ATT 10 - Geotech Report.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

Cheyenne Veteran’s Affairs Medical Center (VAMC) Addition

Cheyenne, Wyoming

April 12, 2022

Revised January 26, 2023

Terracon Project No. 24215057 (Revised)

Prepared for:

Apogee Consulting Group, P.A.

Cary, North Carolina

Prepared by:

Terracon Consultants, Inc.

Cheyenne, Wyoming

Terracon Consultants, Inc. 1505 Old Happy Jack Road Cheyenne, Wyoming 82001

P (307) 632 9224 F (307) 635 5756 terracon.com

REPORT C OVER LETTER TO SIGNR

April 12, 2022

Revised January 26, 2023

Apogee Consulting Group, P.A.

1151 Kildaire Farm, Suite 120

Cary, North Carolina 27511

Attn: Mr. Samuel Crawford

P: 919.535.3686

E: scrawford@acg-pa.com

Re: Geotechnical Engineering Report

Cheyenne Veteran’s Affairs Medical Center (VAMC) Addition

2360 East Pershing Boulevard

Cheyenne, Wyoming

Terracon Project No. 24215057 (Revised)

Dear Mr. Crawford:

We have completed the Geotechnical Engineering services for the project referenced above. This study was performed in general accordance with Revised Terracon Proposal No. P24215057 dated February 25, 2022. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations, floor slabs, and pavements for the proposed project. We have revised this report based on discussions with the design team to include helical pile recommendations.

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 Consultants, Inc.

Mary L. Tardona Eric D. Bernhardt, P.E. (WY, CO, SD, ND)

Senior Staff Geologist Senior Associate

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

DEEP FOUNDATIONS – HELICAL PILES

SEISMIC CONSIDERATIONS

FLOOR SLABS

BELOW-GRADE STRUCTURES

LATERAL EARTH PRESSURES

PAVEMENTS

CORROSIVITY

GENERAL COMMENTS

FIGURES

Note: This report was originally delivered in a web-based format. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

Cheyenne Veteran’s Affairs Medical Center (VAMC) Addition

2360 East Pershing Boulevard

Cheyenne, Wyoming Terracon Project No. 24215057 (Revised)

Revised January 26, 2023

INTRODUCTION

A geotechnical engineering report has been completed for the proposed medical center addition to be located at 2360 East Pershing Boulevard in Cheyenne, Wyoming. Four (4) borings, designated

B-1, B-3, B-5, and B-6 were performed to depths of about 30½ feet below existing ground surface within the proposed building addition footprint and pavement areas. Due to existing underground utilities in the area, it was agreed upon by the Client to not perform Borings B-2 and B-4 in order to mitigate the risk of a utility strike. Maps showing the site and boring locations are shown in the Site

Location and Exploration Plan sections, respectively. Boring logs and laboratory testing data are included in the Exploration Results section of this report.

The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor system design and construction

■ Site preparation and earthwork ■ Seismic site classification

■ Demolition considerations ■ Lateral earth pressures

■ Excavation considerations ■ Pavement design and construction

The recommendations contained in this report are based on the results of field and laboratory testing, engineering analyses, experience with similar soil conditions and structures, and our understanding of the proposed project.

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 geologic and topographic maps.

Cheyenne Veteran’s Affairs Medical Center (VAMC) Addition ■ Cheyenne, Wyoming

January 26, 2023 ■ Terracon Project No. 24215057 (Revised)

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Item Description

Location

The project is located at 2360 East Pershing Boulevard in Cheyenne, Wyoming. Approximate coordinates near the center of the site are 41.1477ºN and 104.7862ºW.

See Site Location

Existing

Improvements

The site is located at the existing VAMC facility and includes associated parking areas/drive lanes and infrastructure.

Current Ground

Cover

The current ground surface consists of existing concrete/asphalt pavement, concrete flatwork, and landscaping.

Existing Topography The site is generally flat; we measured an elevation change across our boring locations of about 2½ feet.

PROJECT DESCRIPTION

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

Item Description

Information Provided

This report is based on information provided by Mark Norris and the

Apogee Team via emails, phone conversations, and conference calls from

August 25, 2021 through January 2023. The following documents were provided:

■ Statement of Work prepared by Cheyenne Department of Veterans

Affairs Medical Center (VAMC) dated February 2021

■ Concept Scope Footprint

■ As-build drawings prepared by LRS federal dated August 23, 2021

Project Description

We understand the proposed project consists of the construction of a new building addition to the southern portion of the existing Emergency

Department facility.

A small infill addition is also planned at the existing entry on the south side of the existing building.

Proposed Structure We understand the larger addition will be approximately 7,000 square feet and is planned to be designed to support a second story at a future date.

Building Construction

We assume the building addition will be of wood- or steel-framed construction supported on helical pile foundations with a concrete slab-on-grade floor. A spread footing foundation can be used for the small infill addition at the existing entry to the south side of the existing building.

Finished Floor Elevation We assume FFE will match that of existing improvements.

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Assumed Maximum

Loads

■ Columns: 100 to 300 kips

■ Walls: 1 to 5 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

Grading Based on existing site improvements, we assume minimum cut/fills on the order of about 1 to 2 feet will be required to achieve final grades.

Below-Grade Structures We understand the proposed addition is planned to include pipe basements of approximately 5 to 6 feet deep.

Pavements

We assume both rigid (concrete) and flexible (asphalt) pavement sections should be considered.

Assumed traffic is as follows:

■ Autos/light trucks: 2,000 vehicles per day

■ Light delivery and trash collection vehicles: 10 vehicles per week

■ Tractor-trailer trucks: <25 vehicles per week

The pavement design period is 20 years.

If project information or assumptions vary from what is described above or if location of construction changes, we should be contacted as soon as possible to confirm and/or modify our recommendations accordingly.

GEOTECHNICAL CHARACTERIZATION

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

Exploration Results section and the GeoModel can be found in the Figures section 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

Surficial

Materials

About 3 to 6 inches of concrete or asphalt pavement overlying about 2 to 4 inches of apparent base course.

Existing, Undocumented

Fill

Clayey sand with fine grained gravel, fine to coarse grained sand.

Brown to dark brown. Encountered in Boring No. B-1 only.

Silty/Clayey

Sand

Very loose to dense silty/clayey sand with varying amounts of gravel. Fine to coarse grained. Brown to light brown and tan.

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Model Layer Layer Name General Description

4 Sand

Medium dense to very dense well to poorly graded sand with varying amounts of silt and gravel. Fine to coarse grained. Brown to light brown and tan.

As noted in General Comments, this characterization is based upon widely spaced exploration points across the site, and variations are likely.

Groundwater

The boreholes were observed while drilling and shortly after completion for the presence and level of groundwater. Groundwater was not observed in the borings while drilling, or for the short duration the borings were allowed to remain open.

Groundwater levels can and should be expected to fluctuate in response to site development and with varying seasonal and weather conditions and other factors not evident at the time the borings were performed. While not likely, it is possible groundwater may be present during construction or at other times in the life of the facility. Although we do not believe groundwater will impact the proposed construction, surface water should be taken into consideration, and proper site drainage should be implemented in design and construction.

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 some geotechnical conditions that could impact design, construction and performance of the building and other site improvements. These include the presence of undocumented fill encountered in boring B-1, and layers of loose to very loose sands within the upper 10 to 15 feet throughout the proposed building area. These conditions will require particular attention in project planning, design and during construction and are discussed in greater detail in the following sections.

Existing, Undocumented Fill

Existing undocumented fill was encountered to a depth of up to about 5 feet in Boring B-1. Existing fill could exist at other locations on the site and extend to greater depths. Because the fill was only encountered in this boring and because of its close proximity to the existing building, we believe it may have been placed during the construction of that existing building. However, we do not possess any definitive information regarding whether the fill was placed under the observation of a geotechnical engineer. Undocumented fill can present a greater than normal

Responsive ■ Resourceful ■ Reliable 5 risk of post-construction movement of foundations, slabs, pavements and other site improvements supported on or above these materials. Consequently, it is our opinion existing fill on the site should not be relied upon for support and should be removed down to native soil, moisture conditioned and recompacted prior to new fill placement and/or construction. It is also our understanding that a basement extending about 5 feet below surrounding grades is planned for this addition, which should eliminate some of the existing fill.

If existing fill is encountered below proposed pavement construction areas, consideration could be given to supporting pavements on a minimum of 8 inches of scarified, moisture conditioned, and recompacted fill materials provided some risk of pavement settlement can be accepted. If the client cannot accept the risk of pavement settlements, existing fill materials encountered below proposed pavement areas should be removed and re-compacted or replaced prior to placement of site grading fills or aggregate base course material. At a minimum, we recommend thoroughly proof-rolling subgrade below pavements to delineate areas needing repair prior to pavement construction.

Loose Sands

Loose to very loose sandy soils were encountered to depths of approximately 2 to 15 feet below existing ground surface within all borings completed at this site. Particularly, the materials were encountered in the upper 15 feet in Boring Nos. B-1, B-3, and B-6. These materials present a risk for potential settlement of shallow foundations, floor slabs, and other improvements. The native sandy soils can also be susceptible to disturbance and loss of strength under repeated construction traffic loads and unstable conditions could develop. Stabilization of loose to very loose sands may be required at some locations to provide adequate support for construction equipment and proposed structures. Terracon should be contacted if these conditions are encountered to observe the conditions exposed and to provide guidance regarding stabilization

(if needed).

EARTHWORK

The following presents recommendations for site preparation, excavation, subgrade preparation and placement of engineered fills on the project. Earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing soils, and other geotechnical conditions exposed during the construction of the project.

Site Preparation

Site preparation should commence with removal of existing asphalt and concrete pavements or flatwork. Materials containing organics (if any) should be wasted from the site.

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As noted in the Geotechnical Characterization, about 5 feet of existing fill was encountered in

Boring B-1 and these materials may be encountered at other locations. In particular, we anticipate some fills/backfills will be encountered adjacent to the existing building and in existing utility trenches. We have no records to indicate the fill was placed in a controlled manner, and therefore, assume the fill is uncontrolled. Uncontrolled fills can present a risk of post-construction movement of foundations, concrete slabs, pavements and other site improvements supported on these materials. Consequently, we recommend existing fills be removed and re-compacted or replaced below the building addition and pavement areas 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.

As an alternative in pavement areas only, if the owner elects to construct pavements on the existing fill we recommend the following. Once the planned subgrade elevation has been reached, the entire pavement area should be proof-rolled. Areas of soft or otherwise unsuitable material should be undercut and recompacted or replaced with either new structural fill or reworked, moisture conditioned and recompacted onsite soils. It should be noted that this alternative requires the owner to accept some additional risk of pavement distress due to uncontrolled fills.

Existing underground utilities are located 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 below the planned building addition be removed or relocated as part of site preparation. The resulting trenches should be backfilled with on-site or imported soils approved by Terracon.

Exposed surfaces should be free of mounds and depressions that could prevent uniform compaction. Following completion of stripping and rough grading but prior to placement of new fill, the exposed ground should be scarified, moisture conditioned as needed and re-compacted.

The subgrade should then be proof-rolled to help delineate weak or disturbed areas at or near the ground surface. Unsuitable areas should be improved by moisture adjustment and compaction or by undercutting and placement of suitable compacted fill.

Our experience and laboratory testing indicate the subgrade materials below existing flatwork will likely have relatively high moisture content and will tend to deflect and deform (pump) under construction traffic wheel loads. This condition is most likely due to moisture collecting in the subgrade through cracks or seams in the flatwork and lack of natural evaporation which would allow for drying of the subgrade. After removal of flatwork, the contractor should expect unstable subgrade materials will need to be stabilized prior to construction of new improvements.

Consequently, Terracon recommends a contingency be provided in the construction budget to stabilize and correct weak/unstable subgrade.

Based on the size of the project area and subgrade conditions encountered, Terracon anticipates the subgrade can be stabilized by scarifying the exposed soils to a depth of at least 12 inches, processing the scarified materials, allowing the soils to dry, and then compacting the subgrade

Responsive ■ Resourceful ■ Reliable 7 materials in-place. If scarifying and drying is performed, several days may be required before the subgrade is stable enough for recompaction and construction, depending on weather conditions and other factors. However, the contractor should be prepared to perform more aggressive stabilization methods. More aggressive stabilization techniques could involve undercutting weak areas and replacement with select granular fill and possibly geosynthetics, or by placing a layer of crushed rock and crowding it into the subgrade until a firm base is obtained. In any case, the appropriate method of stabilization should be determined once the entire excavation is performed and the full extent of the unstable subgrade conditions can be observed.

Demolition

Demolition of the existing parking lot, courtyard, and entryway concrete flatwork where the proposed additions are planned should include complete removal of all pavements, landscaping and exterior flatwork within the proposed construction area. This should include removal of any utilities to be abandoned along with any loose utility trench backfill or loose backfill found adjacent to existing foundations. All materials derived from the demolition of existing pavements and courtyard should be removed from the site.

Fill Material Types

On-site soils free of vegetation, organic matter, debris and other unsuitable materials or low volume change import materials approved by Terracon may be used as fill/backfill material on the site. In general, imported materials meeting the properties presented below should be acceptable for use on the site. However, imported soils should be evaluated and approved by the geotechnical engineer prior to delivery to the site.

Gradation/Property Percent Finer by Weight

(ASTM C136)

3-inch 100

No. 4 Sieve 30 to 100

No. 200 Sieve 70 (max.)

■ Liquid Limit (LL) 35 (max.)

■ Plasticity Index (PI) 15 (max.)

■ Maximum Volumetric Expansion (%) 1

1. Measured on a sample compacted to about 95 percent of the ASTM D 698 maximum dry density at about

2 percent below optimum water content. The sample is confined under a 250 psf surcharge load and inundated with water.

Other import fill material types may be suitable for use on the site depending upon proposed application and location on the site and could be tested and approved for use on a case-by-case basis.

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Compaction Requirements

Structural and general fill/backfill should meet the following compaction requirements.

Item Description

Fill 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

Compaction requirements 1 At least 95% of the standard Proctor maximum dry density (ASTM D698)

Moisture content on-site or import cohesive soils (clay)

0 to +3% of the optimum moisture content as determined by the standard Proctor test

Moisture content onsite or import sands 2 -3 to +3% of the optimum moisture content as determined by the standard Proctor test

1. Engineered 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.

2. The contractor should expect some moisture adjustment and processing of the site soils or import materials will be needed prior to or during compaction operations. In particular, some of onsite clay/clayey soils appear to have in-place moisture content in excess of the soil’s optimum moisture content. The contractor should expect considerable moisture adjustment of these soils may be needed prior to or during backfilling operations. Spreading and drying should be anticipated in order to bring the soils into working moisture ranges for proper compaction. If ample space is not available to spread and dry soils or if inclement weather does not allow for timely drying of the materials, then imported soils may be required.

3. Moisture conditioned cohesive soils (clays) should not be allowed to dry out. A loss of moisture within these materials will likely result in an increase of the materials swell potential. Subsequent wetting of these materials could result in undesirable movements.

4. 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. Moisture conditioned cohesive soils (clays) should not be allowed to dry out. A loss of moisture within these materials will likely result in an increase of the materials swell potential.

Subsequent wetting of these materials could result in undesirable movements.

Excavation and Utility Trench Construction

We believe the soils encountered in our exploratory borings can be excavated with conventional excavation equipment. Groundwater seepage is not expected for excavations shallower than about 30½ feet below current site grades. However, if seepage occurs or rain or snow-melt water develops, it should be removed as soon as possible. In order to reduce the potential for subgrade destabilization of the bottom of excavations, consideration should be given to performing excavations remotely with trackhoes or other low ground pressure (LGP) excavation equipment.

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Excavations should be made with sufficient working space to permit construction including backfill placement and compaction. Backfill should consist of approved on-site soil or approved import materials. 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 addition and pavement areas.

Utility trenches are a common source of water infiltration and migration. Utility trenches that penetrate beneath the structure 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.

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 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. The excavations for the project should not undermine existing foundations. Excavations extending below existing adjacent foundations may require shoring of excavations or underpinning of existing foundations to protect the structural integrity of the existing building. 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. If any excavation extends to a depth greater than 20 feet, according to OSHA regulations, the side slopes must be designed by a professional engineer. As a safety measure, it is recommended 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.

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 widely spaced exploratory test borings. 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.

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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 and/or to the extent possible.

Grades must be adjusted to provide positive drainage away from existing structures and proposed site improvements during construction and maintained throughout the life of the proposed facility.

Infiltration of water into utility or foundation excavations must be prevented during construction.

Landscaped irrigation adjacent to the foundation system should be minimized. Plants placed close to foundation walls should be limited to those with low moisture requirements. The importance of proper irrigation practices cannot be over emphasized. Irrigation should be limited to the minimum amount needed to maintain vegetation; application of more water will increase likelihood of slab and foundation movements.

The ground surface should be sloped in such a manner that water will not pond between or adjacent to the building addition, existing building 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 grade beams and in utility and sprinkler line trenches should be well compacted and free of construction debris to reduce moisture infiltration. We recommend exterior foundation wall backfill consist of on-site or approved import clays to reduce infiltration and conveyance of surface water through the backfill. Some settlement of 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 foundation.

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

Planters located adjacent to the structure (if any) should be self-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 well beyond the limits of the backfill zone 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.

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Water permitted to pond near or adjacent to the perimeter of the structure (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 addition 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

As discussed under Site Preparation, unstable subgrade conditions are anticipated to be encountered after removal of existing flatwork and pavement. Should unstable subgrade conditions be encountered, they will need to be corrected prior to the placement of new fill or construction. Consequently, Terracon recommends a contingency be provided in the construction budget to stabilize and correct weak/unstable subgrade. The Site Preparation section provides discussion of possible methods of stabilization based on our experience, the subgrade conditions encountered in our exploratory borings and the size of the project area. Regardless, the appropriate method of stabilization should be determined once the entire excavation is performed, and the full extent of the unstable subgrade conditions can be observed.

The subgrade should be evaluated by a Terracon representative upon completion of over-excavation and subsequent backfilling operations. Once backfill is placed and the subgrade is prepared, it is important measures be planned and taken to reduce drying of the near surface materials. If the fill dries excessively prior to grade beam or floor slab construction, then it will be necessary to rework the upper, drier materials just prior to construction. Likewise, completed subgrades that have become saturated, frozen, disturbed or altered by construction activity should be restored to the conditions recommended in this report.

Construction Observation and Testing

The earthwork efforts should be monitored under the guidance of Terracon. Monitoring should include documentation of over-excavation and reworking/replacement of existing fill soils (as described above), proof-rolling and mitigation of areas delineated by the proof-roll to require mitigation. Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by the Geotechnical Engineer prior to placement of additional lifts.

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

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SHALLOW FOUNDATIONS

We understand a small building addition is planned to enclose an entry area on the southern portion of the existing building. We believe foundations for this new addition area can consist of spread footing foundations.

Spread Footing Design Recommendations

Item Description

Bearing material Existing soils with some ground modification (if necessary) to improve any soft soils exposed.

Maximum net allowable soil bearing pressure

1,000 psf

Minimum embedment below finished grade for frost protection

36 inches

Estimated post-construction movement based on structural loads provided

About 1-inch total movement and differential movement on the order of about ½ to ¾ inches

Ultimate passive pressure 250 psf/ft.

Ultimate coefficient of sliding friction

0.40 times the vertical dead load

1. The allowable soil bearing pressure applies to dead loads plus design live load conditions and is the maximum pressure that should be transmitted to the bearing soils in excess of the minimum surrounding overburden pressure at the footing base elevation. Assumes unsuitable bearing soils, if encountered, will be undercut and replaced with engineered fill.

2. For perimeter footings and footings beneath unheated areas. Interior column pads and footings in heated areas should bear at least 18 inches below the adjacent grade (or the top of the floor slab) for confinement of the bearing materials and to develop the recommended bearing pressure.

3. Foundation movement will depend upon variations within the subsurface soil profile, structural loading conditions, embedment depth of footings, thickness of compacted fill, and the quality of the earthwork operations. Settlement estimates are based on the assumed structural loads and resulting foundation geometry. If actual foundation loads vary significantly from those assumed, we should be contacted to review our recommendations. Additional foundation movements could occur if surface water infiltrates the foundation soils; therefore, proper drainage away from the foundation system should be provided in the final design, during construction and maintained throughout the life of the structure.

4. The sides of the excavation for spread footings must be nearly vertical and the concrete should be placed neat against these vertical faces or backfill must be compacted to at least 95 percent of the standard Proctor maximum dry density for the passive earth pressure value to be valid. Passive pressure requires movement to generate the resistance and should only be used when movement is tolerable and the soil is well compacted and will not be removed. The passive resistance and friction factor are ultimate values. As such, appropriate factors of safety should be applied.

Differential settlement between the addition and the existing building is expected to approach the magnitude of the total settlement of the addition. Expansion joints should be provided between

Responsive ■ Resourceful ■ Reliable 13 the existing building and the proposed addition to accommodate differential movements between the two structures. Underground piping between the two structures should be designed with flexible couplings and utility knockouts in foundation walls should be oversized, so minor deflections in alignment do not result in breakage or distress.

New footings should bear at or near the bearing elevation of immediately adjacent existing foundations. Depending upon their locations and current loads on the existing footings, footings for the new small entry way addition could cause settlement of adjacent walls. To reduce this concern and risk, clear distances at least equal to one half of the new footing widths should be maintained between the addition’s footings and footings supporting the existing building.

Footings should be proportioned to reduce differential foundation movement. Proportioning on the basis of relative constant dead-load pressure can provide a means to reduce differential movement between adjacent footings. Footings should be detailed and reinforced as necessary to reduce the potential for distress caused by differential foundation movement.

Spread Footing Construction Considerations

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 underpinned 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. If excavations need to extend below the depths of existing foundations, we should be contacted to evaluate conditions and provide additional recommendations, if needed. Also, 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 thick loose lifts.

Where soils are loosened during excavation or in the forming process for footings or if otherwise unsuitable materials are present at foundation bearing depth, these materials should be removed to minimum depths determined by the geotechnical engineer and the resulting excavation should be backfilled up to footing base elevation with either lean concrete or approved fill material placed and compacted as described in the Earthwork section of this report. This is illustrated in the sketches below.

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The base of foundation excavations should be free of water and loose soil prior to concrete placement. Concrete should be placed soon after excavating to reduce bearing soil disturbance.

Should the soils at bearing level become excessively dry, disturbed or saturated, or frozen, the affected soil should be removed prior to placing concrete.

Completed foundation excavations should be observed and evaluated by a representative of

Terracon well in advance of forming footings and placement of reinforcing steel to confirm satisfactory bearing materials are present and subsurface conditions are consistent with those encountered in our borings. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required.

DEEP FOUNDATIONS – HELICAL PILES

We understand helical pile foundations are the preferred foundations for support of the larger building addition at this project site. Based on the subsurface conditions encountered at our boring locations on this site and the anticipated foundation loads, helical pile foundations bearing in native soil should be suitable for support of the proposed building additions. Design recommendations for foundations for the proposed building addition and related structural elements are presented in the following sections. An experienced helical pile contractor should be consulted to review the Boring Logs to evaluate the use of this foundation system.

The following table lists input values for use in LPILE analyses. Modern versions of LPILE provide estimated default values of kh and E50 based on strength and are recommended for the project.

Since deflection or a service limit criterion will most likely control lateral capacity design, no safety/resistance factor is included with the parameters.

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Stratigraphy L-Pile Soil

Model

’ (pcf)

Ks (pci) Depth Below Ground

Surface (feet) Material

0 to 30.5 Silty/Clayey Sand Sand 35 110 90

1. See Subsurface Profile in Geotechnical Characterization for more details on Stratigraphy.

2. Definition of Terms:

Su: Undrained shear strength

: Internal friction angle

’: Effective unit weight

We do not recommend using vertically installed helical piles to resist lateral loads without approved lateral load test data, as these types of foundations are typically designed to resist axial loads. Only the horizontal component of the allowable axial load should be considered to resist the lateral loading and only in the direction of the batter. Terracon should be retained to observe helical pile installation to verify that proper bearing materials have been encountered during installation.

In accordance with local building code requirements, a load test should be performed by the helical pile installer to validate achieving the allowable design load. Load tests should be performed using helical piles consistent in size and materials with those piles planned for use during construction. Similarly, the same installation techniques and equipment planned for use during installation of production piles should be used when installing piles for load testing.

If a helical pile foundation system is selected by the project team, we recommend the helical pile designer follow the recommendations presented in Chapter 18 of the applicable International

Building Code (IBC). We recommend the helical bearing plates for each helical pile bear in the native, medium dense to dense sand soils encountered below the site. The helical pile designer should select the size and number of helical bearing plates for each helical pile based on planned loads and bearing materials described in our exploratory boring logs. Torque measurements during installation of helical piles should be used to verify the axial capacity of the helical piles. Terracon should be provided with the torque to capacity relationships for each type of pile used on the project for our review and comment prior to mobilization to the site. We recommend the helical pile installation contractor provide confirmation that the installation equipment has been calibrated within one year of installation at this project. The helical foundations should be installed by a qualified specialty contractor per the manufacturer’s recommendations.

We recommend a minimum distance of 15 inches from the edge of the pile caps to the center of each pile. Multiple helical piles within a single pile cap should be spaced apart at least 12 inches or equal to the largest helical bearing plate, whichever is greater. Helical piles are generally spaced several helical bearing plate diameters apart on-center to avoid efficiency effects. Because helical pile shafts are generally several times smaller than the helical bearing plates, their shafts are very

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SEISMIC CONSIDERATIONS

The 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 encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is D. Subsurface explorations at this site were extended to a maximum depth of 30½ 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.

FLOOR SLABS

Based on our boring data, a concrete slab-on-grade should be a suitable floor system for the proposed building addition, provided the recommendations presented in the Earthwork section of this report are followed. All slabs-on-grade undergo some movement. We believe risk of movement is low for the soil conditions encountered on this site and estimate settlement of slabs-on-grade constructed on properly prepared subgrade to be less than 1 inch. Where slab movement cannot be accepted or must be reduced, we are available to discuss floor movement mitigation techniques upon your request.

Design Recommendations

Item Description

Floor slab support

8-inch zone of moisture conditioned and compacted subgrade. Existing fill, where present, should be removed and re-worked.

Modulus of subgrade reaction

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

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

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

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1. If heavy floor loading is expected, we recommend the provision of a 6-inch layer of compacted aggregate base course below the slab. Slab reinforcement and thickness should be designed by a qualified engineer based on actual loads imposed and on intended slab use.

We recommend the following precautions be observed where slabs-on-grade are used. These precautions will not eliminate slab movement, but they tend to reduce damage when movement occurs. Additional floor slab design and construction recommendations are as follows:

■ Positive separations and/or isolation joints should be provided between slabs and foundations, columns or utility lines to allow free vertical movement. This detail can reduce cracking when movement of the slab occurs. Non-bearing partition walls placed on the floor slab (if any) should be designed and constructed to allow at least 1 inch of slab movement.

■ Frequent control joints should be provided in slabs to control the location and extent of cracking in accordance with the American Concrete Institute (ACI). For additional recommendations refer to the ACI Design Manual.

■ 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/barrier, 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/barrier.

■ Other design and construction considerations, as outlined in the ACI Design Manual, Section 302.1R are recommended.

Floor Slab Construction Considerations

Fill/backfill placed beneath slabs should be moisture conditioned and compacted as described in the Earthwork section of this report. Soils loosened during excavation or other construction activities should be removed or recompacted as described in this report. Floor slabs should not be constructed on frozen subgrade.

Once fill is placed and the subgrade is prepared, it is important measures be planned and taken to reduce drying of the near surface materials. If the fill dries excessively prior to building construction, then it will be necessary to rework the upper, drier materials just prior to installing floor slabs.

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On most project sites, site grading is generally accomplished early in the construction phase.

However; as construction proceeds, the subgrade may be disturbed due to utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab subgrade may not be suitable for placement of base and/or concrete and corrective action will be required.

We recommend the area underlying the floor slab be proof-rolled shortly before slab construction.

Particular attention should be paid to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with properly compacted fill. Floor slab subgrade areas should be moisture conditioned and properly compacted to the recommendations in this report shortly before placement of the base and/or concrete.

BELOW-GRADE STRUCTURES

An approximately 5 to 6 feet deep pipe basement is planned for this project.

LATERAL EARTH PRESSURES

Design Parameters

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

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Lateral Earth Pressure Design Parameters

Earth Pressure

Condition

Coefficient for

Backfill Type

Surcharge

Pressure 3, 4, 5 p1 (psf)

Effective Fluid Pressures (psf) 2, 4, 5

Unsaturated 6 Submerged

Active (Ka) Granular - 0.24

Fine Grained - 0.41

(0.32)S

(0.45)S

(32)H

(45)H

At-Rest (Ko) Granular - 0.38

Fine Grained - 0.58

(0.52)S

(0.58)S

(52)H

(65)H

Passive (Kp) Granular – 4.20

Fine Grained - 2.46

(568)H

(276)H

1. For active earth pressure, wall must rotate about base, with top lateral movements 0.002 H to 0.004 H, where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance.

2. Uniform, horizontal backfill, compacted to at least 95% of the ASTM D 698 maximum dry density, rendering a maximum unit weight of 138 pcf for the granular fill, and 100 pcf for the fine-grained material.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction…