A01 GeoTech Report iHouse.pdf

iHouse 19 Unit Apartment Building

Tonalea, AZ

Appendix A2

GeoTech Report 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

DRAFT GEOTECHNICAL EXPLORATION

REPORT

IHS IDIQ IHOUSE

INDIAN ROUTE 6290

TONALEA, ARIZONA

Prepared for:

Johnson Smitthipong & Rosamond Associates, Inc.

5210 E. Williams Circle, Suite 600 Tucson, Arizona

Prepared by:

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

ATEK Project # 240012

June 5, 2024

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

CHANDLER, AZ 85226 F (480) 656-9658

June 5, 2024 ATEK Project #240012

Daniel Hargreaves, AIA, FCSI, ISCS, CDT, RAS, LEED Assoc.

Director of Operations Johnson Smitthipong & Rosamond Associates, Inc.

5210 E. Williams Circle, Suite 600 Tucson, Arizona

Regarding: DRAFT Geotechnical Exploration Report

Project: IHS IDIQ iHouse

Indian Route 6290 Tonalea, Arizona

Dear Mr. Hargreaves:

ATEK Engineering Consultants, LLC is pleased to present the attached DRAFT Geotechnical Exploration Report for the IHS IDIQ iHouse located in Tonalea, Arizona within the Navajo Nation.

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

Antonio Lopez, P.E. Armando Ortega, P.E.

Geotechnical Group Manager Principal Geotechnical Engineer

Distribution: (1) Addresses (Electronic Copy)

TABLE OF CONTENTS

1. INTRODUCTION

Project Description Purpose Scope of Services

2. FIELD EXPLORATION

General Soil Test Borings Percolation Test Boring

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

4.4.3. Expansive Soils

Seismic Considerations Earth Fissures and Land Subsidence

5. ENGINEERING ANALYSES AND RECOMMENDATIONS

Earthwork

5.1.1. Frost Heave

5.1.2. Spread Footings

5.1.3. Sidewalks and Exterior Slabs

5.1.4. Pavement Site Preparation and Grading

5.1.5. Aggregate Base Course

5.1.6. Engineered Fill

5.1.7. Soil-Cement

Excavation

5.2.1. Trench Backfill

5.2.2. Temporary Excavations

5.2.1. Permanent Excavations and Slopes

Structures

5.3.1. Shallow Spread Footings

5.3.1.1. Structural Slab

5.3.2. Resistance to Lateral Loads

5.3.2.1. Wall Drainage

5.3.2.2. Backfill Placement

Moisture Protection Corrosion Potential

5.5.1. Electrical Resistivity

5.5.2. Sulfate and Chloride Content

Pavement Areas

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

DRAFT Geotechnical Exploration 240012 IHS IDIQ iHouse Tonalea, Arizona Page 1 of 24

1. INTRODUCTION

This report presents the results of our draft geotechnical exploration for the IHS IDIQ iHouse located in Tonalea, Arizona within the Navajo Nation. 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 proposed project is the construction of a new 19-unit apartment complex in

Tonalea, Arizona just north of the Inscription House Health Clinic. The proposed apartment building will be a one-story building with an approximate footprint of 18,000 square feet. The proposed construction is wood stud framing with stucco and CMU

Veneer. Additionally, improvements include parking areas, Recreational Vehicle spaces, and storm drain site retention.

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 the limitations presented herein. Attention is directed to the “Limitations” section of this report.

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2. FIELD EXPLORATION

General

Prior to the start of drilling, the Arizona 811 and the Navajo Tribal Utility Authority was contacted to locate existing utilities at the boring locations. The field exploration was performed on May 21, 2024. Three soil borings were drilled to a depth of twenty (20) feet below existing grade. The soil test borings were drilled using a truck mounted CME-

55 power drill rig equipped with 7 and ¼-inch outside diameter hollow stem augers.

The percolation test was drilled using a truck mounted CME-55 power drill equipped with 15-inch outside diameter solid 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.

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.

Tonalea, Arizona Page 3 of 24

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.

Percolation Test Boring

Percolation testing was completed in general accordance with the Arizona

Administrative Code Title 18, Chapter 9, A 310 Section F and the sides of the test hole were sleeved with an impermeable surface. The percolation depths and recorded rates are presented in the following table.

Percolation

Test Location

Percolation Depth Below

Existing Grade (feet)

Percolation

Rate (min/inch)

Soil Type (USCS)

P-1 3.0 1.0 SP-SM

Siltation, vegetation growth and other factors tend to slow infiltration rates within the basin. The infiltration rates provided above are unfactored field measurements and a proper reduction factor should be applied in the retention design.

The excavation of the retention basin should be accomplished with light weight excavation equipment to avoid compaction of the exposed native soils. No traffic should be allowed within the retention basin after construction. It should be noted that compaction of the basin will reduce the infiltration rates. If compaction within the basin floor occurs, the exposed surface should be scarified to a minimum depth of

8-inches and left uncompacted.

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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;

• Undisturbed ring density;

• Standard Proctor;

• Swell potential of soil;

• pH test;

• Resistivity test;

• Sulfate content;

• And chloride content.

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

4. GENERAL SITE CONDITIONS

Surface Conditions

The project is located approximately 1,000 feet north of the Inscription House Health

Clinic in Tonalea, Arizona. The project site is bound by Indian Route 6290 on the east, undeveloped land to the north and west, and the residential staff quarters housing to the south. Rough graded earthen roads connect the project site to the existing residential subdivision. At the time of our field study project site had heavy vegetation.

Subsurface Conditions

Residual soils were encountered at the project site. In general, these surface soils consist of Silty Sand (SM). These soils were found to have a relative density ranging from loose to very dense. The underlying subsurface soils encountered during our field exploration consisted of Silty Sand (SM). These soils were found to have a relative

Tonalea, Arizona Page 5 of 24 density of very dense. Potential sandstone can be encountered at a depth of 5 feet below existing grade or deeper. 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.

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 the tested undisturbed ring samples collected during our field study resulted in 0.63 percent indicating a slight collapse potential.

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4.4.3. Expansive Soils

Residual soil was encountered on the project site and generally have poor to good engineering properties. Expansive soils are soils with the potential for an increase in volume with an increase in moisture content. Based on the information collected during our field study and subsequent laboratory testing, we anticipate expansive-susceptible soils will be encountered during construction. Additionally, based on ASTM 4546, the expansive potential of the remolded sample collected during our field study, in the upper 5 feet, indicated an expansive potential.

Seismic Considerations

The project site is located in northern Arizona which is an area of low seismic activity.

The following values were developed using the Seismic Design Maps by Structural

Engineers Association by Location, the ASCE 7-16 Reference 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…………………………………………………36.597353˚

Central Longitude……………………………………………-110.791619˚

Tonalea, Arizona Page 7 of 24

Earth Fissures and Land Subsidence

The project site is located in an area with no documented earth fissures and in an area without measured land subsidence.

5. ENGINEERING ANALYSES AND RECOMMENDATIONS

Earthwork

All existing structural remnants, fill, pavement, topsoil, vegetation and organic soils should be removed from below structural areas. 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 D

Fa, Site Coefficient 1.6

Fv, Site Coefficient 2.4

Ss, Mapped Spectral Acceleration at 0.2‐second Period 0.243 g

S1, Mapped Spectral Acceleration at 1.0‐second Period 0.071 g

SMS, Spectral Acceleration at 0.2‐second Period Adjusted for Site Class 0.389 g

SM1, Spectral Acceleration at 1.0‐second Period Adjusted for Site Class 0.171 g

SDS, Design Spectral Response Acceleration at 0.2‐second Period 0.259 g

SD1, Design Spectral Response Acceleration at 1.0‐second Period 0.114 g

Tonalea, Arizona Page 8 of 24

5.1.1. Frost Heave

This project is in an area with an anticipated frost depth of 30 inches based on Coconino

County Arizona Community Development Table R301.2(1) between elevation 5,700 to

7,100 above sea level. To protect against frost heave, the use of fine-grained soils should be avoided in and around structural areas. The potential for snowpack adjacent to the structural areas may allow significant moisture to increase into fills around the outer edge of foundations therefore the exterior should be graded for positive drainage away from the structural areas. Also, to reduce the potential for moisture migration, refer to section 5.4 of this report.

5.1.2. Spread Footings

The existing surface soils should be removed to a minimum depth of one (1) foot below bottom of proposed spread footing elevation or below the existing surface elevation, whichever is deeper. The excavation of the site soils should be within the entire footprint of the structure and extend laterally for a minimum distance of five (5) feet beyond the perimeter of structure. The exposed subsurface soils should be scarified to a depth of eight (8) inches: moisture conditioned to within two (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

D698. The excavated soils should be replaced with soil-cement per section 5.1.7 of this report to bring the site to finish pad elevation.

5.1.3. Sidewalks and Exterior Slabs

The site soils tested as part of this project exhibit swelling potential and should not be used within one foot of finished subgrade. The existing surface soils below concrete flatwork (sidewalks and exterior slabs) should be replaced with one foot of soil-cement per section 5.1.7.

Tonalea, Arizona Page 9 of 24

5.1.4. Pavement Site Preparation and Grading

The pavement section presented in this report is based on the site soils encountered during our field exploration. The native soils should be scarified to a depth of twelve

(12) inches: moisture conditioned to within two (2) percent of optimum moisture content and compacted to a minimum of ninety-five (95) percent of maximum dry density. Optimum moisture content and maximum dry density should be determined by

ASTM Test Method D 698.

5.1.5. Aggregate Base Course

The aggregate base used in support of Portland cement concrete and asphaltic concrete pavements should conform to the local governing agency and/or Maricopa Association of Governments (MAG) Section 702 Specifications. The plasticity index of the fraction of material passing the No. 40 sieve should not exceed five when tested in accordance with ASTM Test Method D 4318. Coarse aggregate should have a percent of wear, when subjected to the Los Angeles abrasion test (ASTM Test Method C 131), of no greater than 40 when exposed to a maximum of 500 revolutions.

A minimum of four (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 (8) inches and compacted to a minimum of 95 percent of maximum dry density below Portland cement concrete and one hundred percent of maximum dry density below asphaltic concrete pavements as determined by ASTM Test Method D 698 or as specified by local

Tonalea, Arizona Page 10 of 24 specification. The moisture content during compaction should be maintained within two percent of optimum moisture content.

5.1.6. 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 geotechnical engineer. All engineered fills should be compacted as noted in section 5.

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

• general site grading

• foundation areas

• foundation backfill

• pavement areas

2. Imported soils with low expansive potentials could be used as fill material for the following:

• general site grading

• foundation areas

• interior floor slab areas

• foundation backfill

• exterior slab areas

• pavement areas

3. 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)

Tonalea, Arizona Page 11 of 24

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 3 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)

4. Imported soils (low-frost susceptible) should conform to the following:

Percent finer by weight

Gradation (ASTM C136)

3"………………………………………………………………………………….100

No. 4 Sieve ……………………………………………………………….25-60

No. 200 Sieve…………………………………………………………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 3 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)

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

6. Frozen soils should not be used as fill or backfill.

Tonalea, Arizona Page 12 of 24

7. 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.

8. All fill soils to be used beneath the foundations; slabs and pavements should be approved by the Geotechnical Engineer. Fill should be placed in eight (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.

5.1.7. Soil-Cement

The soil cement should be constructed and replaced in general accordance with

Maricopa Association of Governments (MAG) Section 311. The mix design prepared by the Contractor should attain a minimum 7-day compressive strength of 200 psi.

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

Tonalea, Arizona Page 13 of 24 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 shallow excavations in the site soils can most likely be accomplished by conventional earth moving equipment in good operating condition.

Excavations deeper than five feet may require specialized equipment. Refusal blow counts, greater than 50 blows per foot, were encountered from 5 feet to 20 feet below existing grade on potential sandstone. 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.

5.2.1. 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

Tonalea, Arizona Page 14 of 24

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.

Care must be used during compaction of backfill against stem 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 in close proximity to the below ground structures or earth retaining structures.

5.2.2. 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.

Tonalea, Arizona Page 15 of 24

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

Sand (SM). 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 inclination of 1½(h):1(v) or flatter for excavations 20 feet or less in depth. Steeper cut slopes may be utilized for excavations less than five (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.

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5.2.1. Permanent Excavations and Slopes

We recommend all permanent cut and fill slopes in soil be constructed at a gradient no steeper than 3(h):1(v). During wet weather, erosion could become a problem. Proper drainage and maintenance is recommended. To reduce the potential for surface erosion, a berm or "V" ditch may be located at the top of slopes subject to significant overland water flows in order to intercept and redirect surface runoff.

Fill placed on slopes steeper than 5(h):1(v) should be benched into the existing slope. It is recommended that the slope face be compacted as presented in the earthwork section of this report.

Structures

5.3.1. Shallow Spread Footings

The anticipated frost depth for the project area is 30-inches below existing site grade.

Therefore, concrete slabs and post-tensioned slab-on-ground foundations should have turn downs which extend below the anticipated frost depth.

Allowable Bearing Pressure for Shallow Foundations

Footing Depth Below

Finished Grade (ft.)*

Allowable

Bearing

Pressure

(psf)

2.5 2,500

3.0 3,000

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

Tonalea, Arizona Page 17 of 24

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 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.

5.3.1.1. Structural Slab

The subgrade in the structural slab area should be prepared as recommended in section

5.1.

For design of structural slabs on grade, a modulus of subgrade reaction, ks, of 200 pci is recommended for slabs bearing on competent soils prepared as recommended above.

However, this ks value is based on a bearing area of one square foot. In order to account

Tonalea, Arizona Page 18 of 24 for size effects a reduction is recommended for larger areas. The following approximation of ks (based on Terzaghi’s equation) can be used for mats of various dimensions.

ks (in pci) = 200[(B+1)/(2B)]2 where B is the width of the mat (in feet)

Additionally, it is recommended that a thicken edge be constructed on the slab to minimize the potential for edge damage.

5.3.2. 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 37 Pounds per Cubic Foot (PCF). Restrained walls should be designed to withstand a residual or long-term at-rest (Ko) earth pressure condition of 56 PCF.

A passive EFP of 300 PCF may be used for shallow spread footings. A coefficient of friction of 0.39 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.

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.

Tonalea, Arizona Page 19 of 24

5.3.2.1. Wall Drainage

The above-recommended values do not include lateral pressures due to hydrostatic forces. Therefore, wall backfill should be free draining and provisions should be made to collect and dispose of excess water that may accumulate behind earth retaining structures. In cases where site soils become saturated an equivalent fluid pressure of

90 PCF should be used.

Wall drainage should be collected by continuous perforated drainpipes, filter fabric, and gravel connected to weep holes. The drainpipe must run parallel to the wall. We recommend drain rock consist of durable stone having 100 percent passing the 1-inch sieve and zero percent passing the No. 4 sieve. Synthetic filter fabric should have an equivalent opening size (EOS), U.S. Standard Sieve, of between 40 and 70, a permeability of at least 0.02 centimeters per second and minimum puncture strength of 50 pounds.

5.3.2.2. Backfill Placement

All backfill should be placed and compacted in accordance with recommendations provided above for engineered fill. Care must be used during compaction of backfill against the below ground tanks 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 walls.

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.

Tonalea, Arizona Page 20 of 24

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

5.5.1. 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

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

“moderately corrosive”. It should be noted that these corrosion conditions are for the soils at submerged moisture conditions. Resistivities at drier moisture contents would be less corrosive than the results of the test.

Sample Location pH Resistivity (Ohm-cm)

Bulk Sample B-1 8.1 3,400

Tonalea, Arizona Page 21 of 24

The pH values of the samples tested were slightly basic. 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.

5.5.2. Sulfate and Chloride Content

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 a negligible corrosion potential.

Sample Location Design Life (yrs)

16 Gage 14 Gage 12 Gage

Bulk Sample B-1 107 139 192

Tonalea, Arizona Page 22 of 24

Pavement Areas

The on-site soils should be suitable as pavement subgrade soils provided all unsuitable debris, rubble, oversized cobbles, etc. are removed. A flexible and/or rigid pavement is recommended for the pavement areas. The recommended pavement sections are based on the assumption that the subgrade soils are prepared in accordance with section 5.1 of this report.

The flexible pavement section should consist of Central Plant Mix Asphaltic Concrete

Pavement (AC) on compacted Aggregate Base Course (ABC) as recommended in the table below. Flexible pavement should be placed in accordance with MAG Section 321 and local municipality standards.

PAVEMENT AREA

ASPHALT SURFACE

THICKNESS (IN)

AGGREGATE BASE COURSE

THICKNESS (IN)

Parking Areas* 3.0 6.0

Our calculations for design of the pavements section is based upon our classification of the subsurface soils, the calculated traffic in 18 kips equivalent single axle loads, the site preparation and grading recommendations provided above. A design life of 20 years was used in design.

Areas subject to sustained, heavy concentrated loads, such as dumpster areas should be paved with Portland Cement Concrete (PCC). A pavement section of 6 inches of PCC on 4 inches of aggregate base course is recommended in these areas. We should be contacted for additional recommendations if there are any areas subjected to volumes of traffic heavier than those assumed for this report.

Tonalea, Arizona Page 23 of 24

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.

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.

Tonalea, Arizona Page 24 of 24

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 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 #: 240012

Date: 5/20/2024

Drawn by: M Mendoza

Site Location Map - Sheet 1 of 1

IHS IDIQ iHouse

Tonalea, Arizona

Basemap provided by ArcGIS 111 South Weber Drive, Suite 1 Chandler, AZ 85226

LEGEND

Project area

APPENDIX B

Sample Location Plan

Project #: 240012

Date: 5/20/2024

Drawn by: M Mendoza

Basemap provided by Google Earth

Boring Location Plan - Sheet 1 of 1

IHS IDIQ iHouse

Tonalea, Arizona

Indian Rte 6290

Tonalea, AZ 86044

Project Address

111 South Weber Drive, Suite 1 Chandler, AZ 85226

LEGEND

Boring Location Percolation Location

B-1

B-2

B-3

PR-1

APPENDIX C

FIELD STUDY AND BORING LOGS

APPENDIX C

FIELD STUDY

BORINGS

The subsurface conditions at the site were explored on May 21, 2024, 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

IHS IDIQ – iHouse 19 Unit Apartment

Johnson Smitthipong & Rosamond Associates, Inc.

KEY

C-1 Drafted By: AM

Date: May, 2024

Project Number:

240012

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 TUBE

(3 inch outside diameter)

WATER LEVEL

(level after completion)

WATER LEVEL

(level where first encountered)

GENERAL NOTES

1. Lines separating strata on the logs represent approximate boundaries only. Actual transitions may be gradual.

2. No warranty is provided as to the continuity of soil or rock conditions between individual sample locations.

3. Logs represent general soil or rock conditions observed at the point of exploration on the date indicated.

4. In general, the Unified Soil Classification designations presented on the logs were based on visual classification in the field, modified where appropriate by visual classifications in the office, and/or laboratory gradation and index testing.

5. NA = Not Analyzed

LOG KEY

C-2 Drafted By: AM

P L

A S T

IC

IT

Y

IN

D E

X

PE

R

C E

N T

P A

S

SI

N G

#2

SI

E

V E

60 GRADATION CHART

SILTS AND CLAYS - REFER TO PLASTICITY CHART

GM & GC - SM & SC -

REFER TO REFER TO

PLASTICITY CHART PLASTICITY CHART

BORDERLINE - REQUIRES DUAL SYMBOLS BORDERLINE - REQUIRES DUAL SYMBOLS

GW AND GP - REFER TO CC AND CU SW AND SP - REFER TO C C AND CU

10 20 30 40 50 60 70 80 90 100

PERCENT PASSING #4 SIEVE

PLASTICITY CHART

CH

CL

OH or MH

CL-ML

ML or OL

10 20 30 40 50 60 70 80 90 100

LIQUID LIMIT

DEFINITIONS OF SOIL FRACTIONS

SOIL FRACTION PARTICLE SIZE RANGE

Boulders Greater than 300mm (12in.)

Cobbles 300mm to 75mm (12in. to 3in.)

Coarse Gravel 75mm to 19mm (3in. to 3/4in.)

Fine Gravel 19mm (3/4in.) to No. 4 sieve Coarse Sand No. 4 sieve to No. 10 sieve Medium Sand No. 10 sieve to No. 40 sieve Fine Sand No. 40 sieve to No. 200 sieve Fines less than No. 200 sieve

CHARTS & DEFINITIONS

IHS IDIQ – iHouse 19 Unit Apartment

Johnson Smitthipong & Rosamond Associates, Inc.

Tonalea, Arizona

KEY

C-3Drafted By: AM

Date: May, 2024

N Relative Firmness

0 - 4

Very soft

5 - 8 soft

9 - 15

Moderately firm

16 - 30

Firm

31 - 50

Very firm

51+

Hard

N Relative Density

0 - 4

Very loose

5 - 10

Loose

11 - 30

Medium dense

31 - 50

Dense

51+

Very dense

N Relative Consistency

0 - 2

Very soft

3 - 4 soft

5 - 8

Moderately stiff

9 - 15

Stiff

16 - 30

Very Stiff

31+

Hard

TERMINOLOGY USED ON THE BORING LOGS TO DESCRIBE

THE FIRMNESS, DENSITY, OR CONSISTENCY OF SOILS

The standard penetration resistance (N) in blows per foot is obtained by the ASTM D1586 procedure using 2" O.D., 1 3/8" I.D. samplers.

1. Terms for description of partially saturated and/or cemented soils including clays, cemented granular materials, silts and silty and clayey granular soils.

2. Terms for description of cohesionless, uncemented sands and sand-gravel mixtures.

3. Terms for description of clays which are saturated or near saturation.

TERMINOLOGY USED TO DESCRIBE SOILS

C-4 Drafted By: AM

SM

2-4

26-50/2''

50/2''

50/3''

50/3'' 20.3

SILTY SAND (SM), 70% fine to medium grained sand, 30% fines, loose, nonplastic, reddish brown, slightly moist, no cementation, weak reaction to HCl

Very dense, brown, weak cementation, no reaction to HCl, (weathered sandstone)

Light brown, moist

Bottom of auger @ 20.0 feet bgs.

Bottom of sampler @ 20.3 feet bgs.

No groundwater encountered.

Swell Potential of Soil=3.15%

NV NP6.2

11.3 100.3

California

D R

IL

L

O P

E R

A T

IO

N ft

Notes:

ATEK Project Number:

SPT

Core Barrel

B-1

Time After Drilling

240012

IHS IDIQ iHouse

Shelby

Penetrometer

Grab Sample

CME-55 5/21/2024

M O

IS

T

U R

E C

O N

T E

N T

D R

Y D

E N

S

IT

Y pc f)

Depth To Water (ft)

WATER LEVEL OBSERVATIONS

Wildcat

LOG OF EXPLORATORY BORING B-1

G R

A P

H

IC

L O

G

See Location Plan

Date Started:Drilling Equipment:

PI

Hand Auger

Driller:

Upon Completion of Drilling

Not Encountered

Operation Types:

Logger:

S A

M P

LE

Split Spoon

Excavated Pit

Sampler Types:

ft

Bulk Sample

While Drilling

Project Name:

Borehole Location:

Borehole Number:

D E

P T

H ft)

5/21/2…