Attachment 07 - GeoTech Report - Ambulance Garage.pdf

Report Cover Page

I hereby certify that this engineering document was prepared by me or under my direct personal supervision and that I am a duly licensed Professional Engineer under the laws of the State of Iowa.

February 17, 2023 Mustafa F. Qaisi, P.E. Date

My license renewal date is December 31, 2024.

Ambulance Garage Geotechnical Engineering Report

February 17, 2023 | Terracon Project No. 06225122.01

Prepared for:

Anderson Engineering of Minnesota, L.L.C.

13605 1st Avenue N, Suite 100 Plymouth, MN 55441

2640 12th Street SW Cedar Rapids, Iowa 52404

P (319) 366-8321 Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

February 17, 2023

Anderson Engineering of Minnesota, L.L.C.

13605 1st Avenue N, Suite 100 Plymouth, MN 55441

Attn: Mr. Tom Olesak, NCARB, LEED AP E: tolesak@ae-mn.com

Re: Geotechnical Engineering Report Ambulance Garage 601 Highway 6 Iowa City, Iowa Terracon Project No. 06225122.01

Dear Mr. Olesak:

We have completed subsurface exploration and geotechnical engineering services for the referenced project in general accordance with Terracon Proposal No. P06225122, dated July 29, 2022. This report presents the findings of the subsurface exploration and provides geotechnical recommendations regarding earthwork and the design and construction of foundations, floor slabs, and pavements 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

Mustafa F. Qaisi, P.E. Justin D. Widdel, P.E.

Project Engineer Department Manager

Geotechnical Engineering Report Ambulance Garage | Iowa City, Iowa February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials i

Table of Contents Introduction Project Description Site Conditions Geotechnical Characterization Seismic Site Class Geotechnical Overview Earthwork

Site Preparation Soil Stabilization Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Micropile Foundations Micropile Design Parameters Micropile Installation

Helical Piers Floor Slabs

Floor Slab Design Parameters Floor Slab Construction Considerations

Pavements General Pavement Comments Pavement Subgrade Preparation Minimum Pavement Section Thicknesses Pavement Drainage Pavement Design and Construction Considerations Pavement Maintenance

Frost Considerations General Comments

Figures GeoModel

Attachments

Exploration and Testing Procedures Site Location and Exploration Plan Exploration and Laboratory Results

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials ii

Supporting Information

Note: This report was originally delivered in a web-based format. Blue 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 will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

Refer to each individual Attachment for a listing of contents.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical Engineering services performed for the proposed Ambulance Garage to be located at the VA Iowa City Healthcare facility at 601 Highway 6 in in Iowa City, Iowa. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Seismic site classification per IBC

■ Site preparation and earthwork

■ Building foundation design and construction

■ Floor slab design and construction

■ Pavement design and construction

■ Frost considerations

The geotechnical engineering Scope of Services for this project included the advancement of two soil borings, laboratory testing, engineering analysis, and preparation of this report. The following previous Terracon projects were reviewed in preparation of the recommendations provided in this report:

■ Bedrock Probes performed for VA PACT Expansion (Terracon Project No.

06155627).

■ Geotechnical Engineering Report for VA Medical Center Addition (PACT) (Terracon Project No. 06105663.01 dated August 8, 2011).

Drawings showing the site and the current and previous boring/bedrock probe locations are shown on the Site Location and Exploration Plan, respectively. The results of the field and laboratory testing performed are included on the boring logs in the Exploration and Laboratory Results section.

Project Description

Item Description

Information Provided

The Concept Floor Plan dated 12/9/2022 was provided by Anderson Engineering with the requested boring locations via email on December 16, 2022. A schematic Grading and Erosion Control Plan was also provided via email on January 26, 2023.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 2

Item Description

Project Description

A 1,500 square foot ambulance garage is planned on the west of building 1 at the Iowa City VA Hospital

Building Construction

The building construction will consist of a single story, slab on grade building with precast walls.

Finished Floor Elevation

710.80 Feet

Maximum Loads

■ Columns: 50 kips

■ Walls: 2 kips per linear foot (klf)

■ Slabs: 100 pounds per square foot (psf)

Grading

■ Cuts of about 2 feet or less

■ Fills of about 1 foot or less

Below-Grade Structures

None

Retaining Walls None anticipated

Pavements New PCC drives located west, north and south of the proposed Ambulance Garage.

Site Conditions

Item Description

Project Location

■ The project is located at 601 Highway 6 in Iowa City, Iowa.

■ Latitude/Longitude (approximate) 41.6636, -91.5494

■ See Site Location

Existing Improvements

The Ambulance Garage is planned to be placed west of the existing VA Hospital building which has a basement level that extends about 13 feet below the first floor level of the Hospital.

We understand the adjacent building is supported on drilled shaft foundations.

Current Ground Cover

PCC and gravel surfacing

Topography Existing grades generally decrease to the south with ground surface elevations within the pavements and the Ambulance Garage area ranging from about 710 to 700 feet.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 3

Geotechnical Characterization

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of the site. Conditions observed at each exploration point are indicated on the individual logs. The individual logs can be found in the Exploration and Laboratory Results and the GeoModel can be found in the Figures attachment of this report.

As part of our analyses, we identified the following model layers within the subsurface profile. For a more detailed view of the model layer depths at each boring location, refer to the GeoModel.

Model Layer

Layer Name General Description

1 Surficial Crushed Limestone

2 Fill Poorly Graded Sand, Sandy Silt, and Lean Clay with varying amounts of sand and gravel

3 Upper Clay Lean Clay with varying amounts of sand

4 Lower Clay Fat Clay with varying amounts of sand 5 Sand Sand with varying amounts of silt and clay

6 Bedrock Completely to moderately weathered limestone

The boreholes were observed for the presence and level of groundwater while drilling/sampling prior to initiating mud-rotary drilling techniques at about 9 feet below ground surface. The borings were observed for the presence of groundwater during drilling and sampling. Groundwater was not encountered in the borings performed for this project prior to mud-rotary drilling. Based on our experience with soil borings and drilled shaft excavations on the western portion of the VA site, groundwater is typically encountered in the “Lower Clay” and “Sand” model layers indicated in the table above or sometimes not encountered above the bedrock layer. When observed in historic borings in the project vicinity, groundwater was observed at elevations ranging from about 681.5 to 685.5 feet.

Although the groundwater table is anticipated to be deeper in the soil profile, perched water conditions could be encountered in the upper existing fill layer and/or sand seams within the clay strata.

The water level observations are noted on the boring logs in Exploration and Laboratory Results. Groundwater conditions may be different at the time of construction.

Groundwater conditions may change because of seasonal variations in rainfall, runoff, and other conditions not apparent at the time of drilling. Longer-term observations using cased holes or piezometers, sealed from the influence of surface water, would be

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 4 required for a better evaluation of the groundwater conditions on this site. Long-term groundwater monitoring was outside the scope of services for this project.

Seismic Site Class

The seismic design requirements for buildings and other structures are based on Seismic Design Category. Site Classification is required to determine the Seismic Design Category for a structure. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of ASCE 7 and the International Building Code (IBC). Based on the soil properties observed at the site and as described on the exploration logs and results, as well as shear wave velocity survey data obtained for the PACT VA Medical Center Addition (Terracon Project No. 06105663), our professional opinion is for that a Seismic Site Classification of C be considered for the project. Subsurface explorations at this site were extended to a maximum depth of 45 feet. The site properties below the boring depth to 100 feet were estimated based on our experience and knowledge of geologic conditions of the general area and previous seismic site survey performed in the vicinity. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

Geotechnical Overview

Based on the subsurface conditions on the site, the geotechnical considerations for the Ambulance Garage include the potential for existing fill and lower strength native soils, as well as excavation/construction adjacent to existing building and utilities. Further details are provided below.

Existing fill was in encountered in the borings to depths of about 7 to 8.5 feet below existing grade, and the existing fill is anticipated to extend to deeper depths closer to the existing building associated with backfill of the existing basement level. The existing fill material consisted of crushed limestone, lean clay with varying amounts of sand and gravel, as well as poorly graded sand. Based on the variability of the material composition, SPT N-values ranging from 6 to 17 blows per foot, and varying moisture contents, the existing fill encountered in the borings does not appear to have been placed in a controlled manner with uniform compactive effort. Support of floor slabs and pavements on or above existing fill soils is discussed in this report. However, even with the recommended construction testing services, there is an inherent risk for the owner that compressible fill or unsuitable material within or buried by the fill will not be discovered. This risk of unforeseen conditions cannot be eliminated without completely

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 5 removing the existing fill, but can be reduced by performing additional testing and evaluation as discussed in the Earthwork section.

Shallow foundations should extend through any existing fill and bear directly on suitable native soil or compacted fill extending to suitable native soil. As discussed on a conference call with the Architect and Structural Engineer on February 6, 2023, overexcavations to remove existing fill and support the Ambulance Garage foundations at adjacent basement bearing elevation (i.e., use of stepped footings) could be challenging due to relatively deep excavations required and other constraints such existing utilities, adjacent structures, groundwater, and the potential for shoring/bracing of the excavations. In addition, the native soils at the base of the overexcavations are anticipated to consist of soft lean clay and overexcavation and crushed stone backfill would be required to improve the bearing soils of the proposed Ambulance Garage foundations.

As discussed on the conference call, an alternative to conventional shallow foundations is an intermediate foundation system such as helical piers that extend through the existing fill and lower strength native soils and bear on suitable native soil Micropiles extending to bedrock could also be considered. Design and construction recommendations for the micropiles and helical piers are provided in the Micropile Foundations and Helical Pier sections.

The recommendations contained in this report are based upon the results of field and laboratory testing (presented in the Exploration and Laboratory Results), engineering analyses, and our current understanding of the proposed project. The General Comments section provides an understanding of the report limitations.

Earthwork

Earthwork is anticipated to include clearing and grubbing, excavations, and fill placement. The following sections provide recommendations for use in the preparation of specifications for the work. Recommendations include critical quality criteria, as necessary, to render the site in the state considered in our geotechnical engineering evaluation for foundations, floor slabs, and pavements.

Site Preparation

Existing vegetation, topsoil, and root mats should be removed from the construction areas. Excessively wet or dry and desiccated material should either be removed, or moisture conditioned and compacted. Soft and/or low-density soil should be removed or compacted in place prior to placing new fill. Subgrade conditions should be observed by Terracon during construction.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 6

We recommend the proposed floor slabs and pavements be supported on at least 18 inches of low plasticity cohesive or approved granular structural fill where existing fill soils are encountered. We anticipate this minimum thickness of new structural fill will help provide a more predictable, uniform subgrade support.

After performing undercuts to remove unsuitable materials and to provide the minimum amount of new structural fill below the floor slab and pavements, the exposed subgrade should be proofrolled by the contractor and tested by Terracon. Obviously unstable subgrades should not be proofrolled to reduce disturbance of the subgrade soils, until after these soils have been stabilized. Proofrolling could be accomplished by using heavy, rubber-tired construction equipment or a tandem-axle dump truck (loaded to a gross weight of about 25 tons). This surficial proofroll would help to provide a stable base for the compaction of new structural fill, and delineate low density, soft, or disturbed areas that may exist below subgrade level. Soft, low density, and disturbed areas should be scarified, moisture conditioned, and recompacted or replaced with approved structural fill.

All exposed areas which will receive fill, once properly cleared and benched where necessary, should be scarified to a minimum depth of 10 inches, moisture conditioned as necessary, and compacted per the compaction requirements in this report.

Soil Stabilization

The site soils could become unstable with typical earthwork and construction traffic, especially after precipitation events. Effective site drainage should be completed early in the construction sequence and maintained after construction to avoid potential strength and/or stability issues.

Corrective measures may be required to increase subgrade stability during subgrade preparation. The designer/owner should budget for additional costs to provide the required corrective measures. Based on our experience in soils of these types, crushed stone working mat 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.

Incorporation of hydrated lime, portland cement, or Class C fly ash could be considered for chemical stabilization and/or reduce the plasticity of inorganic soils. Chemical modification should be performed by a pre-qualified contractor having experience with successfully stabilizing subgrades in the project area on similar sized projects with similar soil conditions.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 7

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of grade-supported slabs and pavements.

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 slab and pavement construction.

Fill Material Types

Fill placed in confined excavations 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 the isolated and potentially deeper excavations would reduce the potential for differential settlement for building components.

Care should also be taken to avoid inter-layering of granular soils and clay soils during fill placement. This could result in perched water conditions and lead to development of frost lenses and loss of subgrade strength both during and after construction. If granular soils are placed above clay soils, we suggest the subgrades have significant slope to drain/subdrain locations or that trench subdrains be installed.

Structural fill should meet the following material property requirements:

Fill Type 1 USCS Classification Acceptable Locations for

Placement

Low plasticity cohesive 2

CL-ML, CL

(LL ≤ 45 and PI ≤ 23) General site grading fill

Granular 3 GW, GP, GM, GC

SW, SP, SM, SC

General site grading fill

Unsuitable

CL/CH, CH, ML, MH, OL,

OH, PT

Green (non-structural) locations

On-site Soils

CL, SP, SC, CH

(GW or GP) 4

Per USCS classifications in this table.

On-site soils generally appear suitable for reuse as structural.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 8

Fill Type 1 USCS Classification Acceptable Locations for

Placement

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 site.

2. Low plasticity cohesive soil has a liquid limit less than or equal to 45 and a plasticity index less than or equal to 23.

3. Specific material requirements will need to be satisfied based on intended use and should be approved by the geotechnical engineer.

4. Approximately 1 to 4 feet of crushed limestone was encountered at the surface of Borings B-201 and B-204, respectively. Additional evaluation of the crushed stone gradation and fines content would be required to determine the USCS classification.

Consideration could be given to undercutting the crushed limestone layer and stockpiling it for reuse as structural fill pending further evaluation and acceptance of this material for reuse by Terracon during construction.

Appropriate laboratory tests, including Atterberg Limits for cohesive soils, organic content tests for dark colored soils and/or those that exhibit a noticeable odor, and standard Proctor (ASTM D698) moisture-density relationship tests should be performed on proposed fill materials prior to use as structural 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.

Fill Placement and Compaction Requirements

New structural fill should meet the compaction requirements provided in the table below.

Item Structural Fill

Maximum Lift Thickness

9 inches or less in loose thickness when heavy, self-propelled compaction equipment is used

4 inches in loose thickness when hand-guided equipment (i.e.

jumping jack or plate compactor) is used; may be increased to 6 inches if the fill is a granular material

Minimum Compaction

Requirements 1,2

98% of max. below foundations and within the upper foot of pavement and interior slab subgrades that will be exposed to Ambulance traffic.

95% of max. below floor slabs (not exposed to Ambulance traffic), and below one foot of pavement subgrade

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 9

Item Structural Fill

Water Content

Range 1

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

Granular: typically at -3% to +3% of optimum; sufficient to achieve compaction without pumping or bulking when proofrolled

1. Maximum density and optimum water content as determined by the standard Proctor test (ASTM D 698).

2. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least 70% relative density (ASTM D 4253 and D 4254). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Utility Trench Backfill

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

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

Grading and Drainage

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

Exposed ground should be sloped and maintained at a minimum 5% away from the building for at least 10 feet beyond the perimeter of the building. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork. After construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 10 program. Where paving or flatwork abuts the structure, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Earthwork Construction Considerations

Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of the floor slab. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

When groundwater is encountered, a temporary groundwater control system should be installed. We expect that sump pits and pumps would generally be adequate for removing seepage that occurs in clay soils. Where water bearing sand soils are encountered, more extensive dewatering measures such as sheeting/shoring and well points may be required.

As a minimum, excavations should be performed in accordance with OSHA 29 CFR, Part 1926, Subpart P, “Excavations” and its appendices, and in accordance with any applicable local and/or state regulations.

Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. Under no circumstances shall the information provided herein be interpreted to mean Terracon is assuming responsibility for construction site safety or the contractor's activities; such responsibility shall neither be implied nor inferred.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (i.e., gravel surfacing, vegetation, topsoil), evaluation and remediation of poorly compacted or otherwise unsuitable fill materials, as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 11

The foundation installation should be evaluated by the Geotechnical Engineer. If unanticipated conditions are observed, the Geotechnical Engineer should prescribe mitigation options.

In addition to the documentation of the essential parameters necessary for construction, the continuation of the Geotechnical Engineer into the construction phase of the project provides the continuity to maintain the Geotechnical Engineer’s evaluation of subsurface conditions, including assessing variations and associated design changes.

Micropile Foundations

Micropile Design Parameters

We understand that micropiles are being considered by the VA for the Ambulance Garage. Micropile design should be in accordance with Chapter 5 of Federal Highway Administration Micropile Design and Construction Reference Manual.

The minimum bond length should be established in moderately weathered limestone formation anticipated at elevations ranging from about 664 to 667 feet. The equation for determining the required bond length for a single micropile in moderately weathered limestone is as follows:

Where, Lb = Bond length PG – allowable = Maximum compression or tension load for design FS = The appropriate factor of safety which is recommended to be 2.5 αbond = grout to ground ultimate bond strength

Db = diameter of the drill hole

The ultimate bond strength (αbond) of 225 psi is recommended for micropiles establishing bond lengths in the moderately weathered limestone layer. A minimum bonded length of 10 feet is recommended, regardless of the service capacities.

Micropile Installation

Based on the lower strength clays, sand seams and layers, and groundwater encountered in the borings, cased drilling procedures will be required in the overburden

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 12 and upper portion of the highly weathered bedrock. Due to the potential for seams of clay and sand in the limestone, flushing should be performed to remove any loose rock and soil materials from the drill holes. If grout takes exceed 1.5 times the theoretical volume of the drilled hole, then secondary grouting and redrilling may be required to complete foundation installation. Our geotechnical engineer should review conditions at the time of construction to determine appropriate measures.

There may be a potential for communication of grout between drill holes especially if the micropiles are performed at close spacing. The contractor should monitor adjacent drill holes for evidence of grout communication during drilling. Adjacent drill holes should not be advanced until the micropile grout in its vicinity has set.

Terracon should be retained to observe micropile installation to evaluate the depth to competent bedrock during drilling. If elevations to moderately weathered limestone vary from the anticipated elevations discussed above, the micropiles should be advanced to achieve the minimum bond length in the moderately weathered limestone stratum.

Micropiles designed and constructed in accordance with the recommendations in this report have estimated maximum settlements of less than ½ inch.

Helical Piers

As an alternative to supporting the Ambulance Garage on micropiles, the garage may be supported on helical piers. We estimate that limited resistance will be available in the soft to medium stiff clay soils and the helical piers should extend into the stiff to very stiff fat clay layer (GeoModel layer 4) to develop capacity and to reduce the potential for settlement from the lower strength lean clay soils.

Helical piers are typically designed and installed by a specialty contractor. Helical piers consist of varying diameter helices (auger blades) welded to a section of steel rod. Rod extensions are used above the section with the helices. The piers are screwed into the ground with a calibrated torque-head either braced in position or mounted to a skid steer. Increased pier capacity (up to a limit) is achieved by increasing the applied torque during installation. Due to the specialty nature of this foundation system, we recommend that a ‘performance specification’ be used on this project.

Items such as pier spacing, pier length, and element capacity should be determined by an experienced and qualified specialty contractor familiar with this procedure in conjunction with the geotechnical and structural engineers for this project. As mentioned above, we recommend that the helical piers should extend through the lower strength lean clay soils to bear in the underlying stiff to very stiff fat clay soils (Geomodel layer 4). We recommend that the pier designer provide settlement estimates and allowable load capacities under the design loading conditions and the project structural engineer

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 13 should review these estimates to determine if additional piers may be required to further reduce the anticipated movement.

We recommend that a Terracon representative be on site during pier installation to observe and document the installation procedures, and to note the torque applied to each pier. Terracon should review the proposed test procedures with the contractor prior to testing. If unsuitable materials are encountered at planned depths, it may be necessary to extend the foundations deeper to suitable materials.

Floor Slabs

Design parameters for floor slabs assume the requirements for Earthwork have been followed. Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

Floor Slab Design Parameters

The use of a vapor retarder should be considered beneath concrete slabs on grade covered with wood, tile, carpet, or other moisture sensitive or impervious coverings, when the project includes humidity-controlled areas, or when the slab will support

Item Description

Floor Slab Support1

■ Minimum 6 inches of free-draining crushed aggregate (less than 6% passing the U.S. No. 200 sieve) compacted to at least 95% of ASTM D698

■ At least 12 inches of properly compacted, low plasticity cohesive or granular subgrade soils should be present below floor slab base course.

o The exposed subgrade should be scarified, moisture conditioned, and recompacted as noted in Earthwork prior to placing undercut backfill

Estimated Modulus of Subgrade Reaction 2

100 pounds per square inch per inch (psi/in) for point loads;

can be increased to 150 psi/in if at least 12 inches of compacted crushed limestone is placed below the free-draining crushed aggregate layer.

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

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

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 14 equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

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

Floor Slab Construction Considerations

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

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

Pavements

General Pavement Comments

We recommend the pavements be supported on at least 18 inches of newly placed low plasticity cohesive or granular structural fill. The recommended granular subbase can be considered part of the 18-inch layer. We expect the pavement subgrade materials will be placed and compacted following the recommended in the Earthwork section.

Support characteristics of subgrade for pavement design do not account for frost heave or shrink/swell movements. Thus, the pavement may be adequate from a structural standpoint, yet still experience cracking and deformation due to frost heave or shrink/swell related movement of the subgrade.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 15

Pavement Subgrade Preparation

There is often a time lapse between the end of site grading operations and commencement of paving. Subgrades prepared early in the construction process can become disturbed by construction traffic, weather, and other factors. Non-uniform subgrades often result in poor pavement performance and local failures relatively soon after pavements are constructed. Depending on the contractor’s use of paving equipment, measures may be required to improve subgrade strength for support of heavily loaded trucks.

Before paving, and where recommended by Terracon, pavement subgrades should be evaluated by proofrolling in the presence of a Terracon representative using rubber tire equipment with a gross weight of about 25 tons, such as a partially loaded tandem axle dump truck, prior to commencement of actual paving operations. Proofrolling helps in delineating soft or disturbed areas that may exist at or near the exposed subgrade level.

Areas exhibiting excessive deflection and/or rutting should be corrected as recommended in the Earthwork section.

Minimum Pavement Section Thicknesses

Traffic patterns and anticipated vehicle loading conditions were not provided at the time of this report; therefore, a formal pavement design is not provided. We understand the pavement is currently planned to be 8-inch thick portland cement concrete which, in our opinion, meets our typical minimum pavement thickness based on local design practice for the assumed loading conditions. We recommend the pavement be placed on 6 inches of aggregate base meeting gradations for IDOT Section Nos. 4121, 4123, or 4132.Edge restraints (i.e., concrete curbs or aggregate shoulders) should be planned along curves and areas of maneuvering vehicles. A maintenance program that includes surface sealing, joint cleaning and sealing, and timely repair of cracks and deteriorated areas will increase the pavement’s service life. As an option, thicker sections could be constructed to decrease future maintenance.

Proper joint spacing will be required to prevent excessive slab curling and shrinkage cracking. Joints should be sealed to prevent entry of foreign material and doweled where necessary for load transfer. PCC pavement details for joint spacing, joint reinforcement, and joint sealing should be prepared in accordance with ACI 330 and ACI 325.

Pavement Drainage

Subsurface drainage systems (i.e., a permeable base and subdrains) below pavement areas generally prolong the life of a pavement and help to prevent saturation of the pavement subgrade that can result in a reduction of subgrade strength and/or possible heaving. The use of a granular base will also reduce the potential for frost action.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 16

We recommend installing a subdrain system along the shoulders (or back of curb) of new pavement areas, including all openings in the pavement such as decorative landscaped islands or intake structures, and a minimum of every 50 feet on center, to improve long term pavement performance. The pavement subgrade should be crowned at least 2 percent to promote the flow of water towards the subdrains. Design recommendations for the subdrains are provided in the following table:

Subdrain Design Recommendations

Item Description

Pavement aggregate base

A minimum of 6 inches of material meeting the specifications for:

■ IDOT Section No. 4121, Gradation No. 12a;

■ IDOT Section No. 4123, Gradation No. 14; or

■ IDOT Section No. 4132, Gradation No. 30

Subdrain pipe

■ Minimum 4-inch diameter

■ Piper perforations should be appropriately sized to prevent free-draining granular material from entering the subdrain pipe

■ Pipe invert should be at least 3½ feet below proposed grade

■ Subdrain lines should be sloped to provide positive gravity drainage to a reliable discharge point

■ Embedded in at least 4 inches of trench backfill material

Subdrain trench backfill 1

■ IDOT porous backfill (Section 4131), or

■ Free-draining granular material encapsulated with non-woven geotextile filter fabric

1. The subdrain trench backfill should extend up to and be hydraulically connected to the recommended aggregate base layer below the pavements.

Pavement Design and Construction Considerations

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

Openings in pavements, such as decorative landscaped areas, are sources for water infiltration into surrounding pavement systems. Water can collect in the islands and migrate into the surrounding subgrade soils thereby degrading support of the pavement.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 17

Islands with raised concrete curbs, irrigated foliage, and low permeability near-surface soils are particular areas of concern. The civil design for the pavements with these conditions should include features to restrict or collect and discharge excess water from the islands. Examples of features are edge drains connected to the stormwater collection system, longitudinal subdrains, or other suitable outlets and impermeable barriers preventing lateral migration of water such as a cutoff wall installed to a depth below the pavement structure.

Pavement Maintenance

Preventive maintenance should be planned and provided for through an on-going pavement management program. Maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment. Pavement care consists of both localized (e.g., crack and joint sealing and patching) and global maintenance (e.g., surface sealing). Additional engineering consultation is recommended to determine the type and extent of a cost-effective program. Even with periodic maintenance, some movements and related cracking may still occur, and repairs may be required.

Pavement performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of pavements:

■ Final grade adjacent to paved areas should slope down from the edges at a minimum 2%.

■ Subgrade and pavement surfaces should have a minimum 2% slope to promote proper surface drainage.

■ Install pavement drainage systems surrounding areas anticipated for frequent wetting.

■ Install joint sealant and seal cracks immediately.

■ Seal all landscaped areas in or adjacent to pavements to reduce moisture migration to subgrade soils.

■ Place compacted, low permeability backfill against the exterior side of curb and gutter.

Frost Considerations

The soils on this site 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 (NFS) fill with less than 6 percent passing the U.S. No. 200 sieve or structural slabs (for instance, structural stoops in front of building doors).

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 18

Placement of NFS material in large areas may not be feasible; however, the following recommendations are provided to help reduce potential frost heave:

■ Provide surface drainage away from the building and slabs, and toward the site drainage system.

■ Install drains around the perimeter of the building, stoops, below exterior slabs, and connect them to the site drainage system.

■ Grade clayey subgrades so groundwater potentially perched in overlying more permeable subgrades, such as sand or aggregate base, slope toward a site drainage system.

■ Place NFS fill as backfill beneath slabs critical to the project.

■ Place a 3 horizontal to 1 vertical (3H:1V) transition zone between NFS fill and other soils.

■ Place NFS materials in critical sidewalk areas.

As an alternative to extending NFS fill to the full frost depth, consideration can be made to placing extruded polystyrene or cellular concrete under a buffer of at least 2 feet of NFS material.

General Comments

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration.

Variations will occur between exploration point locations or due to the modifying effects of construction or weather. The nature and extent of such variations may not become evident until during or after construction. Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials 19 solely for information purposes to support the services provided by Terracon to our client. Reliance upon the services and any work product is limited to our client and is not intended for third parties. Any use or reliance of the provided information by third parties is done solely at their own risk. No warranties, either express or implied, are intended or made.

Site characteristics as provided are for design purposes and not to estimate excavation cost. Any use of our report in that regard is done at the sole risk of the excavating cost estimator as there may be variations on the site that are not apparent in the data that could significantly affect excavation cost. Any parties charged with estimating excavation costs should seek their own site characterization for specific purposes to obtain the specific level of detail necessary for costing. Site safety and cost estimating including excavation support and dewatering requirements/design are the responsibility of others.

Construction and site development have the potential to affect adjacent properties. Such impacts can include damages due to vibration, modification of groundwater/surface water flow during construction, foundation movement due to undermining or subsidence from excavation, as well as noise or air quality concerns. Evaluation of these items on nearby properties are commonly associated with contractor means and methods and are not addressed in this report. The owner and contractor should consider a preconstruction/precondition survey of surrounding development. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

February 17, 2023 | Terracon Project No. 06225122.01

Facilities | Environmental | Geotechnical | Materials

Figures

Contents:

GeoModel

E le va ti o n

M

S L

(f ee t)

NOTES:

Layering shown on this figure has been developed by the geotechnical engineer for purposes of modeling the subsurface conditions as required for the subsequent geotechnical engineering for this project.

B-201 B-202

This is not a cross section. This is intended to display the Geotechnical Model only. See individual logs for more detailed conditions.

2640 12th St SW

Ambulance Garage

601 Highway 6 West | Iowa City, IA

Cedar Rapids, IA

Terracon Project No. 06225122

GeoModel

LEGEND

Lean Clay with varying amounts of sand3

Fat Clay with varying amounts of sand4

Sand with varying amounts of silt and clay5

Aggregate Base Course Fill

Lean Clay Fat Clay

Fat Clay with Sand Silty Sand

Clayey Sand Poorly-graded Sand

Bedrock Lean Clay with Sand

Model Layer General DescriptionLayer Name

Crushed Limestone1

Poorly Graded Sand, Sandy Silt, and Lean Clay with varying amounts of sand and gravel2

6 Completely to Weathered Limestone

Upper Clay

Lower Clay

Sand

Surficial

Fill

Bedrock

8.5

31.5

40.5

February 17, 2023 | Terracon…