20-1-5-072.Geotech Report. Laundry Facility Renovation.pdf

Geotechnical Engineering Report

Planned Laundry Facility Renovation

1100 North College Avenue

Fayetteville, Arkansas

GTS Project No. 20-1-5-072

June 9, 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

1100 North College Avenue, Fayetteville, Arkansas

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

Foundation Type Discussion

Micropile Foundation Design Recommendations

Micropile Foundation Construction Recommendations

General Guidelines

Load Test

Floor Slab Support Recommendations

Floor Slab-On-Grade Design

IBC Site Classification

MASS GRADING RECOMMENDATIONS

Stripping of Surface Concrete Pavement

Evaluation of Existing Fill

General Mass Grading Recommendations

Weather and Instability Related Considerations

Fill Placement

Re-Use of On-Site Soils as Fill

Utility Trench Backfill

Rock Excavation Potential

1100 North College Avenue, Fayetteville, Arkansas

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 Low-Shear-Strength Near-Surface Soils at Boring Locations Table 3: Micropile Geotechnical Design Values Table 4: Lateral Earth Pressure Coefficients Table 5: Recommended Soil Compaction Table 6: Soil Fill Material Requirements Table 7: Laboratory Test Method Designations

LIST OF APPENDICES

A

Boring Location Diagrams

Boring Logs

B

Laboratory Data

1100 North College Avenue, Fayetteville, Arkansas

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 materials were encountered immediately below the concrete pavement section at the performed boring locations. The fill materials consisted of a combination of sandy lean clay, fat clay with sand, clayey sand and fine sand soils. The fill had variable very low to moderate, yet generally low, shear strength and extended to depths of about 3 ½ to 5 feet below existing grades.

The native soils encountered immediately beneath the existing fill generally consisted of a combination of lean clays with variable amounts of sand, as well as clayey sand with variable amounts of silt and gravel. These soils extended to depths of about 9 ½ to 11 feet below existing grades. The native soils had variable very low to moderate, yet generally low, shear strength during drilling and sampling.

The basal stratum at this site consisted of poorly to well cemented sandstone and hard shale starting at depths of about 9 ½ to 11 feet below existing grades. Hard drilling conditions were encountered within the sandstone and shale bedrock starting at depths of about 13 ½ to 14 feet below existing grades. The hard drilling was required to penetrate hard shale or to penetrate layers of moderately cemented sandstone. All borings were drilled to their planned depths without encountering auger refusal material.

Geotechnical Considerations for Development

Existing fill material was encountered to depths of about 3 ½ to 5 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 sample borings. It is the opinion of GTS that there is a high risk associated with supporting future foundations loads above the existing fill.

1100 North College Avenue, Fayetteville, Arkansas

Weak soils were encountered within the near-surface soils, approximately 6 ½ to 8 ½ feet below existing grades. These low-shear-strength soils consisted of clays and sands (existing fill as well as native soils). 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.

Foundation Support Recommendations

Based on the borings and anticipated structural loads, we recommend the planned building expansion be supported on a deep foundation system bearing in well cemented sandstone and hard shale encountered at depths of about 9 ½ to 11 feet below existing grades. Deep foundation systems may consist of micropiles.

We recommend using ultimate grout-to-soil bond strengths of 10 psi for the native clays and sands and 150 psi for sandstone and shale bedrock starting at depths of about 9 ½ to 11 feet below existing grades. We recommend micropiles penetrate at least 2 feet into the sandstone and shale bedrock. The top 5 feet of soils should be ignored in design. In addition, due to relatively small diameters of micropiles, end bearing should also be ignored in design. The recommended bond strength values are for Type A micropiles using only gravity when grouting. A factor of safety of at least 2 shall be applied to the recommended ultimate bond strengths. At least one verification load test should be performed on a non-production or production pile.

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

International Building Code (IBC), 2012 Edition.

Floor Slab-on-Grade Support

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. However, additional fill materials may likely be required to stabilize the on-site soils if site conditions are similar to those at the time of drilling and sampling.

1100 North College Avenue, Fayetteville, Arkansas

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 dock of

Building 9 and the pavement area immediately north of Building 9. The footprint area of the project site is approximately 0.1 acre and consists of existing concrete pavement that generally slopes downward from the northwest to the southeast with approximately 2 feet of topographical relief.

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

Building 9 has a basement and an existing retaining wall having a height of about 4 feet separates the existing pavement and the north basement wall of Building 9. Bracing extends from the retaining wall to the north wall of Building 9 at 3 locations. The gap between the retaining wall and the north basement wall of Building 9 is about 3 feet.

1100 North College Avenue, Fayetteville, Arkansas

Planned Development

The project consists of renovating and extending the existing loading dock and installing a new cart wash system. We anticipate the new dock area will house the new cart wash system.

Construction activities will include demolition of a portion of the existing enclosed dock and extending the dock northward and eastward. We anticipate the new dock will be enclosed, and the structure will consist of structural steel framing, metal panel siding and concrete slab-on-grade. We understand that micropile foundation is under consideration by the client for the planned building expansion structures.

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

Figure 2: General Layout of the Planned Development

GTS assumes that the differential settlement of the parking deck will need to be limited to ½ inch or less within 50 feet of length. We understand that maximum column loads of about 5 kips or less and maximum wall loads of about 10 kips or less per lineal foot are anticipated by the design team for the planned building expansion.

Planned New Pavement

Planned Building Expansion

Planned Replaced Pavement

1100 North College Avenue, Fayetteville, Arkansas

The existing pavement located within a distance of about 4 feet outside of the planned building expansion is planned to be replaced, as outlined in green in Figure 2. We understand that new paved parking and drive areas were previously planned in the north side of the planned structures, as outlined in blue in Figure 2; however, we understand that this “planned new pavement” is no longer planned at this time. Providing pavement sections and pavement support recommendations are outside of our scope of services and are not included in this report. Pavement design services may be provided upon request.

Planned Site Grading

Specific grading plans were not provided to GTS for the planned development at the time of this report. However, a site plan, undated, titled “20138-VA-Layout1” was provided for this development by the client. Based on the provided site plan, we understand that the first floor of the existing structure Building 9 is at a finish floor elevation (FFE) of EL 1456.0 feet. The basement floor of the existing Building 9 is at finish floor elevations (FFEs) of EL 1445.4 feet.

Additionally, the ground surface elevation for the existing pavement adjacent to the existing

Building 9 is at elevation of about EL 1451.5 feet.

For the purposes of this report, GTS assumed that the final grades of the planned building expansion will generally match the existing grades of the Building 9. This will require maximum fill depths of about 4 ½ feet or less in the planned building expansion footprint.

1100 North College Avenue, Fayetteville, Arkansas

SUMMARY of SUBSURFACE FINDINGS

Surface

The surface of the performed boring locations generally consisted of concrete pavement at the performed boring locations at the time of field sampling. At Boring B-2, the existing concrete pavement section consisted of about 6 inches of concrete overlying about 4 inches of crushed gravel subbase material. However, at Borings B-1, B-3 and B-4, the ground surface generally consisted of about 6 inches of concrete paving with no discernible underlying crushed gravel.

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

1100 North College Avenue, Fayetteville, Arkansas

1100 North College Avenue, Fayetteville, Arkansas

1100 North College Avenue, Fayetteville, Arkansas

Subsurface Soils and Rock

Existing Fill

Existing fill materials were encountered immediately below the concrete pavement section at the boring locations. The existing fill consisted predominantly of a combination of sandy lean clay, fat clay with sand, clayey sand and fine sand soils. The existing fill extended to depths of 3 ½ to

5 feet below existing grades.

The fill material had variable very low to moderate, yet generally low, shear strength during drilling and sampling. Standard penetration test (SPT) N-values of 2 to 16 blows per foot (bpf) were recorded for the existing fill.

Native Overburden Soils

The native soils encountered below the existing fill materials generally consisted of a combination of low plasticity (lean) clays with variable amounts of sand, as well as clayey sand with variable amounts of silt and gravel at the performed boring locations. Sandstone fragments were intermittently encountered within these soils. These soils extended to depths of about 9 ½ to 11 feet below existing grades.

The native soils had variable very low to moderate, yet generally low, shear strength during drilling and sampling. N-values of 1 to 11 bpf were recorded for these soils.

Sandstone and Shale

Apparent bedrock consisting of poorly to well cemented sandstone and hard shale was encountered below the native overburden soils at the performed boring locations. The bedrock was apparently encountered beginning at depths of about 9 ½ to 11 feet below existing grade 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 increased while the degree of weathering decreased with increasing depth into the hard shale. Hard shale was encountered beginning at depths of 13 ½ to 14½ feet below ground surface of Borings B-1, B-3 and B-4. N-values of 26 bpf to 50 blows per 3 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 13 ½ to 14 feet below existing grades at the performed boring locations. Auger refusal material was not encountered above a depth of 15 feet below the existing ground surface at any of the performed boring locations.

The depths to hard drilling conditions are summarized in Table 1, on the following page.

1100 North College Avenue, Fayetteville, Arkansas

Table 1: Depths to Hard Drilling Conditions

Boring Number Depths to/Elevation of Hard Drilling Conditions

(Feet below Existing Grades)

B-1 13 ½ / 1438

B-2 13 ½ / 1438

B-3 14 / 1437 ½

B-4 13 ½ / 1438

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 13 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

GEOTECHNICAL ENGINEERING ANALYSIS

Geotechnical Considerations

Existing Fill

Existing fill materials were encountered immediately below the concrete pavement section 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 fine sand soils. The existing fill extended to depths of 3 ½ to 5 feet below existing grades.

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.

Concrete floor slabs span weak zones much more effectively than concentrated foundation loading. Also, clients/owners typically have a higher tolerance for cracks developing in floor slabs compared to building structures. However, the client/owner should understand that some premature surface distress and increased maintenance may occur in future floor slab sections supported above the existing fill. If the owner is risk-averse, the only means of eliminating this risk is to remove the existing fill material full-depth and to replace the existing fill with new, approved fill material, placed and compacted in standard-thickness lifts. However, the risk can be reduced if the existing fill is partially left in-place by performing thorough testing and evaluation of the existing fill as recommended in this report. We recommend that a minimum of 1 foot of new, approved select fill material be constructed over existing fill after thorough subgrade observation, evaluation and testing to support new concrete floor slabs.

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 onto the sandstone and shale bedrock encountered below the fill using a deep foundation system.

If the design team is willing to accept risk of unpredictable settlement of floor slabs supported above the existing fill, a layer of select fill could be constructed over thoroughly tested and evaluated existing fill. Provided the recommendations in this report are followed, the risk associated with constructing floor slabs as discussed in this report should be low.

1100 North College Avenue, Fayetteville, Arkansas

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 6 ½ 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 2 below.

Table 2: 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 3 ½ to 6 ½ 3, 4

B-2 0 to 2, 4 to 7 ½ 1, 3, 4

B-3 5 to 7 ½ 3

B-4 0 to 8 ½ 2, 4

The low strength of these on-site soils is due, in part, to the relatively high moisture contents encountered within these soils at the time of drilling and sampling. We anticipate unstable soils will likely develop during wet site conditions, during freeze-thaw conditions and when the soils are subjected to repetitive construction traffic. Ground improvement will likely be required, and recommendations are provided in the Mass Grading Recommendations section of this report.

Supporting foundation loads above these weak soils will result in soil consolidation, which will result in relatively large settlement of the planned building structures. 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 soils below these near-surface weak soils.

Foundation Type Discussion

Based on the borings and anticipated structural loads as well as the conversation with the client, we recommend the planned building expansion be supported on deep foundation systems

1100 North College Avenue, Fayetteville, Arkansas bearing in well cemented sandstone and hard shale bedrock encountered at depths of about 9 ½ to 11 feet below existing grades.

We understand that micropiles are under considerations by the client for this project site.

Recommendations for micropile foundations are provided in this report. GTS can discuss other ground improvement and/or foundation alternatives with the design team upon request.

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 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 these values by the design engineer.

Lateral resistance can be modeled using L-pile or equivalent software with the parameters shown in the table below.

Table 3: 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 5 Existing fill/Native Soils 0 0 n/a

5 to top of weathered rock

Loose to Medium Dense

Clayey Sand and Firm to

Stiff Sandy Lean Clay

10 20 n/a

Variable, 9

½ to 11

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.

1100 North College Avenue, Fayetteville, Arkansas

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.

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.

Floor Slab Support Recommendations

New floor slabs-on-grade may be supported directly on a minimum of 1 foot of new approved select fill material, placed and compacted above tested and approved existing fill . Additional fill material is likely to be required to support new floor slabs if the on-site soils are weak and unstable in the building footprint.

Risks associated with supporting floor slabs-on-grade above the existing fill material are discussed at the beginning of the Geotechnical Engineering Analysis section of this report.

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.

1100 North College Avenue, Fayetteville, Arkansas

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

100 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. AHTD 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.

Figure 3: General Floor Slab-on-Grade Section

1100 North College Avenue, Fayetteville, Arkansas

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

MASS GRADING RECOMMENDATIONS

Stripping of Surface Concrete Pavement

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

At a minimum, surface organics and surface concrete pavement and underlying crushed gravel should be removed from the planned areas of new development. Removal depths of approximately 1 foot or less are generally anticipated, based on the results of the borings. This depth does not include the depth to stump and grub of the existing trees, if present at the site.

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 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.

Evaluation of Existing Fill

During mass grading, existing fill material is anticipated to be exposed intermittently in the building footprint areas at the project site.

If the Owner is allowing the planned floor slabs to be constructed above the existing fill, exposed existing fill should be tested and evaluated for suitability to support the planned floor slabs and for the presence of deleterious materials during mass grading. GTS should evaluate the existing fill material at the project site and provide additional recommendations during mass grading. Test pits could be performed during mass grading to evaluate the extent and composition of the existing fill. Portions of the existing fill material containing unsuitable and/or deleterious materials should be removed full depth from areas of new construction.

General Mass Grading Recommendations

After stripping surface organics, concrete pavements and crushed gravel, we recommend that additional undercuts be performed, as required, to reach a minimum depth of 1 foot below plan finished subgrade elevations. 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 by observing overlapping passes with a loaded tandem-axle dump truck (i.e., proofrolling) weighing at least 25 tons. If proofrolling the exposed soils is impractical, the stability of the soils may be evaluated through excavation of test pits or an engineer’s hand probe rod.

1100 North College Avenue, Fayetteville, Arkansas

If the soils are stable during proofrolling and at depths of 2 feet or more below plan finished grades, 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 finished subgrade should be performed immediately prior to placement of the base course material.

Where unstable areas are identified by proofrolling, they should be scarified, moisture conditioned and compacted, or removed and replaced full-depth with new, select fill. Alternatively, further undercuts may be performed to expose stable soils.

Potential instabilities when on-site soils at the undercut depth are moist to wet are considered in the Weather and Instability Related Considerations report section.

Weather and Instability Related Considerations

Soil instability is directly related to the moisture within and below the exposed soils. When moist to wet, the on-site near-surface soils will be unstable. If the exposed soils are unstable, they may be scarified and allowed to dry to achieve stability if the construction timeframe and prevailing weather conditions allow. Even with adequate time and weather, stable subgrade may not be achievable if the thickness of the soft soil is greater than 1 to 1½ feet. Further undercuts may also be performed to expose stable soils.

Methods of ground improvement could include scarification, moisture conditioning and recompaction and removal of unstable materials and replacement with granular fill (with or without geogrid or geotextile). The appropriate method of improvement, if required, would be dependent on factors such as schedule, weather, the size of the area requiring ground improvement, and the nature of the instability. More detailed recommendations can be provided during construction as the need for ground improvement occurs.

Alternatively, bridging lifts may be considered to stabilize the soils if they remain unstable beginning at a 3-foot undercut depth. The top 8 inches of bridging lifts should be compacted to project specifications. The thickness of the bridging lift will depend on site conditions at the time of site grading and should be evaluated and recommended by GTS. The top of all bridging lifts may not be within 18 inches of plan finished subgrade elevations.

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

1100 North College Avenue, Fayetteville, Arkansas 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 planned building subgrade consist of select fill material. Additionally, select fill material may be reused as bridging lift 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 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 silt-based soils and fat clay soils may not be reused below the planned structures. These silt-based soils may be reused in planned landscaping areas at the discretion of the design team.

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.

On-site lean clay, sand and gravel soils are anticipated to be suitable for reuse as general fill material. Portions of the on-site sand and gravel may also be reused as select fill materials provided that the soil has a high fraction of sand and gravel and meets the requirements 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.

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.

1100 North College Avenue, Fayetteville, Arkansas

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 very dense gravel and well cemented sandstone and hard shale beginning at depths of about 13 ½ to 14 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 13.

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.

1100 North College Avenue, Fayetteville, Arkansas

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 4: 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 4 require the following:

1100 North College Avenue, Fayetteville, Arkansas

• 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 4 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.

1100 North College Avenue, Fayetteville, Arkansas

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 5, Table 6 and the paragraphs on the following page.

Table 5: 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 6: 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.

1100 North College Avenue, Fayetteville, Arkansas

Design and construction plans should provide for rapid, positive drainage away from the building areas both during construction and at completion of the project, including any planned irrigation lines.

1100 North College Avenue, Fayetteville, Arkansas

SUBSURFACE EXPLORATION and PROCEDURES

The current subsurface exploration consisted of evaluating and sampling 4 sample boring locations to planned depths of 15 feet below existing grades or to auger refusal depths, whichever was least.

The boring locations were established in the field by GTS using a recreation-grade hand-held GPS unit. The approximate boring locations are shown on the attached Boring Location Diagram. We estimated ground surface elevations at the boring locations using a site plan, undated, titled

“20138-VA-Layout1”, provided by the design team. The preliminary grading plan, undated, was provided by the design team via electronic mail on June 3, 2020. The estimated ground surface elevations are shown near the top of the boring logs and are rounded to the nearest half foot. The locations and elevations of the borings should be considered accurate only to the degree implied by the methods used to define them. The results of the borings are attached to this report.

The borings were drilled with a track-mounted Geoprobe 7720DT drill rig. Disturbed samples and estimates of the in-situ shear strength of the soil were obtained using an automatic-hammer-driven split barrel sampler in general accordance with the Standard Penetration Test at the boring locations.

The soil and rock samples obtained in the field were sealed to reduce moisture loss and taken to the GTS soil laboratory for further examination, testing, and classification. The results of laboratory tests on select samples are shown on the boring logs and are attached to this report.

Field logs were prepared during the drilling and sampling of the borings. These logs report sampling methods, sampling intervals, soil and groundwater conditions, and notes regarding soil and drilling conditions observed between sample depths. The final boring logs, included in this report, have been prepared based on the field logs and have been modified, where appropriate, based on the results of the laboratory observation.

1100 North College Avenue, Fayetteville, Arkansas

LABORATORY TESTING and PROCEDURES

The soil samples were examined in the laboratory and classified based on a visual estimate of the soil's texture and plasticity.

The table below provides the American Society for Testing and Materials (ASTM) test designation for each type of laboratory test assigned for this project.

Table 7: Laboratory Test Method Designations

Laboratory Test Test Designation Method (if applicable)

Moisture Content of Soil and Rock ASTM D 2216-10 Method A

Visual Classification of Soil Types ASTM D 2488

Atterberg Limits ASTM D 4318 Method A

Sieve Analysis ASTM D 6913 Method A

USCS Classification ASTM D 2487

GEOTECHNICAL REPORT LIMITATIONS

The recommendations contained in this report are based on our interpretation of subsurface conditions encountered at the discrete boring locations. Variations between the subsurface conditions anticipated in this report and actual project site conditions may occur away from the boring locations.

If significant differences between the findings of the borings and site conditions are observed, GTS should be contacted to assess the variation and, if necessary, reevaluate the recommendations contained in this report.

ENVIRONMENTAL EXCLUSION

A Geotechnical Engineering report assesses the engineering properties of soil and rock. No environmental assessment of a project site is performed during a geotechnical exploration. If the owner is concerned about the potential for environmental hazards at the project site, additional studies should be performed by GTS.

1100 North College Avenue, Fayetteville, Arkansas GTS Project No. GTS 20-1-5-072

Arkansas ● Oklahoma ● Missouri ● Kansas ● Texas ● Colorado ● New Mexico ● Mississippi ● Tennessee ● Louisiana

APPENDIX A

Boring Location Diagram

Boring Logs

Boring Location Diagram with Overlay of Topographic Survey

B-1

B-3

B-4

B-2

Boring Location Diagram

B-1

B-4

B-3

B-2

2.5

7.5

12.5

17.5

Surface Description=Concrete El.=1451.5

CONCRETE = 6 Inches El.=1451.0

FILL - predominantly sandy lean clay firm, brown, orange and dark gray, with trace sandstone fragments, fat clay and fine-grained sand pockets

El.=1447.0 CLAYEY SAND, with gravel loose, dark brown

El.=1446.5

SILTY, CLAYEY SAND

loose, brown and dark gray, with trace sandstone fragments and organic staining

El.=1443.0

SANDY LEAN CLAY

stiff, orange and light gray, with fine-grained sand pockets and trace sandstone fragments below 8½ feet

El.=1442.0

SANDSTONE

poorly to moderately cemented, fine-grained, dark brown and tan

- cave-in at completion of drilling at 13 feet

El.=1438.0

SHALE

highly to slightly weathered, dark gray and tan

El.=1436.5

BOTTOM OF BORING AT 15 FEET

FILL

SC

SC-

SM

CL

50/2"

LOG OF BORING NO.B-1

Planned Laundry Facility Renovation 1100 North College Avenue, Fayetteville, Arkansas

Project No.: 20-1-5-072 Location: See Attached Boring Location Diagram

COMPLETION DEPTH: 15 ft. DEPTH TO WATER: DURING DRILLING: Dry DATE: 5/22/20 AT COMPLETION: Dry RIG: Geoprobe 7720DT, Track Mounted, Auto-Hammer Assisted AT 24 HOURS: Backfilled

D E

P T

H

F T

S Y

M B

O L

S A

M P

L E

S

S A

M P

L E

N o

R E

C O

V E

R Y in

DESCRIPTION OF MATERIAL

U S

C S

20 40 60 80

PL LL

WATER CONTENT, %

0.4 0.8 1.2 1.6

LAB. COHESION, TSF

HAND PENETROMETER, TSF

B L

O W

S P

E R

F T

7.5

12.5

17.5

Surface Description=Concrete El.=1451.5

CONCRETE = 6 Inches El.=1451.0

CRUSHED GRAVEL = 4 Inches El.=1450.7

FILL - predominantly clayey sand loose, brown, dark gray and tan, sandstone fragments

- soft, predominantly brown, orange, yellow and tan sandy lean clay, with trace sandstone fragments below 1 foot

- stiff to very stiff, predominantly tan and orange fat clay with sand and trace sandstone fragments below 2 feet

- medium dense, predominantly orange fine-grained sand, with sandstone fragments below 2½ feet

El.=1448.0

CLAYEY SAND

loose, brown, with…