AC_RTA_Geotech_Vert_2017-07-12.pdf

REPORT OF

SUBSURFACE

EXPLORATION

AND

GEOTECHNICAL

ENGINEERING

SERVICES

Aviation Complex Vertical Component

Newport News, Virginia

G E T Project No: WM15-190G

February 2, 2016 Rev May 5, 2016

PREPARED FOR:

ADMINISTERED BY:

1592-E Penniman Road Williamsburg, VA 23185 Phone: (757) 564-6452 www.getsolutionsinc.com

1592 Penniman Road, Suite E Williamsburg, Virginia 23185 Phone: (757)-564-6452 Fax: (757)-564-6453 info@getsolutionsinc.com

February 2, 2016 Rev May 5, 2016

TO: HNTB Corporation 2900 South Quincy Street, Suite 600 Arlington, VA 22206

Attn: Mr. Brian Pieplow

RE: Report of Subsurface Exploration and Geotechnical Engineering Services

Aviation Complex Vertical Component Newport News, Virginia G E T Project No. WM15-190G

Dear Mr. Pieplow:

In compliance with your instructions, we have completed our Subsurface Exploration and Geotechnical Engineering Services for the above referenced project. The results of this study, together with our recommendations, are presented in this report.

Often, because of design and construction details that occur on a project, questions arise concerning subsurface conditions. G E T Solutions, Inc. would be pleased to continue its role as Geotechnical Engineer during the project implementation.

We appreciate the opportunity to work with you on this project. We trust that the information contained herein meets your immediate need, and should you have any questions or if we could be of further assistance, please do not hesitate to contact us.

Respectfully Submitted, G E T Solutions, Inc.

James R. Wheeler Project Geologist

Bruce R. Spiro, P.E.

Principal Engineer Virginia Reg. # 015791

Copies: (1) Client

TABLE OF CONTENTS

Report of Subsurface Exploration and Geotechnical Engineering Services Aviation Complex – Vertical Component

EXECUTIVE SUMMARY ............................................................................................................... i

1.0 PROJECT INFORMATION

1.1 Project Authorization

1.2 Project Location and Description

1.3 Purpose and Scope of Services

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

2.2 Laboratory Testing

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

3.2 Subsurface Soil Conditions

3.3 Groundwater Discussion

4.0 EVALUATIONS AND RECOMMENDATIONS

4.1 Clearing and Grading

4.2 Subgrade Preparation

4.3 Structural Fill and Placement

4.4 Suitability of On-site Soils

4.5 Deep Foundation Recommendations

4.5.1 Axial Compression Capacity Recommendations - Driven Concrete Piles

4.5.2 Lateral Capacity Analysis - Driven Concrete Piles

4.5.3 Pile Group Settlement

4.5.4 Test Pile Program

4.5.5 Dynamic Testing

4.5.6 Production Pile/Acceptance Criteria

4.5.7 Allowable Driving Stresses

4.5.8 Hammer Types and Energies

4.5.9 Adjacent Structures

4.6 Below-Grade Construction

4.7 Earth Pressures from Earthquakes

4.8 Shallow Foundation Design Recommendations (Lightly-loaded Features) 18

4.9 Settlements (Lightly-loaded Features)

4.10 Foundation Excavations (Lightly-loaded Features)

4.11 On-site Shrink/Swell Properties

4.12 Seismic Evaluation

4.13 Liquefaction Potential

5.0 CONSTRUCTION CONSIDERATIONS

5.1 Anticipated Excavation Characteristics

5.2 Excavation Stability

5.3 Dewatering

5.4 Site Utility Installation

5.5 Structure Protection and Monitoring

5.6 Construction Monitoring and Inspections

5.7 Excavations

6.0 REPORT LIMITATIONS

TABLE OF CONTENTS

Report of Subsurface Exploration and Geotechnical Engineering Services Aviation Complex – Vertical Component

APPENDICES

APPENDIX I BORING LOCATION PLAN

APPENDIX II SUMMARY OF SOIL CLASSIFICATION

APPENDIX III SUMMARY OF LABORATORY CLASSIFICATION RESULTS

APPENDIX IV SOIL TEST BORING LOGS

APPENDIX V GENERALIZED SOIL PROFILES

APPENDIX VI CONSOLIDATION TEST RESULTS

APPENDIX VII CALCULATIONS

APPENDIX VIII L-PILE ANALYSES

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016 Aviation Complex – Vertical Component Rev May 5, 2016 i

EXECUTIVE SUMMARY

The Project site is located on a 75 Acre parcel generally opposite the south side of an existing Runway. This site is currently being used for training operations. The new construction at this site will consist of building a new Aviation Training Facility to include various structures and ancillary buildings, pavements and Taxiways. It is anticipated that the larger structures will be primarily of steel-frame design. The facilities are anticipated to be 2 to 3 story (including penthouses) with a stick-framed steel superstructure. Exterior masonry veneer will be employed up the second floor with insulated metal panel from second floor to roof. Any smaller ancillary structures will be single-story pre-engineered metal buildings. Additional analyses were performed as part of the Aviation Complex – Horizontal Component design package. The results of these explorations, along with associated laboratory analyses and design evaluations, will be presented under separate cover.

Our field exploration program included seventeen (17), 80-foot deep Standard Penetration Test (SPT) borings within the vicinity of the new structure’s proposed footprint.

The natural subsurface soils were generally arranged in a 3-layer configuration as described in the Table below:

Subsurface Soil Conditions

AVERAGE

DEPTH (ft)

STRATUM DESCRIPTION

RANGES OF

SPT(1) N-VALUES

to

0.2 - 0.7 Surficial 2 to 8 inches of Topsoil –

0.2 – 0.7 to

2 - 6 I

Red, orange, brown and tan, Sandy CLAY (CL) with varying amounts of Silt, and trace fibrous organics

3 – 18

2 - 6 to

38 - 46

II

Brown and gray SAND (SP-SM, SM, SC) with varying amounts of Silt and Clay

3 – 21

24 - 26 to

28 - 32 IIa

Intermediate layer of Soft, Gray, Silty and Sandy

CLAY (CL, CH)

*This layer was not encountered in borings generally oriented toward the western third of the site

WOH – 3

38 - 46 to

III

Gray and Brown SAND (SM, SC) with varying amounts of Silt, Clay, Gravel, and marine shell fragments; Gray Sandy CLAY (CL) with varying amounts of Silt, and marine shell fragments

“Yorktown Formation”

3 – 12

Notes: (1) SPT = Standard Penetration Test, N-Values in Blows-per-foot (Uncorrected for Automatic Hammer or Overburden)

The initial groundwater-level was measured to occur at depths ranging from about 5 to 8 feet below existing grades at the boring locations corresponding to elevations of 0 to 3 feet NAVD88.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016 ii

The stabilized groundwater-level (recorded 24 hours after drilling) was measured as a part of the Aviation Complex – Horizontal Component package and is to be reported separately.

The following evaluations and recommendations were developed based on our field exploration and laboratory-testing program:

We recommend that the frame of the proposed structure be supported on a deep foundation system comprised of square, pre-cast, pre-stressed concrete (SPPC) piles. Pile design characteristics and lateral capacity analyses are provided in Section 4.5 of the report.

Smaller, more lightly-loaded ancillary structures may be supported by shallow spread foundations. Shallow spread foundation design characteristics are discussed in Section 4.8 of the report.

The shallow subsurface natural CLAY (CL) soils encountered at the boring locations do not appear to meet the criteria recommended in this report for reuse as structural fill; however, these soils may be used as fill in green areas. Shallow subsurface natural SAND (SP-SM, SM) soils were also encountered on site and appear to meet the recommended criteria for reuse as structural fill given that they are within the recommended moisture constraints.

The project’s budget should include an allowance for subgrade improvements.

Based on the laboratory classification results, the shallow subsurface soils encountered within the upper 10 feet at the boring locations are not considered to be expansive in accordance with 1803.5.3 of the 2012 International Building Code.

The subsurface granular soils recovered within the upper 80 feet at the project site are expected to have adequate resistance against liquefaction during a magnitude 6.5 earthquake or smaller.

Based on our experience in the vicinity of the project site and the composition of the soils recovered within the upper 80 feet (maximum explored depth) at the boring locations, the site characteristics are indicative of a Site Class “D” in accordance with Table 1613.5.2 of the 2012 International Building Code. If the site classification is critical to the structural design it will be necessary to perform a 100-foot deep CPT boring with shear wave velocity measurements to substantiate this site classification.

This summary briefly discusses some of the major topics mentioned in the attached report.

Accordingly, this report should be read in its entirety to thoroughly evaluate the contents.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Newport News, Virginia G E T Project No. WM15-190G

1.0 PROJECT INFORMATION

1.1 Project Authorization

G E T Solutions, Inc. has completed our subsurface exploration and geotechnical engineering services for the proposed Aviation Complex – Vertical Component project located in Newport News, Virginia. The geotechnical engineering services were conducted in general accordance with the scope presented in G E T Proposal No. USACOE-VB15-371G. Authorization to proceed with our services was received from the client in the form of an executed Master Agreement and Task Order dated July 26, 2015.

1.2 Project Location and Description

The Project site is located on a 75 Acre parcel generally opposite the south side of an existing Runway. This site is currently being used for training operations. The site boundaries are limited by the wetland delineations that are identified in the 2012 Environmental Assessment documents published by HNTB. A Site Vicinity Map and General Location Plan are not included in this reporting per request of the Client.

The proposed main Hangar area is predominantly an open, grassy field currently in use as a training area. Surface elevations range around +6 to +8 MSL in this area. Moderately dense woods surround the project location, and a marshy area comprising the upper reaches of a drainage feature lies to the north of the site, between the proposed Hangar site and the existing Runway. A taxiway bridge crossing of this marsh is planned as a separate feature of the project development, and is reported along with other Horizontal elements of the project under separate cover.

This current report addresses preparing geotechnical design data for the vertical construction (Structures) component of the Aviation Complex in Newport News, Virginia.

It is anticipated that the Hangar structures will be primarily of steel-frame design. The Hangars and Med/ Ops facility will be 2 to 3 story (including penthouses) with a stick-framed steel superstructure. Exterior masonry veneer will be employed up the second floor with insulated metal panel from second floor to roof. Any smaller ancillary structures will be single-story pre-engineered metal buildings. Up to 6 to 8 ft of structural FILL material is anticipated to be placed to achieve the required final site grades.

The approximate loads associated with the main structure have been provided by USACOE structural division and are as follows:

Maximum Hangar Column Load: 450 kips Intermediate Hangar Column Load: 120 kips Minimum Column Load: 50 kips Maximum Column Load – Shop Area: 150 kips Exterior Wall Load: 6 kips/lf Ground Floor Slab: 100 - 300 psf (300 psf in isolated areas only) Typical Hangar Slab: Designed per pavement section requirements from Horizontal design component – not addressed herein.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Deep foundation support is anticipated for the new Hangar structure. The slab area of the main Hangar bays will be designed to match the surrounding taxiway pavement and will therefore be addressed as part of the Horizontal study report. Ancillary, lightly loaded structures are anticipated to be supported on shallow foundations.

If any of the noted information is incorrect or has changed, please inform G E T Solutions, Inc. so that we may amend the recommendations presented in this report, if appropriate.

1.3 Purpose and Scope of Services

The purpose of this study was to obtain information on the general subsurface conditions at the proposed project site. The subsurface conditions encountered were then evaluated with respect to the available project characteristics. In this regard, engineering assessments for the following items were formulated:

1. General assessment of the soils revealed by the borings performed at the proposed development and reviewed on available geotechnical data.

2. General location and description of potentially deleterious material encountered in the borings that may interfere with construction progress or structure performance, including existing fills or surficial/subsurface organics.

3. Evaluation of the on-site soils for re-use as structural fill.

4. Feasibility of utilizing a deep foundation system for support of the proposed structure. Design parameters required for the foundation system, including pile type and length, design parameters, testing, and installation criteria.

5. Shallow foundation recommendations for lightly-loaded, Ancillary structures.

6. Soil design parameters required for establishing lateral stress distribution diagrams and hydrostatic design recommendations for below-grade wall systems.

7. Assessment of the shallow subsurface soils’ expansive properties in accordance with the 2012 International Building Code.

8. Assessment of the soils’ resistance against liquefaction.

9. Seismic site class determination in accordance with the 2012 International

Building Code.

The scope of services did not include an environmental assessment for determining the presence or absence of wetlands or hazardous or toxic material in the soil, bedrock, surface water, groundwater or air, on or below or around this site.

Newport News, Virginia G E T Project No. WM15-190G

2.0 FIELD AND LABORATORY PROCEDURES

2.1 Field Exploration

In order to explore the general subsurface soil types and to aid in developing structure foundation design parameters, the following exploration program was performed:

Seventeen (17) 80-foot deep Standard Penetration Test (SPT) borings (designated as SS-1 through SS-17) were drilled within the vicinity of the new structure’s proposed footprint.

Additional SPT borings were performed as part of the Aviation Complex – Horizontal design package. The results of these explorations, along with associated laboratory analyses and design evaluations, will be presented under separate cover.

Standard Penetration Tests were performed in the field in general accordance with ASTM D 1586. The tests were performed continuously from the existing ground surface to depths of 12 feet, and at 5-foot intervals thereafter. The soil samples were obtained with a standard 1.4” I.D., 2” O.D., 30” long split-spoon sampler. The sampler was driven with blows of a 140 lb. hammer falling 30 inches, using an automatic hammer. The number of blows required to drive the sampler each 6-inch increment of penetration was recorded and is shown on the boring logs.

The sum of the second and third penetration increments is termed the SPT N-value (uncorrected for automatic hammer and overburden pressure). A representative portion of each disturbed split-spoon sample was collected with each SPT, placed in a glass jar, sealed, labeled, and returned to our laboratory for review.

The SPT boring locations were established and staked in the field by a representative of G E T Solutions, Inc. using a hand-held Global Positioning System (GPS) device and corroborated with easily identifiable landmarks. These locations were first approved by the client.

Subsequently, the SPT boring locations were surveyed by the client, who provided the following coordinate location and elevations indicated in Table I on the following page:

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Table I - Schedule of SPT Boring Coordinates and Elevations

Boring Location Northing Easting Elevation

SS-1 3576948.572 12032396.93 6.139

SS-2 3576846.455 12033101.16 7.975

SS-3 3576680.191 12033271.92 7.845

SS-4 3576705.553 12033059.47 9.438

SS-5 3576639.751 12032872.33 8.573

SS-6 3576519.150 12033056.33 9.658

SS-7 3576619.385 12033210.33 8.673

SS-8 3576213.816 12034009.53 5.277

SS-9 3576462.605 12033255.57 8.156

SS-10 3576477.048 12033404.16 8.553

SS-11 3576321.262 12033287.25 8.220

SS-12 3576284.750 12033473.40 8.530

SS-13 3576252.887 12033653.27 7.630

SS-14 3576136.302 12033547.18 7.958

SS-15 3576115.809 12033673.74 7.899

SS-16 3576088.828 12033872.90 7.045

SS-17 3576040.454 12033745.70 7.697

The SPT boring locations are shown on the attached “Boring Location Plan” (Appendix I), which was developed based on a site plan provided by the client.

Two (2) relatively undisturbed, 3-inch diameter, thin-walled Shelby tube samples were collected from the boring locations at depths identified in Table II. The Shelby tube samples were obtained by hydraulically pressing a 3-inch outside diameter Shelby tube into the targeted soils using the drill rig. The tubes were sealed in general accordance with ASTM standards and returned to G E T Solutions, Inc.’s Virginia Beach laboratory for extraction, classification and consolidation testing (per ASTM D 2435).

Table II - Schedule of Shelby Tubes

Boring Location Depth Shelby Tube Extracted

SS-5 24-26 feet below grades SS-7 25-27 feet below grades

2.2 Laboratory Testing

Representative portions of all soil samples collected during drilling were sealed in glass jars, labeled and transferred to our laboratory for classification and analysis. A Project Engineer performed the soil classification in general accordance with ASTM Specification D 2487 and D 2488. A summary of the soil classification system is provided in Appendix II.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Thirty-five (35) representative split spoon soil samples were selected and subjected to natural moisture, #200 sieve wash, and Atterberg Limits testing in order to corroborate the visual classification. These test results are summarized in the table presented in Appendix III and in the soil test boring logs presented in Appendix IV. The general subsurface soil profiles are presented in Appendix V.

Two (2), one-dimensional consolidation test was performed at our Virginia Beach laboratory in general accordance with ASTM D 2435 on the specimens extracted from the Shelby tube samples obtained at the locations indicated in Table II above.

The consolidation test results are presented in Table III below. The comprehensive test results are provided in Appendix VI.

Table III - Consolidation Test Results

Boring No.

Depth (ft)

Overburden (tsf)

Pc

(tsf) OCR Cc Cr eo

SS-5 24-26 1.05 2.1(1) 2.0(1) 0.355(1) 0.010(1) 0.893

SS-7 25-27 1.05 2.1(1) 2.0(1) 0.230(1) 0.015(1) 0.906

Note(s): (1) Values obtained from re-constructed consolidation curve.

3.0 SITE AND SUBSURFACE CONDITIONS

3.1 Site Geology

The project site is located within the Atlantic Coastal Plain physiographic province. Bedrock of the Late Mesozoic age is present at depths of greater than 2,000 ft, and is overlain by Lower and Upper Cretaceous, Tertiary, Pleistocene and Recent Sediments.

Across the outer Coastal Plain, the Pliocene age Yorktown Formation of the Tertiary Period is widespread, occurring from Maryland to North Carolina. Its age is estimated as between 4.8 million and 2.8 million years and is estimated to have been deposited during three transgressive episodes. The depositional environment was shallow marine in nature, consisting of inner shelf, barrier-island, estuarine and lagoonal patterns. The Yorktown Formation is a glauconitic, fossiliferous, Silty to Clayey greenish-gray fine Sand. This material has been preconsolidated by an increased effective overburden pressure generated due to a drop in the sea level at the end of the Tertiary Period, and by previously overlying sediments, which eroded away as the sea level subsequently lowered.

As sea levels rose during the Pleistocene Epoch of the Quaternary Period, areas were filled and overlain by soils of the Lynnhaven, Poquoson, Windsor and Shirley members of the Tabb Formation. The Tabb Formation is composed of fluvial and estuarine sand, clay, organic soil and peat. In localized areas, Recent Holocene sediments, primarily marsh or swamp, colluvium, and alluvium, overlies the Tabb Formation.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Based on our review of existing geologic and soil boring data, the geologic stratigraphy encountered in our subsurface explorations generally consisted of marine deposited Sands, Silts and Clays of the Windsor and Shirley Members of the Tabb Formation overlain by Recent sediments and man-placed Fill deposits. The Yorktown Formation underlies the project site, and extends to significant depth.

3.2 Subsurface Soil Conditions

A summary of our SPT soil test borings is presented below in Table IV.

Table IV - Subsurface Soil Conditions

AVERAGE

DEPTH (ft)

STRATUM DESCRIPTION

RANGES OF

SPT(1) N-VALUES

to

0.2 - 0.7 Surficial 2 to 8 inches of Topsoil –

0.2 – 0.7 to

2 - 6 I

Red, orange, brown and tan, Sandy CLAY (CL) with varying amounts of Silt, and trace fibrous organics

3 – 18

2 - 6 to

38 - 46

II

Brown and gray SAND (SP-SM, SM, SC) with varying amounts of Silt and Clay

3 – 21

24 - 26 to

28 - 32 IIa

Intermediate layer of Soft, Gray, Silty and Sandy

CLAY (CL, CH)

*This layer was not encountered in borings generally oriented toward the western third of the site

WOH – 3

38 - 46 to

III

Gray and Brown SAND (SM, SC) with varying amounts of Silt, Clay, Gravel, and marine shell fragments; Gray Sandy CLAY (CL) with varying amounts of Silt, and marine shell fragments

“Yorktown Formation”

3 – 12

Notes: (1) SPT = Standard Penetration Test, N-Values in Blows-per-foot (uncorrected)

The subsurface descriptions are of a generalized nature provided to highlight the major soil strata encountered. The records of the subsurface exploration are included in Appendix IV (Boring Log Sheets) and in Appendix V (Generalized Soil Profiles) which should be reviewed for specific information as to the individual borings. The stratifications shown on the records of the subsurface exploration represent the conditions only at the actual boring locations. Variations may occur and should be expected between boring locations. The stratifications represent the approximate boundary between subsurface materials and the transition may be gradual.

It is noted that the topsoil designation references the presence of surficial organic laden soil, and does not represent any particular quality specification. It is recommended this material be tested for approval prior to use.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

3.3 Groundwater Discussion

The initial groundwater-level was recorded at the boring locations and as observed through the wetness of the recovered soil samples during the drilling operations. The initial groundwater-level was measured to occur at depths ranging from 5 to 8 feet below the existing site grades at the boring locations corresponding to elevations of approximately 0 to 3 feet NAVD88. The boreholes were backfilled upon completion for safety considerations.

As subsurface soils begin to dry moisture moves upwards through the soil profile by means of capillary action. Based on the subsurface soil composition, these initial groundwater-level readings (based on the relative wetness of the soils) could be in part attributed to the capillary action of the soils.

Groundwater conditions will vary with environmental variations, tidal fluctuations, and seasonal conditions, such as the frequency and magnitude of rainfall patterns, as well as man-made influences, such as existing swales, drainage ponds, underdrains and areas of covered soil (paved parking lots, sidewalks, etc.). Seasonal groundwater fluctuations of 2 feet are common in the project’s area; however, greater fluctuations have been documented. We recommend that the contractor determine the actual groundwater levels at the time of the construction to determine groundwater impact on the construction procedures.

4.0 EVALUATIONS AND RECOMMENDATIONS

Our recommendations are based on the previously discussed project information, our interpretation of the soil test borings, and our observations during our site reconnaissance. If the proposed construction should vary from what was described, we request the opportunity to review our recommendations and make any necessary changes.

Based on the anticipated structural loads in combination with the subsurface soil conditions, it is our recommendation that the frame of the main Hangar structure be supported by means of driven concrete piles. The deep foundation recommendations are provided in Section 4.5 of this report. Consideration was given to shallow foundation support for this main structure; however, due to the magnitude of the structural loads and anticipated total and differential settlements, deep foundation support appears to be the most preferable option. Further assessment of shallow foundation options can be undertaken on request.

4.1 Clearing and Grading

The proposed construction areas should be cleared by means of removing the topsoil and any other unsuitable materials. It is estimated that a cut of up to 8 to 10 inches in depth will be required to remove the topsoil. This cut is expected to extend deeper in isolated areas or tree removal areas in order to remove deeper deposits of organic soils, or unsuitable soils, which become evident during the clearing. It is recommended that the clearing operations extend laterally at least 5 feet beyond the perimeter of the proposed construction area. The excavations associated with the site clearing should be backfilled with compacted structural fill as described in Section 4.3 of this report.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

To reduce the potential for subgrade improvements (undercutting due to saturated soils in conjunction with heavy construction traffic), it is recommended that the grading operations be performed during the drier months of the year (historically April through November). This should minimize these potential problems, although they may not be eliminated. If grading is attempted during the winter months, undercutting of wet soils should be anticipated. However, during the drier months of the year, wet soils could be dried by disking or implementing other drying procedures to achieve moisture contents necessary to achieve adequate degrees of compaction.

The site should be graded to enhance surface water runoff to reduce the ponding of water.

Ponding of water often results in softening of the near-surface soils. In the event of heavy rainfall within areas to receive fill, we recommend that the grading operations cease until the site has had a chance to dry.

Any undercut and backfill should be performed under the observation of a representative of G E T Solutions, Inc. who will evaluate the composition of the recovered soils.

Recommendations concerning the subgrade improvements (as necessary) will be provided in the field following the testing procedures.

4.2 Subgrade Preparation

Following the clearing operation, the exposed subgrade soils should be densified with a large static drum roller. After the subgrade soils have been densified, they should be evaluated by G E T Solutions, Inc. for stability. Accordingly, the subgrade soils should be proofrolled to check for pockets of loose material hidden beneath a crust of better soil. Several passes should be made by a large rubber-tired roller or loaded dump truck over the construction areas. The number of passes will be determined in the field by the Geotechnical Engineer depending on the soils conditions. Any pumping or unstable areas observed during proofrolling (beyond the initial cut) should be undercut and/or stabilized at the direction of the Geotechnical Engineer.

4.3 Structural Fill and Placement

Following the approval of the natural subgrade soils by the Geotechnical Engineer, the placement of the fill required to establish the design grades may begin. Any material to be used for structural fill should be evaluated and tested by G E T Solutions, Inc. prior to placement to determine if they are suitable for the intended use. Suitable structural fill material should consist of sand or gravel containing less than 25% by weight of fines (SP, SM, SW, GP, GW), having a liquid limit less than 20 and plastic limit less than 6, and should be free of rubble, organics, clay, debris and other unsuitable material.

All structural fill should be compacted to a dry density of at least 95 percent of the Modified Proctor maximum dry density (ASTM D 1557). In general, the compaction should be accomplished by placing the fill in maximum 10-inch loose lifts and mechanically compacting each lift to at least the specified minimum dry density. A representative of G E T Solutions, Inc.

should perform field density tests on each lift as necessary to assure that adequate compaction is achieved.

Backfill material in utility trenches within the construction areas should consist of structural fill (as previously above), and should be compacted to at least 95 percent of ASTM D 1557. This fill should be placed in 4 to 6 inch loose lifts when hand compaction equipment is used.

Newport News, Virginia G E T Project No. WM15-190G

Care should be used when operating the compactors near existing structures to avoid transmission of the vibrations that could cause settlement damage or disturb occupants. In this regard, it is recommended that the vibratory roller remain at least 25 feet away from existing structures; these areas should be compacted with small, hand-operated compaction equipment.

4.4 Suitability of On-site Soils

Based on the laboratory testing program, the shallow subsurface natural CLAY (CL) soils encountered at the boring locations do not appear to meet the criteria recommended in this report for reuse as structural fill; however, these materials may be used as fill in green areas.

Shallow subsurface natural SAND (SP-SM, SM) soils were also encountered at the boring locations within depths that may be excavated during site activities. These appear to meet the criteria recommended in this report for reuse as select fill; however significant moisture manipulation is expected as these soils are located near or below the groundwater table. This manipulation will likely require stockpiling of wet soils and/or placing the material in thin layers.

The goal of these methods is to dry the soils to within +/- 2% of their optimum moisture at the time of compaction which could prove time consuming and cost prohibitive. Again, it is important that during excavation, the deposits of natural CLAY (CL) soils and deleterious organic materials are segregated from the suitable granular soils (SAND containing less than 25% by weight of fines).

Further classification testing (natural moisture content, gradation analysis, and Proctor testing) should be performed in the field during construction to evaluate the suitability of excavated soils for reuse as structural fill. That said, the Uncontrolled FILL materials should not be expected to be suitable for reuse and the project’s budget should include an allowance for imported structural fill.

4.5 Deep Foundation Recommendations

We recommend that the frame of the proposed main Hangar structure and any other heavily loaded structures be supported by means of a deep foundation system comprised of Square, Pre-stressed, Precast, Concrete (SPPC) piles (12”, 14”, and/or 16” sections). The following sections describe the pile resistance analyses and provide our recommendations for factored static axial compressive, tensile, and lateral pile resistance, pile testing program, and pile construction criteria. In addition, we have provided estimates of potential settlement.

4.5.1 Axial Compression Capacity Recommendations - Driven Concrete Piles

We conducted pile capacity analyses using static formulas with coefficients recommended by Geoffrey Myerhoff and George Sowers. The analyses include the contributions of shaft friction and end bearing to the pile resistance. The piles are expected to derive the majority of their resistance from the deeper Stratum III soils (Yorktown Formation) at the depths presented in Table V.

The soil materials typically exhibit time-dependent strength characteristics; consequently shaft friction and end bearing support tend to increase from initial installation through a process termed “soil setup”. Essentially, the dynamics of driving piles will cause excess pore pressures to develop, thereby decreasing driving resistance during initial pile installation. The pile capacities developed during driving are usually much lower than the design values. Once driving is complete, the excess pore pressures will dissipate with time (and soil setup occurs)

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016 and the nominal resistance of the pile will increase. Based upon our experience with similar projects in the area, 5 to 7 days is usually required for the full pore pressures to dissipation and soil setup to occur.

For the reasons previously described, it is not recommended to confirm pile resistance with a simple driving criterion such as number of hammer blows per foot of advanced pile. Instead, driving criteria will likely consist of a target tip elevation and/or certain embedded length in a bearing material with specified driving resistance. The specified driving resistance should be based on a Wave Equation Analysis of the contractor’s selected hammer.

Table V provides our recommended pile type and embedment depths for the structures’ foundations. The Factored Resistance shown is based on a Resistance Factor of 0.65 applied to Nominal calculated pile resistance. It is recommended that the test program rely on dynamic testing. The capacity of a group of piles spaced at least 3 pile diameters apart, center to center, can be taken as the sum of the individual resistances with no further reduction factor. If closer pile spacing is anticipated, the Geotechnical Engineer should be contacted to evaluate the efficiency of the specific pile group. The final order lengths and tip elevations will be adjusted based on the results of the test piles and load test programs. Calculations for the pile resistances presented below are provided in Appendix VII. Given the placement of up to 6 to 8 ft of structural Fill material and this impact on the underlying cohesive soil layers, and considering the consolidation characteristics of these soils (ie.,OCR 2.0 and above), Negative Skin Friction effects on the piles should not be a contributing factor.

Table V –Pile Design Recommendations

Pile Type &

Dimensions

Pile Tip

Embedment

Elevation(1) (ft)

Factored Resistance in Compression (tons)

Factored Resistance in Tension (tons)

Pre-Augering

Depth (ft)

12” SPPC -55 to -60 90 - 110 40

10-15 14” SPPC -55 to -60 115 - 130 45

16” SPPC -55 to -60 140 - 160 50

Notes: (1) Based on ground surface elevation data provided by Client.

We recommend pre-augering the pile locations to depths of 10 to 15 feet below grade prior to driving in order to assist pile alignment and initial driving. This is also necessary to help in minimizing the effects of vibrations from the driving effort and to reduce the potential for pile breakage. Following the pre-augering, the piles should be installed and advanced by driving with an impact hammer to their design tip embedment depths. The soils within the vicinity of the pile may densify during driving. This densification will increase with each successive pile; thus possibly signaling that pile driving “capacity” is encountered before the piles reach their design tip elevations. The Geotechnical Engineer should be retained to review driving records and field reports to determine whether the pile can adequately support the design loads. To reduce the likelihood of this phenomenon, it is recommended to install the piles starting from the center of the pile cap outwards. If the pile driving hammer is not properly matched to the pile type, size, and subsurface conditions, it may reach practical refusal before the pile reaches the design tip embedment depth, or the required resistance.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

4.5.2 Lateral Capacity Analysis - Driven Concrete Piles

We conducted our lateral analyses using L-Pile, a computer software package by ENSOFT.

The software requires as input, quantitative data related to strength and deformation behavior of the subsurface materials, the structural properties of the pile, and an understanding of shaft/soil interaction during lateral loading. The program calculates the lateral deflections, internal moment forces, and internal shear forces experienced by a pile subjected to the specific loading conditions. The program does not analyze whether the pile is structurally capable of resisting the moments and shear stresses generated. This analysis should be performed by the project Structural Engineer.

According to the 2012 IBC, Section 1810.3.3.2, “the allowable (lateral) load shall not be more than one-half of the load that produces a gross lateral movement of 1 inch (25 mm) at the lower of the top of foundation element and the ground surface”. Therefore, the lateral capacity analysis was divided in two steps. Step one consisted of determining the lateral load that produces a gross lateral movement of 1 inch. The second step consisted of performing the lateral capacity analysis with ½ the load calculated in Step 1. Summaries of the lateral capacity analyses for 12-, 14-, and 16-inch SPPC piles are presented on the following pages in Table VI through Table VIII. The results of these analyses are presented in Appendix VIII (“L-Pile Analyses”).

Table VI - Lateral Capacity Analysis (IBC)

Characteristics 12” SPPC* 12” SPPC*

Pile Length/Embedment Depth 65 65

Pile-Head Fixity Conditions Free-end Fixed-end

P1=Lateral Load that Produces 1-inch of Lateral Deflection (kips)

16.7 36.6

P2=½ P1 (per 2012 IBC, Section 1810.3.3.2) (kips) 8.4 18.3

Maximum Lateral Deflection (in.) 0.334 0.252

Axial Load (tons) 90 90

Maximum Moment Reaction (ft-lb) 31937 70766

Maximum Shear Reaction (kips) 8.4 18.3

*A concrete compressive strength of 6,000 psi was used to model the pile.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

Table VII - Lateral Capacity Analysis (IBC)

Characteristics 14” SPPC* 14” SPPC*

Pile Length/Embedment Depth 65 65

Pile-Head Fixity Conditions Free-end Fixed-end

P1=Lateral Load that Produces 1-inch of Lateral Deflection (kips)

22.5 48.5

P2=½ P1 (per 2012 IBC, Section 1810.3.3.2) (kips) 11.2 24.2

Maximum Lateral Deflection (in.) 0.324 0.248

Axial Load (tons) 115 115

Maximum Moment Reaction (ft-lb) 46568 103920

Maximum Shear Reaction (kips) 11.2 24.2

Table VIII - Lateral Capacity Analysis (IBC)

Characteristics 16” SPPC* 16” SPPC*

Pile Length/Embedment Depth 65 65

Pile-Head Fixity Conditions Free-end Fixed-end

P1=Lateral Load that Produces 1-inch of Lateral Deflection (kips)

29.1 62.0

P2=½ P1 (per 2012 IBC, Section 1810.3.3.2) (kips) 14.5 31.0

Maximum Lateral Deflection (in.) 0.313 0.247

Axial Load (tons) 140 140

Maximum Moment Reaction (ft-lb) 64236 144935

Maximum Shear Reaction (kips) 14.5 31.0

4.5.3 Pile Group Settlement

Based on the results of load tests performed on piles driven in similar soils conditions, it is anticipated that the total butt settlements (including elastic shortening) will not exceed about ½-inch, which is the settlement necessary to mobilize the soil/pile capacity in combination with the pile group settlements due to the stress increase in the underlying soils.

4.5.4 Test Pile Program

We recommend that a test pile program utilizing dynamic methods be implemented for the purpose of assisting in the development of final embedment depths, confirming the design capacities of the piles, and confirming the contractor’s equipment and installation methods are acceptable. The test program should involve test or “indicator” piles to provide an indication of various driving or installation conditions. We recommend at least ten (10) indicator piles. It is

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016 important to note the relationship between the required testing and our design assumptions. The Geotechnical Engineer should monitor the driving of these test piles. The geotechnical engineer will require all of the test piles to be re-tapped following a waiting period of at least 7 days to check for pile/soil setup.

The test pile locations should be selected by the geotechnical engineer. The piles should be driven using the drive system submitted by the contractor and approved by the Geotechnical Engineer. Test pile lengths should be 10 feet longer that the estimated design length to ensure that the required capacity is developed, and to allow for refinement of estimated capacities. The indicator piles installed during the Test Pile Program, which satisfy the Geotechnical Engineer’s requirements for proper installation, may also be used as permanent project piles.

4.5.5 Dynamic Testing

Dynamic testing was developed as a method of improving upon the reliability of the wave equation and other dynamic predictions by actually measuring the acceleration and strain of a pile during driving. This technique was developed in the mid-1960s and has been continuously refined. The use of dynamic pile testing has permitted the possibility of checking the driving stresses in the pile and the hammer performance during pile driving. It is also possible to estimate the static capacity of the pile based upon the strain and acceleration measurements taken during pile driving.

The test pile installation should be monitored by the Geotechnical Engineer using the PDA, an electronic device that records driving stresses and pile/soil interactions, among other things.

The PDA results will confirm that the pile driving system (hammer type/energy, cushion type/ thickness, etc.) can successfully install the piles without over stressing them in compression or tension. In addition to performing PDA testing during the initial drive, it is essential that the test pile re-strikes also be monitored with the PDA.

No sooner than 7 days after installation, all of the test piles should be re-struck while being monitored with the PDA. This test establishes the “static capacity” of the pile. The initial hammer blow during re-strike activities is critical to the quality of dynamic data with respect to capacity interpretation. The contractor should make every effort to insure an initial high-energy blow of the hammer. After several blows during re-strike activities, pore pressures increase, soil setup diminishes, and ultimately pile capacities (as recorded by the PDA) decrease. Loss of estimated static capacity following repeated hammer blows is the reason the initial blows are critical.

The dynamic data recorded by the PDA during re-strike testing should be further refined by using CAPWAP® analysis. CAPWAP® analysis, not the initial assessment of capacity determined by the PDA, should be the basis of static pile capacity estimates. Interpretation of CAPWAP® data, in the context of the soils subsurface conditions and previous static pile capacity estimates, should allow the Geotechnical Engineer to estimate ultimate pile capacities and recommend appropriate production pile lengths.

Our previous experience with PDA indicates that a significant cost savings may be realized if PDA is properly utilized to monitor the installation of test piles, confirm pile capacity in production installations, and monitor potentially damaging stresses during driving. The use of PDA permits the confirmation of allowable compression and uplift capacities and pile integrity on several piles for a cost similar to or less than that of a single full-scale static load test. We recommend the owner retain the services of the Geotechnical Engineer to perform the dynamic testing, not the installation contractor, to avoid possible conflicts of interest.

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016

4.5.6 Production Pile/Acceptance Criteria

Utilizing the driving records for the tested piles and the results of the dynamic analysis of the driving conditions (WEAP), the pile capacity versus driving resistance (BPF) may be more accurately estimated; and depending on the results of these analyses a static load test or some adjustment to the design capacity or depth may be necessary.

The piles should be installed to the embedment depths identified or as refined by the Geotechnical Engineer following the pile test program. These piles should be driven to the dynamic driving resistance as determined in the field by the Geotechnical Engineer, or to practical refusal, whichever comes first.

Based on our experience with pile installation, it is essential that driving be terminated immediately if refusal is reached to prevent damage to the piles. The pile-driving hammer should be properly matched to the pile to provide sufficient energy to install the pile without damaging it.

The installation of all deep foundation systems should be in accordance with the local Building Code requirements. In addition, a qualified Geotechnical Engineer or representative should monitor the installation of all piles. General pile installation guidelines are provided below.

1. The piles should be evaluated and designed for the axial stresses by the project structural engineer. All of the piles in a foundation element should be of the same type and of equal load carrying capacity.

2. The pile-driving hammer should be capable of driving the pile to at least 3 times the design load without over-stressing the pile in tension or compression. At all times, the hammer should be operated at the chamber pressure, speed, etc. as recommended by the manufacturer.

3. Pile driving should be as continuous an operation as possible and should proceed without stopping over the last 3 feet of penetration. During pile installation, the contractor should exercise caution as not to over stress the piles.

Piles shall not be driven beyond practical refusal.

4. The contractor should exercise caution in pile driving so that the effects of heave are minimized. Careful monitoring by the contractor for possible heave during driving should be exercised. All piles that heave ¼ inch or more should be re-driven unless otherwise instructed by the Geotechnical Engineer.

5. Piles should be installed under continuous monitoring by a qualified Senior

Engineering Technician or Geotechnical Engineer in order to make field judgments of pile penetration and construction and to check for satisfactory foundation support conditions. Driven piles should be monitored for penetration resistance, blow counts, during pile driving and hammer action.

4.5.7 Allowable Driving Stresses

Guidelines from the Prestressed Concrete Institute (PCI), American Society of Civil Engineers (ASCE), and the American Association of State Highway Transportation Officials (AASHTO) indicate that maximum compressive stresses, imposed on driven precast concrete piles during

Report of Subsurface Exploration & Geotechnical Engineering Services February 2, 2016 installation, should be less than the following equation: 0.85 x f’c (concrete compressive strength, psi) - fpe (effective pre-stressing after losses from relaxation). The three groups differ on the maximum tensile stresses. PCI recommends 6 x (f‘c)

0.5 + fpe; AASHTO and ASCE recommend 3 x (f‘c)

0.5 + fpe. We recommend using the consensus value for the maximum compressive stress, and the ASCE/AASHTO recommended value for the maximum tensile stress.

4.5.8 Hammer Types and Energies

In comparing hammers of equal energy, the Prestressed Concrete Institute (PCI) states that hammers with heavier rams and lower impact velocities are less likely to cause damaging stresses in concrete piles. Hammers with proportionally higher ram weights and short stroke heights (low impact velocities) are usually air, steam and hydraulic driven, and not diesel fueled.

It has been our experience that air, steam and hydraulic hammers are more appropriate for the installation of precast concrete piles than similarly sized (in terms of energy) diesel hammers.

We recommend that the contractor use an air, steam or hydraulic driven hammer whose ram weight is roughly equal to 0.5 to 1.0 times the weight of the pile itself. The actual determination of an acceptable ram weight should be determined through the results of the Test Pile Program.

If the contractor elects to use a diesel hammer, we recommend a critical, detailed review of the contractor’s Wave Equation Analysis prior to driving the test piles.

4.5.9 Adjacent Structures

When considering the suitability of a driven pile foundation, consideration should be given to the integrity of nearby structures (if applicable). Due to the large amount of energy required to install driven deep foundations, vibrations of considerable magnitude are generated. These vibrations may affect nearby structures. These structures can, due to their proximity, be detrimentally affected by the construction unless proper protection measures are taken. In addition, experience has shown that these construction features will often lead adjacent property owners to conclude that damage to their property has taken place, even though none has occurred. It is therefore recommended that a thorough survey of the adjacent property be made prior to starting construction. This will help to better evaluate real claims and refute groundless nuisance claims. The survey should include, but not be limited to, the following:

1. Visually inspect…