Indepth Murf Pkg Impr Geophysics Terracon Geo Eng Rpt 18195130.pdf

REPORT COVER PAGE

Geotechnical Engineering Report

18-407 Murfreesboro Parking Improvements Geophysics Murfreesboro, TN

March 13, 2020 Terracon Project No. 18195130

Prepared for:

Apogee – Engineers l Architects

Cary, NC

Prepared by:

Terracon Consultants, Inc.

Nashville, TN

Terracon Consultants, Inc. 5217 L inbar Drive, Suite 309 Nashvi l le , TN 37211 P (615) 333 6444 F (615) 333 6443 terracon.com

REPORT COVER LETTER TO SIGN

March 13, 2020

Apogee – Engineers l Architects 1151 Kildaire Road, Suite 120 Cary, NC 27511

Attn: Ms. Alex Kramer, E.I.

P: (919) 535 3958 E: akramer@acg-pa.com

Re: Geotechnical Engineering Report 18-407 Murfreesboro Parking Improvements Geophysics 3400 Lebanon Pike Murfreesboro, TN Terracon Project No. 18195130

Dear Mr./Ms. Kramer:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. P18195130 dated August 27, 2019. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of pavements for the proposed project.

We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report or if we may be of further service, please contact us.

Sincerely, Terracon Consultants, Inc.

John Hill McAlister III, P.E. David A. Been P.E.

Staff Geotechnical Engineer Senior Geotechnical Consultant

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

PAVEMENTS

GENERAL COMMENTS

FIGURES

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

PHOTOGRAPHY LOG

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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INTRODUC TION

Geotechnical Engineering Report 18-407 Murfreesboro Parking Improvements Geophysics

3400 Lebanon Pike Murfreesboro, TN

Terracon Project No. 18195130 March 13, 2020

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Parking Lot Addition to be located at 3400 Lebanon Pike in Murfreesboro, TN. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Pavement design and construction

■ Groundwater conditions ■ Site preparation and earthwork

The geotechnical engineering Scope of Services for this project included the advancement of additional 15 test borings to depths ranging from approximately 5 ½ to 24 ½ feet below existing site grades.

Maps showing the site and boring locations are shown in the Site Location and Exploration Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs in the Exploration Results section.

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Item Description

Parcel Information

The project is located at the VA Medical Center at 3400 Lebanon Pike in Murfreesboro, TN.

Latitude/Longitude (approximate):

West Parking Lot: 35. 91176° / -86. 38018° See Site Location

Existing Improvements Predominantly undeveloped land, existing parking lot

18-407 Murfreesboro Parking Improvements Geophysics ■ Murfreesboro, TN March 13, 2020 ■ Terracon Project No. 18195130

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Item Description Current Ground Cover Grass, scattered trees, asphalt paved parking lot

Existing Topography

The ground surface within the area of the proposed west parking lot expansion slopes gently downward to the southwest from approximately El.

590 to El. 576 feet, MSL. We note that the El. 576 contour interval is mapped as a shallow closed depression approximately 350 feet in diameter.

Geology1 Ridley Limestone: Thick-bedded, brownish-gray limestone, fine-grained, with minor mottlings of magnesian limestone; slightly cherty. Thickness 90 to 150 feet

1. References: Greene, D.C., and Wolfe, W.J., 2000, Superfund GIS - 1:250,000 Geology of Tennessee, USGS, (geo250k). Hardeman, W.D., Miller, R.A., and Swingle, G.D., 1966, Geologic Map of Tennessee:

Division of Geology, Tennessee Department of Environment and Conservation, 4 sheets, scale 1:250,000

We also collected photographs at the time of our field exploration program. Representative photos are provided in our Photography Log.

PROJECT DESCRIPTION

Our initial understanding of the project was provided in our proposal and was discussed during project planning. A period of collaboration has transpired since the project was initiated, and our final understanding of the project conditions is as follows:

After the original geotechnical report for this project was issued on July 18, 2019 (Terracon Project No. 18195015), several conference calls took place to describe the findings and discuss options for the project. Additional exploration areas to the East of the existing parking lot were requested to be investigated. Foresite Group provided renderings of possible layout arrangements for parking expansion on the East and West sides of the existing parking lot. The West parking lot expansion plan from drawing number CS102 dated 4/25/2019 was used to place boring locations for the scope of work proposed.

Item Description

Information Provided

Information regarding the original project was provided in email correspondence between Ms. Alex Kramer of Apogee and Mr. David Been of Terracon. Following the original geotechnical report, the design team and John McAlister with Terracon participated in several conference calls. The client has decided to expand the exploration of the parking area amidst the findings from the first report.

Project Description The site plan provided by Apogee indicates that the existing parking lot is to be renovated and possible additions to the East and the West.

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Item Description

Grading/Slopes

Based on existing site grades, we anticipate up to 5 feet of cut and 5 feet of fill may be required to develop final grades.

Final slope angles of as steep as 3H:1V (Horizontal: Vertical) are expected.

Free-Standing Retaining Walls

Retaining walls are not expected to be constructed as part of site development to achieve final grades.

Pavements

We assume both rigid (concrete) and flexible (asphalt) pavement sections should be considered.

Anticipated traffic is as follows:

■ Autos/light trucks: 1,000 vehicles per day

■ 48-foot fire pumper truck: 1 vehicle per week

The pavement design period is 20 years.

Estimated Start of Construction 2020

GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and pavement options. Conditions encountered at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration Results section and the GeoModel can be found in the Figures section of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer Layer Name General Description 1 Fill Lean clays with chert, limestone, and asphalt fragments

2 Fat Clay Yellowish red to red high plasticity clays with varying amounts of angular limestone and chert particles consistencies are stiff. These clays have a potential for shrink swell

3 Lean Clay Yellowish to reddish brown low plasticity clays with varying amounts of angular limestone and chert particles consistencies varied from soft to very stiff

Our subsurface exploration typically encountered 3 to 7 inches of topsoil underlain by fill consisting of lean clay and/or natural lean clays with chert. Boring B-6 was performed in the existing parking lot and initially penetrated a pavement section consisting of 3 inches of asphaltic concrete over 6 inches of crushed aggregate base. The depth to auger refusal typically varied from 4 ¾ feet to 8 ¾ feet below the existing grade. The lean clay overburden was commonly stiff

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Responsive ■ Resourceful ■ Reliable 4 to very stiff, but could have slightly inflated N-values due to the presence of chert and limestone fragments within the soil stratum. Boring B-5 encountered very soft soils throughout the soil column until the boring was terminated at an auger refusal depth of 22 ¼ feet below existing grade.

The current parking lot addition borings, B-7 through B-17, were drilled on the east side of the existing parking lot and to the west of Southview Drive. Borings B-18 through B-21 were drilled to the south of the existing parking lot and around the area that was previously explored as a potential karst feature. The borings encountered fill material in some of the northern most borings.

See the table below for locations and depth of fill materials observed during our exploration. The fill typically contained organics and some large rock pieces. Results of standard penetration tests (N-values) within the fill varied from 6 to over 50 blows per foot (bpf) and were sometimes exaggerated by rock fragments contained in the fill and may not represent the true strength of the fill. Low sample recovery in the fill at a couple of borings can be an indication of loose zones and/or oversize rock fragments. Due to the presence of organics, large rock fragments and relatively low SPT N-values, the fill does not appear to have been placed in thin, well-compacted lifts with proper technical oversight and is considered to be uncontrolled.

Natural lean clays transitioning into fat clays were encountered below the fill or topsoil layers in each boring. The natural soils generally displayed medium stiff to stiff consistencies except in borings B-8, 16, 18, and 21 where soft consistencies were encountered. Borings B-18 through B-21 were drilled in the area that previously indicated potential karst activity in boring B-5. Borings B-18 and B-21 also displayed signs of soil softening with depth, which is a common indicator of karst activity. Boring B-18 met auger refusal at a depth of 24 ½ feet while boring B-21 encountered auger refusal at a depth of 8 ½ feet. The remaining borings in the parking lot typically encountered auger refusal between 6 and 8 feet below existing grade on average. See table below and attached boring logs for further detail of encountered subsurface conditions:

Boring No.

Topsoil Thickness

(in)

Approx. Fill Thickness, (ft)

Approx. Depth to Refusal, ft.

B-1 7 -- 6 ¾

B-2 3 -- 8 ¼

B-3 6 3 4 ¾

B-4 7 2 5 ¾ B-5 6 -- 22 ¼ 1

B-6 -- 32 8 ¾

B-7 4 4 10 B-8 4 -- >103

B-9 3 2 5 ½

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Boring No.

Topsoil Thickness

(in)

Approx. Fill Thickness, (ft)

Approx. Depth to Refusal, ft.

B-10 3 5 8 ½

B-11 4 3 >103

B-12 4 2 8

B-13 4 -- >103

B-14 3 -- 6

B-15 5 -- 6

B-16 4 -- 8 ½

B-17 4 -- 5 ½ B-18 5 -- 24 ½1

B-19 5 2 18

B-20 4 -- 8 B-21 5 -- 8 ½1

1. Possible karst feature as interpreted by observed soil softening with depth

2. Fill contained asphalt particles

3. Borings did not encounter auger refusal and were terminated at indicated depth

The site is underlain by carbonate limestone that is highly susceptible to dissolution along joints and bedding planes in the rock mass. This results in voids and solution channels within the rock strata and a highly irregular bedrock surface. The weathering of the bedrock and subsequent collapse or erosion of the overburden into these openings results in what is referred to as karst topography. Any construction in karst topography is accompanied by some degree of risk for future internal soil erosion and ground subsidence that could affect the stability of the proposed structures. Our review of the available topographic mapping revealed closed depressions approximately 2000 to 3000 feet away to the East and North of this site . Additionally, borings B- 5, B-18 and B-21 encountered apparent karst activity in the form of soil softening throughout the soil profile before terminating at auger refusal depths of approximately 8 ½ to 24 ½ feet below existing grade on apparent limestone bedrock.

The boreholes were observed while drilling and after completion for the presence and level of groundwater. Groundwater was not observed in the borings while drilling, or for the short duration the borings could remain open. Due to the low permeability of the soils encountered in the borings, a relatively long period may be necessary for a groundwater level to develop and stabilize in a borehole. Long term observations in piezometers or observation wells sealed from the influence of surface water are often required to define groundwater levels in materials of this type.

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Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Perched water can develop within porous fill and on top of bedrock. The possibility of groundwater level fluctuations and perched water should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

The original geotechnical scope was to explore the West side of the existing parking lot. After encountering fill material, fat clays, and potential karst activity, the scope was expanded to include the eastern and southern edges of the existing parking area. Based on the information obtained from our subsurface exploration, the site can be developed for the proposed parking lot improvements. Due to the potential karst activity and undocumented fill, subgrade remediation may be required during construction to address potential karst-related drop outs or soft and unstable soils

■ Karst Activity - The site is situated in karst terrain and the risk for sinkhole development should be recognized in this geological setting. The Murfreesboro area has a history of karst activity and sinkhole development. Any construction in karst terrain is accompanied by some risk for future internal erosion and ground subsidence for soil supported structures. In addition, several closed depressions are shown on the published USGS topographic mapping within a half-mile radius of the site

Our subsurface exploration encountered soil softening in the initial boring B-5 and additional borings B-18 and B-21. In a karst feature, soil is transported by water into fractures or joints in the bedrock.

This movement of soil is known as piping. Over time, the soil is slowly transported and eroded away from the rock surface up through the soil column until the soil mass can no longer support its own weight. The soil collapses into the void and thus a sinkhole can appear at the ground surface. Soft and very soft soils as noted in borings B-5 and B-18 indicate that soils are being piped into the bedrock and strength of the soil has greatly diminished. Part of the scope of our additional borings was to explore several areas around boring B-5. Based on the findings of these additional borings, it appears that the karst feature is limited to the general area around borings B-5 and B-18. Some of the soil soften extended towards boring B-21, but generally the bedrock surface rose in elevation in the borings further away from B-5 and B-18. Our opinion based off our experience is that the origination point, or throat of this karst feature is likely in the near vicinity of borings B-5 and B-18, although a larger area surrounding the feature has been impacted.

Two types of karst remediation common to this area are construction of an inverted rock filter or a cap grouting program. An inverted rock filter requires excavating loose and low strength soils that have been eroded by the karst feature down to the fracture in the bedrock, also known as the throat.

Once there, filter fabric and large granular fill such as shot rock are placed in the excavation. Once

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Responsive ■ Resourceful ■ Reliable 7 the excavation has been nearly filled with rock, the filter fabric is then wrapped over the rock so that soil does not pass into the granular fill. The pros with this method are that it can generally be constructed by a grading contractor using conventional construction equipment. The cons are disposal of the spoils generated from excavation and that conventional excavation equipment can be limited by depth. In a grouting program, a specialty grouting contractor is employed to drill holes down to the bedrock fractures and seal off future soil piping by placing grout under pressure. The pressurized grout pumped into the soil also increases the density of the softened soils. The pros are low site disturbance and the ability to manage large features without excavating soils. The cons are that a specialty contractor must be utilized which can affect the cost of the repair and schedule.

■ Existing Fill – As summarized in the above table, Borings B-3, B-4, B-7, B-9, B-10, B-11, B-12 and B-19 encountered about 2 to 5 feet of existing clay fill containing organics, chert and limestone fragments. Boring B-6 encountered 3 feet of fill containing asphalt particles. Documentation regarding fill placement was not available. Based on the low SPT N-values (2 to 6 blows per foot) and organics content recorded in the fill it appears that the fill was placed in an uncontrolled manner without proper compaction and technical observation. Because of these factors and the unknown aspects of the existing fill, it poses a potential risk for excessive pavement settlement. This risk cannot be eliminated without removing the fill in its entirety. Provided the Owner is willing to accept the potential risk of pavement settlement, the fill may remain in the pavement areas given that it passes proof roll test and is further evaluated by a Terracon engineer. The engineer should be allowed to perform test pits and DCP testing at the time of construction to help delineate soft and unsuitable soils for pavement support. Low strength soils (N-value of about 5 or less) similar to soils encountered in borings B-3 and B-6, where encountered, should be undercut and replaced or recompacted at the time of construction. We estimate up to 2 feet of undercut and replacement may be necessary in soft areas around borings B-3 and B-6. The additional borings containing fill (B-7, 9, 10, 11, 12 and 19) typically displayed N-values of 9 or more blows per foot in the upper portion of the fill material. We note these values could be inflated due to the presence of rock and chert fragments. The fill material may remain in place at the Owner’s risk provided that the existing material passes a proof roll test. Any soft soil delineated during the proof roll test should be undercut and replaced with new engineered fill. The undercut soils can be reused if the material meets our fill criteria and is placed per our recommendations as outlined herein. Much of the fill material sampled during our additional boring exploration contained excess organic material and should not be reused as structural fill. Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Earthwork section.

n Fat Clay – High plasticity clays (CH) were encountered in the borings B-1, B-2, B-3, B-10, B-15, B-17, B-18, and B-19. These soils have some potential for shrink and swell with changes in moisture content. This volume change potential presents a risk of some pavement movement and/or cracking with changes in soil moisture conditions if located relatively close to the subgrade surface. The effective conventional approach to help minimize shrink and swell potential of fat clays is to remove the fat clay and replace it with at least 1 foot of low volume change engineered fill or to chemically modify the soil’s properties. We understand that the project has a narrow

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Responsive ■ Resourceful ■ Reliable 8 margin for grading costs and that typical undercut and replace with low volume change engineered clay fill may not be economically feasible. This clayey material was observed to be generally stiff where encountered near the surface. The high plasticity clays can remain in place, provided that they are stable under proof roll testing and moisture conditioned to optimum or slightly greater than optimum moisture content prior to further fill placement. The client must except some risk for potential pavement movements and cracking and recognize that additional pavement maintenance may be required to preserve pavement lifespan.

The General Comments section provides an understanding of the report limitations.

EARTHWORK

Earthwork is anticipated to include clearing and grubbing, and possible fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for pavements.

Site Preparation

Prior to placing fill, existing vegetation and root mat should be removed. Complete stripping of the topsoil should be performed in the proposed parking/driveway areas.

We recommend that the exposed subgrade be thoroughly evaluated by a geotechnical engineer prior placement of new fill. The soils on the site are sensitive to disturbance from construction equipment traffic, particularly during wet periods. The subgrade should be proof rolled with a loaded tandem axle dump truck. The proof-rolling should be performed under the direction of the Geotechnical Engineer. Areas excessively deflecting under the proof-roll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should be removed or possibly modified by stabilization (bridging) techniques in pavement areas as outlined herein. We expect near surface softer soils at/near borings B-3, B-4, B-5, B-6, B-10, B-11, B-16, B-18, B-19 and B-21 could fail during proof roll test and may require remediation.

The site is located within an active karst terrain. Therefore, site grading should incorporate passive measures to minimize water ponding onsite and surface water should not be allowed onsite to penetrate into the ground. A thorough visual assessment of the site by a Terracon geotechnical engineer for any karst issues will be necessary once site clearing is performed but before any fill is placed. The risks associated with karst topography can be mitigated by careful attention to the details of site preparation. Site design should include provisions for positive drainage, and water should not be allowed to pond on the site, either during or after construction. Surface runoff should be conveyed off the property. If possible, consideration may be given not to use permeable pavers and use some other type of detention system which will minimize water penetration into the ground.

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The grading contractor should be alert during construction to any indication of possible incipient sinkholes within the subsurface. Given the risk for karst related problems, it is essential that stripping and proof rolling operations be observed by the geotechnical engineer to detect the presence of any near surface karst features that may require repair. Any sinkhole features encountered during the site grading, or during later stages of construction, should be reviewed by the geotechnical engineer and further exploration may be warranted to confirm that conventional repair techniques can be used.

Existing Fill

As noted in Geotechnical Characterization, borings B-3, B-4, B-6, B-7, B-9, B-10, B-11, B-12 and B-19 encountered existing fill to depths ranging from about 2 to 5 feet. The fill appears to have been placed without proper engineering control and compaction as displayed by the moderately low SPT N-values and presence of some organics and asphalt particles. Support of pavements, on or above existing fill soils, is discussed in this report. However, even with the recommended construction procedures, there is inherent risk for the owner that compressible fill or unsuitable material, within or buried by the fill will, not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill, but can be reduced by following the recommendations contained in this report.

If the owner elects to construct pavements on the existing fill, the following protocol should be followed. Once the topsoil has been stripped and any planned cuts made, the entire pavement area should be proof rolled. Areas of soft or otherwise unsuitable material should be undercut and replaced with either new structural fill or suitable, existing on site materials. The fill conditions should be thoroughly evaluated by a Terracon engineer via test pits, DCP testing and proof rolling to confirm it suitability for slab and pavement support. Any weak or unsuitable soils uncovered during this evaluation should be undercut and replaced with new engineered fill as directed by the engineer.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures, pavements or constructed slopes. General fill is material used to achieve grade outside of these areas. Earthen materials used for structural and general fill should meet the following material property requirements:

Soil Type 1 USCS Classification Acceptable Parameters

Low Plasticity Cohesive CL, CL-ML5 Liquid Limit less than 45, Plasticity index less than 25 can be used at all locations and elevations

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Soil Type 1 USCS Classification Acceptable Parameters

High Plasticity Cohesive 2 CH Liquid Limit greater than 50 (should only be placed 2 feet or more below finished subgrade)

Granular GW 3 Less than 8% Passing #200 sieve, can be used at all locations and elevations

Clean well graded processed rock, shot rock (max. rock size 12 inches) or surge stone (max. rock size 6 inches) 4

-- Can be used at all locations and elevations

1. Structural and general fill should consist of approved materials free of organic matter and debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the Geotechnical Engineer for evaluation prior to use on this site.

2. CH soils should not be used within 2 feet of finished subgrade in building area and 2 feet below finished subgrade in other structural fill areas.

3. Similar to crushed limestone aggregate, limestone screenings, or granular material such as well graded gravel or crushed rock.

4. Approval of shot rock and surge stone should be made prior to placement. Any shot rock containing more than 5% clay fines should not be used as engineered fill.

5. If silty soils are used as engineered fill, we expect some difficulties will be experienced during compaction due to moisture sensitive nature of these soils. Stringent moisture control techniques will be required in the field to achieve compaction.

Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift Thickness

8 inches or less in loose thickness when heavy, self-propelled compaction equipment is used 4 to 6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used Shot rock can be placed in 12 to 18-inch thick horizontal layers, depending on particle size and compaction equipment weight

Same as Structural fill

Minimum Compaction Requirements 1, 2, 3

98% of max. 95% of max.

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Item Structural Fill General Fill

Water Content

Range 1

Low plasticity cohesive: -1% to +2% of optimum High plasticity cohesive: 0 to +3% of optimum Granular: -2% to +2% of optimum

As required to achieve min.

compaction requirements

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

3. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254).

Earthwork Construction Considerations

Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to pavement construction. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over, or adjacent to, construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted, prior to floor slab construction. Should unstable subgrade conditions develop, stabilization measures will need to be employed. Subgrade stabilization techniques are discussed in the following paragraphs:

n Scarification and Recompaction - It may be feasible to scarify, dry, and recompact the exposed soils. The success of this procedure would depend primarily upon favorable weather and sufficient time to dry the soils. Even with adequate time and weather, however, stable subgrades may not be achievable if the thickness of the soft soil is greater than 1 to 1-½ feet.

n Chemical Stabilization – If the required subgrade stabilization is relatively extensive, chemical modification may be more practical than scarification and recompaction, or undercutting and placement of crushed stone, with or without geotextiles. The use of Portland cement or by-product lime (lime kiln dust) or quick-lime could be considered for shallow stabilization, or stabilization after partial undercutting. We recommend stabilization methods be further evaluated at the time of construction. We recommend that a mix design be performed with samples of the chemical agent to be used and the site soils. This will aid in optimizing the mix design and evaluating for potential negative reactions such as sulfate induced heave. Since the agents can vary significantly in terms of chemical composition, it will be important that samples of the actual proposed modifying agent be used in the laboratory mix design. With all chemical modification methods, proper mixing and control of clod sizes, moisture conditions, and compaction are critical. We recommend that only experienced contractors perform chemical modification and that they provide detailed

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Responsive ■ Resourceful ■ Reliable 12 descriptions of their proposed procedures and equipment, as well as a list of projects successfully completed in the last 5 years.

n Crushed Stone with Geogrid - Crushed stone with high modulus geogrid (such as Tensar TX160 geogrid or equivalent) could be used to improve subgrade stability. Typical undercut depths would likely range from 2 to 4 feet below finished subgrade elevation. The geogrid could be placed after underground work such as utility construction is completed. Equipment should not be operated above the geogrid until one full lift of crushed stone fill is placed above.

The maximum particle size of granular material placed over geogrid should not exceed 1-½ inches. Geogrid can also be considered for severe subgrade conditions during winter months.

It should be expected that minimum of 10 to 12 inches of select fill will be required with any geogrid application. The geogrid product manufacturer should recommend select fill gradation requirements for compatibility with their product.

n Shot Rock – Shot rock or processed surge stone may be used for subgrade stabilization.

Shot rock should be clean and well graded and placed in 12 to 18-inch thick lifts. Depending on subgrade condition, the first lift of shot rock directly placed over soft subgrade should be free of fines. Thickness of shot rock required to achieve subgrade stability will be dependent upon subgrade condition at the time of grading. A test strip may be constructed in the field for shot rock application in the presence of a Terracon engineer to determine the minimum required shot rock thickness to achieve subgrade stability

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local, and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety, or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and topsoil, proof rolling, and mitigation of areas delineated by the proof roll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of

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Responsive ■ Resourceful ■ Reliable 13 compacted fill in the building areas and 5,000 square feet in pavement areas. One density and water content test should be performed for every 50 linear feet of compacted utility trench backfill.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

PAVEMENTS

General Pavement Comments

Pavement designs are provided for the traffic conditions and pavement life conditions as noted in Project Description and in the following sections of this report. A critical aspect of pavement performance is site preparation. Pavement designs noted in this section must be applied to the site which has been prepared as recommended in the Earthwork section.

Pavement Design Parameters

Traffic patterns and anticipated loading conditions were not available. However, we anticipate that traffic loads will be produced primarily by automobile traffic and a limited number of emergency vehicles such as a 48 foot fire pumper truck. Two pavement section alternatives have been provided. If heavier traffic loading is expected, this office should be provided with the information and allowed to review these pavement sections. A design life of 20 years was assumed to develop the total traffic used in thickness design. A California Bearing Ratio (CBR) value of 5 has been estimated for approved existing clay fill material or new engineered fill. To help obtain this CBR value in the field, the upper 12 inches of pavement subgrades should be compacted to at least 98 percent of the standard Proctor density at moisture content within -1 to +3 percent of its optimum moisture. Any weak soils encountered in pavement areas should be undercut and replaced with approved engineered fill.

Climatic conditions are considered in the design subgrade support value listed above and in the paving material characteristics. Recommended paving material characteristics, taken from the Tennessee Department of Transportation’s (TDOT) 2012 edition of Standard Specifications for Road and Bridge Construction are included for the asphalt concrete sections.

A modulus of subgrade reaction of 100 pci was used for the PCC pavement designs. This value was empirically derived based upon our experience with the describe soil type subgrade soils and our understanding of the quality of the subgrade as prescribed by the Site Preparation conditions as outlined in Earthwork.

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Pavement Section Thicknesses

The following table provides options for AC and PCC Sections:

Asphaltic Concrete Design

Layer Thickness (inches)1

AC Surface 2 1 ½

AC Base2 1 ½

Aggregate Base 3 6

1. See Project Description for more specifics regarding pavement loading conditions.

2. All materials should meet the current State of TN department of Transportation (TDOT) Standard

Specifications for Highway and Bridge Construction.

n Asphaltic Surface – TDOT Section 903.11 for Surface Course, Grading E n Asphaltic Base – TDOT Section 903.06 for Hot Mix Asphalt Leveling Course, Grading B-M n Portland concrete should be 4,000 psi compressive strength at 28 days, 4-inch maximum slump and 5 to 7 percent air entrained, 6-sack min. mix. PCC pavements are recommended for trash container pads and in any other areas subjected to heavy wheel loads and/or turning traffic such as entrance aprons.

n A minimum 1.5-inch surface course should be used on ACC pavements

3. Section 903.05 for Aggregate Base Course material, Class A, Grading D

Portland Cement Concrete Design

Layer Thickness (inches)

Light Duty 1 Dumpster Pad 3

PCC 2 5 7

Aggregate base 3 4 4

1. See Project Description for more specifics regarding traffic classifications.

2. All materials should meet the current Tennessee Department of Transportation (TDOT) Standard

Specifications for Highway and Bridge Construction.

3. In areas of anticipated heavy traffic, fire trucks, delivery trucks, or concentrated loads (e.g. dumpster pads), and areas with repeated turning or maneuvering of heavy vehicles.

Areas for parking of heavy vehicles, concentrated turn areas, and start/stop maneuvers could require thicker pavement sections. Edge restraints (i.e. concrete curbs or aggregate shoulders) should be planned along curves and areas of maneuvering vehicles. A maintenance program including surface sealing, joint cleaning and sealing, and timely repair of cracks and deteriorated

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Concrete for rigid pavements should have a minimum 28-day compressive strength of 4,000 psi, and be placed with a maximum slump of 4 inches. Although not required for structural support, a minimum 4-inch thick base course layer is recommended to help reduce potential for slab curl, shrinkage cracking, and subgrade pumping through joints. Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. Joints should be sealed to prevent entry of foreign material and doweled where necessary for load transfer.

Where practical, we recommend early-entry cutting of crack-control joints in PCC pavements.

Cutting of the concrete in its “green” state typically reduces the potential for micro-cracking of the pavements prior to the crack control joints being formed, compared to cutting the joints after the concrete has fully set. Micro-cracking of pavements may lead to crack formation in locations other than the sawed joints, and/or reduction of fatigue life of the pavement.

Openings in pavements, such as decorative landscaped areas, are sources for water infiltration into surrounding pavement systems. Water can collect in the islands and migrate into the surrounding subgrade soils thereby degrading support of the pavement. This is especially applicable for islands with raised concrete curbs, irrigated foliage, and low permeability near-surface soils. The civil design for the pavements with these conditions should include features to restrict or collect and discharge excess water from the islands. Examples of features are edge drains connected to the storm water collection system, longitudinal subdrains, or other suitable outlets and impermeable barriers preventing lateral migration of water such as a cutoff wall installed to a depth below the pavement structure.

Dishing in parking lots surfaced with ACC is usually observed in frequently-used parking stalls (such as near the front of buildings), and occurs under the wheel footprint in these stalls. The use of higher-grade asphaltic cement, or surfacing these areas with PCC, should be considered. The dishing is exacerbated by factors such as irrigated islands or planter areas, sheet surface drainage to the front of structures, and placing the ACC directly on a compacted clay subgrade.

Rigid PCC pavements will perform better than ACC in areas where short-radii turning and braking are expected (i.e., entrance/exit aprons) due to better resistance to rutting and shoving. In addition, PCC pavement will perform better in areas subject to large or sustained loads. An adequate number of longitudinal and transverse control joints should be placed in the rigid pavement in accordance with ACI and/or AASHTO requirements. Expansion (isolation) joints must be full depth and should only be used to isolate fixed objects abutting or within the paved area.

PCC pavement details for joint spacing, joint reinforcement, and joint sealing should be prepared in accordance with ACI 330 and ACI 325. PCC pavements should be provided with mechanically reinforced joints (doweled or keyed) in accordance with ACI 330.

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Pavement Drainage

Pavements should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. In addition, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the granular subbase.

Pavement Maintenance

The pavement sections represent minimum recommended thicknesses and, as such, periodic maintenance should be anticipated. Therefore, preventive maintenance should be planned and provided for through an on-going pavement management program. Maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment.

Maintenance consists of both localized maintenance (e.g., crack and joint sealing and patching) and global maintenance (e.g., surface sealing). Preventive maintenance is usually the priority when implementing a pavement maintenance program. Additional engineering observation is recommended to determine the type and extent of a cost-effective program. Even with periodic maintenance, some movements and related cracking may still occur and repairs may be required.

Pavement performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of pavements:

■ Final grade adjacent to paved areas should slope down from the edges at a minimum 2%.

■ Subgrade and pavement surfaces should have a minimum 2% slope to promote proper surface drainage.

■ Install below pavement drainage systems surrounding areas anticipated for frequent wetting.

■ Install joint sealant and seal cracks immediately.

■ Seal all landscaped areas in or adjacent to pavements to reduce moisture migration to subgrade soils.

■ Place compacted, low permeability backfill against the exterior side of curb and gutter.

■ Place curb, gutter and/or sidewalk directly on clay subgrade soils rather than on unbound granular base course materials.

GENERAL COMMENTS

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather.

The nature and extent of such variations may not become evident until during or after construction.

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Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client.

Reliance upon the services and any work product is limited to our client, and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly impact excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing.

Site safety, and cost estimating including, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

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FIGURES

Contents:

GeoModel

-26

-24

-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2

E L

E V

A T

IO

N

M

S L

(f ee t)

18-407 Murfreesboro Parking Improvements Geophysics Additional Work Murfreesboro, TN Terracon Project No. 18195130

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

B-7 B-8 B-9 B-10 B-11 B-12 B-13 B-14 B-15 B-16 B-17 B-18 B-19 B-20 B-21

GEOMODEL

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

Yellowish to reddish brown low plasticity clays with varying amounts of angular limestone and chert particles consistencies varied from soft to very stiff

LEGEND

Topsoil

Fill

Lean Clay

Fat Clay

Model Layer General DescriptionLayer Name

Lean clays with chert, limestone, and asphalt fragments1

Yellowish red to red high plasticity clays with varying amounts of angular limestone and chert particles consistencies are stiff. These clays have a potential for shrink swell

Lean Clay

Fill

Fat Clay

0.34

5.5

8.5

0.34

0.25

0.41

3.5

0.34

8.5

0.34

5.5

0.41

24.5

0.34

0.41

8.5

ATTACHMENTS

March 13, 2020 ■ Terracon Project No. 18195130

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EXPLORATION AND TESTING PROCEDURES

Field Exploration

Number of Borings Boring Depth (feet) Planned Location

B-1 through B-6 10 or auger refusal Pavements for original scope

B-7 through B-21 10 or auger refusal Pavements for additional scope

Boring Layout and Elevations: Unless otherwise noted, Terracon personnel provided the boring layout. Coordinates were obtained with a handheld GPS unit (estimated horizontal accuracy of about ±10 feet) and approximate elevations were obtained by interpolation from the schematic site plan provided by Alex Kramer of…