Attachment 1 - Geotechnical Engineering Report.pdf

Geotechnical Engineering Report Proposed DVA IC Building # 2 Renovation/Addition

VA Medical Center, Iowa City, Iowa

June 22, 2011

Terracon Project No. 06105660.01

Prepared for:

Shive-Hattery, Inc.

Prepared by:

Terracon Consultants, Inc.

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TABLE OF CONTENTS

Page

EXECUTIVE SUMMARY ............................................................................................................... i

1.0 INTRODUCTION

2.0 PROJECT INFORMATION

2.1 Project Description

2.2 Site Location and Description

3.0 SUBSURFACE CONDITIONS

3.1 USDA NRCS Soil Mapping

3.2 Typical Subsurface Profile

3.3 Groundwater Conditions

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

4.2 Site Preparation and Earthwork

4.2.1 Demolition Considerations

4.2.2 Excavation Considerations

4.2.3 Site Preparation

4.2.4 Fill Types and Compaction

4.2.5 Compaction Requirements

4.2.6 Grading and Drainage

4.3 Spread Footings/Intermediate Foundation System

4.3.1 Soil Improvement Methods

4.3.2 Spread Footings Design Recommendations

4.4 Deep Foundation

4.4.1 Drilled Shaft Foundations

4.4.2 Driven H-Piles Design Considerations

4.4.3 Deep Foundations Lateral Earth Pressures

4.5 Construction Adjacent to Existing Building

4.6 Seismic Considerations

4.7 Floor Slabs

4.7.1 Design Recommendations

4.7.2 Construction Considerations

4.8 Frost Considerations

5.0 GENERAL COMMENTS

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TABLE OF CONTENTS – continued

Exhibit No.

Appendix A – Field Exploration Site Location Plan ................................................................................................ A-1 Boring Location Plan ............................................................................................ A-2 Subsurface Soil Profile ......................................................................................... A-3 Boring Logs .......................................................................................................... A-4 Field Exploration Description ............................................................................... A-5

Appendix B – Laboratory Testing Laboratory Test Description ................................................................................. B-1

Appendix C – Supporting Documents General Notes ...................................................................................................... C-1 General Notes - Sedimentary Rock Classification ............................................... C-2 Unified Soil Classification System ........................................................................ C-3

Proposed DVA IC Building # 2 Renovation/Addition ■ Iowa City, Iowa June 22, 2011 ■ Terracon Project No. 06105660.01

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EXECUTIVE SUMMARY

A geotechnical exploration has been performed for the referenced project in Iowa City, Iowa.

Terracon’s geotechnical engineering scope of work for this project consisted of drilling and sampling four (4) test borings to depths of about 24 to 41 feet below the existing site grades.

Based on the subsurface information obtained from this exploration, the site is suitable for the proposed construction. The following geotechnical considerations were identified on this project:

Special design and construction considerations will be required on this project due to the anticipated foundation loads, presence of existing fill materials and lower strength native soils at the site and proximity of the site to existing structure and utilities.

Existing fill materials were encountered in Borings 1, 3, and 4 to depths of about 5 to 6 feet below grade underlain by lower strength native soils (lean clay to silty clay) to depths of about 17½ to 19 feet. These soils are not suitable for support of shallow foundations based on the supplied loading conditions and the resulting higher than normal total and differential settlement.

The proposed addition can be supported on conventional spread footings on subgrade soils that have been improved with methods such as “Geopier® Impact™ Piers, Vibro- Replacement Stone Columns™, or other similar aggregate pier systems that extend through the existing fills and lower strength soils to suitable native soils.

The proposed addition can also be supported on a deep foundation system of drilled shafts extending into bedrock. Driven H-piles extending to competent bedrock can also be considered; however, vibration from pile driving will be an issue for safety of the adjacent structures and utilities.

Protection of neighboring structures, utilities and other improvements will need to be established, and will be the responsibility of the site grading and earthwork contractor(s). A performance specification for protection of the existing improvements is recommended.

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

Excavations extending below bearing level of the existing foundations and slabs 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.

The existing variable fill materials present at the site also pose a risk for grade supported slab movement and potential distress. As a minimum, we recommend at least 18 inches of properly compacted engineered fill be provided below the slabs.

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Most of the on-site soils consisting of inorganic lean clay and/or lean clay to silty clay appear suitable for use as structural fill; however, significant moisture conditioning should be anticipated if the on-site soils are used as fill.

Based on the results of the seismic survey, subsurface information obtained from this exploration, and the 2009 International Building Code (IBC), the seismic site classification for this site is C.

Construction of the foundations and earthwork on the project should be observed and evaluated by Terracon. The evaluation of earthwork should include observation and testing of engineered fill, subgrade preparation, foundation bearing materials, and other geotechnical conditions exposed during construction.

This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled GENERAL COMMENTS should be read for an understanding of the report limitations.

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GEOTECHNICAL ENGINEERING REPORT

PROPOSED DVA IC BUILDING # 2 RENOVATION/ADDITION

VA MEDICAL CENTER, IOWA CITY, IOWA

Terracon Project No. 06105660.01 June 22, 2011

1.0 INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed DVA IC Building # 2 Renovation/Addition at the VA Medical Center in Iowa City, Iowa. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

subsurface soil conditions groundwater conditions foundation design and construction floor slab design and construction site preparation and earthwork seismic site classification per IBC excavation considerations

The geotechnical engineering scope of work for this project included the advancement of four

(4) test borings to depths of about 24 to 28 feet below the existing grades where practical auger or sampler refusal in the underlying limestone bedrock was achieved. After achieving auger refusal, Borings 2 and 4 were advanced about 10 and 13 feet, respectively, using diamond bit core drilling procedures.

A Site Location Plan (Exhibit A-1), a Boring Location Plan (Exhibit A-2), the subsurface soil profile (Exhibit A-3) and boring logs (Exhibit A-4) are included in Appendix A of this report. The results of the laboratory testing performed on soil and rock samples obtained from the site during the field exploration are included on the attached boring logs. Descriptions of the field exploration and laboratory testing are included in their respective appendices.

Terracon had performed previous subsurface explorations for the existing Buildings 40 and 41 near this site in June 2003 (Laboratory Building, Terracon Project No. 06035646, report dated July 10, 2003), July 2005 (Research Building No. 41, Terracon Project No. 06055659, reports dated July 28, 2005 and December 13, 2005), and February 2009 (CSI Building Addition, Terracon Project No. 06095614, report dated February 27, 2009). The information obtained from these prior explorations was also used in developing the recommendations contained in this report.

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2.0 PROJECT INFORMATION

2.1 Project Description

ITEM DESCRIPTION

Site layout Refer to the Site Location Plan (Exhibit A-1) and Boring Location Plan (Exhibit A-2) in Appendix A.

Proposed Structures ■ Renovation/addition to the existing DVA IC Building # 2

Structure Type

■ The proposed addition will be a two-story, slab-on-grade structure with about 2,000 square feet in plan area.

Below Grade Areas ■ None

Finished floor elevation The finished floor elevation of the addition is expected to match with that of the existing facility.

Maximum loads (assumed)

The project is in planning stage at this time. The following loading conditions are based on the information provided.

■ Columns: 300 kips;

■ Walls: 5 klf;

■ Uniform Floor Loads: 100 psf.

Maximum allowable settlement (assumed)

■ Total: 1-inch;

■ Differential: 2/3 total settlement

Cut & fill requirements Minimal cut and fill thicknesses - within 2 feet (assumed)

2.2 Site Location and Description

ITEM DESCRIPTION

Location

■ The project site is located within the existing VA Medical Center premises in Iowa City, Iowa;

■ The project site is located adjacent to the existing 10-story main VA Hospital building.

Site topography

■ Existing structures, pavements, and utilities;

■ Based on supplied preliminary drawings, the existing grade elevations at the site vary between about 693½ and 695 feet.

3.0 SUBSURFACE CONDITIONS

3.1 USDA NRCS Soil Mapping

A review of the United States Department of Agriculture - Natural Resources Conservation Service (USDA NRCS) Soil Survey of Johnson County, Iowa indicates that Fayette silt loam is the primary soil type present at undisturbed locations of this site. The classifications provided are for the USDA

Responsive ■ Resourceful ■ Reliable 3 textural soil classification system for approximately the upper 60 inches of the soil profile.

According to the soil survey, these soil types present severe limitations for building construction activities due to steep slope and shrink-swell characteristics associated it.

3.2 Typical Subsurface Profile

Specific subsurface conditions encountered at the boring locations are indicated on the individual boring logs. Stratification boundaries on the boring logs represent the approximate location of changes in soil and rock types. In-situ, the transition between native materials may be gradual. Based on the results of the exploration, subsurface conditions on this site can be generalized as follows:

Description Approximate Depth to

Bottom of Stratum (feet)

Material Encountered Consistency/Den sity

Surficial 2 to 11 inches

7 to 8 inches of concrete over crushed limestone (Borings 1 and 2)

2 to 3 inches of Asphalt over crushed limestone (Borings 3 and 4)

N/A

Stratum 1 5 to 6

(Borings 1, 3, & 4)

Existing fill materials - primarily composed of lean clay with traces of crushed stone and asphalt

N/A

Stratum 2 17½ to 22 Lean clay to silty clay Soft to stiff

Stratum 3 26 to 27

(Borings 3 & 4) Lean to fat clay

Medium stiff to very stiff

Stratum 4 23½ to 27

(Borings 1 & 2) Sandy lean clay, trace gravel Stiff to very stiff

Stratum 51 24 to 41 Limestone

Highly to moderately weathered to auger/sampler refusal

1. Bottom of Borings.

Please review the attached boring logs for a detailed description of the conditions encountered at the individual boring locations.

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3.3 Groundwater Conditions

The borings were monitored for the presence and level of groundwater during drilling and sampling. At the time of drilling, groundwater level was observed in Borings 3 and 4 at depths of about 26 to 27 feet below the existing grades. Groundwater was not encountered in Borings 1 and 2 at that time. After completion of the drilling operations, the boreholes were backfilled with on-site soils and pavements patched, as applicable.

The water level observations at the time of drilling provide an approximate indication of the groundwater conditions existing on the site at the time the borings were drilled. The absence of groundwater in Boring 1 and 2 does not necessarily mean that they were terminated above the water table, since, for the lower permeability clay soils encountered in the borings, a longer time may be required to develop representative water level in the borehole. Longer-term observations using cased holes or piezometers, sealed from the influence of surface water, would be required for a better evaluation of the groundwater conditions on this site.

The Johnson County Soil Survey report was also reviewed for information relating to anticipated seasonally high groundwater levels. The primary soil type present in undisturbed areas of the site is reported to have apparent seasonal high groundwater levels at depths of 6½ feet or more below its natural grades.

Fluctuations of the groundwater levels will likely occur due to seasonal variations in the amount of rainfall, runoff, and other factors not evident at the time the borings were performed. In addition, perched water can develop within existing variable fills and/or high permeability soils overlying less permeable soils following periods of heavy or prolonged precipitation. Therefore, groundwater levels during construction or at other times in the future will be higher or lower than the levels indicated on the boring logs.

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

Based on the results of this exploration and the planned construction, it is our opinion that special design and construction measures will be required on this project due to:

anticipated foundation loads, presence of existing fill at the site, lower strength native soils, easily disturbed subgrades, demolition and construction adjacent to existing structures and utilities.

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Based on the subsurface data and conditions encountered in our borings and the anticipated foundation loads, total settlement on the order of 2 inches was computed. Thus, we recommend the proposed addition be supported on conventional spread footings following a soil improvement system of aggregate piers in order to control total and differential settlements.

The proposed addition can also be supported on drilled shafts extending into suitable bedrock.

Driven H-piles extending to competent bedrock can also be considered; however, vibration from pile driving will be an issue for the safety and integrity of the adjacent structures and utilities.

Existing fill soils were encountered in Borings 1, 3, and 4 to depths of about 5 to 6 feet below grade. Based on the test results and composition of the fill, it appears that the fill may not have been placed as engineered fill with consistent control of moisture and density. Lower strength native soils (soft clay) were also encountered in Boring 2 near the surface. Such soils should be anticipated at other unexplored locations also. It should be noted that structures supported over uncontrolled fills and lower strength soils would be at risk for greater than normal settlements and subsequent distress.

Provided the owner is willing to accept the risk and potential for adverse performance, in our opinion, the floor slabs for the addition could be supported over portions of the existing fill. As a minimum, we recommend at least 18 inches of properly compacted structural fill be present below the grade supported floor slabs.

New foundations placed adjacent to existing foundations and grade supported slabs may cause some additional settlement of the existing structures. Care should be taken to avoid undermining existing foundations and slabs. Excavations extending below bearing level of the existing foundations should be avoided. Due to the proximity of the existing structure, sheeting and shoring may be required where excavations below foundations and/or slabs of the existing structure are planned.

It should be noted that the site soils are susceptible to disturbance from construction activities, particularly if the soil has high natural moisture content or is wetted by surface water or seepage. Care should be taken during construction to minimize disturbance of the subgrade soils.

4.2 Site Preparation and Earthwork

4.2.1 Demolition Considerations

Demolition excavations will occur near or adjacent to existing structures and other improvements.

These excavations will likely extend through existing fills and lower strength native soils.

Demolition and/or site grading plans should include preparations for sheeting and bracing of excavations, dewatering, and monitoring of existing structures and improvements at the site.

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It is important that the demolition of the existing structures and other improvements be performed with close observation and testing. Any unsuitable fill and lower strength native materials encountered should also be removed at this time. Grade supported slabs may be supported on the new fill placed in the demolition excavations where existing grades are near final grades. The demolition contractor(s) should be aware of project requirements for backfilling so that removal of these fill materials and replacement under controlled conditions is not necessary to provide proper support of grade-supported slabs.

We anticipate that existing utility lines may extend through the proposed addition area. It has been our experience that poorly compacted backfill is commonly found in utility line trenches. Utility lines should be re-routed outside of the addition areas whenever feasible. Whether the utility lines are abandoned or not, any poorly compacted backfill above the lines should be removed and replaced.

4.2.2 Excavation Considerations

Any excavations necessary for removal of existing structures or utilities, as well as for the new construction, should be carefully planned and executed, especially adjacent to existing buildings, pavements, and utilities. These excavation activities have the potential to induce settlement and/or lateral movement of adjacent structures. The existing structures should be monitored before and during construction for any indications of settlement and/or lateral movement. A precondition survey of neighboring improvements prior to construction is recommended. Construction activities should be terminated and Terracon should be contacted if any movement of the existing structures adjacent to construction area is observed.

Proper shoring and bracing of excavations to prevent disturbance and/or undermining of the adjacent structures, utilities, and other improvements will be the responsibility of the demolition, site grading and foundation contractor(s). We recommend that a performance specification be developed that includes such provisions.

All excavations should comply with the requirements of OSHA 29CFR, Part 1926, Subpart P, "Excavations" and its appendices, as well as other applicable codes. This document states that the excavation safety is the responsibility of the contractor. Reference to this OSHA requirement should be included in the project specifications. Slope heights, slope inclinations and/or excavation depths should in no case exceed those specified in local, state or federal safety regulations, including current OSHA excavation and trench safety standards. If any excavations extend to a depth greater than 20 feet, according to OSHA regulations, side slopes and/or bracing must be designed by a professional engineer. Flatter slopes than shoes required by OSHA could be required in areas where existing fills, lower strength soils, and/or groundwater seepage are present.

4.2.3 Site Preparation

Surficial materials, debris from removal of existing pavement and utilities, and any otherwise unsuitable materials should be removed from the construction area. Wet or dry material should

Responsive ■ Resourceful ■ Reliable 7 either be removed or moisture conditioned and recompacted. Soft, dry and/or lower strength soils should be either removed or compacted in place prior to placing new fill.

After rough grade has been established, wherever possible, the exposed subgrade should be proofrolled by the contractor and test probed by Terracon. Proofrolling on clay subgrades could be accomplished by using heavy, rubber-tired construction equipment or a tandem axle dump truck with a gross weight of about 10 tons in floor slab areas. In addition, the subgrade should be scarified, moisture conditioned, and recompacted. This surficial compaction and proofroll would help to provide a stable base for the compaction of new structural fill, and delineates low density, soft, or disturbed areas that may exist below the subgrade level. Soft or loose areas should be undercut, moisture conditioned, and recompacted or replaced with approved structural fill. Subgrade conditions should be observed by Terracon personnel during construction.

Corrective measures will probably be required to increase subgrade stability during subgrade preparation. The owner should budget for additional costs to provide the required corrective measures. Based on our experience in soils types encountered in the borings, crushed stone thicknesses on the order of 1 to 2 feet could be required to stabilize subgrade soils. A geotextile stabilization material could also be placed below the crushed stone to help stabilize the subgrade soils. As an alternative, the unstable subgrade soils could be undercut, scarified on-site, and compacted with moisture and density control in maximum 9-inch loose lifts up to final subgrade elevation to provide a uniform thickness of well-compacted material. Chemical stabilization using Class C flyash, Portland cement or hydrated lime could also be considered.

Upon completion of grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs. Construction traffic over the completed subgrade should be avoided to the extent practical. 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 construction.

4.2.4 Fill Types and Compaction

New fills placed for the project should be low plasticity cohesive soil or granular soil. Fill placed in confined excavations such as utility trenches should consist of relatively clean and well-graded granular material. This should provide for greater ease of placement and compaction in confined areas where larger compaction equipment cannot be operated. The use of granular fill in these isolated and potentially deeper excavations would reduce the potential for differential settlement for the structure components.

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Structural fill should meet the following material property requirements:

Fill Type 1 USCS Classification Acceptable Location for Placement

Low Plasticity Cohesive2

CL, CL-ML General site grading fill

Granular

GW, GP, GM, GC

SW, SP, SM, SC

General site grading fill, below foundations and slabs

Unsuitable MH, OL, OH, PT Green (non-structural) locations

On-Site Soils CL, CL-ML Most of the site soils, as encountered in the borings, generally appear suitable for reuse as structural fill.2, 3

1. Structural fill should consist of approved materials that are free of organic matter and debris.

Frozen material should not be used, and fill should not be placed on a frozen subgrade. A sample of each material type should be submitted to the geotechnical engineer for evaluation prior to use on this project.

2. Low plasticity cohesive soils (CL, CL-ML) would have a liquid limit of 45 or less and a plasticity index of 23 or less.

3. Some sorting will be required in order to remove any unsuitable materials and debris from the existing fills.

4.2.5 Compaction Requirements

Moisture conditioning of the site soils will likely be required if they are used as engineered fill.

Appropriate laboratory tests, including Atterberg Limits for cohesive soils, and Standard Proctor (ASTM D698) moisture-density relationship tests should be performed on proposed fill materials prior to their use as engineered fill. Further evaluation of any on-site soils or off-site fill materials should be performed by Terracon prior to their use in compacted fill sections.

Recommended degree of compaction and moisture content criteria for engineered fill materials are as follows:

Material Type and Location

Per the Standard Proctor Test (ASTM D 698)

Minimum Compaction Requirement (%)1

Range of Moisture Contents for Compaction1

Minimum Maximum

Low Plasticity Cohesive

Below foundations 98 -2% +3%

Above foundations and below slabs

95 -2% +3%

Granular2,3

Below foundations 98 -3% +3%

Above foundations and below slabs

95 -3% +3%

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Material Type and Location

Per the Standard Proctor Test (ASTM D 698)

Minimum Compaction Requirement (%)1

Range of Moisture Contents for Compaction1

Minimum Maximum

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

Should the results of the in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the test should be reworked and retested as required until the specified moisture and compaction requirements are achieved.

2. 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 as per ASTM D 4253-00 and D 4254-00.

3. Specifically, moisture levels should be maintained at levels satisfactory for compaction to be achieved without the granular fill material bulking during placement or pumping when proofrolled.

We recommend that fill be placed and compacted on stable subgrades in lifts of 9 inches or less in loose thickness when heavy, self-propelled compaction equipment is used. Lift thickness should be reduced to 4 inches in loose thickness when hand equipment (e.g., jumping jack, vibratory plate compactor, etc.) is used. A vibrating smooth drum compactor should not be used on clay soils. All new fill placement and compaction should be observed and tested by Terracon personnel.

4.2.6 Grading and Drainage

Final surrounding grades should be sloped away from the addition on all sides. In addition, roof drainage should be collected by a system of gutters and downspouts and transmitted by pipe to the storm water drainage system or discharged a minimum of 5 feet away from the addition. As an alternative, splash blocks may be used as long as the ground surface is paved and slopes away from the addition.

4.3 Spread Footings/Intermediate Foundation System

The proposed addition can be supported on conventional spread footings on subgrade soils that have been improved with intermediate foundation systems such as “Geopier® Impact™ Piers, Vibro-Replacement Stone Columns™, or other similar aggregate pier systems that extend through the existing fills and lower strength soils to suitable native soils.

4.3.1 Soil Improvement Methods

The above mentioned soil improvement methods are proprietary systems and are designed by licensed contractors who could provide further information regarding these foundation options.

Typically, foundations supported by aggregate pier system can be designed with net allowable bearing pressures ranging from 4,000 to 6,000 psf. Structures supported on aggregate piers would experience somewhat larger total and differential settlements than those supported on

Responsive ■ Resourceful ■ Reliable 10 deep foundations. Due to the specialty of these soil improvement methods, we recommend that a performance specification be used for the system. We would be pleased to provide additional information upon request.

4.3.2 Spread Footings Design Recommendations

DESCRIPTION VALUE

Foundation bearing material Site soils improved by intermediate foundation system or aggregate piers.

Net allowable bearing pressure 4,000 to 6,000 psf on aggregate piers1

Minimum dimensions Columns: 30 inches Walls: 16 inches

Minimum embedment depth below finished grade

42 inches - for perimeter footings and other footings in unheated areas

24 inches - for interior footings in heated areas

Total estimated settlement 1 inch

Estimated differential settlement ⅔ of total settlement

1. Net allowable bearing pressure to be provided by the aggregate pier designer.

Finished grade is defined as the lowest adjacent grade within five feet of the foundation for perimeter (or exterior) footings and finished floor level for interior footings. The allowable foundation bearing pressures apply to dead loads plus design live load conditions. The design bearing pressure may be increased by one-third when considering total loads that include wind or seismic conditions. The weight of the foundation concrete below grade may be neglected in dead load computations.

Footings, foundation walls, and masonry walls (if any) should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities in masonry walls (if any) is recommended.

The soil conditions at and below the foundation bearing depths should be observed and thoroughly tested by Terracon to confirm that the bearing soils are suitable for support of the foundations. The excavations should be probed or otherwise sampled at each isolated spread footing and at regular intervals along continuous footings.

4.4 Deep Foundation

The proposed addition can be supported on a deep foundation system of either drilled shafts extending into the underlying limestone bedrock or driven H-piles driven to bedrock.

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4.4.1 Drilled Shaft Foundations

The proposed addition can be supported on a deep foundation system of drilled shafts extending into bedrock. Limestone bedrock was encountered in the borings at depths of about 23½ to 27 feet below the existing grades. Based on the test results on the rock core obtained from Borings 2 and 4, the underlying bedrock material can be classified as moderately hard to hard formation with a RQD values ranging from about 14% to 83%.

The design parameters provided in the DRILLED SHAFT DESIGN SUMMARY table should be used for the design of drilled shaft foundations. The values presented for allowable side friction include a factor of safety of approximately 2, and are for uplift loads only. The values presented for allowable end bearing include a factor of safety of approximately 3. Side friction should be ignored within the frost zone and for compressive loading. Drilled shafts should be spaced at least 3 shaft diameters apart (center-to-center) if side friction is used for uplift loads.

DRILLED SHAFT DESIGN SUMMARY

Material Type Allowable Skin

Friction1 (psf)

Allowable End Bearing Pressure2

(psf)

Frost Zone, 0 to 3½ feet - - - -

Native Clay/Silt 150 - -

Highly Weathered Bedrock 750 - - Moderately Weathered Bedrock 1,500 80,000

1. For uplift loading only.

2. Shafts should extend at least one diameter into moderately weathered bedrock for end bearing to be considered.

Tensile reinforcement should extend to the bottom of shafts subjected to uplift loading. Buoyant unit weights of the soil and concrete should be used in the calculations below the highest anticipated groundwater elevation.

We recommend a minimum shaft diameter of 30 inches be used in order to permit cleaning and testing of the shaft bottoms. Drilled shafts should have a minimum center-to-center spacing of 3 diameters. Closer spacing may require a reduction in axial load capacity. Axial capacity reduction can be determined by comparing the allowable axial capacity determined from the sum of individual shafts in a group versus the capacity calculated using the perimeter of the shaft group acting as a unit. The lesser of the two capacities should be used in design.

Post-construction settlements of drilled shafts designed and constructed as described in this report are estimated to range from about ½ to ¾ inch. Differential settlement between individual shafts can typically be estimated at ½ to ⅔ the total settlement.

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The use of temporary steel casing and/or slurry drilling procedures is recommended at this site during drilled shaft construction in order to prevent collapse of the sidewalls within existing fills and lower strength soils and to control groundwater seepage. Difficult drilling conditions should be expected in the weathered bedrock, and the potential for hard bedrock drilling conditions should also be anticipated.

Use of a telescoping casing arrangement can be considered to avoid handling long casing lengths. The lower casing, in particular, should be of sufficient length and stiffness and have an appropriate cutting edge to allow it to be firmly seated into the bedrock in order to seal out groundwater. If possible, excess water should be evacuated from the casing in order to place concrete in the "dry”.

Care should be taken so that the sides and bottom of the excavation are not disturbed during construction. The bottom of the shaft excavation should be free of loose material before concrete placement. Concrete should be placed as soon as possible after the foundation excavation is completed to reduce the potential disturbance of the bearing surface.

Concrete for "dry" drilled shaft construction should have a slump of about 5 to 7 inches.

Concrete should be directed into the shaft utilizing a centering chute. Concrete for "wet" shaft construction would require higher slump concrete.

While withdrawing casing, care should be exercised to maintain concrete inside the casing at a sufficient level to resist earth and hydrostatic pressures acting on the casing exterior. Arching of the concrete, loss of seal and other problems can occur during casing removal and result in contamination of the drilled shaft. These conditions should be considered during the design and construction phases. Placement of loose soil backfill should not be permitted around the casing prior to removal.

Terracon should be retained to observe all drilled shaft excavations to evaluate the suitability of the bearing materials and to verify that conditions in the drilled shaft excavations are consistent with those encountered in the test borings. If unsuitable materials are encountered at planned depths, it may be necessary to deepen the shaft.

4.4.2 Driven H-Piles Design Considerations

H-piles driven to practical refusal in the limestone bedrock/shale could be used for support of the structure, and would derive their compressive load capacities from end bearing. Allowable design compressive load capacities of driven steel piles could be calculated by taking the allowable steel working stress of 12 kips per square inch (ksi) for piles driven to refusal times the cross-sectional steel area. For example, an HP 10x42 pile could be used for this project and an allowable design load of about 148 kips could be used for piles driven to practical refusal

Responsive ■ Resourceful ■ Reliable 13 in the underlying bedrock. Typical rock penetration for driven piles will vary based on pile size and location across the building area.

Pile caps and grade beams should extend at least 4 feet below lowest adjacent grade to avoid uplift due to frost. Individual pile settlement should be on the order of 1/2 –inch when designed according to the criteria presented in this report. Differential settlement between individual piles can typically be estimated at ½ to 2/3 the total settlement.

The contractor should select a driving hammer and cushion combination which is capable of installing the selected piling without overstressing the pile material. The hammer should have a rated energy in foot-pounds at least equal to 15 percent of the design compressive load capacity in pounds. The contractor should submit the pile driving plan and the pile hammer – cushion combination to the engineer for evaluation of the driving stresses in advance of pile installation. During driving a maximum of 12 blows per inch is recommended to reduce the potential of damage to the piles.

If practical refusal is experienced above the anticipated rock surface elevation, then the pile may be on a boulder or other obstruction and a replacement pile should be driven. If this occurs, the situation should be evaluated by Terracon during the pile driving operations.

Difficult driving could also be encountered in the existing random fill and weathered rock.

Consideration should be given to using protective points and/or flange stiffening if H-piles are used. The contractor should be prepared to cut or splice piles, as necessary. Splicing of piles should be in accordance with specifications provided by the project structural engineer.

Pile driving conditions, hammer efficiency, and stress on the pile during driving could be better evaluated during installation using a Pile Driving Analyzer (PDA). A Terracon representative should observe pile driving operations. Each pile should be observed and checked for buckling, crimping and alignment in addition to recording penetration resistance, depth of embedment, and general pile driving operations.

The existing facility (structures and subsurface utilities) should be observed prior to pile installation to document their condition. These structures should also be observed during pile installation for any indications of movement. Pile driving should be stopped and Terracon contacted if movement or cracking of the existing structures is observed. Monitoring vibration levels during pile driving should be considered. It should be understood that although vibrations from pile driving may be below levels that will cause structural damage, they may be felt by occupants of the adjacent buildings. The potential impact of driving piles at this site should be considered when evaluating this alternative. Terracon is able to perform vibration monitoring upon request.

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4.4.3 Deep Foundations Lateral Earth Pressures

The drilled shafts and H-piles can be designed to resist lateral loads using the design parameters provided in the following table. Passive resistance for perimeter foundation elements beneath unheated areas should be ignored at least 3½ feet below the lowest adjacent finished grade for frost protection.

The material properties presented below should be used for estimating the lateral capacity of fixed or free-headed shafts/piles. These values represent the material properties present in the site vicinity and have been assigned for use in a computer program for lateral load analysis such as LPILE. These values are representative of the materials encountered in the borings. Since deflection or a service limit criterion will most likely control lateral capacity design, no safety/resistance factor is included with these parameters.

CRITERIA FOR LATERAL SHAFT/PILE CAPACITIES

Material Property Recommended Value

Material

Native lean clay, lean clay to silty clay, and lean to fat clay

Native sandy lean clay, trace gravel (glacial till)

Highly Weathered

Bedrock

Moderately Weathered

Bedrock

Moist Unit Weight1 (pcf) 115 125 155 165

Saturated Unit Weight1

(pcf) 120 130 155 165

Submerged Unit Weight1

(pcf) 60 70 95 105

Cohesion2,3 (psf) 5003 2,0003 20,000 350,000

Internal Friction Angle2,4

(degrees) 244 264 - - - -

E50 (strain) 0.01 - 0.02 0.005 - 0.007 0.004 0.002

Soil Modulus kh – Static4 (pci) 30 - 100 500 - 1,000 - - - -

1. Submerged unit weight should be used below the expected water table.

2. Should be ignored within frost depth.

3. Ignore cohesion in clay and silty clay soils for “drained” conditions.

4. “Drained” conditions only for clay and silt soils.

5. Soil modulus (kh) for static loading; for cyclical loading of clays, values should be no more than 40% of the values shown.

Group action for lateral resistance of shafts/piles should be taken into account when spacing is less than six (6) diameters (center to center), and design parameters for allowable passive resistance in the direction of the load should be reduced in accordance with the following table.

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Shaft/Pile Spacing (Diameters) Reduction Factors

6D 1.0

4D 0.85

3D 0.65

The shafts/piles should be spaced at least three diameters apart (center-to-center) if they will be used to resist lateral loads. Pile caps and/or grade beams could be subject to uplift loading due to frost action; thus, perimeter foundation elements beneath unheated areas should extend at least 3½ feet below the lowest adjacent finished grade for frost protection.

It should be noted that the load capacities provided herein are based on the stresses induced in the supporting soil and rock strata. The structural capacity of the shafts/piles should be checked to assure that they can safely accommodate the combined stresses induced by axial and lateral forces. Lateral deflections of shafts/piles should be evaluated using an appropriate analysis method, and will depend upon the shaft/pile’s cross section area, length, configuration, stiffness and “fixed head” or “free head” condition. We can provide additional analyses and estimates of lateral deflections for specific loading conditions upon request.

4.5 Construction Adjacent to Existing Building

Differential settlement between the addition and the adjacent/existing structure is expected to approach the magnitude of the total settlement of the addition. Expansion joints should be provided between the existing building and the proposed addition to accommodate differential movements between the two structures. Underground piping between the two structures should be designed with flexible couplings and utility knockouts in foundation walls should be oversized, so minor deflections in alignment do not result in breakage or distress. Care should be taken during any excavation adjacent to existing foundations, so as not to disturb any existing foundation bearing soils.

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

Support of the addition on existing foundations is not expected, but if increasing the loads on existing foundations is considered, then additional building settlements could occur. The structural capacity of the existing foundations should be evaluated by a licensed structural engineer where any increase in loading is planned.

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4.6 Seismic Considerations

The International Building Code (IBC) requires structural design to be in accordance with the appropriate site class definition for soil profile type. Based upon the Site Class Definitions in Table 1615.1.1 of the 2006 International Building Code, and the average shear wave velocity of 1,800 ft/s derived from our seismic survey data, Terracon recommends a Class C seismic site classification for design.

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

2006 International Building Code Site Classification (IBC) 1

C

Site Latitude N 41° 39.81’

Site Longitude W 91° 32.89’

1 Note: In general accordance with the 2006 International Building Code, Table 1615.1.1.

4.7 Floor Slabs

We recommend all the existing variable fill materials be removed and replaced with properly compacted, structural fill. However, if the owner is willing to accept the risk of possible floor slab distress as a result of supporting the floor slabs on existing variable fill materials, it may be possible to support the floor slabs over a portion of these materials. As a minimum, we recommend at least 18 inches of properly compacted low plasticity material be present below the floor slabs where existing fill materials are present.

4.7.1 Design Recommendations

Floor grade slab Slab-on-grade Portland cement concrete

Grade slab support

Minimum 6 inches of well-graded (less than 6% passing the U.S. No. 200 sieve) crushed aggregate compacted to at least 95% of ASTM D 698

At least 18 inches of new structural fill should be present below floor slabs where portions of existing fill materials are left in place for floor slab support

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Unheated areas subject to frost Minimum of 3½ feet of clean (less than 6% passing the U.S.

No. 200 sieve) material below slabs.

Modulus of subgrade reaction 100 pounds per square inch per inch (psi/in). The modulus value was obtained based on our experience with similar subgrade conditions.

It should be noted that settlements of floor slabs supported on existing fill materials cannot be accurately predicted, but could be larger than normal and result in some cracking. Frequent control joints are recommended in the floor slabs where existing fill materials are present to help control any cracking. A higher than normal percentage of steel reinforcement should be considered in floor slabs to provide additional strength and help control crack displacement.

Additional replacement of existing fill materials below the slab areas with new structural fill could also be considered to help reduce the risk and to provide a more uniform bearing surface. Any unsuitable subgrade materials observed during construction should be overexcavated and replaced with new structural fill.

Slabs-on-grade should be isolated from structures and utilities to allow for their 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.

4.7.2 Construction Considerations

The floor slab subgrade should be prepared in accordance with Section 4.2 (Site Preparation and Earthwork) of this report. Care should be taken to maintain the subgrade moisture content, prior to construction of the floor slabs. If the subgrade should become desiccated, the affected material should be removed or these materials should be scarified, moistened, and recompacted prior to floor slab placement. In addition, we recommend the placement of the new fills for floor slab support be placed as far in advance of slab construction as possible to allow settlement of the underlying soils from the weight of the new structural fill, and thereby, reduce post-construction total and differential settlements.

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 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Where floor slabs are tied to perimeter walls or turn-down slabs to meet structural or other construction objectives, our experience indicates that any differential movement between the walls and slabs will likely be observed in adjacent slab expansion joints or floor slab cracks that

Responsive ■ Resourceful ■ Reliable 18 occur beyond the length of the structural dowels. The structural engineer should account for this potential differential settlement through use of sufficient control joints, appropriate reinforcing or other means.

Where practical, we recommend “early-entry” cutting of crack-control joints in floor slabs.

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

4.8 Frost Considerations

The site soils are frost susceptible and small amounts of water can affect the performance of the slabs on-grade. Exterior slabs should be anticipated to heave during winter months. If frost action needs to be eliminated in critical areas, we recommend the use of non-frost susceptible structural or structural slabs (e.g., structural stoops in front of outer doors). Placement of non-frost susceptible material in large areas may not be feasible; however, the following recommendations are provided to help reduce potential frost heave:

Providing surface…