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Allumbaugh Street Bridge over the Ridenbaugh Canal Geotechnical Engineering Report ACHD Project No. 822042 & GIS No. 205289 Boise, Idaho Prepared for:

Keller Associates, Inc.

100 E Bower St, Suite 110 Meridian, Idaho 83642

Geotechnical Engineering Report Allumbaugh Street Bridge over the Ridenbaugh Canal | Boise, Idaho June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials i

Table of Contents Report Summary .............................................................................................. i Introduction Project Description Site Conditions Geotechnical Characterization Seismic Site Class Geotechnical Overview Earthwork

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

Shallow Foundations Design Parameters Foundation Construction Considerations Scour and Erosion Protection

Lateral Earth Pressures Design Parameters

Corrosivity General Comments

Figures GeoModel

Attachments

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

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 Allumbaugh Street in Boise, Idaho. The bridge over the Ridenbaugh Canal will be replaced with a wider structure to accommodate the new roadway improvements. We anticipate the new bridge structure will be supported on spread footing foundations.

Geotechnical Characterization

Fill material was encountered in borings B-1 and B-2 to 7½ and 9½ feet below ground surface (BGS), respectively.

Groundwater was encountered in boring B-1 at 21 feet BGS.

Groundwater monitoring performed by Terracon about 80 feet north of the bridge indicates that the groundwater high was in late June, at a depth of 13.5 feet BGS.

Earthwork

Remove existing fill where observed (or) Geotechnical engineer to further evaluate areas where existing fill is present after site stripping.

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

Aggregate Base and Subbase should be compacted in accordance with ISPWC Sections 801 and 802, and ACHD Supplemental Specifications, as appropriate.

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

Shallow Foundations

Shallow foundations are recommended for supporting the bridge.

Allowable bearing pressure is noted in a graph within the report.

Expected settlements: Approximately 1-inch total.

Over-excavation 36 inches of existing soils and replacing with properly compacted Structural Fill/Aggregate Base beneath foundations.

Minimum embedment of 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.

Structural Fill/Aggregate Base must meet requirements in Earthwork

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 Allumbaugh Street bridge over the Ridenbaugh Canal in Boise, 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

■ Demolition considerations

■ 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 a phone call and email from Keller between June 10, 2022 and January 9, 2023. This includes a conceptual figure provided via email on December 13, 2022.

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Item Description

Project Description

Ada County Highway District (ACHD) proposes to reconstruct and widen Allumbaugh Street around the Ridenbaugh Canal in Boise, Idaho. This will include the bridge crossing over the Ridenbaugh Canal will be replaced with a wider structure to accommodate the new roadway improvements. The proposed bridge will be about 30 feet long and 68 feet wide with approach slabs. We anticipate the new bridge structure will be supported on spread footing foundations.

Proposed Structure

According to information provided by Keller, the crossing over the Rudabaugh Canal will be a three-lane bridge. The proposed bridge will be about 30 feet long and 68 feet wide with approach slabs.

Maximum Loads No structural loading information was provided by Keller for the bridge.

Embankment and Grading

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

Free-Standing Retaining Walls

None anticipated

Pavements Geotechnical services associated with new pavement sections were not requested and are not part of our scope of work.

Stormwater Management

Geotechnical services associated with stormwater management were not requested and are not part of our scope of work.

Design method AASHTO LRFD Bridge Design Specifications, 9th Edition, 2020.

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.

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Item Description

Site Location

The project is located where Allumbaugh Street crosses the Ridenbaugh Canal between Franklin Road and Douglas Street in Boise, Idaho.

Approximate Site Latitude/Longitude: 43.6049º, -116.2663º See Site Location Map

Existing Improvements

The site is currently an existing two-lane bridge that carries Allumbaugh Street over the Ridenbaugh Canal with a sidewalk on the west side of the bridge.

Current Ground Cover

Allumbaugh Street is paved with asphalt with gravel-surfaced shoulders. Near the abutments, the banks of the canal are lightly vegetated on the southeastern portion, with mature trees on the banks to the east and west.

Existing Topography

Allumbaugh 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 Native Soils Sands and gravels with varying clay and silt contents.

Groundwater was encountered in boring B-1 at 21 feet BGS. Water was not flowing in the canal at the time of our exploration. As part of Roadway and ADA Improvements, Part 1 (ACHD Project No. 720004, ITD Key No. 20259 and Terracon Project No.

62215029), a piezometer was installed, and groundwater monitoring was performed

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Facilities | Environmental | Geotechnical | Materials 4 about 80 feet north of the Allumbaugh Bridge in boring A-1. The highest groundwater observed was in late June 2022 at 13.50 feet BGS.

Groundwater conditions may be different at the time of construction. Groundwater conditions may change because of seasonal variations in the amount of water within Ridenbaugh Canal, as well as on variations in irrigation, rainfall, runoff, and other conditions not apparent at the time of exploration. The evaluation of these factors was beyond the scope of this report.

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

0.195 g

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

0.069 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 E) 0.133 g SDS, Modified Ss for Project Site (Site Class E) 0.312 g SD1, Modified S1 for Project Site (Site Class E) 0.165 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 30½ 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.

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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 loose to very dense native gravels with varying silt, clay, and sand content. Groundwater was encountered in B-1 at 21 feet BGS of exploration drilling. In late June 2022, groundwater was observed at 13.50 feet BGS about 80 feet north of the Allumbaugh Bridge as part of Roadway and ADA Improvements, Part 1 (ACHD Project No. 720004, ITD Key No. 20259 and Terracon Project No. 62215029).

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.

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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.

Soil Type 1 Materials

Structural Fill/Subbase

Subbase 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 Subbase 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, 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.

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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 the Ridenbaugh Canal. If construction occurs when water is in the canal, 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 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 canal, 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 Structural Fill.

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.

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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 Structural Fill/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. As a total of two borings were drilled for the proposed bridge, 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.

Shallow Foundations

If the site has been prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations. The native soils encountered at anticipated bearing depths were loose therefore we recommend over-excavation and replacement of 36 inches of native gravels.

Design Parameters

Item Description Foundation Type Conventional shallow spread footings

Nominal (ultimate) Bearing Capacity See graph below

Required Bearing Stratum 1

Over-excavate and replace with 36 inches of properly compacted Structural Fill/Aggregate Base extending to undisturbed native gravel sediments

Minimum Embedment below

Finished Grade 2

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.

Minimum Foundation Dimensions 36 inches

Recommended resistance factor to be used with the nominal bearing capacity for strength limit state design 3

0.45

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Item Description Presumptive bearing pressure for settlement less than 1 inch See graph below

Recommended resistance factor to be used with the bearing pressure for service limit state design 3

1.0

Ultimate coefficient of friction to resist sliding

Precast footings: 0.50 Cast-in-place footings: 0.650

Recommended resistance factors when designing resistance to sliding 3 Precast footings: 0.90

Cast-in-place footings: 0.80

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 granular soils encountered in our borings.

Foundation Construction Considerations

As described in the previous subsections, foundations for the bridge and headwalls, may be supported on a layer of compacted Structural Fill/Aggregate Base that is placed on undisturbed native soils. If used, the layer of compacted fill should extend laterally from the foundation edges a horizontal distance equal to 2/3 of the depth of the compacted fill below the footing base elevation.

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 Aggregate Base.

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

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Scour and Erosion Protection

The proposed structure, wing walls, and canal banks should be protected from scour and erosion. The bearing capacity and settlement estimates provided in this report are based on the assumption that scour will be prevented. If scour does occur, bearing capacity could be reduced and settlement could increase.

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 Granular -

0.28 (0.28)S (35)H (82)H

At-Rest (Ko) Horizontal Granular -

0.44 (0.44)S (55)H (92)H

Active (Ka) 2:1 Granular -

0.42 (0.42)S (52)H (91)H

At-Rest (Ko) 2:1 Granular -

0.64 (0.64)S (80)H (106)H

Active (Ka) 4:1 Granular -

0.33 (0.33)S (41)H (85)H

At-Rest (Ko) 4:1 Granular -

0.55 (0.55)S (68)H (99)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.

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Active earth pressures are applicable for a wall that is free to rotate. At-rest earth pressures are appropriate for a wall that is restrained at the top. Some movement of the structure would be required to mobilize the full passive pressure. Because of this, passive pressures are often neglected when resisting sliding. If passive pressures are needed to resist sliding, appropriate reductions should be applied.

The recommended design lateral earth pressures do not include load factors or a factor of safety. Appropriate load and resistance factors should be determined in accordance with AASHTO. These values presented above are for horizontal backfill only. The walls should be designed to support hydrostatic pressures or be designed with sufficient drainage so that hydrostatic pressures do not develop. Lateral earth pressures should be adjusted as necessary for surcharge loads, sloping backfill, live loads near the wall (including traffic and compaction equipment), and/or seismic loads as appropriate.

Debris, and loose soil should be removed before placing backfill behind walls.

Compaction should be in accordance with Section 202 Part 3.8 of the ISPWC. Adequate compaction of backfill soils is critical to performance of overlying pavements. Care should be taken to avoid over-compacting the backfill adjacent to the walls to reduce the potential for damaging or displacing the structure. Lightweight, hand-operated compaction equipment should be used within 3 feet of any concrete structure or retaining wall. Thinner lifts of the backfill may be needed to achieve the required compaction where lightweight, hand-operated compaction equipment is used.

Corrosivity

The table below lists the results of laboratory electrical resistivity, and pH testing. The values may be used to estimate potential corrosive characteristics of the on-site soils with respect to contact with the various underground materials which will be used for project construction.

Boring Sample

Depth (feet) Soil Description

Electrical Resistivity (Ω-

cm) pH

B-1 9.5-11.0 Clayey Gravel with

Sand 5,700 6.94

We recommend that the design engineers consult with the manufacturers of specific products to determine adequate corrosion protection systems, as needed, for buried metal pipes and other metal objects used on this project.

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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 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

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Figures

Contents:

GeoModel

2,675

2,680

2,685

2,690

2,695

2,700

2,705

2,710

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-1

B-2

Legend

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

GeoModel

Allenbaugh Street | Boise, ID

Terracon Project No. 62225067

Allumbaugh St Br over the Ridenbaugh Canal

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

Clayey Sand with Gravel

Clayey Gravel with Sand

Poorly-graded Sand with Silt and Gravel

Poorly-graded Gravel with Silt and SandPoorly-graded

Gravel with Clay and Sand

Poorly-graded Sand with Clay and Gravel

Model Layer Layer Name General Description

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

2 Sands and gravels with varying clay and silt contents.

Fill Materials

Native Soils

7.5

26.4

30.5

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Exploration and Testing Procedures

Field Exploration

Number of Borings Approximate Boring

Depth (feet) Location

2 26½ to 30½ Bridge structure

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 thin-walled tube sampling procedure, a thin-walled, seamless steel tube with a sharp cutting edge was pushed hydraulically into the soil to obtain a relatively undisturbed sample. 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 with auger cuttings after 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 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

June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials 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.

June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials

Attachments

June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials

Site Location and Exploration Plans

Contents:

Site Location Plan Exploration Plan

Note: All attachments are one page unless noted above.

June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials

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Site Location Map

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

June 14, 2024 | Terracon Project No. 62225067

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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 Grain Size Distribution

2705.3

2698.5

2696.5

2679.6

ASPHALT, about 7" thick

FILL - POORLY GRADED GRAVEL WITH SILT AND SAND, brown and gray, trace clay

CLAYEY SAND WITH GRAVEL (SC), dark brown

CLAYEY GRAVEL WITH SAND (GC), dark brown, dense to very dense, with cobbles

POORLY GRADED SAND WITH SILT AND GRAVEL (SP-SM), brown, very dense

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM), brown, very dense, with cobbles

Boring Terminated at 26.4 Feet

Boring Log No. B-1

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

14.5

5.4

31-20-11

0.7

7.5

9.5

13.0

18.0

26.4

0.9

0.7

0.7

0.8

1.3

1.4

1.1

12-18-14 N=32

4-4-5 N=9

2-3-5 N=8

5-10-40 N=50

13-41-50 N=91

32-61-34

37-50-50/5"

Allenbaugh Street | Boise, ID

Terracon Project No. 62225067 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

CME 75

Hammer Type Automatic

Driller HazTech Drilling

Logged by

Boring Started 11-16-2022

Boring Completed 11-16-2022

Abandonment Method Boring backfilled with Bentonite Surface Capped with Asphalt

Advancement Method 6-inch inner diameter hollow stem auger

Notes

Water Level Observations

21.0 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 obtained from Google Earth Pro

Allumbaugh St Br over the Ridenbaugh Canal

S am pl e

T yp e

W at er C o n te n t

Elevation: 2706 (Ft.) +/-

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 43.6049° Longitude: -116.2663°

Depth (Ft.)

R ec o ve ry

Ft

Fi el d T es t

R es u lt s

2708.2

2704.5

2699.5

2678.5

ASPHALT, about 8.5" thick

FILL - POORLY GRADED SAND WITH SILT AND GRAVEL, trace clay, brown

FILL - POORLY GRADED SAND WITH SILT AND GRAVEL, with organics, dark brown

FILL - CLAYEY GRAVEL WITH SAND, with cobbles, dark brown

POORLY GRADED GRAVEL WITH CLAY AND SAND (GP-GC), brown, loose, with cobbles

POORLY GRADED SAND WITH CLAY AND GRAVEL (SP-SC), light brown, very dense

POORLY GRADED GRAVEL WITH SILT AND SAND (GP-GM), brown to gray, very dense, with cobbles

Boring Terminated at 30.5 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

6.6

3.3

0.8

4.5

7.0

9.5

13.0

18.0

30.5

1.1

0.7

0.5

0.8

0.6

1.2

0.5

6-13-10 N=23

2-3-2 N=5

2-2-4 N=6

2-8-7

2-2-2 N=4

60-70/1"

20-49-50/5"

90/6"

50/6"

Allenbaugh Street | Boise, ID

Terracon Project No. 62225067 Boise, ID

11849 W Executive Dr Ste G

Drill Rig

CME 75

Hammer Type Automatic

Driller HazTech Drilling

Logged by

Boring Started 11-16-2022

Boring Completed 11-16-2022

Abandonment Method Boring backfilled with Bentonite Surface Capped with Asphalt

Advancement Method 6-inch inner diameter 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 obtained from Google Earth Pro

Allumbaugh St Br over the Ridenbaugh Canal

S am pl e

T yp e

W at er C o n te n t

Elevation: 2709 (Ft.) +/-

Atterberg Limits

LL-PL-PI

See Exploration PlanLocation:

Latitude: 43.6048° Longitude: -116.2662°

Depth (Ft.)

R ec o ve ry

Ft

Fi el d T es t

R es u lt s

0.0010.010.1110100

16 2044 100

U.S. Sieve Numbers

63 2 10 14 506 2001.5 83/4 1/23/8 30 403 601 140

HydrometerU.S. Sieve Opening in Inches

Grain Size Distribution

SandGravel

Grain Size (mm) coarse fine coarse finemedium Silt or ClayCobbles

Percen t C o arser b y W eig h tPe rc en t Fi n er b y

W ei g h t

ASTM D422 / ASTM C136 / AASHTO T27

Facilities | Environmental | Geotechnical | Materials

LL PL PI Cc CuDescription

CLAYEY SAND with GRAVEL

POORLY GRADED SAND with CLAY and GRAVEL

29.1

5.2

0.41

%CobblesD60

0.568

5.103

D100

26.87

%Clay%Sand%Gravel

16.9

41.0

54.0

53.8

0.0

0.0

D10

0.19

D30

0.085

0.627

37.5

%Fines %Silt

Boring ID

7.5 - 9.5

15 - 15.6

B-1

B-2

7.5 - 9.5

15 - 15.6

Depth (Ft)Boring ID

B-1

B-2

Depth (Ft)

11849 W Executive Dr Ste G

Boise, IDTerracon Project No. 62225067

Allenbaugh Street | Boise, ID

Allumbaugh St Br over the Ridenbaugh Canal

Supporting Information

Contents:

General Notes Unified Soil Classification System

Ring Sampler

Shelby Tube

Standard Penetration Test

Facilities | Environmental | Geotechnical | Materials

> 4.00

2.00 to 4.00

1.00 to 2.00

0.50 to 1.00

0.25 to 0.50 less than 0.25

Unconfined Compressive Strength Qu (tsf)

Allumbaugh St Br over the Ridenbaugh Canal

Allenbaugh Street | Boise, ID

Terracon Project No. 62225067 11849 W Executive Dr Ste G

Boise, ID

N

(HP)

(T)

(DCP)

UC

(PID)

(OVA)

Standard Penetration Test Resistance (Blows/Ft.)

Hand Penetrometer

Torvane

Dynamic Cone Penetrometer

Unconfined Compressive Strength

Photo-Ionization Detector

Organic Vapor Analyzer

Water Level After a Specified Period of Time

Water Level After a Specified Period of Time

Cave In Encountered

Water Level Field Tests

Water Initially Encountered

Sampling

Water levels indicated on the soil boring logs are the levels measured in the borehole at the times indicated.

Groundwater level variations will occur over time. In low permeability soils, accurate determination of groundwater levels is not possible with short term water level observations.

General Notes

Location And Elevation Notes

Exploration point locations as shown on the Exploration Plan and as noted on the soil boring logs in the form of Latitude and Longitude are approximate. See Exploration and Testing Procedures in the report for the methods used to locate the exploration points for this project. Surface elevation data annotated with +/- indicates that no actual topographical survey was conducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from topographic maps of the area.

Soil classification as noted on the soil boring logs is based Unified Soil Classification System. Where sufficient laboratory data exist to classify the soils consistent with ASTM D2487 "Classification of Soils for Engineering Purposes" this procedure is used. ASTM D2488 "Description and Identification of

Soils (Visual-Manual Procedure)" is also used to classify the soils, particularly where insufficient laboratory data exist to classify the soils in accordance with ASTM D2487. In addition to USCS classification, coarse grained soils are classified on the basis of their in-place relative density, and fine-grained soils are classified on the basis of their consistency. See "Strength Terms" table below for details. The ASTM standards noted above are for reference to methodology in general. In some cases, variations to methods are applied as a result of local practice or professional judgment.

Exploration/field results and/or laboratory test data contained within this document are intended for application to the project as described in this document. Use of such exploration/field results and/or laboratory test data should not be used independently of this document.

Relevance of Exploration and Laboratory Test Results

Descriptive Soil Classification

> 30

15 - 30

8 - 15

4 - 8

2 - 4

Hard

> 50 Very Stiff

Stiff

Medium Stiff

Soft

Very Soft

30 - 50

10 - 29

4 - 9

0 - 3Very Loose

Loose

Medium Dense

Dense

Very Dense

Relative Density of Coarse-Grained Soils

(More than 50% retained on No. 200 sieve.)

Density determined by Standard Penetration Resistance

Consistency of Fine-Grained Soils

(50% or more passing the No. 200 sieve.)

Consistency determined by laboratory shear strength testing, field visual-manual procedures or standard penetration resistance

0 - 1

Relative Density Consistency Standard Penetration or

N-Value (Blows/Ft.)

Standard Penetration or N-Value

(Blows/Ft.)

Strength Terms

June 14, 2024 | Terracon Project No. 62225067

Facilities | Environmental | Geotechnical | Materials

Unified Soil Classification System Criteria for Assigning Group Symbols and Group Names Using

Laboratory Tests A

Soil Classification Group

Symbol Group Name B

Coarse-Grained Soils:

More than 50% retained on No. 200 sieve

Gravels:

More than 50% of coarse fraction retained on No. 4 sieve

Clean Gravels:

Less than 5% fines C

Cu≥4 and 1≤Cc≤3 E GW Well-graded gravel F

Cu<4 and/or [Cc<1 or Cc>3.0] E GP Poorly graded gravel F

Gravels with Fines:

More than 12% fines C

Fines classify as ML or MH GM Silty gravel F, G, H

Fines classify as CL or CH GC Clayey gravel F, G, H

Sands:

50% or more of coarse fraction passes No. 4 sieve

Clean Sands:

Less than 5% fines D

Cu≥6 and 1≤Cc≤3 E SW Well-graded sand I

Cu<6 and/or [Cc<1 or Cc>3.0] E SP Poorly graded sand I

Sands with Fines:

More than 12% fines D

Fines classify as ML or MH SM Silty sand G, H, I

Fines classify as CL or CH SC Clayey sand G, H, I

Fine-Grained Soils:

50% or more passes the

No. 200 sieve

Silts and Clays:

Liquid limit less than

Inorganic:

PI > 7 and plots above “A” line J CL Lean clay K, L, M

PI < 4 or plots below “A” line J ML Silt K, L, M

Organic:

݀݁݅ݎ݀ ݊݁ݒ ܮܮ ݀݁݅ݎ݀ ݐ݊ ܮܮ

< 0.75 OL

Organic clay K, L, M, N

Organic silt K, L, M, O

Silts and Clays:

Liquid limit 50 or more

Inorganic:

PI plots on or above “A” line CH Fat clay K, L, M

PI plots below “A” line MH Elastic silt K, L, M

Organic:

݀݁݅ݎ݀ ݊݁ݒ ܮܮ ݀݁݅ݎ݀ ݐ݊ ܮܮ

< 0.75 OH

Organic clay K, L, M, P

Organic silt K, L, M, Q

Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat A Based on the material passing the 3-inch (75-mm) sieve.

B If field sample contained cobbles or boulders, or both, add “with cobbles or boulders, or both” to group name.

C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay.

D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay.

E Cu = D60/D10 Cc =

F If soil contains ≥ 15% sand, add “with sand” to group name.

G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

H If fines are organic, add “with organic fines” to group name.

I If soil contains ≥ 15% gravel, add “with gravel” to group name.

J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay.

K If soil contains 15 to 29% plus No. 200, add “with sand” or

“with gravel,” whichever is predominant.

L If soil contains ≥ 30% plus No. 200 predominantly sand, add

“sandy” to group name.

M If soil contains ≥ 30% plus No. 200, predominantly gravel, add

“gravelly” to group name.

N PI ≥ 4 and plots on or above “A” line.

O PI < 4 or plots below “A” line.

P PI plots on or above “A” line.

Q PI plots below “A” line.

DxD

)(D