Attachment 07-Geotech Report-Columbus.pdf

Geotechnical Engineering Report

Chalmers P. Wylie VA Care Center Improvements

Columbus, Ohio

October 16, 2020

Terracon Project No. N4185341

Prepared for:

Guidon Design, Inc.

Indianapolis, Indiana

Prepared by:

Terracon Consultants, Inc.

Columbus, Ohio

Terracon Consultants, Inc. 800 Morrison Road Gahanna, Ohio 43230

P (614) 863 3113 F (614) 863 0475 terracon.com

Guidon Design, Inc.

1221 North Pennsylvania Street

Indianapolis, Indiana 46202

Attn: Ms. Stacey Paul, P.E.

P: (317) 800-6388

E: spaul@guidondesign.com

Re: Geotechnical Engineering Report

Chalmers P. Wylie VA Care Center Improvements

Columbus, Ohio

Terracon Project No. N4185341

Dear Ms. Paul:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with our proposal (Proposal No. PN4185341 dated

September 18, 2018 and work authorization (Subcontract for Professional Consulting Services) dated August 25, 2020.

This report presents the findings of the subsurface exploration and provides geotechnical engineering recommendations concerning earthwork, pavement and the design and construction of foundations 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.

Ganesh Vairavan Kevin M. Ernst, P.E.

Senior Staff Engineer Principal, Office Manager

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

FOUNDATION RECOMMENDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

PAVEMENTS

PERCOLATION TEST

GENERAL COMMENTS

FIGURES

Note: This report was originally delivered in a web-based format. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION AND TESTING RESULTS

SUPPORTING INFORMATION

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

http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

Chalmers P. Wylie VA Care Center Improvements

Columbus, Ohio Terracon Project No. N4185341

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed improvements to the existing Chalmers P. Wylie VA Care

Center located at 420 North James Road, Columbus, Ohio. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Seismic site classification per IBC

■ Site preparation and earthwork ■ Pavement design and construction

The geotechnical engineering Scope of Services for this project included the advancement of seven test borings designated B-1 through B-6 and PT-1 to depths ranging from approximately 6 to 30 feet below existing site grades. The scope also included performing a percolation test at the location of the proposed underground infiltration tank.

Maps showing the site and boring locations are shown in the SITE LOCATION AND

EXPLORATION PLANS section of this report, respectively. The results of the laboratory testing performed on select soil samples obtained during the field exploration is included on the boring logs and separately 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 topographic maps.

Item Description

Parcel Information

The project site is located at the existing Chalmers P. Wylie VA Care Center at 420 North James Road, Columbus, Ohio. The approximate coordinates of the site are 39.9813N, 82.908W.

See SITE LOCATION PLAN.

Existing

Improvements

The project site is inside the existing Chalmers P. Wylie VA Care Center facility, east of the existing ‘Engineering Building’.

Chalmers P. Wylie VA Care Center Improvements ■ Columbus, Ohio

October 16, 2020 ■ Terracon Project No. N4185341

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Item Description

Current Ground

Cover Asphalt pavement, topsoil, and grass.

Existing Topography

Based on publicly available maps (Google Earth), the project site appears to be relatively level with ground surface elevations ranging from approximately

791 to 793 feet.

PROJECT DESCRIPTION

Our understanding of the project is as follows:

Item Description

Project Description

Based on the provided information, the project includes addition of a building with an approximate footprint of 2,000 square feet to the existing

‘Engineering Building’. The project will also include relocation of the existing pavements associated with the ‘Engineering Building’ and installation of a new underground detention pond. The detention pond is proposed to be located south of the existing VA Medical Center, approximately 490 feet west of the Engineering Building.

Finished Floor Not provided; assumed to be approximately 792 feet.

Maximum Loads

The following loads were provided via email form (Company Name) dated

October 14, 2020:

■ Columns: 25 kips

■ Slab: 100 psf

■ Walls: 3 kips per linear foot (assumed)

Grading A grading plan was not available during the preparation of this report.

Minimal grading consisting of cut/fill of +/- 1 to 2 feet is anticipated.

Pavements

Not provided. We have assumed the following light duty traffic loading information:

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

■ Delivery trucks: 3 vehicles per day

■ Trash collector trucks: 2 vehicles per week

The pavement design period is 20 years.

Estimated Start of Construction

Not provided.

If the project information presented above is not consistent with the proposed development, please inform us so that our recommendations can be reviewed and revised, if necessary.

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GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation 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

Approximate Depth to the Bottom of the Layer Below

Existing Site Grades

(feet)

Surficial Layer Topsoil/asphalt

Asphalt underlain by aggregate base: 0.8 to 1.5 feet (Borings B- 1 to B-3)

Aggregate base: 1 feet (Boring B-4)

Topsoil: 0.3 feet (Borings B-5, B- 6, and PT-1)

1 Existing Fill

Existing fill that can be described as clayey gravel and poorly graded gravel with varying amounts of sand, and poorly graded sand with varying amounts of gravel.

3.5 to 6 feet

2 Upper Clay Lean clay with varying amounts of sand and gravel; very soft to medium stiff

10 to 18.5 feet

Borings B-3 to B-6 and PT-1 were terminated within this layer at depths ranging from approximately 6 to 10 feet.

3 Lower Clay Lean clay with varying amounts of sand and gravel; stiff to hard

Undetermined: Borings B-1 and B-2 were terminated within this layer at depths ranging from 20 to 30 feet.

Groundwater Conditions

The borings were observed during and after completion of drilling for the presence and level of groundwater. Groundwater was encountered only in the borings B-2 and B-4 as shown on the table below.

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Boring ID

Approximate Depth of Groundwater Below Existing Site Grades

While Drilling (ft) Upon Completion of Drilling

(ft)

B-2 23.5 24

B-4 6 7.5

Groundwater was not observed in the remaining borings. Due to the low permeability of the soils encountered in the borings, a relatively long period of time may be necessary for a groundwater level to develop and stabilize in a borehole in these materials. 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.

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. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

The recently completed test borings indicated a surficial layer (topsoil/asphalt) underlain by existing fill soils. The existing fill soils were further underlain by very soft to medium stiff native cohesive soils to approximate depths ranging from 13.5 to 18.5 feet below existing site grades. In borings B-1 & B-2, these marginal strength soils were further underlain by stiff to hard, native cohesive soils to the boring termination depths ranging from 20 to 30 feet below existing site grades.

Three foundation options are discussed in FOUNDATION RECOMMENDATIONS section of this report which includes shallow foundations with isolated undercut and replacement with granular structural fill or lean concrete, helical piers, and micropiles.

The existing fill soils encountered at the proposed building location are not suitable for floor slab support. Therefore, the existing fill soils should be removed entirely from within and 10 feet beyond the building footprint and replaced with structural fill consistent with recommendations provided in the EARTHWORK section of this report.

Reworked existing fill generally appear suitable for pavement support provided the subgrade is proofrolled and unstable areas remediated by stabilizing or undercutting of the unstable subgrade materials. Proofrolling of exposed subgrades for pavement areas during site preparation process is an important aspect of the earthwork operations to provide for suitable subgrade for pavement

Responsive ■ Resourceful ■ Reliable 5 support. Proofrolling and remediation of any soft, loose, or unstable areas should be performed as outlined in the EARTHWORK section of this report.

Support of pavements on or above existing fill soils is discussed in this report. However, even with the recommended measures and construction testing, there is a risk that unsuitable materials within or buried by the fill will not be discovered. This risk of unforeseen conditions cannot be eliminated without removing the fill but can be reduced by thorough exploration and testing during construction.

A proposed grading plan was not available at the time of this report preparation. Grading to prepare the proposed building pad is anticipated to consist of up to 2 feet of cut and fill.

Groundwater was encountered in the borings B-2 and B-4 at depths ranging from approximately 6 to 24 feet below existing site grades. However, trapped water infiltration or groundwater seepage may be encountered in shallower excavations during construction, especially after a period of heavy precipitation and depending on when the construction is performed. In such an event, sump and pumping methods or more rigorous methods may be required for temporary dewatering. The contractor is responsible for employing appropriate temporary dewatering methods to control seepage and facilitate construction.

Close monitoring of the construction operations discussed herein will be critical in achieving the design subgrade support. We therefore recommend that Terracon be retained to monitor this portion of the work.

The GENERAL COMMENTS section provides an understanding of the report limitations.

EARTHWORK

Earthwork is anticipated to include topsoil/asphalt removal, excavations, and 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 foundation, floor slab and pavement support.

Site Preparation

As an initial measure of site preparation, topsoil, asphalt and aggregate base, or any other surficial deleterious material (e.g. debris, desiccated soil, high organic content soil, frozen soil, etc.) should be completely removed to expose the underlying soil subgrade in areas that support the proposed building and associated pavements. Any materials consisting of vegetation and organic matter should be wasted off site or could be re-spread in landscaped areas after completion of grading operations. Stripping depths across the site could vary considerably. We recommend actual

Responsive ■ Resourceful ■ Reliable 6 stripping depths be evaluated by a representative of Terracon during construction to aid in preventing removal of excess material.

Removal and/or relocation of any “to be abandoned” utilities should also be performed prior to rough site grading activities. We would anticipate removal and relocation, or re-routing, of any existing utilities and catch basins which may currently exist within the footprint of the proposed development area that would interfere with new construction. Any abandoned underground pipes, left in place, should be fully grouted. Excavations created due to utility relocations should be backfilled with granular structural fill material, placed and compacted in accordance with the recommendations provided in the following paragraphs or with lean concrete or flowable fill. If lean concrete is used as backfill, the contractor should refer to the project drawings to confirm that the concrete backfill materials will not conflict with any new item installations or construction.

Backfill above utilities to be abandoned in place by grouting should be evaluated in area where these materials will provide subgrade support for new fill or structures. Unsuitable existing backfill should be undercut and replaced with structural fill.

After the removal of surficial layer, we recommend undercutting the existing fill soils within and 10 feet beyond the proposed building pad area. Following this excavation, the exposed surface should be inspected by a geotechnical engineer or trained engineering technician. Any unstable areas should be stabilized by using #2 or larger size stone, or using suitable geogrid and a lift of

#2 stone as a stabilizing lift. The top of the open-graded (e.g. #2) stone should be thoroughly choked off with finer-graded stone (such as ODOT 304 crushed limestone) to prevent migration of fine soils into the open-graded stone. A drainage outlet for the open-graded stone should be provided to reduce the potential for water softening of cohesive soils due to trapped water.

After performing the initial site preparation activities, the exposed soil subgrades within the limits of the proposed building and associated pavements should be proofrolled with heavy pneumatic tired construction equipment, such as a loaded dump truck weighing at least 20 tons. Densification of granular soils, if encountered, should be performed with a heavy drum vibratory compactor. A geotechnical engineer or their representative should observe the densification/proofrolling to aid in locating unstable subgrade materials and assessing the subgrade.

Groundwater was encountered in the borings B-2 and B-4 at depths ranging from approximately 6 to 24 feet below existing site grades. However, trapped water infiltration or groundwater seepage may be encountered in shallower excavations during construction, especially after a period of heavy precipitation and depending on when the construction is performed. In such an event, sump and pumping methods or more rigorous methods may be required for temporary dewatering. The contractor is responsible for employing appropriate temporary dewatering methods to control seepage and facilitate construction.

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Fill Material Types

Fill required to achieve design grade should be classified as structural fill. Structural fill is material used below, or within 10 feet of structures and pavements. Earthen materials used for structural fill should meet the following material property requirements:

Fill Type 1 USCS Classification Acceptable Location for Placement

Lean clay

CL

(LL<40 & PI<22)

All locations and elevations. Not suitable for the recommended isolated undercut underneath the bottom of footings.

Well graded granular SW or GW2 All locations and elevations

On-Site Native Soils CL

The use of on-site CL soils as structural fill should meet the requirements for “acceptable location for placement” indicated above. Moisture conditioning of the onsite soils should be anticipated. Onsite naïve soils are not suitable for use within 8 feet below the proposed bottom of footings.

1. Structural fill should consist of approved materials free of organic matter, and particles larger than 3 inches in any dimension 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. Crushed limestone aggregate, limestone screenings, or granular material such as sand, gravel or crushed stone.

Fill Compaction Requirements

Structural fill should meet the following compaction requirements.

Item Structural 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 dry compactor) is used

Minimum Compaction

Requirements 1, 2

98% of maximum dry density (Standard proctor)

Water Content

Range

Low plasticity cohesive: -2% to +3% of optimum

Granular: Workable moisture levels

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Item Structural Fill

1. Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved. The compacted subgrade should also not indicate rutting and pumping under construction traffic.

2. Specifically, moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proofrolled. Soils removed which will be used as structural fill should be protected to aid in preventing an increase in moisture content due to rain.

Utility Trench Backfill

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches, which could migrate below the building. The trench should provide an effective trench plug that extends at least 5 feet from the face of the building exterior. The plug material should consist of cementitious flowable fill or low permeability clay.

The trench plug material should be placed to surround the utility line. If used, the clay trench plug material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated previously in this report.

Grading and Drainage

All grades must provide effective drainage away from the building during and after construction and should be maintained throughout the life of the structure. Water retained next to the building can result in soil movements greater than those discussed in this report. Greater movements can result in unacceptable differential floor slab and/or foundation movements, cracked slabs and walls, and roof leaks. The roof should have gutters/drains with downspouts that discharge onto splash blocks at a distance of at least 10 feet from the building.

Based on our short-term observations, groundwater seepage/trapped infiltration may be encountered in shallow excavations during construction, especially if the construction is started after the period of heavy precipitation. In such an event, sump and pumping methods might be required for the temporary dewatering.

Earthwork Construction Considerations

Excavations for the proposed structure are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of foundations and pavements. Construction traffic over the completed subgrades should be avoided to the extent possible. 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

Responsive ■ Resourceful ■ Reliable 9 materials should be scarified, moisture conditioned, and recompacted prior to pavement construction.

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.

Open cut excavations should not remain exposed to weather conditions for an extended period.

Seepage or low strength conditions may dictate flatter slopes than those recommended by OSHA.

If the above mentioned backslopes cannot be followed due to site constraints or other reasons, temporary earth retention system(s) will be required for excavation support. Terracon can provide recommendations for such systems, upon request.

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, topsoil and unsuitable/unstable soils, proofrolling, and mitigation of areas delineated by the proofroll 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.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. In the event unanticipated conditions are encountered, the

Geotechnical Engineer should prescribe mitigation options.

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.

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FOUNDATION RECOMMENDATIONS

Three foundation options are discussed in this section of the report which includes shallow foundations with isolated undercut and replacement with granular structural fill or lean concrete, helical piers, and micropiles.

Shallow Foundations with Isolated Undercut

The existing marginal strength soils (very soft to medium stiff native cohesive soils) encountered at the proposed location of the building addition are not suitable for direct foundation support. To reduce adverse settlement impacts, we recommend undercutting appropriately such that at least

6 feet of granular structural fill or lean concrete is present beneath the footings. This recommended undercut depth is based on exterior and interior footing embedment depths of 3 and 2 feet below finished grade, respectively. Footing over-excavations should be widened beyond the footing footprint by 2 feet for every 3 feet of excavation depth below the bottom of the footing. The footing over-excavation should be backfilled to establish the design bearing elevation with granular structural fill or lean concrete. It is recommended that new building footings bear on this newly placed structural granular fill or lean concrete. Design recommendations for shallow foundations to support the proposed building are presented below.

Item Description

Maximum net allowable bearing pressure 1, 2 1,500 psf

Required bearing stratum 3 At least 6 feet of granular structural fill or lean concrete

Minimum foundation dimensions Columns: 48 inches

Continuous: 18 inches

Ultimate coefficient of sliding friction 4 0.30 (ultimate)

Minimum embedment below finished grade 5, 6

Exterior footings in unheated areas: 36 inches

Interior footings in heated areas: 24 inches

Estimated maximum total settlement from structural loads 2

1 inch

Estimated maximum differential settlement 2, 6

About 2/3 of total settlement in the new addition area and 1 inch between the existing building and new addition.

1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. An appropriate factor of safety has been applied. Values assume that exterior grades are no steeper than 20% within 10 feet of structure.

2. Values provided are for maximum loads noted in PROJECT DESCRIPTION.

3. Granular structural fill in accordance with the EARTHWORK section of this report.

4. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should be neglected for foundations subject to net uplift conditions.

5. Embedment necessary to reduce the effects of frost and/or shrink/swell soils.

6. If a different embedment depth is used for the footings, Terracon should be notified to access the required amount of structural granular fill or lean concrete required underneath the bottom of the footing.

7. Expansion joints should be incorporated between the existing building and new addition to accommodate differential settlements.

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Construction Adjacent to Existing Building

Expansion joints should be provided between the existing building and the proposed addition to accommodate differential movements between the two structures. Underground piping between the two structures should be designed with flexible couplings and utility knockouts in foundation walls should be oversized, so minor deflections in alignment do not result in breakage or distress.

Care should be taken during excavation adjacent to existing foundations, to avoid disturbing existing foundation bearing soils.

New footings should bear at or near the bearing elevation of immediately adjacent existing foundations. Depending upon their locations and current loads on the existing footings, footings for the new addition could cause settlement of adjacent walls. To reduce this concern and risk, clear distances at least equal to the new footing widths should be maintained between the proposed addition’s footings and footings supporting the existing building.

Where the excavation extends below bottom of existing footings, underpinning or excavation bracing and or/shoring will be needed to reduce the risk for undermining the existing building footings. Plans of the foundation of the existing structures should be reviewed and compared to the planned activities to evaluate contingencies for the excavation methods.

Design Parameters - Uplift Loads

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils. As illustrated on the subsequent figure, the effective weight of the soil prism defined by diagonal planes extending up from the top of the perimeter of the foundation to the ground surface at an angle, , of 40 degrees from the vertical can be included in uplift resistance.

The maximum allowable uplift capacity should be taken as a sum of the effective weight of soil plus the dead weight of the foundation, divided by an appropriate factor of safety. A maximum total unit weight of 120 pcf should be used for the backfill. This unit weight should be reduced to

58 pcf for portions of the backfill or natural soils below the groundwater elevation.

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Foundation Construction Considerations

Due to the presence of marginal strength soils, we recommend that the footings of the proposed addition bear on at least 6 feet of granular structural fill or lean concrete, assuming that the minimum embedment depth recommended above will be used. Over-excavation for granular structural fill or lean concrete placement below footings should be conducted as shown in the diagram below. Over-excavation for compacted engineered fill or lean concrete placement below footings should extend laterally beyond all edges of the footings at least 8 inches per foot of over-excavation depth below footing base elevation.

Once the undercut excavation is made, the exposed subgrade soils should be examined by geotechnical personnel to determine that suitable bearing materials have been encountered.

Should the undercut excavation expose materials that require stabilization with #2 stone or durable dump-rock prior to fill placements, provisions should be made to “drain” these materials to a nearby storm sewer or other drainage outlet. Any #2 stone or dump rock should be suitably choked-off at the top so as to prevent overlying finer grained materials from migrating into this open-graded material.

The over-excavation should then be backfilled up to the footing base elevation with lean concrete or granular structural fill material such as ODOT Item 304 crushed limestone dense-graded aggregate placed in lifts of 8 inches or less in loose thickness (4 inches or less if using hand-guided compaction equipment) and compacted according to the recommendations provided in

Earthwork section of this GeoReport. The over-excavation and backfill procedure are described in the following figure.

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Helical Piers

Hot dipped galvanized helical piers socketed into at least stiff native clay can be used for support of the building addition. Helical piers would be designed and installed by a specialty contractor.

Due to the specialty of this foundation system, we recommend that a performance specification be used on the project.

Helical piers consist of varying diameter helices (auger blades) welded to a section of steel rod.

Rod extensions are used above the section with the helices. The piers are screwed into the ground with a calibrated torque-head either braced in position or mounted to a skid steer.

Increased pier capacity (up to a limit) is achieved by increasing the applied torque during installation. Helical soil pier systems are capable of achieving allowable vertical compressive capacities of 25 to 50 kips, depending on the bearing soil strata, the number of piers, and the diameter of helices utilized.

Particulars regarding such items as pier spacing, pier length, and element capacity should be determined by an experienced and qualified specialty contractor familiar with this procedure in conjunction with the geotechnical and structural engineers for this project. Terracon recommends that the helical piers should extend to bear in the underlying at least stiff native cohesive soils.

We recommend that settlement estimates and allowable load capacities be provided for the piers under the design loading conditions. The project structural engineer should review these estimates to determine if additional piers may be required to further reduce the anticipated movement.

We recommend that a Terracon representative be on site during pier installation to observe and document the installation procedures, and to note the torque applied to each pier. Terracon should review the proposed test procedures with the contractor prior to testing.

OR LEAN

CONCRETE

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Micropiles

Micropiles can be also be considered to be used as a foundation system. Micropile is a small diameter cast-in-place foundation element that is used to transfer the structural loads to deeper competent soil materials. The geotechnical capacity of the micropiles is based on the grout-to-ground resistance of the pile around its perimeter, or the skin friction resistance within a certain bond zone. In general, the design of micropiles is best performed by a specialty contractor followed by a field load test.

In general, the diameter of the micropiles is in the order of 4 to 12 inches and they should be embedded in the competent natural soil layers. The micropiles will typically be reinforced with a single, large-diameter reinforcing steel bar or an outer steel casing. The micropile contractor shall select the drilling method and the grouting procedures used for the installation of the micropiles, subject to the approval of the Geotechnical Engineer.

Particulars regarding such items as pile spacing, pile length, and element capacity should be determined by an experienced and qualified specialty contractor familiar with this procedure in conjunction with the geotechnical and structural engineers for this project. We recommend that a

Terracon representative be on site during pier installation to observe and document the installation procedures. Terracon should review the proposed test procedures with the contractor prior to testing.

SEISMIC CONSIDERATIONS

The seismic design requirements for buildings and other structures are based on Seismic Design

Category. Site Classification is required to determine the Seismic Design Category for a structure.

The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC).

Based on the soil properties encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is D. Subsurface explorations at this site were extended to a maximum depth of about 30 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

FLOOR SLABS

The existing fill soils within and 10 feet beyond the proposed building pad should be undercut and replaced with structural fill. Design parameters for floor slabs assume the requirements for

EARTHWORK have been followed. We recommend removal and replacement of the existing fill

Responsive ■ Resourceful ■ Reliable 15 soils within and 10 feet beyond the proposed building pad with structural fill. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

Floor Slab Design Parameters

Item Description

Floor slab support 1 Minimum 6 inches of free-draining (less than 6% passing the U.S. No. 200 sieve) crushed aggregate compacted to at least 98% of ASTM D 698 2, 3

Estimated modulus of subgrade reaction 2 100 pounds per square inch per inch (psi/in) for point loads

1. Floor slab areas should be structurally independent of any building footings or walls to reduce the possibility of floor slab cracking caused by differential movements between the slab and foundation.

2. Modulus of subgrade reaction is an estimated value based upon our experience with the subgrade condition, the requirements noted in EARTHWORK, and the floor slab support as noted in this table. It is provided for point loads. For large area loads the modulus of subgrade reaction would be lower.

3. Free-draining granular material should have less than 6 percent fines (material passing the #200 sieve).

Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions.

The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Saw-cut control joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations refer to the ACI Design Manual. Joints or cracks should be sealed with a water-proof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks beyond the length of the structural dowels. The Structural Engineer should account for potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

Floor Slab Construction Considerations

Finished subgrade, within and for at least 10 feet beyond the floor slab, should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade should become damaged or desiccated prior to construction of floor slabs, the affected material should be removed, and structural fill should be added to replace the

Responsive ■ Resourceful ■ Reliable 16 resulting excavation. Final conditioning of the finished subgrade should be performed immediately prior to placement of the floor slab support course.

The Geotechnical Engineer should approve the condition of the floor slab subgrades immediately prior to placement of the floor slab support course, reinforcing steel, and concrete. Attention should be paid to high traffic areas that were rutted and disturbed earlier, and to areas where backfilled trenches are located.

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.

Subgrade Preparation

On most project sites, the site grading is accomplished relatively early in the construction phase.

However, as construction proceeds, excavations are made into these areas, rainfall and surface water saturates some areas, heavy construction traffic disturbs the subgrade and many surface irregularities are filled in with loose soils to improve trafficability temporarily. As a result, the pavement subgrades should be carefully evaluated as the time for pavement construction approaches.

We recommend the moisture content and density of the upper 12 inches of the subgrade be evaluated and the pavement subgrades be proof-rolled within two days prior to commencement of actual paving operations. Areas not in compliance with the required ranges of moisture or density should be moisture conditioned and recompacted. Particular attention should be paid to anticipated high traffic areas and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the materials with properly compacted fills.

After proofrolling and repairing deep subgrade deficiencies, the entire subgrade should be scarified and developed as recommended in SITE PREPARATION to provide a uniform subgrade for pavement construction. Areas that appear severely desiccated following removal of topsoil may require further undercutting and moisture conditioning. If a significant precipitation event occurs after the evaluation or if the surface becomes disturbed, the subgrade should be reviewed by qualified personnel immediately prior to paving. The subgrade should be in its finished form at the time of the final review.

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Pavement Design Parameters

Provided site preparation recommendations in this report are followed to prepare the pavement subgrade, a CBR value of 3 can be considered for preliminary pavement design. This value needs to be verified by performing laboratory tests (laboratory CBR tests) on the representative on-site soil subgrade samples as the project progresses into final design and construction phase.

The minimum pavement section thicknesses presented in the section Estimates of Minimum

Pavement Thickness below are based on anticipated traffic loading information presented in the

PROJECT DESCRIPTION of this report. We have anticipated that the traffic loads will be produced primarily by automobile traffic, delivery trucks, and occasional trash removal trucks. The thickness of pavements subjected to heavy truck traffic should be determined using expected traffic volumes, vehicle types, and vehicle loads and should be in accordance with local, city or county ordinances.

For areas subject to concentrated and repetitive loading conditions such as dumpster pads or loading dock areas, we recommend the use of a Portland Cement Concrete (PCC) pavement.

For areas where PCC pavements, a subgrade modulus of 110 pci may be used for pavement design purposes.

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 parking lots and drives should slope down from pavement edges at a minimum 2%;

◼ The subgrade and the pavement surface should have a minimum ¼ inch per foot slope to promote proper surface drainage;

◼ Install pavement drainage 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; and, ◼ Place curb, gutter and/or sidewalk directly on clay subgrade soils rather than on unbound granular base course materials

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Estimates of Minimum Pavement Thickness

The following table provides options for Asphaltic Concrete and for Portland Cement Sections:

Typical Pavement Section Thickness (inches)

Traffic Area Alternative

Asphalt

Concrete

Surface

Course

Asphalt

Concrete

Base

Course

Portland

Cement

Concrete 1

Aggregate

Base

Course 2

Total

Thickness

Light Duty 3

(automobiles and occasional delivery trucks)

PCC -- -- 6.0 6.0 12.0

AC 2.0 2.0 -- 6.0 10.0

1. 4,000 psi at 28 days, 4-inch maximum slump and 5 to 7 percent air entrained, 6-sack min. mix. At least 7.0 inch thick PCC pavements are recommended for trash container pads and in any other areas subjected to heavy wheel loads and/or turning traffic.

2. ODOT 304 crushed limestone base material.

3. In accordance with assumed traffic information included in the PROJECT DESCRIPTION section of the report.

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. The subgrade and the pavement surface should have a minimum

¼ inch per foot slope to promote drainage. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the base layer.

If not already in place, Spider or Finger Drains should be installed at all existing drainage structures within the pavement limits. Four (4) - inch diameter perforated drain tile should be installed with positive slope to extend 10 feet beyond each face of the structure with the invert 18 inches minimum below the pavement surface. The drains should be backfilled with free draining open graded granular material.

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

Responsive ■ Resourceful ■ Reliable 19 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.

PERCOLATION TEST

Percolation tests were performed at boring location PT-1 at an approximate depth of 4 feet below existing ground surface. The infiltration test results are included in the Exploration and Testing

Results section of this report.

The field test results provided in this report are not intended to be design rates. They represent the result of our test, at the depth and location where it was performed. The design rate should be determined by the designer by applying an appropriate factor of safety. With time, the bottoms of infiltration systems tend to plug with organics, sediments, and other debris. Long term maintenance will likely be required to remove these deleterious materials to help reduce decreases in actual infiltration rates. In addition, the infiltration rate may be affected by the following factors, which should be considered when selecting the factor of safety:

■ Water Quality: The infiltration tests were performed with clear, potable water, whereas the storm water will likely not be clear, but may contain organics, fines, and grease/oil. The presence of these deleterious materials will tend to decrease the rate that water percolates from the infiltration systems. Design of the storm water infiltration systems should account for the presence of these materials and should incorporate structures/devices to remove these deleterious materials.

■ Soil Variability: We expect the infiltration rates of the soils could be different than measured in the field due to variations in fines content. The design elevation and size of the proposed infiltration system should account for this expected variability in infiltration rates.

Infiltration/percolation tests should be performed after construction of the infiltration system to verify the design infiltration rates. It should be noted that siltation and vegetation growth along with other factors may affect infiltration rates of the infiltration areas.

In order to reduce the effect of infiltration on foundation settlement, all water quality basins and any other infiltration basins or trenches should be located at a distance of 20 feet away from any existing or proposed foundation systems.

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.

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

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.

Support of pavements on or above the existing fill soils is discussed in this report. However, even with the recommended construction testing services, there is an 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 performing additional testing and evaluation during construction.

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.