A10-5 For RFI 154 - Geotech Reports.pdf

GEOTECHNICAL

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

WHITERIVER INDIAN HOSPITAL

200 WEST HOSPITAL DRIVE

WHITERIVER, ARIZONA

Prepared for:

Mabbet and Associates, Inc.

105 Central Street, Suite 4100 Stoneham, Massachusetts

Prepared by:

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

ATEK Project # 230211

April 4, 2025

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

CHANDLER, AZ 85226 F (480) 656-9658

April 4, 2025 ATEK Project #230211

Stephen A. Vetere, P.E., LSP, LEP Mabbet and Associates, Inc.

105 Central Street, Suite 4100 Stoneham, Massachusetts

Regarding: Geotechnical Exploration Report

Project: Whiteriver Indian Hospital

200 West Hospital Drive Whiteriver, Arizona

Dear Mr. Vetere:

ATEK Engineering Consultants, LLC is pleased to present the attached Geotechnical Exploration Report for the Whiteriver Indian Hospital located in Whiteriver, Arizona within the Fort Apache Indian Reservation. 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. SUBSURFACE EXPLORATION

Phase 1 – Soil Test Borings

2.1.1. Soil Sampling

2.1.2. Percolation Test Boring

Phase 2 – Rock Coring Seismic Refraction survey Refraction Microtremor

3. LABORATORY TESTING

4. GENERAL SITE CONDITIONS

Surface Conditions Subsurface Conditions

4.2.1. Soils

4.2.2. Rock

Groundwater Conditions Geologic Hazards

4.4.1. Liquefaction Potential

4.4.2. Collapsible Soils

4.4.3. Expansive Soils

Site-Specific Ground Motion Hazard Analysis Seismic Considerations Earth Fissures and Land Subsidence

5. ENGINEERING ANALYSES AND RECOMMENDATIONS

Earthwork

5.1.1. Frost Depth

5.1.2. Frost Consideration

5.1.3. Rock Socketed Drilled, Cast-in-Place, Concrete Shafts

5.1.3.1. Grade Beam

5.1.3.1. Structural Slab

5.1.4. Spread Footings – EMS and Facility Maintenance

5.1.5. Concrete Flatwork

5.1.6. Pavement Site Preparation and Grading

5.1.7. Aggregate Base Course

5.1.8. Engineered Fill

Excavation

5.2.1. Trench Backfill

5.2.2. Temporary Excavations

5.2.1. Permanent Excavations and Slopes

Structures

5.3.1. Rock Socket Axial Capacities

5.3.1.1. Factor of Safety

5.3.1.2. Settlement

5.3.1.3. Allowable Uplift Capacities

5.3.1.4. Shaft Group Resistance

5.3.3. Shallow Spread Footings - EMS and Facility Maintenance

5.3.3.1. Continuous and Isolated Footings - EMS and Facility

Maintenance

5.3.3.2. Structural Slab - EMS and Facility Maintenance

5.3.4. Resistance to Lateral Loads

5.3.4.1. Wall Drainage

5.3.4.2. 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 APPENDIX E – Seismic Refraction Survey APPENDIX F – Refraction Microtremor APPENDIX G – Allowable Rock Socket Capacities APPENDIX H – Geology Cross Section Profile

Geotechnical Exploration 230211 Whiteriver Indian Hospital Whiteriver, Arizona Page 1 of 36

1. INTRODUCTION

This report presents the results of our geotechnical exploration for the Whiteriver

Indian Hospital located in Whiteriver, Arizona within the Fort Apache Indian

Reservation. 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 a new four-story Hospital facility within the premises of the existing Whiteriver Indian Hospital in Whiteriver, Arizona. The building footprint will be approximately 103,500 square feet and a gross total square footage of approximately

406,000 square feet. The building construction will be a Type IA with concrete and steel components. The building will be supported on deep foundations embedded in rock sockets. The improvements include a free-standing Emergency Medical Services building with an approximate footprint of 4,600 square feet. Additional improvements include approximately 1,335 parking spaces.

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.

Whiteriver, Arizona Page 2 of 36

2. SUBSURFACE EXPLORATION

The subsurface exploration was completed in two which included several drilling techniques and geophysical surveys. Prior to the start of drilling, the Arizona 811, the

Tribal Utility Authority and Indian Health Service Facilities were contacted to locate existing utilities at the boring locations.

Phase 1 – Soil Test Borings

Phase 1 consisted of drilling fourteen borings using the Hallow Stem Auger (HSA) method. This field exploration was performed from August 18, 2024, to August 21, 2024. Fourteen soil borings were drilled to depths ranging between ten (10) and fifty

(50) feet below existing grade, one percolation soil boring was drilled to a depth of five

(5) feet below existing grade. Auger refusal was encountered at borings designated B-

1, B-4, B-5, B-6, B-7, and B-9. The drilling method was changed from HSA to Overburden

Drilling Excentric (ODEX) which uses a percussive air-hammer for boring designated as

B-3 to gather information on depth of bedrock to plan and facilitate phase 2. 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 for the soil borings and a 15-inch solid stem auger for the percolation test boring. Due to rig accessibility, boring designated as B-15 was advanced using a hand auger, to a depth on two and a half (2.5) feet below existing grade. The percolation test and boreholes 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 and percolation test, the boreholes were backfilled with excavated materials.

2.1.1. Soil Sampling

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

Whiteriver, Arizona Page 3 of 36

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.

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.

2.1.2. 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 a permeable 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)

P-1 5.0 33.0

Whiteriver, Arizona Page 4 of 36

Since percolation rates tend to slow with time as the basins “silt in”, we recommend an appropriate factor of safety be used in conjunction with these percolation rates when designing the basins.

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.

Phase 2 – Rock Coring

Based on the findings in Phase 1 a rock coring subcontracted was brought in to gather additional samples and explore the rock formation. Four borings were completed between October 21, 2024, to October 23, 2024 using a double tube core barrel drilling method. The four borings were advanced to depths ranging between thirty-five (35) and sixty-five (65) feet below existing grade. The borings were advanced through the overburden soils with truck mounted CME-75 power drill rig equipped with an 8-inch outside diameter HSA. The drilling method was changed to rock coring once the rock formation was encountered. The coring equipment used was an HQ3 wireline with an outside diameter 3 and 3/8-inch outside diameter (2 and 3/8-inch inner diameter). 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 drilling, the boreholes were backfilled with excavated materials.

Seismic Refraction survey

The subsurface soil conditions were also evaluated using seismic refraction methods.

The seismic refraction method uses the principle in which the velocity of the seismic refraction wave passes through a material, is directly related to the stiffness of the

Whiteriver, Arizona Page 5 of 36 subsurface material. As the velocity of this wave increases, the stiffness of the material increases. The waves used in this study consist of seismic compressive waves (p-waves). P-wave velocities of the subsurface strata are often correlated to the amount of effort required to excavate or rip through a subsurface soil material.

Four seismic refraction survey lines were completed on July 26, 2024. Seismic velocities, calculated zone thickness and depth to velocity zone boundaries for each interpreted bedrock or soil types are depicted in Figures 3 through 10 presented in

Appendix E. The results of the seismic refraction survey should be used with caution and only used as guidelines.

Refraction Microtremor

One refraction microtremor (ReMI) survey line was performed on the project site as part of the subsurface study. The purpose of the ReMI survey was to provide a calculated average shear waver velocity (Vs) of the subsurface materials to a depth of 100 feet for use in establishing a site class in accordance with the 2018 International Building Code.

Results of the ReMI survey are presented in Appendix F.

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;

• Hydrometer;

• One-dimensional consolidation;

• Standard Proctor;

• Swell potential of soil;

• Undisturbed ring density;

• pH tests;

• Resistivity tests;

Whiteriver, Arizona Page 6 of 36

• Sulfate content;

• Chloride content;

• Direct shear;

• Unconfined compressive strength.

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 south of the existing Whiteriver Indian Hospital in Whiteriver, Arizona within the Fort Apache Indian Reservation. The project site is bound to the south by Arizona State Route 73, 402 Old Sawmill Road to the east, Apache Behavioral

Health Services to the west, and the Whiteriver Hospital to the north. The surface south of Apache Circle was covered with dense vegetation and an oval parking lot was located south of the eastern half of the existing hospital. A few pedestrian paths were observed on the southern portion of the project site. The topography of the site generally slopes down towards State Route 73. A sudden change in elevation of 20 to 30 feet was observed just south of Apache Circle.

Subsurface Conditions

Subsurface conditions at the site generally consist of fine-grained soils overlying basalt.

A discussion of the subsurface materials encountered is presented in the following sections. Detailed description of the deposits are provided in our boring logs presented in Appendix C.

4.2.1. Soils

The overburden soils primarily consist of fine grain soils with a mixture of Clay, Silts and Sands. These soils had a low to medium plasticity and were found to have a relative

Whiteriver, Arizona Page 7 of 36 firmness ranging from moderately firm to very firm. In addition, these fine-grained soils had varying amounts of interbedded layers of gravel. Based on our exploratory borings the thickness of the residual soils ranged from 10 feet on the eastern side and

45 feet on the western side of the project site.

4.2.2. Rock

Rock was encountered at various boring locations completed for this project. The bedrock encountered was vesicular basalt and basalt with varying degrees of weathering. Core recovery was generally greater than 90 percent and RQD values were generally greater than 85 percent. The basalt was found to be weak to strong. Based on the rock recoveries, it is presumed that a younger basalt flow overlays and older basalt flow. This rock formation is mapped as Quaternary Basalt (Qb). For additional information see logs in Appendix C and Geology Cross Section Profile in Appendix H.

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, rock formation and groundwater conditions encountered at the project site during this study, the potential for soil liquefaction is considered to be negligible.

Whiteriver, Arizona Page 8 of 36

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 a 11.7 percent indicating a severe collapse potential.

4.4.3. Expansive Soils

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. 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.

Site-Specific Ground Motion Hazard Analysis

At the request of the client a site-specific ground motion hazard analysis was conducted by Kleinfelder, Inc. and is presented in the letter report titled Site-Specific Ground Motion Hazard Analysis, Proposed Whiteriver Indian Hospital Addition, 200 W. Hospital Drive, Whiteriver, Arizona 85941, Kleinfelder Project Number 25004546.001A, dated April 4, 2025. This letter report is presented under separate cover.

Seismic Considerations

The project site is located in eastern 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-

Whiteriver, Arizona Page 9 of 36 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…………………………………………………33.8753423˚

Central Longitude……………………………………………-109.9605721˚

Earth Fissures and Land Subsidence

The project site is located in an area with no documented earth fissures (Natural

Hazards in Arizona by Arizona Geological Survey) and in an area without a measured land subsidence (Arizona Land Subsidence Areas by Arizona Department of Water

Resources).

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

Seismic Design Factors Value

Site Class C Fa, Site Coefficient 1.3 Fv, Site Coefficient 1.5 Ss, Mapped Spectral Acceleration at 0.2‐second Period 0.261 g S1, Mapped Spectral Acceleration at 1.0‐second Period 0.082 g SMS, Spectral Acceleration at 0.2‐second Period Adjusted for Site Class 0.339 g SM1, Spectral Acceleration at 1.0‐second Period Adjusted for Site Class 0.123 g SDS, Design Spectral Response Acceleration at 0.2‐second Period 0.226 g SD1, Design Spectral Response Acceleration at 1.0‐second Period 0.082 g

Whiteriver, Arizona Page 10 of 36 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 footing system as presented in the following sections.

5.1.1. Frost Depth

Based on review of the building codes and standards of the neighboring town of Pinetop-

Lakeside the frost depth is 18-inches. 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 through earthwork operations, refer to section 5.4 of this report.

5.1.2. Frost Consideration

The site soils are frost susceptible, and small amounts of water can affect the performance of the relatively lightly loaded slab-on-grade and concrete flatwork.

Exterior slabs and flatwork should be anticipated to heave during winter months. If frost action needs to be eliminated in critical areas, we recommend the use of non-frost susceptible engineered fill per section 5.1.8. Placement of non-frost susceptible material in large areas may not be feasible; however, the following recommendations are provided to help reduce potential frost heave:

• Provide surface drainage away from structures and flatwork and toward the site storm drainage system;

• Install drain tiles around the perimeter of the building, stoops, below exterior slabs and pavements, and connect them to the storm drainage system;

Whiteriver, Arizona Page 11 of 36

• Grade clayey subgrades such that groundwater, potentially perched, in overlying more permeable subgrades, such as sand or aggregate base, drain toward the site drainage system;

• Place non-frost susceptible fill as backfill beneath slabs and flatwork that are critical to the project;

• Place a 3 horizontal to 1 vertical (3H:1V) transition zone between non-frost susceptible soils and other soils.

5.1.3. Rock Socketed Drilled, Cast-in-Place, Concrete Shafts

Rock socketed drilled, cast-in-place, concrete shaft (deep foundations) should be utilized to support the four-story hospital building, including roof mechanical equipment, and rooftop helipad. The deep foundation excavation should be advanced with single-flight auger, rock auger, or bucket auger bits to the design tip elevation.

The depth of excavation should be verified by measurement and inspection. The bottom of the hole should be cleaned such that no more than three inches of loose material remains. Depending on the type of auger used and the depth of the shaft excavation, alternative cleaning techniques, including hand cleaning or vacuuming, may be required. Due to the variability of the rock formation, we recommend verification predrilling to insure at a minimum of 5-feet of competent rock below drilled shaft bottom elevation. Rock socketed shafts may require additional excavation if competent rock is not encountered within 5-feet of first bedrock contact elevation.

Cohesionless soils were encountered at varying depths which may cave during drilling operations, see Boring Logs in Appendix C for additional information.

A minimum shaft diameter of 36-inches should be drilled to allow for proper cleaning, bottom preparation and inspection. Provisions should be made for removal of groundwater from the drilled shafts excavations. While groundwater is not anticipated, the drilled pier contractor should have pumps on hand to remove water in the event seepage into the drilled pier is encountered. Concrete slumps ranging between 6 and

Whiteriver, Arizona Page 12 of 36

8 inches should be specified to fill irregularities along the sides and bottom of the drilled hole, displace water as it is placed (if encountered), and permit placement of reinforcing cages into the fluid concrete. Temporary protective steel casing may be used to prevent side wall collapse, water intrusion, and to allow worker to safely enter, clean and inspect the drilled shaft. The protective casing many be extracted as the concrete is placed in the drill shaft, providing that a sufficient head of concrete is maintained inside the steel casing to prevent soil or water intrusion in the shaft. The concrete should be placed into the drilled shaft though a chute to reduce side flow or segregation. The socket face should be cleaned prior to concrete placement. Cleaning will require hand cleaning or washing of a mud smear forms on the face of the rock.

The geotechnical engineer or his representative should approve the rock socket surface prior to concrete placement.

5.1.3.1. Grade Beam

The site soils exhibit a swell potential and poses the risk of post construction movement. The grade beam should be supported on one foot of aggregate base course in areas not in contact with deep foundations, or void forms should be used. The aggregate base course should be moisture conditioned to within two (2) percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density.

5.1.3.1. Structural Slab

A structural slab may be used to transfer the warehouse loads to the grade beam/deep foundations. Void boxes may be used under the structural slab to reduce vertical movements of the structural slab due to expansive soils. The void boxes should have a height of at least 6 inches. The void boxes may consist of carboard carton.

Whiteriver, Arizona Page 13 of 36

5.1.4. Spread Footings – EMS and Facility Maintenance

The EMS, Facility Maintenance building and ancillary buildings can be supported on shallow spread footings. The existing surface soils should be removed to a minimum depth of three (3) feet 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. Any oversized material (larger than 3-inches) should not be used in backfill. The excavated material should then be moisture conditioned to within two (2) percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density and used as engineered fill to within one (1) foot of finished pad elevation. Optimum moisture content and maximum dry density should be determined by American Society for Testing and Materials (ASTM) D 698.

Engineered Fill material meeting the recommendations for Imported Soils and low-susceptible soils presented in section 5.1.8 of this report should be placed within one

(1) foot of the finished pad elevation. These soils should be 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 D 698.

5.1.5. Concrete Flatwork

The site soil tested as part of this project exhibit swelling potential and should not be used within eight (8) inches of the finished subgrade elevation. The existing surface soils should be removed to a minimum depth of one (1) foot below bottom of proposed concrete flatwork. Concrete flatwork includes sidewalks, exterior concrete slabs or concrete flatwork not subjected to loads. In addition, the exposed subsurface soils

Whiteriver, Arizona Page 14 of 36 should be scarified to a depth of six (6) inches: moisture conditioned to within two (2) percent of optimum moisture content and compacted to a minimum of 95 percent of maximum dry density. Engineered Fill material meeting the recommendations for

Imported Soils and low-susceptible soils presented in section 5.1.8 of this report should be placed within eight (8) inches of the finished subgrade elevation. These soils should be 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 D 698.

5.1.6. Pavement Site Preparation and Grading

The pavement section presented in this report is based on the site soils encountered during our field exploration. Any material with a diameter larger than three (3) inches within the pavement area should be removed prior to base course placement. 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.

5.1.7. Aggregate Base Course

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

Whiteriver, Arizona Page 15 of 36

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 specification. The moisture content during compaction should be maintained within two percent of optimum moisture content.

5.1.8. 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 can be used as fill material for the following:

• general site grading

• below foundation

• pavement areas

• up to 1-foot within finished pad

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

Whiteriver, Arizona Page 16 of 36

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)

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 144 psf surcharge and submerged.

Corrosion Potential (PPM)

Sulfate Content (ARIZ 733)……………………………………………….1,000(max)

Chloride Content (ARIZ 736)…………………………………………………500(max)

4. In addition to the above, imported low-frost susceptible soils should conform to the following:

Percent finer by weight

Gradation (ASTM C136)

3"………………………………………………………………………………… 100

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

No. 200 Sieve…………………………………………………………………15 (max)

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

Whiteriver, Arizona Page 17 of 36

6. 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.

7. All fill soils to be used beneath the foundations; slabs and pavements should be approved by the Geotechnical Engineer. The 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.

Excavation

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

7 and ¼-inch outside diameter hollow stem augers and core barrels. 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.

Whiteriver, Arizona Page 18 of 36

It is anticipated that shallow excavations in the site soils can most likely be accomplished by conventional earth moving equipment in good operating condition.

Bedrock was encountered at various depths ten (10) to forty (40) feet below existing surface elevation. In general, bedrock elevation is shallower at the eastern portion of the project and deeper on the western side. Auger refusal was encountered at these depths and the drilling method was changed to rock coring see core logs in Appendix C and Geology Cross Section Profile in Appendix H. Excavations in bedrock may require specialized excavation equipment. Based on geophysical surveys completed for this project the qualitative excavatability can be moderate to severe for unweathered to slightly weathered basalt and severe for unweathered basalt. Please refer to Section 4 and the boring logs, and seismic refraction survey presented in Appendix C and E 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

Whiteriver, Arizona Page 19 of 36

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.

Whiteriver, Arizona Page 20 of 36

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 Sandy

Clays. In our opinion, these soils would be considered a Type B soil when applying OSHA regulations. For this soils type OSHA recommends a maximum slope inclination of

1(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.

Whiteriver, Arizona Page 21 of 36

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. Rock Socket Axial Capacities

Drilled concrete foundation axial capacities were calculated using the methods presented in AASHTTO (Edition 2002) Section 4.6.5.3. The side resistance (4.6.5.3.2-1) and tip capacities (4.6.5.3.1-1) were calculated based on Unconfined Compressive Strength

(UCS) of the rock (basalt). The drilled shaft resistance was computed assuming a rock socket depth of at least 2.0D, where D is the shaft diameter.

The following table provides rock design parameters used in our analysis. Design Charts in Appendix G present the recommended allowable downward and uplift capacities of various diameters of straight, drilled, cast-in-place concrete rock sockets.

Whiteriver, Arizona Page 22 of 36

Parameter Symbol Estimated Value

Reference

Unit Weight γ 150 pcf Appendix D Unconfined Compressive Strength qu 3,500 psi Appendix D Rock Quality Designation RQD 80% Appendix D Geologic Strength Index GSI 60% Hoek & Diederichs (2006) Elastic Modulus of Intact Rock Ei 4,200 ksi Table 4.4.8.2.2B Elastic Modulus of Rock Em 2,100 ksi Hoek & Diederichs (2006) Modulus Ratio (Open Joints) Em/Ei 0.5 Table 4.4.8.2.2-3 Reduction Factor αE 0.528 Table 4.4.8.2.2-4

Drilled shafts for the building foundations should be rock socketed into the basalt rock which is approximately 10 to 40 feet below existing elevation grade, refer to boring logs in Appendix C and geology profiles in Appendix H. Note that the underlying rock is composed of two distinct flows/layers and a minimum of 5-feet of competent rock is required below bottom drilled shaft which may require penetration into the lower layer.

This should be verified with a pilot hole before shaft construction. The site topography and geology profile vary which may result in different length drilled shafts. A minimum drilled shaft diameter of three (3) feet is recommended for the proposed building to allow for proper cleaning, bottom preparation and inspection.

5.3.1.1. Factor of Safety

Due to the variability of the rock formation encountered during our field study a factor of safety of 3.0 was used for both side resistance and tip resistance.

5.3.1.2. Settlement

For drilled shaft socketed into rock, settlement of ½ inch or less can be expected.

Settlement would occur rapidly during construction of the foundation system.

Whiteriver, Arizona Page 23 of 36

5.3.1.3. Allowable Uplift Capacities

The allowable uplift axial capacities presented in the capacity chart presented in

APPENDIX G. The allowable uplift capacity provided in the chart in APPEDIX G has an approximate factor of safety of 3.0.

5.3.1.4. Shaft Group Resistance

The minimum recommended center-to-center pier spacing is 2.5 times the pier diameter (2.5D). No group axial reduction is required for drilled shafts with center-to-center spacing equal to or greater than 2.5D.

5.3.2. Drilled Shaft Lateral Analyses

Computer software is available which models the lateral behavior of a pile or drilled shaft using estimated non-linear response of the soil. For a given pile loading, an iterative solution is employed to determine the deflection of the pile vs. depth, from which stresses within the pile are determined. Recommendations are provided in the following sections for the use of the computer programs LPILE.

5.3.2.1. Lateral Analyses Using LPILE

Recommended soil parameters for use in LPILE to analyze lateral soil interaction are presented in the tables below. For drilled shafts adjacent to slopes and for the direction of loading toward the slope face, it is recommended that lateral support be neglected in the upper part of the slope where the slope face is closer to the shaft than three shaft diameters (or 10 feet minimum).

Whiteriver, Arizona Page 24 of 36

Recommended Soil Type to

Model

Approximate Elevation

Range (ft)

Unit Weight (pcf)

Elastic Modulus

(ksi)

Unconfined Compressive

Strength (psi)

RQD

Soil Strain Ratio, ε50

Weak Rock Varies 150 2,100 3,500 80 0.005 pcf = pounds per cubic foot psf = pounds per square foot ksi= Kips per square inch

5.3.2.2. Lateral Drilled Shaft Group Effects

According to AASHTO (2002) Section 4.6.5.6.1.4, drilled shafts in a group may be considered to act individually under lateral load when the center-to-center (CTC) spacing is greater than 2.5 diameters in the direction normal to loading.

Pile Cap Configuration CTC Spacing of 3D CTC Spacing of 8D pile cap in intimate contact with soil

0.8 1.0 pile cap not in intimate contact with soil

0.6 1.0

For intermediate spacing, the reduction value may be determined by linear interpolation. The above reduction factors apply to parallel loading only. Reduction factors should be applied to all shafts in a group regardless of shaft arrangement (i.e.

end of row or middle of row), and all other portions of AASHTO Interim Bridge

Specification 4.6.5.6 apply.

The recommended lateral reduction factors should be applied by reducing the p-values in the p-y curves by multiplying the internally generated p-values by the above reduction factors. There is a provision in LPILE for the user to input a p-multiplier to modify the internally generated p-y curves in this way. For COM624, it may be

Whiteriver, Arizona Page 25 of 36 necessary to have the program output the internally generated p-y curves, and then to manually re-enter the factored p-y curves.

5.3.2.3. Construction Considerations

The following paragraphs provide construction considerations for drilled shafts. As mentioned earlier, we recommend that the drilled shafts be installed according to

ADOT Standard Specification 609, which includes submission of a detailed installation plan to the Engineer by the contractor.

Our evaluation of the excavation characteristics of the on-site materials is based on the results of our exploratory borings, site observations, and experience with similar materials.

The drilled shafts should be inspected and evaluated to check adequate bearing material has been reached and that the bearing surface has been suitably cleaned. The foundation concrete should be designed so that it satisfies the requirements of Sections

609 and 1006 of ADOT Standard Specifications. Due to the variability of the site rock formation a pilot hole will be needed to verify a minimum of 5 feet of competent rock below the bottom of the shaft.

Where possible, the drilled shafts should be constructed in the “dry” (i.e. no more than

3 inches of water covering the base of the drilled shaft excavation). Also, the bottom of the hole should be cleaned such that no more than 3 inches of loose material remains.

Depending on the type of auger used and the depth of the pier excavation, alternative cleaning techniques, including hand cleaning or vacuuming, may be required. For drilled shafts constructed in the “dry”, the concrete may be placed by the free-fall method.

This method consists of using a vertical section of concrete chute to direct the concrete flow out of the truck in a vertical stream of concrete with a relatively small diameter.

The stream should be directed to avoid hitting the sides of the drilled shaft or the reinforcing cage, which could cause concrete segregation. Adequate compaction will

Whiteriver, Arizona Page 26 of 36 be achieved by free-fall of the concrete up to the top 10 feet. The top 10 feet of concrete should be vibrated in order to achieve proper compaction. The concrete should be designed so that the slump during placement is in the range of 6 to 8 inches for dry, uncased conditions.

Where the drilled shaft are constructed in the “wet”, a tremie pipe connected either to a hopper or concrete pump should be used to displace the water in the drilled shaft excavation upwards as the concrete is placed. If this method is used, detailed procedures should be submitted by the contractor for review and approval by the geotechnical engineer. The top 10 feet of concrete should be vibrated in order to achieve proper compaction. The concrete should be designed so that the slump during placement is in the range of 7 to 9 inches for conditions other than a dry, uncased hole.

Where it is anticipated that drilled shafts may be constructed in the “wet”, a minimum of 6-inches of concrete cover over reinforcing steel should be provided.

5.3.2.4. Casing

Permanent casing may be used to protect the drilled shaft from potential shaft wall collapse. Casing may be left in the ground after drilled-shaft concrete placement.

5.3.2.5. Excavation

Drilled shaft excavations should be advanced with single-flight auger, rock auger, or bucket auger bits to the design tip elevation. The depth of excavation should be verified by measurement and inspection. The bottom of the hole should be cleaned such that no more than three inches of loose material remains. Depending on the type of auger used and the depth of the shaft excavation, alternative cleaning techniques, including hand cleaning or vacuuming, may be required.

Cohesionless soils were encountered at varying depths which may cave during drilling operations, see Boring Logs in Appendix C for additional information.

Whiteriver, Arizona Page 27 of 36

5.3.2.6. Steel and Concrete Placement

We recommend steel reinforcement and concrete be placed immediately upon completion of each shaft excavation. Concrete used for shaft construction should be discharged vertically into the drilled hole to minimize aggregate segregation. Under no circumstances should concrete be allowed to free-fall against either the steel reinforcement or the sides of the excavation during shaft construction.

For construction in a dry hole, concrete should be placed through a suitable tube or tremie, so that it is channeled in such a manner to free-fall and clear the walls of the excavation and reinforcing steel until it strikes the bottom.