L15PS00204_Supplemental_GEOTECHNICAL_REPORT.pdf

Geotechnical Engineering Report Proposed BLM Field Office, DO #45

Cottonwood, Idaho October 8, 2013

Terracon Project No. 62095020F

Prepared for:

J-U-B Engineers, Inc.

Boise, Idaho

Prepared by:

Terracon Consultants, Inc.

Boise, Idaho

Proposed BLM Field Office, DO #45 ■ Cottonwood, Idaho October 8, 2013 ■ Terracon Project No. 62095020F

Responsive ■ Resourceful ■ Reliable

TABLE OF CONTENTS

Page No.

EXECUTIVE SUMMARY

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Description

2.2 Site Location and Description

3.0 SUBSURFACE CONDITIONS

3.1 Typical Subsurface Profile

3.2 Groundwater

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

4.2 Earthwork

4.2.1 Rock Excavation

4.2.2 Site Clearing and Subgrade Preparation

4.2.3 Fill Materials and Placement

4.2.4 Grading and Drainage

4.2.5 Utility Excavations

4.2.6 Earthwork Construction Considerations

4.3 Foundations

4.3.1 Spread Footing Recommendations – Office Building

4.3.2 Spread Footing Recommendations – Storage Building

4.3.3 Foundation Construction Considerations

4.4 Seismic Considerations

4.5 Floor Slabs

4.6 Pavements

4.6.1 Asphalt Pavement Sections

4.6.2 Portland Cement Concrete Pavement Section

4.6.3 Pavement Design Considerations

4.6.4 Pavement Construction Considerations

5.0 GENERAL COMMENTS

APPENDIX A – FIELD EXPLORATION

Exhibit A-1 Boring Location Plan Exhibit A-2 Field Exploration Description Boring Logs

APPENDIX B – LABORATORY TESTING

Exhibit B-1 Laboratory Test Description Exhibit B-2 Consolidation/Swell Test

APPENDIX C – SUPPORTING DOCUMENTS

Exhibit C-1 General Notes Exhibit C-2 Unified Soil Classification System Exhibit C-3 Description of Rock Properties

EXECUTIVE SUMMARY

A geotechnical exploration has been performed for the proposed BLM Field Office to be constructed in Cottonwood, Idaho. Field explorations included drilling eight test borings within the proposed project area. Based on the information obtained from our subsurface exploration, the site can be developed for the proposed project. The following geotechnical considerations were identified:

■ The site is currently occupied by existing buildings with associated parking and landscaped areas. We understand that prior to construction the existing improvements will be removed from the site. Removal should include the existing building, foundations, slabs, pavement section materials, utilities (including trench backfill), debris, and other man-made items, including subsurface features. Native soils that are disturbed during removal of these items should also be removed. Vegetation and topsoil should be stripped from areas that are within the construction zone.

■ Fill soils were encountered in the borings drilled at the site to depths up to about 2 feet. In their current condition, these fill soils are not suitable for support of the proposed building or pavement and should be removed from proposed construction areas.

■ Highly plastic, fat clay soils are present on this site. Such soils are commonly referred to as “expansive” because they expand or swell with increases in their moisture content.

These soils also contract or shrink as their moisture content decreases. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion.

However, even if these procedures are followed, some movement and cracking in the structure should be anticipated. The severity of cracking and other cosmetic damage such as uneven floor slabs will probably increase if any modification of the site results in excessive wetting or drying of the expansive soils. It may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction, such as complete replacement of expansive soils. We would be pleased to discuss construction alternatives with you.

■ Weathered basalt rock and basalt tephra were encountered in our borings at depths ranging from about 1 to 7 feet below the existing ground surface. Variation in the top elevation of basalt rock can occur abruptly in short horizontal distances. The basalt rock encountered in the borings was moderately to highly weathered and the basalt tephra was highly to completely weathered. Some very broken or completely weathered portions of these materials may be rippable with heavy construction equipment with rippers.

However, portions of the rock will likely not be rippable, and the Contractor should be prepared to utilize hydraulic or pneumatic hammers to assist in rock removal. Due to the anticipated relatively shallow rock thickness that may require excavation, blasting is not recommended.

■ Within the borings for the proposed office building, moderately to highly weathered basalt rock was encountered in three of the borings, and highly to completely weathered basalt tephra was encountered in the remaining boring. These materials were encountered at depths ranging from about 2 to 3½ feet below the existing site grade. Due to the variation in the elevation of basalt rock/tephra as encountered in the borings in the office building, and also due to the variation in the support characteristics of the basalt rock and the basalt tephra, the proposed office building footings should be supported on Structural Fill extending to and placed directly on the undisturbed basalt rock/tephra. Footings should have a minimum of 12 inches of Structural Fill beneath them.

■ Within the borings drilled at the location of the proposed storage building, weathered rock was encountered at depths ranging from about 5 to 7 feet below the existing site grade. Due to this depth to rock, the proposed foundations of the storage building may be founded on shallow spread footings supported on the undisturbed native soils.

■ Based on the 2009 International Building Code, the seismic site classification for this site is C.

This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The General Comments Section should be read for an understanding of the report limitations.

Responsive ■ Resourceful ■ Reliable 1

GEOTECHNICAL ENGINEERING REPORT

PROPOSED BLM FIELD OFFICE, DO #45

COTTONWOOD, IDAHO

Terracon Project No. 62095020F October 8, 2013

1.0 INTRODUCTION

This report presents the results of geotechnical engineering services performed for the proposed Bureau of Land Management (BLM) field office to be constructed in Cottonwood, Idaho.

Our services consisted of drilling borings to determine subsurface conditions, performing laboratory testing on representative soil samples, performing engineering analyses of the subsurface soils, and preparing this report. The purpose of these services is to provide information and/or geotechnical engineering recommendations relative to:

■ subsurface soil conditions ■ groundwater conditions at the time of the field exploration ■ earthwork

■ seismic considerations ■ foundation design and construction

■ pavement design and construction ■ floor slab design and construction

2.0 PROJECT INFORMATION

2.1 Project Description

Information regarding the proposed project is presented in the table below. These descriptions are based on information provided to us in the Scope of Work document included in the RFP and based on communications from J-U-B.

Item Description1

Site layout

The proposed improvements will include construction of an office building and storage building. The project will also include a storage yard and paved parking areas. Refer to the Boring Location Plan presented in Appendix A. The proposed construction will require the demolition of the existing on site structures.

Responsive ■ Resourceful ■ Reliable 2

Item Description1

Structures

Office Building: A proposed office building with a footprint measuring approximately 7,250 square feet will be constructed at the site. Project details are still being determined, but the proposed building may be one or two stories. It is anticipated the structure will be wood or steel frame, with a slab-on-grade floor.

Storage Building: An approximately 6,000 square foot storage building will be constructed south of the proposed office building.

We anticipate the storage building will be a single-story, wood- or steel-frame structure with a slab-on-grade floor system.

Assumed maximum building loads

Columns: 80 kips

Walls: 3 kips per linear foot

Grading Grading is anticipated to be relatively minor and generally limited to providing a level construction area. We have assumed maximum cuts and fills will be approximately 3 feet or less.

Retaining & basement walls We assume the proposed structures will not include basements or other below grade areas.

Pavement design criteria

Paved parking areas and a storage yard are planned for the project. We assume that asphalt pavement sections will be constructed in these areas.

Based on information provided by the BLM, we understand that total vehicle traffic on the project’s pavements will include approximately 175 vehicles per week. The majority of these vehicles will be cars and pickup trucks, but will also include recreational vehicles and a garbage truck once per week.

Storm water disposal Exploration for storm water disposal is not included in our scope of services.

1. In the event these details are inconsistent with final design criteria, we should be contacted so that we may update our recommendations as needed.

2.2 Site Location and Description

Item Description

Location The project site is located southwest of the intersection of Cottonwood Butte Road and East Street in Cottonwood, Idaho.

See the Vicinity Map and Boring Location Plan in Appendix A.

Existing site features

The site is developed with seven existing single-story BLM buildings, including two garage buildings that are not attached to the other structures. We understand these structures do not have basements. Concrete sidewalks are located near the perimeters of the structures.

A storage yard is located on the west side of the project area. An existing metal storage shed is located within the storage yard.

Parking areas are located near the existing buildings.

Responsive ■ Resourceful ■ Reliable 3

Item Description

Surrounding developments

North: Cottonwood Butte Road followed by Cottonwood Catholic Cemetery.

South: Single-story residences.

East: East Road followed by a Cottonwood City Cemetery.

West: Single-story residences.

Current ground cover

The storage yard and the eastern most parking areas are both covered with gravel. A parking/drive area that crosses through the project area is surfaced with asphalt pavement. Small lawn areas are located near the buildings and at the north and east perimeters of the site. Shrubs and several mature trees are growing within the project area.

Existing topography

The elevations at the boring locations ranged from about 3,607 feet at a boring in the southern portion of the property to 3,613 feet in the boring located in the northeastern portion of the project area.

3.0 SUBSURFACE CONDITIONS

A description of our field exploration is presented in Appendix A. Laboratory tests were conducted on selected soil samples obtained during our exploration. A description of the laboratory testing is presented in Appendix B.

3.1 Typical Subsurface Profile

Specific conditions encountered at each boring location are indicated on the individual boring logs, which are presented in Appendix A. Stratification boundaries on the logs represent the approximate locations of changes in soil types; in-situ, the transition between materials may be gradual. Based on our borings and laboratory testing, generalized soil conditions for the project site are presented in the following table.

Description Approximate Depth1 to

Bottom of Stratum Material Encountered Consistency/Density

Stratum 1 >½ to 2 feet

Fill: Within borings B-1 to B-3 the ground surface was covered with asphalt pavement over granular fill materials. Within borings B-4 to B- 8, the ground surface was covered with granular fill materials.

Responsive ■ Resourceful ■ Reliable 4

Description Approximate Depth1 to

Bottom of Stratum Material Encountered Consistency/Density

Stratum 2 1 to 7 feet

Lean to fat clay with varying amounts of sand and gravel.

Published geologic information of the project area and correlations to soil index properties indicate the clay soils have a potential to swell/shrink with changes in moisture content. A swell test was performed on a sample of the native clay soils. At the soil’s natural moisture content the soil sample did not exhibit swell potential. However, if the soil sample was allowed to dry prior to testing, it is possible that soil swelling would occur.

Medium stiff to stiff

Stratum 3 Extended to the maximum depth explored of 20½ feet

In seven of the eight borings drilled for this project, this stratum consisted of moderately to highly weathered basalt rock. Within the remaining boring (B-5), this stratum consisted of highly to completely weathered basalt tephra (welded combination of ash and rock materials ejected during volcanic eruption). Boring B-6 encountered auger refusal in basalt rock at a depth of about 12 feet.

1. Depth below existing ground surface, as encountered in our borings.

3.2 Groundwater

The borings were monitored during drilling for the presence and level of groundwater.

Groundwater was not encountered within the borings at the time of our exploration.

Fluctuations of the depth to groundwater may occur due to seasonal variations in the amount of irrigation, rainfall, runoff, and other factors not evident at the time the borings were performed.

Evaluation of these factors is beyond the scope of this exploration.

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

Based on the materials encountered in the borings drilled at this site, it is our opinion that the site is suitable for support for the proposed structures, provided the recommendations included

Responsive ■ Resourceful ■ Reliable 5 in this report are incorporated into project design and construction. Primary geotechnical considerations identified during the exploration are summarized below.

■ The site is currently occupied by existing buildings with associated parking and landscaped areas. We understand that prior to construction the existing improvements will be removed from the site. Removal should include the existing building, foundations, slabs, pavement section materials, utilities, and other man-made items. Native soils that are disturbed during removal of these items should also be removed. Vegetation and topsoil should be stripped from existing landscaped areas that are within the construction zone.

■ Fill soils were encountered in each of the borings drilled at the site to depths up to about 2 feet. In their current condition, these fill soils are not suitable for support of the proposed building or pavement and should be removed from proposed construction areas.

■ Highly plastic, fat clay soils are present on this site. Such soils are commonly referred to as “expansive” because they expand or swell with increases in their moisture content.

These soils also contract or shrink as their moisture content decreases. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion.

However, even if these procedures are followed, some movement and cracking in the structure should be anticipated. The severity of cracking and other cosmetic damage such as uneven floor slabs will probably increase if any modification of the site results in excessive wetting or drying of the expansive soils.

If the risk of potential expansion of the native clay soils and the resulting movement and cracking of the structures is not acceptable to the project owner, the on-site clay soils should be completely removed from beneath the proposed building areas. Based on our borings, the depth of overexcavation required to remove these soils would be approximately 2 to 3½ feet below the existing site ground surface in the proposed office building and about 5 to 7 feet in the proposed storage building area. If these soils are completely overexcavated, they should be replaced with Structural Fill meeting the requirements of Section 4.2.3 of this report.

■ Weathered basalt rock and basalt tephra were encountered in our borings at depths ranging from about 1 to 7 feet below the existing ground surface. Variation in the top elevation of basalt rock can occur abruptly in short horizontal distances. The basalt rock encountered in the borings was moderately to highly weathered and the basalt tephra was highly to completely weathered.

Specific conclusions and recommendations regarding these geotechnical considerations, as well as other geotechnical aspects of design and construction are presented in the following

Responsive ■ Resourceful ■ Reliable 6 sections. The recommendations contained in this report are based upon the results of field and laboratory testing, engineering analyses, and our current understanding of the proposed project.

4.2 Earthwork

The recommendations presented in this report for design and construction of foundations, slabs, and pavements are contingent upon the successful performance of the tasks related to the earthwork recommendations outlined in this section.

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

4.2.1 Rock Excavation

Weathered basalt rock and basalt tephra were encountered in our borings at depths ranging from about 1 to 7 feet below the existing ground surface. Variation in the top elevation of basalt rock can occur abruptly in short horizontal distances. Care should be taken when excavating foundations to avoid disturbing the supporting rock. Disturbed rock is not suitable for support of the proposed structure and should be removed from beneath the foundations.

The basalt rock encountered in the borings was moderately to highly weathered and the basalt tephra was highly to completely weathered. Some very broken or completely weathered portions of these materials may be rippable with heavy equipment with rippers. However, portions of the rock will likely not be rippable, and the Contractor should be prepared to utilize hydraulic or pneumatic hammers to assist in rock removal. Due to the anticipated relatively shallow rock thickness that may require excavation, blasting is not recommended.

4.2.2 Site Clearing and Subgrade Preparation

We understand that prior to construction, the existing improvements will be removed from the site. Removal should include the existing buildings, foundations, slabs, pavement section materials, debris, utilities, and other manmade items, including all subsurface features. Existing fill soils should be completely removed from proposed building and pavement areas, including from existing utility trenches. Vegetation, topsoil, and root systems should be stripped from areas that are within the construction zone. Stripped materials consisting of topsoil, vegetation, and organic materials should be wasted off site, or used in proposed landscaped areas after completion of grading operations. Special care should be taken to remove all soils disturbed during demolition and removal of the existing structures. Exposed surfaces should be free of mounds and depressions that could prevent uniform compaction.

After removal of the materials described above is complete, the top 8 inches of the subgrade soils in building and pavement areas should be scarified, moisture conditioned to within 0 percent to 3 percent above optimum moisture content, and compacted to 92 percent of the

Responsive ■ Resourceful ■ Reliable 7 maximum dry density, as determined by ASTM D1557. Scarification and recompaction should not be performed in areas where rock/tephra is exposed at the subgrade elevation. Special measures including thorough mixing and additional time may be needed when moisture conditioning the on-site clay soils to allow these soils to absorb water to achieve a uniform moisture condition.

Structural Fill, aggregates, floor slabs, and pavements should be placed over the exposed clay soils immediately following subgrade preparation to reduce the potential for the prepared clay subgrade to dry. If Structural Fill, floor slab support materials, or the pavement section aggregates are not immediately placed, and the subgrade soils are allowed to dry, subgrade soils should be reworked by scarifying, moisture conditioning, and compacting, as described above.

4.2.3 Fill Materials and Placement

Material requirements for soils used as Structural Fill beneath the proposed building areas are outlined in the table below.

Building Area

3-inch minus gravel and sand meeting the requirements of the Idaho Standards for Public Works Construction (ISPWC) Section 801, Uncrushed Aggregates.

Backfill placed outside the building footprint against exterior building footings should be composed of the native clay soils. Site fill used within proposed parking areas and other locations outside of the buildings, should meet the requirements presented below.

Import Soils for Use in Parking and Other Areas Outside the Building

Sieve Size Percent Passing

6-inch 100

No. 4 15 - 100

No. 200 Less than 25

Liquid limit should be less than 30 percent, the plasticity index should be less than 10 percent, and the organic content should be less than 3 percent.

Fill should be placed in maximum 8-inch-thick, loose lifts, adjusted to near optimum moisture content, and compacted to the minimum percentages of either maximum dry density or relative density shown in the following table, whichever is appropriate for the material being used. Each lift of fill should be tested at various locations within the structure’s footprint and parking/drive areas to verify it meets the density requirements presented in the following table.

Responsive ■ Resourceful ■ Reliable 8

Location Percent of Maximum Dry

Density, ASTM D1557 Percent Relative Density, ASTM D4253/D4254

Beneath building, slabs, and paved areas

95 80

Other areas of fill and backfill, including backfill against the outside of exterior foundation walls

90 75

4.2.4 Grading and Drainage

All grades must provide effective drainage away from the building during and after construction.

Water permitted to pond next to the building can result in larger settlement or expansion than anticipated. These greater movements can result in unacceptable differential floor slab movements, cracked slabs and walls, and roof leaks. Estimated movements described in this report are based on effective drainage for the life of the structure and cannot be relied upon if effective drainage is not maintained.

Exposed ground should be sloped at a minimum 5 percent away from the building for at least 10 feet beyond the perimeter of the building. After building construction and landscaping, we recommend verifying final grades to document that effective drainage has been achieved.

Grades around the structure should also be periodically inspected and adjusted as necessary, as part of the structure’s maintenance program.

4.2.5 Utility Excavations

Utility trenches are a common source of water infiltration and migration. All utility trenches that penetrate beneath the buildings should be effectively sealed to restrict water intrusion and flow through the trenches that could migrate below the building. We recommend constructing an effective clay “trench plug” that extends at least 5 feet out from the face of the building exterior.

The plug material should consist of clay compacted at a water content at or above the soils optimum water content. The clay fill should be placed to completely surround the utility line and be compacted in accordance with recommendations in this report

4.2.6 Earthwork Construction Considerations

Special attention should be given to removing and properly backfilling and compacting holes resulting from the removal of the existing site improvements. Failure to remove existing manmade features and tree root systems and to properly backfill and compact the resulting excavations may result in cracking of overlying floor slabs, foundations, and pavements.

Exposed soils will likely be susceptible to rutting or pumping under construction traffic when wet.

Soils that rut, pump, or are otherwise disturbed are not suitable for support of foundations, floor slabs, or pavements, and should be removed and replaced with Structural Fill. Measures that

Responsive ■ Resourceful ■ Reliable 9 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.

Grading operations should be controlled to prevent water from flowing into construction areas.

Excessive wetting or drying of the foundation excavation soils should be avoided during construction. Excess water should be promptly removed. If groundwater is encountered in utility trenches or other excavations, dewatering will be required.

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.

4.3 Foundations

The proposed structures can be founded on shallow spread footings. Due to different depths to rock encountered in the office building and storage building areas, we have provided different foundation recommendations for each of these structures. Design recommendations and construction considerations are presented in following subsections.

4.3.1 Spread Footing Recommendations – Office Building

Within the borings for the proposed office building, moderately to highly weathered basalt rock was encountered in three of the borings, and highly to completely weathered basalt tephra was encountered in the remaining boring. These materials were encountered at depths ranging from about 2 to 3½ feet below the existing site grade. Due to the variation in the elevation of basalt rock/tephra as encountered in the borings in the office building, and also due to the variation in the support characteristics of the basalt rock and the basalt tephra and the overlying soils, the proposed office building should be founded on shallow spread footings supported on structural fill extending to and placed directly on the undisturbed basalt/tephra. Footings should have a minimum of 12 inches of Structural Fill beneath them. The Structural Fill should be placed in accordance with Section 4.2.3 of this report. Design recommendations for the proposed office building’s foundations are presented in following subsections.

Description Criteria

Foundation type Conventional shallow spread footings.

Bearing material

Footings should be founded on structural fill extending to and placed directly on the undisturbed basalt/tephra. Footings should have a minimum of 12 inches of Structural Fill beneath them. The Structural Fill should be placed in accordance with Section 4.2.3 of this report.

Net allowable bearing pressure 3,000 psf1

Responsive ■ Resourceful ■ Reliable 10

Minimum footing width Columns: 36 inches

Walls: 24 inches

Minimum embedment depth below lowest adjacent permanent finished grade or floor slab

Exterior footings: 36 inches (for frost protection)

Interior footings not subject to frost: 18 inches

Estimated settlement Total: Less than 1 inch

Differential: Typically ½ to ¾ of the total settlement

Ultimate coefficient of friction to resist sliding

0.45 (An appropriate factor of safety should be applied to this value for use in design).

1. The allowable bearing capacity may be increased by 1/3 for support of temporary loads such as those generated by wind and seismic events.

Footings should be supported on a uniform layer of at least 12 inches of Structural Fill placed and compacted in accordance with Section 4.2.3 of this report. This fill layer should extend laterally from the foundation edges a distance equal to 2/3 of the depth of the compacted fill below the footing base elevation, as shown in the adjacent figure.

It may be necessary to make foundation excavations wide enough to allow access for large compaction equipment or use thinner lifts to facilitate compaction to the specified density.

4.3.2 Spread Footing Recommendations – Storage Building

Within the borings drilled at the location of the proposed storage building, weathered rock was encountered at depths ranging from about 5 to 7 feet below the existing site grade. Due to this depth to rock, the proposed foundations may be founded on shallow spread footings supported on the undisturbed native soils. Design recommendations for the storage building’s foundations are presented below.

Foundation type Conventional shallow spread footings.

Bearing material Existing native soils or Structural Fill supported directly on undisturbed native soils.

Net allowable bearing pressure 2,000 psf1

Responsive ■ Resourceful ■ Reliable 11

Minimum footing width Columns: 36 inches

Walls: 24 inches

Minimum embedment depth below lowest adjacent permanent finished grade or floor slab

Exterior footing: 36 inches (for frost protection)

Interior footings not subject to frost: 18 inches

Estimated settlement Total: 1 inch or less

Differential: Typically ½ to ¾ of the total settlement

Ultimate coefficient of friction to resist sliding

0.30 (An appropriate factor of safety should be applied to this value for use in design.)

1. The allowable bearing capacity may be increased by 1/3 for support of temporary loads such as those generated by wind and seismic events.

4.3.3 Foundation Construction Considerations

Care should be taken when excavating the foundations to avoid disturbing the supporting soils.

Soils that rut, pump, or are otherwise disturbed are not suitable for support of foundations and should be removed and replaced with compacted Structural Fill.

4.4 Seismic Considerations

IBC1 Seismic Design Parameters

Description Value

Site classification2 C

Ss, Short period spectral response acceleration (Site Class B)3 0.30g (for Site Class B)

S1, 1-second period spectral response acceleration (Site Class B)3 0.09g (for Site Class B)

1. Based on Section 1613 of the 2009 International Building Code (IBC).

2. Based on the 2009 IBC, the seismic site class is determined from a soil profile extending to a depth of 100 feet. The current scope does not include a boring to a depth of 100 feet. The borings for this project extended to a maximum depth of approximately 20½ feet, and the seismic site classification assumes that rock conditions similar to those encountered in the lower portions of the borings continue below the maximum depth of the subsurface exploration. If desired, a geophysical exploration could be performed to confirm the site classification, or possibly justify a more favorable site classification.

3. Accelerations shown above should be adjusted as required by the IBC to account for the Site Classification.

4.5 Floor Slabs

Interior floor system Slab-on-grade concrete

Floor slab support

Minimum 6 inches of ¾-inch-minus crushed aggregate base1 compacted in accordance with Section 4.2.2 of this report.

Aggregate base should be supported on soils prepared in accordance with Section 4.2 of this report.

1. Aggregate base should meet the requirements of ¾-Inch (Type 1) crushed aggregate in the ISPWC, Section 802.

Responsive ■ Resourceful ■ Reliable 12

Structural Fill, aggregates, and floor slabs should be placed over the exposed clay soils immediately following subgrade preparation to reduce the potential for the prepared clay subgrade to dry. If Structural Fill or floor slab support materials are not immediately placed and the subgrade soils are allowed to dry, subgrade soils should be reworked by scarifying, moisture conditioning, and compacting, as described in Section 4.2 of this report.

Floor slabs should be structurally independent of building footings and walls to reduce the potential of floor slab cracking caused by differential movements between the slab and foundation.

The use of a vapor retarder should be considered beneath concrete slabs on grade that will be covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer and slab contractor should refer to ACI 302 and ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

4.6 Pavements

Based on the traffic distribution discussed in Section 2.1, pavement sections were design based on an estimated 14,000 equivalent single-axle loads. If traffic volumes will exceed this value, Terracon should be notified in order to provide pavement sections designed for higher levels of traffic. Design and construction considerations are also presented below.

4.6.1 Asphalt Pavement Sections

An asphalt pavement section for this project was designed in general accordance with the National Asphalt Pavement Association (NAPA) publication “Design of Hot Mix Asphalt Pavements for Commercial, Industrial, and Residential Areas.” The following flexible pavement section should be placed on subgrade soils prepared in accordance with Section 4.2 of this report.

Material Thickness

Asphalt concrete1 3 inches

Crushed aggregate base course (3/4 Inch – Type 1)1 9 inches

Total thickness 12 inches

1. Asphalt concrete and aggregate base should conform to the applicable sections of the ISPWC.

Following subgrade preparation, the base aggregates should be moisture conditioned to near optimum moisture content, placed in uniform lifts, and compacted to at least 95 percent of the maximum dry density as determined by ASTM D1557.

The asphalt concrete should be compacted to a minimum of 92.0 percent of the maximum theoretical density, as determined by AASHTO T 209. The asphalt concrete should meet

Responsive ■ Resourceful ■ Reliable 13

ISPWC requirements for a ½-inch maximum size Class III mix. Asphalt cement should be PG 58-28.

4.6.2 Portland Cement Concrete Pavement Section

For areas subject to concentrated and repetitive loading conditions such as dumpster pads, truck delivery docks and ingress/egress aprons, we recommend using the Portland cement concrete pavement section presented in the following table. For dumpster pads, the concrete pavement area should be large enough to support the container and tipping axle of the refuse truck. The following rigid pavement section should be placed on subgrade soils prepared in accordance with Section 4.2.

Material Thickness

Portland Cement Concrete1 7 inches

Crushed aggregate base course (3/4 Inch – Type 1)1

4 inches

Total thickness 11 inches

1. Portland cement concrete and aggregate base should conform to the applicable sections of the ISPWC.

As a minimum, the concrete pavements should be reinforced with 6-inch by 6-inch, W2.0xW2.0 welded wire mesh. Reinforcement of concrete with wire mesh does not prevent cracking of the concrete. However, the wire mesh aids in reducing the potential for opening of shrinkage cracks in the concrete. Wire mesh should be located approximately 2 inches below the top of the slab.

An adequate number of longitudinal and transverse control joints should be placed in the rigid pavement in accordance with ACI and/or AASHTO requirements. Control joints should be saw cut ¼ of the depth of the concrete. Sawing should be performed as soon as the slab can be cut without inducing significant spalling (usually within 4 to 8 hours of concrete placement).

Expansion (isolation) joints must be full depth and should only be used to isolate fixed objects abutting or within paved areas.

Sealing of construction joints is essential to protect the subgrade and promote long-term performance of concrete pavement. Sealing should occur as soon as possible (in accordance with sealant manufacturer’s instructions) to reduce infiltration of water into the base course and subgrade.

4.6.3 Pavement Design Considerations

Long-term pavement performance will be dependent on several factors, including reducing or preventing increases in subgrade moisture content and providing preventive maintenance. In general, increases in the moisture content of subsurface soils can result in adverse effects to

Responsive ■ Resourceful ■ Reliable 14 the pavement section. These adverse effects typically result from frost susceptibility or loss of subgrade strength with increases in moisture content.

Openings in the pavement surface, such as landscape islands, are sources for water infiltration into the surrounding pavement section and subgrade. Water can collect in the islands and migrate into the underlying subgrade soils, thereby degrading support of the pavement. This is especially applicable for islands with raised concrete curbs, irrigated vegetation, and near-surface soils with low permeability. The civil design for pavements with these conditions should include features to restrict or collect and discharge excess water from the islands. Examples of these features are edge drains connected to the storm-water collection system or other suitable outlet and impermeable barriers that reduce lateral migration of water such as a cutoff wall installed to a depth below the pavement section. The following should be considered as minimum recommendations in the design and construction of pavements:

■ Provide a minimum 2% grade in the ground surface away from the edge of pavements.

■ Provide a minimum 2% cross slope for the subgrade and pavement surface to promote proper surface drainage.

■ Install pavement drainage at the perimeter of areas where frequent wetting, such as from irrigation or other sources of water, is anticipated.

■ Install joint sealant and seal cracks promptly.

■ Seal all landscaped areas adjacent to pavements to reduce moisture migration to subgrade soils.

■ Place compacted low-permeability backfill against the exterior side of curb and gutter.

Preventive maintenance should be planned and provided as a part of an asphalt pavement management program. These maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment. Preventative maintenance consists of both localized maintenance (e.g. crack and joint sealing and patching) and global maintenance (e.g. surface sealing for asphalt pavements). This type of maintenance is usually the first priority when implementing a planned pavement maintenance program and generally provides a relatively high return on investments for pavements. Even with periodic maintenance, some movements and related cracking may still occur and require repair.

4.6.4 Pavement Construction Considerations

Structural Fill and pavement aggregates should be placed over the exposed clay soils immediately following subgrade preparation to reduce the potential for the prepared clay subgrade to dry. If Structural Fill or the pavement section aggregates are not immediately placed and the subgrade soils are allowed to dry, subgrade soils should be reworked by scarifying, moisture conditioning, and compacting, as described in Section 4.2 of this report.

Responsive ■ Resourceful ■ Reliable 15

Pavement sections should be placed on properly prepared subgrade, as described in Section

4.2 of this report. As construction proceeds, the subgrade may be disturbed or altered due to utility excavations, construction traffic, desiccation, or rainfall. As a result, the subgrade may become unsuitable for pavement support. The long-term effects of localized areas of inadequately prepared subgrade may result in cracks or potholes in the pavement. Therefore, the subgrade should be carefully evaluated at the time of paving for signs of disturbance or excessive rutting. If disturbance or rutting has occurred, subgrade areas should be reworked, moisture conditioned, and properly compacted to the recommendations in this report immediately prior to constructing the pavement section asphalt or Portland cement concrete.

In areas of prepared subgrade or partial thickness pavement, the Contractor should limit traffic to equipment necessary to construct the pavement section. Heavily loaded vehicles operating on these surfaces may cause significant damage, resulting in deterioration and reduction in pavement life.

5.0 GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, foundation construction, and other earth-related construction phases of the project.

The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between borings, across the site, 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. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided.

The scope of services for this project does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, and 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.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either expressed or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the

Responsive ■ Resourceful ■ Reliable 16 event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing.

APPENDIX A

FIELD EXPLORATION

11849 West Executive Drive, Suite G Boise, Idaho 83713

PH. (208) 323-9520 FAX. (208) 323-9592

A-1

ExhibitVICINITY MAPProject Manager:

Drawn by:

Checked by:

Approved by:

RJO

JB

RJO

RJO

Project No.

Scale:

File Name:

Date:

62095020F

Vicinity Map

8/27/2013

U.S.G.S. 7.5 MINUTE SERIES TOPOGRAPHIC MAP

COTTONWOOD, IDAHO QUADRANGLE

DATED 1967, PHOTOREVISED 1981

PROPOSED BLM FIELD OFFICE – DO #45

COTTONWOOD, IDAHO

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND

IS NOT INTENDED FOR CONSTRUCTION PURPOSES

As Shown

PROJECT SITE

Responsive ■ Resourceful ■ Reliable Exhibit A-2

Field Exploration Description The subsurface exploration consisted of drilling eight borings in the proposed project area. The approximate locations of the explorations are shown on the Boring Location Plan included in this appendix.

The boring locations were selected by Terracon based on the locations of the proposed building and pavement areas, and also considering access constraints caused by the existing site improvements. After completion of the borings, the boring locations, with the exception of boring B-7, were recorded by J-U-B surveyors. The surveyed boring locations and elevations are presented on the boring logs, which are presented in this appendix.

The borings were drilled to depths ranging from about 5 to 20½ feet below the existing ground surface with a truck-mounted drill rig equipped with continuous-flight hollow-stem augers.

Boring B-6 was terminated at a depth of about 12 feet due to auger refusal in basalt rock. A Terracon field engineer recorded logs of the borings during the drilling operations.

Relatively undisturbed samples were obtained using a thin-walled Shelby tube sampler.

Disturbed soil samples were obtained at various depths in the borings using a 2-inch-outside-diameter split-spoon sampler driven in general accordance with the Standard Penetration Test (SPT). The result of the SPT is an N-value. The N-value is the number of blows from a 140-pound hammer falling from a height of 30 inches that are required to drive the split-spoon sampler the last 12 inches of an 18-inch interval (or the distance indicated).

N-values are shown on the boring logs. Descriptions of the materials encountered are presented on the boring logs in this appendix.

The N-value provides a reasonable estimate of the relative in-place density of non-cemented sandy type materials. However, the N-value only provides an indication of the relative stiffness of cohesive materials, since the penetration resistance of these soils may be affected by the moisture content. Considerable care must be exercised in interpreting the N-value in gravelly soils, particularly where the size of the gravel particles exceeds the inside diameter of the sampling spoon.

An automatic SPT hammer was used to advance the split-spoon sampler in the borings performed on this site. A greater efficiency is typically achieved with the automatic hammer compared to the conventional safety hammer operated with a cathead and rope. Published correlations between the SPT values and soil properties are based on the cathead and rope method. The higher efficiency of the automatic hammer affects the standard penetration resistance blow count (N-value) by increasing the penetration per hammer blow over what would be obtained using the cathead and rope method. The effect of the automatic hammer's efficiency has been considered in the interpretation and analysis of the subsurface information for this report.

LEGEND

A-2

FIG No.BORING LOCATION DIAGRAM

PROPOSED BLM FIELD OFFICE – DO #45

COTTONWOOD, IDAHO

Project Manager:

Drawn by:

Checked by:

Approved by:

RJO

JWB

RJO

RJO

Project No.

Scale:

File Name:

Date:

62095020F

N.T.S boringlocationdiagram

9/10/2013 11849 W. Executive Drive, Suite G Boise, ID 83713

PH. (208) 323-9520 FAX (208) 323-9592

NOTES:

1. Locations are approximate.

2. Based on image provided by the BLM.

3. For general location use only, not intended for construction purposes.

APPROXIMATE

BORING LOCATION

B-1

B-2

B-3

B-4

B-5

B-6

B-7

B-8

0.2 0.7

2.0

20.3

FILL - ASPHALT CONCRETE

FILL - SILTY GRAVEL WITH SAND , brown, crushed gravel LEAN CLAY (CL), trace sand, brown, stiff

BASALT, gray, moderately to highly weathered

Boring Terminated at 20.3 Feet

1.5

1.2

0.2

0.2

0.3

0.2

3610.5

3609.5

127-7-8 N=15

40-50/4" N=50/4"

50/2" N=50/2"

50/4" N=50/4"

50/4" N=50/4"

50/5" N=50/5"

50/4" N=50/4"

G R

A P

H

IC

L O

G See Exhibit A-2

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

LOCATION

DEPTH

Latitude: 46.0632411° Longitude: -116.3486658°

T H

IS

B

O R

IN

G

L O

G I

S N

O T

V A

L

ID

IF

S

E P

A R

A T

E D

F R

O M

O R

IG

IN

A L

R E

P O

R T

G E

O S

M A

R T

L O

G -N

O W

E L

F .G

P J

T E

R R

A C

O N

.G D

/1

/1

SITE:

Groundwater not encountered

WATER LEVEL OBSERVATIONS

Advancement Method:

Hollow Stem Auger

Abandonment Method:

Backfilled with soil cuttings upon completion.

11849 W. Executive Dr., Suite G Boise, Idaho

Notes:

Project No.: 62095020F

Drill Rig: CME-75

Boring Started: 8/26/2013

BORING LOG NO. B-1

J-U-B EngineersCLIENT:

Driller: Haz-Tech Drilling, Inc.

Boring Completed: 8/26/2013

PROJECT: Proposed Field Office - DO #45

1 Butte Drive Cottonwood, Idaho

Exhibit:

See Exhibit A-3 for description of field procedures.

See Appendix B for description of laboratory procedures and additional data (if any).

See Appendix C for explanation of symbols and abbreviations.

A-1

R E

C O

V E

R Y

F t.)

ELEVATION (ft)

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

F

IE

L D

T E

S T

R E

S U

L T

S

D E

P T

H

F t.)

S A

M P

LE

T

Y P

E

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

Surface Elev.: 3611.4 (Ft.)

LL-PL-PI

ATTERBERG

LIMITS

0.3 0.7

3.5

20.7

FILL - ASPHALT CONCRETE

FILL - SILTY GRAVEL WITH SAND , brown, crushed GRAVELLY FAT CLAY WITH SAND (CH), brown, stiff, (decomposed basalt rock)

BASALT, gray, moderately to highly weathered

Boring Terminated at 20.7 Feet

1.4

0.3

0.2

0.2

0.2

0.6

3609.5

3589.5

223-4-9 N=13

50/5" N=50/5"

50/4" N=50/4"

50/4" N=50/4"

50/4" N=50/4"

43-50/2" N=50/2"

50-21-29

G R

A P

H

IC

L O

G See Exhibit A-2

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

LOCATION

DEPTH

Latitude: 46.0629942° Longitude: -116.3486838°

T H

IS

B

O R

IN

G

L O

G I

S N

O T

V A

L

ID

IF

S

E P

A R

A T

E D

F R

O M

O R

IG

IN

A L

R E

P O

R

O S

M A

R T

L O

G -N

O W

E

F .G

P J

T E

R R

A C

O N

.G

/1

SITE:

Groundwater not encountered

WATER LEVEL OBSERVATIONS

Advancement Method:

Hollow Stem Auger

Abandonment Method:

Backfilled with soil cuttings upon completion.

11849 W. Executive Dr., Suite G Boise, Idaho

Notes:

Project No.: 62095020F

Drill Rig: CME-75

Boring Started: 8/26/2013

BORING LOG NO. B-2

J-U-B EngineersCLIENT:

Driller: Haz-Tech Drilling, Inc.

Boring Completed: 8/26/2013

PROJECT: Proposed Field Office - DO #45

1 Butte Drive Cottonwood, Idaho

Exhibit:

See Exhibit A-3 for description of field procedures.

See Appendix B for description of laboratory procedures and additional data (if any).

See Appendix C for explanation of symbols and abbreviations.

A-2

R E

C O

V E

R Y

F t.)

ELEVATION (ft)

P E

R C

E N

T F

IN

E

S

W A

T E

R C

O N

T E

N T

F

IE

L D

T E

S T

R E

S U

L T

S

D E

P T

H

F t.)

S A

M P

LE

T

Y P

E

W A

T E

R L

E V

E L

O B

S E

R V

A T

IO

N

S

Surface Elev.: 3610.3 (Ft.)

LL-PL-PI

2.0

4.5 5.0

15.2

FILL - ASPHALT CONCRETE

FILL - SILTY GRAVEL WITH SAND , brown, crushed

SANDY FAT CLAY (CH), brown, stiff

SANDY LEAN CLAY WITH GRAVEL (CL), brown BASALT, very dense, gray, moderately to highly weathered

Boring Terminated at 15.2 Feet

0.7

0.8

0.2

0.2

0.2

3606.5

3602.5

4-8-10 N=18

4-7-6 N=13

35-50/4" N=50/4"

50/4" N=50/4"

50/2" N=50/2"

50/2" N=50/2"

53-18-35

G R

A P

H

IC

L O

G See Exhibit A-2

Hamme…