Attachment 4 - ACC Geotechnical Report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report V.A. Ambulatory Clinic

Omaha, Nebraska

October 26, 2017

Terracon Project No. 05175126

Prepared for:

Heritage Foundation

Omaha, Nebraska

Prepared by:

Terracon Consultants, Inc.

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

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

REPORT COVER LETTER TO SIGN

Heritage Foundation

10050 Regency Circle, Suite 101

Omaha, Nebraska 68114

Attn: Mr. Chad Beeson

P: 402-980-9862

E: cbeeson@hservices.org

Re: Geotechnical Engineering Report

V.A. Ambulatory Clinic

42nd Street and Woolworth Avenue

Dear Mr. Beeson:

We have completed the geotechnical exploration services for the above referenced project. This study was performed in general accordance with our proposal number P05175126 authorized

July 27, 2017. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon Consultants, Inc.

Ryan D. Sisk, E.I. Michael D. Ringler, P.E.

Staff Geotechnical Engineer Senior Engineer

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REPORT TOPICS

REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

DEEP FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

BELOW GRADE STRUCTURES

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 logo in the top right corner will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLAN

EXPLORATION RESULTS (Boring Logs and Laboratory Data)

SUPPORTING INFORMATION (General Notes, Unified Soil Classification System)

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INTRODUCTION

Geotechnical Engineering Report

V.A. Ambulatory Clinic

42nd Street and Woolworth Avenue

Omaha, Nebraska

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed ambulatory clinic to be located at the VA Hospital at 42nd

Street and Woolworth Avenue in Omaha, Nebraska. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ soil conditions ■ foundation design and construction

■ groundwater conditions ■ seismic site classification per IBC

■ site preparation and earthwork ■ lateral earth pressures

■ floor slab design and construction ■ pavement design and construction

■ frost considerations

The geotechnical engineering scope of services for this project included the advancement of one soil boring to a depth of approximately 45 feet below existing grade. Site and boring locations are shown in the Site Location and Exploration Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained during the field exploration are included on the boring log in the Exploration Results section of this report.

As described in Site Conditions, Terracon performed a geotechnical exploration at the site in

2010. Information from that exploration was also reviewed when generating recommendations for this report, and pertinent information from the previous exploration is attached to this report.

SITE CONDITIONS

Item Description

Parcel Information

The project is located at the existing V.A. Hospital facility located in the southeast corner of 42nd Street and Woolworth Avenue in Omaha, Nebraska.

The ambulatory clinic is planned northeast of the main hospital entrance.

Latitude / Longitude: 41° 14.61' N / 95° 58.40' W (See Site Location)

V.A. Ambulatory Clinic ■ Omaha, Nebraska

October 26, 2017 ■ Terracon Project No. 05175126

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Existing

Improvements

The site of the proposed ambulatory clinic and connector is surfaced with grass and paved parking areas and driveways. Utility lines extend through the clinic footprint, and large trees are also present.

Site History An aerial photo from 1941 indicates the site was a golf course prior to construction of the hospital facility.

Existing Topography

Topographic information presented in the Facility Plot Plan by the Veterans

Administration, dated July 9, 2002, indicates the ground surface across the proposed ambulatory clinic footprint generally slopes down to the east with about 25 feet of grade change. Grade elevations range from about 1232 feet along the driveway near the existing hospital, to about 1207 feet near the east end of the building pad.

Previous reports

Geotechnical Engineering Report, SD1 Submittal Report, Preliminary

Exploration and Recommendations, Terracon Project No. 05105105, dated

January 24, 2011.

Geotechnical Engineering Report, SD2 Submittal Report, Design Exploration and Recommendations, Terracon Project No. 05105105, dated August 9, 2011.

Supplement to Schematic Design 2 Report, Pile Load Test Program, Nebraska-Western Iowa Health Care System, Veterans Administration

Hospital, South 42nd Street and Woolworth Avenue, Omaha, Nebraska, Terracon Project Number 05105105R04, dated March 2, 2012.

PROJECT DESCRIPTION

Project Description

Approximately 160,000 square feet of clinical office in a three-story building with a fourth level mechanical penthouse and a concourse along the west side of the building which connects to the existing VA Hospital. New surface parking will be constructed north of the building.

Proposed Structure

Three-story building with fourth level mechanical penthouse. A one-story connecting concourse structure will be present along the west side of the building, which will connect the First Floor level of the new building to the main level of the existing hospital.

Building Construction

Structural steel and concrete-on-metal-decks with moment frames to resist lateral loads. Below-grade walls will be cast-in-place concrete. Support for the clinic is anticipated to be provided by auger-cast-piles. Support for the structurally independent connector concourse is expected to be provided by shallow spread footing foundations.

Finished Floor Elevation First Floor: 1234.42 feet

Ground Floor: 1218.42 feet

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Maximum Loads

Columns: 750 kips for clinic; 75 kips for 1-story concourse

Walls: 6 klf for clinic basement walls; 2 klf for 1-story concourse

Slabs: 100 psf

Grading/Slopes

Based on the Ground Floor FFE of 1218.42 feet, the building will generally transition from cut at the west end to fill at the east end. Maximum cuts will vary from about 3 feet in the NW corner to about 12 feet in the SW corner, and maximum fills will vary from about 10 feet in the SE corner to about 13 feet in the NE corner. The connector concourse between the southwest corner of the clinic to the hospital will require less than 3 feet of cut or fill.

Below Grade Areas

Lower level (Ground Floor) will “walk-out” to the east, north, and south. The west wall of the clinic will serve as a retaining wall to provide grade separation from the driveway (approximate elevation of 1232 feet) down to the lower level.

Free-Standing Retaining Walls

An approximately 16-ft. tall retaining wall is anticipated near a Ground Floor exit at the southwest corner of the new clinic, adjacent to the connector concourse.

Pavements

Reconstruction of a portion of the paved parking lot is anticipated on the north side of the clinic.

Anticipated traffic is as follows:

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

■ Light delivery and trash collection vehicles: 10 vehicles per week

■ Tractor-trailer trucks: <1 vehicle per week

The pavement design period is 20 years.

GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

Subsurface conditions at the boring location can be generalized as follows:

Stratum Approximate Depth to

Bottom of Stratum Material Description Consistency/Density

Surface 6 inches Portland Cement Concrete N/A

Surface 8 inches Aggregate base N/A

1 8 feet Fill: Lean Clay N/A

2 45 feet1 Lean Clay Very Stiff to Stiff

1. Termination depth.

Conditions encountered at the boring location are indicated on the boring log in the Exploration

Results section and are attached to this report. Stratification boundaries on the boring log

Responsive ■ Resourceful ■ Reliable 4 represent the approximate location of changes in native soil types; in situ, the transition between materials may be gradual.

Variations can occur between the boring and cone sounding locations, and across the site.

Additional variations can occur due to previous grading and construction.

Groundwater Conditions

Groundwater was not observed in the boring during or shortly after completion of drilling operations.

At the time the boring was drilled, the groundwater table at the boring location was apparently below the maximum drilling depth. However, fluctuations in the groundwater table can occur and perched water can develop over low permeability soil strata following periods of heavy or prolonged precipitation. This possibility should be considered when developing design and construction plans and specifications for the project. Long term monitoring in cased holes or piezometers would be necessary to accurately evaluate the potential range of groundwater conditions on the site.

GEOTECHNICAL OVERVIEW

It is our opinion the existing fill encountered in Boring B-23 is not suitable for foundation or floor slab support. We recommend existing fill be removed from below the connector and replaced with structural fill.

Placing grade-raise fill will impose new loads to the native clays. The native clays will respond by consolidating and causing settlement. We recommend preloading / surcharge loading with settlement monitoring at the east end of the ambulatory clinic footprint. Additional discussion and recommendations are provided in Earthwork.

It is our opinion the native lean clays are suitable for support of the connector loads on spread footing foundations. An overexcavation and backfill procedure is recommended below spread footings when low-density loess is present at footing foundation bearing level (for example, as is possible in the area of Boring B-05). Additional discussion and recommendations are provided in

Shallow Foundations.

We recommend the moderate to heavy loads of the ambulatory clinic be supported on a deep foundation system consisting of ACIP piles. Additional discussion and recommendations are provided in Deep Foundations.

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EARTHWORK

Site Preparation

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 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.

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.

It is our experience poorly compacted backfill is commonly found in utility line trenches. Utility lines should be re-routed outside of the new building area, and utility trench backfill should be reworked and recompacted.

We recommend the ambulatory clinic slab be underlain by an aggregate base, in turn underlain by at least 12 inches of low-plasticity cohesive fill. The western edge of the building footprint will be formed in cut, so we recommend the soils be undercut to allow development of the full 12-inch thickness. A scarification and recompaction process can be implemented to form the lower 6 inches of the 12-inch thickness in-place.

Boring B-23 was drilled in the parking stalls east of the main entrance, and encountered fill to about 7 feet, in turn underlain by native clay. It is our opinion the fill is not suitable for support of the connector. Therefore, we recommend this material be removed from below the slabs and footings of the connector and replaced with structural fill. The removal should be performed below the footprint of the connector, and should extend five feet laterally beyond the outside edge of the footing.

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We recommend at least 8 inches of reworked and recompacted fill be provided below exterior pavements. This can be accomplished by scarifying the soil at subgrade level to a depth of about

8 inches, moisture conditioning, and then compacting as recommended below. Fill which cannot be recompacted as recommended should be undercut and replaced with stable fill.

Proofrolling is recommended in various areas. 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. Unstable subgrades may require placement of crushed concrete or crushed rock and geogrid. Initially, 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. If the subgrade holds up well under the initial loading, proofrolling may be attempted with a fully-loaded, tandem-axle, dump truck with a minimum gross weight of 25 tons or other equipment providing an equivalent subgrade loading. After removing the unsuitable materials and stabilizing the weak subgrades, the site should be filled to design grades with structural fill as recommend in this report.

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, existing fill removal, utility abandonment, site excavation, 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

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. For example, the footings could be underpinned, or sheeting/shoring could be installed.

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 structures be collected and reviewed prior to starting construction. Test pits can 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.

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We understand the existing hospital has varying lower-level floors, including basement levels.

Foundation support of the existing hospital is reportedly provided by a deep foundation system of

ACIP piles.

Fill Material Types

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 3

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.

Aggregate base 4 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 5

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.

Free-Draining

Granular Fill 6 SP, SW, GP, GW Free-draining retaining wall backfill. Imported.

On-Site Soils 7 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. 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.

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Fill Type 1 USCS Classification Acceptable Location for Placement

4. 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.

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

6. Well-graded, free-draining granular material used as drainage backfill adjacent to below-grade walls.

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.

7. 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.

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.

Fill Compaction Requirements

Structural fill should meet the following compaction requirements.

Item Description

Fill Lift Thickness 1 8 inches or less in loose thickness

Compaction Requirements 2, 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 5 Workable moisture levels.

1. 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.

2. 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.

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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 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. 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).

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 floor slab and pavement subgrades immediately prior to paving.

Surcharge Loading

Discussion: The expected grade raises in the eastern portion of the ambulatory clinic will cause stress increases extending into the native clay soils. The compressible soils will respond by consolidating and causing settlement. We estimate 4 to 6 inches of settlement will occur due to the planned grade raise. We recommend these settlements occur prior to installation of the ambulatory clinic foundations by implementing preloading and surcharge loading, as follows.

Preload and Surcharge Load Placement: We recommend the preloading and surcharge loading process be initiated by placing permanent fill up to floor slab subgrade level within the building footprint and for a distance of 20 feet around the building perimeter. We then recommend placing preload fill and surcharge fill to a vertical distance of at least 4 feet above FFE / exterior final grade.

The preload fill and top of surcharge fill should extend at least 15 feet laterally beyond the east, south, and north sides of the perimeter of the ambulatory clinic. The side slopes of the surcharge can be about 1H:1V beyond the east, south, and north sides of the perimeter of the ambulatory clinic.

Proceeding west from the east edge of the ambulatory clinic, within the building footprint, the surcharge should be carried to full height until the height of permanent fill is about 3 feet. The side

Responsive ■ Resourceful ■ Reliable 10 slopes of the west end of the surcharge should be no steeper than 3H:1V within the building footprint of the ambulatory clinic.

We can review the preload/surcharge plans to confirm that our recommendations have been interpreted as intended. The final configuration of the preload/surcharge fill should be verified by an as-built survey.

The preload fill and surcharge fill can be tracked into place with loaded scrapers or dump trucks, in lifts of 12 inches or less in loose thickness. A minimum compaction criterion is not required, but the as placed material should have a minimum in situ wet unit weight of 100 pcf. Topsoil strippings / unsuitable material can be used for surcharge material, provided the 100 pcf minimum weight is achieved.

Settlement Monitoring: We recommend a settlement monitoring program be implemented to measure the amount and rate of settlement due to the permanent fill and surcharge fill. We recommend at least two settlement monuments be installed for settlement monitoring in the eastern portion of the ambulatory clinic footprint. The monuments should be installed on the permanent fill at design subgrade level, prior to placing the preload / surcharge fill.

We recommend the monuments consist of 2-foot square steel plates. A metal coupler should be welded to the center of the plate to allow metal riser pipes to be added. Plastic PVC pipe should be installed around the steel pipe for protection.

We recommend the elevations of the settlement monuments be surveyed to the nearest 100th of a foot, and the elevations of the ground surface adjacent to the monuments be surveyed to the nearest

10th of a foot, according to the following schedule:

Surcharge Interval Monitoring Schedule

At Time of Monument Seating Initial Readings

During Preload / Surcharge Fill Placement Daily

For Four Weeks Following Surcharge Fill Placement Three times per week

Between Four and Twelve Weeks Following Surcharge Fill Placement Two times per week

More Than Twelve Weeks Following Surcharge Fill Placement Once per week

A settlement period of 2 to 3 months is estimated, based on the proposed site grading and recommended surcharge load, with more time anticipated in the eastern portion of the site and in arrears receiving more fill. We anticipate about 1/3 of the settlement will occur during fill placement.

These are only estimates based on our experience with projects of this type, the soil conditions observed in the borings, and the laboratory test results. Other factors affecting the effective drainage path and permeability of the soils may reduce the time for the settlement to occur. Monitoring of settlements will allow for direct measurement. At least one month of settlement data will be required before we can begin to project total settlements and refine the estimated time period.

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Utility Trench Backfill

Utility trenches are a common source of water infiltration and migration. Utility trenches that penetrate beneath the building should be sealed to restrict water intrusion and flow into the building envelope. We recommend a plug of flowable fill or lean clay be installed to surround the utility line in the trench from the building face to at least 5 feet out from the face of the building exterior. If a clay plug is used, the clay material should be placed and compacted to comply with the water content and compaction recommendations for structural fill stated in this report.

Utility trenches in un-paved areas should be capped with either pavement or at least 18 inches of cohesive fill to promote drainage of surface water and prevent surface water infiltration.

Earthwork Construction Considerations

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

Safety and Health Administration (OSHA) regulations and applicable local, state, and federal safety regulations to provide stability and safe working conditions. The contractor is usually responsible for designing and constructing stable, temporary excavations and should shore, slope or bench the sides of the excavations as required, to maintain stability of the excavation sides and bottom. Construction site safety generally is the sole responsibility of the Contractor, who shall also be solely responsible for the mean, methods, and sequencing of construction operations.

Although the native clays in the borings are stiff, they will be susceptible to disturbance from heavy loads or repetitive construction traffic. In addition, precipitation and surface water can soak into these soils, raising their moisture content and making them more susceptible to disturbance.

Surface water should not be allowed to pond on the site and soak into the soil during construction.

Construction staging should provide drainage of surface water and precipitation away from the structure and construction 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 is recommended to avoid ponding and associated subgrade deterioration and corrections.

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.

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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.

Grading and Drainage

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 buildings and pavement areas to help prevent post-construction wetting of the bearing soils. We recommend final grades for seeded and landscaped areas be sloped at least 5 percent within 10 feet around the building to direct surface water well away from the building. We recommend cohesive backfill be placed in utility trenches and adjacent to building 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 building.

Pavements or sidewalks installed adjacent to the buildings 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.

Permanent Slopes

We recommend permanent grading slopes have inclinations of 3H:1V or flatter. We anticipate a slope about 15 feet high will result east of the ambulatory clinic. Based on our experience and a cursory review, we believe this slope will have a safety factor in excess of 1.5 based on the expected slope materials and comparison to slope stability charts developed by Taylor (Fundamentals of Soil

Mechanics, 1948). If a steeper slope is required, Terracon should be retained to evaluate the proposed slopes.

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The slopes are expected to be formed in native loess, or composed of compacted fill derived from loess. Loess has a high silt content. As a result, slopes exposing or formed of this material are 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.

SHALLOW FOUNDATIONS

Support Discussion

It is our recommendation that the moderate to heavy structural loads of the ambulatory clinic be supported on a deep foundation system. Additional discussion and recommendations are provided in Deep Foundations.

We recommend the existing fill under the connector be removed and replaced with structural fill.

Following this procedure, support of the connector footings on spread footings appears feasible.

The native soils encountered in the borings are loess. Loess soils are known to be collapse-susceptible upon wetting, particularly when the soils exist at relatively low in situ dry densities.

Based on the boring information from B-05, zones of relatively low-density (dry unit weight less than about 85 pcf) and moisture-sensitive soils are anticipated if footings for the connector / concourse bear at about elevation 1215 feet. In this case, it is our opinion that collapse or consolidation of these soils is a concern for this structure. Adverse foundation settlement and performance is expected should the low-density soils become wetted at any time during the life of the structure.

In order to provide a uniform bearing stratum beneath footing foundations, and to reduce the potential for post-construction wetting of the low-density native soils, we recommend that an overexcavation and recompaction procedure be performed of these soils are encountered at footing bearing level. The overexcavation should be backfilled with low-plasticity cohesive fill placed and compacted as recommended in Earthwork.

Although moisture-sensitive native loess soils will still be present below the densified zone, the relatively low permeability of the densified layer will help reduce the rate of vertical infiltration of water into the underlying soils. Recommendations concerning exterior grading to help prevent port-construction wetting are presented in Earthwork.

Design Parameters

If the site is prepared in accordance with the requirements noted in Earthwork, the following design parameters are applicable for shallow foundations for the connector.

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Description Column Wall

Net allowable bearing pressure 1 2,000 psf 2,000 psf

Minimum dimensions 30 inches 18 inches

Minimum embedment below finished grade for frost protection 2 42 inches 42 inches

Approximate total settlement 3 <1 inch <1 inch

Estimated differential settlement 3 <⅔ inch between columns <⅔ inch over 40 feet

1. The net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. Assumes any fill or soft soils, if encountered, will be undercut and replaced with structural fill.

2. And to reduce the effects of seasonal moisture variations in the subgrade soils. For perimeter footings and footings beneath unheated areas. If construction extends into freezing weather, we recommend that either all footings extend to frost depth (as measured from adjacent grade at the time of construction) or that the foundations be protected from the elements by straw, frost blankets, or similar means.

3. The foundation settlement will depend upon the variations within the subsurface soil profile, the structural loading conditions, the embedment depth of the footings, the thickness of compacted fill, and the quality of the earthwork operations.

Construction Considerations

The bearing materials exposed in all foundation excavations should be observed and tested by a

Terracon representative. If unsuitable bearing materials are encountered in a footing excavation, the excavation should be extended deeper to suitable materials. The footing could bear directly on the suitable materials at the lower level or on lean concrete backfill placed back up to design bearing level. The footings could also bear on approved, properly compacted backfill extending down to the suitable materials. Overexcavation for compacted backfill placement below footings should extend laterally at least 8 inches beyond the edges of the footings for each foot of depth below footing base elevation. The overexcavation should then be backfilled up to the footing base elevation with approved fill placed and compacted as recommended in Earthwork. The adjacent figures depict these options.

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The clay soils on this site are susceptible to disturbance from construction activities, particularly if the soils have high natural moisture contents or become wetted by surface water or seepage.

Care should be taken during excavation and construction of footings to avoid disturbing the bearing soils. The base of all foundation excavations should be free of water and loose material prior to placement of concrete. Concrete should be placed within a few hours after excavating to reduce disturbance of the bearing materials. If the materials at bearing level become excessively dry, disturbed or saturated, the affected material should be removed prior to placing concrete. A

2- to 3-inch lean concrete “mud mat” could be placed in the base of the foundation excavations to reduce the potential for disturbance of bearing soils and provide a stable working surface.

Interaction Between New and Existing Structures

Some overlap in stress distribution between new and existing building foundations may occur, which may cause movement of the existing foundations and support structures. Excavations for new foundations should not extend below bearing levels, pile caps, or grade beams of existing structures.

Since the connector will attach to both the existing hospital and the ambulatory clinic, both of which are / will be supported on deep foundations, connections with sufficient flexibility to accommodate independent movement should be utilized. Differential settlement between the connector and adjacent structures may approach the maximum total settlement presented above for the new footings. New footing foundations should not be within the active zone of existing soil retaining or basement walls, otherwise structural analysis would be required to evaluate the effect of the footing load on the existing wall.

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DEEP FOUNDATIONS

Augered and Cast-in-Place (ACIP) Pile Design Parameters

It is our recommendation that the ambulatory clinic be supported on a deep foundation system consisting of ACIP piles. Based on the results of the pile load testing program conducted at the site in November 2011, we recommend the following design parameters for ACIP piles.

ACIP Pile Design Parameters 1

Approximate Elevation

(feet)

Allowable Unit Skin Friction in Compression (psf) 2, 3, 4

Allowable End Bearing

Pressure (psf) 5, 6 above 1190 550 Neglect

1190 - 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. Allowable side friction values include a factor of safety of approximately 2.

3. Skin friction should be neglected within 3½ feet of adjacent grade for frost protection. Pile caps and grade beams should extend a minimum of 3½ feet below the lowest adjacent grade.

4. Recommended unit skin friction in uplift is ⅔ of the recommended skin friction in compression. Uplift loads can be resisted by the skin friction in uplift 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 loads, the reinforcing bar should be extended down to the elevation which is used to resist the uplift loads. We recommend the bar be installed, with centralizers, after the ACIP pile is grouted. A bar which cannot be installed full length should be pulled and the pile re-drilled. A reinforcing cage can also be placed in the top section of the pile, but the installation depth will be limited based on pile diameter and installation considerations.

Reinforcing installed within piles should include centering devices to assure the steel has adequate concrete cover.

5. Use of end bearing requires at least 5 feet of penetration into the bearing stratum.

6. Allowable end bearing values include a factor of safety of approximately 3.

The ACIP piles will derive capacity primarily from skin friction. We recommend a center-to-center pile spacing of 3.0D for pile groups of 7 piles or less, to maintain a safety factor of at least 2.0 for axial compressive loading. We should be contacted if a pile group of 7 or more piles is required for this project.

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The estimated maximum settlement of a single auger-cast pile foundation designed and constructed in accordance with our recommendations is less than ½-inch. The estimated settlement for a pile group will be greater than that for an individual pile, and will depend on element capacity, pile group capacity, pile group orientation, and tip bearing level. For a 5-pile group with tip bearing at about elevation 1125 feet, we estimate a pile group settlement of about

1 inch.

It is recommended that Terracon review and comment on specifications developed for pile installation and monitor pile installation.

Lateral 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. 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

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 ACIP piles, especially if the pile tops are fixed from rotation. The following parameters may be used for lateral load analysis of ACIP piles 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.

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Recommended Design Parameters for Lateral Load Resistance

Elevation, ft Recommended Soil Model Type

Effective Unit Weight (pcf)

Cohesion (psf) 1

E50 Static k Value for Subgrade Modulus (pci)

Above 1183 Stiff Clay 115 1,500 0.007 500

1183 – 1173 Soft Clay 55 500 0.020 30

1173 – 1128 Medium Stiff Clay 55 750 0.010 100

1128 – 1106 Stiff to

Very Stiff Clay 55 2,000 0.005 750

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

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

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

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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% and a grout head of 7 feet). The quantity of the concrete grout placed in each element should be checked against the calculated volume required to obtain design pile dimensions. It is recommended that Terracon review and comment on specifications developed for pile installation, and monitor 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, typically overnight. 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 a blocking pile (e.g., diagonal corners of a 5-pile group with an “X” configuration blocked by the center pile), the clear distance spacing can be reduced to 12 feet.

SEISMIC CONSIDERATIONS

The 2015 International Building Code (2015 IBC), on which design for…