Geotechnical Report Terracon no 05215161R01.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

VA Hospital Campus - Chiller Building

Omaha, Nebraska

July 27, 2021

Terracon Project No. 05215161

Prepared for:

HFS Company

San Antonio, TX

Prepared by:

Terracon Consultants, Inc.

Omaha, NE

Terracon Consultants, Inc . 15080 A Circle Omaha, Nebraska 68144

P (402) 330 2202 F (402) 330 7606 terracon.com

REPORT C OVER LETTER TO SIGN

July 27, 2021

HFS Company

8718 Botts Street

San Antonio, TX 78217

Attn: Mr. Nick Andrews

P: (210) 881 9714

E: Nick@hfscompany.com

Re: Geotechnical Engineering Report

VA Hospital Campus - Chiller Building

SEC, 4200 Woolworth Avenue

Omaha, Nebraska

Terracon Project No. 05215161

Dear Mr. Andrews:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. P05215161 dated July

7, 2021. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations, floor slabs, and pavements for the proposed VA Hospital Campus - Chiller Building project.

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

Sincerely, Terracon Consultants, Inc.

Sajjad Satvati, Ph.D., E.I. Michael D. Ringler, P.E.

Senior Staff Engineer Senior Engineer

Distribution: Addressee (pdf)

Martin, Nancy L.

Typewriter for

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

DEEP FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

LATERAL EARTH PRESSURES AND DRAINAGE

PAVEMENTS

FROST CONSIDERATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the

GeoReport logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

SITE LOCATION PLAN

INFORMATION FROM REPORT 05105105

http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

VA Hospital Campus - Chiller Building

SEC, 4200 Woolworth Avenue

Omaha, Nebraska Terracon Project No. 05215161

July 27, 2021

INTRODUCTION

This report presents the results of our geotechnical engineering services performed for the proposed VA Hospital Campus – Chiller Building in the SEC, 4200 Woolworth Avenue in Omaha, Nebraska. We used a boring log performed for a previous project at the site to develop the recommendations for this report. Maps showing the site and boring location are shown on Site

Location and Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained during the field exploration are included on the boring logs in Exploration

Results.

Our work was completed in general accordance with Terracon proposal-agreement no. P05215161 dated July 7, 2021.

The purposes of this report are to provide information and geotechnical engineering recommendations relative to:

■ Soil conditions ■ Seismic site classification per IBC

■ Groundwater conditions ■ Lateral earth pressures

■ Site preparation and earthwork ■ Pavement design and construction

■ Foundation design and construction ■ Frost considerations

■ Floor slab design and construction

VA Hospital Campus - Chiller Building ■ Omaha, Nebraska

July 27, 2021 ■ Terracon Project No. 05215161

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SITE CONDITIONS

Item Description

Parcel Information

The project is located at the Veteran’s Administration (VA) Hospital Campus at the SEC, 4200 Woolworth Avenue in Omaha, Nebraska.

Approx. Latitude/Longitude: 41.2433° N, 95.9716° W.

See Site Location

Existing

Improvements /

Current Ground

Cover

The new chiller building is planned along the east edge of VA Hospital

Campus, north of XBUILDING2 and south of the fuel tanks. The existing

XBUILDING2 and fuel tanks are reportedly supported on spread footing foundations. The existing XBUILDING2 has a basement level with elevation

1186.03 feet and three above-grade levels.

An existing single-story building is within the footprint of the proposed chiller building and will be removed; otherwise, the ground surface within the new building area is surfaced with concrete paving.

An existing 5-foot concrete retaining wall is east of the building footprint (east side low), and trees are located east of the retaining wall.

An existing foundation reportedly exists in the southeast portion of the new building and is expected to be removed.

Existing Topography

Based on the Civil Survey map, developed by HFS, dated June 29, 2021, the building area is relatively flat, and the existing elevation is about 1,197 feet.

The western edge of the site has an upward slope west from the new building.

Previous Reports

Geotechnical Engineering Report, SD2 Submittal Report, Veterans

Administration Hospital, Terracon Project No. 05105105, report dated August

9, 2011. We used our existing information for Boring B-8 from this report to evaluate site conditions and provide recommendations for the Chiller

Building.

Geotechnical Engineering Report, V.A. Ambulatory Clinic, Terracon Project

No. 05175126, report dated September 14, 2017.

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PROJECT DESCRIPTION

Item Description

Information Provided

Civil plans, developed by HFS, dated June 29, 2021.

Building sections, developed by HFS, dated June 29, 2021.

Pier and framing plans, developed by HFA, dated July 1, 2021.

Project Description

Two-story, slab-on-grade building supported on drilled shafts. Two housekeeping pads with 325 psf loads are located in the eastern portion of the building, and two housekeeping pads with 310 psf loads are located in the western portion of the building. The new building will have no basement level.

Finished Floor Elevation 1,196.5 feet.

Maximum Loads

(assumed)

■ Columns: 180 kips

■ Walls: 2 to 3 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

■ XMFR House keeping pads on east: 325 psf

■ WCC House keeping pads on west: 310 psf

Grading/Slopes

According to the site plan CG-110, provided by HFS, dated June 29, 2021, finished floor elevation is expected to be at 1,196.5, MSL.

Less than 1 foot of cut/fill is expected to be required to develop final grade.

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

Free-Standing Retaining

Walls

An approximate 5-foot tall concrete retaining wall exists on east edge of the site and is expected to remain.

Pavements Concrete pavements are expected west/southwest of the building area.

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GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

We have developed a general characterization of the soil and groundwater conditions based upon our review of the boring information, the geologic setting, and our understanding of the project.

This characterization, termed GeoModel, forms the basis for our geotechnical evaluations and recommendations for site preparation and earthwork, foundation options, and pavement options.

Conditions encountered at each exploration point are indicated on the boring log. The boring log can be found in Exploration Results section.

Variations can occur between boring locations and across the site. Previous grading and construction may have created additional variations.

Groundwater Conditions

The borehole was observed while drilling and after completion for the presence and level of groundwater. In addition, delayed water levels were also obtained in some borings. The water levels observed in the boreholes are provided on the boring logs in Exploration Results, and are summarized below.

Boring Number Approximate Depth to Groundwater while Drilling (feet)

Approximate Depth to

Groundwater after Drilling (feet)

B-8 17 16 (after 7 days)

1. Below ground surface

A relatively long period of time is necessary for a groundwater level to develop and stabilize in a borehole. Longer term monitoring in cased holes or piezometers would be required for a more accurate evaluation of the groundwater conditions and seasonal fluctuations.

Groundwater level fluctuations occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the boring was performed. Therefore, groundwater levels during construction or at other times in the life of the structure may vary from than the levels indicated on the boring log. In addition, perched water can occur overlying compacted cohesive fill or over dense clay layers. The possibility of groundwater level fluctuations and development of perched water conditions should be considered when developing the design and construction plans for the project.

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GEOTECHNICAL OVERVIEW

We understand the building will be supported on deep foundation (drilled shaft) system. From our experience and evaluations, it appears drilled shafts are suitable for support of the planned building. Additional discussion and recommendations are provided in Deep Foundations.

Support of the main level slabs on-grade appears feasible. The slabs should be supported on a layer of compacted fill. Any existing fill below the slabs should be reworked and recompacted, or removed and replaced. Additional site preparation recommendations including subgrade improvement and fill placement are provided in Earthwork. Floor Slabs addresses slab-on-grade design of the building. The basement wall of the existing building should be evaluated with respect to any new loads imposed by grade-raise fills or house keeping pad loads, as described in Lateral

Earth Pressures.

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

EARTHWORK

Site Preparation

Stripping of existing pavement, vegetation, organic topsoil, and any other materials unsuitable for re-use as engineered fill should be performed within all cut, fill, building, and pavement areas. A stripping depth of about 6 to 9 inches is expected to be adequate in most areas to remove vegetation and root zone; however, areas requiring deeper stripping may be encountered. We recommend that site stripping and subgrade preparation procedures extend at least 5 feet beyond building walls and 2 feet beyond the edges of proposed pavements when feasible. A Terracon geotechnical representative should help evaluate actual stripping depths at the time of construction.

We understand the existing building footings (both the existing building on the site and the reported previous building) will be razed and we assume utility lines service the existing building. It is our experience that poorly compacted backfill is common adjacent to below-grade foundations and in utility line trenches. Utility lines should be re-routed outside of the new building area. Whether the utility lines are abandoned or not, any poorly compacted backfill above the lines and adjacent to existing foundations should be removed and replaced.

Tree and shrub root systems should be thoroughly removed from the building area, 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.

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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.

The soil boring indicates the native clays are wet and soft. These materials will not hold up well under construction traffic and activity. At a minimum, we recommend 12 inches of granular fill be installed below the floor slab (and any granular base as recommended in Floor Slabs) to help protect the wet clay and provide a working surface, although a greater thickness can be installed to further reduce risks.

We recommend providing at least 9 inches of controlled fill below exterior pavements, and this can be installed by scarifying and moisture-conditioning then recompacting the native clays.

Where granular surfacing is installed in laydown areas, scarification and recompaction is not required if the granular material passes a proofroll prior to paving. In soft areas, we recommend implementing on of the following options:

◼ Undercutting and Replacement with Structural Fill – Unstable subgrade soils can be undercut down to stable material, and replaced with structural fill. This option is typically most effective when the thickness of unstable material is less than 3 feet.

◼ Undercutting and Replacement with Crushed Stone/Aggregate – Unstable subgrade soils can be undercut and replaced with crushed stone, an approved crushed concrete and/or gravel. If the depth of instability extends more than 2 feet below grade, placement of geogrid reinforcement would help limit the undercut depth. Geotextile or geogrid should ideally be installed after underground work, such as utility construction, is completed.

Equipment should not be operated above the fabric or geogrid until one full lift of crushed stone fill is placed above it. The maximum particle size of granular material placed over geotextile fabric or geogrid generally should not exceed 1½ inches. Gradation requirements for granular material provided by the geosynthetic product manufacturer should be verified prior to material purchase and delivery to the site.

◼ Chemical Treatment – Unstable or high moisture clay soils can be chemically treated with hydrated lime, portland cement, or Class C fly ash. These treatments will require a contractor with experience in chemically treating clay soils. With this option, the chemical agent can typically be incorporated into the soils to nominal depths of about 1 foot. If thicker zones require stabilization, then removal of the upper soils will be needed prior to initiating the chemical modification.

The treatment rates and incorporation process should be evaluated in the laboratory prior to construction, and Terracon can provide suggested specifications for chemical treatment

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o 4 to 6 percent for hydrated lime, o 10 to 12 percent for portland cement, and o 14 to 16 percent for Class C fly ash.

Chemical treatment of the subgrades should occur just prior to slab construction operations to limit disturbance from weather and construction activities, and treated subgrades will require protection. The use of chemical agents can impact the operation of adjacent facilities and/or the property of individuals (e.g., airborne dust), and this should be considered by the designer and contractor.

Proofrolling is recommended prior to placing fill. 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 compaction or by undercutting and placement of suitable compacted fill. Proofrolling may be accomplished with a fully loaded, tandem-axle dump truck or other equipment providing an equivalent subgrade loading. A minimum gross weight of 25 tons is recommended for the proofrolling equipment.

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

Terracon can assist in identifying existing fill soils 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.

Construction Adjacent to Existing Structures

We recommend information concerning foundation types, bearing levels, design pressures, and subgrade preparation for the existing building be researched during project design. We recommend that available records (such as previous soils reports, construction plans) and interviews with personnel familiar with the existing structures be collected and reviewed prior to starting construction of the building. Test pits should be performed to verify bearing levels and supporting soils below the existing structure. We would be pleased to assist in evaluating this information with respect to the proposed construction.

Care should be taken to avoid undermining existing footings and grade-supported slabs.

Excavations extending below bearing level of the existing footings should be avoided. If such excavations are necessary, Terracon should be consulted regarding requirements for sloping, shoring, bracing, or underpinning based on actual conditions encountered during construction.

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Fill Material Types

Structural fill should meet the following material property requirements:

Fill Type USCS Classification Acceptable Location for Placement

Low-plasticity, cohesive soil

CL

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

Moderate-plasticity, cohesive soil

CL

(LL ≤ 45 and 10 ≤ PI ≤ 25) 2 Below exterior pavements.

Granular 3 SP, SW, GW Below interior slabs-on-grade.

Granular fill for stabilization

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.

On-site soil

5 CL

Generally appears suitable for use as low-plasticity or moderate-plasticity cohesive fill.

1. Structural fill should consist of approved materials that are free of organic matter or debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. Each proposed fill material should be sampled and evaluated by the geotechnical engineer prior to its delivery and/or use.

2. LL = Liquid Limit, PI = Plasticity Index. Fill meeting a PI of 10 to 20 is preferred; however, based on our knowledge and experience, we anticipate that finding fill soils meeting a PI of 20 or less may be difficult. Utilizing lean clay soils with a liquid limit of less than 45 percent and a plasticity index between

20 and 25 percent is generally accepted in the area, although this will somewhat increase the risk of shrink-swell movement due to the fill soils.

3. A well graded granular material, 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. Terracon can review proposed materials. Using a material similar to NDOT Crushed Rock for Surfacing, with 6% or less fines (material passing the #200 sieve) for this layer will improve subgrade stability during compaction and slab construction.

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, although crushed concrete is subject to degradation under repetitive traffic loads and so should be used with caution in high traffic areas.

Terracon can review proposed materials.

5. Sorting of topsoil and 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 of the on-site soils will be necessary to facilitate compaction.

Terracon should be retained to evaluate proposed fill materials, including sampling and performing laboratory tests on proposed fill to evaluate compliance with the project specifications. We can also review data for proposed materials which are generated by the contractor or suppliers.

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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-operated equipment (i.e.

jumping jack or plate compactor) is used

9 to 12 inches for a granular stabilization layer on soft or wet clay subgrade

Minimum Compaction

Requirements 1, 2, 3, 4

98% of maximum within 6 inches of finished pavement subgrade

95% of maximum all other locations

Water Content Range

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

Granular: Workable moisture levels

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

698).

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

3. Crushed stone / crushed concrete placed over a subgrade composed of wet or soft clay should not be overcompacted; overcompaction can cause subgrade disturbance and loss of strength of the underlying subgrade. In these areas, we recommend that the granular layer be drifted into place in advance of compaction equipment. 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 that the subgrade below exterior pavements be rough-graded as needed, and then scarified and recompacted. We recommend this process include 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. Specifically, 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).

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

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Utility Trench Bedding and Backfill

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

We also recommend constructing an effective clay “trench plug” that extends at least 5 feet out from the face of the building exterior. The plug material should consist of either cementitious flowable fill or low permeability clay. The trench plug should be placed to completely surround the utility line.

Construction Considerations

Any areas of standing surface water should be drained as far in advance of construction as possible.

Any saturated soils should be removed prior to placing fill or proceeding with construction.

The clays encountered in the borings will be sensitive to disturbance from construction activity and water seepage. If precipitation occurs immediately prior to or during construction, the near-surface clay soils could increase in moisture content and become more susceptible to disturbance.

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.

Surface water should not be allowed to pond and soak into the soil during construction. Construction staging should provide drainage of surface water and precipitation away from the building and pavement areas. Any water that collects over or adjacent to construction areas should be promptly removed, along with any softened or disturbed soils. Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to avoid ponding and associated delays due to precipitation and seepage.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs and pavements. Construction traffic over the completed subgrade should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. 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 floor slab and pavement construction.

As a minimum, all temporary excavations should be sloped or braced as required by Occupational

Safety and Health Administration (OSHA) regulations to provide stability and safe working conditions. Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. All excavations should comply with

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Trench Safety Standards.

Exterior Grading

Poor site drainage and ponding of surface water can increase the potential for frost heave or settlement. Excessive moisture can reduce bearing capacity and contribute to slab and pavement settlement and cracking.

Finished grading slopes should promote drainage away from the buildings and pavements. We recommend final grades for seeded and landscaped areas be sloped at least 5 percent within 10 feet around the buildings. We recommend cohesive backfill be placed in utility trenches and adjacent to building foundations, 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 buildings. Pavements or sidewalks installed adjacent to the building should slope away from the building 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.

SHALLOW FOUNDATIONS

In our opinion, the slabs supporting the XFMR house keeping loads and the WCC house keeping loads can be supported on tested and approved soil at shallow depths. We estimate settlements of between ½-inch and 1 inch for these slabs. Isolating the pads mats from the adjacent, lightly-loaded, grade-supported slabs is recommended in order to allow the mats to move independently of the slabs.

The basement wall of the existing building should be evaluated with respect to the new loads imposed by the XFMR house keeping pad, as described in Lateral Earth Pressures.

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DEEP FOUNDATIONS

Drilled Shaft Design Parameters

It is our recommendation that foundation loads of the new chiller building be supported on a deep foundation system consisting of straight-sided drilled shafts. We recommend the following design parameters for drilled shafts.

Straight-Sided Drilled Shaft Design Parameters

Approximate

Elevation (feet)

Allowable Unit Skin Friction in

Compression (psf)

Allowable End Bearing

Pressure (psf)

Above 1157 350 Neglect

1157 – 1126 550 Neglect

1126 – 1107 650 8,000

1107 - 1085 900 12,000

1. Design capacities are dependent upon the method of installation and quality control parameters.

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

2. Applicable for compressive loading only, and includes a safety factor of about 2. Reduce to ⅔ of values shown for uplift loading. Effective weight of shaft can also be used to resist uplift loads.

3. Includes a safety factor of about 3. Shafts should extend at least one diameter into the bearing stratum and to a minimum of 15 feet below existing grade for end bearing to be considered.

A Terracon representative should log the stratigraphy in the shaft excavations to confirm that the soil conditions are similar to those encountered in the boring and are capable of carrying the anticipated loads.

Pile caps and grade beams should extend at least 3½ feet below adjacent grade for frost protection. Due to the potential effects of frost and moisture variations on near-surface soil conditions, we recommend that the soils within 3½ feet of final grade be assumed to develop no axial load resistance. For drilled shaft foundations designed and constructed as recommended in this report, total estimated settlements are not anticipated to exceed ½ inch.

Lateral Loading Design

The structure 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 Below-Grade Structures are recommended for pile caps and grade beams, although care will be needed close to the basement wall to avoid new loads on the basement wall. 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

Responsive ■ Resourceful ■ Reliable 13 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

Below-Grade Structures, 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 drilled shafts, especially if the pile tops are fixed from rotation. The following parameters may be used for lateral load analysis of drilled shafts using the computer modeling programs L-Pile or Group. We request the opportunity to have further input on lateral pile evaluations when the chosen foundation system details and loading conditions are known, and we can be retained to perform the lateral load analyses.

Soil Parameters for Lateral Load Analysis 1, 2

Depth (ft.) L-Pile Soil Model Su (psf)

(pcf) ε50 Static k (pci)

Above 1173 Soft Clay 500 55 0.020 30

1173 - 1128 Medium Stiff Clay 750 55 0.010 100

1128 - 1106 Stiff to Very Stiff Clay 2,000 55 0.005 750

1. Angle of internal friction is taken as 0 degrees since the soils are cohesive.

2. Definition of Terms:

Su: Undrained shear strength

: Internal friction angle, Moist unit weight ε50: Non-default E50 strain

K: Horizontal modulus of subgrade reaction

3. Buoyant unit weight values should be used below design water level.

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.

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Group Reduction Factors – Laterally Loaded Piles

Pile Spacing, center-to-center

(Diameter)

Reaction 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

Drilled Shaft Construction Considerations

Drilled shaft installation should generally conform with ACI 336.1, “Specification for the

Construction of Drilled Piers.” Straight-sided shafts are recommended. Successful installation of the drilled shafts will depend to a large extent on the suitability of the equipment and installation procedures used. Conventional excavating and drilling equipment should be provided to penetrate the soils encountered in the boring. Methods and equipment used for drilled shaft installation should leave the side and bottom of the shaft free of loose and disturbed material which would prevent the concrete from contacting undisturbed soil.

Fine sand soil was encountered below about 9 feet and ground water was encountered at about 16 feet in Boring B-8. The contractor should be required to mobilize equipment to use slurry or wet method of drilled shaft construction. The slurry head should be kept above the water table to counteract seepage pressures and help prevent cave-in. Concrete should be placed within a few hours of excavating. If this is not possible, the shaft should be re-drilled with a larger diameter auger and cleaned prior to placing concrete.

The volume of concrete placed should be checked against the calculated volume required to obtain design shaft dimensions. Terracon should review and comment on specifications developed for shaft installation, and actual shaft installation should be monitored by a Terracon representative.

SEISMIC CONSIDERATIONS

Based upon the results of the borings, we estimate the project site as “Site Class D” according to the 2012 International Building Code (IBC), which references Chapter 20 of ASCE-7. This site class assumes that soils similar to the native soils encountered at the bottom of Boring B-1 continue to a depth of 100 feet. A more detailed and accurate Site Class evaluation can be achieved by retaining Terracon to perform a deeper soil boring, to perform a cone sounding with shear wave measurements, or to use the SeisOpt®ReMi™ method to develop the full depth shear wave profile.

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FLOOR SLABS

Design Recommendations

Item Description

Floor slab support 1 Aggregate base (see below) underlain by low-plasticity cohesive fill prepared according to Earthwork.

Modulus of subgrade reaction 2 100 pounds per square inch per inch (psi/in) for point loading conditions.

Aggregate base course/capillary break 3 4 inches of free draining granular material

1. Floor slabs 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 will be lower.

3. The floor slab design should include a capillary break, comprised of compacted, granular material, as described in Earthwork.

Slabs-on-grade should be isolated from structures and utilities to allow independent movement.

Joints should be constructed at regular intervals as recommended by the American Concrete

Institute (ACI) to help control the location of any cracking. Keyed and doweled joints should be considered. The owner should be made aware that differential movement between the slabs and foundations could occur.

The use of a vapor retarder should be considered beneath concrete slabs on grade that will be 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.

Construction Considerations

On most project sites, the floor slab subgrades are developed early in the construction phase.

However as construction proceeds, the subgrade may be disturbed due to foundation installation, utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab subgrade may not be suitable for placement of base rock and concrete and corrective action will be required.

We recommend the floor slab subgrade be rough graded and then proofrolled with a loaded tandem axle dump truck prior to fine grading and placement of base rock. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with compacted fill. All floor slab subgrades should be moisture

Responsive ■ Resourceful ■ Reliable 16 conditioned and properly compacted to the recommendations in this report immediately prior to placement of the aggregate base course and concrete.

LATERAL EARTH PRESSURES AND DRAINAGE

Design Parameters

The lateral earth pressure recommendations given in this section are applicable to the design of rigid retaining walls subject to slight rotation, such as cantilever, or gravity type concrete walls.

These recommendations are not applicable to the design of modular-block retaining walls (also termed segmental retaining walls).

Reinforced concrete walls with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to those indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement. The recommended design lateral earth pressures do not include a factor of safety and do not provide for hydrostatic pressure on the walls.

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Earth Pressure Coefficients

Earth Pressure

Conditions

Coefficient for

Backfill Type

Equivalent Fluid

Density (pcf)

Surcharge

Pressure, p1 (psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.33

Lean Clay - 0.42

(0.33)S

(0.42)S

(40)H

(50)H

At-Rest (Ko) Granular - 0.46

Lean Clay - 0.50

(0.46)S

(0.50)S

(55)H

(60)H

Passive (Kp) Granular - 3.0

Lean Clay - 2.4

Applicable conditions to the above include:

■ For active earth pressure, wall must rotate about base, with top lateral movements of about

0.002 H to 0.004 H, where H is wall height

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

■ Uniform surcharge, where S is surcharge pressure; the surcharge load should include the load on top of the slab, which we understand is about 310 psf to 325 psf for the housekeeping pads

■ In-situ soil backfill weight a maximum of 120 pcf

■ Horizontal backfill, compacted between 95 and 98 percent of standard Proctor maximum dry density

■ No hydrostatic pressure acting on wall

■ No loading from compaction equipment

■ No loading from nearby footings, drilled shafts, or slabs

■ No dynamic loading

■ No safety factor included in soil parameters

■ Ignore passive pressure in frost zone

Backfill placed against structures should consist of granular drainage fill or low plasticity cohesive soils. For the granular values to be valid, the granular backfill must extend out from the base of the wall at an angle of at least 45 and 60 degrees from vertical for the active and passive cases, respectively. To calculate the resistance to sliding, a value of 0.45 should be used as the ultimate coefficient of friction between the footing and the underlying soil.

To control the water level behind the retaining wall, we recommend a perimeter drain be installed behind the wall as described in Drainage of Cantilever Retaining Walls. If this is not possible, then combined hydrostatic and lateral earth pressures should be calculated using the values shown in the following table.

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Undrained Lateral Earth Pressure Parameters

Backfill Type Active Condition 1, 2 At-Rest Condition 1, 2

Clay Backfill 89 pcf 94 pcf

Granular Backfill 83 pcf 91 pcf

1. These pressures do not include the influence of surcharge, equipment, or floor loading, which should be added.

2. Calculated using a saturated soil unit weight of 125 pcf.

These pressures do not include the influence of surcharge, equipment or floor loading, which should be added. Footings and other loads located adjacent to walls may have a significant effect on lateral pressures. Placement of footings in wall backfill should be avoided unless structural analyses are performed to evaluate the resulting loads and effects on the wall. To avoid excessive lateral wall loads, heavy compaction equipment should not be operated within a distance out from new or existing walls equal to the height above the base of the wall.

Drainage of Cantilever Retaining Walls

A perforated rigid plastic or metal drain line should be installed behind the walls to prevent hydrostatic loading on the walls. The invert of a drain line around the walls should be at least 6 inches below the adjacent slabs. The drain line should be sloped to provide positive gravity drainage to a sump or other suitable outlet. The drain line should be surrounded by free-draining granular material graded to prevent the intrusion of soil fines into the granular material or the intrusion of the granular material into the drain pipe perforations. Alternatively, a coarse, clean, free-draining granular material could be used to surround the pipe if this material is encapsulated with suitable filter fabric.

At least a 2-foot wide section of free-draining granular fill is recommended for backfill above the drain line and adjacent to the wall and should extend up to the slab;

if the drain pipe is around the exterior of the building, then a cohesive fill cap should be installed as shown in the schematic.

A prefabricated drainage structure may be used above a drain line and the surrounding filter, in lieu of

Responsive ■ Resourceful ■ Reliable 19 free-draining granular fill. A prefabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion, and is fastened to the wall prior to placing backfill.

PAVEMENTS

General Pavement Comments

At a minimum, pavement subgrades should be prepared in accordance with the recommendations presented in Earthwork. Typical construction in this area is not to place a granular base below exterior pavements for this type of project. Rather, the exterior pavements are supported directly on the cohesive subgrade soils. We have provided pavement sections for full depth pavements supported on a clay subgrade. However, the incorporation of a drained granular base would improve the pavement performance and anticipated life. If the project design results in a granular base being installed below exterior pavements, Terracon should be retained to provide additional recommendations. For example, subdrains are recommended in conjunction with a granular base to prevent water from ponding in the granular base. If a granular base is not incorporated, we recommend finger drains be installed in low areas of the pavement and adjacent to storm drain intakes to allow drainage of surface water that infiltrates into the subgrade.

Design Recommendations

A formal pavement design should be completed with actual traffic loads and planned equipment.

We recommend considering the following pavement sections as typical minimums:

◼ Standard Duty Pavements: For parking areas subjected to low volumes of automobile traffic, a full-depth ACC section having a total thickness of at least 6 inches, or a PCC pavement section having a thickness of at least 5 inches, is recommended.

◼ Heavy-Duty Pavements: Automobile driveways carrying weekly, single-unit garbage and delivery trucks require increased pavement thicknesses. A minimum 7-inch thick ACC section, or a minimum 6-inch thick PCC section, is recommended in these areas.

◼ Truck Pads: A minimum 7-inch thick PCC section is recommended for aprons in truck loading docks, delivery truck parking areas, and refuse pick-up areas. Such areas should have a concrete section wide enough to accommodate the vehicles that would use it.

Terracon has observed dishing in some parking lots surfaced with ACC. Dishing is usually observed in frequently-used parking stalls (such as near the front of the building), and occurs under the wheel footprint in these stalls. The use of higher grade asphaltic cement such as PG70-34, or surfacing these areas with PCC, is recommended. The dishing is exacerbated by factors such as irrigated islands or planter areas, sheet surface drainage to the front of the building, and placing the ACC directly on a compacted clay subgrade. The use of lower grade asphalt cement, such as PG64-34

Responsive ■ Resourceful ■ Reliable 20 is relatively common in this area and may be considered, but would provide lower reliability against rutting and creeping during warm weather.

Minimum surface course thicknesses of 2 inches in automobile areas and 3 inches in driveways are recommended for asphaltic cement concrete pavement sections. An ACC base course thickness of 4 inches is recommended.

We recommend that ACC and PCC pavement specifications reference Sections 400 and 500, respectively, of the City of Omaha Standard Specifications for Public Works Construction, 2014

Edition. We recommend a surface mix type SPR for ACC pavements and mix type L65 for PCC pavements.

Proper joint spacing will also be required to prevent excessive slab curling and shrinkage cracking. Joints should be sealed to prevent entry of foreign material and dowelled where necessary for load transfer. The contractor should submit a joint layout plan for approval by the engineer prior to placement of concrete. The plan should identify the location of all joints in the pavement which should be designed to avoid acute angles in accordance with the guidance in

ACI 330R-33 sections 3.7, 3.11 and Figure C.1 Typical Joint Layout for Parking Area.

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

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

We recommend joints be sealed to help prevent moisture infiltration, including a sprayed concrete sealer and a hot-pour joint sealer. The use of backer rods is not recommended.

In addition to the joint sealing recommendations above, modifying the concrete mix can also be considered to improve the durability of the concrete. To reduce Alkali Silica Reactivity (ASR) and help reduce the concrete permeability, consideration should be given to using Type IP and IPF

(Duracem F) cement. Other pozzolans such as slag can also be considered to decrease permeability. We also recommend a water-reducing admixture be utilized to facilitate a water-cement ratio of not more than 0.42, preferably closer to 0.4. A ready-mixed concrete producer, local to the project, should be consulted regarding mix performance and material availability. In addition, a mix design prepared in accordance with ACI 211.5R should be submitted for review by the design team prior to construction.

A formal pavement design has not been completed for this project. The above recommended pavement sections are typical minimum values and thicker pavement sections could be used to reduce maintenance and extend the expected service life of the pavements. Periodic maintenance will also extend the service life of the pavements and should include patching and repair of deteriorated areas, crack sealing, and surface sealing. We recommend that a California Bearing

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Ratio (CBR) test and a formal pavement design be completed if unusually high vehicle loads or frequencies are anticipated.

Construction Considerations

Construction scheduling often involves grading…