36E77619R0084-0003005.pdf

Geotechnical Engineering Report Veteran’s Administration Medical Center (VAMC) Parking Garage

4101 Woolworth Avenue Omaha, Nebraska

January 5, 2018 Terracon Project No. 05175212

Prepared for:

Nagel Architects & Engineers

Elm Grove, Wisconsin

Prepared by:

Terracon Consultants, Inc.

Omaha, Nebraska

Terracon Consultants, Inc. 15080 A Circ le Omaha, Nebraska 68144 P [402] 330 2202 F [402] 330 7606 terracon.com

January 5, 2018

Nagel Architects & Engineers 13100 Watertown Plank Road Suite 200 Elm Grove, WI 53122

Attn: Mr. Kenneth Shane ken.shane@nagel.us

Re: Geotechnical Engineering Report VAMC Parking Garage 4101 Woolworth Avenue Omaha, Nebraska Terracon Project No. 05175212

Dear Mr. Shane:

Terracon Consultants, Inc. (Terracon) has completed a subsurface exploration for the referenced project. The accompanying geotechnical report presents the findings of the subsurface exploration and provides geotechnical recommendations for the design and construction of parking garage foundations and grade-supported slabs for this project.

We appreciate the opportunity to provide the geotechnical services for this project. Please contact us if you have any questions regarding the attached report, or if we may be of further service.

Sincerely, Terracon Consultants, Inc.

Gopala K. Allam, E.I. Michael D. Ringler, P.E.

Sr. Staff Engineer Senior Engineer

GKA/MDR:gka/nlm

Distribution: Addressee (PDF)

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TABLE OF CONTENTS

Page

INTRODUCTION

PROJECT UNDERSTANDING

Site Location Project Description

EXPLORATION AND TESTING PROCEDURES

GEOTECHNICAL CHARACTERIZATION

Typical Profile Groundwater Conditions

GEOTECHNICAL OVERVIEW

Foundation Support Discussion Wet, Low-Strength Subgrades

SITE PREPARATION

Stripping and Subgrade Preparation Sub-Slab Drainage System Structural Fill Composition Requirements Structural Fill Compaction Requirements Construction Considerations and Drainage Landscaping and Finish Grading Permanent Slopes

DEEP FOUNDATIONS

Discussion Deep Foundation Alternatives ACIP Piles Axial Design General ACIP Pile Design Considerations Lateral Design ACIP Pile Installation

SEISMIC CONSIDERATIONS

PARKING GARAGE SLABS

Design Considerations Construction Considerations

CANTILEVER RETAINING WALLS

Construction Considerations Permanent Design Drainage

GENERAL COMMENTS

ATTACHMENTS

MAPS (Site Location, Exploration Plan) EXPLORATION RESULTS (Cone Penetrometer Sounding Plots) SUPPORTING INFORMATION (CPT General Notes)

ADDITIONAL INFORMATION FROM 2010 REPORT

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GEOTECHNICAL ENGINEERING REPORT

VAMC PARKING GARAGE

4101 WOOLWORTH AVENUE

OMAHA, NEBRASKA

Terracon Project No. 05175212 January 5, 2018

INTRODUCTION

This report presents the results of our subsurface exploration for the Veteran’s Administration Medical Center (VAMC) Parking Garage project at 4101 Woolworth Avenue in Omaha, Nebraska.

Six cone soundings, extending to depths ranging from about 120 to 121 feet, were performed to obtain information on the subsurface conditions. The individual CPT sounding logs are attached to this report. The approximate cone sounding locations are shown on the Exploration Plan.

We also used subsurface information gathered as part of our 2010 geotechnical exploration at the site. Soil borings B-2, B-3, B-13, B-15, B-16, and B-17 and cone sounding EC-1 were located close to the footprint of the currently-planned garage, and are included in the appendix of this report.

The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

n soil conditions n deep foundation design and construction n groundwater conditions n parameters for determining lateral load resistance of foundation elements n site stripping n lateral earth pressures and drainage for cantilever retaining walls n subgrade preparation for grade-supported slabs n recommended seismic design response spectra, including SDS and SD1 n site class determination for seismic design n computed seismic response spectrum at the ground surface

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PROJECT UNDERSTANDING

Site Location

Item Description

Site Information

The project is located at the existing Veteran’s Administration Medical Center (VAMC), 4101 Woolworth Avenue, Omaha, NE.

Approximate Latitude: 41° 14' 41.52" N/ Longitude: 95° 58' 24.31" W.

See Site Location.

Existing improvements Parking lot.

Existing Topography Based on our review of the topographic survey, the subject site slopes down to the southeast. About 7 feet of elevation difference was estimated between the cone penetrometer sounding locations.

Previous Reports

Geotechnical Engineering Report, SD2 Design Report, Terracon Project No.

05105105, report dated August 9, 2011.

Supplement to Geotechnical Engineering Report, SD2 Design Report, Terracon Project No. 05105105, report dated March 2, 2012.

Project Description

Item Description

Proposed Structure The project includes construction of a three-level parking structure, approximately 325 feet x 125 feet in plan dimension. The parking structure will be designed for vertical expansion to six levels.

Construction Type Concrete pre-cast construction with poured in place foundations.

Maximum loads Columns: 1300 kips Interior Shear Wall Gravity Load: 25 kips per linear foot maximum Slabs: 150 pounds per square foot maximum

Grading/slopes

Two at-grade vehicle entries are planned, one at each end of the parking garage. The east side entry will be about 8 feet lower than the west entry. A portion of the deck on the west end will be below grade by about 5 to 6 feet.

Slopes of 3H:1V(Horizontal:Vertical) or flatter are expected.

Below Grade Structures

Portion of the existing garage at the west end will be about 5 to 6 feet below grade.

Free-Standing Retaining Walls Assumed wall at the west end lower level of the garage.

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EXPLORATION AND TESTING PROCEDURES

The cone sounding locations were laid out by the Terracon drill crew relative to the existing features.

The approximate cone sounding locations are shown on the Exploration Plan. The GPS coordinates included on the cone sounding data plots are approximate and were obtained with a handheld GPS unit with an anticipated accuracy of about +/- 20 feet. Ground surface elevations at the cone sounding locations were interpolated from the topographic survey provided by the client.

The locations and elevations of the cone soundings should be considered accurate only to the degree implied by the means and methods used to define them.

We advanced the six cone soundings with a truck-mounted cone rig using a piezometric electronic cone penetrometer (CPTU). This device includes a cone-tipped sounding unit attached to steel rods with flush joint couplings. The sounding unit has electronic strain gauges that measure point resistance and sleeve friction, a transducer that measures pore water pressure and an inclinometer that measures verticality of the sounding unit. The readings from the cone instruments are transmitted acoustically through the rods to a computer at the surface that stores the data and provides real-time display of the cone results. A depth encoder device monitors penetration depth and speed as the rods are pushed slowly into the ground. The cone unit records the measured values at 2-cm intervals. No soil samples are gathered through this subsurface investigation technique.

CPTU testing is conducted in general accordance with ASTM D5778 "Standard Test Method for Performing Electronic Friction Cone and Piezocone Penetration Testing of Soils.

The resistance to penetration can be correlated with soil strength and density properties, and soil types can be estimated. The CPTU sounding provides detailed information on stratigraphy and a measure of the in situ soil properties for foundation evaluations. It should be noted that the soil types included on the data plots are interpretations based on empirical correlation and should be evaluated accordingly.

GEOTECHNICAL CHARACTERIZATION

Typical Profile

Subsurface conditions from 2010 borings (B-3, B-13, B-15, B-16, and B-17) can be generalized as follows:

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Description Approximate Depth to Bottom of Stratum Material Consistency/ Density

Surface N / A n Pavement: Borings B- 13, B-15, B-16, n Vegetation, root zone:

remaining borings:

N / A

Stratum 1 (Fill)

Encountered in B-3 and B-15.

To depths of about 2 to 9 feet.

Lean Clay: Borings B-3, B-

15. N / A

Stratum 2 (Peorian Loess)

Encountered in all borings.

To depths of about 33 to 48 ft in Borings B-2, B-3, B-13, B-15, B-16, and B-17.

Lean Clay, often dark brown or brown near the surface and becoming light brown and light grayish brown with increasing depth; lower several feet is reddish brown in most borings.

Generally Very Stiff to Stiff

Becoming Medium Stiff to Soft with increasing depth in Borings B-3 B-15, and B-17.

Stratum 3 (Loveland Loess)

Encountered in Borings B-2, B-3, B-13, B-15, and B-16.

To termination depths of Borings B-2, B-3, B-15, B- 16, and B-17.

To depths of about 118 feet in Borings B-13 and B-17.

Lean Clay, generally light reddish brown.

n Upper portion is higher plasticity (sometimes Lean to Fat Clay) in Boring B-17.

Generally Stiff to Medium Stiff.

Soft layers in Boring B-17.

Upper few feet are Very

Stiff in Borings B-13.

Lower several feet are

Very Stiff in Borings B-3.

Stratum 4

Encountered in Borings B-13 and B-17.

To termination depths of Borings B-13 and B-17.

Fat Clay, generally gray to grayish brown to reddish brown.

Very Stiff.

The recently-completed electronic cone penetrometer soundings indicated soil stratigraphy similar to that described above in soil borings from 2010 report. Our interpretation of the soundings indicates a surface layer of dry clay that extends to depths of about 5 feet. It is our opinion that this surface layer is probably clay as described in the borings above, but the dry nature of the clay causes its behavior type as interpreted using the cone data to manifest as a granular material (silt or sand mixture). The cone soundings extended to depths of about 120 to 121 feet below existing grade and terminated in cohesive material. Conditions encountered at each cone sounding location are indicated on the individual plots attached to this report.

Variations can occur between boring and cone sounding locations, and across the site. Construction associated with previous grading, construction, and other items may have created additional variations.

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Groundwater Conditions

We used a groundwater depth of about 35 feet for the cone interpretations based on the groundwater levels from the piezometers installed at this site during the 2010 subsurface exploration.

GEOTECHNICAL OVERVIEW

Foundation Support Discussion

The soil borings encountered variable thicknesses of existing fill underlain by native clay which extended to the depths explored. Terracon is not familiar with compaction specifications associated with the areal fill represented in the borings, and we have not been provided any reports of observations or density tests performed during fill placement. Any such records would aid our evaluation of the existing fill. Our lab tests and observations indicate the fill soils to be relatively well compacted; however, localized overexcavation and replacement of poorly compacted or unstable soils may be required. Complete removal is necessary to remove risks associated with the fill. With careful site preparation and observations, it appears feasible to leave most of the fill in-place underneath the slabs and pavements with a low level of risk.

We recommend the heavy loads of the parking garage be supported on a deep foundation system.

From our experience and evaluations, it appears auger-cast-in-place (ACIP) piles may be more efficient and economical than drilled shafts or driven piles. However, ACIP pile lengths for some of the structures will be longer than usual. We recommend the ACIP piles extend to the very stiff to hard clays. Additional discussion and recommendations are provided in subsection Deep Foundations.

Wet, Low-Strength Subgrades

The boring information indicates relatively wet clay soils are present close below the surface of Boring B-3. Similarly, relatively wet clay soils are anticipated close below the parking garage lower-level slab.

These soils will be unstable under construction equipment and fill placement. Care should be taken during construction to avoiding disturbing these soils. In some areas, it may be sufficient to limit construction activity to light equipment. In other areas, it will be necessary to chemically stabilize and/or undercut and place granular fill; a geogrid may also be appropriate below the granular fill. We recommend consideration be given to designating haul roads at the onset of construction, and then surfacing these roads with crushed stone, to serve as a durable layer for construction equipment and reduce weather related delays to construction.

Additional discussion and recommendations are provided in subsection Site Preparation.

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SITE PREPARATION

Stripping and Subgrade Preparation

Any areas of standing water should be drained well in advance of construction. Any surface muck or silt, or soils softened by standing water, should be removed.

In preparing the site for construction, we recommend all deleterious materials such as paving, vegetation, root zone, organic topsoil, and soft, frozen or otherwise unsuitable materials be stripped from within the proposed construction, building, pavement, and areas of cut or to receive fill. An average stripping depth of 9 inches is recommended to remove vegetation and root zone for bidding purposes. Actual stripping depths will vary, and should be evaluated by a Terracon representative during construction.

Tree and shrub root systems should be thoroughly removed from the construction areas, and removed to at least 3 feet below exterior pavement subgrade level. This applies both to trees currently on the site and to trees removed in the past several years. An effort should be made to locate records, plats or photographs indicating the past location of trees or other large vegetation.

In addition, some of the natural soils may have been desiccated by the tree roots. Any soils desiccated by trees or shrub roots should be removed and replaced with approved fill.

Utility lines should be re-routed outside of the parking garage area. It is our experience that poorly compacted backfill is commonly found in utility line trenches; existing backfill should be reworked and recompacted.

It is our experience that a saturated zone often develops immediately below existing pavements.

The saturated zone forms when surface water infiltrates through cracks in the paving, and then is prevented from draining or evaporating by the paving. It is our experience that this saturated zone typically is not more than about 6 inches thick, but it may be necessary to scarify, dry, and recompact this layer where encountered.

We recommend a drainage system be installed below the lower-level slab. Details concerning the drainage system are presented in subsection Sub-Slab Drainage System. We recommend the drainage system and granular drainage fill be installed only immediately prior to placing slab concrete.

The soils below design subgrade elevation are composed of native lean clay soils. We recommend 12 inches of low-plasticity cohesive fill be provided below the granular drainage fill.

Similarly, we recommend entrance drives and associated pavements be supported on at least 12 inches of low-plasticity cohesive fill, but a granular drainage layer is not required below entrance drives and associated pavements. We recommend the soils either:

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Responsive Resourceful Reliable 7 05175212r01.docx n be undercut to allow development of the full 12-inch thickness, or n the soils be undercut to 6 inches below top of subgrade and a scarification and recompaction process be implemented to form the lower 6 inches of the 12-inch thickness in-place.

Proofrolling of existing fill is recommended. Proofrolling aids in providing a firm base for compaction of fill and delineating soft or disturbed areas that may exist below subgrade level. Unsuitable areas observed at this time should be improved by scarification and recompaction or by undercutting and replacement with structural fill. Proofrolling may be accomplished with a third- to half-loaded, tandem-axle, dump truck with a gross weight of 15 tons or other equipment providing an equivalent subgrade loading. After removing any unsuitable materials and stabilizing the weak subgrades, the site should be filled to design grades with structural fill as recommend in this report.

Scarification and recompaction is recommended in some areas. When recommended, scarification should be performed to a depth of about 8 inches, and the scarified soil then moisture-adjusted and recompacted as recommended in Structural Fill Compaction Requirements. Scarified soil which cannot be recompacted to the recommended degree should be undercut and replaced with stable fill.

Slippage can occur if fill is placed on slopes steeper than about 5 horizontal to 1 vertical (5H:1V).

Therefore, we recommend that slopes steeper than about 5H:1V be flattened or benched prior to placing fill. We recommend this process consist of removing vegetation and sod, and then forming benches or horizontal steps wide enough to accommodate construction equipment, and separated by vertical risers less than 2 feet high.

Terracon should be retained to monitor stripping, subgrade stability, foundation and existing fill removal, utility abandonment, site excavation, removal of unsuitable materials, and proofrolling.

Terracon can assist in identifying unstable existing fill or low-strength native soils that should be undercut and removed, as well as identifying additional corrective measures for conditions that may become apparent during construction.

Sub-Slab Drainage System

We recommend a subslab drainage system be installed below the parking garage slab. The subslab drainage system should include drainage pipe installed in trenches and a granular drainage layer. All drainage pipe should be provided with cleanouts.

The drainage pipes should consist of 3 or 4-inch diameter schedule 40 PVC pipes sloped, or laid level if needed in isolated areas, to provide positive drainage to sump pits and pumps or other suitable outlets. The drainage pipe slots or perforations should be sized to prevent infiltration of the drainage fill. The drainage pipes should be installed around the edge of the slab and at center-to-center spacing of approximately 30 feet under the parking garage slab.

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The drainage pipes should be laid in 12-inch wide trenches extending at least 12 inches below the bottom of the granular base layer (into the clay subgrade). A non-woven geotextile such as Contech C60NW, or equivalent, should be used to line the bottom and sides of the trenches, and the geotextile should extend onto the subgrade at least 3 feet away from the trenches. A 2-inch layer of granular drainage fill material should be placed over the fabric in the bottom of the trench, then the pipes should be laid on the granular layer before backfilling the remainder of the trench with drainage fill.

We recommend an aggregate base composed of 6 inches of crushed stone be provided immediately below the parking garage slabs, in turn underlain by at least 12 inches of granular drainage fill. If it is necessary to protect the garage slab from frost heave, the thickness of granular drainage fill should be increased to 24 inches.

The drainage fill and aggregate base materials should meet the recommendations of Structural Fill Composition Requirements, and should be placed and compacted in accordance with Structural Fill Compaction Requirements.

We recommend the subslab drainage system be installed only immediately prior to slab concrete placement. We do not recommend using the granular drainage fill as a durable layer during construction. For example, the granular fill would become fouled by dirt and cuttings during construction and installation of the foundation system. In addition, there would be a risk of crushing of the pipes.

If a durable layer of crushed stone or crushed concrete is installed below the granular drainage fill, then the subdrains should extend down to the base of the durable layer.

Terracon can provide further recommendations and review of the drainage systems as design progresses.

Structural Fill Composition Requirements

We recommend structural fill meet the following material composition requirements:

Fill Type 1 USCS Classification Acceptable Location for Placement Low Plasticity

Cohesive

CL

(LL<45 and 10<PI<20) 2 All locations and elevations.

Moderate Plasticity Cohesive 8

CL

(LL<45 and 10<PI<25) 2

Landscaped areas, and more than 2 feet below subgrade level of exterior pavements.

Cohesive “cap” CL (LL<50 and 10<PI<25) 2

Clay or topsoil used behind curbs as a cap over drainage systems in landscaped areas, to promote vegetative growth, to promote drainage of surface water, and to help prevent infiltration of surface water.

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Fill Type 1 USCS Classification Acceptable Location for Placement

Aggregate base 5 SP, SW, GP, GW As a leveling course and capillary break immediately beneath grade-supported floor slabs. Placed only immediately prior to concrete placement. Imported.

“Bridge Lift” granular materials 4 GP, GW

As the initial lift of fill on soft and wet clay subgrade soils, and where the subgrade soils will not provide suitable support for construction equipment or placement and compaction of overlying fill. Imported.

“Durable Layer” 6 GP, GW As the upper layer of fill in areas subjected to construction traffic, and for use with haul roads.

Imported.

Free-Draining Granular Fill 7 SP, SW, GP, GW Free-draining retaining wall and subslab drainage system backfill. Imported.

On-Site Soils 3 Varies Suitable for use as fill if meeting the criteria of “Low Plasticity Cohesive,” “Moderate Plasticity Cohesive,” or “Cohesive Cap”.

1. Controlled, compacted fill should consist of approved materials that are free of organic matter, debris, and particles larger than 3 inches in maximum dimension. 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.

2. LL = Liquid Limit, PI = Plasticity Index.

3. Sorting of on-site soils containing debris, organics, etc., will be necessary. Delineation of unsuitable on-site soils should be performed in the field by a Terracon representative. Moisture conditioning will be required for the on-site soils.

4. Well-graded, crushed stone or crushed concrete, containing 100 percent passing the 3-inch sieve and less than 10 percent fines. Crushed stone or crushed concrete. Terracon can review proposed materials.

5. A well graded crushed stone, with 100 percent passing the 1-inch sieve, less than 6 percent passing the No. 200 sieve, and less than about 40 percent passing the No. 40 sieve. Crushed stone is recommended for improved stability and durability during construction; however, not directly adjacent to a vapor barrier. Using a material similar to NDOR Crushed Rock for Base Course, with 6% or less fines (material passing the #200 sieve) for this layer will improve subgrade stability during compaction and slab construction. Terracon can review proposed materials.

6. Well-graded crushed stone, with a maximum particle size of about 2 inches and less than about 6 percent fines. A material similar to NDOR Crushed Rock for Base Course can be considered for this layer. Crushed concrete can be used but is subject to degradation under repetitive traffic loads, and so should be used with caution. Terracon can review proposed materials.

7. Well-graded, free-draining granular material used as drainage backfill adjacent to below-grade walls and in the granular drainage layer below the parking garage and tunnel slabs. A general gradation should be 100% passing the 1½-inch sieve, about 60 percent passing the No. 10 sieve, and less than 6 percent fines. A material similar to NDOR 47B Fine Aggregate for Concrete can be considered for this layer. Terracon can review proposed materials.

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Fill Type 1 USCS Classification Acceptable Location for Placement

8. Fill meeting a PI of 10 to 20 is preferred. However, based on the Atterberg limits test results, some of the on-site soils have a PI in the range of 20 to 25. We would prefer this material be used for fill in landscaped areas. Utilizing lean clay soils with a liquid limit of less than 45 percent and a plasticity index between 20 and 25 percent can be considered more than 2 feet below exterior pavements, although this will somewhat increase the risk of shrink-swell movement due to the fill soils. Terracon can review proposed materials.

We should be retained to evaluate and perform laboratory tests on proposed fill materials, to evaluate compliance with the project specifications. We can also review laboratory tests of proposed fill soils provided by suppliers and contractors.

Structural Fill Compaction Requirements

Item Description

Fill Lift Thickness 5 8 inches or less in loose thickness Compaction Requirements 1,3

Upper 8 inches of pavement subgrade 4

All other locations

98% of the material’s standard Proctor maximum dry density (ASTM D 698).

95% of the material’s maximum standard Proctor dry density (ASTM D 698)

Moisture Content Cohesive Soil Within the range of -2 to +3 percent of the optimum moisture content value as determined by the standard Proctor test at the time of placement and compaction.

Moisture Content Granular Material 2 Workable moisture levels.

1. We recommend engineered fill be tested for moisture content and compaction during placement.

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.

2. Moisture levels should be maintained low enough to allow for satisfactory compaction to be achieved without the cohesionless fill material pumping when proofrolled or containing excess water (ponding).

3. A coarse granular layer used as a bridge lift should not be overcompacted, which can cause subgrade disturbance and loss of strength of the underlying subgrade. In these areas, we recommend the compaction be accomplished with 2 or 3 mutually perpendicular passes of each thin lift with light-weight vibratory compaction equipment. Instead of a strict compaction requirement, consideration should be given to using visual evaluation of material stability using factors such as surface stability and aggregate interlock when evaluating compaction and performance of the granular material.

4. Consideration can be given to compacting all fill below pavements to 95% during mass grading.

Immediately prior to paving, we recommend the subgrade below exterior pavements be rough-graded as needed, and then scarified and recompacted. We recommend this process include

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Item Description scarifying the subgrade to a depth of about 8 inches, moisture conditioning the scarified soil to within -2 to +3 percent of the material’s optimum, and compacting the scarified soil to at least 98%.

Scarified soils which cannot be recompacted to this degree should be undercut and replaced with stable material.

5. Reduced lift thicknesses are recommended in confined areas (e.g., utility trenches, pile cap and grade beam excavations, foundation and retaining wall backfill) and when hand-operated compaction equipment is used.

We should be retained to monitor fill placement, and to perform field density tests as each lift of fill is place in order to evaluate compliance with the design requirements. We should be retained to evaluate slab and pavement subgrades immediately prior to paving.

Construction Considerations and Drainage

Samples of the native soils have high moisture contents and will be easily disturbed by construction activity. Disturbed soils lose a significant portion of their strength, so we recommend protecting the soils from disturbance during the construction process. Disturbance can come from construction activity and also from allowing water to accumulate and soak into the subgrade. Care should be taken to prevent wetting and disturbance of the soils by grading the site to drain, limiting the stripping and removal to the amount necessary, placing a granular layer, and limiting construction traffic. The use of remote equipment is recommended for excavations into wet clay, and proofrolling is not recommended on wet clays.

Weather conditions (e.g., freeze-thaw cycles, standing water, saturation, and desiccation) can disturb the subgrade. Any soils which become saturated, frozen or desiccated during the grading process should be scarified and recompacted, or removed and replaced.

Construction activity should be monitored, and should be curtailed if the construction activity is causing subgrade disturbance. A Terracon representative can help with monitoring and developing recommendations to avoid subgrade disturbance.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of overlying slabs and pavements. Construction traffic on the subgrade should be avoided, or a designated haul road should be constructed. If the subgrade should become frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to slab construction.

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Landscaping and Finish Grading

Poor site drainage and ponding of surface water can result in water accumulating below slabs and pavements and/or increase the moisture content of the subgrade below slabs and pavements.

Excessive moisture increases the risk of frost heave, can reduce the soil's bearing capacity, and thus contribute to slab and pavement settlement and cracking.

Finished grading slopes should promote drainage away from the parking garage and pavements.

We recommend final grades for seeded and landscaped areas be sloped at least 5 percent within 10 feet around the parking garage to direct surface water well away from the parking garage. We recommend cohesive backfill be placed in utility trenches and adjacent to foundations and curbs, and this fill be compacted to at least 95 percent of standard Proctor maximum dry density to help prevent surface water infiltration. Roof drains should be extended to discharge on pavements or in lawn areas more than 5 feet from the parking garage. Pavements or sidewalks installed adjacent to the parking garage should slope away from the parking garage at a grade of 2% or more.

Overwatering of grass or landscaping vegetation is a significant source of water, and should be avoided near the buildings and pavements. Sprinkler heads should be adjusted to miss the exterior building walls and pavements. Automated watering systems should be programmed to not run after natural rain events, and to not overwater. Any utility leaks should be promptly repaired. Lining the bottom of irrigated planter areas along the buildings with an impermeable moisture barrier, and installing tile lines leading to gravity outlets or sump pits and pumps, would also help to control surface water that infiltrates into these features.

Permanent Slopes

The slopes are expected to be formed in native loess, or composed of compacted fill derived from loess. Seasonal seepage can occur from natural loess soils, and after periods of heavy or prolonged rainfall. The seepage could cause minor, long-term maintenance concerns with the slope, such as erosion and localized slumps or soft areas. These surface developments typically do not jeopardize the deep seated stability of the slope, but could mar the surface of the slope and, if allowed to progress, could eventually affect the property behind the top of the cut slope.

The clay soils at this site have a high silt content. As a result, slopes exposing or formed of this material are highly susceptible to surface erosion, sediment transport and sloughing, and will be difficult to maintain. Surface runoff should be diverted away from the slopes. Erosion protection will be required. If a vegetative cover is planned, temporary erosion protection may be required until the vegetation can be established.

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DEEP FOUNDATIONS

Discussion

It is our recommendation that the proposed parking garage be supported on a deep foundation system. The borings and cone soundings encountered a firm bearing stratum (very stiff fat clay and/or glacial till) at elevations ranging from about 1088 to 1132 ft. A deep foundation element extending into the firm bearing stratum will derive capacity primarily from skin friction, unless the deep foundation element extends a great distance into the glacial till. We expect deep foundation elements which obtain most of their capacity through skin friction will be more economical than elements which rely on significant tip capacity. Deep foundation systems which are long and slender are more conducive to obtaining capacity primarily through skin friction.

Deep Foundation Alternatives

It is our opinion that several types of deep foundation systems could be considered for this project, including:

n Straight-sided drilled shafts n Driven steel piles (“H” piles or pipe piles) n Auger-cast-in-place (ACIP) piles

Risks and benefits are associated with each of these alternatives. Some considerations for the selection of a deep foundation system include economic and schedule factors, the soil stratigraphy and strata support capabilities, handling and potential off-site disposal of cuttings/spoils, and noise impacts to the hospital and nearby businesses and residences.

Driven piles will generate minimal spoils compared to drilled shafts and ACIP piles. However, driven piles will have greater vibration and noise impacts to the hospital and nearby businesses and residences. In addition, driven pile capacities would be optimized if driven to refusal in a high-end-bearing stratum (such as limestone), allowing the full axial compressive structural capacity to be used; a high-end-bearing stratum was not encountered in our borings. Welding of the piles will be required to achieve the installed lengths required. Driven piles, especially high-displacement piles such as closed-end pipe piles, present a risk of lateral soil displacement and heave of the ground surface. Driven piles are not expected to be economically favorable when compared with ACIP piles.

Drilled shafts will generate significant spoils. We anticipate slurry will be required to install shafts, which is an additional disposal item. Drilled shafts will not have vibration impacts, but will have noise impacts to the hospital and nearby businesses and residences. The noise impacts are similar between drilled shafts and ACIP piles. Similar to driven piles, drilled shaft capacities would be optimized if extended to bear in a high-end-bearing stratum (such as limestone), allowing

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ACIP piles will generate significant spoils, similar to drilled shafts. ACIP piles will not have vibration impacts, but will have noise impacts to the hospital and nearby businesses and residences. The noise impacts are similar between drilled shafts and ACIP piles. ACIP piles are well-suited when extended into a very stiff clay bearing layer, such as glacial till, since sufficient embedment can be provided to generate full end bearing. End bearing cannot be relied upon when ACIP piles encounter practical auger refusal on the surface of a high-end-bearing stratum (such as limestone).

For this project, it is our opinion ACIP piles will be more efficient and economical than drilled shafts or driven piles. However, ACIP piles extending into the glacial till will be longer than usual.

We understand 16-inch ACIP piles require a jump in crane and rig size when extending more than about 95 feet below the pile cap (more than about 100 feet in total drill length). Even if ACIP pile lengths of 100 to 110 feet are required to meet settlement criteria, we anticipate ACIP piles will be more appropriate and economical than drilled shafts or driven piles for this project.

For this reason, this report presents discussions and recommendations for ACIP piles and spread footing foundations. We would be pleased to participate in discussions if other foundation types are considered.

ACIP Piles Axial Design

Four test piles were installed and load tested as part of 2010 project. Two test piles were located along the north side of the proposed parking garage.

Our 2010 report recommended an allowable compressive axial capacity of 150 kips for a single, 16-inch diameter ACIP pile extending between elevations of 1210 ft and 1120 ft.

We understand the maximum column loads of 1,300 kips (strength and sustained) were reported by Nagel Architects and Engineers for the parking garage. We recommended ACIP piles bear at least 5 feet into the firm bearing stratum, encountered at elevations of about 1088 ft in Boring B-17 and 1101 ft in Boring B-13, in order to limit settlements to about 1 inch or less.

Based on the pile load test results, we recommend allowable compressive axial capacities of ACIP piles be calculated using the following values:

Elevation (feet)

Allowable Compressive End Bearing Capacity (psf) 2, 3

Allowable Unit Skin Friction in Compression (psf) 1, 4, 5

Above 1185 --- 550

1185 - 1166 --- 350

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1166 - 1120 --- 550 1088 in B-17

1120 - ---------------------- 1101 in B-13

8,000 650

1088 in B-17 below ---------------------- 1101 in B-13

12,000 900

1. Side resistance should be neglected within 42 inches of final grade due to frost effects.

2. Allowable end bearing includes a safety factor of between 2 and 3.

3. Use of end bearing requires at least 5 feet of penetration into the indicated soil layer.

4. Allowable unit skin friction includes a safety factor of about 2.

5. Allowable unit skin friction in uplift can be obtained by multiplying the compressive skin friction within the reinforced length of the pile by ; total uplift resistance includes the frictional resistance plus the effective weight of the concrete used in the foundation elements, pile caps, and grade beams.

Based on the above values, we calculate the following allowable axial compressive capacities (rounded down to the nearest 5 kips):

Pile Information Allowable Axial Compressive Capacity, kips

16-inch diameter ACIP pile, bearing elevations from 1210 ft to 1083 ft (near B-17) 310

16-inch diameter ACIP pile, bearing elevations from 1210 ft to 1096 ft (near B-13) 275

General ACIP Pile Design Considerations

Probe piles are also recommended within particular structure areas when the pile capacity and/or settlement criteria are contingent on the piles extending to / into the firm bearing stratum. A Terracon engineer can provide additional input on the probe pile locations during design development.

Frost action beneath pile caps and grade beams can cause uplift loads on the piles. To avoid uplift loads, the base of the pile caps and grade beams should extend a minimum of 3½ feet below the lowest adjacent grade.

Design of the piling as structural members should be in accordance with applicable building codes.

When designing to resist uplift loading, of the allowable compressive load capacity can be used along with the effective weight of the foundation. Tensile load resistance of ACIP piles should be neglected unless the piles are adequately reinforced. At a minimum, a single centered #9 reinforcing bar should be installed for the upper 60 feet of each ACIP pile; for a pile resisting uplift

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A bar which cannot be installed full length should be pulled and the pile re-drilled.

Lateral Design

The structures will be required to resist lateral loads generated by wind, lateral earth pressures, product storage, and seismic events as prescribed by the International Building Code (IBC). The design guidelines presented in subsection Cantilever Retaining Walls are recommended for pile caps and grade beams. If needed, additional lateral resistance can also be provided by deepening the pile caps or grade beams. Please note the portion of grade beams and pile caps subject to frost should be neglected when evaluating lateral resistance. When the grade beams and pile caps are not subject to frost, then the lateral resistance can be evaluated started at 2 feet below the adjacent floor slab.

When considering the lateral resistance of pile elements, the passive resistance values listed in subsection Cantilever Retaining Walls, applied to the projected width of the pile elements, can be used for a conservative initial estimate. It is our experience a more favorable design is usually achieved by using a computer modeling program (e.g., L-Pile, Group). Parameters for lateral load resistance calculations will vary from structure to structure, and with varying floor levels and pile cap depths. We can provide parameters for specific locations when details concerning pile caps and pile bearing elevations are determined.

Terracon can provide additional lateral and moment load analysis for individual piles and pile groups once detailed foundation design information becomes available. It is our experience significant lateral load can be supported by ACIP piles, especially if the pile tops are fixed from rotation. We can provide further input on lateral evaluations when the system details and loading conditions are known.

The allowable passive resistance applies to the projected diameter of the shaft and requires some movement to mobilize resistance. Group action for lateral resistance of shafts should be taken into account when spacing is less than 8 diameters (center to center). For a group of shafts oriented parallel to a lateral load, design parameters for allowable passive resistance should be reduced in accordance with the following table.

Group Reduction Factors – Laterally Loaded ACIP Piles

Shaft Spacing (Diameters)

Reduction Factors Leading Row Second Row Third Row and Higher

8D 1.0 1.0 1.0 5D 0.9 0.85 0.7 3D 0.8 0.6 0.4

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Design of the piles as structural members should be in accordance with applicable building codes.

Lateral load resistance of piles should be neglected unless the shafts are adequately reinforced.

Reinforcement should include centering devices to assure the steel has adequate concrete cover, and it should slide readily into place under its own weight using gravity. Reinforcement which does not slide into place in this manner should be pulled and the pile re-drilled. Installation of a pile cage may be required within the upper portion of a pile in order to help resist lateral loads.

Since installing a long reinforcing cage can be problematic, it may be appropriate to design the foundation elements with deeper pile caps or grade beams or utilize other means of lateral support where high lateral loads occur.

ACIP Pile Installation

The successful completion of ACIP piles depends to a large extent on the equipment and installation procedures. ACIP piles are constructed by extending continuous hollow-stemmed augers to a predetermined depth. A fluid cement grout is then injected under pressure through the center of the hollow shaft as the augers are withdrawn, leaving a continuous concrete pile.

We recommend the bid documents require the contractor to show experience with similar or greater ACIP pile installation depths than the depths expected for this project.

Care should be taken during the ACIP pile element installation because of the potential for both “necking” and “overdrilling” during the installation procedure. The soft clay soils in the borings are susceptible to loosening upon overdrilling, and can also cause necking if the auger withdrawal procedure is rushed. Controlled withdrawal of the auger will be necessary and a sufficient head of grout should be maintained in the auger system at all times to prevent necking down of the fluid grout due to hydrostatic pressures (for example: a minimum overpump of 120 percent, a grout head of 7 feet, or as achieved in the test piles). The quantity of the concrete grout placed in each element should be checked against the calculated volume required to obtain design pile dimensions; a minimum overpump of 115% or as achieved in the test pile is recommended. It is recommended that Terracon review and comment on specifications developed for pile installation, and monitor actual pile installation on a full-time basis.

If a pile encounters refusal on apparent rubble within existing fill, we recommend the rubble be removed and replaced with compacted fill. Although cobbles and boulders were not encountered in the soil borings, such erratics are possible and can create difficult drilling conditions when the ACIP piles extend into glacial till. Should a specific element encounter refusal above design tip elevation, Terracon should be consulted to help evaluate pile capacity and condition.

Installing adjacent ACIP piles with clear distance spacing of less than 15 feet should be delayed until mortar in the initial pile has set. This is recommended to avoid possible grout intrusion between the piles which could jeopardize the integrity of both piles. If two piles are separated by

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SEISMIC CONSIDERATIONS

Seismic Site Classification

For the 2010 exploration, Terracon used a seismic refraction system (SRS) consisting of a seismograph and 24 geophones to perform a site-specific seismic class survey along 5 specific lines. One of the survey line was located just north of the proposed parking garage. A linear array of 24 geophones was placed in accessible areas as illustrated in the attached diagram. A computer was used to record refraction microtremors produced by ambient seismic noise. The data was then processed using a wavefield-transformation data-processing technique and an interactive Rayleigh-wave dispersion-modeling tool. The refraction microtremor method exploits aspects of spectral analysis of surface waves (SASW) and multi-channel analysis of surface waves (MASW) to derive a shear wave profile and an average shear-wave velocity along the array for a corresponding depth of about 100 feet.

The average shear-wave velocity analysis and recommendations presented in this report are based upon the data obtained from the seismic refraction systems performed at the indicated locations and on the indicated date. This analysis does not reflect variations that may occur between test locations or across the site, or variations that may occur throughout the year, such as groundwater fluctuations. The refraction microtremor method is an approximate method, and one of many methods that can be used to determine shear-wave velocities. There are other costlier methods that can be used to further increase the accuracy of the seismic site classification and shear-wave profile.

The on-site Vs tests indicate the upper 100 feet of the profile have average values that range from 750 to 930 feet/sec. Therefore, the Site Class is D in accordance with Section 1613.5.2 of the

2009 IBC.

Site-Specific Spectrum Analysis

For our 2010 report, we performed a site-specific spectrum analysis using the 2009 International Building Code (2009 IBC), which allows two procedures for determining design ground motions:

1. General Procedure Response Spectrum. In this method, the design response spectrum is determined using the following steps: (1) Develop the Maximum Considered Earthquake (MCE) spectrum using mapped (2002 USGS) values of spectral acceleration at periods of

0.2 and 1.0 seconds, (2) Determine the Site Class using shear wave velocity (Vs) measurements from the upper 100 feet of the soil profile, (3) Adjust the MCE spectrum for site class, and (4) Develop the Design Response Spectrum (DRS) by scaling the adjusted MCE spectrum by -rds.

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2. Site-Specific Procedure Response Spectrum per ASCE 7-05.