3-ATTACHMENT C - GEOTECHNICAL REPORT.pdf

www.ATEKEC.com

111 South Weber Drive, Chandler, Arizona 85226 – Office 480-659-8065 2015 North Forbes Boulevard, Suite 103, Tucson, Arizona 85745 – Office 520-638-8142

GEOTECHNICAL EXPLORATION REPORT

CROSSROAD EAST SEWER LIFT

STATION

HAYDEN ROAD AND ARIZONA STATE

ROUTE 101 LOOP

SCOTTSDALE, ARIZONA

Prepared for:

Wilson Engineers 1620 West Fountainhead Parkway Suite 501 Tempe, Arizona 85282

Prepared by:

ATEK Engineering Consultants, LLC 111 South Weber Drive, Suite 1 Chandler, Arizona 85226

ATEK Project # 190100

October 17, 2019

Expires 9/30/2021

ATTACHMENT C

111 SOUTH WEBER DRIVE, SUITE 1 WWW.ATEKEC.COM P (480) 659-8065

CHANDLER, AZ 85226 F (480) 656-9658

October 17, 2019 ATEK Project #190100

Srikanth Yamani, P.E., Project Manager Wilson Engineers 1620 West Fountainhead Parkway, Suite 501 Tempe, Arizona 85282

Regarding: Geotechnical Exploration Report

Project: Crossroad East Sewer Lift Station

Hayden Road and Arizona State Route 101 Loop Scottsdale, Arizona

Dear Mr. Yamani:

ATEK Engineering Consultants, LLC is pleased to present the attached Geotechnical Exploration Report for the Crossroad East Sewer Lift Station project located in Scottsdale, Arizona. The purpose of our study was to explore and evaluate the subsurface conditions at the proposed site to develop geotechnical engineering recommendations for project design and construction.

Based on our findings, the site is considered suitable for the proposed construction, provided geotechnical recommendations presented in the attached report are followed. Specific recommendations regarding the geotechnical aspects of the project design and construction are presented in the attached report. The recommendations contained within this report are dependent on the provisions provided in the Limitations and Recommended Additional Services sections of this report.

We appreciate the opportunity of providing our services for this project. If you have questions regarding this report or if we may be of further assistance, please contact the undersigned.

Sincerely, ATEK Engineering Consultants, LLC

James P Floyd, P.E. Armando Ortega, P.E.

Project Manager Principal Geotechnical Engineer

Distribution: (1) Addresses (Electronic Copy)

Expires 9/30/2020

TABLE OF CONTENTS

1. INTRODUCTION

Project Description Purpose Scope of Services

2. FIELD EXPLORATION

General Soil Test Borings

3. LABORATORY TESTING

4. GENERAL SITE CONDITIONS

Surface Conditions Subsurface Conditions Groundwater Conditions Geologic Hazards

4.4.1. Liquefaction Potential

4.4.2. Collapsible Soils

Seismic Considerations Earth Fissures and Land Subsidence

5. ENGINEERING ANALYSES AND RECOMMENDATIONS

Earthwork

5.1.1. Mat Foundation for Lift Station

5.1.2. Spread Footings Electrical Pad, Shade Structure and Site Wall

5.1.3. Concrete Flat Work

5.1.4. Aggregate Base Course

5.1.5. Engineered Fill

Design Values for Buried Pipes

5.2.1. Soil Loads on Buried Flexible Pipes

5.2.2. Design Values for Buried Flexible Pipes

5.2.3. Flexible Pipe Trench Width Recommendations

5.2.4. Flexible Pipe Construction Considerations

5.2.5. Soil Loads on Buried Rigid Pipes

Excavation

5.3.1. Trench Backfill

5.3.2. Temporary Excavations

Structures

5.4.1. Mat Foundation

5.4.2. Shallow Spread Footings

5.4.3. Resistance to Lateral Loads

Moisture Protection Corrosion Potential

5.6.1. 10-point System

5.6.1.1. Electrical Resistivity

5.6.1.2. Oxidation-Reduction (Redox) Potential

5.6.1.3. Sulfides

5.6.1.4. Moisture

5.6.1.5. Corrosion (Concrete)

6. CLOSURE

Limitations Recommended Additional Services

APPENDIX A – Site Location Map APPENDIX B – Sample Location Plan APPENDIX C – Field Study and Boring Logs APPENDIX D – Laboratory Test

Geotechnical Exploration 190100 Crossroad East Sewer Lift Station Scottsdale, Arizona Page 1 of 26

1. INTRODUCTION

This report presents the results of our geotechnical exploration for the Crossroad East

Sewer Lift Station located in Scottsdale, Arizona. A Site Location Map is presented in

Appendix A of this report. The following sections of this report describe our understanding of the project and our scope of services.

Project Description

The project consists of a new sewer lift station, sewer line and sewer force main. The project is located north of Arizona State Route 101 Loop, west of Scottsdale Water

Campus and east of Hayden Road. It is understood that the lift station and sewer line will be approximately 25 and 40 feet below the existing site surface elevation, respectively. The sewer lift station will be supported on a reinforced mat foundation.

The site improvements will include an eight (8) foot tall concrete masonry unit (CMU) walls, electrical pad, and shade structure. These secondary structures will be supported on relatively shallow spread footings or reinforced concrete slabs with a thicken edge.

Purpose

The purpose of this geotechnical study was to evaluate the general surface and subsurface conditions at the site, and to present recommendations related to geotechnical aspects of design and construction of the proposed project.

Scope of Services

Our study included a site reconnaissance, subsurface exploration, soil sampling, field and laboratory testing, engineering analyses, and preparation of this report. This report presents geotechnical recommendations for design and construction of proposed structures. The recommendations contained in this report are subject to

Scottsdale, Arizona Page 2 of 26 the limitations presented herein. Attention is directed to the “Limitations” section of this report.

2. FIELD EXPLORATION

General

Prior to the start of drilling, the Arizona Blue Stake Center was contacted to locate existing utilities at the boring locations. The field exploration was performed on

September 30, 2019. Three soil borings were drilled to depths ranging between fifteen (15) and fifty (50) feet below existing grade. The soil test borings were drilled using a truck mounted CME-75 power drill rig equipped with 7 and ¼-inch outside diameter hollow stem augers. The borings were located in the field at the approximate locations shown on the Sample Location Plan included in Appendix B of this report. Upon completion of the borings, the boreholes were backfilled with excavated materials.

Soil Test Borings

Disturbed and relatively undisturbed samples were taken at the direction of the field engineer during drilling operations. Relatively undisturbed samples of the subsurface materials were obtained using a California sampler with a 2.5-inch inside diameter and a 3.0-inch outside diameter. Disturbed samples were obtained using a Standard

Penetration/Split Spoon Sampler (SPT) with a 1.5-inch inside diameter and 2.0-inch outside diameter. The California and the SPT samplers were driven 12 and 18 inches, respectively, using a 140-pound hammer falling 30 inches, and blow counts for successive 6-inch penetration intervals were recorded. After the sampler was withdrawn from the borehole, the samples were removed, sealed to minimize moisture loss, and submitted to the laboratory.

Scottsdale, Arizona Page 3 of 26

Soil classifications made in the field from auger cuttings and samples were re-evaluated in the laboratory after further examination and testing. The soils were classified in accordance with the Unified Soil Classification System presented in

Appendix C.

Sample classifications, blow counts recorded during sampling, and other related information, were recorded on the soil boring logs. The boring logs are presented in

Appendix C. The information presented on the logs are a combination of factual and interpretive information. Lines delineating subsurface strata and group symbols are based on field observations made at the time of the field study. Actual subsurface lines delineating subsurface strata may be gradual and vary.

3. LABORATORY TESTING

Selected soil samples from the borings were tested in the laboratory for classification purposes and to evaluate their engineering properties. The laboratory tests included:

Gradation;

Atterberg limits;

Moisture content;

One-dimensional consolidation;

Sulfate content;

Chloride content;

pH tests;

Resistivity tests;

Redox Potential;

Sulfide content;

And expansion index.

A brief description of each test performed on the soil samples and the results are presented in Appendix D of this report.

Scottsdale, Arizona Page 4 of 26

4. GENERAL SITE CONDITIONS

Surface Conditions

The sewer lift station is located approximately five hundred feet north of Arizona

State Route 101 Loop and approximately fifteen hundred feet east of North Hayden

Road. At the time of our field study the site was located in a native desert area with dense native vegetation adjacent to the Central Arizona Project (CAP) Water

Treatment Plant (WTP). Topography was relatively flat across the site.

Subsurface Conditions

As indicated by the exploratory borings, in general the surface soils consist of Silty

Clayey Sand with Gravel (SC-SM), Clayey Sand (SC), and Silty Sand (SM) with low plasticity. These soils were found to have a relative firmness/density ranging from firm to hard/loose to very dense. The underlying subsurface soils encountered during our field exploration consisted of Clayey Sand with and without Gravel (SC), Sand with

Gravel (SP), and Sandy Clay (CL). These soils were found to have a relative firmness/density ranging from very firm to hard/very dense. For additional information see Boring Logs presented in Appendix C.

Groundwater Conditions

Groundwater was not encountered within the soil test borings and it is anticipated that groundwater will not be a factor in design or construction of the planned improvements. It should be noted that soil moisture conditions within the area may vary depending on rainfall and/or runoff conditions not apparent at the time of our field study.

Scottsdale, Arizona Page 5 of 26

Geologic Hazards

4.4.1. Liquefaction Potential

Based on the site soils and groundwater conditions encountered at the project site during this study, the preliminary potential for soil liquefaction is considered to be negligible.

4.4.2. Collapsible Soils

Collapsible soils are soils with the potential for a decrease in volume with an increase in external load or moisture content. These soils are typically found in areas of alluvial deposits with semi-arid to arid climates. Based on the information collected during our field study and subsequent laboratory testing, we anticipate collapse-susceptible soils will be encountered during construction. Based on ASTM D 5333, a calculated collapse potential, IC, of one of the undisturbed ring samples collected during our field study resulted in 5.4 percent, indicating a moderate collapse potential.

Seismic Considerations

The project site is located in north-central Arizona which is an area of low seismic activity. The following values were developed using the ATC Hazard by Location

(https://seismicmaps.org/) the 2015 International Building Code (IBC) and are based on knowledge of local geologic conditions, and subsurface soils encountered during our study. A 100-foot soil test boring was not advanced during our field study. The geographic coordinates listed below were used in developing the seismic design factors.

Central Latitude…………………………………………………33.655155˚

Central Longitude……………………………………………-111.903072˚

Scottsdale, Arizona Page 6 of 26

Earth Fissures and Land Subsidence

The project site is located in an area with no documented earthen fissures and in an area with a measured land subsidence of zero and two inches over the past nine years. (http://data.azgs.az.gov/hazard-viewer/ and Total Land Subsidence in the

Northeastern Phoenix and Scottsdale Areas, Maricopa County for the measure between the dates May 8, 2010 and to April 15, 2019).

5. ENGINEERING ANALYSES AND RECOMMENDATIONS

Earthwork

The following sections present earthwork recommendations based on our understanding of the project, the finding of our field exploration, results of the laboratory tests and engineering analysis. Based on the finding of our field exploration, laboratory test results and engineering analysis, it is our opinion that the proposed construction can be supported on a spread footing system as presented in the following sections.

Seismic Design Factors Value

Site Class C

Fa, Site Coefficient 1.2

Fv, Site Coefficient 1.7

Ss, Mapped Spectral Acceleration at 0.2-second Period 0.211 g

S1, Mapped Spectral Acceleration at 1.0-second Period 0.066g

SMS, Spectral Acceleration at 0.2-second Period Adjusted for Site Class 0.253 g

SM1, Spectral Acceleration at 1.0-second Period Adjusted for Site Class 0.111 g

SDS, Design Spectral Response Acceleration at 0.2-second Period 0.169 g

SD1, Design Spectral Response Acceleration at 1.0-second Period 0.074 g

Scottsdale, Arizona Page 7 of 26

5.1.1. Mat Foundation for Lift Station

It is understood that the lift station will bear at a depth of approximately twenty-five feet below the existing site surface elevation and will be supported on a reinforced concrete mat foundation. Based on the soils encountered during our field study, it is anticipated that hard/very dense soils will be encountered at this depth. These undisturbed native soils may be used to support the lift station. If loose soils are encountered below the lift station foundation ATEK should be contacted for alternative grading recommendations.

To aid in concrete curing and in providing a level based it is recommended that the existing soils be removed a minimum depth of 12-inches and replaced with aggregate base course. The aggregate base course should be moisture conditioned to within 2 percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density. Optimum moisture content and maximum dry density should be determined by American Society for Testing and Materials (ASTM) D 698. The over excavation of site soils should extend laterally for a minimum distance of 3-feet beyond the perimeter of footing.

5.1.2. Spread Footings Electrical Pad, Shade Structure and Site Wall

It is anticipated that the electrical pads, shade structure and site wall will be relatively lightly loaded near surface bearing pads supported on spread footings. The existing surface soils should be removed to a minimum depth of 1-foot below bottom of proposed spread footing elevation. The exposed subsurface soils should be scarified to a depth of 8-inches: moisture conditioned to within 2 percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density. The excavated material should then be moisture conditioned to within 2 percent of optimum moisture. These soils should be compacted to a minimum of 95 percent of maximum dry density. Optimum moisture content and maximum dry density should be determined by ASTM D 698. We recommend that the entire footprint of the pad be

Scottsdale, Arizona Page 8 of 26 over excavated. The over excavation of the site soils should expend laterally for a minimum distance of 1-feet beyond the perimeter of the pad.

5.1.3. Concrete Flat Work

The existing site soils should be scarified to a depth of 12-inches; moisture conditioned to within 2 percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density. Optimum moisture content and maximum dry density should be determined by ASTM Test Method D 698.

5.1.4. Aggregate Base Course

A minimum of 4-inch layer of clean, granular material should be placed beneath concrete slabs to serve as a leveling base, and to aid in concrete curing. The material should conform to the gradation requirements set by the local governing agency and/or MAG section 702 specifications for Aggregate Base Course (ABC). The use of moisture barriers beneath the floor slabs may be helpful, but is not a geotechnical requirement; however, the architect or the slab designer should evaluate their need.

All aggregate base material should be placed in lifts not greater than eight inches and compacted to a minimum of 95 percent of maximum dry density below Portland cement concrete and 100 percent of maximum dry density below asphaltic concrete pavements as determined by American Society for Testing and Materials (ASTM) Test

Method D 698 or as specified by local specification. The moisture content during compaction should be maintained within two percent of optimum moisture content.

5.1.5. Engineered Fill

Engineered fill may consist of native soils and/or imported soils. Pea gravel and poorly-graded materials should not be used as engineered fill unless approved by the

Scottsdale, Arizona Page 9 of 26 geotechnical engineer. All engineered fills should be compacted as noted in section

5.

1. Native soils or imported soils with low expansive potentials should be used as fill material for the following:

general site grading foundation areas interior floor slab areas foundation backfill exterior slab areas pavement areas

2. Imported soils (if required) should conform to the following:

Percent finer by weight

Gradation (ASTM C136)

3"………………………………………………………………………………………………100

No. 4 Sieve……………………………………………………………………………50-100

No. 200 Sieve……………………………………………………………………50 (max)

Liquid Limit………………………………………………………………………30 (max)

Plasticity Index…………………………………………………………………15 (max)

Swell Test

Maximum Swell Potential ……………………………………………………1.5 %*

*Measured on a sample compacted to approximately 95 percent of the ASTM D

698 maximum dry density at about 2 percent below optimum water content.

The sample is confined under a 100 psf surcharge and submerged.

Corrosion Potential (PPM) Sulfate Content (ARIZ 733)……………………………………………….1,000(max) Chloride Content (ARIZ 736)…………………………………………………500(max)

3. Aggregate base should conform to MAG and/or local governing specifications.

Scottsdale, Arizona Page 10 of 26

4. The following are intended to guide in establishing adequate support for the conventional foundation elements:

Any natural washes, depressions or new excavations which are to be filled, should be widened as necessary to accommodate compaction equipment and provide a level base for placing fill.

Any engineered fill (backfill) materials placed beneath the foundations should meet the requirements for Engineered Fill Materials.

All footing excavations should be relatively level and free of loose or disturbed material and inspected by a qualified representative of the

Geotechnical Engineer.

5. All fill soils to be used beneath the foundations; slabs and pavements should be approved by the Geotechnical Engineer. Fill should be placed in 8-inch loose lifts, moisture conditioned to within 2 percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density. Fill materials placed at depth greater than five (5) feet should be compacted to 100 percent of maximum dry density to finished grade elevation. Optimum moisture content and maximum dry density should be determined by ASTM Test Method D 698.

Design Values for Buried Pipes

The following sections provide design information relative to flexible and rigid pipes.

The recommendations provided within the following sections are based on the pipe being installed by open cut excavations.

5.2.1. Soil Loads on Buried Flexible Pipes

The pipe loading pressure for flexible pipes such as PVC, HDPE, or welded steel may be determined by calculating the soil overburden pressure, adding the live load pressures and multiplying by the pressure transfer coefficient Cp. The coefficient Cp

Scottsdale, Arizona Page 11 of 26 typically varies from 0.65 to 2.0 depending on the type and degree of compaction of the bedding and initial backfill materials. The value of Cp may be determined from the pipe manufacturers or may be conservatively estimated as Cp = 2.0. For aggregate base or clean washed sand bedding and initial backfill materials compacted as recommended in this report, a Cp value of 0.80 is recommended for design.

5.2.2. Design Values for Buried Flexible Pipes

Flexible pipes typically derive part of their resistance to ring deflection from the initial backfill and trench wall soils. Evaluation of ring deflection of buried pipes under soil and live loads may be determined using the Iowa Formula. The elastic modulus of the soils surrounding the pipe, or E’, may be evaluated by knowing the trench width, the pipe diameter, the elastic modulus of the initial backfill (E’b), and the elastic modulus of the native trench wall soils (E’n - also termed Constrained

Modulus). Recommendations for pipe design using the Iowa Formula are presented in the following table.

The following table presents recommended E’b values for use in the Iowa Formula for proposed initial backfill materials placed and compacted in accordance with our recommendations. The value of E’b is a lateral modulus of subgrade reaction for the initial backfill material. For E’b values at depths between the intervals presented below, the E’b value between data points may be determined by linear interpolation.

The recommended E’b values presented in the following table apply to aggregate base or graded sand bedding and initial backfill material along the sides of the pipe at the recommended level of compaction. These values are applicable for pipe design where the initial backfill width is at least 2 times the pipe diameter (D) on each side of the pipe (trench width of 5D).

Scottsdale, Arizona Page 12 of 26

E’b Values for Design of Buried Flexible Pipes

Soil Type Depth to Springline Recommended E’b

(psi)

Pipe Bedding and Initial Backfill (aggregate base or graded sand)

1,900 2,000 2,100

Notes: 1. The above design values are based on “Evaluation of the Modulus of Soil Reaction, E’, and its Variation With Depth,” by Hartley & Duncan, dated June 1982.

2. Based on providing at least 2 pipe diameters of backfill on each side of pipes.

Where the zone of backfill beside the pipe is less than 2D, the E’b values resented above may not be applicable and the constrained soil modulus E’n will affect flexible pipe design. The actual lateral soil modulus at the pipe depth will lie somewhere between E’b and E’n depending on the trench width.

Based on the field and laboratory data obtained along the pipeline alignments, we recommend an E’n value of 3,000 psi (AWWA M45, 1996) be used for design of flexible pipes. This value is applicable to the undisturbed native soils encountered at the site.

For trench widths less than 5D, the design E’ may be calculated by multiplying E’b by the Soil Support Combining Factors (Sc) presented in the following table, where Bd is the trench width at pipe springline and D is the diameter of the pipe.

Design E’ = Sc(E’b)

Sc Values For Design of Buried Flexible Pipes (Soil Support Combining Factor)

E’n/E'b Bd /D 1.5

Bd /D 2.0

Bd /D 2.5

Bd /D 3.0

Bd /D 4.0

Bd /D 5.0

0.1 0.15 0.30 0.60 0.80 0.90 1.00

0.2 0.30 0.45 0.70 0.85 0.92 1.00

0.4 0.50 0.60 0.80 0.90 0.95 1.00

0.6 0.70 0.80 0.90 0.95 1.00 1.00

0.8 0.85 0.90 0.95 0.98 1.00 1.00

1.0 1.00 1.00 1.00 1.00 1.00 1.00

1.5 1.30 1.15 1.10 1.05 1.00 1.00

2.0 1.50 1.30 1.15 1.10 1.05 1.00

3.0 1.75 1.45 1.30 1.20 1.08 1.00 ≥5.0 2.00 1.60 1.40 1.25 1.10 1.00

Source: “AWWA M45,”, 1996.

Scottsdale, Arizona Page 13 of 26

5.2.3. Flexible Pipe Trench Width Recommendations

According to ASTM D 2321, “Standard Practice for Underground Installation of

Thermoplastic Pipes for Sewers and other Gravity-Flow Applications”, the minimum trench width for flexible pipes should be the greater of 16 inches greater than the pipe diameter or 1.25 times the pipe diameter plus 12 inches. For flexible pipes, the trench width should be kept to a minimum to reduce the soil loading on the pipes.

Wider trenches will generally impart higher soil loads on buried flexible pipes. Where granular pipe zone backfill is used, the trench should be wide enough to accommodate compaction equipment and shoring along the sides of the pipe. Care should be taken during installation of the pipe zone backfill around the haunches of the pipe (i.e., from the bottom of the pipe to springline) such that voids are eliminated and the backfill material is firm and unyielding. Lateral restraint against ring deflection for the pipes will be provided by the stiffness of the pipe zone backfill material and/or the trench wall soils.

5.2.4. Flexible Pipe Construction Considerations

Flexible pipes require uniform support from bedding materials especially in haunch areas to prevent overloading. The pipeline designers should evaluate the proximity of adjacent pipelines, excavations, and their related effects on the proposed construction. If proper trench wall support cannot be provided in a portion of the pipe trench, we recommend consideration be given to the use of lean concrete or

Controlled Low Strength Material (CLSM) initial backfill around the pipes.

5.2.5. Soil Loads on Buried Rigid Pipes

Soil loads on buried rigid pipes such as concrete or clay pipes can be analyzed using the Marston’s Formula as follows:

Wc = Cd ү Bd

Scottsdale, Arizona Page 14 of 26

Cd = Load Coefficient based on Kμ’ ү = Moist unit weight of backfill material (pcf)

Bd = Width of trench at top of pipe (ft)

The coefficient Cd is dependant on the back fill type, which is depend on the pipe manufacture’s recommendation or local municipality requirements, the trench width, and pipe installation depth. Where the ratio of the backfill depth to trench width at the top of the pipe (H/Bd) is at least 1 and where trench width, at top of pipe, is no greater than 3 times the pipe diameter, the value of Cd may be determined using the following formula for load coefficient, Cd:

-2Kμ’ (H / Bd)

Cd = 1 - e____________

2Kμ’

K = Active earth pressure coefficient μ’ = Friction coefficient between fill material and sides of trench

H = Backfill height above the pipe crown

The product Kμ’ is the above referenced equation is dependent on the backfill type, degree of compaction, and moisture content. The following table provides estimates for the Kμ’ product based on various soil types.

Scottsdale, Arizona Page 15 of 26

Soil Type Kμ’

Clay (CL,CH) 0.12

Silt (ML) 0.13

Silty Sand (SM) 0.15

Well and Poorly Graded ‘Clean’ Sands

(SW, SP)

0.165

Sandy Gravels and Cobbles

(GW, GP, GM, GC)

0.18

Source: ASCE (1982)

Based on soils encountered during our field study, we recommend using a Kμ’ value of

0.18 for design and a wet soil unit weigh, ү, equal to 125 pcf for soil backfill material.

Excavation

The field sampling and exploration was performed using a truck-mounted drill rig with

7 and ¼-inch outside diameter hollow stem augers. We present the following general comments regarding ease of excavation with the understanding that they are opinions based on the test borings. The project consultant and contractor should become familiar with this report including boring logs to evaluate potential hard dig conditions. Please note that excavation characteristics are best evaluated by performing test excavations with the size and type of equipment the contractor plans on using at the site, which was not conducted as part of this study.

It is anticipated that excavations in the site soils between the surface and a depth of fifteen can most likely be accomplished by conventional earth moving equipment in good operating condition. Due to the presence of subsurface cementation, deep excavations may require specialized excavating equipment. Sloughing and caving of near surface soils should be considered during grading operations. Please refer to

Section 4 and the boring logs presented in Appendix C of this report for more information.

Scottsdale, Arizona Page 16 of 26

5.3.1. Trench Backfill

Materials

Pipe zone backfill (i.e., material beneath and in the immediate vicinity of the pipe) should consist of soil with a maximum particle size less than one inch. Trench zone backfill (i.e., material placed between the pipe zone backfill and finished subgrade) may consist of soil that meets the requirements for structural fill provided above.

If import material is used for pipe or trench zone backfill, we recommend it consist of fine-grained sand. In general, poorly graded coarse-grained sand and gravel should not be used for pipe or trench zone backfill due to the potential for site soil migration into the relatively large void spaces present in this type of material and water seepage along trenches backfilled with coarse-grained sand and/or gravel.

Recommendations provided above for pipe zone backfill are minimum requirements only. More stringent material specifications may be required to fulfill local codes and/or bedding requirements for specific types of pipes. We recommend the project

Civil Engineer develop these material specifications based on planned pipe types, bedding conditions, and other factors beyond the scope of this study.

Compaction Criteria

Backfill of trenches should utilize site soils with particle diameter less than 3-inches, in order to aid compaction and reduce potential differential settlement problems.

Backfilling of utility trenches should be in 12-inch maximum loose lifts, and compacted to a minimum of 90 percent and 95 percent of ASTM D-698 (standard

Proctor), in non-structural areas and structural areas, respectively. Please note that the local governing agency specifications may surpass these trench backfill requirements. Jetting, flooding, or puddling of cohesive backfill soils should not be utilized under any circumstances.

Scottsdale, Arizona Page 17 of 26

Care must be used during compaction of backfill against the lift station walls. Hand operated equipment and thin backfill lifts are suggested to reduce the buildup of additional excessive wall pressure due to compaction method. To reduce the potential for a subsurface wall blowout, heavy construction equipment should not be operated next to the below lift station walls.

5.3.2. Temporary Excavations

General

All excavations must comply with applicable local, state, and federal safety regulations including the current Occupational Safety and Health Administration

(OSHA) Excavation and Trench Safety Standards. Generally, Construction site safety is solely the responsibility of the Contractor, who shall also be responsible for the means, methods, and sequencing of construction operations. We are providing the information below strictly as a service to our client. Under no circumstances should the information be interpreted that ATEK is assuming responsibility for construction site safety or the Contractor’s activities; such responsibility is not being implied and should not be inferred.

Excavations and Slopes

The Contractor should be aware that slope height, slope inclination, or excavation depths (including utility trench excavations) should in no case exceed those specified in local, state, and/or federal safety regulations (e.g., OSHA Health and Safety

Standards for Excavations, 29 CFR Part 1926, or successor regulations). Such regulations are strictly enforced; and, if not followed, could result in substantial penalties to the Owner, Contractor, and/or earthwork subcontractor and/or utility subcontractors.

Near-surface soils encountered during our field study consisted predominantly of silty clayey sands. In our opinion, these soils would be considered a Type C soil when applying OSHA regulations. For this soils type OSHA recommends a maximum slope

Scottsdale, Arizona Page 18 of 26 inclination of 1.5(h):1(v) or flatter for excavations 20 feet or less in depth. Steeper cut slopes may be utilized for excavations less than 5 feet deep depending on the strength, moisture content, and homogeneity of the soils as observed in the field.

Flatter slopes and/or trench shields may be required if loose, cohesionless soils and/or water are encountered along the slope face.

Construction Considerations

Heavy construction equipment, building materials, excavated soil, and vehicular traffic should not be allowed within one-third the slope height from the top of any excavation. Where the stability of adjoining buildings, walls, or other structures is endangered by excavation operations, support systems such as shoring, bracing, or underpinning may be required to provide structural stability and to protect personnel working within the excavation. Shoring, bracing, or underpinning required for the project (if any) should be designed by a professional engineer registered in the State of Arizona.

During wet weather, earthen berms or other methods should be used to prevent runoff water from entering all excavations. All runoff water should be collected and disposed of outside the construction limits.

Structures

5.4.1. Mat Foundation

Mat foundations bearing on engineered fill as presented in section 5.1 of this report may be used to support the proposed structures. An allowable bearing pressure of

7,000 pounds per square foot may be used for mat foundations bearing at a depth of

25 feet below adjacent grade or greater. A one third increase may be applied to the recommended bearing pressure when considering short duration loads, such as wind and seismic.

Scottsdale, Arizona Page 19 of 26

A modulus of subgrade reaction of 400 kips per cubic foot (kcf) should be used for the design of the mat foundation. This value is based on a 1-foot square bearing area and needs to be scaled to account for mat foundation size effects. To obtain the modulus of subgrade reaction for a given mat foundation, the value of 400 kcf should be divided by the width of the effective loaded area, in feet. We estimate that the long-term total and differential settlement of new mat foundations constructed as recommended in this report should be on the order of 1-inch.

5.4.2. Shallow Spread Footings

Shallow spread footings bearing on engineered fill can be used to support the structures as recommended (See section 5.1). Recommended footing depths and allowable bearing pressures are presented below.

Allowable Bearing Pressure for Shallow Foundations

Footing Depth Below

Finished Grade (ft.)*

Allowable

Bearing

Pressure

(psf)

1.5 2,000

2.0 2,500

*Note: Footing depth is defined as the depth below the lowest adjacent finished grade elevation within 5-feet of the edge of the footing.

A one-third increase may be applied to the design bearing pressures when considering short duration loads, such as wind and seismic.

Continuous footings and isolated column footings should have a minimum width of 16-inches and 24 inches respectively. The minimum widths are recommended for ease of construction, and to provide a margin of safety against a local or punching shear

Scottsdale, Arizona Page 20 of 26 failure of the foundation soils. All footings should be reinforced to reduce potential distress caused by differential foundation movement.

All the footing excavations should be observed by the Geotechnical Engineer prior to placement of reinforcing steel and/or concrete. If subsurface conditions are encountered that are different than indicated by the borings, revised recommendations may be required.

Settlement of footings designed as recommended above are estimated not to exceed

1-inch. Differential settlements over, a horizontal distance of 50 feet between similarly loaded footings, are expected to be less than ½-inch and ¾-inch for wall and column footings, respectively. Significant moisture increases above those recommended for compaction could result in additional movements. In order to minimize the sensitivity of the structure to differential settlements, footings should be reinforced to allow for a degree of load redistribution should a localized zone of supporting soils become saturated.

5.4.3. Resistance to Lateral Loads

Proposed walls/structures that will retain soil must be designed to withstand lateral soil pressures. Cantilevered retaining walls, or unrestrained walls subject to lateral earth pressures, should be designed for an equivalent fluid pressure (EFP) of 33 PCF.

Restrained walls should be designed to withstand a residual or long-term at-rest (Ko) earth pressure condition of 50 pounds per cubic foot (PCF).

A passive EFP of 300 PCF may be used for shallow spread footings. A coefficient of friction of 0.36 is recommended for computing lateral resistance between the base of footing and soil in analyzing lateral loads. Vehicular surcharge loads and/or hydrostatic pressure will increase the recommended EFP.

Scottsdale, Arizona Page 21 of 26

Only cohesionless, free-draining granular materials should be used as backfill, adjacent to earth-retaining structures. We recommend that backfill directly behind the walls be compacted with light, hand-held compactors. Heavy compactors and grading equipment should not be allowed to operate within 3 feet of the walls during backfilling, to avoid developing excessive temporary or long-term lateral soil pressures. Positive gravity drainage of the backfill should be provided.

Moisture Protection

Soil support values reduce with an increase of moisture content. Therefore, positive drainage is essential to the successful performance of any structure. Good surface and subsurface drainage should be established during and after construction to prevent the soils below or adjacent to the structural areas and utility trenches from becoming wet.

Infiltration of water into utility or foundation excavations must be prevented during construction. The drainage design must route all storm and sprinkler water away from the structural areas in a positive manner. All water should be diverted away from areas where it could penetrate the ground surface near the structural areas.

Watering of plants should be avoided adjacent to the buildings. Desert-type landscaping is advisable near the structural areas. Plants, which require more water, should be located and drained away from the structural areas.

Corrosion Potential

5.6.1. 10-point System

The 10-point soil evaluation includes the following soil tests: resistivity, pH, oxidation-reduction (redox) potential, sulfides, and moisture. For each of these tests, results are categorized according to their contribution to corrosively. The test results are assigned point values based on Table A.1 found in Appendix A of the American

National Standard for Polyethylene Encasement For Ductile-Iron Pipes Systems

Scottsdale, Arizona Page 22 of 26

(ANSI/AWWA C105/A21.5-99), dated 1999. The above referenced corrosion testing is applicable to carbon steel pipe. A sum of points greater than or equal to 10, is considered corrosive to ductile iron pipes and carbon steel pipe and protection against exterior corrosion should be provided. The sum of points of the site soils sampled is 11 (greater than 10), hence, the site soils be considered corrosive to high carbon steel and protection against exterior corrosion should be provided.

5.6.1.1. Electrical Resistivity

Electrical Resistivity of a soil is a measure of resistance to the flow of electrical current. Corrosion of buried metal is an electrochemical process in which the amount of metal loss due to corrosion is directly proportional to the flow of electrical current

(DC) from the metal into the soil. As a soil’s resistivity decreases, its corrosivity increases.

A commonly accepted correlation between soil resistivity and corrosivity towards ferrous metals is shown in the following table.

Resistivity (ohm-cm) Corrosivity Classification 0 to 1,000 Severely corrosive 1,000 to 2,000 Corrosive 2,000 to 10,000 Moderately corrosive Over 10,000 Mildly corrosive

Resistivity test results indicates 0 to 10 points and the pH test results indicates 3 points in the 10-point soil evaluation across the project location.

Based on the laboratory tests as shown above, this soil would be considered

“corrosive to moderately corrosive”. It should be noted that these corrosion

Sample Location pH Resistivity (Ohm-cm) Bulk Sample B-1 8.7 2,060 Bulk Sample B-2 8.6 1,180 Bulk Sample B-3 8.9 3,440

Scottsdale, Arizona Page 23 of 26 conditions are for the soils at submerged moisture conditions. Resistivity at drier moisture contents would be less corrosive than the results of the test.

The pH values of the samples tested were neutral. In most cases, pH is not a significant factor in corrosion in the near-neutral pH range (5<pH<9).

Estimated life for various gage galvanized CMP, based on Figure 6.7 of the Handbook of Steel Drainage & Highway Construction Products published by American Iron and

Steel Institute Fourth Edition, 1993, is tabulated below. Details of the laboratory test results are presented in the Appendix C of this report.

5.6.1.2. Oxidation-Reduction (Redox) Potential

The redox potential of a soil is significant in assessing corrosion potential because the most common sulfate-reducing bacteria can live only in anaerobic conditions. A negative redox potential indicates that anaerobic conditions present in which sulfate reducers can live. The redox potential of site soils ranged from 101 to 110 mV and results in zero points in the 10-point soil evaluation.

5.6.1.3. Sulfides

A positive sulfides reaction reveals a potential problem caused by sulfate reducing bacteria. A negative sulfides reaction was observed from the soil sample analyzed and results in zero points in the 10-point soil evaluation.

Sample Location Design Life (yrs)

18 Gage 16 Gage 14 Gage Bulk Sample B-1 65 85 105 Bulk Sample B-2 50 65 80 Bulk Sample B-3 80 105 130

Scottsdale, Arizona Page 24 of 26

5.6.1.4. Moisture

The prevailing moisture condition of the soil is important to all soil corrosion. The specific moisture content of the soil is not necessary but rather the drainage characteristics and moisture condition. A conservative classification of the site soils is fair drainage and generally moist which results in 0 point in the 10-point soil evaluation.

5.6.1.5. Corrosion (Concrete)

Selected samples of the near-surface soils encountered at the site were subjected to chemical analysis for the purpose of corrosion assessment. The samples were tested for soluble sulfates, and soluble chlorides. The samples were tested in general accordance with Arizona Test Methods 733, and 736 for soluble sulfates, and soluble chlorides, respectively. The test results are provided in Appendix C.

Based on provisions of American Concrete Institute (ACI) 318 Section 4.3, Table 4.3.1, Requirements for Concrete Exposed to Sulfate-Containing Solutions a sulfate concentration below 0.10 percent by weight (1,000 ppm) is negligible. Based on the laboratory results, sulfate contents of the site soils tested indicate a negligible corrosion potential to concrete.

Based on the laboratory result of the sample collected for this project, chloride contents of the site soils tested indicate negligible corrosion potential.

6. CLOSURE

Limitations

Our professional services have been performed using that degree and skill ordinarily exercised, under similar circumstances, by reputable Geotechnical Engineers practicing in this or similar localities. No warranty is expressed or implied.

Scottsdale, Arizona Page 25 of 26

The recommendations contained in this report are based on our field exploration, laboratory test results, and our understanding of the proposed construction. The subsurface data used in the preparation of this report was obtained from the test borings excavated during the field subsurface exploration. It is anticipated that some variations in the soil conditions will exist on-site. The nature and extent of variations may not be evident until construction occurs. If any conditions are encountered at this site that are different from those described in this report, we should be immediately notified so that we may make any necessary revisions to the recommendations contained in this report. In addition, if the scope of the proposed construction changes from that described in this report, our firm should also be notified.

It is the Client’s responsibility to see that all parties to the project including the designer, contractor, subcontractor, etc. are made aware of this report in its entirety. The use of information contained in this report for bidding purposes should be done at the contractor’s option and risk.

This report is for the exclusive purpose of providing Geotechnical Engineering and/or testing information and recommendations. The scope of services for this project does not include, either specifically or by implication, any environmental assessment of the site or identification of contaminated or hazardous materials or conditions. If the owner is concerned about the potential for such contamination, other studies should be undertaken. This report has also not addressed the site geology and the possible presence of geologic hazards.

This report may be used only by the Client and only for the purposes stated, within a reasonable time from its issuance. Land use, site conditions (both on and off-site), or other factors may change over time, and additional work may be required with the passage of time. Any party, other than the Client, who wishes to use this report, shall

Scottsdale, Arizona Page 26 of 26 notify ATEK of such intended use. Based on the intended use of this report, ATEK may require that additional work be performed and that an updated report be issued.

Recommended Additional Services

The recommendations provided in this report are based on the assumption that an adequate program of tests and observations will be performed during the construction. These tests and observations should be performed by the Geotechnical

Engineer’s representative and should include, but not limited to the following:

Observe and document that any existing surficial vegetation and other deleterious materials have been removed from the site as required in site preparation section.

Approve any material used as import to document that it meets the requirements outlined above before placement.

Monitor the backfill procedures.

Perform field density tests, as needed, to verify compaction compliance. The representative should monitor the progress of compaction and filling operations.

Keep records of on-site activities and progress.

Observation of footing excavations should be performed prior to placement of reinforcing and concrete to confirm that satisfactory bearing materials are present.

Construction testing, including field and laboratory evaluation of fill and backfill materials, concrete and steel should be performed to determine whether applicable project requirements have been met.

APPENDIX A

Site Location Map

Project Site

Site image from earth.google.com.

*Note: not to scale. Drawn By:

190100

October-19

A Lopez

Site Location Map

Crossroad East Sewer Lift Station

Sheet 1 of 1

Project Number:

Date:

ATEK Engineering Consultants, LLC 111 South Weber Drive, Suite 1

Chandler, AZ 85226

APPENDIX B

Sample Location Plan

Legend:

Soil Test Boring

Site image from earth.google.com.

*Note: not to scale.

Date: October-19 Drawn By: A Lopez

Sample Location Plan

Sheet 1 of 1 Crossroad East Sewer Lift Station

Project Number: 190100 ATEK Engineering Consultants, LLC 111 South Weber Drive, Suite 1 Chandler, AZ 85226

B-2

B-1

B-1

B-3

APPENDIX C

FIELD STUDY AND BORING LOGS

APPENDIX C

FIELD STUDY

BORINGS

The subsurface conditions at the site were explored on April 1, 2019, by drilling soil borings using a truck mounted CME drill rig with 7 and a ¼-inch outside diameter hollow stem auger. The locations of soil test borings performed for this study are shown in Appendix B of this report.

The locations of borings were located by visual sighting and pacing from existing site features and, therefore, should be considered approximate. Actual boring locations may vary from those indicated in Appendix B.

Our field engineer maintained a log of the excavations; visually classified soils encountered according to the Unified Soil Classification System (USCS) (see USCS Table); and obtained samples of the subsurface materials.

SAMPLING PROCEDURES

Soil samples obtained from the borings were packaged and sealed in the field to reduce moisture loss and disturbance, and returned to our laboratory for further testing. After borings were completed, they were backfilled with the excavated soils.

LIST OF ATTACHMENTS

The following plates are attached and complete this appendix.

Unified Soil Classification System – C1 Log Key – C2 Charts and Definitions – C3 Terminology Used to Describe Soils – C4 Logs of Soil Borings

UNIFIED SOIL CLASSIFICATION SYSTEM

MAJOR DIVISIONS

USCS TYPICAL

SYMBOL DESCRIPTIONS

WELL-GRADED GRAVELS, GRAVEL-SAND

CLEAN GRAVELS GW MIXTURES WITH LITTLE OR NO FINES

WITH LESS THAN

GRAVELS

5% PASSING NO. 200

GP

POORLY-GRADED GRAVELS, GRAVEL-SAND

(More than half of

SIEVE MIXTURES WITH LITTLE OR NO FINES

coarse fraction is larger than

GM

SILTY GRAVELS, GRAVEL-SILT-SAND

the #4 sieve) GRAVELS WITH MIXTURES

COARSE OVER 12% PASSING

GRAINED NO. 200 SIEVE GC

CLAYEY GRAVELS, GRAVEL-SAND-CLAY

SOILS

MIXTURES

(More than half WELL-GRADED SANDS, SAND-GRAVEL of material

CLEAN SANDS WITH SW

MIXTURES WITH LITTLE OR NO FINES

is larger than LESS THAN 5% the #200 sieve)

SANDS PASSING NO. 200 POORLY-GRADED SANDS, SAND-GRAVEL

SIEVE

SP

MIXTURES WITH LITTLE OR NO FINES

(More than half of coarse fraction is smaller than SILTY SANDS, the #4 sieve) SANDS WITH OVER SM

SAND-GRAVEL-SILT MIXTURES

12% PASSING NO.

200 SIEVE SC

CLAYEY SANDS,

SAND-GRAVEL-CLAY MIXTURES

INORGANIC SILTS & VERY FINE SANDS,

ML SILTY OR CLAYEY FINE SANDS,

CLAYEY SILTS WITH SLIGHT PLASTICITY

SILTS AND CLAYS INORGANIC CLAYS OF LOW TO MEDIUM

CL PLASTICITY, GRAVELLY CLAYS,

(Liquid limit less than 50) SANDY CLAYS, SILTY CLAYS, LEAN CLAYS

FINE

GRAINED

OL

ORGANIC SILTS & ORGANIC SILTY CLAYS

SOILS OF LOW PLASTICITY

(More than half INORGANIC SILTS, MICACEOUS OR of material MH

DIATOMACEOUS FINE SAND OR SILT

is smaller than the #200 sieve) SILTS AND CLAYS

INORGANIC CLAYS OF HIGH PLASTICITY,

CH

FAT CLAYS

(Liquid limit greater than 50)

ORGANIC CLAYS & ORGANIC SILTS

OH

OF MEDIUM-TO-HIGH PLASTICITY

Note: Fine grained soils that plot within the hatched area on the Plasticity Chart, and coarse grained soils with between 5% and 12% passing No. 200 sieve require dual USCS symbols. (See KEY A-3 if provided)

UNIFIED SOIL CLASSIFICATION SYSTEM

KEY

C-1 Drafted By: ALE

Date: October, 2019

Project Number:

190100

LOG SYMBOLS

NON-STANDARD PENETRATION

BULK / GRAB SAMPLE SPLIT SPOON SAMPLER

(1.5-inch O.D. X 0.9-inch I.D.)

MODIFIED CALIFORNIA SAMPLER BDBGM SIZE CORE BARREL

(2 inch inside diameter) (1.65-inch I.D.)

GRAB SAMPLE BW44 SIZE CORE BARREL

(1.75-inch I.D.)

STANDARD PENETRATION HQ-3 SIZE CORE BARREL

SPLIT SPOON SAMPLER (2.4-inch I.D.)

(2.0-inch O.D. X 1.4-inch I.D.)

SHELBY…