4-6-DA26052-26189700 Geotechnical Report.pdf

GEOTECHNICAL INVESTIGATION

PROPOSED WASHBURN BUILDING

800 WEST 200 SOUTH

RICHFIELD, UTAH

PREPARED FOR:

DFCM - STATE OF UTAH

4315 SOUTH 2700 WEST, 3 FLOORRD

TAYLORSVILLE, UTAH 84129-2128

ATTENTION: ROB ROBINSON

PROJECT NO. 1250535 OCTOBER 3, 2025

AGC.,CAGC.,C

Applied Applied GeoTechGeoTech

600600 WWesest t SSandy andy Parkway Parkway • • SSandy, andy, Utah Utah 84070 84070 • • (801) (801) 566-6399 566-6399 • • www.agecinc.comwww.agecinc.com

TABLE OF CONTENTS

EXECUTIVE SUMMARY.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 1

SCOPE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2

SITE CONDITIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 2

FIELD STUDY.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3

SUBSURFACE CONDITIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 3

SUBSURFACE WATER. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4

PROPOSED CONSTRUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4

RECOMMENDATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5 A. Site Grading. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5 B. Foundations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 C. Concrete Slab-on-Grade. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9 D. Lateral Earth Pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 9 E. Seismicity, Faulting and Liquefaction. . . . . . . . . . . . . . . . . . . . . Page 11 F. Water Soluble Sulfates.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 12 G. Pavement.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 12 H. Continuing Services. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 13

LIMITATIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 15

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 16

FIGURES

EXPLORATORY BORING LOCATIONS FIGURE 1

EXPLORATORY BORING LOGS, LEGEND AND NOTES FIGURE 2

CONSOLIDATION TEST RESULTS FIGURES 3-4

SUMMARY OF LABORATORY TEST RESULTS TABLE I

APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC. 1250535

EXECUTIVE SUMMARY

1. The soils encountered in the borings consist of approximately 2½ and 11 feet of fill overlying lean clay in Boring B-1, and lean clay and sandy silt in Boring B-2. Silty sand was encountered below the clay in Boring B-1 at a depth of approximately 12 feet. The sand extended the full depth of the boring, approximately 25½ feet. The clay and sandy silt extended the full depth of Boring B-2, approximately 25½ feet.

2. No subsurface water was encountered in the borings. Slotted pipe was installed in the borings to allow checking for water. No water was in the pipes when checked on September 25, 2025.

3. The building addition may be supported on spread footings bearing on the undisturbed natural soil or on structural fill extending down to the natural undisturbed soil and may be designed for a net allowable bearing pressure of 1,200 pounds per square foot. Footings bearing on at least 2 and 4 feet of structural fill may be designed for net allowable bearing pressures of 2,000 and 3,500 pounds per square foot, respectively.

4. The upper soil consists predominantly of clay and can cause access difficulties for construction equipment when the clay is very moist to wet.

Placement of 1 to 2 feet of granular fill will improve site access conditions when the subgrade consists of very moist to wet clay.

5. Geotechnical information relating to foundations, subgrade preparation, materials and pavement is included in the report.

SCOPE

This report presents the results of a geotechnical investigation for the proposed Washburn building addition to be constructed at 800 West 200 South in Richfield, Utah. The report presents the subsurface conditions encountered, laboratory test results and recommendations for foundations and pavement. The study was conducted in general accordance with our proposal dated July 21, 2025.

Field exploration was conducted to obtain information on the subsurface conditions at the site. Samples obtained from the study were tested in the laboratory to determine physical and engineering characteristics of the on-site soil. Information obtained from the field and laboratory investigations was used to define conditions at the site and to develop recommendations for the proposed foundations and pavement.

This report has been prepared to summarize the data obtained during the study and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations relating to construction are included in the report.

SITE CONDITIONS

At the time of our field study, the site consisted of a landscaped area with several sidewalks crossing the area.

The ground surface at the site is relatively flat with a gentle slope down to the south.

Vegetation at the site consists of grass and some trees.

There is a single-story building north and east of the northern end of the site. There are landscaped areas to the south and west.

FIELD STUDY

Two borings were drilled on September 15, 2025 at the approximate locations indicated on

Figure 1 using 8-inch-diameter hollow-stem auger. The borings were logged and soil samples obtained by an engineer from AGEC. Logs of the subsurface conditions encountered in the borings are presented on Figure 2.

SUBSURFACE CONDITIONS

The soils encountered in the borings consist of approximately 2½ and 11 feet of fill overlying lean clay in Boring B-1, and lean clay and sandy silt in Boring B-2. Silty sand was encountered below the clay in Boring B-1 at a depth of approximately 12 feet. The sand extended the full depth of the boring, approximately 25½ feet. The clay and sandy silt extended the full depth of Boring B-2, approximately 25½ feet.

A description of the soils encountered in the borings follows:

Fill - The fill consists of sandy lean clay and silty to clayey sand. It is moist to very moist, mottled and reddish brown to gray.

Laboratory tests performed on samples of the fill indicate it has moisture contents ranging from 18 to 22 percent and dry densities of 101 to 107 pounds per cubic foot.

Lean Clay - The clay contains occasional thin sand layers. It is medium stiff, moist and reddish brown to gray.

Laboratory tests performed on samples of the clay indicate it has a natural moisture content of 19 percent and natural dry densities of 97 to 101 pounds per cubic foot.

An unconfined compressive strength of 1,060 pounds per square foot was measured for a sample of the clay. Results of a consolidation test on the clay indicate the clay will compress a small to moderate amount with the addition of light to moderate loads. Results of the consolidation tests are presented on Figure 3.

Lean Clay and Sandy Silt - The clay and silt contain sand and occasional gravel lenses. The soil is medium dense, moist to very moist and reddish brown to gray.

Laboratory tests performed on a sample of the clay with silt layers indicate it has a natural moisture contents of 25 percent and a natural dry density of 99 pounds per cubic foot. Results of a consolidation test on the clay with silt indicate it will compress a small to moderate amount with the addition of light to moderate loads.

Results of the consolidation tests are presented on Figure 4.

Silty Sand - The sand has lean clay layers and occasional gravel lenses. It is medium dense, moist and reddish brown to gray.

Results of the laboratory tests are summarized on Table I and are included on the logs of the borings.

SUBSURFACE WATER

No subsurface water was encountered in the borings. Slotted pipe was installed in the borings to allow checking for water. No water was in the pipes when checked on September

25, 2025.

PROPOSED CONSTRUCTION

We understand that the site is planned for a single-story structure with a slab-on-grade floor.

We have assumed maximum column loads of 100 kips and maximum wall loads will be 5 kips per foot.

We have assumed traffic for pavement areas to consist predominantly of cars with two delivery trucks per day and two garbage trucks per week.

If the proposed construction, building loads or traffic is significantly different from what is described above, we should be notified so that we can reevaluate the recommendations given.

RECOMMENDATIONS

Based on the subsurface conditions encountered, laboratory test results and our understanding of the proposed construction, the following recommendations are given:

A. Site Grading

1. Subgrade Preparation

The topsoil, organics, unsuitable fill, debris and other deleterious materials should be removed from below the proposed building, slabs, pavement and other settlement-sensitive improvements.

The upper soil consists predominantly of clay and can cause access difficulties for construction equipment when the clay is very moist to wet.

Placement of 1 to 2 feet of granular fill will improve site access conditions when the subgrade consists of very moist to wet clay.

2. Excavation

We anticipate that excavation at the site can be accomplished with typical excavation equipment. Temporary excavations may be excavated at 1½ horizontal to 1 vertical or flatter. Permanent cut and fill slopes may be constructed at 2 horizontal to 1 vertical or flatter.

3. Materials

Listed below are recommendations for imported structural fill.

Fill to Support Recommendations

Footings Non-expansive granular soil Passing No. 200 Sieve < 35% Liquid Limit < 30% Maximum size 4 inches

Floor Slab (Upper 4 inches)

Sand and/or Gravel Passing No. 200 Sieve < 5% Maximum size 2 inches

Slab Support Non-expansive granular soil Passing No. 200 Sieve < 50% Liquid Limit < 30% Maximum size 6 inches

Materials placed as fill to support the building should be non-expansive granular soil. The existing fill and natural soil are not recommended for use as structural fill, but may be used as site grading fill, and as utility trench and wall backfill if the topsoil, organics and other deleterious materials are removed or they may be used in landscaping areas.

The soil may require moisture conditioning prior to use as fill depending on the soil moisture content at the time of construction. Drying of the soil may not be practical during cold or wet periods of the year.

4. Compaction

Compaction of materials placed at the site should equal or exceed the minimum densities as indicated below when compared to the maximum dry density as determined by ASTM D 1557.

Fill To Support Compaction Criteria

Foundations $ 95%

Concrete Slabs $ 90%

Pavement Base Course Fill placed below Base Course

$ 95% $ 90%

Landscaping $ 85%

Retaining Wall Backfill 85 - 90%

To facilitate the compaction process, fill should be compacted at a moisture content within 2 percent of the optimum moisture content.

The fill should be placed and compacted in thin enough lifts to allow for proper compaction. Fill placed for the project should be frequently tested for compaction.

5. Drainage

The ground surface surrounding the proposed building should be sloped away from the building in all directions. Roof downspouts and drains should discharge beyond the limits of backfill.

The collection and diversion of drainage away from the pavement surface is important to the satisfactory performance of the pavement section. Proper drainage should be provided.

B. Foundations

1. Bearing Material

With the proposed construction and the subsurface conditions encountered, the building addition may be supported on spread footings bearing on the undisturbed natural soil or on compacted structural fill extending down to the natural undisturbed soil. Structural fill should extend down to the undisturbed natural soil and out away from the edge of the footings at least a distance equal to the depth of fill beneath footings.

Topsoil, unsuitable fill, organics, debris and other deleterious materials should be removed from below footing areas.

2. Bearing Pressure

Spread footings bearing on the undisturbed natural soil or on compacted structural fill extending down to the undisturbed natural soil may be designed using a net allowable bearing pressure of 1,200 pounds per square foot.

Footings bearing on at least 2 and 4 feet of structural fill may be designed for net allowable bearing pressures of 2,000 and 3,500 pounds per square foot, respectively.

3. Settlement

We estimate that settlement will be less than 1 inch. The settlement will be differential with respective to the existing building.

4. Temporary Loading Conditions

The allowable bearing pressure may be increased by one-half for temporary loading conditions such as wind or seismic loads.

5. Frost Depth

Exterior footings and footings beneath unheated areas should be placed at least 30 inches below grade for frost protection.

6. Foundation Base

The base of foundation excavations should be cleared of loose or deleterious material prior to fill or concrete placement.

7. Construction Observation

A representative of the geotechnical engineer should observe footing excavations prior to structural fill or concrete placement.

C. Concrete Slab-on-Grade

1. Slab Support

Concrete slabs may be supported on the undisturbed natural soil or on compacted structural fill extending down to the undisturbed natural soil.

Topsoil, organics, unsuitable fill, debris and other deleterious materials should be removed from below proposed slab areas.

2. Underslab Sand and/or Gravel

A 4-inch layer of free-draining sand and/or gravel (less than 5 percent passing the No. 200 sieve) should be placed below floor slabs for ease of construction and to promote even curing of the slab concrete.

3. Vapor Barrier

A vapor barrier should be placed under the concrete floor if the floor will receive an impermeable floor covering. The barrier will reduce the amount of water vapor passing from below the slab to the floor covering.

D. Lateral Earth Pressure

1. Lateral Resistance for Footings

Lateral resistance for footings placed on the natural soil or on compacted structural fill is controlled by sliding resistance between the footing and the foundation soils. A friction value of 0.35 may be used in design for ultimate lateral resistance. A friction value of 0.45 may be used in design for ultimate lateral resistance where at least 2 feet of structural fill is placed below footings. The passive resistance of the soil adjacent footings may be added to the friction resistance.

2. Subgrade Walls and Retaining Structures

The following equivalent fluid weights are given for the design of subgrade walls and retaining structures. The active condition is where the wall moves away from the soil. The passive condition is where the wall moves into the soil and the at-rest condition is where the wall does not move. The values listed below assume a horizontal surface adjacent the wall.

Soil Type Active At-Rest Passive

Clay & Silt 50 pcf 65 pcf 250 pcf

Sand & Gravel 40 pcf 55 pcf 300 pcf

3. Seismic Conditions

Under seismic conditions, the equivalent fluid weight should be increased by

27 pcf for the active condition and 12 pcf for the at-rest condition. A decrease of 27 pcf is recommended for the passive condition. This assumes a peak ground acceleration of 0.45g which represents a 2 percent probability of exceedance in a 50-year period.

4. Safety Factors

The values recommended above assume mobilization of the soil to achieve the soil strength under active and passive conditions. Conventional safety factors used for structural analysis for such items as overturning and sliding resistance should be used in design.

E. Seismicity, Faulting and Liquefaction

1. Seismicity

Listed below is a summary of the site parameters that may be used with the 2021

International Building Code:

Description Value

Site Class D s RS - MCE ground motion (period=0.2s) 0.83g

1 RS - MCE ground motion (period=1.0s) 0.25g aF - Site amplification factor at 0.2s 1.17

VF - Site amplification factor at 1.0s 2.11

GPGA - MCE peak ground acceleration 0.37g

MPGA - Site modified peak ground acceleration 0.45g

Site Class D was selected based on the subsurface conditions encountered and our understanding of the geology in the area.

2. Faulting

The Elsinore Fold is mapped to extend through the proposed building (Utah

Geological Survey, 2025). This is categorized as a Quaternary structure with latest movement between 130,000 and 2.8 million years ago. Greg McDonald of the Utah Geological Survey has indicated no fault study would be needed other than to look at foundation excavations at the time of construction. The geologic structure does not appear to represent a significant hazard due to the great amount of time since latest movement on the structure.

3. Liquefaction

The proposed building is located in an area mapped to have a very low liquefaction potential (Anderson and others, 1994). Based on the subsurface conditions encountered at the site, liquefaction is not considered to be a hazard.

F. Water Soluble Sulfates

One sample of the natural soil was tested for water soluble sulfate content. The sample contained less than 0.1 percent water soluble sulfates indicating the natural soil possesses negligible sulfate attack potential on concrete. No special cement type is needed for concrete placed in contact with soil having negligible sulfate content.

Other conditions may dictate the type of cement to be used in concrete for the project.

G. Pavement

Based on the subsurface conditions encountered, laboratory test results and the assumed traffic, the following pavement support recommendations are given:

1. Subgrade Support

The near surface soil consists predominantly of clay. A California Bearing

Ratio (CBR) value of 3 percent was used in the analysis, which assumes a clay subgrade.

2. Pavement Thickness

Based on the subsoil conditions encountered at the site, assumed traffic as described in the Proposed Construction section of the report, a design life of

20 years for flexible pavement and 30 years for rigid pavement and methods presented by AASHTO, a pavement section consisting of 3 inches of asphaltic concrete overlying 6 inches of base course is recommended. A rigid pavement section consisting of 5 inches of Portland cement concrete placed on a prepared subgrade may be considered as an alternative.

The upper soil consists predominantly of clay and can cause access difficulties for construction equipment when the clay is very moist to wet.

Placement of 1 to 2 feet of granular fill will improve site access conditions when the subgrade consists of very moist to wet clay.

3. Pavement Materials and Construction

a. Flexible Pavement (Asphaltic Concrete)

The pavement materials should meet the specifications for the applicable jurisdiction.

b. Rigid Pavement (Portland Cement Concrete)

The rigid pavement thickness given above assumes that the pavement will have aggregate interlock joints and that a concrete shoulder or curb will be provided.

The pavement materials should meet the specifications for the applicable jurisdiction. The pavement thickness indicated above assumes that the concrete will have a 28-day compressive strength of

5,000 pounds per square inch. Concrete should be air entrained with approximately 6 percent air. Maximum allowable slump will depend on the method of placement but should not exceed 4 inches.

4. Jointing

Joints for concrete pavement should be laid out in a square or rectangular pattern. Joint spacings should not exceed 30 times the thickness of the slab or 15 feet, whichever is smallest. The joint spacings indicated should accommodate the contraction of the concrete and under these conditions steel reinforcing will not be required. The depth of joints should be approximately one-fourth of the slab thickness.

H. Continuing Services

A preconstruction meeting should be held with representatives of the owner, project architect, geotechnical engineer, general contractor, earthwork contractor and other members of the design team to review construction plans, specifications, methods and schedule.

The geotechnical engineer should observe the excavation, earthwork, and foundation phases of the work to determine that subsurface conditions are consistent with those used in the analysis and design. The work should be observed and tested to determine that proper compaction has been achieved during site grading and placement of structural fill.

LIMITATIONS

This report has been prepared in accordance with generally accepted soil and foundation engineering practices in the area for the use of the client for design purposes. The conclusions and recommendations included within the report are based on the information obtained from the borings drilled, the results of laboratory tests and our experience in the area. Variations in the subsurface conditions may not become evident until additional exploration or excavation is conducted. If the subsurface conditions, proposed construction or groundwater level is found to be significantly different from what is described above, we should be notified to reevaluate the recommendations given.

APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC.

Douglas R. Hawkes, P.E., P.G.

Reviewed by Christopher J. Beckman, P.E.

DRH/rs

10-3-2025

REFERENCES

Anderson, L.R., Keaton, J.R., and Rice, J.D., 1994; Liquefaction Potential map for Central Utah, Utah Geological Survey, Contract Report 94-10.

International Code Council, 2020; 2021 International Building Code, Falls Church, Virginia.

Utah Geological Survey, 2025; Utah Geologic Hazards Portal accessed October 1, 2025 at https://maps.geology.utah.gov/hazards.

B-1 B-2

BM - Floor Level Elev. 100' assumed

1250535 Exploratory Boring Locations Figure 1

WASHBURN BUILDING ADDITION

800 WEST 200 SOUTH

RICHFIELD, UTAH0 60 120 feet Approximate Scale

AutoCAD SHX Text N

NOTES:

1. The borings were drilled on September 15, 2025 with 8-inch diameter hollow-stem auger.

2. The locations of the borings were measured approximately by pacing from features shown on Figure 1.

3. The elevations of the borings were measured by automatic level and refer to the benchmark shown on Figure 1.

4. The boring locations and elevations should be considered accurate only to the degree implied by the method used.

5. The lines between materials shown on the boring logs represent the approximate boundaries between material types and the transitions may be gradual.

6. No free water was encountered in the borings at the time of drilling.

7. WC = Water Content (%);

DD = Dry Density (pcf);

-200 = Percent Passing the No. 200 Sieve;

UC = Unconfined Compressive Strength (psf);

WSS = Water Soluble Sulfates (%).

10/12

LEGEND:

California Drive sample taken. The symbol 10/12 indicates that 10 blows from a 140 pound automatic hammer falling 30 inches were required to drive the sampler 12 inches.

Indicates slotted 1½ inch PVC pipe installed in the boring to the depth shown.

Fill; sandy lean clay, silty to clayey sand, moist to very moist, reddish brown to gray, mottled.

Lean Clay and Sandy Silt (CL/ML); sand and occasional gravel lenses, medium stiff, medium dense, moist to very moist, reddish brown to gray.

Lean Clay (CL); occasional thin sand layers, medium stiff, moist, reddish brown to gray.

Silty Sand (SM); occasional gravel lenses, lean clay layers, medium dense, moist, reddish brown to gray.

El ev at io n/ Fe et

Elev. 97½' Elev. 99' B-1 B-2

El ev at io n/ Fe et

8/12

5/12

6/12

6/12

8/12

29/12

6/12

13/12

5/12

4/12

6/12

5/12

5/12

5/12

5/12

4/12

11/12

23/12

WC = 19

DD = 97

-200 = 75

UC = 1,060

WSS <0.001

WC = 19

DD = 101

-200 = 77 WC = 25

DD = 99

-200 = 90

WC = 18

DD = 107

-200 = 55

WC = 22

DD = 101

-200 = 81

Assumed Finish Floor Level

Exploratory Boring Logs, Legend and Notes Figure 2 Approximate Vertical Scale 1" = 8'

1250535

Applied Geotechnical Engineering Consultants, Inc.

APPLIED PRESSURE - ksf

0.1 1.0 10 100

C om pr es si on

Moisture Content 19 % Dry Unit Weight 101 pcf Sample of: Lean Clay with Sand

From: B-1 @ 9 feet

Project No. 1250535

No movement upon wetting

CONSOLIDATION TEST RESULTS Figure 3

Applied Geotechnical Engineering Consultants, Inc.

APPLIED PRESSURE - ksf

0.1 1.0 10 100

C om pr es si on

Moisture Content 25 % Dry Unit Weight 99 pcf Sample of: Lean Clay with Silt Layers

From: B-2 @ 12 feet

No movement upon wetting

Project No. 1250535 CONSOLIDATION TEST RESULTS Figure 4

APPLIED GEOTECHNICAL ENGINEERING CONSULTANTS, INC.

TABLE I

SUMMARY OF LABORATORY TEST RESULTS

PROJECT NUMBER: 1250535

SAMPLE

LOCATION NATURAL

MOISTURE

CONTENT

NATURAL

DRY

DENSITY

(PCF)

GRADATION ATTERBERG LIMITS UNCONFINED

COMPRESSIVE

STRENGTH

(PSF)

WATER

SOLUBLE

SULFATE

SAMPLE CLASSIFICATION

BORING DEPTH

(FEET)

GRAVEL

SAND

SILT/

CLAY

LIQUID LIMIT

PLASTICITY

INDEX

B-1 4 19 97 75 1,060 <0.001 Lean Clay with Sand

9 19 101 77 Lean Clay with Sand

B-2 2 18 107 55 Fill; Sandy Lean Clay

4 22 101 81 Fill; Lean Clay with Sand

12 25 99 90 Lean Clay with Silt Layers