Geotechnical Engineering Report of Remote Communication Link Terminal (RCLT).RCLT

Environmental Services Geotechnical Engineering Construction Materials Testing Special Inspections

1230 N Skyline Drive, Suite C Idaho Falls, ID 83402 (208) 529-8242 Fax (208) 529-6911 www.mti-id.com mti@mti-id.com

MATERIALS

TESTING &

INSPECTION

GEOTECHNICAL ENGINEERING REPORT

of

Remote Communication Link Terminal (RCLT) Tower Replacement

Salmon, ID (Revised 20 August 2018)

Prepared for:

Federal Aviation Administration, ATO Engineering Services 1600 Lind Avenue Southwest Renton, WA 98057

MTI File Number E180017g http://www.mti-id.com/ mailto:mti@mti-id.com

20 August 2018 Page # 2 of 29 e180017g - geo - revised.docx

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Copyright © 2018 Materials

Testing & Inspection

TABLE OF CONTENTS

INTRODUCTION

Project Description Authorization Purpose Scope of Investigation Warranty and Limiting Conditions

SITE DESCRIPTION

Site Access Regional Geology General Site Characteristics Regional Site Climatology and Geochemistry

SEISMIC SITE EVALUATION

Geoseismic Setting Seismic Design Parameter Values

GEOLOGIC HAZARD ASSESSMENT

Regional Faults Historical Seismicity Seismically Induced Surface Rupture, Settlements, and Lateral Spreading Liquefaction Collapsible Soils

SOILS EXPLORATION

Exploration and Sampling Procedures Laboratory Testing Program Soil and Sediment Profile Expansive Soil Considerations Electrical Resistivity, pH, and Water Soluble Sulfate Analysis Volatile Organic Scan

SITE HYDROLOGY

Groundwater

LATERAL EARTH PRESSURES

FOUNDATION DISCUSSION AND RECOMMENDATIONS

Foundation Design Recommendations Raft/Mat Slab Drilled Shaft/Concrete Caisson General Foundation Infiltration

CONSTRUCTION CONSIDERATIONS

Earthwork Dry Weather Wet Weather Soft Subgrade Soils Frozen Subgrade Soils Structural Fill

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Backfill of Walls Excavations Groundwater Control

GENERAL COMMENTS

REFERENCES

APPENDICES

Acronym List Geotechnical General Notes Geotechnical Investigation Boring Log Plate 1: Vicinity Map Plate 2: Site Map Plate 3: Foundation Details

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INTRODUCTION

This report presents results of a geotechnical investigation and analysis in support of data utilized in design of structures as defined in the 2015 International Building Code (IBC). Information in support of groundwater and stormwater issues pertinent to the practice of Civil Engineering is included. Observations and recommendations relevant to the earthwork phase of the project are also presented. Revisions in plans or drawings for the proposed structure from those enumerated in this report should be brought to the attention of the soils engineer to determine whether changes in the provided recommendations are required. Deviations from noted subsurface conditions, if encountered during construction, should also be brought to the attention of the soils engineer.

Project Description

The proposed development is in the southeastern portion of the City of Salmon, Lemhi County, ID, and occupies a portion of the NE¼NW¼ of Section 8, Township 21 North, Range 22 East, Boise Meridian. This project will consist of construction of a self-supporting communications tower that is 30 feet tall. The tower is anticipated to be founded on a raft/mat slab foundation. MTI was verbally informed by Mr. Xiao Jun Mei that the raft/mat slab would be approximately 10 feet by 10 feet in size and would extend approximately 3 feet below existing site grades. Total settlements are limited to 1 inch. As an alternate, a deep foundation system may be considered for the project. MTI has not been informed of the proposed grading plan.

Authorization

Authorization to perform this exploration and analysis was given in the form of a written authorization to proceed from Mr. Xiao Jun Mei of Federal Aviation Administration, ATO Engineering Services to Monica

Saculles of Materials Testing and Inspection (MTI), on 19 January 2018. Said authorization is subject to terms, conditions, and limitations described in the Professional Services Contract entered into between Federal

Aviation Administration, ATO Engineering Services and MTI. Our scope of services for the proposed development has been provided in our proposal dated 29 January 2018 and repeated below.

Purpose

The purpose of this Geotechnical Engineering Report is to determine various soil profile components and their engineering characteristics for use by either design engineers or architects in:

Preparing or verifying suitability of foundation design and placement

Preparing site drainage designs

Indicating issues pertaining to earthwork construction

Scope of Investigation

The scope of this investigation included review of geologic literature and existing available geotechnical studies of the area, visual site reconnaissance of the immediate site, subsurface exploration of the site, field and laboratory testing of materials collected, and engineering analysis and evaluation of foundation materials. Our scope of work did not include pavement section recommendations.

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Warranty and Limiting Conditions

MTI warrants that findings and conclusions contained herein have been formulated in accordance with generally accepted professional engineering practice in the fields of foundation engineering, soil mechanics, and engineering geology only for the site and project described in this report. These engineering methods have been developed to provide the client with information regarding apparent or potential engineering conditions relating to the site within the scope cited above and are necessarily limited to conditions observed at the time of the site visit and research. Field observations and research reported herein are considered sufficient in detail and scope to form a reasonable basis for the purposes cited above.

Exclusive Use

This report was prepared for exclusive use of the property owner(s), at the time of the report, and their retained design consultants (“Client”). Conclusions and recommendations presented in this report are based on the agreed-upon scope of work outlined in this report together with the Contract for Professional Services between the Client and Materials Testing and Inspection (“Consultant”). Use or misuse of this report, or reliance upon findings hereof, by parties other than the Client is at their own risk. Neither Client nor Consultant make representation of warranty to such other parties as to accuracy or completeness of this report or suitability of its use by such other parties for purposes whatsoever, known or unknown, to Client or Consultant. Neither Client nor Consultant shall have liability to indemnify or hold harmless third parties for losses incurred by actual or purported use or misuse of this report. No other warranties are implied or expressed.

Report Recommendations are Limited and Subject to Misinterpretation

There is a distinct possibility that conditions may exist that could not be identified within the scope of the investigation or that were not apparent during our site investigation. Findings of this report are limited to data collected from noted explorations advanced and do not account for unidentified fill zones, unsuitable soil types or conditions, and variability in soil moisture and groundwater conditions. To avoid possible misinterpretations of findings, conclusions, and implications of this report, MTI should be retained to explain the report contents to other design professionals as well as construction professionals.

Since actual subsurface conditions on the site can only be verified by earthwork, note that construction recommendations are based on general assumptions from selective observations and selective field exploratory sampling. Upon commencement of construction, such conditions may be identified that require corrective actions, and these required corrective actions may impact the project budget. Therefore, construction recommendations in this report should be considered preliminary, and MTI should be retained to observe actual subsurface conditions during earthwork construction activities to provide additional construction recommendations as needed.

Since geotechnical reports are subject to misinterpretation, do not separate the soil logs from the report. Rather, provide a copy of, or authorize for their use, the complete report to other design professionals or contractors.

Locations of exploratory sites referenced within this report should be considered approximate locations only.

For more accurate locations, services of a professional land surveyor are recommended.

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This report is also limited to information available at the time it was prepared. In the event additional information is provided to MTI following publication of our report, it will be forwarded to the client for evaluation in the form received.

Environmental Concerns

Comments in this report concerning either onsite conditions or observations, including soil appearances and odors, are provided as general information. These comments are not intended to describe, quantify, or evaluate environmental concerns or situations. Since personnel, skills, procedures, standards, and equipment differ, a geotechnical investigation report is not intended to substitute for a geoenvironmental investigation or a Phase

II/III Environmental Site Assessment. If environmental services are needed, MTI can provide, via a separate contract, those personnel who are trained to investigate and delineate soil and water contamination.

SITE DESCRIPTION

Site Access

Access to the site may be gained via Highway 28 into the town of Salmon. At the intersection of Highway 28 and Challis Street/Highway 93, proceed south-southwest on Challis Street/Highway 93 for approximately 0.25 mile. The site occupies the northeast corner of the county maintenance facility located at 410 Highway 93. The location is depicted on site map plates included in the Appendix.

Regional Geology

The project site is located within the Salmon River Valley in eastern Idaho. Sediments deposited here were derived from Precambrian basement rock, part of what is known as the Salmon River Arch, and rhyolitic formations of the Challis Volcanics (Alt and Hyndman, 1998). Sedimentary basement rock formations were exposed during the Late Cretaceous Period (66 to 80 million years ago) when low-angle thrust faulting occurred during the Laramide Orogeny. Challis Volcanics formed from eruptions during the Eocene Epoch (37 to 58 million years ago) to cover Precambrian rocks. Basement rocks and volcanics were then exposed during basin and range extension during the Miocene Epoch (5.3 to 24 million years ago). Valleys were then filled by eolian deposits during a period that was characterized climatically as dry. When streams and rivers began to flow during the Pleistocene Epoch (0.01 to 2 million years ago), they cut through eolian deposits, reworking these, and developing lake systems within valleys. Local sediments generally consist of clay, clayey sands, and coarse gravels. Since their deposition, these sediments have gradually been eroded by the Salmon and Lemhi Rivers.

General Site Characteristics

This proposed development consists of approximately 504 square feet of flat terrain. Throughout the majority of the site, surficial materials consist of gravel fills. Regional drainage is northwest toward the Salmon River.

Stormwater drainage for the site is achieved by percolation through surficial soils. The site is situated so that it is unlikely that it will receive any stormwater drainage from off-site sources. Stormwater drainage collection and retention systems are not in place on the project site and do not currently exist within the vicinity of the project site.

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Regional Site Climatology and Geochemistry

Average precipitation is on the order of 9 to 12 inches per year. Annual average temperature ranges from 12ºF to 88º F, with extremes ranging from -30º F to 102º F (WRCC). Average annual wind speeds can be up to four miles per hour with a prevailing direction from the south to southwest. The State Transportation Department has adopted anionic asphalt cements. The pH of surface waters, groundwaters and soils in the region typically range from 7 to 9 but can become higher in montmorillonite rich areas (Gallogly, 2002). No indication of abnormal geochemical condition was noted on site. Nominal frost penetration is typically on the order of 30 inches, with extremes ranging to 42 inches.

SEISMIC SITE EVALUATION

Geoseismic Setting

Soils on site are classed as Site Class D in accordance with Chapter 20 of the American Society of Civil

Engineers (ASCE) publication ASCE/SEI 7-10. Structures constructed on this site should be designed per IBC requirements for such a seismic classification. Our investigation did not reveal hazards resulting from potential earthquake motions including: slope instability, liquefaction, and surface rupture caused by faulting or lateral spreading. Incidence and anticipated acceleration of seismic activity in the area is low.

Seismic Design Parameter Values

United States Geological Survey National Seismic Hazard Maps (2008), includes a peak ground acceleration map. The map for 2% probability of exceedance in 50 years in the Western United States in standard gravity

(g) indicates that a peak ground acceleration of 0.292 is appropriate for the project site based on a Site Class D.

The following section provides an assessment of the earthquake-induced earthquake loads for the site, including identification of the earthquake spectral response acceleration for short periods, SMS, and at 1-second period, SM1, adjusted for site class effects as required by the 2015 IBC based on the following equations:

saMS SFS

11 SFS vM

Where:

Fa = Site coefficient defined in Table 1613.3.3(1) in the 2015 IBC.

Fv = Site coefficient defined in Table 1613.3.3(2) in the 2015 IBC.

Ss = The mapped spectral accelerations for short periods.

S1 = The mapped spectral accelerations for 1-second periods.

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The USGS National Seismic Hazards Mapping Project includes a program that provides values for ground motion at a selected site based on the same data that were used to prepare the USGS ground motion maps. The maps were developed using attenuation relationships for soft rock sites; the source model, assumptions, and empirical relationships used in preparation of the maps are described in Petersen and others (1996). The following values are based on a site specific Site Class of D.

Ss and S1 = Mapped Spectral Acceleration Values

Site Class D

Fa = 1.382

Fv = 2.163

Period (sec) Sa (g)

0.2 0.522 (Ss, Site Class D)

1.0 0.159 (S1, Site Class D)

SMS = 0.722

SM1 = 0.344

Design spectral response acceleration parameters as presented in the 2015 IBC are defined as a 5% damped design spectral response acceleration at short periods, SDS, and at 1-second period, SD1, as calculated from the following equations:

MSDS SS

MD SS

For the proposed project site, the 5% damped design spectral response acceleration at short periods, as calculated using the program supplied by the USGS are as follows:

SDS = 0.481

SD1 = 0.230

GEOLOGIC HAZARD ASSESSMENT

This section provides an assessment of the geologic hazards for the site, including the potential for surface fault rupture, seismically induced settlements, and lateral spreading. The hazard evaluation methodology involved one or two steps. First, the potential for occurrence of each type of geologic phenomenon is assessed. If there is a potential for a phenomenon to occur, the second step is to assess whether the phenomenon likely will result in a significant hazard for designated structures. For this evaluation, a significant hazard is defined as one that results in structural damage and threatens life-safety.

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Regional Faults

The subject site is located within the Salmon River Valley. The Salmon River Valley is a fault bounded basin that was formed during the Miocene Epoch associated with basin and range extension. None of the faults along the margins of the valley are known to be active. No faults are mapped on the project site, and no evidence of faulting was observed during the subsurface exploration. The nearest fault noted by MTI is a north trending normal fault mapped approximately 2.3 miles to the west-northwest of the project site.

Historical Seismicity

According to the USGS Earthquakes Program, there have been 559 earthquakes recorded within approximately

50 miles of the project site with magnitudes ranging from 1.5 to 5.6. Most of these earthquakes occurred within the Idaho Seismic Belt to the southwest of Salmon. The closest earthquake noted during MTI’s research occurred on 12 December 2011 approximately 3.2 miles to the southwest of the project site and had a magnitude of 2.6.

Seismically Induced Surface Rupture, Settlements, and Lateral Spreading

Earthquakes generally are caused by a sudden slip or displacement along a zone of weakness, termed a fault, in the Earth’s crust. Surface fault rupture, which is a manifestation of the fault displacement at the ground surface, usually is associated with moderate to large-magnitude earthquakes (magnitudes of about 6 or larger) occurring on active faults having mapped traces or zones at the ground surface. The amount of surface fault displacement can be as much as 10 feet or more, depending on the earthquake magnitude and other factors. The displacements associated with surface fault rupture can have devastating effects on structures and lifelines situated astride the zone of rupture.

As mentioned above, no active faults have been mapped in the vicinity of the site. Based on the absence of nearby active faults, it is the opinion of MTI that the probability of the occurrence of seismically induced surface rupture, settlements, and lateral spreading is negligible.

Liquefaction

Liquefaction is a soil behavior phenomenon in which a soil located below the groundwater surface loses a substantial amount of strength due to strong earthquake ground shaking. Some types of soil tend to compact during earthquake shaking, inducing excess pore water pressure in the saturated soil, which, in turn, causes a reduction in strength of the soil. Recently deposited (i.e., geologically young) and relatively loose natural soils, and uncompacted or poorly compacted fills, are potentially susceptible to liquefaction. Loose sands are particularly susceptible. Loose silts also have potential for liquefaction. Dense natural soils and well-compacted fills have low susceptibility to liquefaction. Clayey soils, gravel sediments, and bedrock generally are not susceptible to liquefaction.

Possible consequences of liquefaction include vertical settlement, lateral displacement, loss of bearing capacity for foundations supported by soil that liquefies, increased lateral loading on structures retaining soil that liquefies, and flotation of lightweight structures embedded in soil that liquefies. Based on the minimal presence of liquefiable soils, it is the opinion of MTI that the probability of liquefaction at the project site is negligible.

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Collapsible Soils

Collapsible soils undergo a sudden decrease in volume due to the addition of water into the soil structure and/or additional loading. Collapsible soils in arid climates are generally associated with alluvial fans produced by intermittent stream flow. The soils dry prior to subsequent deposition and do not become fully consolidated under the overburden stresses. Collapsible soils typically exhibit a loose, honeycomb structure. They typically have a low to relatively low unit weight, low degree of saturation, and a high dry strength. Wetting a collapsible soil results in the loss of capillary tension or the softening, weakening, and dissolving of cemented agents allowing the larger particles to slip past each other into a denser soil structure. Typically, collapsible soils are made up of fine-grained soils.

Collapse potential laboratory testing of onsite soils was outside of MTI’s scope of work for the project.

However, based on the soils conditions encountered onsite and experience with other projects in the vicinity of the site, it is MTI’s opinion that the potential for collapsible soils is negligible.

SOILS EXPLORATION

Exploration and Sampling Procedures

Field exploration conducted to determine engineering characteristics of subsurface materials included a reconnaissance of the project site and investigation by soil boring. The boring was located in the field by means of visual approximation from on-site features or known locations and is presumed to be accurate to within a few feet. The boring was advanced by means of a truck-mounted drilling rig equipped with continuous flight hollow-stem augers. At specified depths, samples were obtained using a standard split-spoon sampler, and

Standard Penetration Test (SPT) blow counts were recorded. Uncorrected SPT blow counts are provided on a log, which can be found in the Appendix. Delayed water level observations were made in the open boring to evaluate groundwater levels. At completion of exploration, the boring was backfilled with loose excavated materials and bentonite holeplug.

Samples have been visually classified in the field by professional staff, identified according to boring number and depth, placed in sealed containers, and transported to our laboratory for additional testing. Subsurface materials have been described in detail on a log provided in the Appendix. Results of field and laboratory tests are also presented in the Appendix. MTI recommends that the log not be used to estimate fill material quantities.

Laboratory Testing Program

Along with our field investigation, a supplemental laboratory testing program was conducted to determine additional pertinent engineering characteristics of subsurface materials necessary in an analysis of anticipated behavior of the proposed structures. Laboratory tests were conducted in accordance with current applicable

American Society for Testing and Materials (ASTM) and American Association of State Highway and

Transportation Officials (AASHTO) specifications, and results of these tests are to be found on the accompanying log located in the Appendix.

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The laboratory testing program for this report included: Soil Resistivity – AASHTO T288, pH of Soil –

AASHTO T289, Water Soluble Sulfate Ion Content in Soil – AASHTO T290, Water Soluble Chloride Content in Soil – AASHTO T291, Atterberg Limits Testing – ASTM D4318, and Grain Size Analysis – ASTM

C117/C136.

Soil and Sediment Profile

The profile below represents a generalized interpretation for the project site. Note that on site soils strata, encountered in the boring location, may vary from the individual soil profiles on the site, which can be found in the Appendix.

Poorly graded gravel with sand fill materials were encountered at ground surface. These materials were brown and exhibited a moisture content slightly moist. Fills were noted to be loose to dense. Fine to coarse-grained sand and 1-inch minus gravel were present throughout.

Lean clays were encountered beneath surficial fill materials. These fine-grained soils were light brown to brown, slightly moist to moist, and had consistencies ranging from soft to medium stiff. Fat clay soils were noted beneath the lean clays. Fat clays were classified as brown, moist to saturated, and medium stiff.

At depth, poorly graded gravel with sand sediments overlain by a thin layer of poorly graded sands were exposed. Poorly graded sands and gravels were brown to grayish brown, saturated, and medium dense to very dense. Fine to coarse-grained sand was noted throughout. Refusal was met on a large boulder present within the poorly graded gravel with sand sediments at depths of 23.5 feet.

Competency of boring sidewalls varied based on soil type. In general, fine grained soils remained stable while more granular sediments slightly caved. However, moisture contents will also affect wall competency with saturated soils having a tendency to readily slough when under load and unsupported.

Expansive Soil Considerations

High-plasticity clay (CH) soils present are highly active and will be subject to volumetric change with fluctuations in moisture content. Such movement will most often be associated with seasonal moisture variation of clayey soils. Ground-supported improvements (i.e., shallow foundations or garage slabs) founded on clay soils will move in response to changes in soil moisture. Movement will be observed as heave if construction occurs when soils are relatively dry then subsequently become wet, and conversely, movement will be observed as settlement if construction occurs when soils are relatively moist and are then allowed to dry.

Given the presence of these clay soils, proper grading is considered to be essential. Positive grades must be maintained surrounding the tower foundation, including exterior slabs or nearby structures. Ground surfaces are to slope away from structures at a minimum of 5 percent for a distance of 10 feet, which allows for positive drainage of surface water away from the buildings. If structures are to be tightly clustered, limiting space between two adjacent foundation systems, subsurface drains may be required to alleviate water ponding during short, intense storm events.

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Electrical Resistivity, pH, and Water Soluble Sulfate Analysis

A grab sample of native lean clay was collected on 28 June 2018 at a depth ranging from 2.5 to 3.0 feet bgs in boring 1. This location is illustrated on the Site Map included in the Appendix. Analysis results are given in the following table:

Soil Analysis Results

Analysis Results

Resistivity 540 Ohms-cm pH 8.50

Water Soluble Sulfate Content 175 ppm

Water Soluble Chloride Content 15 ppm

For soils, electrical resistivity is a function of soil chemistry and moisture content. Galvanic currents, which tend to increase the possibility of corrosion, are more likely to develop in low resistivity soils. The resistivity value obtained is characteristic of soils classified as extremely corrosive to unprotected iron, steel, cast iron, ductile iron, galvanized steel, and dielectric steel or iron. The pH of the sample (8.50) indicates a strongly alkaline soil. A water soluble sulfate content of 175 ppm was determined and is considered to be “Moderate” severity (Class S1) per American Concrete Institute (ACI) 318, Table 19.3.1.1. This investigation is limited in scope and is not intended to represent a comprehensive analysis of corrosivity potential of near-surface native soils. MTI recommends that the cement type used for the project be selected in accordance with ACI 318, Table

19.3.2.1 for an S1 exposure category and class.

Volatile Organic Scan

No environmental concerns were identified prior to commencement of the investigation. Therefore, soils obtained during on-site activities were not assessed for volatile organic compounds by portable photoionization detector. Samples obtained during our exploration activities exhibited no odors or discoloration typically associated with this type of contamination. Groundwater encountered did not exhibit obvious signs of contamination.

SITE HYDROLOGY

Existing surface drainage conditions are defined in the General Site Characteristics section. Information provided in this section is limited to observations made at the time of the investigation. Either regional or local ordinances may require information beyond the scope of this report.

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Groundwater

During this field investigation, groundwater was encountered in the boring at 9.75 feet bgs. Soil moistures in the boring were slightly moist to moist within surficial fills and soils. Within the fat clays, soil moistures ranged from moist to saturated as the water table was approached and penetrated. In the vicinity of the project site, groundwater levels are controlled in large part by the stage and flow of the Lemhi and Salmon Rivers, and to a lesser degree by residential and commercial irrigation activity and leakage from nearby canals. Maximum groundwater elevations likely occur during the late spring and early summer runoff season and continue through the later portion of the irrigation season.

During previous investigations performed in November 2006 and June 2013 within approximately ½-mile to the northeast and east of the project site, evidence of groundwater was noted within numerous test pits at depths ranging from 3.8 to 7.3 feet bgs. Furthermore, according to United States Geological Survey (USGS) monitoring well data within approximately ½-mile of the project site, groundwater was measured at depths ranging between 3 and 15 feet bgs, which equates to groundwater elevations of 3,950 to 3,961 feet above mean sea level (msl).

Based on evidence of this investigation and background knowledge of the area, MTI estimates groundwater depths to remain greater than approximately 3 feet bgs throughout the year. This depth can be confirmed through long-term groundwater monitoring.

LATERAL EARTH PRESSURES

For lateral earth pressure analysis, MTI anticipates that the soils of interest will be the native lean clay and fat clay soils or poorly graded gravel with sand sediments encountered in the boring. For the clay soils, the following values are applicable under non-surcharged, drained conditions.

Lateral Earth Pressure Values for Native Clay Soils

Soil Type: Lean Clay/Fat Clay

Internal Friction Angle: 24 Dry Unit Weight: 90 pcf

Cohesion: 350 psf Buoyant Unit Weight: 55 pcf

Natural Void Ratio: 0.8 Natural Moisture: 32 %

At rest lateral earth pressure: 70 pcf

Ko= 0.6

Active lateral earth pressure: 50 pcf

Ka= 0.4

Passive lateral earth pressure: 282 pcf

Kp= 2.4

1Lateral earth pressure values are in pounds per square foot, per foot of wall (psf/ft). Alternately, the values presented may also be considered as equivalent fluid with units of pounds per cubic foot (pcf).

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Lateral Earth Pressure Values for Native Poorly Graded Gravel with Sand Sediments

Soil Type: Poorly Graded Gravel with Sand

Internal Friction Angle: 35 Dry Unit Weight: 128 pcf

Cohesion: NA Buoyant Unit Weight: 83 pcf

Natural Void Ratio: 0.4 Natural Moisture: 5 %

At rest lateral earth pressure: 57 pcf

Ko= 0.4

Active lateral earth pressure: 36 pcf

Ka= 0.3

Passive lateral earth pressure: 496 pcf

Kp= 3.7

1Lateral earth pressure values are in pounds per square foot, per foot of wall (psf/ft). Alternately, the values presented may also be considered as equivalent fluid with units of pounds per cubic foot (pcf).

Lateral earth pressure values do not incorporate specific factors of safety, and are only applicable for non-surcharged, drained conditions. Factors of safety, if applicable, should be integrated into the structural design of the foundations. For complex structures, deep structures, or structures with significant perimeter landscaping, a soils engineer should be retained as part of the design team in developing appropriate project design parameters and construction specifications.

FOUNDATION DISCUSSION AND RECOMMENDATIONS

Various foundation types have been considered for support of the proposed structure. Two requirements must be met in the design of foundations. First, the applied bearing stress must be less than the ultimate bearing capacity of foundation soils to maintain stability. Second, total and differential settlement must not exceed an amount that will produce an adverse behavior of the superstructure. Allowable settlement is usually exceeded before bearing capacity considerations become important; thus, allowable bearing pressure is normally controlled by settlement considerations.

Considering subsurface conditions and the proposed construction, it is recommended that the structure be founded upon either a raft/mat slab or deep foundation system. Total settlements should not exceed 1 inch if the following design and construction recommendations are observed.

Foundation Design Recommendations

Based on data obtained from the site and test results from various laboratory tests performed, MTI recommends the following guidelines for the net allowable soil bearing capacity:

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Raft/Mat Slab

Soil Bearing Capacity

Raft/Mat Slab Depth

ASTM D1557

Subgrade Compaction

Net Allowable

Soil Bearing Capacity

Raft/mat slabs must bear on at least 3 feet of compacted structural fill reinforced with two layers of Tensar TX

160 geogrid. Geogrid reinforced fill must bear on native lean clay soils.1 The exposed subgrade should be prepared as follows:

1. A layer of Contech C-300 (or equivalent) stabilization fabric must be placed over the exposed native subgrade.

2. Twelve inches of granular structural fill (ISPWC

Type 1 crushed aggregate base) should be placed over the stabilization fabric and be compacted to at least 95% of the maximum dry density as determined by ASTM D1557.

3. A layer of Tensar TX 160 geogrid should be placed over the compacted structural fill followed by 12 inches of compacted structural fill.2 This process should be continued until two layers of geogrid are in place. At least 12 inches of compacted structural fill should be placed over the top layer of geogrid.

All fill must be compacted to at least 95% of the maximum dry density as determined by ASTM D1557.

Geogrid should extend a minimum of 2 feet beyond the footings on all sides. Geogrid should be overlapped a minimum distance of 24 inches between splices. See the attached Plate 3 for graphical representation of this system.

Not Required for

Native Soil

95% for Structural Fill

2,500 lbs/ft2

1It will be required for MTI personnel to verify the bearing soil suitability for each structure at the time of construction.

2Structural fill between layers of geogrid must consist of ISPWC Type 1 crushed aggregate base.

For raft or mat slabs bearing on compacted structural fill material, a modulus of subgrade reaction, k value, of

200 pounds per cubic inch (pci) may be used for the slab design based on correlation to values typically resulting from a 1 foot by 1 foot plate load test. However, depending on how the slab load is applied, the value will need to be geometrically modified. The values should be adjusted for larger areas using the following expression:

Modulus of Subgrade Reaction:

B

B kk s where: ks = coefficient of vertical subgrade reaction for loaded area, k = coefficient of vertical subgrade reaction for a 1 square foot area, and

B = effective width of area loaded, in feet.

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Drilled Shaft/Concrete Caisson

Soil Bearing Capacity

Drilled Shaft/Concrete Caisson Depth ASTM D1557 Subgrade

Compaction

Net Allowable

Soil Bearing Capacity

Drilled shaft/concrete caisson foundations must bear on competent, undisturbed, native poorly graded gravel with sand sediments. Existing lean clay soils, fat clay soils, and fill materials must be completely removed from below foundation elements.1

Excavation depths of approximately 15 feet bgs should be anticipated to expose proper bearing soils.

Not Required for

Native Soil

95% for Structural Fill

8,000 lbs/ft2

1It will be required for MTI personnel to verify the bearing soil suitability for each structure at the time of construction.

Assuming a drilled shaft diameter of 2 to 3 feet and a total depth of 15 feet, an allowable skin friction value of

55 psf should be used. MTI recommends that the upper 2 feet of soil be neglected for design. Note that when designing the drilled shafts to account for both end bearing and skin friction, some vertical mobilization of the drilled shaft will be required in order to attain the full end bearing.

General Foundation Information

A sliding frictional coefficient value of 0.45 should be used for footings bearing on native poorly graded gravel with sand sediments or granular structural fill. Additionally, a safety factor of 3 was used for both the allowable bearing capacities and skin friction values listed above. The IBC allows for a ⅓ increase for short-term loading when designing for the presumptive load bearing values outlined in Table 1806.2. However, as the foundation recommendations in this report deviate from the IBC presumptive load bearing values, MTI does not recommend the ⅓ increase for short-term loading be implemented.

Footings should be proportioned to meet either the stated soil bearing capacity or the 2015 IBC minimum requirements. Total settlement should be limited to approximately 1 inch, and differential settlement should be limited to approximately ½ inch. If designed per the recommendations outlined in this report, upheave of footings is not anticipated to be a concern. Objectionable soil types encountered at the bottom of footing excavations should be removed and replaced with structural fill. Excessively loose or soft areas that are encountered in the footings subgrade will require over-excavation and backfilling with structural fill. To minimize the effects of slight differential movement that may occur because of variations in the character of supporting soils and seasonal moisture content, MTI recommends continuous footings be suitably reinforced to make them as rigid as possible. MTI recommends that the bottom of external footings be 30 inches below finished grade for frost protection.

CONSTRUCTION CONSIDERATIONS

Recommendations in this report are based upon structural elements of the project being founded on either geogrid-reinforced structural fill or competent, native poorly graded gravel with sand sediments. Structural areas should be stripped to an elevation that exposes these soil types.

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Earthwork

Excessively organic soils, deleterious materials, or disturbed soils generally undergo high volume changes when subjected to loads, which is detrimental to subgrade behavior in the area of pavements, floor slabs, structural fills, and foundations. Limited vegetation with associated root systems were noted at the time of our investigation. It is recommended that organic or disturbed soils, if encountered, be removed to depths of 1 foot

(minimum), and wasted or stockpiled for later use. Stripping depths should be adjusted in the field to assure that the entire root zone or disturbed zone or topsoil are removed prior to placement and compaction of structural fill materials. Exact removal depths should be determined during grading operations by MTI personnel, and should be based upon subgrade soil type, composition, and firmness or soil stability.

If underground storage tanks, underground utilities, wells, or septic systems are discovered during construction activities, they must be decommissioned then removed or abandoned in accordance with governing Federal, State, and local agencies. Excavations developed as the result of such removal must be backfilled with structural fill materials as defined in the Structural Fill section.

MTI should oversee subgrade conditions (i.e., moisture content) as well as placement and compaction of new fill (if required) after native soils are excavated to design grade. Recommendations for structural fill presented in this report can be used to minimize volume changes and differential settlements that are detrimental to the behavior of footings, pavements, and floor slabs. Sufficient density tests should be performed to properly monitor compaction. For structural fill beneath building structures, one in-place density test per lift for every

5,000 square feet is recommended. In parking and driveway areas, this can be decreased to one test per lift for every 10,000 square feet.

Dry Weather

If construction is to be conducted during dry seasonal conditions, many problems associated with soft soils may be avoided. However, some rutting of subgrade soils may be induced by shallow groundwater conditions related to springtime runoff or irrigation activities during late summer through early fall. Solutions to problems associated with soft subgrade soils are outlined in the Soft Subgrade Soils section. Problems may also arise because of lack of moisture in native and fill soils at time of placement. This will require the addition of water to achieve near-optimum moisture levels. Low-cohesion soils exposed in excavations may become friable, increasing chances of sloughing or caving. Measures to control excessive dust should be considered as part of the overall health and safety management plan.

Wet Weather

If construction is to be conducted during wet seasonal conditions (commonly from mid-November through

May), problems associated with soft soils must be considered as part of the construction plan. During this time of year, fine-grained soils such as silts and clays will become unstable with increased moisture content, and eventually deform or rut. Additionally, constant low temperatures reduce the possibility of drying soils to near optimum conditions.

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Soft Subgrade Soils

Shallow fine-grained subgrade soils that are high in moisture content should be expected to pump and rut under construction traffic. During periods of wet weather, construction may become very difficult if not impossible.

The following recommendations and options have been included for dealing with soft subgrade conditions:

Track-mounted vehicles should be used to strip the subgrade of root matter and other deleterious debris.

Heavy rubber-tired equipment should be prohibited from operating directly on the native subgrade and areas in which structural fill materials have been placed. Construction traffic should be restricted to designated roadways that do not cross, or cross on a limited basis, proposed roadway or parking areas.

Soft areas can be over-excavated and replaced with granular structural fill.

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Construction roadways on soft subgrade soils should consist of a minimum 2-foot thickness of large cobbles of 4 to 6 inches in diameter with sufficient sand and fines to fill voids. Construction entrances should consist of a 6-inch thickness of clean, 2-inch minimum, angular drain-rock and must be a minimum of 10 feet wide and 30 to 50 feet long. During the construction process, top dressing of the entrance may be required for maintenance.

Scarification and aeration of subgrade soils can be employed to reduce the moisture content of wet subgrade soils. After stripping is complete, the exposed subgrade should be ripped or disked to a depth of 1½ feet and allowed to air dry for 2 to 4 weeks. Further disking should be performed on a weekly basis to aid the aeration process.

Alternative soil stabilization methods include use of geotextiles, lime, and cement stabilization. MTI is available to provide recommendations and guidelines at your request.

Frozen Subgrade Soils

Prior to placement of structural fill materials or foundation elements, frozen subgrade soils must either be allowed to thaw or be stripped to depths that expose non-frozen soils and wasted or stockpiled for later use.

Stockpiled materials must be allowed to thaw and return to near-optimal conditions prior to use as structural fill.

Structural Fill

Soils recommended for use as structural fill are those classified as GW, GP, SW, and SP in accordance with the

Unified Soil Classification System (USCS) (ASTM D2487). Use of silty soils (USCS designation of GM, SM, and ML) as structural fill may be acceptable. However, use of silty soils (GM, SM, and ML) as structural fill below footings is prohibited. These materials require very high moisture contents for compaction and require a long time to dry out if natural moisture contents are too high and may also be susceptible to frost heave under certain conditions. Therefore, these materials can be quite difficult to work with as moisture content, lift thickness, and compactive effort becomes difficult to control. If silty soil is used for structural fill, lift thicknesses should not exceed 6 inches (loose), and fill material moisture must be closely monitored at both the working elevation and the elevations of materials already placed. Following placement, silty soils must be protected from degradation resulting from construction traffic or subsequent construction.

Recommended granular structural fill materials, those classified as GW, GP, SW, and SP, should consist of a

6-inch minus select, clean, granular soil with no more than 50 percent oversize (greater than ¾-inch) material and no more than 12 percent fines (passing No. 200 sieve). These fill materials should be placed in layers not to exceed 12 inches in loose thickness. Prior to placement of structural fill materials, surfaces must be prepared as outlined in the Construction Considerations section. Structural fill material should be moisture-conditioned to achieve optimum moisture content prior to compaction. For structural fill below footings, areas of compacted backfill must extend outside the perimeter of the footings for a distance equal to the thickness of fill between the bottom of foundation and underlying soils, or 5 feet, whichever is less. All fill materials must be monitored during placement and tested to confirm compaction requirements, outlined below, have been achieved.

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Each layer of structural fill must be compacted, as outlined below:

Below Structures and Rigid Pavements: A minimum of 95 percent of the maximum dry density as determined by ASTM D1557.

Below Flexible Pavements: A minimum of 92 percent of the maximum dry density as determined by

ASTM D1557 or 95 percent of the maximum dry density as determined by ASTM D698.

The ASTM D1557 test method must be used for samples containing up to 40 percent oversize (greater than ¾-inch) particles. If material contains more than 40 percent but less than 50 percent oversize particles, compaction of fill must be confirmed by proof rolling each lift with a 10-ton vibratory roller (or equivalent) until the maximum density has been achieved. Density testing must be performed after each proof rolling pass until the in-place density test results indicate a drop (or no increase) in the dry density, defined as maximum density or

“break over” point. The number of required passes should be used as the requirements on the remainder of fill placement. Material should contain sufficient fines to fill void spaces, and must not contain more than 50 percent oversize particles.

Backfill of Walls

Backfill materials must conform to the requirements of structural fill, as defined in this report. For wall heights greater than 2.5 feet, the maximum material size should not exceed 4 inches in diameter. Placing oversized material against rigid surfaces interferes with proper compaction, and can induce excessive point loads on walls.

Backfill shall not commence until the wall has gained sufficient strength to resist placement and compaction forces. Further, retaining walls above 2.5 feet in height shall be backfilled in a manner that will limit the potential for damage from compaction methods and/or equipment. It is recommended that only small hand-operated compaction equipment be used for compaction of backfill within a horizontal distance equal to the height of the wall, measured from the back face of the wall.

Backfill should be compacted in accordance with the specifications for structural fill, except in those areas where it is determined that future settlement is not a concern, such as planter areas. In nonstructural areas, backfill must be compacted to a firm and unyielding condition.

Excavations

Shallow excavations that do not exceed 4 feet in depth may be constructed with side slopes approaching vertical.

Below this depth, it is recommended that slopes be constructed in accordance with Occupational Safety and

Health Administration (OSHA) regulations, Section 1926, Subpart P. Based on these regulations, on-site soils are classified as type “C” soil, and as such, excavations within these soils should be constructed at a maximum slope of 1½ feet horizontal to 1 foot vertical (1½:1) for excavations up to 20 feet in height. Excavations in excess of 20 feet will require additional analysis. Note that these slope angles are considered stable for short-term conditions only, and will not be stable for long-term conditions.

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During the subsurface exploration, boring sidewalls generally…