature, including maps and reports pertaining to the project site and vicinity.

• Conducting a geologic reconnaissance of the site.

• Obtaining permits from the City of Goodyear (COG) to conduct the field work.

• Arranging for appropriate traffic control services to be implemented during our field work activities.

• Marking out the boring locations at the project site and notifying Arizona 811 of the boring locations prior to drilling.

• Drilling, logging, and sampling nine exploratory borings to depths of approximately 9 to 15 feet below ground surface (bgs). The boring logs are presented in Appendix A.

• Collecting soil samples in the borings at approximately 2.5 and 5.0-foot intervals using ASTM International (ASTM) Methods D1586 (Standard Penetration Test with split-spoon barrel sampling of soils) and D3550 (ring-lined barrel sampling of soils) for laboratory testing and analysis.

• Performing laboratory tests on selected samples obtained from the borings to evaluate in-situ moisture content and dry density, gradation, Atterberg limits, consolidation, maximum density and corrosivity characteristics (including pH, minimum electrical resistivity, and soluble sulfate and chloride contents). The in-situ moisture content and dry density results are presented on the boring logs in Appendix A. The remainder of the laboratory test results are presented in Appendix B.

• Performing three field percolation tests at depth of approximately 3 feet bgs. The percolation test results are presented in Appendix C.

• Preparing this report presenting our findings, conclusions, and recommendations regarding the design and construction of the project.

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Our scope of services did not include environmental consulting services such as hazardous waste sampling or analytical testing at the site. A detailed scope of services and estimated fee for such services can be provided upon request.

3 SITE DESCRIPTION

The project alignment extends along the east side of the existing Cotton Lane roadway from

Estrella Parkway to the Gila River bridge crossing in Goodyear, Arizona (Figure 1). At the time of our evaluation, the site consisted of asphalt concrete (AC) paved roadway with partially paved northbound shoulder and the southbound lane had concrete curb with no shoulder. The project alignment was partially-graded and bound by undeveloped desert to the east and west. The Gila

River bridge was located at north end of the project site and the Estrella Parkway roundabout was located at the south end of the project site.

According to the Perryville, Arizona 7.5-Minute United States Geological Survey Topographic

Quadrangle Map (2021), the elevation of the project alignment ranges from approximately

900 feet relative to mean sea level (MSL) at the northern limits near Gila River Bridge to approximately 990 feet MSL at the southern limits near Estrella Parkway. Based on information from this topographic quadrangle map, the ground surface at the site vicinity gently slopes from the south down to the north.

4 AERIAL PHOTOGRAPH REVIEW

Aerial photographs dated 1937 through 2021 from the Maricopa County website and Google Earth were reviewed for this project. A summary of the observations noted for each aerial photograph is presented in Table 1.

Table 1 – Summary of Aerial Photograph Review Photograph

Date(s) Site Adjacent Properties

1937, 1949, 1953, 1976, 1986

Undeveloped desert and several drainage crossing. Agricultural land near Gila River end of alignment.

North: Gila River.

South: Undeveloped desert.

East: Undeveloped desert.

West: Undeveloped desert.

1993, 1996, 1998, 200-2005

Undeveloped desert and several drainage crossing. Agricultural land near Gila River end of alignment.

North: Gila River.

South: Estrella Parkway Alignment. Undeveloped desert. Residential development.

East: Undeveloped desert.

West: Undeveloped desert.

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Table 1 – Summary of Aerial Photograph Review Photograph

Date(s) Site Adjacent Properties

2006, 2007

Cotton Lane construction at Estrella Parkway. Cotton Lane bridge over Gila River construction.

North: Gila River Bridge.

South: Estrella Parkway Alignment. Undeveloped desert. Residential development.

East: Undeveloped desert.

West: Undeveloped desert.

2008, 2009, 2010-2021

Cotton Lane constructed and several basins along southbound alignment (2009), similar to site today.

North: Gila River Bridge.

South: Estrella Parkway Alignment. Undeveloped desert. Residential development.

East: Undeveloped desert.

West: Undeveloped desert.

5 PROPOSED CONSTRUCTION

The project consists of improvements to an approximately 1.5-mile-long segment of Cotton Lane from Estrella Parkway to the Gila River bridge crossing. We understand that Cotton Lane is considered a parkway, however it will be constructed as a major arterial. The proposed improvements will construct an asphaltic concrete northbound lane for the existing roadway to incorporate two travel lanes. Also included are signage and pavement markings, roadway infrastructure for drainage improvements, and needed roadway improvements.

6 FIELD EXPLORATION AND LABORATORY TESTING

The following sections summarize our field exploration and laboratory testing activities.

6.1 Soil Borings

On April 3, 2023, Ninyo & Moore conducted a subsurface exploration at the site in order to observe the subsurface conditions and to collect soil samples for laboratory testing. Our exploration consisted of drilling, logging, and sampling nine small-diameter borings, denoted as shown below in Table 2. The borings were targeted to extend 15 feet deep; hoverer auger refusal on cobbles, possible boulders or possible bedrock was encountered within some of the borings prior to achieving that depth. Surface elevations at these exploration locations were estimated from

USGS. Additionally, the approximate locations of our explorations are presented on Figure 2.

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Table 2 – Test Boring and Percolation Test Locations

Boring Designation

Approximate Location Approximate Elevation(1)

Exploration Depth Project

Location/Alignment Latitude Longitude (feet) (feet)

B-1 33.36318885 -112.4221901 981 9(2) Cotton Lane

B-2 33.36565339 -112.4225042 971 9(2) Cotton Lane

B-3 33.36836041 -112.4221884 952 14 Cotton Lane

B-4 33.37103428 -112.4214523 933 9(2) Cotton Lane

B-5 33.37371434 -112.4207053 925 14 Cotton Lane B-6 33.37640381 -112.4199863 927 9(2) Cotton Lane B-7 33.37904565 -112.4193163 932 11(2) Cotton Lane B-8 33.3815422 -112.4206577 902 15 Cotton Lane B-9 33.38407791 -112.4218358 899 15 Cotton Lane P-1 33.3639 -112.4227 N/A 3 Existing Basin

P-2 33.3688 -112.4225 N/A 3 Existing Basin

P-3 33.38101375 -112.4208572 N/A 3 Existing Basin

Note:

1Vertical Datum – NAVD88.

2Auger refusal on cobbles, possible boulders or possible bedrock was encountered.

The borings were advanced using either a CME-75 truck-mounted drill rig equipped with

HSAs drilling equipment. The borings extended to depths ranging from 9 to 15 feet bgs. Bulk and relatively undisturbed soil samples were collected at selected intervals. Detailed descriptions of the soils encountered are presented on the boring logs in Appendix A.

Ninyo & Moore personnel logged the borings in general accordance with the Unified Soil

Classification System and ASTM International (ASTM) D2488 by observing cuttings and drive samples. Detailed descriptions of the drive sample method used and corresponding ASTM procedure are presented on the cover page of Appendix A. Collected ring samples were trimmed in the field, wrapped in plastic bags, and placed in cylindrical plastic containers to retain in-place moisture conditions. Similarly, the Standard Penetration Test split-spoon samples were placed in resealable bags to help preserve their natural moisture. Bulk samples were also collected from the HSA cuttings and placed in large plastic bags. The selected intervals at which the bulk soil samples were collected are provided on the boring logs in Appendix A.

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6.2 Laboratory Testing

The soil samples collected from our drilling activities were transported to the Ninyo & Moore laboratory in Phoenix for geotechnical laboratory testing. The testing included in-situ moisture content and dry density, gradation, Atterberg limits, consolidation, maximum density, and corrosivity characteristics (including pH, minimum electrical resistivity, soluble sulfates, and chlorides). The corrosivity characteristic testing was performed on bulk soil samples. The results of the in-situ moisture content and dry density testing are presented on the boring logs in

Appendix A. A description of each laboratory test method, ASTM standards and the remainder of the test results are presented in Appendix B.

6.3 Percolation Testing

In order to assist in the evaluation of the infiltration rates at the site, Ninyo & Moore performed three field infiltration (percolation) test denoted as P-1, P-2 and P-3 (Figure 2). The procedure consisted of the insertion of a +/-10-inch diameter impervious casing into undisturbed soil at the depth of +/-3 feet, followed by pre-wetting. The test was continued after the pre-wetting period by refilling the casing with an approximate 6-inch column of water and monitoring the drop in water level as a function of time until relatively steady-state conditions were achieved. A summary of the results are presented in the table below.

Table 3 – Summary of Percolation Test Results

Designation Site Location Factored Percolation

Rate (inch/hour)

P-1 See Table 2 and Figure 2 0.86 P-2 See Table 2 and Figure 2 0.86 P-3 See Table 2 and Figure 2 0.86

The test procedure and the correction factors used were in general accordance with

Maricopa County “Drainage Policies and Standards for Maricopa County”, dated 2018. The results of this test are presented in Appendix C and should be viewed as approximate as they are based on the conditions at the location at the time of our test.

7 GEOLOGIC CONDITIONS

The project site is located in the Sonoran Desert Section of the Basin and Range physiographic province, which is typified by broad alluvial valleys separated by steep, discontinuous, subparallel mountain ranges. The mountain ranges generally trend north-south and northwest-southeast. The basin floors consist of alluvium with thickness extending to several thousands of feet.

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The basins and surrounding mountains were formed approximately 10 to 18 million years ago during the mid- to late-Tertiary. Extensional tectonics resulted in the formation of horsts

(mountains) and grabens (basins) with vertical displacement along high-angle normal faults.

Intermittent volcanic activity also occurred during this time. The surrounding basins filled with alluvium from the erosion of the surrounding mountains as well as from deposition from rivers.

Coarser-grained alluvial material was deposited at the margins of the basins near the mountains.

The surficial geology of the site is described as being Pleistocene aged (10,000 years to 790,000 years) alluvial fan, terrace, and basin floor deposits with Proterozoic (1600 Ma to 1800 Ma) granitic rocks outcrops. The alluvial fan and terrace deposits are generally unconsolidated to weakly consolidated, silts, poorly sorted gravels and sand and may overly stage III to IV calcic horizons

(Demsey, 1989). Granitic rocks include granite, granodiorite, tonalite, quartz diorite, diorite, and gabbro with steep, northeast-striking foliation and jointing. Descriptions of the soils encountered during our subsurface exploration are presented in Section 8.

8 SUBSURFACE CONDITIONS

Our knowledge of the subsurface conditions at the project site is based on the results of our explorations and our understanding of the general geology of the area. The boring logs contains our field test results, as well as our interpretation of the conditions anticipated to exist between actual samples retrieved. Therefore, the boring logs contains both factual and interpretive information. Lines delineating subsurface strata on the boring logs are intended to group soils having similar engineering properties and characteristics. They should be considered approximate, as the actual transition between soil types may be gradual. Note that relative densities of coarse-grained soils and non-elastic silts (non-plastic in this report) include very loose, loose, medium dense, dense and very dense. Consistency of elastic silts and clays include very soft, soft, firm, stiff, very stiff, and hard. Detailed stratigraphic information as well as a key to the soil symbols and terms used on the boring logs are provided in Appendix A.

8.1 Alluvium

Alluvium was encountered at the surface of our borings and extended to the termination depths.

The alluvium generally consisted of heterogeneous interlayered deposits of medium dense to very dense, clayey sand (SC), silty sand (SM), poorly graded gravel (GP), and poorly graded sand with silt (SP-SM) in our borings to the termination depths. Scattered caliche nodules, gravel, possible cobbles and possible bedrock in the form of decomposed granite were also observed in our borings. Auger refusal was encountered in several of our borings.

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8.2 Groundwater

Groundwater was not encountered in our borings during our field exploration along the roadway alignment. Based on well data provided by the Arizona Department of Water Resources (ADWR) for wells along the proposed alignment, the depth to the regional groundwater table is approximately 10 feet bgs or deeper near Gila River and generally 21 feet bgs or deeper.

However, groundwater levels may fluctuate due to the close proximity to Gila River, adjacent ditches and canals, seasonal variations, irrigation, groundwater withdrawal or injection, and other factors.

8.3 Surface Water

Based on the information presented on the Federal Emergency Management Agency Online Map

Viewer, generally the sites lie within Flood Zone X, which is described as an area with

0.2 percent or more chance of flooding each year, in the form of sheet flow with average depths of less than 1-foot. As such, surface water flows and/or seepage may be encountered within the project limits during rain events, and may need to be mitigated during construction. The proposed waterline crosses several washes denoted as Zone A, which is described as an area with

1% probability of flooding every year (100-year floodplain). Since this area of the site is located within a documented floodplain, surface flows may be encountered depending on the construction schedule.

9 GEOLOGIC HAZARDS

The following sections describe regional geologic hazards, including land subsidence, earth fissures, and faults.

9.1 Land Subsidence and Earth Fissures

Groundwater depletion, due to groundwater pumping, has caused land subsidence and earth fissures in numerous alluvial basins in Arizona. It has been estimated that subsidence has affected more than 3,000 square miles and has caused damage to a variety of engineered structures and agricultural land (Schumann and Genualdi, 1986). From 1948 to 1983, excessive groundwater withdrawal has been documented in several alluvial valleys where groundwater levels have been reportedly lowered by up to 500 feet. With such large depletions of groundwater, the alluvium has undergone consolidation resulting in large areas of land subsidence.

In Arizona, earth fissures are generally associated with land subsidence and pose an on-going geologic hazard. Earth fissures generally form near the margins of geomorphic basins where significant amounts of groundwater depletion have occurred. Earth fissures form due to tensional

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Based on our field reconnaissance, aerial photograph review, and our review of published literature, earth fissures are not underlying, or adjacent to the property. The closest documented earth fissure to the site is approximately 9 miles to the north and, therefore, earth fissures are not expected to be a constraint to the project.

9.2 Faulting and Seismicity

The site lies within the Sonoran zone, which is a relatively stable tectonic region located in southwestern Arizona, southeastern California, southern Nevada, and northern Mexico

(Euge et al., 1992). This zone is characterized by sparse seismicity and few Quaternary faults.

Based on our field observations, review of pertinent geologic data, and analysis of aerial photographs, faults are not located on or adjacent to the property.

The closest documented Quaternary fault to the site is the Sand Tank Fault, situated approximately 31 miles to the south of the site. The Sand Tank Fault is situated along the western piedmont of the Sand Tank Mountains, to the southeast of Gila Bend. The fault is a northeast-striking normal fault that dips to the northwest. Documented movement along this fault was as recent as approximately 70,000 years ago during the Late Pleistocene epoch. The slip-rate category of this fault is less than 0.2 millimeters per year (Pearthree, 1998).

10 GEOTECHNICAL CONSIDERATIONS

Based on the results of our subsurface evaluation, laboratory testing, and data analysis, it is our opinion that the proposed construction is feasible from a geotechnical standpoint, provided that the recommendations of this report are incorporated into the design and construction of the proposed project, as appropriate. Geotechnical considerations include the following:

• In general, the near-surface soils are considered to be rippable with heavy-duty excavation equipment. However, scattered caliche nodules, gravel, cobbles, possible boulders and decomposed granite were encountered in our borings, which may be more difficult to excavate, will slow the rate of excavation, and/or necessitate the use of alternate methods of excavation (e.g., blasting, pneumatic hammering, rock teeth for ripping, rock saws, etc.).

• Due to the widely spaced nature of our borings, soil conditions that differ from what was encountered in our borings may be encountered during construction.

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• Due to the heterogeneity of the soil conditions at the site, sloughing of soils during construction may occur where the excavation abut other fill soils from adjacent utilities. In addition, vibration caused by the influence of vibration from nearby traffic may cause sloughing into excavations.

• An earthwork (shrinkage) factor of approximately 5 to 15 percent if the on-site soils are re-used as fill.

• Imported soils and soils generated from on-site excavation activities that exhibit a very low-to low expansion potential can generally be used as engineered fill, provided the oversized or heavily cemented materials are either broken down or wasted. On the basis of our evaluation, many of the on-site soils will be suitable for re-use as engineered fill.

• Groundwater may rise to higher levels than what was reported above due to seasonal fluctuations. Based on groundwater readings from monitoring wells, groundwater is not expected to be a construction restraint. Furthermore, since the site is located within a documented floodplain, surface flows may be encountered depending on the construction schedule.

• Due to the potential for perched groundwater near drainage crossings and the presence of cohesionless soils, care should be taken prior to excavation. The contractor should evaluate the depth of perched groundwater, the need for shoring, and the need for dewatering prior to commencing any excavation.

• The subgrade soils at the sites are corrosive to ferrous metals and the sulfate content of the soils presents a negligible sulfate exposure to concrete.

• No active faults, fissures or land subsidence feature, or other geologic hazards are reported underlying or immediately adjacent to the site.

11 RECOMMENDATIONS

The following sections present our geotechnical recommendations and were developed based on our understanding of the proposed construction (Section 5), the observed subsurface conditions

(Section 8), and our experience. In general, the recommendations and guidelines outlined in the

Maricopa Association of Governments (MAG) Standard Specifications and Details and/or any

COG supplement should be used unless recommended differently herein.

If the proposed construction is changed from that discussed herein or subsurface conditions other than those shown on the boring logs (Appendix A) are observed at the time of construction, Ninyo & Moore should be retained to conduct a review of the new information and to evaluate the need for additional recommendations.

11.1 Earthwork

The following sections present our earthwork recommendations for this project. In general, MAG and any COG construction stands and specification are expected to apply, unless otherwise noted herein.

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11.1.1 Preconstruction Survey

It may be desirable to recognize and designate utilities, underground structures, or other features that are near the planned construction and to survey or document

(e.g., photographs, video, official documentation, etc.) their condition before project construction is started. The findings of the survey could be used to document any existing utility damage prior to construction of the proposed project. Such a survey might include limited pot holing or excavation of existing lines using a vacuum truck or hand dig methods.

11.1.2 Excavation Characteristics

Our evaluation of the excavation characteristics of the on-site materials is based on the results of our exploratory borings, site observations, and experience with similar materials. In our opinion, the surface soils may be excavated using conventional heavy-duty earthmoving or excavation equipment; however, due to the widely-spaced nature of our borings, soil conditions encountered during construction may differ from what were encountered in our borings. In addition, scattered caliche nodules, gravel, cobbles, possible cobbles and decomposed granite and were observed in our borings and should be expected to be encountered at various depths along the project alignment.

Equipment and procedures should be used that do not cause significant disturbance to the excavation bottoms. If the subgrade becomes disturbed, it should be compacted before placing the backfill material.

The bottoms of trench excavation should expose competent soils and should be dry and free of loose, soft, or disturbed soil. Any soft, wet, weak, or deleterious materials should be over-excavated to expose strong competent soils.

11.1.3 Temporary Slope Stability

Excavation for this project should be designed in accordance with current applicable, state, and federal trenching guidelines, including the Occupational Safety and Health

Administration (OSHA) requirements for excavation presented in 29 CFR Part 1926

(Revised July 1992), Subpart P, Excavations.

For planning purposes, and according to OSHA soil classification, a “Type C” soil should be considered for this project due to the loose and cohesionless (e.g., sandy and gravelly) nature of the alluvial soils. In general, temporary sloped excavation in competent “Type C” soils should be inclined no steeper than 1.5:1 (H:V), however flatter slopes or shoring may be needed.

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Details for open-cut slopes and shoring based on soil type and groundwater conditions are provided in the latest amended OSHA regulations. These details apply to temporary open-trench excavation up to 20 feet deep. Trenches more than 20 feet deep, or in areas where seepage is encountered should be designed by the contractor’s engineer based on alignment-specific geotechnical analyses. Upon excavation, soil classifications and excavation performance should be evaluated in the field by the geotechnical consultant in accordance with OSHA regulations.

Temporary excavation that encounter groundwater seepage or surface runoff, if any, may need shoring or dewatering. Flatter slopes or bracing should be used if excessive sloughing or raveling is observed. If material is stored or equipment is operated near an excavation, stronger shoring should be used to resist the extra pressure due to superimposed loads.

11.1.4 Vertical Shoring and Trench Boxes

Due to previously described soil conditions, the proposed depth of the excavation, and presence of existing utilizes and structures (e.g., roadways, utilities, and buildings), it may be preferable to shore or brace the trenches rather than using open cuts to the base of the excavations. Temporary earth retaining systems will be subjected to lateral loads resulting from earth pressures. Shored and braced trench excavation may be designed suing the parameters on Figure 3.

The earth pressure values presented on Figure 3 assume that spoils from the excavation or other surcharge loads will not be placed above the excavation within a 1:1 (H:V) plane extending up and back from the base of the excavation. If spoil piles are placed closer than this to the braced excavation, the resulting surcharge loads should be considered in the bracing design. We recommend that an experienced structural engineer design the shoring system. The shoring parameters presented in this report should be considered as guidelines.

The contractor should anticipate repairing cracks in pavements adjacent to shored portions of the excavation due to anticipated lateral displacements of the shoring system. Horizontal and vertical movements of the shoring system should be monitored by a surveyor and the results reviewed by the project Geotechnical Engineer.

Trench boxes may also be a suitable alternative to laying back the side walls; however, due to the presence of granular soils, the excavations may not stand open long enough to install the trench boxes. The contractor should be prepared to deal with these soil conditions and plan accordingly. Once installed, some sloughing is possible at the ends of the trench box;

therefore, any loose material should be removed prior to backfilling of the trench.

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11.1.5 Bottom Stability

Bottom of the excavation should be stable for the purpose of the planned construction.

However, if excavations are open during a heavy rain event, the bottom of the trench may become statured and unstable. Dewatering as discussed in Section 11.1.6.1.6 below may be anticipated in such events.

11.1.6 Construction Dewatering

Excavations that encounter seepage or surface run-off could be dewatered by pumping the water out and away from the excavation. Such zones may call for more aggressive means of dewatering and consultation with a qualified expert. Discharge of water from the excavation to natural drainage channels, if needed, may entail securing a special permit.

11.1.7 Subgrade Preparation

As noted in this report, gravel and cobbles were encountered in our borings. In order to create a more uniform surface, we recommend the native subgrade soils be scarified, moisture-conditioned, and re-compacted to a depth of 6 to 8 inches below the new aggregate base layer for the new pavement or leveling course of new flatwork. This scarified zone should extend 1 foot beyond the lateral limits of the new pavement or flatwork.

Following the improvements as described above, , the resulting exposed surface should be proof-rolled and carefully evaluated for the presence of voids and miscellaneous construction debris material by Ninyo & Moore. Based on this evaluation, additional remediation may be needed. This could include additional over-excavation or scarification of the exposed surface.

This additional remediation, if needed, should be addressed by Ninyo & Moore during the earthwork operations.

11.1.8 Backfill Material and Re-use of On-site Soils

On-site and imported soils that exhibit relatively low PI and very low to low expansive potential are generally suitable for re-use as select, engineered fill. Relatively low PI are defined as a

PI value of 15 or less, as evaluated by ASTM D4318. For this project, soils with a PI 15 or less may be re-used as trench backfill.

In addition, suitable fill should not include organic material, construction debris, or other non-soil fill materials. Rock particles and clay lumps should not be larger than 4 inches in dimension. This material should be disposed of off-site or in non-structural areas.

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Based on MAG guidelines, the definition of “granular backfill” material is material which the sum of the PI and the percent of material passing a No. 200 sieve does not exceed 23.

Fill materials in contact with ferrous metals should also have low corrosion potential

(minimum resistivity more than 2,000 ohm-cm, chloride content less than 25 parts per million

[ppm]). Fill material in contact with concrete should have a soluble sulfate content of less than

0.1 percent.

The Atterberg limits tests performed on soil samples obtained from our borings resulted in PI values of 0 (non-plastic, NP). Based on our test results, the onsite soils are considered suitable for re-use as engineered fill for this project. Additional field sampling and laboratory testing should be conducted by the contractor during construction to better screen for any unsuitable materials.

Generated excavation materials that contain oversize fraction shall not be used as engineered fill unless the material meets the criteria given above and/or the oversize fraction has been processed and removed from the material. Imported backfill material, if utilized, should meet the criteria for imported fill as presented in this report. An earthwork (shrinkage) factor of 5 to 15 percent for the on-site soils is estimated.

11.2 Pipe Bedding and Modulus of Soil Reaction (E’)

We recommend the pipeline being installed using cut-and-cover techniques be supported on

4 inches, or 1/12 the outside diameter of the pipe, whichever is more, of granular bedding material such as sand and gravel, or crushed rock meeting the MAG Section 702 Standard Specifications

(pea gravel or crushed ships are not acceptable). This bedding/pipe-zone backfill should extend

1 foot above the pipe crown. Pipe bedding guidelines are presented on Figure 4. Case should be taken not to allow voids to form beneath the pipe (i.e., the pipe haunches should be continuously supported) to void damaging the pipelines. This may involve fill placement by hand or small compaction equipment. The pipe bedding should be moisture conditioned and compacted as discussed in Section 11.3.

The modulus of soil reaction (E’) is used to characterize the stiffness of the soil backfill placed on the sides of buried pipelines for the purpose of evaluating deflection caused by the weight of the backfill over the pipe. For granular backfill soils for pipes, we recommend using an E’ value of

1,200 pounds per square inch (psi).

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E’ for native materials will vary with material type and stiffness of the trench sidewalls.

Approximate values of E’ for the materials encountered in our borings based on US Bureau of

Reclamation (2013) are presented in Table 4 below:

Table 4 – Modulus of Soil Reaction (E’) for Native Soils

Trench Wall Soil Classification

(USCS)

Approximate E’ (psi)

Loose / Firm Medium Dense / Stiff

Dense – Very Dense / Very Stiff-Hard

Silty/Clayey Sand and Gravel

(SM, SC, SC/SM, GC) 400 700 2500

Sand (SP, GP) 700 1000 4000

11.3 Engineered Fill Placement and Compaction

Engineered fill should be moisture conditioned within the moisture range shown below in Table 5 and mechanically compacted to the percent compaction shown. Engineered fill should generally be placed in 8-inch-thick loose lifts such that each lift is firm and non-yielding under the weight of construction equipment. Jetting and other forms of water consolidation are not recommended for this project.

Special care should be exercised to avoid damaging the pipe or other structures during the compaction of the backfill. Compaction should be accomplished in a manner that inhibits surface water infiltration as well as conveyance of subsurface moisture due to the intersection of natural drainages along the alignment.

Table 5 – Compaction Recommendations

Engineered Fill Description Percent Compaction per ASTM D698 Moisture Content

Scarified Subgrade Below Pavement and Flatwork 95 percent

±2 percent of optimum

Pipe Bedding

Granular Trench Backfill – Within 2 feet below pavement 100 percent

Non-Granular Trench Backfill – Within 2 feet below pavement 100 percent

Trench Backfill – Deeper than 2 feet below pavement 95 percent

AB – Below Pavement 100 percent Note:

*Based on MAG guidelines, the definition of “granular backfill” materials is material in which the sum of the PI and the percent of material passing a No. 200 sieve does not exceed 23.

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11.4 Controlled Low Strength Material (CLSM)

It is our opinion that the backfill zone may be filled with CLSM. CLSM consists of a fluid, workable mixture of aggregate, Portland cement, and water. The use of CLSM has some advantages:

• A Narrower backfill zone can be used, thereby minimizing the quantity of soil to be excavated and possible reducing disturbance to near-by traffic.

• Relatively higher E’ values may be used (E’ = 2,500 psi).

• The support given to the connecting pipes is generally better.

• Because little compaction is needed to place CLSM, there is less risk of damaging the connecting pipes.

• CLSM can be batched to flow into irregularities in the trench bottom and walls.

The CLSM design mix should be in accordance with current MAG or Standard Specifications for

Public Works Construction standards. Additional mix design information can be provided upon request. The 28-day strength of the material should be no less than 50 psi and no more than

120 psi.

Buoyant or uplift forces on the piping should be considered when using CLSM and prudent construction techniques may result in multiple pours to avoid inducing excessive uplift forces.

Sufficient time should be provided to allow the CLSM to cure before placing additional lifts of

CLSM or trench backfill.

11.5 New Pavement Design Summary

The pavement section recommended below is based on the design R-value, traffic information

Aztec Engineering, and the pavement design procedures outlined in the MCDOT Roadway

Design Manual and COG Engineering Design Standards and Policies Manual (EDS & PM).

11.5.1 Design R-value

Tables 6 summarizes the measured and correlated R-value on selected soil samples obtained within the upper 5.0 feet of the planned finished roadway profile from various borings within the project limits. The mean R-value presented below are based on the weighted average using the guidelines in the MCDOT Roadway Design Manual for correlated

R-values.

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Table 6 – Cotton Lane R-Value Summary

Boring No. Sample Depth (ft) Rc1

B-1 1.0 – 2.5 70 B-2 3.5 - 4.3 70 B-3 1.0 – 1.8 70 B-4 3.5 - 5.0 70 B-5 1.0 – 2.5 70 B-6 3.5 - 4.0 70 B-7 1.0 – 2.5 70 B-8 3.5 - 5.0 70 B-9 1.0 – 2.0 70

Rc = 70 Note:

1 Correlated R-value (Rc);

We recommend a design R-value of 70 be used for this project. This value is based on the above-mentioned laboratory results and assumes the pavement subgrade soils will be prepared as recommended herein. We recommend that imported soils (if needed) placed within 3 feet of the finished roadway subgrade demonstrate a construction control R-value of

70 or more.

11.5.2 Traffic Volumes and Growth Rates

Traffic loading information for the proposed Cotton Lane improvements obtained from the

Aztec Engineering for year 2019 was 7,855 vehicles per day. Assuming a growth rate of

2 percent a traffic loading of 8,673 vehicles per day was calculated for the year 2024. The table below presented the traffic loading information used for this project for a 20 year design life.

Table 7 – Traffic Loading Information

Roadway 2024 ADT % Growth1 % Trucks1 Estimated ESAL’s

Cotton Lane 8,673 2.0 5.0 4,206,000 Note:

1Assumed values.

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11.5.3 Resilient Modulus

A design R-value of 70 was utilized in our analysis of the new pavement sections. Based on the design R-value and a seasonal variation factor of 1.0, the resilient modulus of 26,000 pounds per square inch (psi) was used for this roadway since the calculated resilient modulus was more than 26,000 psi.

11.5.4 Drainage Coefficient

A drainage coefficient of 1.0 was obtained from Table 10.2.7 in the Roadway Design Manual.

11.5.5 Serviceability

For major arterial Cotton Lane, an initial serviceability of .5 and a terminal serviceability of

2.5 were used for design the of pavements. The resulting serviceability index loss is 2.0.

11.5.6 Flexible Pavement – Standard Deviation and Level of Reliability

A standard deviation of 0.45 was used for the design of flexible pavement in accordance with current MCDOT policy. Based on Table 10.2.4 for major arterial roads, a reliability of 95 percent was utilized for the design of Cotton Lane. A standard normal deviation (ZR) value of

-1.645 was utilized.

11.5.7 Pavement Design Recommendations

The following section presents our design parameters and recommendations for the new pavements for Cotton Lane. We evaluated the minimum pavement section thickness in accordance with COG Standard Detail G-3216 and the anticipated traffic loading for this major arterial. For this project we utilized the pavement design method noted in the MCDOT

Roadway Design Manual. We recommend that the pavement section provided in the table be used for pavement improvements associated with this project.

Table 8 – Recommended Pavement Section Pavement Section

AC (in) (3/4” Mix)1

AC (in) (3/4” Mix)1

AB

(in)

Pavement Section Thickness (in)

Calculated

SN

Cotton Lane 3.0 3.0 12.0 18.0 3.96

Note:

1 l Minimum from COG Standard Detail G-3216 for Major Arterial.

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We recommend that the AC mix design be performed in accordance with MAG Section 710.

The AB should meet the specifications as outlined in MAG Section 702. AB underlying the pavements should be moisture conditioned and compacted to 100 percent relative compaction at a moisture content generally near optimum.

The pavement sections presented in this section are based on the expected traffic and the existing subgrade soil conditions, and are expected to function with periodic maintenance and overlays if good drainage is provided and maintained. In Arizona, pavement sections often become brittle and experience cracking before the design life is attained, therefore, the asphalt surface needs to be maintained and sealed periodically over its life. If the subgrade soils experience a significant increase in moisture content, accelerated pavement deterioration and increased maintenance should be anticipated. Pavement and base course materials should not be placed when the subgrade is wet. Good surface drainage should be provided away from the edges of paved areas to minimize lateral moisture transmission into the subgrade soils.

11.5.8 Structural Number Check

In accordance with the procedure for flexible pavement design noted in the MCDOT Roadway

Design Manual, and using the above-mentioned parameters, we checked the minimum and calculated structural numbers (SN) for the AC roadway section, as presented below.

Table 9 – SN Summary

Roadway Calculated Minimum

SN

Calculated SN of New Pavement

Cotton Lane 2.85 (2.881) 3.96 Note:

1 Minimum SN for a Major Arterial per MCDOT Roadway Design Manual.

11.6 Corrosion

The corrosion potential of the on-site materials was analyzed to evaluate its potential effect on the ferrous metals used for this project. Corrosion potential was evaluated suing the results of laboratory testing on a sample obtained during our subsurface evaluation that was considered representative of soils along the project alignment.

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Laboratory testing consisted of pH, minimum electrical resistivity, and chloride and soluble sulfate contents. The pH and minimum electrical resistivity tests were performed in general accordance with Arizona Test 236, while the sulfate and chloride content tests were performed in accordance with Arizona Test Method 733 and 736, respectively. The results of the corrosivity tests are presented in Appendix B.

The soil pH value of the tested samples ranged from 8.7 to 9.3, which is considered to be alkaline.

The minimum electrical resistivity ranges from 710 to 898 ohm-cm, which is considered to be corrosive to ferrous materials. The chloride content ranges from 252 to 322 ppm, which also is considered to be corrosive to ferrous metals. The soluble sulfate content of the soil samples ranged from 0.0015 to 0.0020 percent by weight, which is considered to represent negligible sulfate exposure for concrete.

The results of the laboratory testing indicate that the on-site materials are considered corrosive to ferrous materials. If ductile iron is proposed to be installed along a portion of the alignment, we recommend that topsoil, organic soils, existing fill soils, and mixtures of sand and clay not be placed adjacent to buried metallic utilities. Rather, we suggest a relatively clean sand and/or gravel, or CLSM, be placed around buried metal piping. Also, buried utilities of different metallic construction and/or operating temperatures should be electrically isolated from each other to minimize galvanic corrosion problems. In addition, new piping should be electrically isolated from old piping so that the old metal will not increase the corrosion rate of the new metal. A corrosion specialist should be consulted for further recommendations.

11.7 Concrete

Laboratory chemical testing perfumed on select samples of on-site soils indicated a sulfate content ranging from 0.0015 to 0.0020 percent by weight. Notwithstanding the sulfate test results and due to the limited number of chemical tests performed, as well as our experience with similar soil conditions and regional practice, we recommend that “Type II” cement be used for the construction of concrete structures at this site. Due to potential uncertainties as to the use of reclaimed irrigation water, or topsoil that may contain higher sulfate contents, pozzolan or admixtures designed to increase sulfate resistance may be considered.

The concrete should have a water-cementitious materials ratio of no more than 0.50 by weight for normal weight aggregate concrete. The structural engineer should ultimately select the concrete design strength based on project-specific loading conditions. However, higher strength concrete may be selected for increased durability and resistance to shrinkage cracking.

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11.8 Site Drainage

Surface drainage should be provided to divert water away from pavements and off site. Surface water should not be permitted to drain toward the structures or to pond adjacent on pavement areas. Positive drainage is defined as a slope of 2 percent or more for a distance of 5 feet or more away from the structures. Downspouts should discharge to drainage systems away from pavements, and flatwork. Infiltration ponds, if constructed, should be located away from structures, pavements, and flatwork.

11.9 Pre-Construction Conference

We recommend that a pre-construction conference be held. Representatives of the owner, civil engineer, the geotechnical consultant, and the contractor should be in attendance to discuss the project plans and schedule. Our office should be notified if the project description included herein is incorrect, or if the project characteristics are significantly changed.

11.10 Construction Observation and Testing

During construction operations, we recommend that a qualified geotechnical consultant perform observation and testing services for the project. These services should be performed to evaluate exposed subgrade conditions, including the extent and depth of overexcavation, to evaluate the suitability of the on-site materials for use as fill and to observe placement and test compaction of fill soils. If another geotechnical consultant is selected to perform observation and testing services for the project, we request that the selected consultant provide a letter to the owner, with a copy to Ninyo & Moore, indicating that they fully understand our recommendations and they are in full agreement with the recommendations contained in this report. Qualified subcontractors utilizing appropriate techniques and construction materials should perform construction of the proposed improvements.

12 LIMITATIONS

The field evaluation, laboratory testing, and geotechnical analyses presented in this geotechnical report have been conducted in general accordance with current practice and the standard of care exercised by geotechnical consultants performing similar…