18R0026-SpecsVol3-RTA.pdf

RFP W912BU-18-R-0026

US Army Corps of Engineers Philadelphia District

Construct Aircraft Maintenance Hangar

Dover Air Force Base, Delaware

Volume 3 of 3

Construction Solicitation and Specifications

19 February 2019

This page was intentionally left blank for duplex printing.

Appendices Index

TABLE OF CONTENTS

APPENDICES

B-43 GEOTECHNICAL EVALUATION REPORT

Appendix B-43

APPENDIX B-43

GEOTECHNICAL EVALUATION REPORT

Geotechnical Evaluation Maintenance Hangar Dover Air Force Base

Dover, Delaware

July 20, 2017 (Revised December 12, 2017)

Appendix B-43 - Page 1

Appendix B-43 - Page 2

The following report summarizes Duffield Associates, Inc.’s (Duffield) Geotechnical Evaluation for the proposed maintenance hangar at the Dover Air Force Base in Dover, Delaware. This report includes information regarding the field and laboratory-testing programs, the subsurface conditions encountered, and recommendations for the design and construction of the proposed building foundations and slab-on-grade.

The analysis and conclusions presented herein relate to the proposed maintenance hangar facility.

The proposed building is anticipated to be constructed at grade and will have footprint of approximately 85,000 square feet and will contain a large open bay area for aircraft maintenance, as well as offices and electrical and mechanical rooms. Structural loads for the maintenance hangar are anticipated to be on the order of 335 kips for hangar bay columns, 50 kips for office and equipment columns, and 2 to 2.5 kips per foot for wall loads. Aircraft static single wheel loads are anticipated to range between approximately 15 and 25 tons each. Jacks utilized during aircraft maintenance may experience loads on the order of 60 tons. Additional construction at the site includes an exterior concrete apron and bituminous concrete parking lot and access roads for passenger vehicles.

Beneath surficial layers of topsoil and bituminous concrete pavement, the subsurface conditions observed can generally be described as a relatively thin layer of fill overlying predominately natural coarse soils. The fill appeared to be variable in consistency and was observed to depths ranging between approximately 1 to 4.5 feet below the existing ground surface. Beneath the fill, the sand stratum appeared to generally be loose to medium dense with varying amounts of silt and gravel, with occasional stilt lenses. This stratum was underlain by a 4 to 8 foot layer of soft to medium consistency high-plasticity silts and clays overlying a sand layer. In the deeper test boring performed, a layer of high-plasticity silt/clay was observed at depths ranging between 28 and 42 feet to the extent of the test borings.

Based on the observed subsurface conditions and the design information provided by the project team, Duffield provides these comments and recommendations:

The fill materials observed in the test borings were likely placed during previous construction and building demolition, and may have not been placed as controlled structural fill. Due to the uncertainty associated with existing fill, it is recommended that the fill be removed in its entirety from beneath the maintenance hangar building pad and foundation areas. It may be suitable to construct vehicle passenger parking lot areas on the fill, depending on the conditions observed during construction.

The variation in loading conditions across the building area, as well as variability in thickness, depth, and consistency of the highly plastic silt and clay strata may result in total settlements of 1 ½ to 2 inches, and differential settlements of ½ to 1 ¼ inches. Post-construction settlements (consolidation of high-plasticity soils) may be between 1 and 1 ¼ inches. If these settlement tolerances are acceptable to the structural engineer, the proposed maintenance

Appendix B-43 - Page 3 hangar could be supported on a conventional shallow foundation system and slab-on-grade without system. Foundations should be designed for a maximum allowable bearing pressure of 2,000 psf.

If settlement magnitudes are not within tolerances for the proposed structure, implementing a ground improvement program, such as stone columns or aggregate piers (also known as “rammed aggregate piers” or “vibro stone columns”) could be considered a suitable approach to reducing settlement potential and providing uniform bearing conditions for construction of a shallow footing and slab on grade foundation system. Ground improvement utilizing rammed aggregate piers would involve the construction of piers, of stone aggregate penetrated through the surficial soils and compressible high plasticity silts and clays of Stratum E to the sand soils of Stratum F encountered at a depth of 12 to 18 feet below existing grade. Depending on the improvement plan selected, total settlements on the order of 1 inch and post-construction settlements on the order of ½ inch or less may be achievable.

If this type of ground improvement program is considered, Duffield recommends installing the stone columns throughout the entire building pad area.

It is Duffield’s opinion that a deep foundation system, such as augered cast-in-place (ACIP) piles or driven timber piles are not considered practical at the site, due to the depth and extent of the deeper high-plasticity stratum observed in the deeper test borings performed.

More detailed conclusions and recommendations for design and construction of the foundations, building slabs, and pavement areas are provided in the following report.

Appendix B-43 - Page 4

Duffield has completed our geotechnical evaluation for the proposed Maintenance Hangar at the Dover Air Force Base in Dover, Delaware. The following describes the subsurface conditions observed at the site and our recommendations for the design and construction of the proposed building foundations and site pavements. These services were provided in general accordance with our agreement dated September 26, 2016.

A drawing titled “Dover Air Force Base Aircraft Maintenance Facility, Compressive Floor Plan,” prepared by Michael Baker International, marked “35% Design Submission” on May 1, 2017.

Page 3-6, Figure 3-2 titled “Aircraft Tire Pressure and Ground Loading,” from a document titled “TO 1C-17A-2-00GV-00-1,” undated, which indicates aircraft wheel loading conditions.

Pages from a Malabar International manual for “Model 8730B, 60 Ton Fixed Height Tripod Jack,” dated October 2012.

A document titled “Milcon Planning Charette Report (PCR), FY17 Aircraft Maintenance Hangar, Dover AFB, Delaware, Project No. FJXT13300,” prepared by Michael Baker International, Inc., dated August 8, 2016.

A document titled “Scope of Work, Project Number FJXT133000, FY17 Aircraft Maintenance Hangar Design, Dover AFB, DE,” dated September 1, 2016.

A document titled “Section 01 10 00, A10 Foundations/Floor Slabs, Project Specification Requirements”, provided via electronic mail by Michael Baker on July 7, 2017.

Report prepared by Duffield titled “Geotechnical Investigation, Dover Air Force Base, Dover, Delaware, USACE Contract No. W912BU-11-D0005,” Project No. 8919.GC, dated November 2012.

The project consists of the construction of an approximately 85,000-square-foot maintenance hangar. The proposed structure will contain offices and electrical and mechanical rooms and will contain a large open bay area for aircraft structures.

The proposed building will be constructed at-grade (i.e., no basement level is currently proposed).

At the time of this report, the proposed finished floor elevation was not provided. It is assumed the finished floor elevation will be similar to that of the existing grades, and will require minor regrading (i.e., net cut/fills on the order of 3 feet).

The proposed hangar will consist of structural steel framing with a truss roof system.

Appendix B-43 - Page 5

Structural loads, provided by Michael Baker International, are as follows:

o For the hangar bay columns, typical column loads are estimated to be on the order of 335 kips. The office and equipment areas column loads are anticipated to be on the order of 50 kips;

o Wall loads for the hangar and office areas are anticipated to range between 2 to

2.5 kips per foot;

o Maximum aircraft weight of 585,000 pounds. Maximum static single wheel loads for the aircraft structures are anticipated to range between 29,200 and 49,000 pounds each for the nose and main landing gear wheels, respectively; and o The referenced jack manual indicates jacks utilized during aircraft maintenance may experience loads on the order of 60 tons.

Additional site improvements consist of proposed grass and bituminous concrete pavement vehicle parking lot areas.

The site is located at the Dover Air Force Base in Dover, Delaware.

The location of the proposed hangar is currently occupied by existing grass and bituminous concrete pavement areas.

An existing 1-story building (Building 913), located in the south-west vicinity of the proposed structure was observed to be undergoing demolition during the current evaluation field program. A 2-story building (Building 914), which was formerly located in the footprint of the proposed hangar, was demolished prior to Duffield’s current evaluation.

In addition to the recently demolished buildings located in the vicinity of the proposed hangar, bituminous concrete parking lot areas and several portland cement concrete pads have been removed from the site. Several existing utilities were delineated in the field and identified during the 201 geophysical evaluation (summarized in our 2012 report) and are located within the footprint of the proposed hangar structure.

The site is relatively flat with existing ground surface elevations ranging between approximately 25 to 30 feet (project datum).

Appendix B-43 - Page 6

Duffield performed a previous evaluation at the site, which is summarized in the referenced report titled “Geotechnical Investigation, Site Investigations, Maintenance Hangar, Dover Air Force Base, Dover, Delaware, USACE Contract No. W912BU-11-D0005,” dated November 1, 2012. The evaluation was performed to review the subsurface conditions at the site and provide preliminary design and construction recommendations for the hangar.

The footprint, location, and design of the hangar has been revised since our previous evaluation.

The previous evaluation at the site consisted of the following:

o Geophysical survey of the site including electromagnetic scanning and ground penetrating radar technologies. The geophysical survey was performed between August 18 and 22, 2011 by a subconsultant to Duffield to evaluate the presence of subsurface utilities and anomalies at the site.

o Between September 26 and October 13, 2011, nine Standard Penetration Test borings (B-1, B-1A, and B-2 through B-8) performed in the original proposed building and pavement areas to depths ranging between approximately 10 to 50 feet below the existing ground surface. Two hand-auger borings and two auger borings were performed at the site for additional sample collection.

o Based on observations made during the geophysical survey, five areas were identified as “potential underground storage tanks”. On November 21, 2011, ten “minimally intrusive excavations,” were performed in the five areas utilizing an air/vacuum-extraction system to depths ranging between approximately 4 to 10 feet below the existing ground surface.

In nine of the locations, apparent metal pipes were observed at depths ranging between approximately 4 to 7.3 feet.

o Following completion of the geophysical survey, borings, and minimally intrusive excavations, “as-built” survey was performed at the locations by a subconsultant to Duffield.

o Samples collected during the field program were returned to Duffield Associates’ laboratory for index and property testing on selected samples. The test boring logs and results of the laboratory testing are included herein.

Between April 18 and 26, 2017, eleven (11) Standard Penetration Test (SPT) borings were performed in general accordance with ASTM D 1586 in the vicinity of the proposed building and pavement areas.

Appendix B-43 - Page 7 o Test borings B-9 through B-17 were performed to depths ranging between approximately 20 and 51 feet below the existing ground surface in the proposed maintenance hangar building area.

o Test borings B-18 and B-19 were performed to depths of approximately 10 feet below the existing ground surface in proposed pavement areas.

The test borings were performed by CGC Geoservices, LLC, an affiliate company of Duffield, utilizing an ATV-mounted Diedrich D-50 drill rig with hollow-stem augers and mud-rotary drilling techniques.

The approximate test boring locations are indicated on the enclosed Test Boring Location Sketch. Test boring logs, which describe the conditions observed during the field exploration program, are enclosed.

During the performance of the geophysical survey performed in the previous evaluation at the site, three anomalies were identified as “small metal anomalies”. Duffield reviewed the performance of three minimally intrusive excavations in the vicinity of the previously identified anomalies. The excavations were performed on April 17, 2017, by Underground Services, Inc., a subcontractor to Duffield, utilizing an air/vacuum extraction system to depths ranging between approximately 4.5 to 8 feet below the existing ground surface. In one excavation (SD-13/A-3), an approximately 6 to 8-inch diameter metal pipe was observed at a depth of approximately 4.5 feet below the existing ground surface. In the other locations, no obstructions or utilities were observed during vacuum extraction.

Following the test-boring program, the samples were returned to Duffield’s office and laboratory testing was performed on the selected samples. The results of the laboratory testing are summarized in the enclosed Summary of Laboratory Testing Results table located in the appendices. The results of environmental testing, which was performed on selected samples, will be summarized under a separate cover.

In addition to the laboratory testing performed during the current evaluation, results of laboratory testing performed during the 2012 evaluation are enclosed and were utilized during this evaluation.

Appendix B-43 - Page 8

Based on review of regional mapping by the Delaware Geological Survey and U.S. Geological Survey, the site of the proposed hangar building is located within the Atlantic Coast Plan Geologic Province. The Atlantic Coastal Plain is characterized by sedimentary deposits of fine and coarse-grained soils. The sediments at the site consist predominantly of the Columbia Formation comprised of fluvial sands and gravels in the uppermost deposits. Depth to weathered bedrock in the area of the site is estimated be on the order of 2,000 to 3,000 feet below the existing ground surface.

Beneath surficial layers of topsoil and bituminous concrete pavement, the subsurface conditions observed can generally be described as a relatively thin layer of fill overlying predominately natural coarse soils. The fill appeared to be variable in consistency and was observed to depths ranging between approximately 1 to 4.5 feet below the existing ground surface. Beneath the fill, the sand stratum appeared to generally be loose to medium dense with varying amounts of silt and gravel, with occasional stilt lenses. This stratum was underlain by a 4 to 8 foot layer of soft to medium consistency high-plasticity silts and clays overlying a sand layer. In test borings B-9, B-12, B-15, and B-17, a layer of high-plasticity silt/clay was observed at depths ranging between 28 and 42 feet to the extent of the test borings.

For discussion purposes, the subsurface conditions can be further described as follows:

Appendix B-43 - Page 9

Groundwater was observed in the test boring locations performed during the current evaluation at depths ranging from approximately 6 to 14 feet below the existing ground surface. Groundwater was observed in the previous evaluation at depths ranging between approximately 4.5 and 10 feet below the existing ground surface.

Groundwater mapping information provided by the Delaware Geologic Information Resource indicates that groundwater in the areas of the proposed maintenance hangar may be encountered at depths of less than 3 feet in “normal and wet conditions.” Groundwater levels at the site will be affected by seasonal and annual variations in precipitation. It is estimated that variations in groundwater levels several feet higher or lower than those observed during this evaluation could be experienced during extreme variations in precipitation. Because of the interbedding of coarse-grained materials within the silt/clay strata, it is possible that localized perched groundwater conditions at shallower depths may be encountered during excavation.

SUBSURFACE

STRATUM

APPROXIMATE

THICKNESS (FEET)

GENERALIZED DESCRIPTION[1]

A 0.3 – 1.8 TOPSOIL (approximately 3 to 21 inches) or BITUMINOUS CONCRETE/GRADED AGGREGATE (approximately 12 inches)

B[2] 1.0 – 5.0 FILL/POSSIBLE FILL: varies between fine and coarse-grained materials with no observed debris; (moist, medium to dense or medium to stiff consistency)

C[3] 1.0 – 3.5 Brown, gray SILT, some to trace fine to medium sand, trace gravel (moist, medium to stiff consistency); USCS: ML

D 1.0 – 7.0 Gray, red-brown fine SAND, trace to and silt, some to trace medium to coarse sand, trace gravel (moist to wet, medium dense); USCS: SM, SP-SM, SP

E[4] 4.0 – 8.0 Dark gray SILT/CLAY, trace fine sand, trace organics (soft to medium consistency); USCS: MH, CH

F[4] 14.0 – 23.0 Light gray fine SAND, trace to some silt, trace to some gravel, trace to some medium to coarse sand (wet, loose to medium dense); USCS: SM, SP-SM

G[5] --- Dark gray SILT/CLAY, trace fine sand, trace organics (moist, medium to stiff consistency); USCS: MH, CH

Notes: 1. The soil descriptions utilized herein and on the test boring logs are defined in the attached General Notes.

2. Stratum B not observed in B-17, B-18, or B-19.

3. Stratum C only observed in B-10 and B-18, interlayered in Stratum D.

4. Strata E and F not observed in B-18 and B-19.

5. Stratum G observed in B-9, B-12, and B-17 and not fully penetrated.

Appendix B-43 - Page 10

The “fill” materials of Stratum B were observed in several of the test borings performed during this evaluation and the previous evaluation to depths on the order of approximately 5 feet below the existing ground surface. Due to the variability in fill material texture and consistency, it is possible that the fill material was not placed and compacted in a controlled manner, as structural fill. Consequently, there is inherently more uncertainty in assessing the engineering characteristics of these fill materials and there is a greater risk of detrimental differential settlement for foundations and a slab-on-grade bearing on these soils than on engineered fill or undisturbed soils. Therefore, it is generally not recommended to support structures over uncontrolled fill. However, it may be practical to construct proposed passenger vehicle pavement areas above the Stratum B fill if the subgrade conditions are firm, dry, and free of debris and organic material prior to placement of structural fill. These materials may require additional densification prior to placement of pavement stone base section, and should be proofrolled, as recommended herein, following rough grading, and prior to placement of structural fill.

Based on the field and laboratory testing programs performed during the 2012 and current evaluations, the site is underlain by a layer of compressible high plasticity silt and clay (Stratum E), which was observed to have a thickness ranging between 4 to 8 feet. This stratum was encountered at a depth of approximately 8 to 12 feet below the existing ground surface.

Consolidation testing was performed on four Shelby Tube samples collected during the 2012 evaluation, and on one sample collected during the current evaluation within the area of the proposed maintenance hangar facility. The consolidation testing results indicate that this stratum will exhibit relatively small vertical settlement if the loading conditions applied during and following construction are less than the maximum load that the soil has experienced over geological time. The maximum geologic load is referred to as the “preconsolidation pressure”.

Based on the assumed minor site grading required to achieve proposed grades (i.e., cut/fills on the order of 3 feet), structural loading conditions provided, consolidation results, and the varying depth to the Stratum E compressible soils, analysis indicates that the proposed construction will not induce loads that exceed the pre-consolidation pressure.

It is noted that Stratum G, a high-plasticity silt soil underlies the site at depths of greater than 30 feet. Due to the depth at which this was encountered, it is anticipated that potential consolidation of this layer due to the proposed building loads will not result in detrimental magnitudes of total or differential foundation settlement. However, it is Duffield’s opinion that a deep foundation system, such as augered cast-in-place (ACIP) piles or driven timber piles are not considered practical at the site, due to the depth and extent of the deeper high-plasticity stratum observed in the deeper test borings performed.

Appendix B-43 - Page 11

It is Duffield’s opinion that the “natural” site soils consisting of the medium stiff or stiffer silt (Stratum C) and medium dense or denser sand (Stratum D), observed beneath the topsoil and bituminous concrete (Stratum A) and fill (Stratum B), are generally suitable for supporting the proposed maintenance hangar on a shallow foundation system. The existing fill material, where encountered during construction of the maintenance hangar should be removed in its entirety from the building area. Structural fill, placed and compacted above natural site soils, as recommended herein, is also considered suitable for shallow foundation construction and slab-on-grade systems.

Analysis indicates that the maintenance hangar foundations bearing on the natural soils or on compacted structural fill could be sized for a maximum allowable bearing pressure on the order of 2,000 pounds per square foot (psf). This analysis has assumed a shallow foundation system with a minimum width of 3 feet for isolated footings and 2 feet for continuous footings, and a minimum burial depth of 18 inches for interior footings and a minimum of 32 inches for exterior footings.

Estimates of foundation settlement were performed to aid in evaluating the effects of the structural loads on the subsurface conditions. Based on foundation loads and variable subsurface conditions, it is estimated that the structure, supported by a conventional shallow spread footing foundation system, would experience total settlement magnitudes in the footing areas ranging from approximately 1½ to 2 inches. Post-construction settlement (consolidation of the high plasticity Stratum E) are estimated be range between ¾ to 1¼ inch in the footing areas and on the order of 1 inch in slab-on-grade areas experiencing higher-concentrated loads (i.e., beneath aircraft wheels). These magnitudes of settlement are due primarily to consolidation of the high plasticity Stratum E. Differential settlement across the building pad area could range between 1 to 1 ¼ inches due to variable soil conditions and differences in loading between hangar and office areas, as well as non-uniform loading conditions across the slab. There is also an increased potential for differential settlement across portions of the site that were previously occupied by existing buildings, because the soils may have experienced more load-induced settlement.

If the design structural loading is different than that assumed herein, the estimated settlement magnitude may also be different. The design team should review the loads assumed herein and the estimated settlement magnitudes, and compare them with the design conditions and the tolerances established for the structure. If the loading conditions assumed herein are not accurate, additional analysis may be required to evaluate the settlement magnitude under the design conditions.

The estimated magnitudes of total and differential settlement discussed above are generally higher than typical tolerance limits for similar type structures. However, the actual settlement

Appendix B-43 - Page 12 tolerance of the building should be verified with the project’s structural engineer prior to construction.

If settlement tolerances are considered to be unacceptable, it is Duffield’s opinion that a ground improvement plan such as construction of stone columns or aggregate piers (also known as “rammed aggregate piers” or “vibro stone columns”) may be a suitable approach to reducing settlement potential and providing uniform bearing conditions for construction of a shallow footing and slab on grade foundation system. Ground improvement utilizing rammed aggregate piers would involve the construction of piers of stone aggregate penetrated through the surficial soils and compressible high plasticity silts and clays of Stratum E to the sand soils of Stratum F encountered at a depth of 12 to 18 feet below existing grade. This soil improvement technique generally involves driving a mandrel through the unsuitable boring soils and subsequently filling the void created by the mandrel with stone, compacted in a number of lifts with a hydraulic ram during the extraction of the mandrel.

A ground improvement system typically allows for standard construction practices following improvement program and the construction of a stabilization layer (i.e., a stone and geogrid layer) to transition from the improved subgrade to the new construction. Depending on the scope of the ground improvement program, a shallow foundation system constructed over an “improved subgrade” typically could be designed for an allowable bearing capacity on the order of 3,000 to 4,000 pounds per square foot (psf) with post construction settlements on the order of 1 inch or less.

If the use of some type of ground improvement is to be considered further, Duffield can provide the names of several specialty contractors who have experience in the design and installation of different types of aggregate piers that can improve the foundation performance of the types of soils encountered at this site. Due to differences in the proprietary design and construction methods, the different specialty contractors will probably have varying approaches to improving the soils at the site, and therefore, it may be beneficial, economically, to further evaluate such a system.

Due to the limited grading information to date, it is assumed that only minor regrading (i.e., net cuts/fills on the order of 3 feet) will be required to achieve the finished pavement grades. Based on the test borings performed across the site, the shallow subsurface conditions generally consisted of coarse-grained miscellaneous fill material and natural fine and coarse-grained soils.

The predominately-shallow fine-grained soils observed during the performance of the test borings generally correspond to American Association of State Highway and Transportation Officials (AASHTO) classification A-4 and A-5, which are considered “poor” subgrade soils.

The shallow coarse-grained soils observed at the site, generally correspond to AASHTO classification A-1 and A-2, which are considered “good” subgrade soils. “Good” soils are considered better draining and less frost susceptible materials than the fine-grained “poor” subgrade materials.

Appendix B-43 - Page 13

1.

It is Duffield’s opinion that the natural site soils encountered below the surficial topsoil, bituminous concrete, and fill soils (Strata A and B, respectively) are generally considered suitable for supporting the proposed maintenance hangar on a shallow spread footing foundation and slab-on-grade system following subgrade preparation and review, as discussed further herein. Structural fill, placed, compacted and reviewed, as recommended in this report, is also considered suitable for supporting shallow foundations.

It is recommended that the proposed foundation be designed for a maximum net allowable bearing pressure of 2,000 pounds per square foot. Based on the results of the analysis performed as part of this evaluation, it is estimated that total foundation settlement for the proposed maintenance hangar should be between 1½ and 2 inches. Post-construction settlement is anticipated to range between 1 and 1¼ inches. Differential settlement is estimated to range between ½ and 1¼ inch across the site.

2.

As discussed further herein, ground improvement of the site soils supporting the hangar building footing and slab-on-grade is considered an alternative to reduce potential total and differential settlement estimated for a conventional shallow foundation system constructed over the existing, unimproved site soils. It is Duffield’s opinion that ground improvement across the building area, prior to construction of shallow foundations and slab-on-grade, could be achieved by utilizing stone columns such as rammed aggregate piers or vibro replacement stone column foundations, bearing in the Stratum F sand soils. These proprietary, performance based systems should be designed by a professional engineer registered in the State of Delaware.

3.

The miscellaneous fill materials of Stratum B may not consist of “engineered fill” (e.g., placed in controlled lifts and compacted to specified criteria). Due to their potential variability, previously placed uncontrolled fills are typically not considered suitable for supporting building foundations and should be removed in their entirety where encountered in the building pad area (defined as the areas extending a minimum of 5 feet beyond the footing perimeter).

4.

The base of all footings in areas exposed to frost should be placed at least 32 inches below final exterior grade.

Interior foundations in insulated areas should be placed at least 18 inches below the proposed finished floor elevation.

Appendix B-43 - Page 14

All continuous wall footings should be at least 2-feet wide, and all isolated column footings should be at least 3-feet wide, regardless of bearing pressure.

If a winter construction schedule is proposed for the foundations, provisions for the protection of shallow foundations from frost heave during construction should be included in the contract specifications.

5.

Ground-supported floor slabs should be designed as free floating and should not be connected to the other structural elements (e.g., walls, framing, etc.) of the buildings.

Isolation joints should be utilized at the interface of proposed ground-supported floor slabs and structural elements to accommodate potential differential settlement.

For the conventional “spread footing and slab-on-grade alternative”, to reduce the potential of detrimental slab movement due to compressible soils underlying the site and variable depths of structural fill needed to achieve finished grade, it is recommended that following final slab-on-grade subgrade preparation as outlined herein, it is recommended to construct a stone stabilization layer consisting of a biaxial geogrid (Synteen SF-11 or equivalent) installed over the prepared subgrade followed by placement of a minimum of 12 inches of Type B graded aggregate prior to the placement of drainage stone subbase.

A minimum 10-mil polyethylene vapor barrier and free-draining subbase, consisting of at least 4 inches of poorly graded crushed stone aggregate, such as AASHTO SP-57 stone, should be provided beneath all floor slabs.

Subgrade conditions for the “spread footing and slab-on-grade alternative”, should be modeled for design utilizing a subgrade modulus, KS of 150 pci, provided subgrade preparation is performed as recommended in this report.

6.

Based on the subsurface conditions encountered, during the field exploration at the site and the review of regional geologic maps, a “D” site classification is recommended for the analysis of seismic conditions, as defined by 1613.3.2 of the 2015 International Building Code and Chapter 20 of the American Society of Civil Engineers Minimum Design Loads for Buildings and Other Structures (ASCE/SEI 7-10).

7.

Masonry walls should be provided with frequent control joints placed at architecturally convenient locations (e.g., windows and doorways) to provide a “preferred” location for differential settlement to occur to reduce the potential for cracking of the walls.

Appendix B-43 - Page 15

8.

Based on the proposed construction and the observed depth to groundwater, it is not anticipated that significant amounts of groundwater will be encountered during construction of shallow foundations. Due to varying amounts of fine-grained soil and the previously placed fill encountered at the site, localized perched water conditions may be encountered at shallow depths, and stormwater could accumulate in open excavations or low areas during construction. It is recommended that wherever groundwater is encountered during excavations, the resulting excavation should be over-excavated by at least 4 inches and replaced with AASHTO SP-57 stone to protect the exposed subgrade soils and to facilitate sumping.

9.

The localized shallow fine-grained soils observed during the performance of the test borings generally correspond to American Association of State Highway and Transportation Officials (AASHTO) classification A-4 and A-5, which are considered “poor” subgrade soils. The localized areas of shallow coarse-grained soils observed in some test borings performed at the site, generally correspond to AASHTO classification A-1 and A-2, which are considered “good” subgrade soils. “Good” soils are considered better draining and less frost susceptible materials than the fine-grained “poor” subgrade materials.

California Bearing Ratio (CBR) testing was performed on a bulk sample recovered from B-13 and B-19 between the approximate depths of 0.0 feet to 2.0 feet to aid in determining the support values for the near surface soils observed at the site. Based on the results of the CBR testing and a target compactive density of 95% from the Modified Proctor test, a CBR value on the order of 6 is recommended for pavement section design.

It is recommended that a woven geotextile fabric (e.g., ACF HSP2, or equivalent) be placed between the pavement section aggregate base course and prepared subgrade. The purpose of this geotextile is to maintain the integrity of the pavement base course aggregate and reduce pavement maintenance. The woven geotextile fabric layer should be placed directly over the carefully prepared and reviewed subgrade. Adjacent rows of fabric should be overlapped a minimum of 24 inches. The fabric should be placed in a stretched (no wrinkles) state.

All pavement materials and construction should be in accordance with the requirements of the U.S. Air Force and USACE.

10.

Site grading should be designed to provide positive drainage away from the proposed construction area. Positive site drainage should be maintained throughout the construction activities.

Appendix B-43 - Page 16

11.

Existing utilities were encountered in the proposed building footprint during construction, and it is recommended that these utilities be removed and relocated outside of the building area. The resulting excavations for removed utilities should be backfilled with structural fill, placed and compacted in accordance with the recommendations of this report. Alternatively, existing pipes could be abandoned, left in place, and grouted “full.” If the utilities cannot be relocated outside of the proposed building area, or if new utilities are proposed, foundations should be designed to bear at, or below, the invert elevations of the pipe.

12.

This evaluation had been based on assumptions regarding design loads and grades for the proposed structure. The assumptions considered in this evaluation should be verified by the project team prior to the completion of their design. If the proposed loading or grading conditions vary from those considered herein, Duffield should be notified to possibly modify the recommendations provided herein as required.

Appendix B-43 - Page 17

Site preparation will be contingent in part for the foundation support alternative selected for the hangar and slab-on-grade. For the conventional “spread footing and slab-on-grade alternative”, at the start of construction, the building area site should be stripped of topsoil and previously placed uncontrolled fill, and rough excavated to proposed grades. Following rough grading and prior to footing excavation, placement of fill, or construction of the pavements or floor slabs, it is recommended that the exposed subgrade be proofrolled. The proofrolling should be performed using a minimum of two passes of a 10-ton static roller in the presence of a qualified soils technician working under the supervision of a geotechnical engineer. The purpose of the proofrolling is to identify yielding subgrade conditions. The proposed construction area should be proofrolled at least 10 feet beyond the construction perimeters.

Yielding, or otherwise unsuitable subgrade conditions encountered within the proposed building area, should be undercut to firm subgrade conditions and backfilled with compacted structural fill in accordance with the recommendations of this report. Alternatively, shallow yielding conditions, as determined by a qualified soils technician working under the supervision of a geotechnical engineer, could be stabilized through moisture conditioning of the exposed subgrade and recompaction. A qualified soils technician working under the supervision of a geotechnical engineer should confirm the consistency and texture of the exposed soils with the conditions encountered by this evaluation.

2.

All shallow foundations should be placed on firm, dry, non-frozen subgrade consisting of natural silt/clay soils of Stratum C or sand soils of Stratum D or on structural fill (or stabilization layer), placed and compacted as recommended herein. Foundation excavations should be reviewed by a qualified technician working under the supervision of a geotechnical engineer who is familiar with the recommendations of this report.

Subgrade review should be performed prior to the placement of reinforcing steel or concrete, and should verify the presence of medium stiff or stiffer silt/clay, medium dense or denser sands, or structural fill placed and compacted as recommended herein. If these conditions are not encountered at the proposed foundation depth, additional excavation should be performed until they are uniformly encountered across the base of the foundation’s excavation or, if acceptable to the project geotechnical engineer, the natural sand soils can be densified in place. Foundation undercut areas should be backfilled with structural fill as recommended herein.

Appendix B-43 - Page 18

3.

The quality of ground improvement during stone column installation is highly dependent on the construction method and appropriate construction quality control. Only contractors that can demonstrate experience in the installation of the propriety stone column ground improvement for similar projects and subsurface conditions should be allowed to bid on this project. Prior to the start of construction, the contractor should submit ground improvement design including analysis, details, specification and a quality control plan signed and sealed by a Delaware registered professional engineering for review and approval by the Owner’s representative as well as proposed installation and construction quality control methods.

A qualified engineering technician should be on site during construction to review installation.

The technician should maintain records of installation depth, compaction effort, and stone quality and quantity, and well as document the implementation of the submitted quality control plan.

4.

On-site soils free of organic material, topsoil, miscellaneous fill, debris, and rock fragments in excess of 3 inches in their largest dimension may be suitable as structural fill.

A majority of the on-site materials that will be available as fill from the excavations will consist of coarse-grained fill material of Stratum B and sand soils of Stratum D. These soils are considered suitable for backfill, as long as the moisture content of the soils is within the range in which the specified compaction requirements can be achieved.

If sufficient quantities of suitable on-site soils are not available for structural fill, imported borrow consisting of predominately granular soils conforming to the requirements of Delaware Department of Transportation Standard Specifications Borrow Type C (Backfill) should be utilized. AASHTO SP-57 stone could also be utilized as structural fill at locations, as recommended by the project engineer, and should be considered for localized, relatively deep fills such as foundation undercuts or utility trenches and as a base beneath the slabs.

5.

Structural fill should be placed in loose lifts with a maximum thickness of 8 inches.

Each lift of fill placed within the proposed building construction area (defined as the area extending at least 5 feet beyond the foundation element perimeters) and the site pavements should be compacted to at least 95% of the maximum dry density, as determined by the Modified Proctor test (ASTM D 1557).

Structural fill for utility trenches located outside of the proposed construction areas should be compacted to at least 90% of the Modified Proctor maximum dry density.

The placement and compaction of structural fill should be monitored on a full-time basis by a qualified technician working under the supervision of a geotechnical engineer.

Appendix B-43 - Page 19

6.

All utility and foundation excavation should be performed in accordance with OSHA guidelines.

Typically, medium stiff or stiffer silt/clay soils can be characterized by OSHA CFR Part 1926 Excavation Standards as Type C soils, and granular soils and previously placed fill can be characterized by OSHA CFR Part 1926 Excavation Standards as Type B soils. Should it be required, all temporary sheeting, shoring, benching, and sloping should be designed by a qualified engineer registered in the State of Delaware.

7.

The shallow silt soils of Stratum C are considered moisture sensitive. Exposure of these soils to precipitation and construction traffic may weaken the soils and result in yielding subgrade conditions. In addition, if foundation excavations are left open, precipitation may result in the collection of water within the excavation. Provisions for removal of water by drainage or sumping are recommended. Subgrade soils disturbed by precipitation and construction traffic should be either scarified and re-compacted or undercut and replaced with structural fill as previously discussed.

8.

If “perched” groundwater is encountered, localized sumping may be required to control stormwater runoff into excavations during construction. It is recommended that wherever groundwater is encountered during shallow foundation or utility excavations, the resulting excavation should be over excavated by at least 4 inches and replaced with AASHTO SP-57 stone to protect the exposed subgrade soils and to facilitate sumping.

9.

All contractors interested in bidding on phases of this work, which involve subsurface conditions, should be given full access to this report so that they can develop their own interpretations of the available data.

10.

It is recommended that the project budget include provisions for the cost for independent construction monitoring of the earthwork and foundation construction by a qualified engineering firm retained by the Owner, to review conformance of construction with the recommendations of the project geotechnical evaluation, as well as the project plans and specifications.

Appendix B-43 - Page 20

The recommendations of this report have been prepared according to generally accepted soil and foundation engineering practice, and are based on the conditions encountered by the test borings and infiltration tests performed at the site. Although soil quality has been inferred from the interpolation of the sampling data, you should explicitly note that subsurface conditions beyond the test borings are, in fact, unknown. Should any conditions encountered during construction differ from those described in this report, this office should be notified immediately in order to review, and possibly modify these recommendations. This report applies solely to the size, type, and location of the structure described herein. In the event that changes are proposed, this report will not be considered valid unless the changes have been reviewed and the recommendations of this report modified and re-approved in writing by Duffield Associates, Inc.

Appendix B-43 - Page 21

B- 1/

1A

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B-

B- 7/

7A

B-

B- 6/

6A

B-

B- 5/

5A /5

B

SD

-1

3/ A-

SD

-1

1/ A-

SD

-1

2/ A-

N O

TE

TH

IS

S

KE

TC

H

IS

A

D

AP

TE

D

F R

O M

A D

R

AW

IN

G

T

IT

LE

D

"R

EV

IS

ED

S

IT

E

LA

YO

U

T, " P

R

EP

AR

ED

BY

M

IC

H

AE

L

BA

KE

R

IN

TE

R

N

AT

IO

N

AL

, D

AT

ED

F

EB

R U

AR

Y

, 2

7.

KE

Y:

A

PP

R

O

XI

M

AT

E

TE

ST

B

O R

IN

G

L O

C

AT

IO

N

PP

R

O

XI

M

AT

E

VA

C U

U M

E

XT

R

AC

TI

O

N /A

N O

M O

LY

L

O C

AT

IO

N

B-

SD

-1

1/ A-

DUFFIELD

DRAWN BY:

DESIGNED BY:

CHECKED BY:

FILE:

D A

T E

SC

A

L E

SH

E

E T

PR

O

JE

C

T N

O

TEST BORING AND VACUUM EXTRACTION LOCATION SKETCH

MAINTENANCE HANGAR

DOVER AIR FORCE BASE

DOVER~KENT COUNTY~DELAWARE

J

U L

Y

1"

.G V

FI

G

U R

E

JJ

ARS

JJ

B-8919GV-02

RF

P

W9

BU

-1 8- R-

Ap pe nd ix B

-4

Pa ge

APPROXIMATE

SITE LOCATION

SITE LOCATION SKETCH

MAINTENANCE HANGAR

DOVER AIR FORCE BASE

DOVER~KENT COUNTY~DELAWARE

18 JULY 2017

1"=2000'

8919.GV

FIGURE 1

JJ

ARS

JJ

A-8919GV-01

CHECKED BY:

DRAWN BY:

FILE:

DESIGNED BY:

SHEET:

PROJECT. NO.

SCALE:

DATE:

DUFFIELD

NOTE:

THIS SKETCH IS ADAPTED FROM TWO, 7.5 MINUTE SERIES U.S.G.S TOPOGRAPHIC MAPS

TITLED "LITTLE CREEK" AND "FREDERICA", DELAWARE, DATED 2016

Appendix B-43 - Page 23

Appendix B-43 - Page 24

Appendix B-43 - Page 25

Appendix B-43 - Page 26

Appendix B-43 - Page 27

Appendix B-43 - Page 28

Appendix B-43 - Page 29

Appendix B-43 - Page 30

Appendix B-43 - Page 31

Appendix B-43 - Page 32

Appendix B-43 - Page 33

Appendix B-43 - Page 34

Appendix B-43 - Page 35

Appendix B-43 - Page 36

Appendix B-43 - Page 37

Appendix B-43 - Page 38

Appendix B-43 - Page 39

Appendix B-43 - Page 40

Appendix B-43 - Page 41

Appendix B-43 - Page 42

Appendix B-43 - Page 43

Appendix B-43 - Page 44

Appendix B-43 - Page 45

Appendix B-43 - Page 46

Appendix B-43 - Page 47

Appendix B-43 - Page 48

Appendix B-43 - Page 49

Appendix B-43 - Page 50

Appendix B-43 - Page 51

Appendix B-43 - Page 52

Appendix B-43 - Page 53

Appendix B-43 - Page 54

Appendix B-43 - Page 55

Te st

Bo rin g N um be r Sa m pl e N um be r Sa m pl e D ep th

(fe et

Vi su al D es cr ip tio n [1

N at ur al

M oi st ur e C on te nt [2

(A

ST

M

D

6)

Le ss

T ha n N o.

Si ev e

(A

ST

M D

0)

U

SC

S C la ss ifi ca tio n

(A

ST

M D

7)

At te rb er g Li m its

(A

ST

M D

8) U nc on fin ed

C om pr es si ve

St re ng th

(A

ST

M D

6) q u

(k sf

C on so lid at io n Te st [2

(A

ST

M D

5) Li qu id

Li m it

Pl as tic ity

In de x

P c

(k sf

C

’ c C

’ r

B-

S-

4.

6.

G ra y fin e to m ed iu m S

AN

D

, l itt le s ilt , t ra ce c oa rs e sa nd

.5

.6

SM

S-

.0

8.

R ed

-b ro w n m ed iu m to c oa rs e

SA

N D a nd

G R

AV

EL

tra ce s ilt, tr ac e fin e sa nd

.7

8.

SP

-S

M

B-

S-

.0

4.

Li gh t b ro w n fin e to m ed iu m S

AN

D

, l itt le s ilt , l itt le co ar se s an d

.4

.8

SM

B-

S-

6.

8.

G ra y fin e to m ed iu m S

AN

D

, l itt le c oa rs e sa nd , l itt le s ilt

.5

.4

SP

-S

M

S-

.0

6.

D ar k br ow n fin e to m ed iu m S

AN

D

, l itt le o rg an ic s, li ttl e si lt, tr ac e gr av el

.0

.4

SM

B-

S-

.0

6.

Li gh t b ro w n m ed iu m to c oa rs e

SA

N

D , l itt le s ilt

, l gr av el , t ra ce fi ne s an d

.0

.9

SP

-S M

B-

1A

0.

2.

FI

LL

gr ay fi ne to m ed iu m s an d an d si lt, li ttl e gr av el tra ce c oa rs e sa nd

9.

.1

SM

2.

4.

R ed -b ro w n fin e

SA

N D a nd

S

IL

T, tr ac e gr av el

.5

.6

SM

ST

-1

5.

D ar k gr ay

C

LA

Y, tr ac e fin e sa nd

, t ra ce or ga ni cs

.6

.1 C

H

3.

0.

0.

B-

S-

4.

6.

O ra ng e, b ro w n fin e to m ed iu m

S

AN

D , t ra ce c oa rs e sa nd

, t ra ce s ilt

2.

SP

S-

8.

.0 D ar k gr ay

S

IL

T, tr ac e fin e to c oa rs e sa nd , t ra ce or ga ni cs

.0

.6 M

H

B-

S-

2.

4.

Li gh t g ra y fin e

SA

N

D , l itt le m ed iu m s an d, tr ac e si lt

8.

8.

SP

-S

M

2.

D ar k gr ay

C

LA

Y, tr ac e fin e sa nd

, t ra ce o rg an ic s

.9

.0

C H

3.

B-

S-

8.

G y m ed iu m to c oa rs e

SA

N

D , t ra ce s ilt

, t ra ce fi ne sa nd

.2

5.

SP

-S

M

4.

D ar k gr ay

C

LA

Y, s om e fin e sa nd

, t ra ce o rg an ic s

.0

.9

C H

1.

B-

S-

0.

2.

Li gh t b ro w n

SI

LT

a nd fi ne to m ed iu m

S

AN

D , t el

, t ra ce c oa rs e sa nd

.6

.8 M

L

B-

S-

0.

2.

Li gh t o ra ng e, b ro w n fin e

SA

N D a nd

S

IL

T, tr ac e m ed iu m s an d

.5

.6

SM

N ot es

1) U

SC

S

- U ni fie d

So il

C la ss ifi ca tio n Sy st em

2)

C on so lid at io n re su lts p re se nt ed in th is ta bl e ar e co m pr es si on in de x an d re co m pr es si on in de x va lu es C

’ c an d C

’ r.

T he c on so lid at io n te st re su lts p re se nt ed in th e Ja nu ar y la bo ra to ry s um m ar y ta bl e an d te st re po rts a re th e va lu es

C c an d

C r.

Th e re la tio ns hi p of th es e pa ra m et er s is a s fo llo w s:

p an d p

, w he re e o is th e in iti al v oi d ra tio

RF

P

W9

BU

-1 8- R-

Ap pe nd ix B

-4

Pa ge

E

O T

E C

H N

IC

A

L

IN

V E

ST

IG

A T

IO

N

, D O

V E

R A

IR

F

O R

C E

B A

SE

M

A

IN

T E

N A

N C

E H

A N

G

R

D O

V E

R , K

E N

T C

O U

N T

Y , D

E L

A W

A

U

SA

C E

C O

N T

R A

C T

N O

. W

2B U

-1 1-

D -0

T

A

SK

O R

D E

R N

O . 0

D uf fie ld

A ss oc ia te s, c.

Pr oj ec t N o.

9.

Ja nu ar y tte rb er g Li its

(A

S

TM

D

8)

Tr ia xi al

C om pr es on

“R

” T es t ( A

S

TM

D

C on so lid at io n Te st (A

S

TM

D

5)

B in g N um be r S am pl e N um be r S am pl e D

V is ua l

D es cr ip tio n

[1

N at ur al

M oi st ur e

C on te nt

[2

(A S

TM

D

6)

Le ss

T ha n N o.

ie

TM

D

0)

C S

C la ss ifi ca tio n (A

S

TM

D

7) it

P la st ic x

S pe ci fic vi ty (A

TM

U nc on pr es tre ng q u

(k sf

To ta l c

(k sf ffe ct iv e c’

(k sf

C c C r

S

2.

3.

D ar k gr ay

, d ar k br ow n

C

LA

Y a nd fi to iu m s an d, tr ac e gr av el

, t ra ce c oa rs e

.7

.1

C L

S -2

4.

5.

G ra y, li gh t g ra y C

LA

Y

, s om e fin e to m ed iu

, t ra ce c oa rs e sa nd

, t ra ce g ra ve l

.1

.5 C

L

S -3

5.

6.

Li gh t g ra y, g ra y, w hi te m ed iu m to fi ne S

A N

D lit tle s ilt

, t ra ce g ra ve l, tra ce c oa rs e

.4

S M

T-

9.

gh t g…