Solicitation Attachment 5 - Geotechnical Report.pdf

REPORT OF GEOTECHNICAL SUBSURFACE EXPLORATION

NCANG MSA BUILDING

MINUTEMAN WAY

CHARLOTTE, NORTH CAROLINA

SUMMIT PROJECT NO. 5404.500

Prepared For:

Mr. Robert Fritz Mott Macdonald

111 Wood Avenue South Iseline, NJ 08830

Email: Robert.fritz@mottmac.com

Prepared By:

SUMMIT Engineering, Laboratory & Testing, P. C. (SUMMIT) 3575 Centre Circle Drive

Fort Mill, South Carolina 29715

December 21, 2018 i

December 21, 2018

Mr. Robert Fritz Mott Macdonald 111 Wood Avenue South Iseline, NJ 08830 Email: Robert.fritz@mottmac.com

Subject: Report of Geotechnical Subsurface Exploration NCANG MSA Building Minuteman Way Charlotte, North Carolina SUMMIT Project No. 5404.500

Dear Mr. Fritz:

SUMMIT Engineering, Laboratory & Testing, P. C. (SUMMIT) has completed a geotechnical subsurface exploration for the NCANG MSA Building – Location 2 site located off of Minuteman Way in Charlotte, North Carolina. These geotechnical services were performed in general accordance with our Proposal No. P2018-548B-G, dated May 11, 2018. This report contains a brief description of the project information provided to us, general site and subsurface conditions revealed during our geotechnical subsurface exploration and our general recommendations regarding foundation design and construction.

SUMMIT appreciates the opportunity to be of service to you on this project. If you have any questions concerning the information presented herein or if we can be of further assistance, please feel free to call us at (704) 504-1717.

Sincerely yours, SUMMIT Engineering, Laboratory & Testing, P. C.

Todd A. Costner, E.I. Robert L. Price, P.E.

Senior Professional Geotechnical Department Manager rprice Typewritten Text 12/21/18

Report of Geotechnical Subsurface Exploration SUMMIT Project No. 5404.500 NCANG MSA Building December 21, 2018 ii

TABLE OF CONTENTS

SECTION Page

EXECUTIVE SUMMARY ........................................................................................................... iii

1.0 INTRODUCTION

1.1. Site and Project Description

1.2. Purpose of Subsurface Exploration

2.0 EXPLORATION PROCEDURES

2.1. Field Exploration

3.0 AREA GEOLOGY AND SUBSURFACE CONDITIONS

3.1. Physiography and Area Geology

3.2. Generalized Subsurface Stratigraphy

3.2.1. Surface Materials

3.2.2. Existing Fill Soils

3.2.3. Residual Soils

3.2.4. Partially Weathered Rock and Auger Refusal

3.2.5. Groundwater Level Measurements

4.0 EVALUATIONS AND RECOMMENDATIONS

4.1. General

4.2. Shallow Foundation Recommendations

4.3. Retaining Wall Recommendations

4.4. Seismic Site Class

4.5. Low to Moderate Plasticity Moisture Sensitive Soils (MH)

4.6. Wet Weather Conditions

4.7. Floor Slabs

4.8. Pavements Subgrade Preparation

4.9. Cut and Fill Slopes

5.0 CONSTRUCTION CONSIDERATIONS

5.1. Abandoned Utilities/Structures

5.2. Site Preparation

5.3. Difficult Excavation

5.4. Temporary Excavation Stability

5.5. Structural Fill

5.6. Engineering Services During Construction

6.0 RELIANCE AND QUALIFICATIONS OF REPORT

APPENDIX 1 Figure

Site Vicinity Map Boring Location Plan ReMi Profile Location Plan .............................................................................................. 2A

APPENDIX 2 - Boring Logs

APPENDIX 3 – ReMi test Results iii

EXECUTIVE SUMMARY

SUMMIT has completed a geotechnical subsurface exploration for the NCANG MSA Building project. The purpose of this exploration was to obtain general information regarding the subsurface conditions and to provide geotechnical recommendations regarding foundation support of the proposed construction. The exploration consisted of two (2) soil test borings (identified as B-1 and B-2). The approximate test locations are shown on the Figure 2 provided in Appendix 1.

The following geotechnical engineering information was obtained as a result of the soil test borings:

• Surface Materials – Surficial organic soils (topsoil) was observed at the existing ground surface of Boring B-1 with a thickness of approximately 2 inches. A 4-inch layer of asphalt pavement underlain with a 2-inch layer of stone aggregate was observed at the existing surface of Boring B-2.

• Existing Fill Soils - Existing fill (disturbed) soils were encountered beneath the surface material in Borings B-1 and B-2 to approximate depths of 1.5 and 3 feet below the existing ground surface, respectively. When sampled, the existing fill soils generally consisted of sandy silts (ML). The Standard Penetration Resistances (SPT N-values) in the existing fill soils were 13 and 15 blows per foot (bpf).

• Residual Soils - Residual (undisturbed) soils were encountered below the surface materials, and existing fill soils and extended to the maximum termination depth. These residual soils generally consisted of elastic silts (MH), sandy silts (ML), and silty sands (SM). The Standard Penetration Resistances (SPT N-values) in the residual soils ranged from 11 to 39 bpf.

• Partially Weathered Rock (PWR) and Auger Refusal – A stratum of partially weathered rock (PWR) conditions were encountered in Boring B-2 between the approximate depths of 17 to 22 feet below the existing ground surface. PWR is defined as soil-like material exhibiting SPT N-values in excess of 100 bpf. Auger refusal conditions were not encountered in the borings. Auger refusal is defined as material that could not be penetrated by the drilling equipment used during our field exploration.

• Groundwater Levels - At the time of drilling, groundwater was not observed in the borings.

• Foundation Support - Based on the results of our borings, the proposed structures can be adequately supported on shallow foundations systems provided site preparation and compacted fill recommendation procedures outlined in this report are implemented. An allowable net bearing pressure of up to 3,000 pounds per square foot (psf) can be used for design of the foundations bearing on approved undisturbed residual soils, or on structural fill compacted to at least 95 percent of its Standard Proctor maximum dry density.

• Seismic Site Class – We have evaluated the Seismic Site Classification for this project site in accordance with Chapter 16, Section 1613.5.2 of the 2012 North Carolina Building Code, Site Class Definitions using Soil Shear Wave Velocity results obtained during a December 2014 geotechnical subsurface exploration. We recommend this project be designed using a Seismic iv

Site Class of Class of “C” (Very Dense Soil and Soft Rock) as defined in Table 1613.5.4 Site Class Definitions

Please note that the information provided in this executive summary is intended to be a brief overview of project information and recommendations from the geotechnical report. The information in the executive summary should not be used without first reading the geotechnical report and the recommendations described therein.

Report of Geotechnical Services SUMMIT Project No. 5404.500

1.0 INTRODUCTION

1.1. Site and Project Description

The NCANG MSA Building site is located off of Minuteman Way in Charlotte, North Carolina.

A vicinity map showing the project’s general location is provided as Figure 1. At the time of our field exploration, the subject site was grass covered yards, building and parking lot.

The Client (Mott Macdonald) provided SUMMIT a plan that indicated the configurations of the proposed construction planned for this project. Based on the provided information, we understand the project is planned to include 960 square foot building.

At the time of report preparation, SUMMIT had not been provided structural details of the planned construction indicating proposed loads, foundation bearing elevations, or finished floor elevations.

For this report, SUMMIT assumed the proposed structure will be supported on a shallow foundation system consisting of spread, strip, and/or combined footings and that wall loads will be on the order of 1 to 3 kips per foot and column loads on the order of 50 to 100 kips. Also, grading plans were not available at the time of this report and we have assumed that maximum cut/fill depths will be on the order of 1 to 2 feet over the existing ground surface.

1.2. Purpose of Subsurface Exploration

The purpose of this exploration was to obtain general geotechnical information regarding the subsurface conditions and to provide general preliminary recommendations regarding the geotechnical aspects of site preparation and foundation design. This report contains the following items:

• General subsurface conditions,

• Boring logs and an approximate “Boring Location Plan”,

• Suitable foundation types,

• Allowable bearing pressures for design of shallow foundations,

• Anticipated excavation difficulties during site grading and/or utility installation,

• Remedial measures to correct unsatisfactory soil conditions during site development, as needed,

• Drainage requirements around structures and under floor slabs, as needed,

• Construction considerations,

• Pavement subgrade support guidelines,

• Seismic Site Classification.

2.0 EXPLORATION PROCEDURES

2.1. Field Exploration

SUMMIT visited the site on December 18, 2018 and performed a geotechnical exploration that consisted of two (2) soil test borings (identified as B-1 and B-2). The approximate locations of the borings are shown on the Figure 2 - “Boring Location Plan” provided in Appendix 1. The borings were located by professionals from our office using the provided plan, recreation-grade handheld

GPS, existing topography, and aerial maps as reference. Since the boring locations were not surveyed, the location of the borings should be considered approximate.

The soil test borings were performed using an ATV-mounted CME 550X drill rig and extended to an approximate depth of 25 feet below the existing ground surface. Hollow-stem, continuous flight auger drilling techniques were used to advance the borings into the ground. Standard Penetration

Tests (SPT) were performed within the mechanical borings at designated intervals in general accordance with ASTM D 1586. The SPT “N” value represents the number of blows required to drive a split-barrel sampler 12 inches with a 140-pound hammer falling from a height of 30 inches.

When properly evaluated, the SPT results can be used as an index for estimating soil strength and density. In conjunction with the penetration testing, representative soil samples were obtained from each test location and returned to our laboratory for visual classification in general accordance with ASTM D 2488. Water level measurements were attempted at the termination of drilling. The results of these tests are presented on the individual boring logs provided in Appendix

2 at the respective test depth.

3.0 AREA GEOLOGY AND SUBSURFACE CONDITIONS

3.1. Physiography and Area Geology

The subject property is located in Charlotte, North Carolina, which is located in the south central

Piedmont Physiographic Province. The Piedmont Province generally consists of well-rounded hills and ridges which are dissected by a well-developed system of draws and streams. The

Piedmont Province is predominantly underlain by metamorphic rock (formed by heat, pressure and/or chemical action) and igneous rock (formed directly from molten material) which were initially formed during the Precambrian and Paleozoic eras. The volcanic and sedimentary rocks deposited in the Piedmont Province during the Precambrian era were the host of the metamorphism and were generally changed to gneiss and schist. The more recent Paleozoic era had periods of igneous emplacement, with episodes of regional metamorphism resulting in the majority of the rock types seen today.

The topographic relief found throughout the Piedmont Province has developed from differential weathering of theses igneous and metamorphic rock formations. Ridges developed along the more easily weathered and erodible rock. Because of the continued chemical and physical weathering, the rocks in the Piedmont Province are generally covered with a mantle of soil that has weathered in-place from the parent bedrock below. These soils have variable thicknesses and are referred to as residual soils, as they are the result of in-place weathering. Residual soils are typically fine-grained and have a higher clay content near the ground surface because of the advanced weathering. Similarly, residual soils typically become more coarse-grained with increasing depth because of decreased weathering. As weathering decreases with depth, residual soils generally retain the overall appearance, texture, gradation and foliations of their parent rock.

3.2. Generalized Subsurface Stratigraphy

General subsurface conditions observed during our geotechnical exploration are described herein.

For more detailed soil descriptions and stratifications at a particular field test location, the respective “Boring Logs”, provided in Appendix 2 should be reviewed. The horizontal stratification lines designating the interface between various strata represent approximate boundaries. Transitions between different strata in the field may be gradual in both the horizontal and vertical directions. Therefore, subsurface stratigraphy between test locations may vary.

3.2.1. Surface Materials

Surficial organic soils (topsoil) was observed at the existing ground surface of Boring B-1 with a thickness of approximately 2 inches. A 4-inch layer of asphalt pavement underlain with a 2-inch layer of stone aggregate was observed at the existing surface of Boring B-2.

3.2.2. Existing Fill Soils

Existing fill (disturbed) soils were encountered beneath the surface material in Borings B-

1 and B-2 to approximate depths of 1.5 and 3 feet below the existing ground surface, respectively. When sampled, the existing fill soils generally consisted of stiff sandy silts

(ML). The Standard Penetration Resistances (SPT N-values) in the existing fill soils were

13 and 15 blows per foot (bpf).

Based on historical aerial photographs and our site observations, previous grading activities and/or development have occurred on the property. As such, the contractor should anticipate the presence of fill soils, active or abandoned utility lines, and/or construction debris even though fill soils were not encountered in the borings performed for this exploration. If fill soils are encountered at other locations in the field during construction, the fill soils should be evaluated by the Geotechnical Engineer-of-Record, or his authorized representative, with respect to the criteria outlined in Section 5.0 – Construction

Considerations.

3.2.3. Residual Soils

Residual (undisturbed) soils were encountered below the surface materials and existing fill soils and extended to the maximum termination depth. These residual soils generally consisted of very stiff elastic silts (MH), stiff to very stiff sandy silts (ML), and medium dense to dense silty sands (SM). The Standard Penetration Resistances (SPT N-values) in the residual soils ranged from 11 to 39 bpf.

3.2.4. Partially Weathered Rock and Auger Refusal

A stratum of partially weathered rock (PWR) conditions were encountered in Boring B-2 between the approximate depths of 17 to 22 feet below the existing ground surface. PWR is defined as soil-like material exhibiting SPT N-values in excess of 100 bpf. When sampled, the PWR generally breaks down into silty sands with rock fragments.

Auger refusal conditions were not encountered in the borings. Auger refusal is defined as material that could not be penetrated by the drilling equipment used during our field exploration.

3.2.5. Groundwater Level Measurements

At the time of drilling, groundwater was not observed in the borings performed during this exploration. However, the moisture conditions of the soil samples were noted and the cave-in depths within each borehole were measured at the time of drilling. Both moisture conditions within the soil and caving soils may be an indication of the presence of groundwater.

It should be noted that groundwater levels tend to fluctuate with seasonal and climatic variations, as well as with some types of construction operations. Therefore, water may be encountered during construction at depths not indicated in the borings performed for this exploration.

4.0 EVALUATIONS AND RECOMMENDATIONS

4.1. General

Our preliminary evaluation and recommendations are based on the project information outlined previously and on the data obtained from the field testing program. If the structural loading, geometry, or proposed building locations are changed or significantly differ from those outlined, or if conditions are encountered during construction that differ from those encountered by the borings, SUMMIT requests the opportunity to review our recommendations based on the new information and make the necessary changes.

Grading plan information with proposed foundation bearing elevations was not available for our review at the time of this report. Finish grade elevations of proposed construction in conjunction with the proposed foundation bearing elevation can have a significant effect on design and construction considerations. SUMMIT should be provided the opportunity to review the project grading plans prior to their finalization with respect to the recommendations contained in this report.

4.2. Shallow Foundation Recommendations

Based on the results of the soil test borings, and our assumptions regarding site grading and assumed structural building loads, the proposed structures can be adequately supported on shallow foundation systems provided site preparation and compacted fill recommendation procedures outlined in this report are implemented. An allowable net bearing pressure of up to 3,000 pounds per square foot (psf) can be used for design of the foundations bearing on approved undisturbed residual soils, or on approved structural fill compacted to at least 95 percent of its Standard Proctor maximum dry density. Please refer to section 5.0 of this report for more information.

Provided the procedures and recommendations outlined in this report are implemented and using the assumed loads, we have estimated a total settlement of less than 1 inch for footing design pressures of 3,000 psf.

To avoid punching type bearing capacity failure, we recommend wall foundation widths of 18 inches or more. Exterior foundations and foundations in unheated areas should be designed to bear at least 12 inches below finished grade for frost protection. To reduce the effects of seasonal moisture variations in the soils, for frost protection and for bearing capacity, it is recommended that all foundations be embedded at least 12 inches below the lowest adjacent grade.

All footing excavations and undercutting remediation operations should be evaluated by the

Geotechnical Engineer-of-Record or his qualified representative to confirm that suitable soils are present at and below the proposed bearing elevation and that the backfill operations are completed with the recommendations of this report. This evaluation may include hand-auger and DCP testing.

If evaluation with DCP testing encounters lower penetration resistances than anticipated or unsuitable materials are observed beneath the footing excavations, these bearing soils should be corrected per the Geotechnical Engineer-of-Record’s recommendations.

4.3. Retaining Wall Recommendations

Design Parameters for backfill properties (i.e., friction angle, earth pressure coefficients) should use the values in the table below. These parameters are based on suitable soils with a minimum moist unit weight of 120 pcf. SUMMIT should be retained to test the actual soils used for construction to verify these design assumptions. To reduce long term creep or deflections to the wall system, desirable wall backfill soils should be used. These include non-plastic, granular soils

(sands and gravels). However, these soils may not be available on site.

Soil Parameters for Wall Backfill

Backfill Type

Allowable Bearing Capacity

(psf)

Friction Angle (deg)

Modulus of Subgrade Reaction

(pci)

Active Earth

Pressure Coefficient

Ka

Passive Earth

Pressure Coefficient

Kp

Coefficient of Earth

Pressure at Rest Ko

Slide Friction

Residuum 3,000 28° 200 0.361 2.77 0.531 0.4

Fill 3,000 24 o 150 0.421 2.37 0.593 0.4

Soils classified as elastic silts (MH) and/or fat clays (CH) shall not be used for wall backfill or in the retained zone as shown in Table 1610.1 of the 2015 IBC. If on-site soils are used as backfill within the reinforced zone, the wall designer should address the need for wall drainage and the possibility of long-term, time-dependent movement or creep in their design.

At the time of report preparation, we were not provided retaining wall plans or specifications.

Therefore, we request the opportunity to review the wall plans and specifications once they are finalized. Also, we recommend an external stability analysis (including global stability) of the proposed wall(s) be conducted once the site layout and wall geometry is complete.

4.4. Seismic Site Class

SUMMIT has evaluated the Seismic Site Classification for this project site in accordance with

Chapter 16, Section 1613.5.2 of the 2012 North Carolina Building Code, Site Class Definitions using Soil Shear Wave Velocity results obtained during a December 2014 geotechnical subsurface exploration. We recommend this project be designed using a Seismic Site Class of Class of “C”

(Very Dense Soil and Soft Rock) having an average shear wave velocity of 1,237 ft/sec as defined in Table 1613.5.4 Site Class Definitions. The approximate location of the ReMi Profile run was performed as shown on the Boring Location Plan (Figure 2A) included in Appendix 1 of this report. The results of the ReMi test are presented in graphical form in Appendix 3 – ReMi Shear

Wave Testing Results.

4.5. Low to Moderate Plasticity Moisture Sensitive Soils (MH)

Low to moderate plasticity and moisture sensitive (elastic silts) soils were encountered in Boring

B-1 between the approximate depths of 1.5 to 5.5 feet below the existing ground surface. These fine-grained soils are susceptible to moisture intrusion and can become soft when exposed to weather and/or water infiltration. Consequently, some undercutting and/or reworking (drying) of the near-surface soils may be required depending upon the site management practices and weather conditions present during construction.

Should these materials be left in-place, special consideration should be given to providing positive drainage away from the structure and discharging roof drains a minimum of 5 feet from the foundations to reduce infiltration of surface water to the subgrade materials.

Note: Since Low to Moderate Plasticity and Moisture Sensitive Soils can become remolded (i.e., softened) under the weight of repeated construction traffic and changes in moisture conditions, these soils should be evaluated and closely monitored by the Geotechnical Engineer-of-Record or his qualified representative prior to and during fill placement. Additional testing and inspections of moisture sensitive soils may be warranted such as laboratory testing, field density (compaction) testing, hand auger borings with dynamic cone penetrometer (DCP) testing and/or test pit excavations.

4.6. Wet Weather Conditions

Contractors should be made aware of the moisture sensitivity of the near soils and potential compaction difficulties. If construction is undertaken during wet weather conditions, the surficial soils may become saturated, soft, and unworkable. The contractor can anticipate reworking and/or recompacting soils may be needed when excessive moisture conditions occur. Additionally, subgrade stabilization techniques, such as chemical (lime or lime-fly ash) treatment, may be needed to provide a more weather-resistant working surface during construction. Therefore, we recommend that consideration be given to construction during the dryer months.

Surface runoff should be drained away from excavations and not allowed to pond. Concrete for foundations should be placed as soon as practical after the excavation is made. That is, the exposed foundation soils should not be allowed to become excessively dry or wet before placement of concrete. Bearing soils exposed to moisture variations may become highly disturbed resulting in the need for undercutting prior to placement of concrete. If excavations must remain open overnight, or if rainfall becomes imminent while the bearing soils are exposed, we recommend that a 2- to 4-inch-thick “mud-mat” of lean (2000 psi) concrete be placed on the bearing soils before work stops for the night.

SUMMIT recommends that special care be given to providing adequate drainage away from the building areas to reduce infiltration of surface water to the base course and subgrade materials. If these materials are allowed to become saturated during the life of the slab section, a strength reduction of the materials may result causing a reduced life of the section.

4.7. Floor Slabs

Slab-on-grade floor systems may be supported on approved residual soils, or newly compacted fill, provided the site preparation and fill placement procedures outlined in this report are implemented. Depending upon the amount of cuts and/or fills, unsuitable soils such as areas which deflect, rut or pump excessively during proof-rolling may require remediation as described in

Section 5.2. We recommend floor slabs be isolated from other structural components to allow independent movement of the slab and the building foundation elements.

Immediately prior to constructing a floor slab, the areas should be proof-rolled to detect any softened, loosened or disturbed areas that may have been exposed to wet weather or construction traffic. Areas that are found to be disturbed or indicate pumping action during the proof-rolling should be undercut and replaced with adequately compacted structural fill. This proof-rolling should be observed by the staff professional or a senior soils technician under his/her direction.

Proof-rolling procedures are outlined in the “Site Preparation” section of this report.

4.8. Pavements Subgrade Preparation

The pavement sections can be adequately supported on approved non-high plasticity residual soils, or newly compacted fill, provided the site preparation and fill placement procedures outlined in this report are implemented. Immediately prior to constructing the pavement section, we recommend that the areas be proofrolled to detect any softened, loosened or disturbed areas that may have been exposed to wet weather or construction traffic. Areas that are found to be disturbed or indicate instability during the proofrolling should be undercut and replaced with adequately compacted structural fill or repaired as recommended by the Geotechnical Engineer. This proofrolling should be observed by the staff professional or a senior soils technician under his/her direction. Proofrolling procedures are outlined in the “Site Preparation” section of this report.

Due to prevalence of near surface low to moderate to high plasticity elastic silts, remediation of pavement subgrade soils may be recommended (as determined by the Geotechnical Engineer during construction) including undercutting and replacement with additional NCDOT ABC stone. Alternatively, lime stabilization of pavement subgrade may be a more economical option and SUMMIT can provide lime stabilization mix design services if requested. This may be more pronounced depending on the time of the year and seasonal conditions at the time of pavement construction. We recommend contingency for some remediation efforts for the subgrade soils be considered during the planning stage.

4.9. Cut and Fill Slopes

Permanent project slopes should be designed with geometry of 3 horizontal to 1 vertical or flatter.

The tops and bases of all slopes should be located 10 feet or more from structural limits and 5 feet or more from parking limits. Fill slopes should be properly compacted according to the recommendations provided in this report. In addition, fill slopes should be overbuilt and cut to finished grade during construction to achieve proper compaction on the slope face. All slopes should be seeded and maintained after construction and adhere to local, state and federal municipal standards, if applicable.

5.0 CONSTRUCTION CONSIDERATIONS

5.1. Abandoned Utilities/Structures

SUMMIT recommends that any existing utility lines and foundations be removed from within proposed building and pavement areas. The utility backfill and foundation material should be removed and the subgrade in the excavations should be evaluated by a geotechnical professional prior to fill placement. The subgrade evaluation should consist of visual observations, probing with a steel rod and/or performing hand auger borings with Dynamic Cone Penetrometer tests to evaluate their suitability of receiving structural fill. Once the excavations are evaluated and approved, they should be backfilled with adequately compacted structural fill. Excavation backfill under proposed new foundations should consist of properly compacted structural fill, crushed stone, flowable fill or lean concrete as approved by the Geotechnical Engineer-of-Record.

5.2. Site Preparation

Topsoil, organic laden/stained soils, construction debris and other unsuitable materials should be stripped/removed from the proposed construction limits. Stripping and clearing should extend 10 feet or more beyond the planned construction limits. Upon completion of the stripping operations, we recommend areas planned for support of foundations, floor slabs, parking areas and structural fill be proof-rolled with a loaded dump truck or similar pneumatic tired vehicle (minimum loaded weight of 20 tons) under the observations of a staff professional. After excavation of the site has been completed, the exposed subgrade in cut areas should also be proof-rolled. The proof-rolling procedures should consist of four complete passes of the exposed areas, with two of the passes being in a direction perpendicular to the proceeding ones. Any areas which deflect, rut or pump excessively during proof-rolling or fail to “tighten up” after successive passes should be undercut to suitable soils and replaced with compacted fill.

The extent of any undercut required should be determined in the field by an experienced staff professional or engineer while monitoring construction activity. After the proof-rolling operation has been completed and approved, final site grading should proceed immediately. If construction progresses during wet weather, the proof-rolling operation should be repeated after any inclement weather event with at least one pass in each direction immediately prior to placing fill material or aggregate base course stone. If unstable conditions are experienced during this operation, then undercutting or reworking of the unstable soils may be required.

5.3. Difficult Excavation

Based on the results of our soil test borings and dependent on final grades, it appears that the majority of general excavation for footings and utilities will be possible with conventional excavating techniques. We anticipate that the residual soils can be excavated using pans, scrapers, backhoes, and front end loaders.

Even though Partially Weathered Rock (PWR) material was encountered in Boring B-2 and auger refusal conditions were not encountered in the borings performed for this exploration, the depth and thickness of partially weathered rock, boulders, and rock lenses or seams can vary dramatically in short distances and between the boring locations; therefore, soft/hard weathered rock, boulders or bedrock may be encountered during construction at locations or depths, between the boring locations, not encountered during this exploration.

The table below may be used as a quick reference for rippability of in-place materials.

Summary of Rippability Based on SPT N-Values

N-Values as Shown on Boring Logs Description of N-Values Anticipated Rippability

60 < N-Value N-values less than 60 bpf These materials may generally be excavated with heavy-duty equipment such as a Caterpillar D-8 with a single-shank ripper

60 < N-Value < 50/3” N-values more than 60 bpf, but less than 50 blows per 3 inches of penetration

These materials are considered marginally excavatable, even with heavy-duty equipment.

50/3” < N-Value N-values more than 50 blows per 3 inches of penetration

Blasting and/or removal with impact hammers is typically required to excavate these materials.

*This table is for general information only. Actual rippability is dependent upon many other factors as stated above.

Care should be exercised during excavations for footings on rock to reduce disturbance to the foundation elevation. The bottom of each footing should be approximately level. When blasting is utilized for foundation excavation in rock, charges should be held above design grades. Actual grades for setting charges should be selected by the contractor and he should be responsible for any damage caused by the blasting. All loose rock should be carefully cleaned from the bottom of the excavation prior to pouring concrete. Footing excavations in which the rock subgrade has been loosened due to blasting should be deepened to an acceptable bearing elevation.

In our professional opinion, a clear and appropriate definition of rock should be included in the project specifications to reduce the potential for misunderstandings. A sample definition of rock for excavation specifications is provided below:

Rock is defined as any material that cannot be dislodged by a Caterpillar D-8 tractor, or equivalent, equipped with a hydraulically operated power ripper (or by a Cat 325 hydraulic backhoe, or equivalent) without the use of drilling and blasting.

Boulders or masses of rock exceeding ½ cubic yard in volume shall also be considered rock excavation. This classification does not include materials such as loose rock, concrete, or other materials that can be removed by means other than drilling and blasting, but which for any reason, such as economic reasons, the

Contractor chooses to remove by drilling and blasting.

5.4. Temporary Excavation Stability

Localized areas of soft or unsuitable soils not detected by our borings, or in unexplored areas, may be encountered once grading operations begin. Vertical cuts in these soils may be unstable and may present a significant hazard because they can fail without warning. Therefore, temporary construction slopes greater than 5 feet in height should not be steeper than two horizontal to one vertical (2H:1V), and excavated material should not be placed within 10 feet of the crest of any excavated slope. In addition, runoff water should be diverted away from the crest of the excavated slopes to prevent erosion and sloughing.

Should excavations extend below final grades, shoring and bracing or flattening (laying back) of the slopes may be required to obtain a safe working environment. Excavation should be sloped or shored in accordance with local, state and federal regulations, including OSHA (29 CFR Part 1926) excavation trench safety standards.

5.5. Structural Fill

Soil to be used as structural fill should be free of organic matter, roots or other deleterious materials. Structural fill should have a plasticity index (PI) less than 25 and a liquid limit (LL) less than 50 or as approved by the Geotechnical Engineer-of-Record. Compacted structural fill should consist of materials classified as either CL, ML, SC, SM, SP, SW, GC, GM, GP, or GW per ASTM D-2487 or as approved by the Geotechnical Engineer-of-Record. Off-site borrow soil should also meet these same classification requirements. Non-organic, low-plasticity on-site soils are expected to meet this criterion. However, successful reuse of the excavated, on-site soils as compacted structural fill will depend on the moisture content of the soils encountered during excavation. We anticipate that scarifying and drying of portions of the on-site soils will be required before the recommended compaction can be achieved. Drying of these soils will likely result in some delay.

All structural fill soils should be placed in thin (not greater than 8 to 12 inches) loose lifts and compacted to a minimum of 95 percent of the soil's Standard Proctor maximum dry density

(ASTM D 698) at near optimum moisture content (±2%). The upper 1 foot of structural fill within the parking and drive areas should be compacted to a minimum of 100 percent of the soil's Standard

Proctor maximum dry density (ASTM D 698) at near optimum moisture content. Some manipulation of the moisture content (such as wetting, drying) may be required during the filling operation to obtain the required degree of compaction. The manipulation of the moisture content is highly dependent on weather conditions and site drainage conditions. Therefore, the grading contractor should be prepared to both dry and wet the fill materials to obtain the specified compaction during grading. Sufficient density tests should be performed to confirm the required compaction of the fill material.

5.6. Engineering Services During Construction

As stated previously, the engineering recommendations provided in this report are based on the project information outlined above and the data obtained from field tests. However, unlike other engineering materials like steel and concrete, the extent and properties of geologic materials (soil) vary significantly. Regardless of the thoroughness of a geotechnical engineering exploration, there is always a possibility that conditions between borings will be different from those at the boring locations, that conditions are not as anticipated by the designers, or that the construction process has altered the subsurface conditions. This report does not reflect variations that may occur between the boring locations. Therefore, conditions on the site may vary between the discrete locations observed at the time of our subsurface exploration.

The nature and extent of variations between the borings may not become evident until construction is underway. To account for this variability, professional observation, testing and monitoring of subsurface conditions during construction should be provided as an extension of our engineering services. These services will help in evaluating the Contractor's conformance with the plans and specifications. Because of our unique position to understand the intent of the geotechnical engineering recommendations, retaining us for these services will also allow us to provide consistent service through the project construction. Geotechnical engineering construction observations should be performed under the supervision of the Geotechnical Engineer-of-Record from our office who is familiar with the intent of the recommendations presented herein. This observation is recommended to evaluate whether the conditions anticipated in the design actually exist or whether the recommendations presented herein should be modified where necessary.

Observation and testing of compacted structural fill and backfill should also be provided by our firm.

6.0 RELIANCE AND QUALIFICATIONS OF REPORT

This geotechnical subsurface exploration has been provided for the sole use of Mott Macdonald.

This geotechnical subsurface exploration should not be relied upon by other parties without the express written consent of SUMMIT and Mott Macdonald.

The analyses and recommendations submitted in this report were based, in part, on data obtained from this exploration. If the above-described project conditions are incorrect or changed after the issuing of this report, or subsurface conditions encountered during construction are different from those reported, SUMMIT should be notified and these recommendations should be re-evaluated based on the changed conditions to make appropriate revisions. We have prepared this report according to generally accepted geotechnical engineering practices. No warranty, express or implied, is made as to the professional advice included in this report.

APPENDIX 1 – Figures

APPENDIX 2 – Boring Logs

PROJECT NUMBER 5404.500 PROJECT LOCATION Charlotte, North Carolina

PROJECT NAME NCANG MSA BuildingCLIENT Mott MacDonald

ABBREVIATIONS

TV

PID

UC

ppm

TORVANE

PHOTOIONIZATION DETECTOR

UNCONFINED COMPRESSION

PARTS PER MILLION

LIQUID LIMIT (%)

PLASTIC INDEX (%)

MOISTURE CONTENT (%)

DRY DENSITY (PCF)

NON PLASTIC

PERCENT PASSING NO. 200 SIEVE

POCKET PENETROMETER (TSF)

LL

PI

W

DD

NP

-200

PP

Standard Penetration Test

SAMPLER SYMBOLSLITHOLOGIC SYMBOLS

(Unified Soil Classification System)

WELL CONSTRUCTION SYMBOLS

KEY TO SYMBOLS

Water Level at Time Drilling, or as Shown

Water Level After 24 Hours, or as Shown

Water Level at End of Drilling, or as Shown

ASPHALT: Asphalt

BLANK

FILL: Fill (made ground)

GP: USCS Poorly-graded Gravel

MH: USCS Elastic Silt

MLS: USCS Sandy Silt

SM: USCS Silty Sand

TOPSOIL: Topsoil

PWR: Partially Weathered Rock

SUMMIT Engineering, Laboratory & Testing, P.C.

3575 Centre Circle Fort Mill, South Carolina 29715 704.504.1717 summit-companies.com

SPT

SPT

SPT

SPT

SPT

SPT

SPT

SPT

18ft

Approx. 2" of Topsoil

(ML) FILL:

Stiff Light Brown Slightly Micaceous Slightly Clayey Sandy SILT

(MH) RESIDUUM:

Very Stiff Yellowish Red and White Sandy Elastic SILT

(ML) Very Stiff Light Gray, Gray and Yellow Sandy SILT

(ML) Very Stiff Light Gray and White Sandy SILT

(ML) Very Stiff Light Gray, Gray and Yellow Sandy SILT

(ML) Stiff Moist Olive Gray and White Slightly Sandy SILT

Bottom of Boring at 25 feet bgs, Boring Terminated

4-4-9 (13)

5-8-11 (19)

5-9-12 (21)

8-12-14 (26)

6-7-9 (16)

8-8-17 (25)

5-5-6 (11)

6-7-8 (15)

NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring Location

GROUND ELEVATION

LOGGED BY Adam Jordan

DRILLING METHOD Hollow Stem Auger

DRILLING CONTRACTOR SUMMIT

CHECKED BY T. Costner

DATE STARTED 12/18/18 COMPLETED

AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 18' bgs

AT END OF DRILLING ---

HOLE SIZE 6 inches

GROUND WATER/CAVE-IN:

AFTER DRILLING ---

R E

C O

V E

R Y

(R

Q D

20 40 60 800 100

PL LLMC

FINES CONTENT (%)

20 40 60 800 100

G R

A P

H

IC

LO

G

E

LE

V A

T

IO

N (f t.

5.0

10.0

15.0

20.0

25.0

S A

M P

LE

T

Y P

E N

U M

B E

R

MATERIAL DESCRIPTION

B

LO

W C

O U

N T

S (N

V A

LU

E

SPT N VALUE

20 40 60 800 100

BORING NUMBER B-1

PROJECT NUMBER 5404.500 PROJECT LOCATION Charlotte, North Carolina

PROJECT NAME NCANG MSA BuildingCLIENT Mott MacDonald

SUMMIT Engineering, Laboratory & Testing, P.C.

3575 Centre Circle Fort Mill, South Carolina 29715 704.504.1717

SPT

SPT

SPT

SPT

SPT

SPT

SPT

16.5ft

Approx. 4" of Asphalt Pavement (GP) Approx. 2" of Stone Aggregate

(ML) FILL:

Stiff Reddish Brown Slightly Clayey Sandy SILT

(SM) RESIDUUM:

Medium Dense Light Olive Brown and White Micaceous Silty

SAND

(SM) Dense Light Olive Brown and White Micaceous Silty SAND

(SM) Partially Weathered Rock (PWR) when sampled becomes Light Olive Brown and White Micaceous Silty SAND with Rock Fragments

(SM) Dense Light Olive Brown and White Micaceous Silty SAND with Rock Fragments

Bottom of Boring at 25 feet bgs, Boring Terminated

6-6-9 (15)

6-6-7 (13)

6-7-8 (15)

5-5-7 (12)

20-22-17 (39)

33-34-50 (50/4")

13-14-18 (32)

NOTES Refer to Figure 2 "Boring Location Plan" for Approx. Boring Location

GROUND ELEVATION

LOGGED BY Adam Jordan

DRILLING METHOD Hollow Stem Auger

DRILLING CONTRACTOR SUMMIT

CHECKED BY T. Costner

DATE STARTED 12/18/18 COMPLETED

AT TIME OF DRILLING --- GW NE ATD / Caved in Depth @ 16.5' bgs

AT END OF DRILLING ---

HOLE SIZE 6 inches

GROUND WATER/CAVE-IN:

AFTER DRILLING ---

R E

C O

V E

R Y

(R

Q D

20 40 60 800 100

PL LLMC

FINES CONTENT (%)

20 40 60 800 100

G R

A P

H

IC

LO

G

E

LE

V A

T

IO

N (f t.

5.0

10.0

15.0

20.0

25.0

S A

M P

LE

T

Y P

E N

U M

B E

R

MATERIAL DESCRIPTION

B

LO

W C

O U

N T

S (N

V A

LU

E

SPT N VALUE

20 40 60 800 100

BORING NUMBER B-2

PROJECT NUMBER 5404.500 PROJECT LOCATION Charlotte, North Carolina

PROJECT NAME NCANG MSA BuildingCLIENT Mott MacDonald

SUMMIT Engineering, Laboratory & Testing, P.C.

3575 Centre Circle Fort Mill, South Carolina 29715 704.504.1717

APPENDIX 3 – ReMi Test Results

-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0 500 1000 1500 2000 2500 3000

D ep th , f t

Shear-Wave Velocity, ft/s

Vs100' = 1237 ft/s

NCANG, BLDG 51: Vs Model