S-28-25_Geotechnical_Engineering_Report.pdf

Report Cover Page

Ice Slicer Building Geotechnical Engineering Report

Cheyenne, Wyoming

February 26, 2025 | Terracon Project No. 24255003

Prepared for:

City of Cheyenne

2101 O’Neil Avenue, Room 207

Cheyenne, Wyoming 82001

1505 Old Happy Jack Road

Cheyenne, WY 82001

P (307) 632-9224

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

February 26, 2025

City of Cheyenne

2101 O’Neil Avenue, Room 207

Cheyenne, Wyoming 82001

Attn: Adele Bartel, P.E.

P: (307) 637-6263

E: abartel@cheyennecity.org

Re: Geotechnical Engineering Report

Ice Slicer Building

110 Cleveland Place

Cheyenne, Wyoming

Terracon Project No. 24255003

Dear Ms. Bartel:

We have completed the scope of Geotechnical Engineering services for the project referenced above in general accordance with Terracon Proposal No. P24255003 dated

January 14, 2025. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon

Crystal M. Romo Eric D. Bernhardt, P.E.

Assistant Project Manager Regional Geotechnical Manager

Geotechnical Engineering Report

Ice Slicer Building | Cheyenne, Wyoming

Facilities | Environmental | Geotechnical | Materials i

Table of Contents Report Summary .............................................................................................. i Introduction Project Description Site Conditions Geotechnical Characterization

Groundwater Conditions Seismic Site Class Corrosivity Water Soluble Sulfate

Geotechnical Overview Undocumented Fill Low Strength Soils

Earthwork Demolition Excavation General Site Preparation Foundation Subgrade Preparation Soil Stabilization Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Shallow Foundations Design Parameters – Compressive Loads Foundation Construction Considerations

Floor Slabs Floor Slab Design Parameters Floor Slab Construction Considerations

General Comments

Figures

GeoModel

Attachments file://///Plnxwofds01/0024/Data/Geotech%20Cheyenne/Geotech.%20Report%20and%20Proposal%20Templates/GeoReport%20Template/COPY%20PASTE%20GeoReport%20Template%202023.12.13.docx file://///Plnxwofds01/0024/Data/Geotech%20Cheyenne/Geotech.%20Report%20and%20Proposal%20Templates/GeoReport%20Template/COPY%20PASTE%20GeoReport%20Template%202023.12.13.docx

Facilities | Environmental | Geotechnical | Materials ii

Exploration and Testing Procedures Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

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

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/ http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials i

Report Summary

Topic Overview Statement

Project

Description

The project includes the demolition of the existing tent building and construction of a new single-story steel building in its place.

Geotechnical

Characterization

Subsurface soil conditions encountered in the borings consisted of the following:

■ Surficial material consists of about 2 to 3 inches of asphalt on top of native soils consisting of very loose to medium dense poorly graded sand, silty sand, and clayey sand

■ Groundwater was encountered in all borings at depths ranging from about 7 to 17 feet below ground surface.

Earthwork

Based on the subsurface conditions encountered and proposed building construction, our earthwork recommendations consist of the following:

■ Remove existing fill below the proposed foundations and floor slabs and backfill with properly compacted structural fill. Excavate a minimum of 2 feet below all foundations and floor slabs and replace with properly compacted, new engineered fill. The exposed native subgrade should be scarified, moisture conditioned as needed and compacted to at least 95% of the standard Proctor maximum dry density (ASTM D698).

■ Loose native soils are anticipated to be encountered during excavations activities; therefore, soil stabilization techniques may be required prior to new engineered fill placement.

Shallow

Foundations

Shallow spread footings can be utilized for the proposed project provided the existing fill soils below the foundation are removed and reworked with proper moisture condition and compaction, prepared in accordance with the Earthwork section.

■ Maximum net allowable bearing pressure of 2,000 psf

■ Minimum embedment depth of 36 inches

■ Total settlement of less than about 1 inch

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.

Facilities | Environmental | Geotechnical | Materials ii

Topic Overview Statement

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

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical

Engineering services performed for the proposed Ice Slicer Building to be located at 110

Cleveland Place in Cheyenne, Wyoming. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Seismic site classification per IBC

■ Site preparation and earthwork

■ Demolition considerations

■ Foundation design and construction

■ Floor slab design and construction

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 understanding of the project conditions are as follows:

Item Description

Project

Description

We understand the project includes the demolition of the existing tent building and construction of a new steel building in its place.

Proposed

Structure

We anticipate the proposed building is planned as a wood frame and/or masonry superstructure supported by a reinforced concrete foundation system and shallow spread footings.

Finished Floor

Elevation

We understand the finished floor elevation will be within 1 to 2 feet of the existing ground surface.

Maximum Loads

(assumed)

■ Columns: 50 kips

■ Walls: 2 to 4 kips per linear foot (klf)

■ Slabs: 200 pounds per square foot (psf)

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Grading/Slopes

The site is relatively flat and grading operations across the site are anticipated to generally include relatively minor amounts of cuts and fills, less than 3 feet.

Below-Grade

Structures None are planned.

Free-Standing

Retaining Walls None are planned.

Pavements None are planned.

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 and our review of publicly available topographic maps.

Item Description

Location

The project is located at 110 Cleveland Place in Cheyenne, Wyoming. The approximate coordinates for the site are

41.1272° N 104.7566° W

See Site Location

Existing

Improvements

At the time of our geotechnical field exploration, the site was a tent building on a concrete pad surrounded by paved parking areas. The building is located in the Cheyenne Street and Alley facility and is located south of Campstool Road and west of

Cleveland Place.

Current Ground

Cover

The ground cover at the site generally consists of asphalt and concrete pavements.

Existing

Topography

The site is relatively flat with an elevation change of less than about 5 feet across the site.

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

Facilities | Environmental | Geotechnical | Materials 3 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 Asphalt About 2 to 3 inches of asphalt was encountered.

2 Non-Plastic Sands

Very loose to medium dense silty sand and poorly graded sand with varying amounts of silt, clay, and gravel. Fine to coarse grained, predominantly tan and browns.

Low to Medium

Plasticity Sands

Very loose to medium dense sand with varying amounts of clay and silt. Fine to coarse grained, predominantly browns and light browns.

Groundwater Conditions

The boreholes were observed for the presence and level of groundwater while drilling and shortly after the completion of drilling. The approximate water levels observed in the boreholes can be found on the boring logs in the Exploration Results and are summarized below.

Boring

Number

Approximate Depth to

Groundwater While

Drilling (feet)

Approximate Depth to

Groundwater After Drilling

(feet)

B-1 13 15

B-2 17 14

B-3 8 7

1. Below ground surface.

It should be recognized that these observations and interpretations represent the groundwater conditions at the time of the field exploration and may not be indicative of other times or other locations. Fluctuations of the groundwater table can occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time field exploration was performed.

Facilities | Environmental | Geotechnical | Materials 4

Seismic Site Class

Seismic design requirements for buildings and other structures are based on Seismic

Design Category. Site Classification is required to determine the Seismic Design

Category for a structure. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of

ASCE 7 and the International Building Code (IBC). Based on the soil properties observed at the site and as described on the exploration logs and results, we recommend a

Seismic Site Classification of D be considered for the project. Subsurface explorations at this site were extended to a maximum depth of about 25.5 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

Corrosivity

The table below lists the results of laboratory pH, soluble sulfate, sulfides, soluble chloride, RedOx, total salts, and electrical resistivity 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.

Corrosivity Test Results Summary

Boring

No.

Sample

Depth

(feet)

Soil

Description pH

Soluble

Sulfate

(mg/kg)

Sulfides

(mg/kg)

Soluble

Chloride

(mg/kg)

RedOx

(mV)

Total

Salts

(mg/kg)

Electrical

Resistivity

(Ω-cm)

B-1 1 to 5 Silty Sand 6.4 2100 Nil 78 +132 400 580

1. Test performed on a saturated soil sample.

These values serve as crucial indicators for assessing the potential corrosive characteristics of on-site soils concerning their interaction with various underground materials slated for project construction. For detailed results of corrosivity testing conducted on soil samples during exploration, please refer to the Chemical Laboratory

Test Results section within the Exploration and Laboratory Results.

It is imperative to note that the corrosion information provided is specific to the samples tested. If the actual soil composition in contact with the structure at the site differs from those tested, additional corrosion testing should be considered. It is important to emphasize that Terracon's expertise does not extend to corrosion engineering. Our scope of work was limited to conducting corrosion laboratory tests on selected samples and presenting the results alongside a brief comparison to selected criteria. Should

Facilities | Environmental | Geotechnical | Materials 5 concerns regarding the corrosion of underground utilities and structures persist, it is strongly recommended to engage the services of a qualified corrosion engineer for further evaluation and guidance tailored to the specific needs of this project.

Water Soluble Sulfate

The sulfate concentration measured in the sample is 2,100 mg/kg which equates to approximately 0.21 percent. Sulfate concentrations in the range of 0.1 to less than 0.2 percent indicate Class 1 exposure to sulfate attack for concrete in contact with the subsoils, according to the American Concrete Institute (ACI) Guide to Durable Concrete.

For Class 1 sulfate exposure, ACI recommends the use of Type II cement (or equivalent) and a maximum water-cement ratio of 0.50. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318.

Geotechnical Overview

Based on geotechnical conditions encountered in our test borings, the site appears suitable for the proposed construction from a geotechnical point of view provided certain precautions and design and construction recommendations presented in this report are followed. We have identified geotechnical conditions that could impact design, construction and performance of the building and other site improvements. This includes the presence of existing fill and unstable subgrade soils. These conditions will require particular attention in project planning, design and during construction and are discussed in greater detail in the following sections.

Undocumented Fill

Fill may be present on-site and may be encountered during demolition on existing structure. We are not aware of documentation of the placement of the existing fill under the testing and observation of a geotechnical engineer. Therefore, for the purpose of this report, the existing fill soils are considered undocumented and should be considered uncontrolled. Uncontrolled fills can present a risk of post-construction movement to foundations, floor slabs, and other site improvements supported on or above these materials. Consequently, we recommend existing fills be removed and replaced with engineered fill within the area of the planned improvements prior to placing any new fill or construction. The existing fill soils should be suitable for reuse in new fills and backfill, provided debris, organics and other unsuitable materials are removed.

Support of floor slabs on or above existing fill materials is discussed in this report.

However, even with the recommended construction procedures, an inherent risk remains for the owner that compressible fill or unsuitable material, within or buried by the fill, will not be discovered. This risk of unforeseen conditions cannot be eliminated without

Facilities | Environmental | Geotechnical | Materials 6 completely removing the existing fill but can be reduced by following the recommendations contained in this report.

Low Strength Soils

Comparatively very loose, low relative density sand soils were encountered below a depth of about 6 feet and extending to a depth of about 10 feet. These materials present a significant risk for potential settlement of foundations and other surficial improvements. These materials can also be susceptible to disturbance and loss of strength under repeated construction traffic loads and unstable conditions could develop.

Stabilization of loose soils will be required at some locations to provide adequate support for construction equipment and proposed improvements. Terracon should be contacted if these conditions are encountered to observe the conditions exposed and to provide guidance regarding stabilization (if needed).

Earthwork

Earthwork is anticipated to include demolition, clearing and grubbing, excavations, subgrade preparation and/or stabilization 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 and floor slabs.

Demolition

Demolition of the existing building and site development should include complete removal of all foundation systems, below-grade structural elements, pavements, and exterior flatwork within the proposed construction area. This should include removal of any utilities to be abandoned along with and loose utility trench backfill or loose backfill found adjacent to existing foundations. All materials derived from the demolition of existing structures and pavement should be removed from the site. The types of foundation systems supporting the existing building are not known.

Our experience suggests a portion of the demolition site features sometimes happens weeks to several months prior to site grading and new construction. Our recommendations for subgrade preparation, fill placement, and other activities associated with earthwork on the project site should be performed during these initial demolition activities. We recommend fill be placed and tested for moisture content and percent compaction during backfill of the excavations made during initial demolition activities. If the fill materials are not properly placed and confirmed with compaction testing, there is an increased risk of movement and poor performance for foundations, Facilities | Environmental | Geotechnical | Materials 7 floor slabs, or other site features constructed on the fill placed as part of restoring the site after initial demolition.

Excavation

We anticipate 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. Based upon the subsurface conditions encountered in the geotechnical exploration, the subgrade soils exposed during constructions are expected to be relatively unstable. In addition, the stability of the subgrade may be affected by precipitation, repetitive construction traffic, or other factors.

The individual contractor(s) is responsive for designing and constructing stable, temporary excavations as required to maintain stability for both the excavation sides and bottoms. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current OSHA excavation and trench safety standards.

General Site Preparation

Site preparation should commence with removal of vegetation, and any loose, soft, or otherwise unsuitable material from the proposed construction areas. Asphalt and concrete pavements or flatwork should be removed at this time as well. Stripped materials consisting of vegetation and organic materials should be wasted from the site or used to re-vegetate landscaped areas or exposed slopes after completion of grading operations.

If unexpected fills or underground facilities are encountered, such features should be completely removed and the excavation thoroughly cleaned prior to backfill placement and/or construction. We understand existing underground utilities may be present in the area of the proposed construction. To provide predictable support and to reduce water migration, we recommend existing utility pipes, associated backfills and any granular bedding materials within the construction area be removed as part of site preparation.

The resulting trenches should be backfilled with engineered fill.

Exposed surfaces should be free of mounds and depressions that could prevent uniform compaction. Following completion of demolition of existing structures, stripping, existing fill removal, and rough grading but prior to placement of new fill, the exposed ground should be scarified, moisture conditioned as needed and re-compacted to specification as described in the Compaction Requirements in this report. The subgrade (outside of the foundation elements) should then be proofrolled with an adequately loaded vehicle such as a fully loaded tandem-axle dump truck. The proofrolling should be performed

Facilities | Environmental | Geotechnical | Materials 8 under the observation of the Geotechnical Engineer or representative. Unsuitable areas

(greater than 1 inch of deflection) should be improved by moisture adjustment and compaction or by undercutting and placement of suitable compacted fill.

Where fill is placed on existing slopes steeper than 5H:1V, benches should be cut into the existing slopes prior to fill placement. The benches should have a minimum vertical face height of 1 foot and a maximum vertical face height of 3 feet and should be cut wide enough to accommodate the compaction equipment. This benching will help provide a positive bond between the fill and natural soils and reduce the possibility of failure along the fill/natural soil interface.

Subgrade Preparation

Subgrade preparation efforts are required in order to render the site suitable for support of a shallow foundation system and help reduce estimated foundation settlement to within tolerable limits. After the project site has been stripped of existing improvements, we recommend over-excavating soil to a depth of at least 2 feet below all foundations and floor slabs and replacing with properly compacted, new engineered fill. We recommend new engineered fill be moisture conditioned and compacted at least 95% of the standard Proctor maximum dry density (ASTM D698) prior to foundation construction. On-site soils are suitable for reuse as fill below foundations and floor slabs.

Care should be used while excavating adjacent to foundations of the existing building to avoid undermining or otherwise disturbing the existing foundation bearing soils.

Excavations should not extend into the stress influence zone of existing foundations unless they are shored, underpinned and/or braced. The stress influence zone is defined as the area below a line projected down at a 1H:1V slope from the bottom edge of the existing foundation.

Over-excavation for structural fill placement below footings and floor slabs should be conducted as shown below. The over-excavation should be backfilled up to the footing base elevation, with onsite soils or import fill material. Over-excavation activities should be performed under the observation of the Geotechnical Engineer or representative.

Facilities | Environmental | Geotechnical | Materials 9

Unsuitable areas of soft/loose subgrade should be delineated and stabilized using one of the methods described in Soil Stabilization section of this report. After subsequent correction of unsuitable areas, the over-excavated area can then be backfilled up to foundation and floor slabs bearing elevations with properly compacted structural fill.

Soil Stabilization

Methods of subgrade improvement, as described below, could include scarification, moisture conditioning and recompaction, removal of unstable materials and replacement with granular fill (with or without geosynthetics), and chemical stabilization. The appropriate method of improvement, if required, would be dependent on factors such as schedule, weather, the size of area to be stabilized, and the nature of the instability.

More detailed recommendations can be provided during construction as the need for subgrade soil stabilization occurs. Performing site grading operations during warm seasons and dry periods would help reduce the amount of subgrade stabilization required.

If exposed subgrade soils are unstable, these soils may be stabilized using one of the methods described below.

■ Scarification and Recompaction — It may be feasible to scarify, dry, and recompact the exposed soils. The success of this procedure would depend primarily upon favorable weather and sufficient time to dry the soils. Stable subgrades likely would not be achievable if the thickness of the unstable soil is greater than 12 inches, if the unstable soil is at or near groundwater levels, or if construction is performed during a period of wet or cool weather when drying is difficult.

■ Crushed Stone — The use of crushed stone or crushed gravel is a common procedure to improve subgrade stability. Typical undercut depths would be expected to range from about 12 to 18 inches below finished subgrade elevation.

The use of high modulus geotextiles (i.e., engineering fabric or geogrid) could

Facilities | Environmental | Geotechnical | Materials 10 also be considered after underground work, such as utility construction, is completed. Prior to placing the fabric or geogrid, we recommend all below-grade construction, such as utility line installation, be completed to avoid damaging the fabric or geogrid. Equipment should not be operated above the fabric or geogrid until one full lift of crushed stone fill is placed above it. The maximum particle size of granular material placed over geotextile fabric or geogrid should not exceed 1½ inches.

■ Chemical Modification — Improvement of subgrades with Portland cement or class C fly ash could be considered for improving unstable soils. Chemical modification should be performed by a prequalified contractor with experience successfully stabilizing subgrades in the project area on similar sized projects with similar soil conditions. Results of chemical analysis of the additive materials should be provided to the geotechnical engineer prior to use. The hazards of chemicals blowing across the site or onto adjacent property should also be considered. Additional testing would be needed to develop specific recommendations to improve subgrade stability by blending chemicals with the site soils. Additional testing could include, but not be limited to, determining the most suitable stabilizing agent, the optimum amounts required, the presence of sulfates in the soil, and freeze-thaw durability of the subgrade.

Further evaluation of the need and recommendations for subgrade stabilization can be provided during construction as the geotechnical conditions are exposed.

Fill Material Types

New engineered fill required to achieve design grade should be classified as structural fill and general fill. Structural fill is material used below, or within 5 feet of foundation elements and floor slabs, or constructed slopes. General fill is material used to achieve grade outside of these areas.

On-site native granular soils free of organics, debris and any other unsuitable materials or low volume change import materials approved by the geotechnical engineer may be used as structural fill or general fill on the site.

Imported materials meeting the properties presented below should be acceptable for use as structural fill or general fill. Other import fill material types may be suitable for use on the site depending upon proposed application and location. However, all imported soils should be evaluated and approved by the geotechnical engineer prior to delivery to the site.

Facilities | Environmental | Geotechnical | Materials 11

Soil Type 1 USCS Classification Acceptable Parameters

(for Structural Fill)

Granular

GW, GP, GM, GC,

SW, SP, SM, SC

■ Maximum particle size of

3 inches

■ Liquid Limit less than 30, Plasticity Index less than

■ Less than 40% passing on No. 200 sieve

Wyoming Department of

Transportation (WYDOT)

Grade W or L

Varies

1. Structural and general fill should consist of approved materials free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the Geotechnical

Engineer for evaluation prior to use on this site. Additional geotechnical consultation should be provided prior to use of uniformly graded gravel on the site.

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift

Thickness

■ 9 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

■ 4 to 6 inches in loose thickness when hand-guided equipment (i.e., jumping jack or plate compactor) is used

Same as structural fill

Minimum

Compaction

Requirements 1,2

At least 95% of the standard Proctor maximum dry density (ASTM D698) for fill/backfill planned in foundation, floor slab, pavement subgrade and trench backfill areas.

92% of standard

Proctor maximum density

Water Content

Range

■ Onsite clay soils: -1 to +3% of the optimum moisture content as determined by the standard Proctor test

■ Onsite or imported granular soils: -3 to +3% of the optimum moisture content as determined by the standard

Proctor test

As required to achieve min.

compaction requirements

Facilities | Environmental | Geotechnical | Materials 12

Item Structural Fill General Fill

1. When compacting within 10 feet of the existing structure, a lightweight compactor should be used and backfill should be placed and compacted in 4 to 6-inch loose lifts.

Use of controlled low-strength materials (also known as flowable fill or lean concrete) may also be considered to reduce risk of undermining.

2. Structural and general fill should be placed and compacted in horizontal lifts, using equipment and procedures that will produce recommended moisture contents and densities throughout the lift. A construction disc or other suitable processing equipment will be needed to thoroughly process the materials and to aid in achieving uniform moisture content throughout the fill.

3. Care should be taken during the fill placement process to avoid zones of dissimilar fill.

Improvements constructed over varying fill types are at a higher risk of differential movement compared to improvements over a uniform fill zone.

Utility Trench Backfill

Trench excavations should be made with sufficient working space to permit construction including backfill placement and compaction. Trench backfill should consist of the on-site soils free of debris and organic matter or approved imported materials Trench backfill should be placed and compacted as described under Compaction Requirements. It is strongly recommended a representative of the geotechnical engineer provide full-time observation and compaction testing of trench backfill within the building area.

Underground piping within or near the proposed structure should be designed and constructed so deviations in alignment do not result in breakage or distress. Utility knockouts in grade beams (if any) should be oversized to accommodate differential movements.

The individual contractor(s) is responsible for designing and constructing stable, temporary excavations in order to maintain stability of excavation sides and bottom as well as any adjacent structures and foundations. Care should be taken during construction to avoid affecting existing and adjacent structure foundations. Excavations for the project should not undermine existing foundations. These conditions will require shoring of excavations and/or underpinning of existing foundations to protect the structural integrity of the existing building. Additional discussion regarding excavating in close proximity to existing foundations is presented in the Foundation Subgrade

Preparation section of this report. Excavations should be sloped or shored in the interest of safety following local and federal regulations, including current Occupational

Safety and Health Administration (OSHA) excavation and trench safety standards. Based on the subsurface conditions encountered in our boring, caving sand soils are not anticipated to be encountered on this site. As a safety measure, we suggest vehicles and soil piles be kept to a minimum lateral distance from the crest of the slope equal to no less than the slope height. Exposed slope faces should be protected against the elements.

Facilities | Environmental | Geotechnical | Materials 13

The soils to be penetrated by the proposed excavations may vary significantly across the site. The soil classifications are based solely on the materials encountered in our exploratory test boring. The contractor should verify similar conditions exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, the actual conditions should be evaluated to determine any excavation modifications necessary to maintain safe conditions.

Should new utilities be installed near existing foundation elements, trench excavations should not be conducted below a downward 1:1 projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

Trench backfill should be mechanically placed and compacted as discussed earlier in this report. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors. Where trenches are placed beneath slabs or footings, the backfill should satisfy the gradation and expansion index requirements of engineered fill discussed in this report. Flooding or jetting for placement and compaction of backfill is not recommended.

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the existing building and/or proposed building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the building. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay. The trench plug material should be placed to surround the utility line.

If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Grading and Drainage

Proper drainage and surface water management is important to the performance of foundations, floor slabs, and other site improvements. The following recommendations are considered good practice for any site and should be implemented where applicable.

Grades must be adjusted to provide positive drainage away from the existing building, proposed building and other site improvements during construction and maintained throughout the life of the proposed facility. Infiltration of water into utility and foundation excavations must be prevented during construction.

Landscaped irrigation adjacent to the building should be minimized. Plants placed close to foundation walls should be limited to those with low moisture requirements.

Landscape located adjacent to the building or other structures (if any) should be self-

Facilities | Environmental | Geotechnical | Materials 14 contained. Sprinkler mains and spray heads should not be installed or allowed to discharge within 5 feet of foundation walls. Roof drains should discharge on pavements or be extended away from the structure a minimum of 10 feet through the use of splash blocks or downspout extensions. Downspouts and extensions should be monitored and maintained in good working condition. Generally speaking, downspouts should not be buried and extended below grade, as these systems can be difficult to monitor and maintain. We recommend constructed slopes of about 12 inches in the first 10 feet (10 percent slope) in landscaped areas around the building and other structures, where practical. The ground surface should be sloped in such a manner that water will not pond between or adjacent to structures and other site improvements. Concrete curbs and sidewalks may “dam” surface runoff adjacent to the building and disrupt proper flow.

Use of “chase” drains or weep holes at low points in the curb should be considered to promote proper drainage.

Backfill against foundations, exterior walls and in utility and sprinkler line trenches should be well compacted and free of construction debris to reduce moisture infiltration.

We recommend exterior foundation backfill consist of on-site or approved import clays to reduce infiltration and conveyance of surface water through the backfill . Foundation wall backfill should be capped with at least 24 inches of clay or clayey sand fill to reduce infiltration and conveyance of surface water through the backfill. Some settlement of foundation wall backfill should be expected even if properly compacted. Areas where backfill has settled should be repaired and re-graded immediately to maintain proper slope away from the building and foundations.

Flatwork will be subject to post construction movement. Maximum grades practical should be used for flatwork to prevent areas where water can pond. Where flatwork abuts the building or other structures, care should be taken that joints are properly sealed and maintained to prevent the infiltration of surface water.

Water permitted to pond near or adjacent to the perimeter of the proposed building or other structures (either during or post-construction) can result in higher soil movements than those discussed in this report. As a result, estimations of potential movement described in this report cannot be relied upon if positive drainage is not obtained and maintained, and water is allowed to infiltrate the fill and/or subgrade.

After building construction and prior to project completion, we recommend verification of final grading be performed to document that positive drainage, as described in this section, has been achieved. Maintenance of surface drainage is imperative subsequent to construction and becomes the responsibility of the owner.

Earthwork Construction Considerations

Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of grade-supported improvements such as slabs-on-

Facilities | Environmental | Geotechnical | Materials 15 grade and pavements. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part

1926, Subpart P, “Excavations” and its appendices and in accordance with any applicable local and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, and pavements), evaluation and remediation of existing fill materials, as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least 2 tests per lift in the building area and one test for every 5,000 square feet of compacted fill in pavement areas. Where not specified by local ordinance, one density and water content test should be performed for every 100 linear feet of compacted utility trench backfill and a minimum of one test performed for every 8 vertical inches of compacted backfill.

If the full-time earthwork observations are not being performed, the testing frequency should be increased.

In areas of foundation excavations, the bearing subgrade should be evaluated by the

Geotechnical Engineer. If unanticipated conditions are observed, the Geotechnical

Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

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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.

Design Parameters – Compressive Loads

Item Description

Maximum net allowable bearing pressure 1, 2

2,000 psf

Required bearing stratum

Minimum 2 feet of properly compacted structural fill.

Foundation dimensions

Columns

2 feet minimum

7 feet maximum

Wall Footings

1.5 feet minimum

3.5 feet maximum

Ultimate passive resistance

(equivalent fluid pressure) 285 psf/ft. (native sand soil)

Sliding coefficient

0.43 (native sand soils)

Minimum embedment below finished grade

36 inches

Estimated total settlement from structural loads

About 1 inch

Estimated differential settlement 2, 7

About ½ to ¾ inch of total settlement

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Values assume exterior grades are no steeper than 20% within 10 feet of structure.

2. Values provided are for maximum loads noted in Project Description. Additional geotechnical consultation will be necessary if higher loads are anticipated.

3. Unsuitable or soft/loose soils should be over-excavated and replaced per the recommendations presented in Earthwork.

4. Use of passive earth pressures require the footing forms be removed and compacted structural fill be placed against the vertical footing face. Assumes no hydrostatic pressure.

5. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Frictional resistance for granular materials is dependent on the bearing pressure which may vary due to load combinations. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the dead load.

6. Embedment necessary to minimize the effects of frost and/or seasonal water content variations.

Facilities | Environmental | Geotechnical | Materials 17

7. Differential settlements are noted for equivalent-loaded foundations and bearing elevation as measured over a span of 50 feet.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the observation of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before foundation concrete is placed.

Floor Slabs

Design parameters for floor slabs assume the requirements for Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab. As previously described, any existing fill present beneath floor slabs should be completely removed and reworked. Depending upon the finished floor elevation, unsuitable, weak, and/or soft to medium stiff clay soils may be observed at the floor slab subgrade level.

Floor Slab Design Parameters

Item Description

Interior floor system Slab-on-grade concrete.

Floor Slab

Support1

Existing fill removed and replaced with 2 feet of newly placed structural fill below the floor slabs to provide uniform support and reduce the risk of movement.

Estimated Modulus of Subgrade

Reaction 2

For limited area loads or concentrated/point loads placed directly on slabs:

■ 100 pounds per square inch per inch (psi/in.) for slabs supported on compacted subgrade consisting of the on-sites soils.

■ 150 psi/in. for slabs supported on at least 6 inches of compacted aggregate base course.

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

Facilities | Environmental | Geotechnical | Materials 18

Item Description

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in Earthwork, and the floor slab support as noted in this table. It is provided for point loads. For large area loads, the modulus of subgrade reaction would be lower.

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

Saw-cut contraction joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations, refer to the ACI Design Manual.

Joints or cracks should be sealed with a waterproof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

Settlement of floor slabs supported on existing fill materials cannot be accurately predicted but could be larger than normal and result in some cracking. Mitigation measures, as noted in Existing Fill within Earthwork, are critical to the performance of floor slabs. In addition to the mitigation measures, the floor slab can be stiffened by adding steel reinforcement, grade beams, and/or post-tensioned elements.

Floor Slab Construction Considerations

Finished subgrade, within and for at least 10 feet beyond the floor slab, should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become damaged or desiccated prior to construction of floor slabs, the affected material should be removed, and structural fill should be added to replace the resulting excavation. Final conditioning of the finished subgrade should be performed immediately prior to placement of the floor slab support course.

The Geotechnical Engineer should observe the condition of the floor slab subgrades immediately prior to placement of the floor slab support course, reinforcing steel, and

Facilities | Environmental | Geotechnical | Materials 19 concrete. Attention should be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled trenches are located.

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.