Amend 0003 Geotech Report - Parking Structure.pdf

REPORT COVER PAGE

Geotechnical Engineering Report Veteran’s Affair’s Parking Structure

St. Cloud, MN

November 13, 2019

Terracon Project No. MP185137

Prepared for:

American Structurepoint, Inc.

Indianapolis, Indiana

Prepared by:

Terracon Consultants, Inc.

Plymouth, Minnesota

Terracon Consultants, Inc. 13400 15 t h Avenue Minneapolis, Minnesota 55441

P (763) 489 3100 F (763) 489 3101 terracon.com

REPORT COVER LETTER TO SIGN

American Structurepoint, Inc.

9 Sheboygan Street

Indianapolis, Indiana 54935

Attn: Mr. Ken Dane, P.E.

P: (317) 547-5580

E: kdane@structurepoint.com

Re: Geotechnical Engineering Report

Veteran’s Affair’s Parking Structure

Veteran’s Drive

St. Cloud, MN

Dear Mr. Dane:

We have completed subsurface exploration for the above referenced project. This study was performed in general accordance with Terracon Proposal No. PMP18137 dated November 1, 2018. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon Consultants, Inc.

Brett W. Larsen, P.E. Dan B. Mahrt, P.E.

Project Engineer Geotechnical Department Manager

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REPORT TOPICS

REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

SEISMIC CONSIDERATIONS

PARKING SLABS

LATERAL EARTH PRESSURES

PAVEMENTS

FROST CONSIDERATIONS

STORMWATER MANAGEMENT CONSIDERATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo will bring you back to this page. For more interactive features, please view your project online at client.terracon.com.

ATTACHMENTS

EXPLORATION AND TESTING PROCEDURES

SITE LOCATION AND EXPLORATION PLANS

EXPLORATION RESULTS (Boring Logs and Laboratory Data)

SUPPORTING INFORMATION (General Notes and Unified Soil Classification System) http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

Veteran’s Affair’s Parking Structure

Veteran’s Drive

St. Cloud, MN

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Parking Structure at the Veterans Affairs (VA) hospital in St.

Cloud, Minnesota.

The geotechnical engineering scope of services for this project included the advancement of

9borings to depths ranging from approximately 5 to 90 feet below existing site grades.

Maps showing the site and boring locations are shown in the Site Location and Exploration

Plan sections, respectively. The results of the laboratory testing performed on soil samples obtained from the site during the field exploration are included on the boring logs in the

Exploration Results section of this report.

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

■ Subsurface soil conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Seismic site classification per IBC

■ Excavation considerations ■ Pavement design and construction

■ Lateral Earth Pressures ■ Frost considerations

■ Stormwater infiltration considerations

SITE CONDITIONS

The following description of site conditions is derived from our site visit in association with the field exploration and our review of publicly available geologic and topographic maps.

Veteran’s Affair’s Parking Structure ■ St. Cloud, MN

November 13, 2019 ■ Terracon Project No. MP185137

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Item Description

Location

The proposed parking structure is planned along Veteran’s Drive to the south of the main VA hospital complex in St. Cloud, Minnesota

Approximate Coordinates: 45.5737, -94.2131

See Site Location

Existing conditions

The site is developed with existing asphalt pavement and a single-story unheated structure (which has a footprint less than 1,000 square feet). Grass and landscaped areas surround the existing parking lot and structure.

Existing topography

Based on review of USGS quadrangle maps, provided site plan, and information from MnTOPO, grade change of about 4 feet is estimated across the site, sloping down from north to south.

Site History

From review of historical aerial photographs, the lot does not appear to have been developed, while the surrounding structures were constructed around

2005.

PROJECT DESCRIPTION

Proposed Parking Structure

The project includes a one-story (above-grade) parking structure with a footprint of about 45,000 square feet. The building also includes one below-grade level, bearing at a depth of approximately 12 feet below grade.

The footprint of the building expands further east outside the area the original borings explored. Per discussions with American Structurepoint, additional explorations were not desired.

Parking Garage Slab Elevations

(provided)

Main Level: 1051 feet

Lower Level: 1039 feet

Building Construction Precast or cast concrete

Maximum Loads (provided by the structural engineer)

■ Columns: 300 to 500 kips

■ Walls: 8 to 10 kips per linear foot (klf)

■ Slabs: 150 pounds per square foot (psf)

Grading/Slopes

Grades around the building are assumed to involve less than 2 feet of cut or fill; however excavations for the below grade level could extend up to about 14 feet below grade.

Cut and fill slopes assumed to be 3H:1V or flatter.

Below Grade Structures The building will have one level of underground parking beneath the building footprint. We anticipate the excavation for the underground parking level will extend approximately 12 feet below grade.

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Pavements

We understand a small surface parking lot may be planned to east of the proposed parking structure. Detailed traffic loads were not provided;

however, we anticipate it would be primarily used by personal vehicles. We have assumed the following :

■ 20 year design life

■ Light duty pavements would be subjected to traffic less than

50,000 18-kip equivalent single-axle loads (ESALs),

■ Heavy duty pavements subject to less than 150,000 ESALs

Stormwater Management Areas

Stormwater will be stored in an underslab stormwater storage system which is comprised of 24, 192-feet long, 24-inch diameter pipes. Water temporarily stored within the system will be pumped to a nearby stormwater pond.

GEOTECHNICAL CHARACTERIZATION

Subsurface Profile

We have developed a general characterization of the subsurface soil and groundwater conditions based upon our review of the data and our understanding of the geologic setting and planned construction. The following table provides our geotechnical characterization.

The geotechnical characterization forms the basis of our geotechnical calculations and evaluation of site preparation, foundation options and pavement options. As noted in General Comments, the characterization is based upon widely spaced exploration points across the site, and variations are likely.

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

Stratum

Approximate

Depth to Bottom of Stratum

Material Description Comments

Surface 3 to 6 inches Topsoil with vegetation

3 inches Asphalt Pavement

Existing Fill 3 feet

Existing Fill—generally sand with fines and variable amounts of gravel

Native Clay 3 to 5 feet Sandy Lean Clay (CL) Dark brown, stiff

Clayey Sand

3 feet Clayey Sand (SC) Dark brown, loose

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Stratum

Approximate

Depth to Bottom of Stratum

Material Description Comments

Native Sand with

Silt and Silty Sand 5 to 90 feet

Sand with Silty (SP-SM) and Silty

Sand (SM)

Medium Dense

Loose and dense in localized areas

Conditions encountered at each boring location are indicated on the individual boring logs shown in the Exploration Results section and are attached to this report. Stratification boundaries on the boring logs represent the approximate location of changes in native soil types; in situ, the transition between materials may be gradual.

Groundwater Conditions

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

Boring Number Approximate Depth to Groundwater while Drilling

(feet)

1 16

2 13

3 18

4 12

5 14

6 13

7 13

8 --2

9 --2

1. Below existing ground surface

2. No free water was observed prior to termination of the boring.

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

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GEOTECHNICAL OVERVIEW

The near surface sandy soils will likely rut under typical construction traffic. Placing crushed stone for construction access, staging and laydown areas should be expected.

Effective drainage should be established early in construction and maintained during and after construction to avoid potential issues for development of subgrades for floor slabs and pavements. If possible, the grading should be performed during the warmer and drier time of the year to avoid issues with freezing materials and . Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Earthwork section.

The Shallow Foundations section addresses support of the building bearing on native medium dense sands or recompacted native sands. We understand despite large column loads it is generally project team’s preference to consider large shallow foundations in lieu of using deep foundations.

The Below-Grade Structures section addresses lateral earth pressures and general construction recommendations for the below grade parking level.

The Parking Slabs for the below grade level should be grade supported.

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

EARTHWORK

Earthwork will 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.

Excavation Considerations

If a basement level is included excavations on the order of 14 feet below ground surface (bgs) are anticipated. Unbraced sloped excavations in native sands are expected to be relatively broad and could potentially encroach upon adjacent structures and streets.

Groundwater is present near the bottom of the proposed below grade-level and dewatering of the below grade excavations should be anticipated. Well-point vacuum systems or a series of deep well

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The contractor is responsible for employing appropriate dewatering methods to control seepage, remove standing water, maintain site drainage, and facilitate construction.

We recommend that a granular working platform be developed in the base of the excavation. The granular base will help prevent disturbance of the subgrade soils from construction traffic. The free-draining, granular working surface should be at least 12 inches thick, but greater thickness may be required if wetter and softer zones are encountered. Recommendations concerning the granular base and drainage system to be placed above any working surface layer are presented in following sections.

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

Safety and Health Administration (OSHA) regulations to provide stability and safe working conditions. Temporary excavations will probably be required during grading operations and installation of utilities. Contractors, by their contract, are usually responsible for designing and constructing stable, temporary excavations and they should shore, slope, or bench the sides of the excavations as required to maintain stability of both the excavation sides and bottom. All excavations should comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards.

Site Preparation

We expect existing pavements and structures in new construction areas will be removed.

Demolition should include complete removal of all abandoned utilities, pavements, and foundations. Site preparation should also include stripping of all vegetation, organic soils, root systems, and any soft, frozen or otherwise unsuitable materials (if encountered). The depth of removal of unsuitable materials should be evaluated by Terracon personnel during construction.

Following stripping, existing fill materials should be completely removed below the footprint area of the planned construction. Subgrade stabilization will be required where saturated and/or loose sands are exposed at the base of the undercut.

Where practical, we recommend the exposed subgrade be proofrolled to help delineate soft, disturbed, or low-density fill zones. Proofrolling should be accomplished using a fully loaded, tandem axle dump truck or other equipment providing an equivalent subgrade loading (minimum gross weight of 25 tons is recommended for the proofrolling equipment). A vibratory smooth drum roller (minimum gross weight of 10 tons) should be used in areas were sands are exposed.

Unstable areas identified by proofrolling should either be undercut to expose stable material and backfilled with structural fill or stabilized as described in this report. In areas where proofrolling is

Responsive ■ Resourceful ■ Reliable 7 not practical due to equipment access limitations, a Terracon representative should evaluate the subgrade by observation and hand probing.

If unstable subgrade conditions be encountered or if they develop during construction operations, stabilization measures will need to be employed. Improvement methods are influenced by schedule, weather, the size of the disturbed area, and the nature of the disturbance. Improvement methods include but are not limited to:

◼ Scarification and Compaction – Soils can be scarified, moisture conditioned (i.e., dried or moistened), and compacted. The success of this procedure depends primarily upon favorable weather and sufficient time to manipulate the soils. Even with adequate time and favorable weather, stable subgrades may not be achieved if the thickness of the unstable material is greater than about 1 to 1½ feet.

◼ Undercutting and Replacement with Crushed Stone/Aggregate – The use of crushed stone, crushed concrete, and/or gravel to replace loose soils could improve subgrade stability.

To limit depths of potential undercuts, the use of a geotextile or geogrid could also be considered after underground work, such as utility construction, is completed. The specifications provided by the geosynthetic manufacturer should be verified prior to material purchase/delivery and placement at the site.

Fill Material Types

Structural fill should meet the following material property requirements:

Fill Type

USCS Classification Acceptable Location for Placement

Drainage Fill

2 SP, SW, GW

Free-draining granular fill, below interior slabs-on-grade and wall backfill. Generally conforming to MNDOT 3149 requirements for coarse filter aggregate.

“Working Platform”

3 GW, GP

Free-draining granular fill, below interior slabs-on-grade and wall backfill. Generally conforming to MNDOT 3136 Requirements for Drainable Stable Base Material.

On-site soil

4 SP, SP-SM, SM

■ Below floor slabs 3

◼ Below foundations of at-grade building area if placed during mass grading on stable subgrades

◼ Below pavements

◼ Backfill of broad areas of below grade excavation, except in wall drainage fill zone unless meeting proper gradation

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Fill Type USCS Classification Acceptable Location for Placement

Non-structural fill ML, CL ■ Green (landscaped areas)

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

2. Well-graded, free-draining granular material. A general gradation should be 100% passing the 1 inch sieve, about 10 percent passing the No. 4 sieve, and less than 5 percent passing No. 200 sieve.

Terracon can review proposed materials.

3. Well-graded crushed stone or crushed concrete with a maximum particle size of about 2 inches and less than about 5 percent passing No. 200 sieve. Terracon can review proposed materials.

4. Sorting of topsoil and on-site soils containing debris, organics, etc., will be necessary. Delineation of unsuitable on-site soils should be performed in the field by a Terracon representative. Moisture conditioning of the on-site soils will be necessary to facilitate compaction.

Granular fill soils should be used directly above exposures of native sand soils for compatibility of drainage characteristics and subgrade support. Care should be taken to avoid interlayering of sand and clay soils as perched water or poorly drained areas could develop. Subsurface trench drains may be needed in areas where poor drainage conditions occur or are created.

Appropriate laboratory tests, including standard Proctor (ASTM D 698) moisture-density relationship tests and Atterberg Limits tests for cohesive soils, should be performed on proposed fill materials prior to their use as structural fill. Further evaluation of any on-site soils or proposed imported fill materials should be performed by Terracon prior to their use in compacted fill sections.

Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

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 equipment (e.g., jumping jack, vibratory plate compactor, etc.) is used

Minimum Compaction Requirements 1, 2, 3

■ 98% of max. below proposed foundations and pavements

■ 95% of max. above foundations, below floor slabs, all other locations

Water Content Range 4 Granular: Workable moisture levels

Low plasticity cohesive: -1% to +3% of optimum

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

D 698).

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

3. Crushed stone / crushed concrete placed over a subgrade of sand should not be overcompacted;

overcompaction can cause subgrade disturbance and loss of strength of the underlying subgrade. In these areas, we recommend that the granular layer be drifted into place in advance of compaction equipment. Compaction be accomplished with 2 or 3 mutually perpendicular passes of each thin lift with light-weight vibratory compaction equipment. Instead of a strict compaction requirement, consideration should be given to using visual evaluation of material stability using factors such as surface stability and aggregate interlock when evaluating compaction and performance of the granular material.

4. Specifically, moisture levels for granular materials should be maintained low enough to allow for satisfactory compaction to be achieved without the granular fill material pumping when proofrolled or containing excess water (ponding).

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

Utility Trench Backfill

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

Grade supported drainage utilities should be installed in accordance with methods outlined in

ASTM D2321 for thermoplastic pipe and ASTM C1479 for precast concrete sewer, storm drain, and culvert pipe. The noted standards provide a variety of support options for utilities based on observed conditions. In our opinion, a minimum bedding of at least 6 inches of coarse filter aggregate (MNDOT Spec 3149H) should be considered beneath below grade utility pipes. A

Terracon representative should observe the condition of subgrades exposed at the base of all utilities to determine that exposed subgrades are suitable and/or direct further overexcavation and replacement with engineered fill.

Grading and Drainage

Surface water should not be allowed to pond on the site and soak into the soil during construction, including the proposed parking level excavation. Construction staging should provide drainage of

Responsive ■ Resourceful ■ Reliable 10 surface water and precipitation away from the building areas. Any water that collects over or adjacent to construction areas should be promptly removed, along with any softened or disturbed soils.

Surface water control in the form of sloping surfaces, drainage ditches and trenches, and sump pits and pumps will be important to avoid ponding and associated delays due to precipitation and seepage.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs. Construction traffic over the completed subgrade should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the subgrade should become frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

Exterior Grading

Ponding of surface water can increase the potential for frost heave or settlement. Excessive moisture can reduce bearing capacity and contribute to slab settlement and cracking.

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

Construction Observation and Testing

The earthwork efforts should be monitored under the direction of the Geotechnical Engineer.

Monitoring should include documentation of adequate removal of vegetation and top soil, proof-rolling and mitigation of areas delineated by the proof-roll to require mitigation.

Each lift of compacted fill should be tested, evaluated, and reworked as necessary until approved by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content at a frequency of at least one test for every 2,500 square feet of compacted fill in the building areas and 5,000 square feet in pavement areas. One density and water content test for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated by the

Geotechnical Engineer or his designated representative. In the event that unanticipated conditions are encountered, the Geotechnical Engineer should be contacted to provide mitigation options.

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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.

SHALLOW FOUNDATIONS

Based on the materials encountered in the borings and our analyses, it is our opinion that spread footings bearing on medium dense sands or mechanically densified sands and structural fill could be used to support the proposed building. Loose sands are anticipated to be encountered at the foundation bearing elevations in some areas, especially if excavations extend below grade for a below grade level. We recommend that a program of surface compaction with an excavator mounted vibratory plate compactor be established during the excavation and preparation phase.

The vibratory plate compactor should be used along proposed footing locations and compaction should continue until no further visual deflections are observed. As an alternative to surface compaction, loose sands could be overexcavated and replaced with compacted engineered fill or lean concrete, as described in Foundation Construction Considerations. If the site has been prepared in accordance with the recommendations provided in Earthwork, the following design parameters are applicable for shallow foundations.

Design Parameters – Compressive Loads

Maximum Net Allowable Bearing pressure 1, 2 4,000 psf

Required Bearing Stratum 3

■ Native medium dense sand

■ Granular structural fill (overexcavation and backfill procedure)

Minimum Foundation Dimensions Columns: 30 inches

Continuous: 18 inches

Ultimate Coefficient of Sliding

Friction 5 Footings on compacted granular material: 0.45

Minimum Embedment below

Finished Grade 6

Unheated areas: 5 feet

Heated areas: 3½ feet

Estimated Total Settlement from

Structural Loads 2

Settlement calculations indicate settlements ranging from less than 1 inch to about 1 ½ inches

Estimated Differential Settlement 2 About 1 inch or less over a span of 50 feet

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1. The maximum net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. An appropriate factor of safety has been applied. Values assume that exterior grades are no steeper than 20 percent within 10 feet of structure.

2. Values provided are for maximum loads noted in Project Description.

3. Unsuitable, disturbed, or soft soils should be over-excavated and replaced per the recommendations presented in the Earthwork.

4. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Should be neglected for foundations subject to net uplift conditions.

5. Embedment necessary to minimize the effects of frost and/or seasonal water content variations. For sloping ground, maintain depth below the lowest adjacent exterior grade within 5 horizontal feet of the structure.

Design Parameters - Uplift Loads

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils. As illustrated on the subsequent figure, the effective weight of the soil prism defined by diagonal planes extending up from the top of the perimeter of the foundation to the ground surface at an angle, , of 20 degrees from the vertical can be included in uplift resistance.

The maximum allowable uplift capacity should be taken as a sum of the effective weight of soil plus the dead weight of the foundation, divided by an appropriate factor of safety. A maximum total unit weight of 100 pcf should be used for the backfill.

Foundation Construction Considerations

Terracon should be retained to observe and test the bearing materials exposed in all foundation excavations. If disturbed or otherwise unsuitable bearing materials are encountered in a footing excavation, the excavation should be extended deeper, as necessary, to suitable materials. The footing could bear directly on the suitable materials at the lower level or on lean concrete backfill

Responsive ■ Resourceful ■ Reliable 13 placed back up to design bearing level. The footings for at-grade building elements could also bear on approved, properly compacted backfill extending down to the suitable materials.

Overexcavation for compacted backfill placement below footings should extend laterally at least

8 inches beyond the edges of the footings for each foot of depth below footing base elevation.

The overexcavation should then be backfilled up to the footing base elevation with approved fill placed and compacted as recommended in Earthwork. The adjacent figures depict these options.

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

SEISMIC CONSIDERATIONS

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 7-10.

Description Value

2012 International Building Code Site Classification

(IBC)

D

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Description Value

1. Seismic site classification in general accordance with the 2012 International Building Code, which refers to

ASCE 7-12.

2. The 2012 International Building Code (IBC) uses a site profile extending to a depth of 100 feet for seismic site classification. Borings at this site were extended to a maximum depth of 90 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. Additional deeper borings or geophysical testing may be performed to confirm the conditions below the current boring depth.

PARKING SLABS

Design parameters for heated parking 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 parking slab.

Heated Parking Slab Design Recommendations

Slab Support 1 Minimum 6 inches of free-draining crushed aggregate compacted to at least

98% of ASTM D 698 2, 3

Estimated Modulus of

Subgrade Reaction 2 150 pounds per square inch per inch (psi/in) for point loads

1. Slabs should be structurally independent of building footings and walls to reduce the possibility of 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 slab support as noted in this table. It is provided for point loads on the slabs. For large area loads, the modulus of subgrade reaction would be lower.

3. Free-draining granular material should have less than 6 percent fines (material passing the #200 sieve).

Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions.

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, or when the slab will support equipment sensitive to moisture. When conditions warrant the use of a vapor retarder, the slab designer should refer to ACI 302 and/or ACI 360 for procedures and cautions regarding the use and placement of a vapor retarder.

Saw-cut control joints should be placed in the slab to help control the location and extent of cracking. For additional recommendations refer to the ACI Design Manual. Joints or cracks should be sealed with a water-proof, non-extruding compressible compound specifically recommended for heavy duty concrete pavement and wet environments.

If a basement level is constructed a system of drain tiles should be installed to drain the granular layer below the lower level parking slab. The drain tiles should consist of perforated pipes with a

Responsive ■ Resourceful ■ Reliable 15 minimum diameter of 4 inches. We recommend the drain tiles be placed around the interior perimeter of the parking garage walls and at roughly 40 to 50 foot intervals under the rest of the parking garage slab.

The inverts of the drain tiles should be installed in trenches which are at least 12 inches wide and incised at least 6 inches into the subgrade. A filter fabric is recommended as a liner in the trenches and lapped on the subgrade around the trenches for a distance of 3 feet beyond the trench edges. The drain tiles should be surrounded by free-draining granular material graded to prevent the intrusion of fines. The free-draining material should not contain particle sizes capable of entering or clogging the drain pipe perforations, or the drain pipes can be wrapped with a filter-fabric “sock” to help prevent infiltration of fines. These drain pipes should be sloped to a reliable discharge point (i.e., a storm sewer or a sump pit and pump). If gravity drainage cannot be provided, the drainage system will require a system of sump pits and pumps. As a precautionary measure, we recommend at least two pumps for redundancy, and the pumping system should be provided with a backup power supply. All drains should be provided with cleanouts.

Where 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 control joints, appropriate reinforcing or other means. The slab can be stiffened as determined by the project Structural Engineer by adding steel reinforcement, grade beams and/or post-tensioned elements.

Slab Construction Considerations

The finished slab subgrade should be protected from traffic, rutting, or other disturbance and maintained in a relatively moist condition until floor slabs are constructed. If the subgrade becomes 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 slab support course.

The Geotechnical Engineer should approve the condition of the subgrades immediately prior to placement of the 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.

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LATERAL EARTH PRESSURES

Design Parameters

Structures with unbalanced backfill levels on opposite sides should be designed for earth pressures at least equal to values indicated in the following table. Earth pressures will be influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction and the strength of the materials being restrained. Two wall restraint conditions are shown. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top.

The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

Lateral Earth Pressure Design Parameters

Earth Pressure

Condition

Coefficient for

Backfill Type

Surcharge

Pressure 3, 4, 5 p1 (psf)

Effective Fluid Pressures (psf) 2, 4, 5

Unsaturated 6 Submerged

Active (Ka) Granular - 0.33 (0.33)S (40)H (80)H

At-Rest (Ko) Granular - 0.47 0.47)S (55)H (90)H

Passive (Kp) Granular - 3.25 --- (390)H (250)H

1. For active earth pressure, wall must rotate about base, with top lateral movements 0.002 H to 0.004 H, where H is wall height. For passive earth pressure, wall must move horizontally to mobilize resistance.

2. Uniform, horizontal backfill, compacted to at least 95 percent of the ASTM D 698 maximum dry density, rendering a maximum unit weight of 120 pcf.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction equipment is not included.

5. No safety factor is included in these values.

6. In order to achieve “Unsaturated” conditions, follow guidelines in Subsurface Drainage for Below Grade

Walls below. “Submerged” conditions are recommended when drainage behind walls is not incorporated into the design.

Responsive ■ Resourceful ■ Reliable 17

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.

For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 degrees from vertical for the active and at rest cases and at an angle of at least 60 degrees for the passive case.

Subsurface Drainage for Below Grade Walls

To reduce hydrostatic pressure behind unbalanced walls, we recommend that a drain system be installed along the wall and extend to the foundation of the below grade walls. The wall drain system should be designed according to the following table.

Wall drainage pipe

◼ Minimum 4-inch diameter perforated pipe

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

◼ Pipe invert should be at least 5 feet below proposed grade, or at the foundation of the below grade walls, whichever is deepest

◼ Drain lines should be sloped to provide positive gravity drainage to a reliable discharge point (e.g., storm sewer, sump pit and pump, etc.)

◼ Pipes should be embedded in at least 4 inches of wall drainage backfill material

Wall drainage backfill

◼ MnDOT Coarse Filter Aggregate or equivalent, or

◼ Free-draining granular material encapsulated with non-woven geotextile filter fabric (Contech C60NW or equivalent)

◼ At least a 2-foot wide section of free-draining granular fill located above the drain line and adjacent to the walls, or

◼ A prefabricated drainage structure1 located above a drain line and the surrounding filter.

1. A prefabricated drainage structure is a plastic drainage core or mesh which is covered with filter fabric to prevent soil intrusion, and is fastened to the walls prior to placing backfill.

If walls must resist combined hydrostatic and lateral earth pressures, then combined hydrostatic and lateral earth pressures should be calculated using the “undrained” values in the previous section.

Water stops and other wall waterproofing measures should also be considered in designs.

PAVEMENTS

General Pavement Comments

Pavement designs are provided for the traffic conditions and pavement life conditions as noted in

Project Description and in the following sections of this report. A critical aspect of pavement

Responsive ■ Resourceful ■ Reliable 18 performance is site preparation. Pavement designs, noted in this section, must be applied to the site, which has been prepared as recommended in the Earthwork section.

Pavement Design Parameters

Pavement thickness can be determined in general accordance with the Minnesota Department of

Transportation (MnDOT), which generally follows AASHTO (1993) guidelines, Asphalt Institute and/or other methods if specific wheel loads, axle configurations, frequencies, and desired pavement life are provided. The following references were utilized to develop recommended pavement sections:

◼ American Concrete Institute (ACI) ACI 330R-08 – Guide for the Design and Construction of

Concrete Parking Lots; and

◼ Minnesota Asphalt Paving Association (MAPA).

Signage should be provided to prevent truck and bus traffic on areas designed for light-duty traffic only. It should be noted that pavements need to satisfy both local and/or county ordinances, especially if the drive is intended for greater use in the future.

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 parking lots and drives should slope down from pavement edges at a minimum 2%;

◼ The subgrade and the pavement surface should have a minimum ¼-inch per foot slope to promote proper surface drainage;

◼ Install pavement subsurface drainage surrounding areas anticipated for frequent wetting (e.g., intake structures, wash racks);

◼ Install joint sealant and seal cracks immediately; and

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

Pavement Section Thicknesses

Opinions of pavement thicknesses are based on the subsurface conditions encountered at the borings, general characterization of the subgrade, our experience on similar projects, and consider that the subgrade is proofrolled, tested, and evaluated as recommended in this report.

Testing such as CBR, resilient modulus, etc. was not part of our scope of service for this project to evaluate the support characteristics of the subgrade; however, these can be performed upon request. The thickness of pavements for these scenarios should be in accordance with local city or county ordinances.

Responsive ■ Resourceful ■ Reliable 19

The following tables summarizes the estimated minimum portland cement concrete (PCC) and asphaltic cement concrete (ACC) pavement thicknesses for the anticipated traffic conditions for the facility. These sections are based on the subsurface conditions encountered at the borings and our experience on similar projects, and consider that all materials are placed on a subgrade prepared and evaluated as recommended in this report.

Pavement Area

PCC over

Granular Base

(inches) 1, 2, 3

ACC over

Granular Base

(inches) 1, 2, 4

Light Duty

5 over 4 3 1/2 over 7

Heavy Duty 6 over 4 4 over 8

1. Pavement materials, mix design, and construction should conform to the current Minnesota

Department of Transportation (MnDOT) Standard Specifications for Construction.

2. The granular base course materials should be placed on a stable subgrade and compacted to at least 98 percent of the material’s standard Proctor maximum dry density. Considers the subgrade is sloped to promote drainage and is prepared in accordance with section 4.2 Earthwork.

3. PCC pavement concrete should have a 28 day compressive strength of at least 4,000 psi.

4. A minimum surface course thickness of 2 inches is recommended with ACC pavements.

Thicker pavement sections could be used to reduce maintenance and extend the expected service life of the pavements.

We recommend using PCC pavements in areas of anticipated concentrated loads (e.g., loading docks) and areas with repeated turning or maneuvering of trucks (e.g., entrance aprons). We also recommend PCC pavement sections include sufficient reinforcing steel and dowels at joints to resist potential flexure and to provide load transfer across transverse joints and to reduce differential movement between pavement slabs.

Construction traffic on the pavements was not considered in developing the recommended minimum pavement thicknesses. If the pavements will be subject to traffic by construction equipment/vehicles, the pavement thicknesses should be revised to consider the effects of the additional traffic loading.

PCC pavements require properly designed and constructed longitudinal joints (parallel to traffic) and transverse joints (perpendicular to traffic) to provide satisfactory performance.

Pavements should be sloped to provide rapid drainage of surface water. Water should not be allowed to pond on or adjacent to the pavements. Ponding of water on or adjacent to the

Responsive ■ Resourceful ■ Reliable 20 pavements could contribute to significant moisture increases in the subgrade soils and subsequent loss of strength and/or possible heaving, leading to premature pavement deterioration.

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 infiltrated surface water from becoming trapped below pavements. Saturation of the pavement subgrade could result in a reduction of subgrade strength (rutting) and/or possible heaving. The use of a granular base will also reduce the potential for frost action.

As described in the previous section, subsurface drainage systems should be considered for any potential low elevation or poorly drained areas, and in vicinity of any landscaping systems with sprinklers. At a minimum, subsurface drains should be installed around catch basins, behind curbs in landscaped areas, and other low points in paved areas. The pavement subgrade should slope toward the subdrain lines.

Typical components for pavement subsurface drainage design are provided in the table below.

Pavement aggregate base

A minimum of 4 inches of material meeting the specifications for MnDOT base aggregate (e.g., crushed stone containing less than 5% passing the

U.S. No. 200 sieve)

Subdrain pipe

◼ Minimum 4-inch diameter

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

◼ Pipes should be installed below aggregate base layer

◼ 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

◼ Free-draining granular material encapsulated with non-woven geotextile filter fabric (Contech C60NW or equivalent)

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

Pavement Maintenance

The pavement sections provided in this report represent minimum recommended thicknesses and, as such, periodic maintenance should be anticipated. Therefore, preventive maintenance should be planned and provided for through an on-going pavement management program.

Preventive maintenance activities are intended to slow the rate of pavement deterioration, and to

Responsive ■ Resourceful ■ Reliable 21 preserve the pavement investment. Preventive maintenance consists of both localized maintenance (e.g., crack and joint sealing and patching) and global maintenance (e.g., surface sealing). Preventive maintenance is usually the first priority when implementing a planned pavement maintenance program and provides the highest return on investment for pavements.

Prior to implementing any maintenance, additional engineering observation is recommended to determine the type and extent of preventive maintenance. Even with periodic maintenance, some movements and related cracking may still occur and repairs may be required.

FROST CONSIDERATIONS

The soils on this site are likely frost susceptible, and water that infiltrates beneath slabs and shallow groundwater can be detrimental to the performance of the slabs. If frost action needs to be eliminated in critical areas, then consideration could be given to use of structural slabs (e.g., structural stoops in front of building doors), or replacement of frost-susceptible soils with non-frost susceptible soils down to the adjacent footing depth. Regardless of which option is chosen, transition areas (either from structural slab to grade-supported slab, or from NFS to frost-susceptible soils) are critical. Where transitions such as these occur, we recommend implementing a 3:1

(Horizontal: Vertical) transition zone between non- or low-frost susceptible soils and other soils.

This transition should also be implemented between structural stoops and adjacent grade-supported slabs to reduce differential movement at the transition.

The following recommendations are provided to help reduce potential frost heave:

◼ Providing surface drainage away from the building and slabs and toward the site storm drainage system;

◼ Grading silty or clayey subgrades such that groundwater potentially perched in overlying more permeable subgrades, such as sand or aggregate base, slopes toward the site drainage system;

◼ Placing non-frost susceptible fill as backfill around stoops.

Non-frost susceptible fill…