W912QR20B0001GeoReport-0002.pdf

REPORT COVER PAGE

Geotechnical Engineering Report Fire-Crash Rescue Station (F/34017)

Wright-Patterson Air Force Base, Fairborn, Greene County, Ohio August 16, 2018

Terracon Project No. N1185200

Prepared for:

Barge Design Solutions, Inc.

Miamisburg, OH

Prepared by:

Terracon Consultants, Inc.

Cincinnati, Ohio

W912QR20B0001-0002

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REPORT TOPICS

REPORT TOPICS

REPORT SUMMARY ....................................................................................................... I

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLAB-ON-GRADE

PAVEMENTS

CORROSIVITY

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange 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.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION, EXPLORATION AND MONITORING WELLS LOCATION PLANS

EXPLORATION RESULTS (Boring Logs and Laboratory Test Data) SUPPORTING INFORMATION (General Notes and Unified Soil Classification System)

ENVIRONMENTAL – SOIL ANALYTICAL TEST DATA

Fire-Crash Rescue Station (F/34017) ■ Wright-Patterson AFB, Fairborn, Ohio August 16, 2018 ■ Terracon Project No. N1185200

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REPORT SUMMARY

Topic 1 Overview Statement 2

Project Description

Single-story slab-on-grade (no basement) with an approximate “T-shaped” footprint. A Base structure footprint of 10,830 GSF with an Option to add 1,000 GSF is currently under consideration.

Maximum loads: Walls - 2 to 4 kips per lineal foot, columns – 50 to 75 kips, floor slab: 200 psf (point loading) Existing hangar slab-on-grade to remain (and be reused) within new structure footprint < 2 feet of cut/fill to achieve final grades Little excavation other than foundation construction Expected traffic on concrete drive/apron – fire trucks/equipment

Geotechnical Characterization

Existing undocumented fill between 2.5 and 5.5 feet deep Lean clays to about 7.5 feet in isolated areas Cohesionless soils: Gravel and Sand with various amounts of silt, medium dense Groundwater typically encountered at ±12 feet below ground surface Site is located within the Huffman Dam flood plain (FEMA Flood Zone A).

Site Preparation /Earthwork

Demolition of existing hangar structure. Waste demolition debris off-site.

Strip topsoil and asphalt concrete pavement, remove vegetation including root matter Remove existing undocumented fill where encountered in structural areas: positive approach is complete undercut, partial undercut can be considered provided risk of some long-term settlement is acceptable.

On-site soils can be considered for reuse as engineered fill following field evaluation and laboratory testing

Foundations

Spread footings bearing within undisturbed, competent natural soils can be considered Allowable bearing capacity = 2,500 lbs/sq ft Expected settlements: < 1 inch total, < ½ inch differential Detect and remove zones of undocumented fill or weak natural soils as noted in Earthwork

Pavements With subgrade prepared as noted in Earthwork Concrete Apron/Drive: Fire trucks/engines, Emergency Vehicles Heavy-duty pavement, minimum 7” PCC with 8” compacted aggregate base 20-year design life

General Comments

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

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

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

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INTRODUCTION

Geotechnical Engineering Report Fire-Crash Rescue Station (F/34017)

5144 Vincent Avenue Wright-Patterson Air Force Base, Fairborn, Greene County, Ohio

Terracon Project No. N1185200 August 16, 2018

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed new Fire-Crash Rescue Station to be located at 5144 Vincent Avenue in Wright-Patterson Air Force Base, Fairborn, Greene County, Ohio. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Seismic site classification per IBC

■ Short-term groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Pavement design and construction

■ Foundation design and construction ■ Soil corrosivity

The geotechnical engineering scope of services for this project included the advancement of four

(4) test borings each to an approximate depth of 21.5 feet below existing site grades.

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

SITE CONDITIONS

The following description of site conditions is derived from our review of publicly available aerial imagery, geologic and topographic maps.

Item Description Parcel Information See Site Location

Existing Improvements

Existing F/34020 hangar facility and associated pavement areas (see Exploration Plan). The existing hangar is a slab-on-grade structure supported on spread footings.

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Item Description Current Ground Cover

Grass cover, scattered vegetation, landscape areas, asphalt concrete pavement

Existing Topography Relatively level. Surface grades typically between El. ±815 feet and ±816 feet

Geology

Greene County lies within the Till Plains section of the Central Lowlands Physiographic Province. Surface topography varies from gently sloping outwash terraces to the rolling hills of the eroding end moraines. Stream valleys dissect the rolling topography throughout Greene County. The present-day Mad River Valley deposits (valley train deposits) were generated from meltwater carrying large amounts of glacially derived sediments pouring down these channels as the ice melted. Meltwater washed out the finer material, leaving thick sequences of coarse outwash sand and gravel.

Based on available published information, most of Wright Patterson AFB Area A is within the Huffman Dam flood plain (FEMA Flood Zone A). There have been several frequency analyses performed on the Huffman retarding basin to establish the 100-year flood pool elevation. USACE performed an updated frequency analysis of Huffman retarding basin for Wright Patterson AFB in 1994 incorporating the effect of CJ Brown Reservoir. Wright Patterson AFB may have adopted elevation 814.3 feet (converted to 813.56 feet NAVD88) for the 100-year pool as a result of that analysis. The 100-year flood elevation for the project site should be confirmed by others.

The project site lies in a flood plain and within an ancient buried valley created by bedrock dissection from a pre-glacial or interglacial river filled with material derived from valley train deposits covered over by an alluvial mantle. Based on the USDA Greene County Soil Survey, the near-surface soils within the project area are from the Warsaw Series consisting of well drained soils formed in loamy sediments and in the underlying gravelly outwash found on outwash plains, terraces, kames, and valley trains. Bedrock underlying the project site is Ordovician Age, sedimentary, form the Cincinnati Group consisting of interbedded limestone, dolomite and shale. Deep tests borings in the area indicate bedrock depth is greater than 100 feet below ground surface.

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PROJECT DESCRIPTION

Our understanding of the project conditions is as follows:

Item Description Information Provided Architectural Plan for Value Engineering dated July 31, 2018

Project Description

The project will consist of the demolition of the existing hangar facility (F/34020) and construction of a new Fire-Crash Rescue Station (F/34017).

The footprint of the new Fire-Crash Rescue Station will overlap and be smaller than the existing hangar footprint. The slab-on-grade portion of the existing hangar that is located within the new structure footprint will be left in-place for reuse.

Proposed Structure

The new Fire-Crash Rescue Station will be a one-story, slab-on-grade structure (no basement) with an approximate “T-shaped” footprint having maximum plan dimensions of about 97 feet in an approximate north-south direction and 155 feet in an approximate east-west direction. A Base structure footprint of 10,830 GSF with an Option to add 1,000 GSF is currently under consideration. The Station will include apparatus bays and living areas.

Building Construction Concrete masonry unit (CMU) block walls, siding: vertical metal panels and brick veneer

Finished Floor Elevation Near existing grades (El. ±816, should be confirmed by Project Civil Engineer)

Maximum Loads Walls: 2 to 4 kips/lf; floor slab-on-grade: 200 psf point loading (should be confirmed by Project Structural Engineer)

Grading/Slopes Cut/fill: < ±2 feet; site is relatively level (should be confirmed by Project Civil Engineer)

Free-Standing Retaining Walls None

Below Grade Areas None

Pavements

New concrete apron/drive from Vincent Avenue to Fire-Crash Rescue Station apparatus bay. The apron will have an approximate length of 73 feet and width of 48 feet.

Traffic: Fire engines/trucks and accompanying emergency vehicles.

Pavement: Portland Cement Concrete (PCC) pavement. 20-year design life;

Estimated Start of Construction Summer 2019

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GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

We have developed a general characterization of the subsurface soil and groundwater conditions based upon our review of the test boring data and our understanding of the geologic setting. The following table provides our geotechnical characterization.

The geotechnical characterization forms the basis of our geotechnical calculations and evaluation of site preparation, and geotechnical design and construction recommendations for foundations, slab-on-grade, and pavement. As noted in General Comments, the characterization is based upon widely spaced exploration points across the site, and variations are likely.

Stratum Approximate Depth to Bottom of Stratum (±feet) Material Description Consistency/Density

Surface 0.4

(only at B-2) Topsoil N/A

Surface 2.5

(at B-1, B-3 and B-4)

Asphalt Concrete Pavement Asphalt Concrete: ±2 to ±7.25 inch Aggregate Base: ±1.9 to ±2.3 feet

Aggregate Base:

Variable

11 2.5 to 5.5 Fill: Lean Clay with various amounts of gravel, Gravel with silt and sand, Sand with silt and gravel Variable

7.5

(only at B-1) Lean Clay (CL) Stiff

Undetermined: Borings terminated within this stratum at the planned depth of approximately

21.5 feet

Gravel with various amounts of silt and sand (GM, GW-GM), Sand with various amounts of silt and gravel

(SP, SP-SM, SM)

Typically medium dense with occasional dense zones

1. The existing fill has been interpreted as undocumented. We have not been provided field inspection records that confirm the controlled placement and compaction of the existing fill.

Conditions encountered at each boring location are indicated on the individual boring logs shown in the Exploration Results section attached to this report. Stratification boundaries on the boring logs represent the approximate location of changes in native soil types; in situ, the transition between materials may be gradual. Also included in the section is a graphic representation of the subsurface profile.

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Groundwater Conditions

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

Boring Number Approximate Depth to

Groundwater while Drilling1

(feet)

Approximate Depth to Groundwater after Drilling1

(feet)

B-1 12.5 not encountered

(borehole caved at ±10 feet)

B-2 12.5 not encountered

(borehole caved at ±10.5 feet)

B-3 12.5 82

B-4 4 13.7

(borehole caved at ±12 feet)

1. Below ground surface

2. Drilling mud used to control soil heave

The short-term groundwater levels are inadequate to characterize long-term groundwater conditions over the design life of the structure. Long-term observations in piezometers or observation wells sealed from the influence of surface water are often required to characterize groundwater conditions.

Consideration could be given to periodically reading the monitoring wells installed in 2013 by others to characterize the groundwater conditions at this site. From experience, seepage is commonly encountered in existing fill (trapped/perched water), along the fill/natural soil interface and the interface of materials with very different permeability.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

The subsurface conditions encountered at the test borings for this study are generally consistent with those encountered at other test borings in the area and published geology. The test borings for this study revealed a subsurface profile consisting of a surface cap of pavement or topsoil underlain by variable depths of existing undocumented fill (between about 2.5 feet and 5.5 feet

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Demolition of the existing structure is anticipated to include removal of all existing walls and the portion of the slab-on-grade that is outside the new structure footprint. The feasibility of leaving the existing structure footings in-place requires specific evaluation. The provided as-built drawings do not appear to clearly indicate the thickness of the existing slab-on-grade (to be reused) and the presence of a vapor retarder. Specific review/evaluation should be performed to determine the thickness and condition of the existing slab-on-grade and whether a vapor retarder is present below the slab-on-grade. The review should include an evaluation of the adequacy of the existing slab-on-grade in consideration of intended future use and design life.

Based on the anticipated structure loads and encountered subsurface conditions, the structure can be supported on spread footings bearing within undisturbed, at least stiff lean clay soils or medium dense gravelly or sandy soils. Excavations for spread footings should be performed with caution so as not to undermine the existing slab-on-grade to remain as part of the new structure.

The Shallow Foundations section provides geotechnical design and construction recommendations for spread footings.

The positive approach to site development in new slab-on-grade and pavement areas is to completely undercut the existing undocumented fill and replace as/with engineered fill placed in accordance with recommendations in the Earthwork section of this report. The feasibility (and cost) of performing a complete undercut requires specific evaluation. Consideration could be given to performing a partial undercut of the existing undocumented fill provided the inherent risk of some long-term settlement over the design life of the structure is acceptable to the Owner. In areas with stringent performance requirements, a complete undercut of the undocumented fill and replacement as/with engineered fill or a structural slab-on-grade is recommended. Additional discussion is included in the Earthwork and Floor Slab-on-Grade sections of this report

The short-term groundwater conditions recorded in the test borings for this study and that reported in the 2013 well logs developed by others (attached) indicates the groundwater level at the site is about ±12 feet below ground surface. The groundwater levels can change during construction and over the design life of the structure being influenced by rainfall and regional hydrogeology.

Seepage (trapped or perched water) should be anticipated within “shallow” excavations and can likely be handled by sump-pumps. Excavations that extend below the groundwater table will require more extensive dewatering systems. The Contractor is completely responsible for selection, design, installation and satisfactory operation of dewatering systems. Consideration should be given to reading the groundwater levels in the referenced 2013 monitoring wells (if accessible) immediately prior to construction to characterize groundwater conditions and aid the evaluation of construction dewatering requirements.

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Review of undocumented fill samples collected from test borings indicates that much of the excavated fill can be considered for reuse as engineered fill. The suitability of all excavated soils for reuse will require evaluation/confirmation during construction. Some culling and moisture conditioning of excavated soils should be expected.

Effective site drainage is important both during construction and over the design life of the structure. Effective site drainage during construction will help reduce subgrade softening/disturbance and associated undercuts. Effective site drainage over the life of the structure will help improve the long-term performance including reducing the potential for premature pavement failures. Earthwork should preferably be performed during the warmer and drier time of the year to reduce the risk for possible undercutting and replacement of unstable subgrade. Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Earthwork section.

The General Comments section provides an understanding of the report limitations.

EARTHWORK

Earthwork will include stripping, clearing and grubbing, excavations and 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, floor slabs-on-grade, and pavements.

Site Preparation

All existing utilities should be clearly marked in the field prior to construction. Surface geophysical surveys (such as GPR) and test pit excavations should be considered, as needed, to locate existing utilities. The existing utilities should be relocated outside the building footprint, as necessary. Any utilities to be abandoned and its backfill should be removed from building and pavement areas. The feasibility of leaving existing utilities in-place requires specific evaluation.

Existing utilities to be abandoned in-place should be filled full with cement grout under pressure.

A preconstruction survey and condition assessment of the existing slab-on-grade to be reused for the new structure should be performed prior to construction. The Demolition Contractor is solely responsible for determining the demolition sequence, means and methods. Appropriate measures should be implemented to protect the existing slab-on-grade portion to be reused for the new structure. All demolition debris should be wasted off site. The feasibility of leaving existing structure footings requires specific evaluation. In areas where the existing footings can be left in place, we recommend that the footing stub wall or pier concrete be terminated a minimum 2 feet below finished exterior grade or slab-on-grade subgrade. All topsoil and existing vegetation

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(including their root mat) should be completely stripped/grubbed within structural areas (building and pavement areas). Consideration could be given to stockpiling the topsoil for reuse in new landscape areas following evaluation by the landscape personnel.

The existing asphalt concrete pavement (including aggregate base) within new structural areas should be stripped (as needed) to expose the underlying subgrade soils. The stripped asphalt concrete should be wasted off site. The aggregate base can be stockpiled for reuse in new pavement areas.

As noted in Geotechnical Characterization, the test borings encountered existing fill to depths ranging from about 2.5 to 5.5 feet below existing surface grades. The fill has been interpreted as undocumented and we have not been provided any field inspection records that confirm its controlled placement and compaction. The positive approach to site development is to completely undercut and replace the existing undocumented fill as/with engineered fill. A partial undercut of existing undocumented fill and replacement as/with engineered fill to support floor slabs-on-grade and pavements can be considered provided the inherent risk that compressible fill or unsuitable material within or buried by the fill will not be discovered is acceptable to the Owner. This risk of unforeseen conditions cannot be eliminated without completely removing the existing undocumented fill, but can be reduced by following the recommendations in this report.

The existing uncontrolled fill in new floor slab-on-grade and pavement areas should be undercut, as appropriate, to provide the recommended minimum engineered fill thickness. The undercutting can be terminated upon encountering natural soils. The need for undercutting of natural soils will depend on the findings of the proof rolling program. The bottom of the undercut areas and other subgrade areas to receive engineered fill should be proof rolled with multiple passes of a loaded (minimum 20 ton) rubber-tired tandem axle dump truck under close observation by geotechnical personnel. In areas where cohesionless soils are exposed at subgrade elevation, rubber-tired equipment may not be suitable for proof rolling and alternative equipment may be required. The contractor shall provide the appropriate equipment for proof rolling soils. Soft, yielding areas should be isolated and remediated prior to placement of engineered fill. Possible remediation methods could include in-place stabilization with stone and/or geogrid/geotextile, undercut and replacement as/with engineered fill, discing and re-compaction. The appropriate remediation method will depend on encountered conditions and should be determined in the field during construction.

Fill Material Types

Fill required to achieve design grade should be classified as engineered fill and general fill.

Engineered fill is material used below, or within 5 feet of structures and pavements. General fill is material used to achieve site grading outside of these areas. Earthen materials used for engineered and general fill should meet the following material property requirements:

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Soil Type 1 USCS Classification Acceptable Location for Placement

Low Plasticity Cohesive

CL, CL-ML

SM, SC

(LL < 40% and PI < 25) All locations and elevations

High Plasticity

Cohesive 2

CH

(LL >50%)

Non-structural fill areas.

Granular GW, GP, GP-GM, GM, SW, SP, SP-SM All locations and elevations

On-Site Soils Varies

The existing undocumented fill soils appear suitable for use as engineered fill. Moisture conditioning and some culling of excavated soils should be anticipated.

The suitability of all excavated soils should be evaluated in the field by geotechnical personnel during construction.

1. Engineered and general fill should consist of approved materials free of organic matter and debris and have a maximum particle size of 4 inches. 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. Materials considered unsuitable for use as engineered fill include CH, ML, MH, OL, OH, PT, pea gravel.

2. Delineation of fat clays should be performed in the field by a Geotechnical Engineer or their representative. High plasticity clay should not be used within the engineered fill areas. The plasticity of clays can be reduced by the addition of lime.

3. Similar to ODOT Item 304 crushed limestone aggregate or granular material such as sand, gravel or crushed stone containing no more than 10% low plasticity fines (passing #200 sieve). Angular aggregate such as crushed limestone is preferred. Aggregate gradation should be less than 2-inch maximum size.

Fill Compaction Requirements

Engineered and general fill should meet the following compaction requirements.

Item Structural Fill

Maximum Lift Thickness

8 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

Minimum Compaction Requirements (Structural Areas) 1

95% of the material’s Modified Proctor maximum dry density

(ASTM D 1557)

Upper 12 inches of engineered fill in pavement areas should be compacted to minimum 98% of the material’s Modified Proctor maximum dry density (ASTM D 1557)

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Item Structural Fill

Minimum Compaction Requirements (Landscape Areas) 1

85% of material’s Modified Proctor maximum dry density (ASTM D 1557) provided long-term plans do not include a structure in these areas

Water Content Range

Cohesive Soil: Within ±3% of optimum moisture content (OMC) as determined by the Modified Proctor test at the time of placement and compaction Granular Soil2: Within ±2% of OMC / Within workable moisture levels

1. Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

2. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proof-rolled.

3. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 75% relative density (ASTM D 4253 and D 4254).

All materials to be used as engineered fill should be tested in the laboratory to determine their suitability and compaction characteristics.

Utility Trench Backfill

All trench excavations should be made with sufficient working space to permit construction including backfill placement and compaction. If utility trenches are backfilled with relatively clean granular material, they should be capped with at least 18 inches of compacted cohesive fill in non-pavement areas to reduce the infiltration and conveyance of surface water through the trench backfill.

Utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the 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 lean clay. The trench plug material should be placed to surround the utility line. If used, the lean clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for engineered fill stated previously in this report.

Grading and Drainage

Effective site drainage is important to satisfactory long-term performance of the structure and pavements. Final surrounding grades should be sloped away from the structure on all sides to prevent ponding of water. Water from roof downspouts should preferably discharge (with piping)

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Effective site drainage is also important during construction to control undercuts associated with ponding of water in excavations and on approved subgrades.

After building construction and landscaping, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted as necessary as part of the structure’s maintenance program. Where paving or flatwork abuts the structure a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Although the exposed subgrade may be relatively stable upon initial exposure, unstable subgrade conditions could develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. The use of light construction equipment would aid in reducing subgrade disturbance. The use of remotely operated equipment, such as a backhoe, would be beneficial to perform cuts and reduce subgrade disturbance. Consideration could be given to establishing “travel corridors” for construction equipment and concrete trucks to control disturbance areas. Should unstable subgrade conditions develop, stabilization measures will be required. The appropriate remediation measure(s) will depend on conditions exposed during construction and requires field evaluation. Consideration could be given to placing a lean concrete mud mat on the approved subgrade to protect the exposed surface from disturbance. The mud mat would also help serve as a work platform.

Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of floor slabs-on-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 and pavement construction.

Based on groundwater conditions encountered at the test borings performed for this study and that reported in the 2013 well logs (by others, see Attachments), the static groundwater table at the site appears to be near an approximate depth of 12 feet below current ground surface. The groundwater

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A more extensive dewatering system will be required for excavations extending below the groundwater table. The design of dewatering systems should consider the radius of influence/drawdown and its impact on surrounding structures to remain. The Contractor is solely responsible for dewatering means and methods.

Trees or other vegetation whose root systems have the ability to remove excessive moisture from the subgrade soils should not be planted next to the structure. Trees and shrubbery should be kept away from the exterior edges of the foundation element a distance at least equal to 1.5 times their expected mature height.

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 monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and topsoil, stripping of pavement, undercutting of existing undocumented fill, proof-rolling and mitigation of areas delineated by the proof-roll program to require remediation.

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. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building areas and 5,000 square feet in pavement areas.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. In the event that unanticipated conditions are encountered, the Geotechnical Engineer should recommend 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

Based on the estimated loads (to be confirmed by Structural Engineer) and encountered subsurface conditions, the new structure can be supported on spread footings bearing within undisturbed, competent natural soils. Design recommendations for spread footings are summarized below.

Design Recommendations

Item Description Maximum Net Allowable Bearing pressure 1 2,500 psf

Required Bearing Stratum Undisturbed natural soils: at-least-medium dense cohesionless soils or at least stiff lean clay soils

Minimum Foundation Dimensions Columns: 24 inches Continuous: 18 inches

Minimum Embedment below

Finished Grade for Frost Protection 2 Footings in unheated areas: 40 inches Footings in heated areas: 33 inches

Estimated Total Settlement from Structural Loads 3 Less than about 1 inch

Estimated Differential Settlement 3 About 1/2 of total settlement

Ultimate Passive Resistance 4 200 psf (uniform distribution across face of footing within natural soils)

Ultimate Coefficient of Sliding Friction 4 0.30

Uplift Resistance5

Consider effective dead weight of the footing and the effective weight of the soil prism defined by vertical planes extending up from the top of the perimeter of the foundation

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Item Description

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. A factor of safety of 3.0 has been considered. Values provided are for maximum loads noted in Project Description. Assumes any unsuitable bearing material will be undercut and the footing will either be lowered to competent natural soils or the overexcavations will be backfilled with lean concrete (minimum f’c = 1,000 psi) to frost depth.

2. And to reduce the effects of seasonal moisture variations in the subgrade materials. Frost depth for footings in heated space and unheated space is based on information for WPAFB in Unified Facilities Criteria (UFC) 3-301-01 (Table E-2 and Figure B-1). The footings should also meet the recommended bearing material criteria.

3. The estimated settlements consider the estimated loads (to be confirmed by Structural Engineer) and the recommended bearing material/depth. Footing settlement will depend upon several factors including variations within the subsurface profile, the structural loading conditions, the embedment depth of the footings, and the quality of the construction operations.

4. The passive resistance should be considered only for footing face bearing directly against natural, at least medium dense cohesionless or at least stiff cohesive soils. The sides of the footing excavation must be nearly vertical and the concrete should be placed neat against these vertical faces for the passive earth resistance values to be valid. If the loaded side is sloped or benched, and then backfilled, the allowable passive resistance will be significantly reduced. Passive resistance should be neglected within the frost depth. If passive resistance is used to resist lateral loads, the base sliding friction should be neglected. The ultimate sliding resistance value considers that mass footing concrete will be placed directly on approved natural soils or lean concrete backfill.

A minimum factor-of-safety of 1.5 is recommended for the sliding friction. Sliding resistance should be neglected for foundations subject to net uplift conditions.

5. A maximum total unit weight of 110 pcf should be used for the backfill. This unit weight should be reduced to 45 pcf for portions of the backfill soils below groundwater. A minimum factor-of-safety of 1.5 is recommended.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the direction of the Geotechnical Engineer. It is recommended that footing excavations be neat (not formed).

Appropriate excavation support (to be determined by Contractor) should be used to maintain the stability of the trench sidewalls and prevent undermining of the soils below the existing slab-on-grade to be reused. Additionally, due to the anticipated presence of cohesionless natural soils at bearing elevation, we strongly recommend that a “toothless” bucket be used to establish the bearing elevation and create a smooth, clean bearing surface. In areas where cohesionless soils are exposed at footing bearing elevation, the exposed soils should be compacted with a vibratory tamper. The base of all footing 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 and control trench sidewall collapse. 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.

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If unsuitable bearing soils are encountered at the base of the planned footing excavation, the excavation should be extended deeper to suitable soils, and the footings could either bear directly on these soils at the lower level or on lean concrete (minimum f’c = 1,000 psi) backfill placed in the excavations. This is illustrated on the sketch below.

It is recommended that backfill above the top of footing consist of flowable fill or well compacted lean clay soils to minimize the potential for trapped water that could soften the surrounding soils (particularly exterior footings). In areas where slab-on-grade is supported on the footing backfill, proper compaction of footing backfill is important to minimize potential for settlement and cracking of floor slab.

SEISMIC CONSIDERATIONS

Code Used Site Classification 2015 International Building Code (IBC) 1 D2

1. In general accordance with Section 1613.3.2 of the 2015 International Building Code (IBC), as modified by UFC 1-200-01 Change 1

2. The 2015 IBC requires a site soil profile determination extending a depth of 100 feet for seismic site classification. In accordance with the RFP, the borings for this study extended to a maximum depth of approximately 21.5 feet and were terminated within natural, medium dense sands with various amounts of gravel. A test boring performed by others in 2013 for Bldg. 4025 in the near vicinity indicates natural, medium dense to dense, predominantly sandy soils extending to a depth of about 100 feet below ground surface. This seismic site class evaluation considers our previous experience in Area A, published geology and that the encountered material (medium dense sands with various amounts of gravel) continues below the maximum depth of the subsurface exploration. Additional exploration to deeper depths could be performed to confirm the conditions below the current depth of exploration.

Alternatively, a surface or borehole geophysical survey could be utilized in order to obtain a more accurate seismic site class.

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Mapped acceleration parameters for the site were determined from the U.S. Geological Survey (USGS) Seismic Design Maps website and are summarized in the table below.

PARAMETER VALUE

Site Coordinates 39.837541°N, -84.047828° W

Site Class D Risk Category IV (essential facility)

Ss 0.158 g Fa 1.600 S1 0.071 g Fv 2.400

PGA 0.080 g

FLOOR SLAB-ON-GRADE

The design intent is to reuse the existing slab-on-grade portion within the new structure footprint and construct new slab-on-grade in isolated areas outside the existing structure footprint, as needed. A review of the as-built records provided by WPAFB for the existing F/34020 hangar facility indicates the slab-on-grade has been in place for over 60 years. The documents do not appear to include information that clearly indicates the thickness of the existing slab-on-grade, aggregate base (if any), and presence of a vapor retarder. Specific evaluation (including slab coring, subgrade sampling, and concrete testing as needed) should be performed to determine existing slab-on-grade section details, condition of concrete and its durability, its suitability for reuse and adequacy of slab-on-grade under new use.

Based on conditions encountered at the test borings, existing undocumented fill soils are anticipated at the subgrade elevation in new slab-on-grade areas. It is recommended that the existing undocumented fill soils be undercut such that the subgrade consists of a minimum 3 feet of engineered fill or competent natural soils. The undercutting of existing soils should be performed with caution so as not to undermine the subgrade soils below the existing slab-on-grade to be reused.

The recommended design parameters for floor slab-on-grade 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.

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Floor Slab-on-Grade Design Parameters

Item Description

Floor Slab Support 1

Subgrade: Undisturbed, competent natural soils or minimum 3 feet of engineered fill in areas of undocumented fill (compacted to minimum 95% Modified Proctor maximum dry density, ASTM D 1557).

Aggregate Base: Minimum 6 inches of free-draining crushed, angular aggregate compacted to 95% of Modified Proctor maximum dry density ASTM

D 1557 3

Estimated Modulus of Subgrade Reaction 2 100 pounds per square inch per inch (psi/in) for point loads

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.

2. Modulus of subgrade reaction is an estimated value based upon published correlations with soil index properties and 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 and requires evaluation.

3. Free-draining granular material should have less than 5 percent fines (material passing the #200 sieve).

Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions.

In areas where existing undocumented fill is left in-place, the long-term performance of the floor slab can be improved by increasing the floor slab stiffness (by using a greater-than-minimum slab thickness, including reinforcing steel or both) and using closer-than-normal spacing for control joints.

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, 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 current ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Saw-cut control 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 water-proof, 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.

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Floor Slab Construction Considerations

On most project sites, the 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 aggregate base and concrete and corrective action will be required. We recommend floor slab-on-grade subgrades be maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become desiccated prior to construction of floor slabs, the affected material should be removed or the materials scarified, moistened, and recompacted.

Upon completion of grading operations in the building area, care should be taken to maintain the recommended subgrade moisture content and density prior to construction of the building floor slab-on-grade.

In situations where the subgrade is expected to be exposed to weather and construction traffic for extended periods, consideration could be given to protecting the approved subgrade with a lean concrete “mud mat” that will also serve as a working platform.

The existing undocumented fill should be undercut, as necessary, to construct the engineered fill zone discussed above. Upon completion of the undercut, the bottom of the undercut should be proof-rolled using multiple passes of loaded rubber-tired dump truck (minimum 20-ton) under close observation by geotechnical personnel. In areas with restricted access to dump truck or cohesionless soils are exposed at subgrade, appropriate heavy construction equipment should be considered. Soft, yielding, unstable areas should be corrected (appropriate method to be field determined based on encountered conditions) prior to placement of engineered fill. All completed subgrade areas should be thoroughly proof-rolled with a loaded tandem-axle dump truck (or appropriate heavy construction equipment in restricted access areas) prior to placement of aggregate base. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and 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. All slab-on-grade subgrade areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to placement of the aggregate base and concrete. The Geotechnical Engineer should approve the condition of the floor slab subgrades immediately prior to placement of the floor slab aggregate base course, reinforcing steel and concrete.

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PAVEMENTS

General…