20-1-5-125.Geotech Report.Equipment Pad_VA Laundry.pdf

Geotechnical Engineering Report

Planned Equipment Pad – Building 9 1100 North College Avenue Fayetteville, Arkansas GTS Project No. 20-1-5-125

October 1, 2020

Geotechnical Engineering | Construction Materials Testing | Environmental Due Diligence

Harrell Design Group, PC

Prepared For:

8016 Tower Point Drive Charlotte, North Carolina 28227 www.gtsconsulting.net

Harrell Design Group, PC

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

TABLE OF CONTENTS

EXECUTIVE SUMMARY

PROJECT DESCRIPTION and INFORMATION

Project Site

Planned Development

Planned Site Grading

SUMMARY of SUBSURFACE FINDINGS

Surface

Subsurface Soils and Rock

Existing Fill

Native Overburden Soils

Sandstone and Shale

Auger Refusal/Hard Drilling Conditions

Water Measurements

GEOTECHNICAL ENGINEERING ANALYSIS

Geotechnical Considerations

Existing Fill

Moisture-Sensitive Soils

Near-Surface Weak Soils

Equipment Pad and Foundation Type Discussion

Shallow Foundation Recommendations

Shallow Foundation Construction Recommendations

General Dimensions

Evaluation of Supporting Material and Over-Excavation Recommendations

Micropile Foundation Design Recommendations

Micropile Foundation Construction Recommendations

General Guidelines

Load Test

Stress and Bearing Interactions with Existing Building Foundations

Floor Slab Support Recommendations

Floor Slab-On-Grade Design

IBC Site Classification

MASS GRADING RECOMMENDATIONS

Stripping of Surface Concrete Pavement

General Mass Grading Recommendations

Fill Placement

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Re-Use of On-Site Soils as Fill

Utility Trench Backfill

Rock Excavation Potential

Temporary Earth Slopes and Excavations

LATERAL LOADING CONDITIONS

GEOTECHNICAL REPORT REQUIREMENTS and SPECIFICATIONS

SUBSURFACE EXPLORATION and PROCEDURES

LABORATORY TESTING and PROCEDURES

GEOTECHNICAL REPORT LIMITATIONS

ENVIRONMENTAL EXCLUSION

LIST of TABLES

Table 1: Depths to Hard Drilling Conditions Table 2: Depths of Existing and Possible Fill Materials at Boring Locations Table 3: Depths of Low-Shear-Strength Near-Surface Soils at Boring Locations Table 4: Shallow Foundation Recommendations Table 5: Micropile Geotechnical Design Values Table 6: Lateral Earth Pressure Coefficients Table 7: Recommended Soil Compaction Table 8: Soil Fill Material Requirements Table 9: Laboratory Test Method Designations

LIST OF APPENDICES

A

Boring Location Diagram

Boring Logs

B

Laboratory Data

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

EXECUTIVE SUMMARY

The term “existing grade” used in this report refers to the ground surface elevations at the time of our field drilling and sampling. “Finished subgrade” is used in this report to describe the designed, top-of-soil elevations at the site after completion of grading.

Based on the soil and rock types and in-place shear strength encountered at the 4 sample borings performed by GTS and based on our current understanding concerning site development plans, summary geotechnical engineering considerations for development of the project site are provided below. The below information should not be used separately from the more comprehensive discussion provided in the body of this report.

Narrative

Soil and Rock Conditions

Existing fill and possible fill materials were encountered immediately below the surface organics at the performed boring locations. The fill materials consisted of a combination of sandy lean clay, fat clay with sand, clayey sand and poorly-graded sand soils. The fill had variable very low to moderate, yet generally very low to low, shear strength and extended to depths of about 3 ½ to 8 ½ feet below existing grades. There was a general trend of increasing moisture content and decreasing shear strength along with increasing depth within the existing fill at the performed boring locations.

Apparent native soils were encountered immediately beneath the existing fill at Boring B-2, only. The native soils consisted of sandy lean clays with residual shale structure. These apparent native soils extended to a depth of about 5 ½ feet and had moderate shear strength during drilling and sampling, where encountered.

The basal stratum at this site consisted of interbedded weathered sandstone and weathered shale. The sandstone was generally poorly to well cemented and the shale consisted of soft to hard clayey shale transitioning to soft to hard shale with depth. The shale and sandstone were encountered beginning at depths of about 5 ¼ to 8 ½ feet below existing grades.

Hard drilling conditions were encountered within the sandstone and shale bedrock starting at depths of about 5 ¼ to 8 ½ feet below existing grades. Auger refusal material was encountered within the sandstone and shale at Borings B-1 and B-2, only, at depths ranging from 10 to 11 ½ feet below the existing ground surface.

Geotechnical Considerations for Development

Existing fill and possible fill materials were encountered to depths of about 3 ½ to 8 ½ feet below the ground surface at the performed boring locations. GTS has no information regarding the placement and compaction history of the existing fill. The fill does not appear to have been compacted in a controlled manner during placement based on the results of our

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence sample borings. It is the opinion of GTS that there is a high risk associated with supporting future foundations loads, future floor slabs-on-grade and placement of fill material above the existing fill.

Weak soils were encountered within the near-surface soils, approximately 3 ½ to 8 ½ feet below existing grades. These low-shear-strength soils consisted entirely of the apparent existing fill materials. These soils are not suitable for supporting typical foundation loads, slabs-on-grade, or new fills without removal and replacement or ground improvement.

Supporting foundation loads above these weak soils will result in soil consolidation, which may result in a potentially large settlement of the planned building structure. Recommendations are provided in this report to reduce the potential large settlement of the structure, through requiring all foundation loads be transmitted onto weathered rock below these near-surface weak soils or through removing all of the existing fill material and underlying weak on-site soils and replacing with new approved fill material, placed and compacted in standard-thickness lifts.

Geotechnical Recommendations

Based on the borings and anticipated structural loads, two options for support of the planned equipment pad are discussed in this report. GTS can also discuss other ground improvement and/or foundation support options with the design team upon request.

The equipment pad can be supported on new, approved fill material that is placed and compacted after the complete removal of all existing fill materials and any underlying weak soils. GTS anticipates that undercut depths of about 3 ½ to 8 ½ feet below existing grades will be required to remove the unsuitable soils from the project site. We recommend that approved soil fill material be placed and compacted at the project site in standard-thickness lifts to reach plan finished grades. After finished grades are achieved, the planned wall/pad foundations may consist of shallow, conventional, open-trench foundations supported entirely on tested and approved, newly placed and compacted fill material. Shallow foundations bearing on these recommended materials may be designed using a net allowable bearing pressure of 2,000 pounds per square foot (psf) for continuous foundations and 2,500 psf for individual, column foundations. We recommend planned new at-grade floor slabs-on-grade be supported on a minimum of 1 foot of select fill material, placed and compacted above stable on-site soils.

The equipment pad can also be supported on a deep foundation system bearing in well cemented sandstone and hard shale encountered at depths of about 5 ¼ to 8 ½ feet below existing grades. The equipment pad can be designed as a structural frame or structural slab supported entirely above the deep foundation system. Micropile foundation recommendations are provided in this report.

The subsurface conditions at this project are consistent with a Site Class D per the

International Building Code (IBC), 2012 Edition.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

PROJECT DESCRIPTION and INFORMATION

Project Site

The project site is located at the existing Veterans Affairs facility nominally located at 1100

North College Avenue in Fayetteville, Arkansas. The project site includes the existing equipment pad and earth slope immediately east of Building 9. The immediate vicinity of the project site generally consists of a grass covered slope that is moderately to steeply sloped downhill to the east with about 10 feet of topographical relief. At the time of the field drilling and sampling, the project site was also occupied by existing concrete equipment pads, elevated utilities and buried utilities. The existing Building 9 is a two-story building with a basement.

The general boundaries of the project site are outlined in yellow in Figure 1, below. Figure 1 is a satellite image provided by Google.

Figure 1: General Boundaries of the Project Site

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Planned Development

The project consists of new concrete equipment pads after the partial removal of existing equipment pads located at the project site. GTS anticipates that one or more retaining walls will be needed to construct the planned equipment pads. The potential retaining walls are anticipated to have maximum lengths of about 40 feet and maximum heights of about 5 feet.

The type of potential retaining walls is unknown to GTS at this time and the design of these retaining walls are understood to be performed by others.

From conversations with the design team, GTS understands that the planned loading on this slab should be less than 150 pounds per square foot (psf).

See Figure 2 below, for a general layout of the planned development.

Figure 2: General Layout of the Planned Development

Planned Site Grading

Specific grading plans were not provided to GTS for the planned development at the time of this report. However from conversations with the design team, we understand that the new equipment

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence pad planned east of Building 9 will have a finish floor elevation (FFE) of EL 1,440.0 feet, which generally matches the highest elevation of the existing equipment pad at the site. Additionally, the ground surface elevation for the grass covered slope adjacent to the existing Building 9 and the equipment pads have elevations that range from about 1,434 to 1,447 feet.

Based on this information, GTS generally anticipates that maximum cut depths of about 1 foot transitioning to maximum fill depths of about 5 feet will be required to reach plan finished subgrade elevations in the new equipment pad area.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

SUMMARY of SUBSURFACE FINDINGS

Surface

The surface of the performed boring locations generally consisted of grass cover at the performed boring locations at the time of field sampling. The rootmat associated with the surface organics was about 2 to 4 inches in thickness at the performed boring locations.

Photographs showing the general surface conditions at the time of drilling and sampling are provided below and on the following page.

Photograph 1 – project site overview, looking south

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Photograph 2 – project site overview, looking west from southeast corner

Photograph 3 – evidence of ground settlement in the vicinity of Boring B-1, looking west

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Subsurface Soils and Rock

Existing Fill

Existing fill and possible fill materials were encountered immediately below the surface organics at the boring locations. The existing fill consisted predominantly of a combination of sandy lean clay, fat clay with sand, clayey sand and poorly graded sand soils. The existing fill extended to depths of 3 ½ to 8 ½ feet below existing grades.

The existing fill material had variable amounts of silt pockets, sand content, clay content and gravel content (shale, sandstone, chert and limestone). Additionally, a strong petroleum odor was encountered near the bottom of the existing fill material at Borings B-3 and B-4.

The fill material had variable very low to moderate, yet generally very low to low, shear strength during drilling and sampling. At most boring locations, there was a trend of decreasing shear strength with increasing depth within the fill material. Standard penetration test (SPT) N-values of 1 to 12 blows per foot (bpf) were recorded for the existing fill.

Native Overburden Soils

Apparent native soils were encountered below the existing fill material at Boring B-2, only. The native soils encountered below the existing fill materials generally consisted of sandy lean clay soils with residual shale structure. These soils extended to depths of about 5 ½ feet below existing grades.

The native soils had low to moderate shear strength during drilling and sampling. An SPT N-value of 9 bpf was recorded for these soils at Boring B-2, only.

Sandstone and Shale

Apparent bedrock consisting of poorly to well cemented sandstone interbedded with soft to hard clayey shale and shale was encountered below the native overburden soils and existing fill materials at the performed boring locations. The bedrock was apparently encountered beginning at depths of about 5 ¼ to 8 ½ feet below existing grades at the performed boring locations and extended to the terminal depths of the borings.

The encountered sandstone and shale had moderate to high shear strength during drilling and sampling. The strength generally increased while the degree of weathering generally decreased with increasing depth into the interbedded sandstone and shale. N-values of 36 bpf to 50 blows per 1 to 5 inches of penetration were recorded for the sandstone and shale.

Auger Refusal/Hard Drilling Conditions

Hard drilling conditions were encountered within the sandstone and shale starting at depths of about 5 ¼ to 8 ½ feet below existing grades at the performed boring locations. Auger refusal

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence material was encountered above a depth of 15 feet below the existing ground surface at only two of the performed boring locations.

The depths to hard drilling conditions and auger refusal material are summarized in Table 1, below.

Table 1: Depths to Hard Drilling Conditions

Boring

Number

Depths to Hard Drilling Conditions

(Feet below Existing Grades)

Depths to Auger Refusal Material

(Feet below Existing Grades)

B-1 8 ½ 10

B-2 6 11 ½

B-3 8 ½ Not encountered

B-4 5 ¼ Not encountered

Water Measurements

Water observations were made by the drill crew during drilling and immediately after completion of drilling. The performed borings were backfilled after completion of drilling for safety reasons, and no further groundwater measurements were possible. The observations made by the drilling crew are shown at the bottom of each boring log. Water was not encountered at the performed boring locations at any times.

The boring cave-in depths noted on the boring logs represent a loss of soil shear strength in the sides of the borings. This may be associated with the presence of perched water and the cave-in depths may correlate to the surface of the groundwater. Cave-in depths of 4 to 8 feet below existing grades when the borings were checked for groundwater at completion of drilling.

The depths to water are intended as isolated measurements of groundwater levels at the time of drilling. The installation and periodic measurement of monitoring wells would be required to establish seasonal piezometric surfaces below this project site.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

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GEOTECHNICAL ENGINEERING ANALYSIS

Geotechnical Considerations

Existing Fill

Existing fill and possible fill materials were encountered immediately below the surface organics at the performed boring locations. The existing fill materials were observed to consist predominantly of a combination of sandy lean clay, fat clay with sand, clayey sand and poorly graded sand soils. The fill included variable amounts of silt, sand content, clay content and gravel content (chert, sandstone, shale and limestone) throughout the boring locations. At two boring locations, a strong petroleum odor was encountered near the bottom of the existing fill material.

The existing fill extended to depths of 3 ½ to 5 feet below existing grades. The depth of the existing fill material encountered at our boring locations is summarized in Table 2 below.

Table 2: Depths of Existing and Possible Fill Materials at Boring Locations

Boring Number Depths of Existing Fill

(feet below existing grades)

B-1 5 ½

B-2 3 ½

B-3 8 ½

B-4 5 ¼

GTS has no information regarding the placement and compaction history of the existing fill.

Based on the results of the borings, it appears that the majority of the fill material was not placed in a controlled manner during placement based on the composition and the in-place strength measured in the fill. Furthermore, portions of the existing fill encountered at the performed boring locations had very-low-to-low shear strength and are unsuitable for supporting shallow foundations, slabs-on-grade, or the placement and compaction of new fill material in their current state.

Because there can be variations in the thickness, quality and composition of existing fill and the potential for unsuitable materials to be buried in the existing fill, it should be recognized that there is assumed risk of unpredictable settlement and structural performance associated with constructing shallow foundations over existing fill. Based on the results of our borings, the risk appears to be high at this project site. This risk to foundations and floor slabs cannot be eliminated unless the full-depth of existing fill is removed and replaced with approved fill.

The recommendations provided in this report attempt to reduce the likelihood of excessive settlement of the planned new structures by recommending all foundation loads be transmitted

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence onto approved native soils and/or sandstone and shale bedrock encountered below the fill using either an overexcavated shallow foundation system or a deep foundation system.

To reduce the likelihood of excessive settlement below future concrete slabs-on-grade, GTS recommends that the full-depth of existing fill be removed and replaced with approved fill.

Alternatively, the concrete slabs may be designed as structural slabs supported entirely above foundations supported above approved native soils and/or sandstone and shale bedrock.

Moisture-Sensitive Soils

The lean clays (portion of the existing fill and portion of native soils) are susceptible to strength loss with increases in moisture content and/or when exposed to repetitive construction traffic.

Ground improvement should be anticipated during wet periods of the year where these soils are exposed.

Near-Surface Weak Soils

Very-low-to-low-shear-strength soils (SPT N-values of 5 bpf or less) were encountered within the near-surface, approximately 4 to 8 ½ feet below the ground surface at the performed boring locations. These low-shear-strength soils consisted of clayey and sandy fill materials as well as native clays and sands. These soils are not suitable for supporting typical foundation loads, slabs-on-grade, or new fills without removal and replacement or ground improvement.

The depths of these low strength soils encountered at our boring locations are shown in Table 3 below.

Table 3: Depths of Low-Shear-Strength Near-Surface Soils at Boring Locations

Boring Number Depths of Weak Soils

(feet below existing grades)

Recorded N-values

(blows per foot)

B-1 2 to 5 ½ 4, 4

B-2 2 to 4 5

B-3 0 to 1, 2 to 8 ½ 1, 2, 2

B-4 0 to 5 ¼ 1, 1, 2

The low strength of these on-site soils is due, in part, to these soils consisting of existing fill material that do not appear to have been placed following standard construction industry practices. These materials are anticipated to be unstable during earthwork activities; however we anticipate further instability will likely develop during wet site conditions, during freeze-thaw conditions and when the soils are subjected to repetitive construction traffic.

Supporting foundation loads and new fill material above these weak soils will result in soil consolidation, which will result in relatively large settlement of the planned foundations and floor

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence slabs-on-grade Recommendations are provided in this report to reduce the potential large settlement of the structure, through requiring all foundation loads be transmitted onto approved native soils or weathered rock below these near-surface weak soils and requiring the existing fill material be removed full-depth below all future floor slabs-on-grade.

Equipment Pad and Foundation Type Discussion

Based on the borings and anticipated structural loads as well as the conversation with the client, the originally planned equipment pad and retaining wall structure will not be suitable at this site without significant site work being performed.

We understand that the design team would prefer to support the equipment pad using a shallow foundation system and floor slabs-on-grade. Recommendations are provided in this report to support the planned equipment pad on a shallow foundation system and with floor slabs-on-grade.

Alternatively, the equipment pad may consist of structural slab supported entirely on a deep foundation system. The foundations for the new equipment pad and/or walls may be supported on a deep foundation system bearing in moderately to well cemented sandstone and hard shale bedrock encountered at depths of about 5 ¼ to 8 ½ feet below existing grades. We anticipate that either straight-shaft drilled piers or micropiles are under consideration by the design team for this project site. Recommendations for micropile foundations are provided in this report and drilled pier foundation recommendations may be provided upon request. GTS can also discuss other ground improvement and/or foundation alternatives with the design team upon request.

Shallow Foundation Recommendations

The planned equipment pad and walls may be supported on a shallow foundation system. The shallow foundations should be designed as conventional, open-trench foundations supported entirely on approved soil fill material, placed and compacted on approved stable soils and rock.

This will require the full-depth removal of the existing fill materials and underlying weak soils from the vicinity of the project site and replacement with new, approved fill material compacted in standard-thickness lifts to reach plan finished subgrade elevations. After the mass grading recommendations discussed in this report are followed, the recommended bearing material is anticipated to be exposed at plan bottom of foundation elevations throughout the equipment pad footprint.

Shallow foundations for the planned building structures may be designed using the information provided in Table 4 on the following page.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

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Table 4: Shallow Foundation Recommendations

Maximum Net Allowable

Bearing Pressure (psf) Bearing Soil Description Depth to Bearing Soils

2,000 (continuous) New, Tested and Approved fill * Placed above Thoroughly Tested and Evaluated On-Site Soils and Rock

Anticipated at Plan Bottom of Foundation Elevations after the Mass Grading Recommendations2,500 (square, column)

* The recommended bearing soils should have moderate shear strength. We recommend reverifying in-place dry density and moisture content of new, approved fill immediately below future foundations after excavation of footing trench.

Total long-term and differential settlement of shallow foundations, designed and constructed as recommended in this report and per the Mass Grading Recommendations section of this report, are estimated to be less than 1 inch (total) and ¾ inch in 50 feet (differential), respectively.

Shallow Foundation Construction Recommendations

General Dimensions

Continuous formed and isolated column foundations should have minimum widths of 18 inches and

30 inches, respectively. A minimum foundation depth of 18 inches below lowest adjoining grades should be used to protect against frost heave.

Evaluation of Supporting Material and Over-Excavation Recommendations

Foundation excavations should be cleaned of loose soils, debris and water. The bottom of all foundation trenches should be observed by GTS to evaluate soils exposed on the bottom of foundation excavations prior to the placement of approved fill, reinforcing bar and concrete.

After following the mass grading recommendations provided in this report, the recommended bearing soils are anticipated to be encountered at plan bottom of foundation elevations throughout the equipment pad footprint.

Where newly placed and compacted fill material is exposed at plan bottom of foundation elevations, we recommend that the new fill be field-tested for in-place density and moisture content immediately before placement of reinforcing bar and concrete. The fill may be scarified, moisture conditioned and recompacted in place to reach the project specifications.

Micropile Foundation Design Recommendations

Based on the soil and rock types encountered at our sample locations and existing site conditions, we anticipate that a micropile system will be the most practical method of constructing the deep

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence foundation system. Micropile design and installation should be performed as discussed in this report and in general accordance with the recommendations in the FHWA Publication No. FHWA-

NHI-05-039, titled “Micropile Design and Construction”, dated June 2005.

Due to the limited information for the basal rock stratum encountered at this site, the micropiles should be designed entirely on side resistance. Mircropiles are recommended to be sized for both length and diameter using the following table. The values in the table assume a Type A installation of grout (i.e., by gravity) and the values in the table are ultimate values.

An appropriate factor of safety, at least 2.5, should be applied to the values shown in Table 5 by the design engineer. Lateral resistance can be modeled using L-pile or equivalent software with the parameters shown in the table below.

Table 5: Micropile Geotechnical Design Values

Depth

(feet)

Type of Soil/Rock Grout to Ground

Bond Strength

(psi)

Horizontal

Modulus of

Soil Reaction:

Kf (psi/in)

Strain at 50% of Ultimate

Compression:

ɛ50

0 to top of weathered rock

Existing fill/Native Soils 0 0 n/a

Variable, 5

¼ to 8 ½

Weathered Sandstone and Shale 150 2,000 0.002

We recommend micropiles penetrate at least 2 feet into the weathered sandstone and shale bedrock. Additionally, a minimum spacing of three pile diameters (measured center-to-center) or greater is required unless an efficiency factor is used in the design.

Micropile Foundation Construction Recommendations

General Guidelines

The micropiles should be installed vertically and should not have an unbonded length (i.e. full depth grout) in order to transfer the vertical loads between the pile cap and the underlying soils.

Prior to grouting, the drilled hole should be cleaned of loose debris. Grout should consist of a high performance, non-shrink grout. The bar should be adequately sized by a structural engineer to withstand the maximum test loads and be resistant to corrosion from water and cementitious materials.

Centralizers should be used during the micropile installation at a spacing not to exceed 7 feet.

The first centralizer should be installed within 18 inches of the end of the bar.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

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The grout compressive strength should be no less than 5,000 psi at 28 days.

Load Test

In order to confirm the design capacity of micropiles, it is recommended that at least 1 micropile be load tested at the site. The test can be performed in either tension or compression, though tension is often the easiest where space is limited. The micropile should be loaded in 10 percent increments to two times (200%) the design load. Vertical movement (pullout or compression) of the test micropile should be recorded to the nearest 0.001 inches via an independent dial gauge at each loading increment. Each incremental load should be held until vertical movement of the micropile has essentially ceased except for the 100%, 150%, and 200% load increments. At these increments, readings shall be taken at 1, 2, 3, 4, 5, 6 and 10 minutes. If the total creep movement exceeds 0.040 inches between 1 and 10 minutes (i.e. one log cycle), then the test load shall be maintained for an additional 50 minutes, with recordings at 20, 30, 40 50 and 60 minutes.

A representative of GTS should be present at the time of testing to evaluate the verification test results and confirm the micropile will achieve their designed capacity without excessive movement.

Stress and Bearing Interactions with Existing Building Foundations

As-built information has not been provided to GTS regarding the existing building’s foundation type and foundation bearing depth. GTS assumes the existing building is supported on a shallow foundation system bearing within 3 feet below basement floor slab elevations.

Care should be taken during any excavation adjacent to existing foundations to not disturb any existing foundation bearing materials. It is recommended, where possible, excavations below existing footings not extend below an imaginary plane extending out and down from outside edge of existing footings at a slope of approximately 2 horizontal to 1 vertical (2H:1V). Even with these criteria, excavations extending below the level of the existing foundations should be backfilled the same day they are excavated. Where this is impractical, shoring or underpinning of existing foundations may be required.

Some overlap in stress distribution from new and existing footings may occur, which may cause minor movement of the existing footings and supported structures. Maintaining a clear distance at least equal to the width of the new column spread footings between the edges of the new and existing footings could significantly reduce this risk. Connections between the new and existing structures should be designed to allow for the anticipated differential movement.

Floor Slab Support Recommendations

New floor slabs-on-grade may be supported directly on new approved select fill material, placed and compacted above tested and approved native soils and/or rock. We recommend that all existing fill material and any underlying weak soils be removed full depth from the equipment pad area before new fill material is placed in this area.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Alternatively, the equipment pad slab could be designed as a structural slab supported by a deep foundation system.

Specific recommendations concerning construction of the floor slab subgrade, including the potential need for additional select fill to stabilize unstable subgrade soils, are provided in the

Mass Grading Recommendations section of this report.

Floor Slab-On-Grade Design

Concrete floor slabs constructed as slab-on-grade and supported on subgrade prepared as recommended in this report can be designed using a modulus of subgrade reaction (k) value of

125 pounds per square inch, per inch.

We recommend that a minimum of 4 inches of free draining gravel or sand be placed beneath the slab-on-grade to act as a capillary break. This layer is termed a “subbase” layer. To be effective as a capillary break, the subbase should have a maximum of 5 percent by dry weight passing the No. 200 sieve. The modulus of subgrade reaction value applies to the top of the subbase layer. The top of the subbase should be compacted using a vibratory plate.

If rutting of the subbase layer is a concern for concrete placement, the subbase layer may be topped with an additional 2 to 4 inches of gravel or sand having sufficient fines to allow compaction. The optional topping layer is termed the “base” layer. The base layer, if used, should be compacted to a minimum of 95 percent Standard Proctor Value (ASTM D 698) at a workable moisture content that allows the density to be achieved. The base layer should have a percent passing the No. 100 sieve ranging from 10 to 30 percent by dry weight. ARDOT Class

7 aggregate base material is acceptable for use as base layer material.

The use of a vapor barrier should be considered beneath concrete slabs on grade that will be moisture-sensitive or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor barrier, the slab designer should refer to ACI 302 “Guide for Concrete Floor and Slab Construction” or ACI 360 “Design of Slab-on-Ground” for procedures and cautions regarding the use and placement of a vapor barrier.

The general components of a floor slab, inclusive of the optional base course, are shown in

Figure 3. The shown reinforcing steel location provides general guidance only. The location and composition of reinforcing steel should be determined by a structural engineer.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence

Figure 3: General Floor Slab-on-Grade Section

IBC Site Classification

The subsurface conditions at this project site are consistent with a Site Class D per the

International Building Code (IBC), 2012 Edition.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

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MASS GRADING RECOMMENDATIONS

Stripping of Surface Concrete Pavement

Mass grading should extend a minimum of 5 feet outside of the equipment pad footprint in all directions, if possible.

At a minimum, surface organics and surface concrete pavement and underlying crushed gravel should be removed from planned areas of new development. If the equipment pad will consist of a floor slab-on-grade, the existing fill material and any underlying weak soils should also be removed from the planned areas of new development. Removal depths of approximately 4 to 8 ½ feet are generally anticipated, based on the results of the borings.

The existing structures should be razed and removed from areas of new development. Also, any other below-grade structures associated with existing and preexisting structures such as utilities should be removed full-depth. Excavations to remove these structures should be backfilled as recommended in this report. The surface concrete pavement and the underlying gravel may be stockpiled for reuse as fill material at the discretion of the design team.

General Mass Grading Recommendations

Structural Floor System

If a structural floor system and deep foundation system will support the planned equipment pad, no further site grading is required after removing surface organics.

Slab-on-Grade

After stripping surface organics, concrete pavements and crushed gravel, existing fill material and any underlying weak and unstable soils, GTS should be present during initial mass grading to evaluate the subgrade conditions.

After the recommended undercut depths are completed, the exposed soils should be evaluated for stability by GTS. We anticipate that proofrolling the exposed soils and rock will not be practical at this site. The stability of the on-site soils may be evaluated through the use of an engineer’s hand probe rod or through the excavation and evaluation of test pits throughout the structure footprint.

If the exposed soils and rock are stable, they are suitable to support the placement and compaction of new, approved fill material up to plan finished grades.

If the prepared subgrade become saturated, desiccated or otherwise damaged prior to construction of the floor slab sections, the affected subgrade material should be scarified, moisture conditioned and compacted prior to placing the base course. Final conditioning of the

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

Geotechnical Engineering Construction Materials Testing Environmental Due Diligence finished subgrade should be performed immediately prior to placement of the base course material.

Generally, if unstable soil conditions are encountered during mass grading GTS recommends that these unstable soils be undercut to expose stable soils or rock.

Fill Placement

Lifts of fill material required to reach plan finished subgrade elevations should be composed of tested and approved fill material and placed per the specifications shown in this report. Fill should be placed in near-horizontal lifts beginning in areas requiring the deepest amount of fill. The fill should be benched into the native soils each lift. Fill should not be placed on frozen, saturated or unstable soils.

We recommend that fill material placed within the top 1 foot of subgrade elevations consist of select fill material. The requirements to meet for general fill, select fill, and base course materials are provided in the Geotechnical Report Requirements and Specifications section of this report.

Re-Use of On-Site Soils as Fill

The existing fill consists of a mixture of soils potentially suitable for general or select fill. However, due to the variability of materials and locations encountered, we do not recommend the existing fill materials be reused as fill material for future development. Portions of the existing fill that meet the specifications provided in this report and are free of deleterious material may be reused as fill material at the discretion of the design team.

The on-site concrete and crushed gravel may be reused as fill material provided that all gravel and concrete fragments are mechanically broken such that all fragments measure less than 3 inches in all dimensions.

On-site lean clay soils are anticipated to be suitable for reuse as general fill material provided in the Geotechnical Report Requirements and Specifications section of this report.

Larger, bulk samples of the on-site soil proposed for use as fill should be obtained in the field during mass grading to confirm the apparent classification of these soils, prior to reuse.

Additionally, all rock will need to be crushed into pieces no greater than 3 inches in any dimension prior to or during reuse.

Soil classifications discussed in this report are based on approximately 2-inch diameter samples obtained during our field sampling. This type of sampling follows industry standards; however, this type of sampling can under- or over-estimate the amount of gravel within a soil formation.

Therefore, larger, bulk samples of the material should be obtained in the field during mass grading to confirm the apparent classification of these soils prior to reuse.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. 20-1-5-125

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We recommend all on-site soils and rock to be reused as fill or imported fill soils be thoroughly tested and evaluated by GTS before reuse.

Utility Trench Backfill

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

Rock Excavation Potential

Rock excavation means and methods are anticipated to be required to penetrate moderately to well cemented sandstone and hard shale beginning at depths of about 5 ¼ to 8 ½ feet below existing grades. The depths where rock excavation techniques are anticipated to be required correspond with the top of hard drilling conditions encountered at the boring locations and summarized in Table 1 on page 12.

In general, track hoes and dozers with rock excavation attachments are expected to be required below the depths where we encountered hard drilling. The use of hydraulic or pneumatic hammers, rock breakers, rock saws and controlled blasting could be required near and below the depths where we encountered competent rock and auger refusal. Greater rock excavation effort is expected in limited access excavations, such as for foundations and utility trenches.

Temporary Earth Slopes and Excavations

Temporary earth slopes will be constructed during development of the project site. The recommended maximum temporary slopes for overburden soils is 3 H:1 V (Horizontal:Vertical) and for the deeper, moderately to well cemented sandstone and hard shale is nearly vertical.

Alternatively, local construction practices allow for benched excavations (4 feet vertical followed by 4 feet horizontal) with an effective slope of 1H:1V.

The contractor, by his contract, is usually responsible for designing and constructing stable, temporary excavations and should shore, slope or bench the sides of the excavations as required to maintain stability of the excavation sides and bottom. All excavations should comply with applicable local, state and federal safety regulations, including the current Occupational Safety and Health Administration (OSHA) Excavation and Trench Safety Standards.

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LATERAL LOADING CONDITIONS

Walls with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to those defined in the below diagram and indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained.

Two wall restraint conditions are shown. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement/rotation at the top of the wall. The "at rest" condition assumes the wall is structurally restrained from movement at the top and should be used for basement walls. The recommended design lateral earth pressures do not include a factor of safety and are based on a drained soil condition behind the wall.

Figure 4: General Section Showing Pressures Acting on Retaining Walls

Table 6: Lateral Earth Pressure Coefficients

Earth Pressure

Conditions

Coefficient for

Backfill Type

Equivalent

Fluid Density

(pcf)

Surcharge

Pressure, p1

(psf)

Earth

Pressure, p2

(psf)

Active (Ka) Granular - 0.33

Native Soils - 0.42

(0.33)S

(0.42)S

(40)H

(50)H

At-Rest (Ko) Granular - 0.50

Native Soils - 0.58

(0.50)S

(0.58)S

(60)H

(70)H

Passive (Kp) Granular - 3.0

Native Soils - 2.4

The values shown in Table 6 require the following:

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For active earth pressure, wall must rotate about base, with top lateral movements of about 0.002 H to 0.004 H, where H is wall height

For passive earth pressure to develop, wall must move horizontally to mobilize resistance.

Uniform surcharge, where S is surcharge pressure

In-situ soil or placed and compacted soil backfill with a maximum weight of 120 pcf

Backfill placed near horizontal, compacted to a minimum of 95 percent of standard Proctor maximum dry density

Loading associated with backfill operations and construction not included in the recommended design values

A drained soil condition exists behind the wall

No dynamic loading acting above the wall

No safety factor included in soil parameters

Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.

For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively. To calculate the resistance to sliding, a value of 0.30 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

To reduce hydrostatic pressure behind the wall (i.e. a “drained” soil condition) we recommend that a minimum 12-inch-wide chimney drain be installed continuously on the back side of the retaining structure, with a collection pipe installed at the top of the foundation. The collection pipe should be rigid, perforated pipe and should be designed to gravity discharge at a location away from the wall and any other planned structures. The values shown in Table 6 assume a drained soil condition and do not include a factor of safety.

If drainage is not possible, then combined hydrostatic and lateral earth pressures should be calculated for lean clay backfill using an equivalent fluid weighing 90 and 100 pcf for active and at-rest conditions, respectively. For granular backfill, an equivalent fluid weighing 75 and 85 pcf should be used for active and at-rest conditions, respectively. The recommended pressures do not include the influence of surcharge, slopes above or below walls, equipment loading or floor loading, which should be added. Heavy equipment should not operate within a distance closer than the exposed height of retaining walls to prevent lateral pressures exceeding those provided.

The upper 2 feet of backfill placed adjacent to the walls should consist of a compacted, relatively impermeable material to limit the downward flow of surface water along the walls.

These soils should be placed following the recommendations provided in this report. Also, positive surface drainage should be developed and maintained around the walls to prevent the ponding of water and to divert drainage away from the walls.

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GEOTECHNICAL REPORT REQUIREMENTS and SPECIFICATIONS

Unless otherwise stated in this report, the recommendations contained in this report are based on the compaction specifications and material types noted in Table 7, Table 8 and the paragraphs on the following page.

Table 7: Recommended Soil Compaction

Type of Material Moisture-Density

Specification

Minimum Dry Density

(percentage of proctor)

Range from Optimum

Moisture Content (%)

Soil Fill Material

ASTM D-698

(Standard Proctor)

-3 to +3

Base Course Material

ASTM D-1557

(Modified Proctor)

Sufficient to Achieve

Compaction

Table 8: Soil Fill Material Requirements

Type of

Soil Fill

Location/Use Maximum

LL

Maximum

PI

USCS

Classifications

Select All Areas 40A 18A GM, GC, GW, GP, SW, SP, SC, Chert

General All Areas Excluding the Top 1 Foot of

Building Areas

May not be used as bridging lift material

45B 20B GM, GC, GW,

GP, SW, SP,

SC, CL, Chert

A Plasticity requirements may be waived provided that the fill has a minimum of 65% retained on the No. 200 sieve.

B Plasticity requirements may be waived provided that the fill has a minimum of 50% retained on the No. 200 sieve.

Fill material should have a maximum nominal aggregate size of 3 inches after placement and compaction.

Fill needed for site grading should be placed in loose lifts not exceeding 9 inches in thickness

(compacted lift thickness of approximately 6 to 7 inches). We recommend the fill be tested for density every lift during mass grading, with a minimum of one test every 2,500 square feet of building area.

The recommended moisture content and compaction of the fill within the building areas should be maintained until fills are completed and floor slabs are constructed.

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Design and construction plans should provide for rapid, positive…