Bridge_1005_and_2001_Geotechnical_Reports.pdf

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Munger Road Bridge #1005 over Drain 10 Geotechnical Engineering Report ACHD Project No.224008 & GIS No. MA214-01 Star, Idaho

November 5, 2024 | Terracon Project No. 62235094 Prepared for:

David Evans and Associates, Inc 9175 W Black Eagle Dr Boise, Idaho 83709

Geotechnical Engineering Report Munger Road Bridge #1005 over Drain 10 | Star, Idaho November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials i

Table of Contents

Report Summary .............................................................................................. i Introduction Project Description Site Conditions Geotechnical Characterization Seismic Site Class Infiltration Testing Geotechnical Overview Earthwork

Site Preparation Excavation Fill Material Types Fill Placement and Compaction Requirements Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Foundations Box Culvert Wing Wall Foundation Construction Considerations

Lateral Earth Pressures Design Parameters

General Comments

Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans Exploration and Laboratory Results Supporting Information

Note: This report was originally delivered in a web-based format. Blue Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

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Report Summary

Topic 1 Overview Statement 2

Project Description

Ada County Highway District (ACHD) is planning to widen Munger Road and to replace bridge #1005 over Drain 10 in Star, Idaho.

The Bridge will be replaced with a box culvert wide enough to accommodate two 11-foot lanes, two 5-foot bike lanes, and two 7-foot sidewalks, and two 2-foot curb and gutters. We anticipate the new bridge to be supported on spread footing foundations and have a wing wall at each opening of the box culvert with the dimensions of approximately 17-18 feet in width and a length of 50 feet.

Geotechnical Characterization

Fill materials were encountered in boring B-5 and B-2 extending to a depth of approximately 3½ feet and 6 feet below ground surface (BGS), respectively. Groundwater was encountered at the time of our exploration and observed at a depth of approximately 9 feet (BGS) in boring B-5 and 8 feet (BGS) in boring B-2.

Earthwork

Remove existing fill beneath the proposed structure where observed.

The subgrade should be prepared as described in Sections 201 and 202 of the ISPWC and ACHD Supplemental Specifications to

ISPWC.

All fill soil should be free of deleterious, organic, or frozen matter.

Shallow Foundations

Shallow foundations, supported by 12 inches of Type I crushed aggregate.

Expected settlements: Approximately 1-inch total.

Embedment of 24 inches to the bottom of the footing for frost protection.

Pavements Pavements are not included in our scope of services. We understand ACHD will provide the pavement section design and recommendations for this project.

General Comments

This section contains important information about the limitations of this geotechnical engineering report.

1. If the reader is reviewing this report as a pdf, the topics above can be used to access the appropriate section of the report by simply clicking on the topic itself.

2. This summary is for convenience only. It should be used in conjunction with the entire report for design purposes.

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Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed new Munger Rd Bridge #1005 to be located over Drain 10 in Star, Idaho. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Seismic site classification

■ Site preparation and earthwork

■ Dewatering considerations

■ Foundation design and construction

■ Lateral earth pressure

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs and as separate graphs in the Exploration Results section.

Project Description

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided

Project information is based on the details provided via email from Mr. Ali Rigeb of David Evans and Associates, Inc (DEA) between September 22, 2023, and June 26, 2024.

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Item Description

Project Description

Ada County Highway District (ACHD) proposes to replace and widen Bridge #1005 over Drain 10 on Munger Road in Star, Idaho. We understand a box culvert with an approximate width of 17-18 feet and length of 50 feet, will be used to convey Drain 10 beneath Munger Rd. We anticipate the new bridge structure and associated wing walls will be supported on spread footing foundations.

Proposed Structure

According to information provided by ACHD and DEA, the crossing over Drain 10 will be widen for two 11-foot travel lanes (one in each direction), two 5-foot wide bike lanes, two 2-foot curb and gutters, and two 7-foot pedestrian sidewalks.

Maximum Loads None provided at the issuance of this report.

Embankments/Grading We understand the grade of the roadway at the structure location is not anticipated to change.

Free-Standing Retaining Walls

None anticipated

Stormwater Management

Infiltration rate testing was conducted for stormwater management. We understand the exact size, type and location of the facility have not yet been determined.

Building Code ASSHTO LRFD Bridge Design Specifications, 9th Edition, Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits, as modifications to our recommendations may be necessary.

Site Conditions

The following description of site conditions is derived from our site visit in association with the field exploration.

Item Description

Parcel Information

The project is located where Munger Road crosses Drain 10 between North Catamaran Way and West Streamview Drive in Star, Idaho.

Approximate Site Latitude/Longitude: 43.7093, -116.5032 See Site Location

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Item Description

Existing Improvements

The site is currently an existing two-lane bridge that carries Munger Road over Drain 10.

Current Ground Cover

Munger Road is paved with asphalt and displays gravel-surfaced shoulders. A guard rail spans the length of the bridge deck on both sides and has light vegetation around Drain 10 banks adjacent to the bridge. A utility pipe crossing is located to the east, spanning the canal.

Existing Topography

Munger Road is relatively flat with localized slopes for surface water drainage.

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration Results and the GeoModel can be found in the Figures attachment of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer

Layer Name General Description

1 Fill Materials Various fills with varying gravel, sand, silt, and clay contents, surfaced with asphalt.

2 Gravels Poorly and well graded gravel with varying amounts of silt and sand. These soils vary in consistency from dense to very dense.

3 Sands Poorly graded sand with varying amounts of gravel and silt. These soils vary in consistency from dense to very dense.

4 Clay Clay with varying amounts of sand and consistency is hard.

During exploration, groundwater was encountered in borings B-2 and B-1 at about 8 and 5 feet BGS (2457 and 2455 feet elevation), respectively. Groundwater conditions may change because of seasonal variations in the amount of water within Middleton Canal, as

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Facilities | Environmental | Geotechnical | Materials 4 well as in variations in rainfall, runoff, irrigation, and other conditions not apparent at the time of drilling. We installed a piezometer for long-term groundwater monitoring.

Groundwater elevation was measured within the piezometer from June 1, 2024 to June 11, 2024 and June 25, 2024 to November 4, 2024 using data loggers. The data loggers were set to record data every 12 hours, two times per day. The table below summarizes the location, surface elevation and the shallowest and greatest elevations at which groundwater was recorded. A graph of the measured groundwater data is also included in Exploration Results.

Location Surface Elevation

(MSL – feet) 1

Shallowest Elevation to Groundwater

(MSL -feet) 2

Greatest Elevation to Groundwater

(MSL - feet) 2

P-3 2463.9 > 2457.9 2456.1 4

1. Elevation of adjacent geotechnical boring, provided by project surveyor.

2. Approximate elevation based on the elevation of the adjacent geotechnical boring, provided by project surveyor.

3. Shallowest elevation of the groundwater was not recorded because the barro logger became submerged. Therefore, the shallowest elevation would be greater than 2457.9.

4. Deepest groundwater elevation was observed at the time of data logger installation.

Seismic Site Class

Seismic ground motion parameters were developed for the project based on Section

3.10 of AASHTO LRFD. The seismic parameters were obtained from the USGS Seismic Design Web Services. These values are presented in the following table and are for an earthquake having a probability of exceedance of 7 percent in 75 years (approximately 1000-year return period).

Ground Motion Parameter Value

Site Soil Classification D 1

PGA, Peak Ground Acceleration Coefficient on Rock (Site Class B) 0.081 g Ss, Horizontal Response Spectral Acceleration Coefficient at 0.2-sec Period on Rock (Site Class B)

0.189 g

S1, Horizontal Response Spectral Acceleration Coefficient at 1.0-sec Period on Rock (Site Class B)

0.068 g

FPGA, Site Factor for PGA 1.6 FA, Site Factor for Ss 1.6 FV, Site Factor for S1 2.4 AS, Modified PGA for Project Site (Site Class D) 0.13 g

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SDS, Modified Ss for Project Site (Site Class D) 0.303 g SD1, Modified S1 for Project Site (Site Class D) 0.163 g

1. Site soil class is based on the soil conditions at the site, including the SPT N values, and the methods presented in Table C3.10.3.1-1 of AASHTO LRFD. Based on AASHTO, the seismic site class is determined from a soil profile extending to a depth of 100 feet. The current scope requested did not include a boring to a depth of 100 feet. The borings for this project extended to a maximum depth of approximately 41½ feet. The above classification is based on the assumption that soil conditions similar to those encountered in the lower portions of the borings continue to a depth of at least 100 feet. If desired, a geophysical exploration could be performed to confirm the site classification, or possible justify a more favorable site classification.

Infiltration Testing

A down hole infiltration test was performed in the boring I-4. Due to a limited space to perform infiltration testing, we understand design level infiltration tests in accordance with Sections 8000 and 8200 of the ACHD Policy Manual were waived by ACHD and borehole test methods would be acceptable for this project. The test was performed in a 5-inch diameter solid pipe that was placed within the test boring. Bentonite was placed in the annular space around the pipe to act as a seal. The test hole was presoaked the day prior to testing. The falling head test was performed with an initial head of water of approximately 2 feet, and the drop in head was measured for a period of about 1 hour or until water completely drained from the boring, whichever occurred first. The head of water was then reestablished, and each test was repeated a total of 4 times. Test results are summarized in the following table:

Boring No.

Approximate Depth of

Test (feet) 1 Soil Type at Depth of Test

Measured Infiltration Rate (inches/hour)

I-4 4½ Silty Sand 14

1. Depth below the existing ground surface.

The field test results are not intended to be design rates; they represent the tests at the depths and locations indicated. The rates used for design should be determined by the designer by applying an appropriate factor of safety. A minimum factor of safety of two and a maximum infiltration rate of 14 inches per hour should be used, and local agency guidance should be considered. A greater factor of safety may be warranted. The designer should select the design factor of safety that considers the severity of the impacts to the public if the system were to fail, the facility geometry, if the facility includes outlet structures, the degree of influent control to reduce siltation and bio-buildup, the quality and frequency of long-term maintenance, etc. In addition, the following factors should be considered when selecting the factor of safety for design:

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Test Procedures: The percolation test was performed through a 5-inch diameter pipe. Percolation rates in large storm water infiltration systems may be different than measured in the relatively small test area.

Water Quality: Percolation tests are typically performed using clear water, whereas the storm water will likely not be clear, but may contain organics, fines, and grease/oil. The presence of these deleterious materials will tend to decrease the rate that water percolates from the infiltration systems. Design of the stormwater infiltration systems should account for the presence of these materials and should incorporate structures/devices to remove these deleterious materials.

Long Term Performance/Maintenance: With time, the bottoms of infiltration systems tend to plug with organics, sediments, and other debris. Long-term maintenance will likely be required to remove these deleterious materials to improve the actual infiltration rate. The designer should base the project design and selection of the infiltration rate on the assumption that little to no maintenance will be performed.

Soil Variability: Based on the soils encountered during our exploration, we expect the percolation rates of the soils could vary over short distances due to variations in fines content, cementation, and soil type. Percolation into soils with a higher percentage of silt or clay or into cemented soil layers would be expected to have lower percolation rates. The design elevations and sizes of the proposed infiltration systems should account for this expected variability in the percolation rate.

Geotechnical Overview

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the test borings, provided that the recommendations provided in this report are implemented in the design and construction phases of this project.

The subsurface materials generally consisted of gravel fills with underlying dense to very dense native sand and gravel with varying amounts silt to the maximum depth explored (41.5 feet BGS) in B-2 and B-5. At the time of exploration drilling, groundwater was encountered in B-2 and B-5 at 8 and 9 feet BGS (2455 feet elevation), respectively.

Groundwater was monitored from June to early November 2024 and the shallowest elevation from these readings would be greater than 2457.9. These results can be found in Exploration Results.

Groundwater will likely be encountered during construction. If groundwater is encountered during construction, a positive means of construction dewatering will be required to complete the excavations and placement of the foundations and backfill.

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Based on the conditions encountered and estimated load-settlement relationships, the proposed structures can be supported on spread foundations.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration Results), engineering analyses, and our current understanding of the proposed project. The General Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include demolition, clearing and grubbing, excavations, and engineered fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations.

Site Preparation

Prior to construction, the subgrade should be prepared as described in Sections 201 and 202 of the ISPWC and ACHD Supplemental Specifications to ISPWC. In general, the existing pavement section, undocumented fills, deleterious materials such as vegetation, root systems, topsoil, and soft, frozen, disturbed, or otherwise unsuitable materials should be completely removed from the proposed construction areas. Surfaces exposed after excavation should be free of mounds and depressions that could prevent uniform compaction. Subgrade soils exposed during construction will be susceptible to rutting or pumping under construction traffic when wet. See Earthwork Construction Considerations.

Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

Fill Material Types

Fill materials should meet the following material property requirements. Regardless of its source, compacted fill should consist of approved materials that are free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

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Soil Type 1 Materials

Structural Fill

Structural Fill should consist of 3-inch or 6-inch minus uncrushed aggregates meeting the requirements of

Idaho Standards for Public Works Construction (ISPWC) Section 801.

Aggregate Base Aggregate Base should meet the requirements for ¾-inch Type I crushed aggregate in accordance with ISPWC Section 802.

1. Frozen material should not be used, and fill should not be placed on a frozen subgrade.

Fill Placement and Compaction Requirements

All fill soil should be free of deleterious, organic, or frozen matter. Aggregate Base and Structural Fill should be compacted in accordance with ISPWC Sections 801 and 802, and ACHD Supplemental Specifications, as appropriate. Embankments should be constructed in accordance with Section 202 Part 3.8 of the ISPWC. In backfill under bridge footings, Structural Fill or Aggregate Base should be compacted to at least 98 percent of the maximum dry density, as determined by AASHTO T 99. Each lift of fill should be tested at various locations within the roadway alignment to verify that it meets the density requirements. Where fill is placed against an existing slope, the slope should be benched to key the new fill into the slope in accordance with ISPWC requirements.

Grading and Drainage

All grades must provide effective drainage away from the bridge during and after construction. Roadway runoff should be collected and discharged away from the bridges and embankment slopes. Effective drainage should be maintained for the life of the structure. Erosion protection should be provided in the area of the bridge to prevent erosion of the canal banks, embankments and to protect the foundations for scour.

Earthwork Construction Considerations

It is recommended that construction of the structures should occur when water is not flowing in Drain 10. If construction occurs when water is in the creek, or soon after, groundwater will likely be encountered during construction. If groundwater is encountered during construction, a positive means of construction dewatering will be required to complete the excavations and placement of the foundations and backfill. The dewatering system should be sized and located such that the groundwater level is

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Facilities | Environmental | Geotechnical | Materials 9 maintained below the bottom of the foundation excavations. Failure to adequately dewater the excavations may lead to failure of temporary slopes, difficulties properly constructing foundations, and/or difficulties placing and compacting backfill material. If dewatering is required, the Contractor should be prepared with proper dewatering methods and equipment. The dewatering system should be designed by the Contractor.

If construction occurs soon after water is drained from the creek, dewatering may still be required due to bank storage and a seasonally elevated perched groundwater level.

Grading operations should be controlled to prevent water from flowing into construction areas. Excessive wetting or drying of the subgrade soils should be avoided during construction. Excess water should be promptly removed.

Soils that rut, pump, or are otherwise disturbed are not suitable for support of foundations or embankments and should be removed and replaced with Aggregate Base.

Measures that may help reduce disturbance of exposed soils include performing earthwork during warm, dry weather, the use of light track-mounted equipment, and avoidance of heavy repeated traffic over a given area.

If fill is placed against a slope, the slope should be benched to key the new fill into the slope. This should be done in accordance with Section 202, Part 3.8, Item A.3 of the

ISPWC.

The Contractor is responsible for designing and constructing stable, temporary excavations as required to maintain stability of the excavation sides and bottom, and for protecting existing facilities/utilities. Excavations should be sloped or shored in accordance with local, state, and federal regulations, including current OSHA excavation and trench safety standards.

Construction Observation and Testing

Earthwork on the project should be observed and evaluated by the Engineer. Monitoring of earthwork should include observation and testing of site clearing and subgrade preparation, placement of Aggregate Base, foundation construction, and other geotechnical conditions exposed during the construction of the project.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Engineer. If unanticipated conditions are encountered, the Geotechnical Engineer should prescribe mitigation options. Observation of the foundation excavations will be critical to evaluate if undocumented fill or unsuitable soils are encountered and properly removed. Variations in soil conditions should be anticipated between and beyond the boring locations.

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Foundations

Geotechnical design parameters for the proposed box culvert and wing wall foundations are presented separately below. If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations.

Box Culvert

The proposed box culvert should be supported on a layer of compacted crushed ¾ inch Type I crushed aggregate as specified in the ISPWC Section 802. The layer of compacted ¾ inch Type I crushed aggregate should have a minimum thickness of 12 inches extending to undisturbed native gravels. Prior to placing the crushed base, all canal sediments, existing fill soils, and any soil disturbed during demolition of the existing culvert should be removed from the box culvert area to expose undisturbed native soils.

Design Parameters

Item Description Foundation Type Box Culvert Floor

Required Bearing Stratum1 At least 12 inches of compacted Aggregate

Base extending to undisturbed native gravels.

Nominal (ultimate, unfactored) bearing capacity (for the box culvert with an exterior width of 17 to 18 feet)

19 kips per square foot (ksf)

Minimum Embedment below Finished

Grade2

24 inches to the bottom of the footing for frost protection. Spread foundations should also be set below the elevation of the channel bottom. We understand footings will be protected against scour and therefore scour is not anticipated. If scour is anticipated, footings should be embedded 24 inches below the anticipated scour depth.

Recommended resistance factor to be used with the nominal (ultimate, unfactored) bearing capacity for strength limit state design

0.45

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Item Description Presumptive bearing capacity for service limit state for settlement of approximately 1 inch or less (for the dimensions of 17 to 18 feet width and 50 feet length)

2.4 ksf

Recommended resistance factor to be used with the bearing capacity for service limit state design.3 1.0

Ultimate coefficient of friction to resist sliding

Precast footings: 0.54

Recommended resistance factors when designing resistance to sliding3 Precast Footings: 0.90

1. Unsuitable or soft soils should be over excavated and replaced.

2. Embedment accounts for frost depth. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

3. Recommended resistance factors are based on AASHTO-LRFD Bridge Design

Specifications, 9th Edition.

Wing Wall

Based on the soil conditions encountered during our field exploration, we recommend the proposed wing walls be founded on spread foundations supported on a 12-inch minimum layer of ¾ inch Type I crushed aggregate placed and compacted over the undisturbed native gravels.

Design Parameters

Item Description Foundation Type Conventional spread footings

Required Bearing Stratum1 At least 12 inches of compacted Aggregate

Base extending to undisturbed native gravels.

Nominal (ultimate, unfactored) bearing capacity (for the wing wall with an exterior width of 1.5 to 4.0 feet)

See graph below

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Item Description

Minimum Embedment below Finished

Grade2

24 inches to the bottom of the footing for frost protection. Spread foundations should also be set below the elevation of the channel bottom. We understand footings will be protected against scour and therefore scour is not anticipated. If scour is anticipated, footings should be embedded 24 inches below the anticipated scour depth.

Recommended resistance factor to be used with the nominal (ultimate, unfactored) bearing capacity for strength limit state design

0.45

Presumptive bearing capacity for service limit state for settlement of approximately 1 inch or less See graph below

Recommended resistance factor to be used with the bearing capacity for service limit state design.3 1.0

Ultimate coefficient of friction to resist sliding

Cast-in-place footings: 0.67 Precast footings: 0.54

Recommended resistance factors when designing resistance to sliding3

Cast-in-place footings: 0.80 Precast Footings: 0.90

1. Unsuitable or soft soils should be over excavated and replaced.

2. Embedment accounts for frost depth. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

3. Recommended resistance factors are based on AASHTO-LRFD Bridge Design

Specifications, 9th Edition.

Standard penetration test (SPT) results from our borings were used to evaluate the strength of the foundation soil for bearing capacity. The ultimate bearing capacity is shown as a function of effective footing width in the chart below. The resistance factor shown above should be applied to the bearing values presented. The bearing capacity shown in the chart below is based on the foundation extending at least 24 inches below adjacent grade and below the elevation of the channel bottom. If foundations will be supported above the bottom of the ditches, we should be notified to modify the estimated bearing capacity and foundation settlement.

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The presumptive bearing pressure versus footing width at the service limit state for a total estimated settlement of approximately 1-inch is presented on the graph below.

Settlement estimates were calculated based on the empirical Hough method and the native silty sand to clayey sand encountered in our borings.

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Foundation Construction Considerations

Terracon should evaluate exposed foundation subgrade conditions during construction prior to placing fill or concrete. Materials at the base of foundation excavations should be free of standing water. Should the soils at bearing level become excessively dry, disturbed, saturated, or frozen, the affected soil should be removed prior to placing concrete. The over-excavated materials should be replaced using compacted Structural Fill or Aggregate Base.

Overexcavation for Structural Fill or ¾ Type I crushed Aggregate Base placement below footings should be conducted as shown below. The overexcavation should be backfilled up to the footing base elevation, with ¾ Type I crushed Aggregate Base placed, as recommended in the Earthwork section.

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Lateral Earth Pressures

Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction, and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown in the diagram below. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The “at-rest” condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

or

AGGREGATE BASE

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Lateral Earth Pressure Design Parameters

Earth Pressure

Condition 1

Backfill Vertical to Horizontal Placement (V feet: H feet)

Coefficient for Backfill

Type 2

Surcharge Pressure 3 p1 (psf)

Equivalent Fluid Pressures

(psf) 2,4

Unsaturated

Submerged

Active (Ka) Horizontal 0.28 (0.28)S (35)H (82)H

At-Rest (Ko) Horizontal 0.44 (0.44)S (55)H (92)H

1. For active earth pressure, wall must rotate about base, with top lateral movements 0.002 H to 0.004 H, where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance. Fat clay or other expansive soils should not be used as backfill behind the wall.

2. Backfill with a maximum unit weight of 125 pcf for granular unsaturated soils and 130 pcf for granular submerged soils and an internal friction angle of 34 degrees.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction equipment is not included.

5. To achieve “Unsaturated” conditions, follow guidelines in Subsurface Drainage for Below-Grade Walls below. “Submerged” conditions are recommended when drainage behind walls is not incorporated into the design.

Active earth pressures are applicable for a wall that is free to rotate and are only appropriate for cohesionless soils. The amount of movement relative to the wall height to develop active earth pressures is presented in AASHTO LRFD Table C3.11.1-1. At-rest earth pressures are appropriate for a wall that is restrained at the top and for cohesive soils. We anticipate that the proposed box culvert structure will be a rigid structure so the at-rest earth pressure condition will apply. If wing walls are structurally connected to the box culvert, the at-rest earth pressure condition will also apply to the wing walls. Some movement of the structure would be required to mobilize the full passive pressure. Relative movements to develop passive resistance are provided in AASHTO LRFD Table 3.11.1-1. In accordance with AASHTO LRFD Table 10.5.5.2.2-1, the resistance factor for the passive earth pressure component of sliding resistance should be 0.50. As described in AASHTO LRFD C10.6.3.4, this resistance factor is based on the lateral foundation movement being less than what is needed to mobilize the full passive pressure. The passive resistance should be neglected in the scour zone or the upper 2 feet of the soils profile, whichever is deeper.

Lateral earth pressures should be adjusted for hydrostatic pressures, surcharge loads including the weight of soil above the top of the structure, sloping fill, live loads near the walls (including compaction equipment and traffic), and/or seismic loads as appropriate.

The live load surcharge for vehicular loads is often modeled as being equivalent to 2 feet of soil with a unit weight of at least 125 pcf, but these loads should be determined in accordance with Tables 3.11.6.4-1 and 3.11.6.4-2 of AASHTO LRFD.

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Fill, debris, and loose soil should be removed before placing backfill behind walls. Prior to the placement of any fill material, compact subgrade to the requirements of Section

202.3.8 in the 2020 Edition ISPWC.

General Comments

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly affect excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating including excavation support and dewatering requirements/design are the responsibility of others.

Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials 18 from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Figures

Contents:

GeoModel

2,420

2,425

2,430

2,435

2,440

2,445

2,450

2,455

2,460

2,465

2,470

E L E

V A

T

IO

N

M S

L

(f e e t)

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

B-2 P-3 I-4 B-5

Legend

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

GeoModel

Munger Road over Dry Creek Canal | Star, Idaho

Terracon Project No. 62235094

Munger Road Bridge #1005

11849 W Executive Dr Ste G

Boise, ID

First Water Observation

Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time.

Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details.

Asphalt Fill Poorly-graded Gravel with Silt and Sand

Poorly-graded Sand

Silty Sand Poorly-graded Gravel with Sand

Well-graded Gravel w/sand

Poorly-graded Sand with Gravel

Poorly-graded Sand with Silt Sandy Lean Clay

Model Layer Layer Name General Description

1 Various fills with varying gravel, sand, silt, and clay contents.

3 Poorly graded sand with varying amounts of gravel and silt.

4 Clay with varying amounts of sand

2 Poorly and well graded gravel with varying amounts of silt and sand.

5 Silt with varying amounts of sand.

Fill

Sands

Clay

Gravels

Silt

22.5

41.5

17.5

4.5

3.5

11.5

15.5

22.5

25.5

27.5

41.5

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Exploration and Testing Procedures

Field Exploration

Number of Borings Approximate Boring

Depth (feet) Location

2 41 ½ Bridge Structure

1 4 ½ Infiltration

1 17 ½ Piezometer 1

1. Soil sampling was not performed during drilling for Piezometer.

Boring Layout and Elevations: Terracon personnel provided the boring layout using handheld GPS equipment (estimated horizontal accuracy of about ±10 feet) and referencing existing site features. Approximate ground surface elevations were estimated using Google Earth. If elevations and a more precise boring layout are desired, we recommend borings be surveyed.

Subsurface Exploration Procedures: We advanced the borings with a truck-mounted, rotary drill rig using hollow stem, continuous flight augers. Four samples were obtained in the upper 10 feet of each boring and at intervals of 5 feet thereafter. In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a 140-pound automatic hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the Standard Penetration Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths. A 3-inch O.D. split-barrel sampling spoon with 2.5-inch I.D. sampler was used for sampling in the gravel layers. Split-barrel sampling procedures are similar to standard split spoon sampling procedure. We observed and recorded groundwater levels during drilling and sampling. For safety purposes, all borings were backfilled in general accordance with IDWR requirements including bentonite and auger cuttings upon their completion. Pavements were patched with cold-mix asphalt.

We also observed the boreholes while drilling and at the completion of drilling for the presence of groundwater. The groundwater levels are shown on the attached boring logs.

The sampling depths, penetration distances, and other sampling information was recorded on the field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory for testing and classification by a Geotechnical Engineer. Our exploration team prepared field boring logs as part of the drilling operations. These field

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials logs included visual classifications of the materials observed during drilling and our interpretation of the subsurface conditions between samples. Final boring logs were prepared from the field logs. The final boring logs represent the Geotechnical Engineer's interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

The project engineer reviewed the field data and assigned laboratory tests. The laboratory testing program included the following types of tests:

■ Moisture Content

■ Grain Size Analysis

■ Atterberg Limits

■ Resistivity

■ pH

The laboratory testing program often included examination of soil samples by an engineer. Based on the results of our field and laboratory programs, we described and classified the soil samples in accordance with the Unified Soil Classification System.

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Attachments

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Site Location and Exploration Plans

Contents:

Site Location Plan Exploration Plan

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Note to Preparer: This is a large table with outside borders. Just click inside the table above this text box, then paste your GIS Toolbox image.

When paragraph markers are turned on you may notice a line of hidden text above and outside the table – please leave that alone. Limit editing to inside the table.

Site Location

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

November 5, 2024 | Terracon Project No. 62235094

Facilities | Environmental | Geotechnical | Materials

Note to Preparer: This is a large table with outside borders. Just click inside the table above this text box, then paste your GIS Toolbox image.

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Exploration Plan

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES MAP PROVIDED BY MICROSOFT BING MAPS

Exploration and Laboratory Results

Contents:

Boring Logs (B-2, P-3, I-4, and B-5) Groundwater Monitoring Graph Grain Size Distribution

2462.6

2440.5

ASPHALT, approximately 4 1/4 inches FILL - POORLY GRADED GRAVEL WITH SILT AND SAND, brown

FILL - SILTY CLAY, brown

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM),

light brown to dark brown, dense to very dense with cobbles

POORLY GRADED SAND (SP), light brown, dense, with lenses of silt

Boring Log No. B-2

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

89.7

0.4

2.0

6.0

22.5

0.8

1.3

1.3

1.1

0.9

1.3

6-30-26 N=56

3-2-3 N=5

11-13-25 N=38

7-14-17 N=31

18-31-44

25-37-35 N=72

35-70

Munger Road over Dry Creek Canal | Star, Idaho

Terracon Project No. 62235094 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

BK-81

Hammer Type Automatic

Driller Haz-Tech Drilling, Inc.

Logged by

LK

Boring Started 05-20-2024

Boring Completed 05-20-2024

Abandonment Method Boring backfilled with auger cuttings and/or bentonite.

Pavement patched with cold-mix asphalt.

Advancement Method Hollow-stem auger

Notes

Water Level Observations Groundwater encountered at 8.0 feet while drilling

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Elevation Reference: Elevations were estimated via Google Earth Pro.

Munger Road Bridge #1005

S am pl e

T yp e

Pe rc en t

Fi n es

W at er C o n te n t

Elevation: 2463 (Ft.) +/-

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 43.7085° Longitude: -116.5032°

Depth (Ft.)

R e co ve ry

Ft

Fi el d T es t

R e su lt s

2432.5

2421.5

POORLY GRADED SAND (SP), light brown, dense, with lenses of silt (continued)

SILTY SAND (SM), light brown, dense

Boring Terminated at 41.5 Feet

Boring Log No. B-2

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

30.5

41.5

1.4

1.4

1.4

1.5

6-17-21 N=38

13-17-20 N=37

16-21-27 N=48

10-23-27 N=50

Munger Road over Dry Creek Canal | Star, Idaho

Terracon Project No. 62235094 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

BK-81

Hammer Type Automatic

Driller Haz-Tech Drilling, Inc.

Logged by

LK

Boring Started 05-20-2024

Boring Completed 05-20-2024

Abandonment Method Boring backfilled with auger cuttings and/or bentonite.

Pavement patched with cold-mix asphalt.

Advancement Method Hollow-stem auger

Notes

Water Level Observations Groundwater encountered at 8.0 feet while drilling

See Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Elevation Reference: Elevations were estimated via Google Earth Pro.

Munger Road Bridge #1005

S am pl e

T yp e

Pe rc en t

Fi n es

W at er C o n te n t

Elevation: 2463 (Ft.) +/-

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 43.7085° Longitude: -116.5032°

Depth (Ft.)

R e co ve ry

Ft

Fi el d T es t

R e su lt s

2445.5

FILL - POORLY GRADED GRAVEL WITH SILT AND SAND, brown

FILL - SILTY CLAY, brown

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM),

light brown to dark brown

Boring Terminated at 17.5 Feet

Piezometer Log No. P-3

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

2.0

6.0

17.5

Munger Road over Dry Creek Canal | Star, Idaho

Terracon Project No. 62235094 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

BK-81

Hammer Type Automatic

Driller Haz-Tech Drilling, Inc.

Logged by

LK

Boring Started 05-21-2024

Boring Completed 05-21-2024

Abandonment Method Boring backfilled with auger cuttings and/or bentonite.

Pavement patched with concrete.

Advancement Method Hollow-stem auger

Notes

Water Level ObservationsSee Exploration and Testing Procedures for a description of field and laboratory procedures used and additional data (If any).

See Supporting Information for explanation of symbols and abbreviations.

Elevation Reference: Elevations were estimated via Google Earth Pro.

Munger Road Bridge #1005

S am pl e

T yp e

Pe rc en t

Fi n es

W at er C o n te n t

Elevation: 2463 (Ft.) +/-

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 43.7085° Longitude: -116.5032°

Depth (Ft.)

R e co ve ry

Ft

Fi el d T es t

R e su lt s

2458.5

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM),

light brown, medium dense

SILTY SAND (SM), dark brown, medium stiff

Boring Terminated at 4.5 Feet

Boring Log No. I-4

W at er L ev el

O bs er va tio ns

D ep th

Ft

Facilities | Environmental | Geotechnical | Materials

G ra p h ic

L o g

M o d el

L ay er

3914.8 NP

2.0

4.5

1.1

8-12-12 N=24

3-3-2 N=5

Munger Road over Dry Creek Canal | Star, Idaho

Terracon Project No. 62235094 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

BK-81

Hammer Type Automatic

Driller Haz-Tech Drilling, Inc.

Logged by

LK

Boring Started 05-20-2024

Boring Completed 05-20-2024

Abandonment Method Boring backfilled with auger…