Solicitation_Attachment_7_-_SUPPLEMENTAL_INFO_17-Aug-2018.pdf

The attached Geotechnical Investigation Report that was completed in December-2016 for the NCANG C-17 Corrosion Control / Fuel Cell Hangar Project shall be considered

Supplemental information only (e.g. non-binding) for the Contractor's use. The Contract Plans and Specifications have taken into consideration the discussions and recommendations in the report and as such the Contract Plans and Specifications govern as construction requirements. The Contractor is required to verify all existing conditions necessary for proper installation, construction, and operation of all elements indicted in, and in accordance with the Contract documents.

REPORT

OF

SUBSURFACE EXPLORATION

NORTH CAROLINA AIR NATIONAL GUARD (NCANG) –

C-17 HANGAR AND FLIGHT SIMULATION FACILITIES

CHARLOTTE, NORTH CAROLINA

ECS PROJECT NO. 08-11868

DECEMBER 5, 2016

REPORT OF SUBSURFACE EXPLORATION

North Carolina Air National Guard (NCANG) C-17 Hangar and Flight Simulation Facilities

Charlotte, North Carolina

Prepared For:

Mr. David Everett, AIA Project Manager

Jacobs Global Buildings 1100 North Glebe Road, Suite 500

Arlington, VA 22201

Prepared By:

ECS CAROLINAS, LLP

1812 Center Park Drive

Suite D Charlotte, NC 28217

ECS Project No:

08-11868

Report Date:

December 5, 2016

Report of Subsurface Exploration Mr. David Everett, AIA NCANG - C-17 Hanger and Flight Simulation Facilities Jacobs Global Buildings Charlotte, North Carolina ECS Project No. 08-11868 Page 2 December 5, 2016

1. INTRODUCTION

1.1. Project Information

The project site is located at the North Carolina Air National Guard (NCANG) at the Charlotte Douglas International Airport in Charlotte, North Carolina, as shown in the Site Vicinity Map (Figure 1) located in the Appendix. The project includes the construction of a 61,600 square feet C-17 Hangar Facility including an enclosed facility for washing aircraft, performing corrosion control, general maintenance, and shop areas to accommodate maintenance and training. In addition, a separate flight crew simulator training facility to support the C-17 mission will be located in the present location of Building #4. The Flight Simulation Facility is anticipated to be on the order of 10,000 square feet. It is our understanding that the current Building #4 will be razed. Additional components of the project will include the existing facility demolition, site preparation, stormwater detention and drainage systems, utilities, fencing, sidewalks, curbs, communications support, fire protection, flexible paving for POV access road, exterior lighting utilities, and Anti-Terrorism/Force Protection (AT/FP) measures.

The C-17 Hangar will consist of a metal framed building with a concrete slab-on-grade. The facilities may be 1 to 2 stories tall. Maximum column and wall footing loads are on the order of 450 kips and 5.5 kips per linear foot, respectively. The Simulator Building is a low-rise building with anticipated maximum column and wall footing loads on the order of 200 kips and 9.5 kips per linear foot, respectively. Anticipated loading conditions were provided by Jacobs.

1.2. Scope of Services

Our scope of services for this phase of the project included a subsurface exploration with soil test borings, engineering analysis of the foundation support options, and preparation of this report with our recommendations. The subsurface exploration included nine (9) soil test borings (B-1 through B-9) to depths ranging from approximately 15 to 40 feet below the existing ground surface. Approximate boring locations are shown on the Boring Location Diagram (Figure 2) included in the Appendix. The soil borings were performed using a Dietrich D-50 ATV drill rig using continuous-flight, hollow-stem augers.

2. FIELD SERVICES

2.1. Test Locations

The soil boring locations and depths were selected by others and located in the field by ECS using GPS and existing landmarks as reference. The approximate boring locations are shown on the Boring Location Diagram (Figure 2) presented in the Appendix of this report and should be considered accurate only to the degree implied by the method used to obtain them. Ground surface elevations at the boring locations were interpolated using Google Earth and should be considered approximate.

2.2. Soil Test Borings

Nine (9) soil test borings were drilled to evaluate the stratification and engineering properties of the subsurface soils at the project site. Standard Penetration Tests (SPT’s) were performed at designated intervals in general accordance with ASTM D 1586. The Standard Penetration Test is used to provide an index for estimating soil strength and density. In conjunction with the penetration testing, split-barrel soil samples were recovered for soil classification at each test interval. Boring Logs are included in the Appendix.

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The drill crew also maintained a field log of the soils encountered at each of the boring locations.

After recovery, each sample was removed from the auger and visually classified.

Representative portions of each sample were then sealed and brought to our laboratory in Charlotte, North Carolina for further visual examination and potential laboratory testing.

Groundwater measurements were attempted at the termination of drilling at each boring location.

2.3. Seasonal High Water Table

A licensed soil scientist was onsite during the drilling of the borings (B-1 through B-9) in order to determine the depth of the seasonal high water table (SHWT). The characteristics of the soil were observed, including texture, depth, slope, the presence of restrictive horizons, depth to seasonal high water table, etc. The assessment was conducted in accordance with current soil science practices and technology. The results of the SHWT study are included in the Appendix of this report.

3. LABORATORY SERVICES

Soil samples were collected from the borings and examined in our laboratory to check field classifications and to determine pertinent engineering properties. Data obtained from the borings, our visual/manual examinations, and laboratory testing are included on the respective boring logs in the Appendix.

3.1 Soil Classification

A geotechnical staff professional classified each soil sample on the basis of color, texture, and plasticity characteristics in general accordance with the Unified Soil Classification System (USCS). The staff professional grouped the various soil types into the major zones noted on the boring logs. The stratification lines designating the interfaces between earth materials on the boring logs and profiles are approximate; in situ, the transition between strata may be gradual in both the vertical and horizontal directions. The results of the visual classifications are presented on the Boring Logs included in the Appendix.

3.2 Laboratory Testing

In addition to visual classification, ECS performed four (4) natural moisture content tests and two

(2) Atterberg Limits tests. The laboratory testing was performed in general accordance with the applicable ASTM standards. The results of the laboratory testing are presented on the respective Boring Log and presented within the Laboratory Testing Summary Sheet included within the Appendix.

4. SITE AND SUBSURFACE FINDINGS

4.1. Area Geology

The site is located in the Piedmont Physiographic Province of North Carolina. The native soils in the Piedmont Province consist mainly of residuum with underlying saprolites weathered from the parent bedrock, which can be found in both weathered and unweathered states. Although the surficial materials normally retain the structure of the original parent bedrock, they typically have a much lower density and exhibit strengths and other engineering properties typical of soil. In a mature weathering profile of the Piedmont Province, the soils are generally found to be finer grained at the surface where more extensive weathering has occurred. The particle size of the

Charlotte, North Carolina ECS Project No. 08-11868 Page 4 December 5, 2016 soils generally becomes more granular with increasing depth and gradually changes first to weathered and finally to unweathered parent bedrock. The mineral composition of the parent rock and the environment in which weathering occurs largely control the resulting soil's engineering characteristics. The residual soils are the product of the weathering of the parent bedrock.

In addition, it is apparent that the natural geology within the site has been modified in the past by grading that included placement of fill materials. The quality of man-made fills can vary significantly, and it is often difficult to access the engineering properties of existing tests performed in soil test borings and the degree of compaction of existing fill soils; however, a qualitative assessment of existing fills can sometimes be made based on the N-values obtained and observations of the materials sampled in the test borings.

4.2. Subsurface Conditions

The subsurface conditions at the site, as indicated by the borings, generally consisted of fill and residual soil to the depths explored. The generalized subsurface conditions are described below. For soil stratification at a particular test location, the respective Boring Log found in the Appendix should be reviewed.

Varying amounts of asphalt was observed at the ground surface at Borings B-2, B-3, B-4, B-6, B-7, B-8, and B-9. Additionally, approximately 10 inches of concrete was observed beneath the asphalt at Borings B-3 and B-5. Approximately 10 inches of concrete was observed at the ground surface at Borings B-1 and B-5. The surficial material depths provided in this report and on the individual Boring Logs are based on driller observations and should be considered approximate. Please note that these reported values should not be used in determining removal quantities.

Fill soils were encountered below the surficial material at each of the boring locations. The fill extended to depths ranging from approximately 3 to 5½ feet below the existing ground surface.

The fill soils encountered generally consisted of Sandy CLAY (CL), Plastic CLAY (CH), Elastic SILT (MH) and Sandy SILT (ML) exhibiting SPT N-values ranging from 3 to 13 blows per foot (bpf).

Residual soil was encountered below the fill soils at each of the boring locations. Residual soils are formed by the in-place chemical and mechanical weathering of the parent bedrock. The residual soils encountered in the borings generally consisted of Sandy SILT (ML), Elastic SILT (MH), Sandy CLAY (CL), and Silty SAND (SM), exhibiting SPT N-values ranging from 4 to 42 blows per foot (bpf) with a majority of the N-values ranging between 6 and 16 bpf. Each of the boring locations was terminated in the residual soils at depths ranging from 15 to 40 feet below the existing ground surface.

4.3. Groundwater Observations

Groundwater measurements were attempted at the termination of drilling at the time of our exploration. Groundwater was encountered at Borings B-6 and B-8 at depths of approximately

34.1 and 29.5 feet below the existing ground surface, respectively. Each of the remaining boring locations was dry when the groundwater measurements were taken. Borehole cave-in depths were observed at each boring location at depths ranging from approximately 16.1 to 34.7 feet below the existing ground surface. Cave-in of a soil test boring can be caused by groundwater hydrostatic pressure, weak soil layers, and/or drilling activities (i.e. drilling fluid circulation or advancement of bit).

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Fluctuations in the groundwater elevation should be expected depending on precipitation, run-off, utility leaks, and other factors not evident at the time of our evaluation. Normally, highest groundwater levels occur in late winter and spring and the lowest levels occur in late summer and fall. Depending on time of construction, groundwater may be encountered at shallower depths and locations not explored during this study. If encountered during construction, engineering personnel from our office should be notified immediately.

4.4. Laboratory Test Results

Moisture content test results of the sampled soils range from approximately 25.5 to 38.0 percent.

Atterberg Limits testing was performed on a selected soil samples from B-1 and B-4 resulting in liquid limits (LL) ranging from 48 to 58 and plasticity indices (PI) ranging from 14-15. The portion of the samples tested was USCS classified as Sandy SILT (ML) for B-1 and Elastic SILT (MH) for B-4. For laboratory test results at a particular test location, the Laboratory Test Summary sheet found in the Appendix should be reviewed.

5. CONCLUSIONS AND RECOMMENDATIONS

The borings performed at this site represent the subsurface conditions at the location of the borings. Due to inconsistencies associated with the prevailing geology and existing fill soils, there can be changes in the subsurface conditions over relatively short distances that have not been disclosed by the results of the test location performed. Consequently, there may be undisclosed subsurface conditions that require special treatment or additional preparation once these conditions are revealed during construction.

Our evaluation of foundation support conditions has been based on our understanding of the site, project information and the data obtained in our exploration. The general subsurface conditions utilized in our foundation evaluation have been based on interpolation of subsurface data between and away from the borings. In evaluating the boring data, we have examined previous correlations between penetration resistance values and foundation bearing pressures observed in soil conditions similar to those at your site.

5.1. Existing Fill

Fill soils were encountered at each of the boring locations and extended to depths ranging from approximately 3 to 5½ feet below the existing ground surface. ECS was not provided with documentation of the previous earthwork activities, thus the fill should be considered undocumented.

Undocumented fill poses risks associated with undetected deleterious inclusions within the fill and/or deleterious materials at the virgin ground fill interface that are covered by the fill.

Deleterious materials can consist of significant amount of organics derived from organic rich strippings, rubbish, construction or demolition debris, stumps and roots, and logs. If these materials are covered over by or are within undocumented fill, the organic materials tend to decompose slowly in the anaerobic conditions in or under the fill. Decomposition can occur over periods ranging from several years to several decades. As the organic materials decompose, a void is created which can create soft conditions and even subsidence in areas above the organics. Where these types of conditions exist under or within undocumented fill, they are sometimes in discreet pockets that can go undetected by normal subsurface exploration techniques, i.e., soil test borings and test pits.

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Due to the depth and quality of the fill soils, we recommend removing and replacing the undocumented fill soils located within the building pad. The excavation should extend a minimum horizontal distance equal to the depth of excavation plus 5 feet. The risk of poor pavement performance can be lowered with the implementation of geogrid reinforcement to the pavement cross section or the use of a more robust pavement design; however, the pavement recommendations provided herein do not include the use of geogrids reinforcement. These methods limit the potential for poor pavement performance, but do not eliminate the risk.

5.2. Moisture Sensitive Soils (MH/CH)

Elastic SILTS (MH) and Plastic CLAYS (CH) were encountered within the fill soils at Borings B-2 and B-4 to depths of approximately 3 feet below ground surface and Elastic SILTS (MH) were encountered within the residual soils at Boring B-4 to a depth of approximately 5½ feet below ground surface. Soils classified as MH/CH are fine-grained and have a Liquid Limit greater than 50 percent. Additionally, MH/CH soils are moisture sensitive soils and tend to shrink and swell with moisture variations.

Residual MH soils with a plasticity index greater than 30 and CH soils should not be used for direct support of project foundations, slabs-on-grade, or pavements. Residual MH soils (PI’s greater than 30) and CH soils encountered within proposed structural areas should be undercut and replaced with low plasticity engineered fill to a minimum depth of 2 feet below foundations and 2 feet below subgrade elevations in slab and pavement areas. Upon completion of the removal, the resulting subgrade soils should be evaluated for stability prior to placement of engineered fill.

5.3. Seismic Site Class

The North Carolina Building Code (NCBC) requires that the stiffness of the top 100-ft of soil profile be evaluated in determining a site seismic classification. The method for determining the Site Class is presented in Section 1615 of the code. The seismic Site Class is typically determined by calculating a weighted average of the N-values or shear wave velocities recorded to a depth of 100 feet within the proposed building footprint. Based on the SPT N-values obtained within the drilled depth of borings, a seismic site class of “D” is considered appropriate for this project.

5.4. Structure Foundations

The following section presents specific recommendations with regard to the foundation design of the proposed C-17 Hangar and Simulation Building. Each foundation recommendation has been made provided the site preparation and fill recommendations outlined within this report are implemented.

For this project, minimum wall and column footing dimensions of 18 and 24 inches, respectively, should be maintained to reduce the possibility of a localized, “punching” type, shear failure.

Exterior foundations and foundations in unheated areas should be embedded deep enough below exterior grades to reduce potential movements from frost action or excessive drying shrinkage. For this region, we recommend footings bear at least 18 inches below finished grade.

As previously mentioned, MH soils with a plasticity index greater than 30 or CH soils should not be used for direct support of foundations or slabs-on-grade. MH and CH soils encountered within 2 feet of soil subgrade should be undercut and replaced with approved engineered fill to a minimum depth of 2 feet below foundations provided that the resulting subgrade is stable.

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C-17 Hangar and Simulator Buildings

The proposed C-17 Hangar and Simulator Buildings can be adequately supported on a shallow foundation system consisting of spread footings bearing on firm undisturbed low plasticity residual soil or newly-placed engineered fill. A bearing capacity of up to 2,500 psf is recommended for foundations bearing on firm undisturbed low plasticity residual soil or newly-placed engineered fill.

Total settlement is anticipated to be less than 1 inch, while differential settlement between columns is anticipated to be less than ½ inch within 30 feet for shallow foundations bearing on low plasticity residual soil or newly-placed structural fill. Foundation geometry, loading conditions, and/or bearing strata different than those described in this report may result in magnitudes of settlement inconsistent with the previous estimates.

5.5. Slab-On-Grade Support

Slabs-on-grade can be adequately supported on undisturbed low plasticity residual soils or newly-placed engineered fill provided the site preparation (Section 6.1) and fill recommendations (Section 6.2) outlined herein are implemented. For a properly prepared site, a modulus of subgrade reaction (ks) for the soil of 90 pounds per cubic inch for the soil can be used. This value is representative of a 30 inch diameter loaded area and may need to be adjusted depending on the size and shape of the loaded area depending on the method of structural analysis.

We recommend the slabs-on-grade be underlain by a minimum of 4 inches of granular material having a maximum aggregate size of 1½ inches and no more than 2 percent fines. Prior to placing the granular material, the floor subgrade soil should be properly compacted, proofrolled, and free of standing water, mud, and frozen soil. A properly designed and constructed capillary break layer can often eliminate the need for a moisture retarder and can assist in more uniform curing of concrete. If a vapor retarder is considered to provide additional moisture protection, special attention should be given to the surface curing of the slabs to minimize uneven drying of the slabs and associated cracking and/or slab curling. The use of a blotter or cushion layer above the vapor retarder can also be considered for project specific reasons.

Please refer to ACI 302.1R96 Guide for Concrete Floor and Slab Construction and ASTM E 1643 Standard Practice for Installation of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs for additional guidance on this issue.

ECS recommends that the slab be isolated from the footings so differential settlement of the structure will not induce shear stresses on the floor slab. Also, in order to minimize the crack width of shrinkage cracks that may develop near the surface of the slab, we recommend mesh reinforcement as a minimum be included in the design of the floor slab. For maximum effectiveness, temperature and shrinkage reinforcements in slabs on ground should be positioned in the upper third of the slab thickness. The Wire Reinforcement Institute recommends the mesh reinforcement be placed 2 inches below the slab surface or upper one-third of slab thickness, whichever is closer to the surface.

Adequate construction joints, contraction joints and isolation joints should also be provided in the slab to reduce the impacts of cracking and shrinkage. Please refer to ACI 302.1R96 Guide for Concrete Floor and Slab Construction for additional information regarding concrete slab joint design.

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5.6. Pavement Considerations

For the design and construction of exterior pavements for vehicular traffic only, the subgrades should be prepared in accordance with the recommendations in the “Site and Subgrade Preparation” and “Engineered Fill” sections of this report. This section does not include pavement recommendations for plane traffic or runway design. The plane apron design has been included in the appendix of this report.

Undisturbed low-plasticity natural soils or newly placed engineered fill can provide adequate support for a pavement structure designed for appropriate subgrade strength and traffic characteristics. Additionally, pavements can be supported on approved existing fill provided that the owner has accepted the risk associated with the existing fill as previously described in this report.

An important consideration with the design and construction of pavements is surface and subsurface drainage. Where standing water develops, either on the pavement surface or within the aggregate base course layer, softening of the subgrades and other problems related to the deterioration of the pavement can be expected. Furthermore, good drainage should help reduce the possibility of the subgrade materials becoming saturated during the normal service period of the pavement.

Based on our past experience with similar developments and subsurface conditions, we present the following design pavement sections, provided the recommendations contained in this report are strictly followed. Based on the soil types encountered in the soil test borings and provided the site grading recommendations outlined herein are implemented, we recommend a CBR value of 4 be used in design of the project pavements. Based upon our previous experience with similar projects, ECS has estimated the provided pavement sections based upon a 20 year life, with equivalent axle loadings of approximately 25,000 and 200,000 ESALs for light-duty and heavy-duty pavements, respectively.

PAVEMENT SECTION RECOMMENDATIONS

Material Designation Light Duty

Asphalt Pavement

Heavy Duty Asphalt

Pavement

Portland Cement Concrete (PCC)

Pavement Asphalt Surface Course (S9.5B) 3 inches 1.5 inches - Intermediate Coarse (I19.0B) - 2.5 inches - Portland Cement Concrete - - 6 inches Aggregate Base Course 6 inches 8 inches 6 inches

ECS should be allowed to review these recommendations and make appropriate revisions based upon the formulation of the final traffic design criteria for the project. It is important to note that the design sections do not account for construction traffic loading. In addition, individual retailers may have minimum pavement sections that were not accounted for during our pavement evaluation.

The aggregate base course materials beneath pavements and sidewalks should be compacted to at least 95 percent of their modified Proctor maximum dry density (ASTM D 1557). Front-loading trash dumpsters frequently impose concentrated front-wheel loads on pavements during loading. This type of loading typically results in rutting of bituminous pavements and ultimately pavement failures and costly repairs. Similarly, drive-thru lanes also create severe risk of rutting and scuffing. Therefore, we suggest that the pavements in trash pickup and drive-thru areas

Charlotte, North Carolina ECS Project No. 08-11868 Page 9 December 5, 2016 utilize the aforementioned Portland Cement Concrete (PCC) pavement section. It may be prudent to use rigid pavement sections in all areas planned for heavy truck traffic. Such a PCC section would typically consist of 6 inches of 4,000 psi, air-entrained concrete over not less than 6 inches of compacted aggregate base course. Appropriate steel reinforcing such as welded-wire fabric and/or rebar and jointing should also be incorporated into the design of all PCC pavements.

It should be noted that these design recommendations may not satisfy the North Carolina Department of Transportation traffic guidelines. Any roadways constructed for public use and to be dedicated to the State for repair and maintenance must be designed in accordance with the State requirements.

5.7. Below Grade Excavation

Information regarding the depth of the planned underground utilities or site grades was not provided at the time of this report. Based on the results of the soil test borings and the anticipated cut/fill depths, we do not anticipate difficult excavation will be encountered.

As noted in the Geology section of this report, the weathering process in the Piedmont can be erratic and significant variations of the depths of the more dense materials can occur in relatively short distances. In some cases, isolated boulders or thin rock seams may be present in the soil matrix.

5.8. Cut and Fill Slopes

ECS does not anticipate cut or fill slopes greater than 10 feet in height. We recommend that permanent cut slopes with less than 10 feet crest height through undisturbed residual soils be constructed at 2:1 (horizontal: vertical) or flatter. Permanent fill slopes less than 10 feet tall may be constructed using engineered fill at a slope of 2.5:1 or flatter. However, a slope of 3:1 or flatter may be desirable to permit establishment of vegetation, safe mowing, and maintenance.

The surface of all cut and fill slopes should be adequately compacted. All permanent slopes should be protected using vegetation or other means to prevent erosion.

A slope stability analysis should be performed on cut and fill slopes exceeding 10 feet in height to determine a slope inclination resulting in a factor of safety greater than 1.4. Upon finalization of site civil drawings, ECS should be contacted to perform slope stability analysis and determine if further exploration is necessary.

The outside face of building foundations and the edges of pavements placed near slopes should be located an appropriate distance from the slope. Buildings or pavements placed at the top of fill slopes should be placed a distance equal to at least 1/3 of the height of the slope behind the crest of the slope. Buildings or pavements near the bottom of a slope should be located at least ½ of the height of the slope from the toe of the slope. Slopes with structures located closer than these limits or slopes taller than the height limits indicated should be specifically evaluated by the geotechnical engineer and may require approval from the building code official.

Temporary slopes in confined or open excavations should perform satisfactorily at inclinations of 2:1. All excavations should conform to applicable OSHA regulations. Appropriately sized ditches should run above and parallel to the crest of all permanent slopes to divert surface runoff away from the slope face. To aid in obtaining proper compaction on the slope face, the fill slopes should be overbuilt with properly compacted structural fill and then excavated back to the proposed grades.

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5.9. Lateral Earth Pressures

ECS understands that below grade walls/loading dock walls may be utilized for the building.

Specifics regarding the below grade walls (i.e. location, height, length, loading, etc.) were unknown at the time of this report. Below grade walls should be designed to withstand the lateral earth pressures exerted upon them, and to resist additional lateral pressures generated by surcharge loads such as traffic loads, adjacent slab loads or from foundations bearing behind the walls.

For wall conditions where wall movement cannot be tolerated or where the wall is restrained at the top, such as the loading dock walls, the “At Rest” earth pressure should be used. For wall conditions where outward wall movement on the order of 0.5 percent of the wall height can be tolerated, the “Active” earth pressure should be used. In the design of loading dock walls to restrain compacted backfill, engineered fill or in-situ residual soils, the coefficient of lateral earth pressure can be used to determine lateral earth pressure loads. Please note that the values presented below are for on-site ML and SM materials. If the wall backfill is imported to the site, ECS should be contacted to review the lateral earth pressure coefficients provided. Moderately to highly elastic/plastic soils (CL, MH, and CH) should not be utilized behind earth retaining structures.

Soil Parameter Coefficient of Lateral Earth Pressure

“At Rest” Earth Pressure (Ko) 0.56 “Active” Earth Pressure (Ka) 0.39

“Passive” Earth Pressure (Kp) 2.56

The lateral earth pressure values presented above assume level backfill fill behind the wall, and do not account for hydrostatic pressures against the walls or surcharge loads from overlying or nearby construction.

Resistance to sliding can be provided by friction between the bottom of the wall foundation and the underlying soils and by passive resistance of soil adjacent to the wall foundation. The passive resistance should only be used in situations where the soil adjacent to the toe of the wall will not be eroded or otherwise removed in the future. A coefficient of friction of 0.35 for concrete bearing on approved soils is recommended.

Drainage behind freestanding retaining walls is considered essential towards relieving hydrostatic pressures. Drainage can be established by providing a perimeter drainage system located just above the below grade/retaining wall footings which discharges by gravity flow to a suitable outlet. This system should consist of “perforated pipe” or “porous wall”, closed-joint drain lines. These drain lines should be surrounded by a minimum 6 inches of free-draining, granular filter material having a gradation compatible with the size of the openings utilized in the drain lines and the surrounding soils to be retained, or by gravel wrapped in filter fabric. The space between the interior face of the wall and the earth fill should be backfilled with a granular fill of porous quality or better extending from the perimeter drainage system to just below the top of the wall. To prevent frost heave effects from acting against these walls, the granular backfill should extend a minimum of 12 horizontal inches behind the wall. The granular backfill should be capped with pavement, concrete, or a 12-inch layer of low permeable silt or clay to minimize the seepage of water into that backfill from the surface. The ground surface adjacent to the below-grade walls should be kept properly graded to prevent ponding of water adjacent to the walls.

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5.10. Mechanically Stabilized Earth (MSE) Wall Design

We understand that retaining walls may be utilized on this project. The performance of the MSE Walls is highly dependent upon sound design and construction practices. The design of the MSE Walls shall consider internal, external and global stability. The following table summarizes the recommended minimum factors of safety (FS) for static design criteria, as recommended by the National Concrete Masonry Association (NCMA).

Table 1 – Minimum Recommended Factors of Safety Failure Mode Static Base Sliding 1.5 Overturning 2.0

Internal Sliding 1.5 Tensile Overstress 1.5

Pullout 1.5 Connection 1.5

Internal Compound Stability 1.3 Bearing Capacity 2.0 Global Stability 1.3 to1.5

The results of the required internal and geotechnical stability analyses are highly dependent upon the engineering properties of the retained, reinforced and foundation zone materials.

Consequently, the design of the MSE Walls requires the assignment of specific engineering properties to the reinforced, retained and foundation zone soils. Required for design are the soil’s total in-place unit weight and peak effective friction angle and cohesion. However, cohesion is typically ignored for all materials except the foundation zone materials.

Maintaining the integrity of the reinforced zone is critical to wall performance. Any below grade utilities should be situated outside the reinforced zone to limit potential conflicts between the reinforcement and below grade structures. The wall designer should contemplate the location and use of any below grade utilities during the design process, and should coordinate with the Civil Engineer where possible to relocate the utilities outside of the reinforced zone.

ECS has completed a subsurface exploration and laboratory testing program. The incorporation of subsurface information and laboratory test results into the design of a MSE Wall requires the evaluation of available information to develop design parameters. The laboratory results provided in this report represent the soil parameters for the materials selected and should be considered for information only. Interpretation of laboratory test results and development of design parameters (i.e. shear strength) is solely the responsibility of the MSE Wall designer.

Regardless of MSE Wall geometry, it is desirable to use select fill materials within the reinforced fill zone of the MSE Wall. Granular fill is typically easier to place and compact, have enhanced drainage characteristics, have greater strengths and are less susceptible to long term movements (creep). The following gradation is recommended for the reinforced zone fill materials.

Table 2 – Gradation Requirements for Reinforced Zone Fill Sieve Size Percent Passing

1 inch 100 No. 4 20 to 100

No. 40 0 to 60 No. 200 0 to 35

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The wall designer should specify allowable backfill material including unit weight, relative compaction and shear strength requirements as well as a testing frequency to verify compaction and design shear strength properties.

In some instances it may be acceptable for low plasticity (LL<50 and PI<20) fine grain soils to be used in MSE Wall construction. However, the use of fine-grained soils can result in poor internal and surface drainage, as well as time dependent movements of the MSE Wall and related components. If fine grained low plasticity soils are used for MSE Wall backfill, we recommend additional internal drainage such as a chimney drain should be incorporated into the final wall design.

The preceding paragraphs and tables are intended to provide a general overview of the design and construction of the MSE Walls. Specific guidance regarding the design and construction of MSE Walls can be found in the current edition of the NCMA Design Manual for Segmental Retaining Walls. The information provided above does not alleviate the MSE Wall designer from any aspect of the design including selection of shear strength parameters, internal wall stability, external wall stability, global stability or settlement estimates.

6. CONSTRUCTION CONSIDERATIONS

6.1. Site Preparation

Prior to construction, the proposed construction area should be stripped of all topsoil, organic material, existing undocumented fill within the building footprint, and other soft or unsuitable material. Upon completion of these razing and stripping operations, the exposed subgrade in areas to receive fill should be proofrolled with a loaded dump truck or similar pneumatic-tired vehicle having a loaded weight of approximately 25 tons. After excavation, the exposed subgrades in cut areas should be similarly proofrolled.

Proofrolling operations should be performed under the observation of a geotechnical engineer or his authorized representative. The proofrolling should consist of two (2) complete passes of the exposed areas, with each pass being in a direction perpendicular to the preceding one. Any areas which deflect, rut or pump during the proofrolling, and fail to be remedied with successive passes, should be undercut to suitable soils and backfilled with compacted fill.

The ability to dry wet soils, and therefore the ability to use them for fill, will likely be enhanced if earthwork is performed during summer or early fall. If earthwork is performed during winter or after appreciable rainfall then subgrades may be unstable due to wet soil conditions, which could increase the amount of undercutting required. Drying of wet soils, if encountered, may be accomplished by spreading and disking or by other mechanical or chemical means. Drying and stabilizing of wet soils by chemical means can generally be achieved by the addition of 2 to 4% lime or cement; however, each case should be analyzed based on soil types and conditions during construction.

6.2. Fill Material and Placement

The project fill should be soil that has less than five percent organic content and a liquid limit and plasticity index less than 50 and 30, respectively. Soils with Unified Soil Classification System group symbols of SP, SW, SM, SC, and ML are generally suitable for use as project fill. Soils with USCS group symbol of CL that meet the restrictions for liquid limit and plasticity index are also suitable for use as project fill. Soils with USCS group symbol of MH or CH (high plasticity soil) or corrosive soils are generally not suitable for use as project fill.

Charlotte, North Carolina ECS Project No. 08-11868 Page 13 December 5, 2016

The fill should exhibit a maximum dry density of at least 90 pounds per cubic foot, as determined by a standard Proctor compaction test (ASTM D-698). We recommend that moisture control limits of -3 to +2 percent of the optimum moisture content be used for placement of project fill with the added requirement that fill soils placed wet of optimum remain stable under heavy pneumatic-tired construction traffic. During site grading, some moisture modification (drying and/or wetting) of the onsite soils will likely be required.

Project fill should be compacted to at least 95 percent of its standard Proctor maximum dry density except within 24 inches of finished soil subgrade elevation beneath slab-on-grade and pavements. Within the top 24 inches of finished soil subgrade elevation beneath slab on grade and pavements, the approved project fill should be compacted to at least 100 percent of its standard Proctor maximum dry density. Aggregate base course (ABC stone) should be in accordance with NCDOT 2012 Standard Specifications Section 1005 Table 1005-1 and should be compacted to 95 percent of modified Proctor maximum dry density. However, for isolated excavations around footing locations or within utility excavations, a hand tamper will likely be required. ECS recommends that field density tests be performed on the fill as it is being placed, at a frequency determined by an experienced geotechnical engineer, to verify that proper compaction is achieved.

The maximum loose lift thickness depends upon the type of compaction equipment used. The table below provides maximum loose lifts that may be placed based on compaction equipment.

LIFT THICKNESS RECOMMENDATIONS

Equipment Maximum Loose Lift

Thickness, in.

Large, Self-Propelled Equipment (CAT 815, etc.) 8 Small, Self-Propelled or Remote Controlled (Rammax, etc.) 6

Hand Operated (Plate Tamps, Jumping Jacks, Wacker-Packers) 4

ECS recommends that fill operations be observed and tested by an engineering technician to determine if compaction requirements are being met. The testing agency should perform a sufficient number of tests to confirm that compaction is being achieved. For mass grading operations we recommend a minimum of one density test per 2,500 SF per lift of fill placed or per 1 foot of fill thickness, whichever results in more tests. When dry, the majority of the site soil should provide adequate subgrade support for fill placement and construction operations. When wet, the soil may degrade quickly with disturbance from construction traffic. Good site drainage should be maintained during earthwork operations to prevent ponding water on exposed subgrades.

We recommend at least one test per 1 foot thickness of fill for every 100 linear ft of utility trench backfill. Where fill will be placed on existing slopes, we recommend that benches be cut in the existing slope to accept the new fill. All fill slopes should be overbuilt and then cut back to expose compacted material on the slope face. While compacting adjacent to below-grade walls, heavy construction equipment should maintain a horizontal distance of 1(H):1(V). If this minimum distance cannot be maintained, the compaction equipment should run perpendicular, not parallel to, the long axis of the wall.

Charlotte, North Carolina ECS Project No. 08-11868 Page 14 December 5, 2016

6.3. Foundation Construction & Testing

Foundation excavations should be tested to confirm adequate bearing prior to installation of reinforcing steel or placement of concrete. Unsuitable soils should be undercut to firm soils and the undercut excavations should be backfilled with compacted controlled fill. Exposure to the environment may weaken the soils at the footing bearing level if the foundation excavations remain open for too long a time; therefore, foundation concrete should be placed the same day that foundations are excavated. If the bearing soils are softened by surface water intrusion or exposure, the softened soils must be removed from the foundation excavation bottom immediately prior to placement of concrete. If the excavation must remain open overnight, or if rainfall becomes imminent while the bearing soils are exposed, a 1- to 3-inch thick "mud mat" of "lean" concrete may be placed on the bearing surface to protect the bearing soils. The mud mat should not be placed until the bearing soils have been tested for adequate bearing capacity.

Foundations undercut should be backfilled with engineered fill. If lean concrete is placed within the undercut zone, the foundation footprint does not require oversizing. However, if soil or ABC stone is used in lieu of lean concrete, the foundation footprint should be oversized on a 1V:1H scale.

We recommend testing all shallow foundations to confirm the presence of foundation materials similar to those assumed in the design. We recommend the testing consist of hand auger borings with Dynamic Cone Penetrometer (DCP) testing performed by an engineer or engineering technician.

7. GENERAL COMMENTS

The borings performed at this site represent the subsurface conditions at the location of the borings only. Due to the prevailing geology and presence of existing undocumented fill, changes in the subsurface conditions can occur over relatively short distances that have not been disclosed by the results of the borings performed. Consequently, there may be undisclosed subsurface conditions that require special treatment or additional preparation once these conditions are revealed during construction.

Our evaluation of foundation support conditions has been based on our understanding of the site and project information and the data obtained in our exploration. The general subsurface conditions utilized in our foundation evaluation have been based on interpolation of subsurface data between and away from the test holes. If the project information is incorrect or if the structure locations (horizontal or vertical) and/or dimensions are changed, please contact us so that our recommendations can be reviewed. The discovery of any site or subsurface conditions during construction which deviate from the data outlined in this exploration should be reported to us for our evaluation. The assessment of site environmental conditions for the presence of pollutants in the soil, rock, and groundwater of the site was beyond the scope of this exploration.

The recommendations outlined herein should not be construed to address moisture or water intrusion effects after construction is completed. Proper design of landscaping, surface and subsurface water control measures are required to properly address these issues. In addition, proper operation and maintenance of building systems is required to minimize the effects of moisture or water intrusion. The design, construction, operation, and maintenance of waterproofing and dampproofing systems are beyond the scope of services for this project.

Site Vicinity Map

Boring Location Diagram

Laboratory Testing Summary

Borelogs

Pavement Design Analysis

SHWT Report

ASFE Documents

APPENDIX

B-1

S-2 3.50 - 5.00 25.5 ML 48 33 15

B-2

S-2 3.50 - 5.00 27.2

B-4

S-2 3.50 - 5.00 38.0 MH 58 44 14

B-7

S-3 6.00 - 6.00 30.1

Laboratory Testing Summary

Notes: 1. ASTM D 2216, 2. ASTM D 2487, 3. ASTM D 4318, 4. ASTM D 1140, 5. See test reports for test method, 6. See test reports for test method

Definitions: MC: Moisture Content, Soil Type: USCS (Unified Soil Classification System), LL: Liquid Limit, PL: Plastic Limit, PI: Plasticity Index, CBR: California Bearing Ratio, OC: Organic Content (ASTM D 2974)

Project No. 11868

Project Name: NCANG C-17 Hangar Project - GEO

PM: Michael R. Bailey

PE: Lee J. McGuinness

Printed On: Monday, November 07, 2016

Sample Source

Sample Number

Depth (feet)

MC1

Soil

Type2 LL

Atterberg Limits3

PL PI

Percent Passing No. 200 Sieve4

Maximum Density

(pcf)

Moisture - Density (Corr.)5

Optimum Moisture

CBR

Value6 Specific Gravity

S-1

S-2

S-3

S-4

S-5

S-6

SS

SS

SS

SS

SS

SS

Concrete Depth [10.5"]

(CL FILL) SANDY CLAY, Reddish Brown, Moist, Stiff

(ML) RESIDUAL- SANDY SILT, Reddish Brown, Moist, Stiff

(ML) SANDY SILT, Reddish Brown to Brown, Moist, Medium Stiff to Stiff

END OF BORING @ 20.0'

10 4833 25.5

CLIENT

Jacobs Global Buildings

JOB #

11868

BORING #

B-1

SHEET

PROJECT NAME

NCANG C-17 Hangar Project - GEO

ARCHITECT-ENGINEER

SITE LOCATION

1st Union Road, Charlotte, Mecklenburg County, NC

NORTHING EASTING STATION

THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN-SITU THE TRANSITION MAY BE GRADUAL.

WL GNE WS WD BORING STARTED 10/28/16 CAVE IN DEPTH @ 16.1'

WL(SHW) WL(ACR) GNE BORING COMPLETED 10/28/16 HAMMER TYPE Manual

WL RIG ATV FOREMAN Trevor DRILLING METHOD 2.25 H.S.A.DRILLING METHOD 2.25 H.S.A.

D E

P T

H

F T

S A

M P

L E

N O

S A

M P

L E

T Y

P E

S A

M P

L E

D

IS

T (I

N

R E

C O

V E

R Y

IN

SURFACE ELEVATION

DESCRIPTION OF MATERIAL

W A

T E

R L

E V

E L S

E L E

V A

T

IO

N

F T

B L O

W S

/6

10 20 30 40 50+

20% 40% 60% 80% 100%

1 2 3 4 5+

ENGLISH UNITS

BOTTOM OF CASING LOSS OF CIRCULATION

CALIBRATED PENETROMETER TONS/FT2

PLASTIC

LIMIT %

WATER

CONTENT %

LIQUID

LIMIT %

ROCK QUALITY DESIGNATION & RECOVERY

RQD% REC.%

STANDARD PENETRATION

BLOWS/FT727

SHWT Identified at Approx. 11.6FT bvoigt Line

S-1

S-2

S-3

S-4

S-5

S-6

SS

SS

SS

SS

SS

SS

ASPHALT

(CH FILL) PLASTIC CLAY, Reddish Brown, Moist, Stiff

(ML) RESIDUAL- SANDY SILT, Brown to Light Brown, Moist, Medium Stiff to Stiff

(ML) SANDY SILT, Light Brown, Moist, Medium Stiff

END OF BORING @ 20.0'

27.2

CLIENT

Jacobs Global Buildings

JOB #

11868

BORING #

B-2

SHEET

PROJECT NAME

NCANG C-17 Hangar Project - GEO

ARCHITECT-ENGINEER

SITE LOCATION

1st Union Road, Charlotte, Mecklenburg County, NC

NORTHING EASTING STATION

THE STRATIFICATION LINES REPRESENT THE APPROXIMATE BOUNDARY LINES BETWEEN SOIL TYPES. IN-SITU THE TRANSITION MAY BE GRADUAL.

WL GNE WS WD BORING STARTED 10/28/16 CAVE IN DEPTH @ 16.8'

WL(SHW) WL(ACR) GNE BORING COMPLETED 10/28/16 HAMMER TYPE Manual

WL RIG ATV FOREMAN Trevor DRILLING METHOD 2.25 H.S.A.DRILLING METHOD 2.25 H.S.A.

D E

P T

H

F T

S A

M P

L E

N O

S A

M P

L E

T Y

P E

S A

M P

L E

D

IS

T (I

N

R E

C O

V E

R Y

IN

SURFACE ELEVATION

DESCRIPTION OF MATERIAL

W A

T E

R L

E V

E L S

E L E

V A

T

IO

N

F T

B L O

W S

/6

10 20 30 40 50+

20% 40% 60% 80% 100%

1 2 3 4 5+

ENGLISH UNITS

BOTTOM OF CASING LOSS OF CIRCULATION

CALIBRATED PENETROMETER TONS/FT2

PLASTIC

LIMIT %

WATER

CONTENT %

LIQUID

LIMIT %

ROCK QUALITY DESIGNATION & RECOVERY

RQD% REC.%

STANDARD PENETRATION

BLOWS/FT726

No SHWT Identified to 20FT

S-1

S-2

S-3

S-4

S-5

S-6

SS

SS

SS

SS

SS

SS

ASPHALT

CONCRETE [10.5"]

(CL FILL) SANDY CLAY, Reddish Brown, Moist, Stiff

(ML FILL) SANDY SILT, Reddish Brown, Moist, Medium Stiff

(ML) RESIDUAL-SANDY SILT, Brown to Light Brown, Moist, Medium Stiff to Stiff

END OF BORING @ 20.0'

CLIENT

Jacobs Global Buildings

JOB #

11868

BORING #

B-3

SHEET

PROJECT NAME

NCANG C-17 Hangar Project - GEO

ARCHITECT-ENGINEER

SITE LOCATION

1st Union Road, Charlotte, Mecklenburg County, NC

NORTHING…