2-1200329 Revised Report, Exchange Park Sewer Upgrade FOR INFORMATION ONLY.pdf

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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 5

PROPOSED CONSTRUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 5

SEISMICITY, FAULTING AND LIQUEFACTION. . . . . . . . . . . . . . . . . . . . . . . . . Page 6

RECOMMENDATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 6 A. Pipe Support.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 B. Uplift Resistance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 7 C. Excavation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 8 D. Backfill. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 10 E. Imposed External Loads. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 11 F. Manhole Design Considerations. . . . . . . . . . . . . . . . . . . . . . . . . Page 11 G. Water Soluble Sulfates.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 11 H. Reducing Flow in Trench Backfill and Bedding . . . . . . . . . . . . . . Page 12

LIMITATIONS.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 13

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 14

FIGURES

EXPLORATORY BORING LOCATIONS FIGURE 1

EXPLORATORY BORING LOGS, LEGEND AND NOTES FIGURE 2

GRADATION TEST RESULTS FIGURES 3-4

SUMMARY OF LABORATORY TEST RESULTS TABLE IFOR IN

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EXECUTIVE SUMMARY

1. Approximately 5 to 9 inches of asphaltic concrete overlying 5 inches of base course underlain by lean clay was encountered in Borings B-1 and B-2.

Approximately 4 feet of fill overlying natural gravel was encountered in Boring B-3. The lean clay in Borings B-1 and B-2 is underlain by gravel at depths of approximately 6 and 3½ feet, respectively. The gravel extends to the full depth of Boring B-1, approximately 15½ feet. Clay was encountered below the gravel in Boring B-2 at a depth of approximately 15 feet and extends to the full depth of this boring, approximately 20½ feet. Gravel and sand were encountered below the fill to the full depth of Boring B-3, approximately 15½ feet.

2. Subsurface water was measured at depths of approximately 8.3, 11.9 and

10.0 feet below the ground surface in Borings B-1, B-2 and B-3, respectively, based on measurements taken on October 21, 2020.

3. The natural undisturbed soil or properly compacted bedding material is suitable to support the proposed sewer line. Precautions should be taken during construction, excavation and dewatering to minimize the disturbance of the soil to remain below the proposed pipe.

4. We anticipate that excavation can be accomplished with heavy duty excavation equipment. Dewatering and shoring should be included in the construction planning.

5. The existing fill and natural soil exclusive of over-sized particles may be considered for use as backfill for the pipeline and manholes if they meet Provo City specifications. Use of the on-site soil will likely require moisture conditioning (wetting or drying) to facilitate compaction, particularly for the soil with a high clay content and soil below the groundwater level. Moisture conditioning may not be practical during cold or wet weather or where there is not adequate area to spread and condition the material.

6. Recommendations related to pipe support, excavation and backfill are included in the report.

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SCOPE

This report presents the results of a geotechnical investigation for the proposed Provo

Exchange Park sewer upgrade from approximately 500 to 1250 North and 600 West in

Provo, Utah. The report presents the subsurface conditions encountered, laboratory test results and recommendations for the proposed sewer line. The study was conducted in general accordance with our proposal dated May 6, 2020.

Field exploration was conducted to obtain information on the subsurface conditions.

Samples obtained from the field investigation were tested in the laboratory to determine physical and engineering characteristics of the on-site soil. Information obtained from the field and laboratory was used to define conditions at the site and to develop recommendations for the proposed sewer reconstruction.

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 related to construction are included in the report.

SITE CONDITIONS

The southern portion of the alignment is in 600 West Street, which is two-lane asphalt-paved road. The road generally extends through residential areas.

The alignment extends west in 980 West Street, which is a two-lane asphalt-paved road.

This road extends through a residential area with some medical buildings to the north and east. At the end of 980 West Street, the alignment crosses a ditch and extends into

Exchange Park. The alignment extends to the north through the park along the east side of the Provo River Parkway trail.

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The area of the alignment slopes gently down to the south.

FIELD STUDY

The borings were drilled on October 19, 2020 at the approximate locations indicated on

Figure 1. The borings were drilled using 8-inch diameter hollow stem auger powered by a truck-mounted drill rig. The borings were logged and soil samples obtained by an engineer from AGEC. Logs of the subsurface conditions encountered in the borings are graphically shown on Figure 2.

SUBSURFACE CONDITIONS

Approximately 5 to 9 inches of asphaltic concrete overlying 5 inches of base course underlain by lean clay was encountered in Borings B-1 and B-2. Approximately 4 feet of fill overlying natural gravel was encountered in Boring B-3. The lean clay in Borings B-1 and

B-2 is underlain by gravel at depths of approximately 6 and 3½ feet, respectively. The gravel extends to the full depth of Boring B-1, approximately 15½ feet. Clay was encountered below the gravel in Boring B-2 at a depth of approximately 15 feet and extends to the full depth of this boring, approximately 20½ feet. Gravel and sand were encountered below the fill to the full depth of Boring B-3, approximately 15½ feet.

A description of subsurface materials encountered in the borings follows:

Base Course - The base course consists of poorly-graded sand with silt and gravel to silty sand with gravel. It is moist and grayish brown.

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Laboratory tests conducted on a sample of the base course indicate it has a moisture content of 7 percent. The results of a gradation test on the base course are presented on Figure 3.

Fill - The fill in Boring B-3 consists of sandy lean clay with gravel. It is moist, brown and contains roots.

Lean Clay - The clay contains small to moderate amounts of sand and occasional gravel. The clay contains occasional silty sand layers. It is soft to medium stiff, moist to wet and brown to gray.

Laboratory tests conducted on samples of the clay indicate it has natural moisture contents of 24 to 37 percent and natural dry densities of 83 to 94 pounds per cubic foot (pcf).

A sample of the clay tested in the laboratory was found to have an unconfined compressive strength of 1,435 pounds per square foot.

Silty Sand with Gravel - The sand is very dense, wet and brown.

Laboratory tests conducted on a sample of the sand indicate it has a natural moisture content of 11 percent and a natural dry density of 126 pcf.

The results of a gradation test on the sand are presented on Figure 4.

Poorly-graded Gravel with Silt and Sand - The gravel contains sand layers, small to moderate amounts of silt, cobbles and possible small boulders. It is dense to very dense, moist to wet and brown.

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Laboratory tests conducted on samples of the gravel indicate it has natural moisture contents of 6 to 9 percent and natural dry densities of 121 to 126 pcf.

Results of gradation tests conducted on samples of the gravel are presented on

Figures 3 and 4.

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

SUBSURFACE WATER

Subsurface water was measured at depths of approximately 8.3, 11.9 and 10.0 feet below the ground surface in Borings B-1, B-2 and B-3, respectively, based on measurements taken on October 21, 2020. Slotted PVC pipe was installed in the borings to facilitate measurement of the water level.

Fluctuations in the water level will occur over time. An evaluation of fluctuations in the subsurface water level is beyond the scope of this report.

PROPOSED CONSTRUCTION

We understand that the project consists of installing approximately 4,000 feet of 24-inch diameter sewer pipe to depths of approximately 10 to 17 feet below the ground surface.

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SEISMICITY, FAULTING AND LIQUEFACTION

Seismicity

The site is located in a seismically active region. A peak horizontal ground acceleration of 0.70g is expected from a seismic event having a 2 percent probability of exceedance in a 50-year period (International Code Council, 2017).

Faulting

There are no mapped active faults extending near the proposed pipe alignment. The closest fault considered to be active is the Wasatch fault located approximately

2 miles east of the site (Utah Geological Survey, 2020).

Liquefaction

The site is located within an area mapped as having a "moderate" potential for liquefaction (Anderson and others, 1994). Research indicates that the soil type most susceptible to liquefaction during a large magnitude earthquake is loose clean sand.

The liquefaction potential for soil tends to decrease with an increase in fines content and density.

A site-specific evaluation of the liquefaction potential would require exploration to a greater depth and is beyond the scope of this report.

RECOMMENDATIONS

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

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A. Pipe Support

The undisturbed natural soil or properly compacted bedding material is suitable to support the proposed sewer pipe.

1. Settlement

Settlement of the proposed sewer line will be a function of the disturbance of the soil beneath the pipe. Disturbance may result from excavation, dewatering and construction activities. Care should be taken to minimize disturbance of the soils below the proposed pipe so that settlement can be maintained within tolerable limits. Disturbed material should be removed and replaced with properly compacted bedding material.

2. Pipe Bedding

Pipe bedding requirements will depend on the design criteria for the pipe based on the manufacturer’s recommendations. Bedding materials should be placed on undisturbed natural soil. If the bearing soil is disturbed, it should be removed and replaced with compacted bedding material. Pipe bedding should meet the criteria given by the pipe manufacturer and Provo City. A filter fabric or properly sized fill should be provided between the natural fine-grained soil and free-draining gravel to prevent particle migration into the gravel.

B. Uplift Resistance

Uplift for the pipe and manholes may be of concern where the pipe or manhole extends below the subsurface water level and is empty. Resistance to these uplift pressures is typically provided by compacted backfill above the pipe or manhole. The uplift resistance from the compacted backfill may be determined using the following soil unit weights:

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Backfill Type Unit Weight, pcf

Natural Clay and Sand Above Water Table 110

Natural Clay and Sand Below Water Table 50

Imported or Natural Gravel with Sand Above Water Table 120

Imported or Natural Gravel with Sand Below Water Table 60

These values are ultimate values and appropriate safety factors should be applied.

C. Excavation

We anticipate that excavation for the proposed sewer line will extend to depths on the order of 10 to 17 feet below the existing ground surface.

Drilling of exploratory borings was relatively slow and difficult with hollow-stem auger and N values in the gravel indicate dense to very dense soil. Based on the drilling conditions and N values, we anticipate that dense to very dense gravel with likely cobbles and possibly small boulders will be encountered in excavations. We anticipate that excavation can be accomplished with heavy duty excavation equipment.

Based on the water levels encountered in the borings and the anticipated depth of the proposed sewer line, excavations are expected to extend on the order of 2 to

6 feet below the groundwater level.

1. Shoring

Care should be taken to maintain the stability of excavations during construction. Proper side slopes or shoring should be provided for safety of workers and to support adjacent facilities. Shoring and trench boxes should

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be designed to restrain the soil mass along with the surcharge from construction equipment and other loads.

Active lateral loads may be calculated using an equivalent fluid weight of

50 and 40 pcf above the water table and 25 and 20 pcf plus the hydrostatic pressure below the water table for cohesive and granular soils, respectively.

The lateral load calculation should include the effect of seepage forces, sloping backfill, surcharge and other loading conditions which are not included in the values given above. An appropriate factor of safety should be used in design for the shoring system and trench boxes.

2. Unretained Excavation Slopes

Temporary unretained excavation slopes may be constructed at 1½ horizontal to 1 vertical or flatter. The excavation slopes indicated above assume that the excavations will be properly dewatered. If water is allowed to flow into the excavations, slopes will need to be significantly flatter. It is the responsibility of the contractor to provide appropriate slopes to assure safe working conditions and stability of adjacent areas. Additional evaluation of excavation slopes by a qualified engineer may be required during the construction process.

3. Excavation Dewatering

Based on the estimated water levels and our understanding of the depth of the proposed sewer line, we anticipate that the water will need to be lowered on the order of 2 to 6 feet to facilitate construction.

The quantity of water produced from the excavation is difficult to predict due to variations of in-situ soil conditions. Dewatering quantities will depend on the depth and size of area dewatered, the free water level, soil type and shoring system used. Assuming an excavation of approximately 8 feet wide

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by 50 feet in length where the water level is lowered 6 feet, a quantity of water on the order of 50 to 500 gallons per minute is estimated. The actual quantity of water required to dewater the excavation may vary significantly due to variations in the subsurface conditions and the length of time dewatering is conducted. Initial dewatering quantities may be higher. Where the excavation ties into existing sewer trenches, the bedding and backfill in the existing trench may contribute water into the excavation, increasing the dewatering needs for the project.

D. Backfill

1. Material

The existing fill and natural soil exclusive of over-sized particles may be considered for use as backfill for the pipeline and manholes if they meet Provo

City specifications. Use of the on-site soil will likely require moisture conditioning (wetting or drying) to facilitate compaction, particularly for the soil with a high clay content and soil below the groundwater level. Moisture conditioning may not be practical during cold or wet weather or where there is not adequate area to spread and condition the material.

2. Compaction

Backfill should be compacted to at least 90 percent of the maximum dry density as determined by ASTM D 1557 or to Provo City standards, whichever is more stringent.

Base course should be compacted to at least 95 percent of the maximum dry density as determined by ASTM D 1557 or to Provo City standards, whichever is more stringent.

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

3. Observation and Testing

We recommend frequent observation and testing as backfill is placed and compacted.

E. Imposed External Loads

The loads imposed on a buried pipeline depend on the width of the trench, subsurface conditions, height of backfill over the pipe, method of installation and backfill conditions. For a flexible pipe, we recommend that the pipe manufacturer’s recommendations be followed to keep pipe deflections within tolerable limits.

F. Manhole Design Considerations

Manholes may bear on the undisturbed natural soil or on properly compacted bedding material extending down to the undisturbed natural soil using a net allowable bearing pressure of 1,500 psf. The weight of the backfill above the base of the manhole may be neglected when sizing footings. Settlement of the manholes will be a function of disturbance of the bearing soils. If disturbance is kept to a minimum, we anticipate that settlement will be less than ½ inch.

G. Water Soluble Sulfates

One sample of the natural soil was tested in the laboratory for water soluble sulfate content. The sample tested was found to have less than 0.1 percent water soluble sulfates. No special cement type is required for concrete placed in contact with the natural soil.

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H. Reducing Flow in Trench Backfill and Bedding

Periodic low permeable cut-offs should be considered in the pipe bedding and backfill. These cut-offs would be provided to reduce the amount of water flowing through the pipe bedding and backfill materials. Cut-offs may consist of low-permeable soil, a clay-bentonite mixture, bentonite granules/pellets or lean concrete.

The cut-offs should be at least 2 feet in length along the pipe alignment. We recommend that cut-offs be provided approximately every 500 feet along the pipe alignment.

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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 in the report are based on the information obtained from the borings drilled at the approximate locations indicated on Figure 1 and the data obtained from laboratory testing. Variations in the subsurface conditions may not become evident until additional exploration or excavation is conducted. If the subsurface conditions or groundwater level is found to be significantly different than what is described in this report, we should be notified to reevaluate our recommendations.

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Jay R. McQuivey, P.E.

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

JRM/bw

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REFERENCES

Anderson, L. R., Keaton, J. R. and Bischoff, J. E., 1994; Liquefaction Potential Map for Utah County, Utah Geological Survey Contract Report 94-8.

International Code Council, 2017; 2018 International Building Code, Falls Church, Virginia.

Utah Geological Survey, 2020; Utah Quaternary Fault and Fold Database, http://geology.utah.gov/resources/data-databases/qfaults/ Accessed October 21, 2020.

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B-3

B-2

B-1

1200329 Exploratory Boring Locations Figure 1

5000 1000 feet Approximate Scale

PROVO EXCHANGE PARK SEWER UPGRADE

500 TO 1250 NORTH 600 WEST

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AutoCAD SHX Text N

Gravel 34% Liquid Limit -

Sand 48% Plasticity Index -

Silt and Clay 18% Sample Location

Sample Description

Gravel 40% Liquid Limit -

Sand 53% Plasticity Index -

Silt and Clay 7% Sample Location

Sample Description

GRADATION TEST RESULTS Figure 3

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Project No. 1200329

B-2 @ 5"

B-2 @ 14'

Base Course; Silty Sand with Gravel

Well-graded Sand with Silt and Gravel

12"8"

6"

5"

4"

3"

2"

1 1/2"

1"

3/4"

1/2"

3/8"

1/4"

No. 4

No. 8

No. 10No. 16

No. 30

No. 40

No. 50

No. 60

No. 80

No. 100No. 2001 Min.4 Min.19 Min.60 Min.

7Hrs.

15 Min.

24 Hrs.

304.8203.2

152.4

127.0

100.0

75.0

50.0

38.1

25.0

19.0

12.5

9.5

6.3

4.750

2.360

2.0001.180

0.600

0.425

0.300

0.250

0.180

0.1500.0750.0370.0190.0090.0050.0020.001

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

P e rc e n t

P a s s in g

Diameter of Particle in Millimeters

Hydrometer Analysis Sieve Analysis

Time Readings U.S. Standard Series Clear Square Openings

Clay to Silt Sand

Fine Medium Coarse

Gravel

Fine Coarse Cobbles Boulders

12"8"

6"

5"

4"

3"

2"

1 1/2"

1"

3/4"

1/2"

3/8"

1/4"

No. 4

No. 8

No. 10No. 16

No. 30

No. 40

No. 50

No. 60

No. 80

No. 100No. 2001 Min.4 Min.19 Min.60 Min.

7Hrs.

15 Min.

24 Hrs.

304.8203.2

152.4

127.0

100.0

75.0

50.0

38.1

25.0

19.0

12.5

9.5

6.3

4.750

2.360

2.0001.180

0.600

0.425

0.300

0.250

0.180

0.1500.0750.0370.0190.0090.0050.0020.001

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

P e rc e n t

P a s s in g

Diameter of Particle in Millimeters

Hydrometer Analysis

Time Readings

Sieve Analysis

U.S. Standard Series Clear Square Openings

Clay to Silt Sand Gravel

Cobbles Boulders Fine CoarseFine Medium Coarse

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Gravel 79% Liquid Limit -

Sand 17% Plasticity Index -

Silt and Clay 4% Sample Location

Sample Description

Gravel 22% Liquid Limit -

Sand 59% Plasticity Index -

Silt and Clay 19% Sample Location

Sample Description

GRADATION TEST RESULTS Figure 4

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Project No. 1200329

B-3 @ 9'

B-3 @ 14'

Poorly-graded Gravel with Sand

Silty Sand with Gravel

12"8"

6"

5"

4"

3"

2"

1 1/2"

1"

3/4"

1/2"

3/8"

1/4"

No. 4

No. 8

No. 10No. 16

No. 30

No. 40

No. 50

No. 60

No. 80

No. 100No. 2001 Min.4 Min.19 Min.60 Min.

7Hrs.

15 Min.

24 Hrs.

304.8203.2

152.4

127.0

100.0

75.0

50.0

38.1

25.0

19.0

12.5

9.5

6.3

4.750

2.360

2.0001.180

0.600

0.425

0.300

0.250

0.180

0.1500.0750.0370.0190.0090.0050.0020.001

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

P e rc e n t

P a s s in g

Diameter of Particle in Millimeters

Hydrometer Analysis Sieve Analysis

Time Readings U.S. Standard Series Clear Square Openings

Clay to Silt Sand

Fine Medium Coarse

Gravel

Fine Coarse Cobbles Boulders

12"8"

6"

5"

4"

3"

2"

1 1/2"

1"

3/4"

1/2"

3/8"

1/4"

No. 4

No. 8

No. 10No. 16

No. 30

No. 40

No. 50

No. 60

No. 80

No. 100No. 2001 Min.4 Min.19 Min.60 Min.

7Hrs.

15 Min.

24 Hrs.

304.8203.2

152.4

127.0

100.0

75.0

50.0

38.1

25.0

19.0

12.5

9.5

6.3

4.750

2.360

2.0001.180

0.600

0.425

0.300

0.250

0.180

0.1500.0750.0370.0190.0090.0050.0020.001

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

P e rc e n t

P a s s in g

Diameter of Particle in Millimeters

Hydrometer Analysis

Time Readings

Sieve Analysis

U.S. Standard Series Clear Square Openings

Clay to Silt Sand Gravel

Cobbles Boulders Fine CoarseFine Medium Coarse

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TABLE I

SUMMARY OF LABORATORY TEST RESULTS

PROJECT NUMBER: 1200329

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 3 24 94 52 Sandy Lean Clay

B-2 5“ 7 34 48 18 Base Course; Silty Sand with Gravel

14 9 121 40 53 7 Well-graded Sand with Silt and Gravel

19 37 83 98 1,435 0.04 Lean Clay

B-3 9 6 79 17 4 Poorly-graded Gravel with Sand

14 11 126 22 59 19 Silty Sand with Gravel