20230522 Geotech report.pdf

REPORT COVER PAGE

Geotechnical Engineering Report Air National Guard Building Addition

St. Paul, Minnesota October 9, 2018

Terracon Project No. MP175151

Prepared for:

Stanley Consultants

Minneapolis, Minnesota

Prepared by:

Terracon Consultants, Inc.

Minneapolis, Minnesota

I hereby certify that this plan, specification, or report was prepared by me or under my direct supervision and that I am a duly Licensed

Professional Engineer under the laws of the State of Minnesota.

Daniel B. Mahrt, PE June 29, 2018

Reg No. 42729

Terracon Consul tants, Inc. 13400 15 t h Avenue P lymouth, Minnesota 55441 P (763) 489 3100 F (763) 489 3101 terracon.com

REPORT COVER LET TER T O SIGN

October 9, 2018

Stanley Consultants 5775 Wayzata Boulevard, Suite 300 Minneapolis, Minnesota 55416

Attn: Mr. Bill Holman, Senior Project Manager P: (952) 738 4331 E: holmanbill@stanleygroup.com

Re: Geotechnical Engineering Report Air National Guard Building Addition 631 Minuteman Drive St. Paul, Minnesota Terracon Project No. MP175151

Dear Mr. Holman:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with our proposal number PMP175151 dated October 26, 2017. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations and floor slabs for the proposed project.

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

Sincerely, Terracon Consultants, Inc.

Levi E. Brown, E.I. Dan B. Mahrt, P.E.

Staff Engineer Department Manager mailto:holmanbill@stanleygroup.com

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REPORT TOPICS

REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

FLOOR SLABS

PAVEMENTS

FROST CONSIDERATIONS

GENERAL COMMENTS

Note: This report was originally delivered in a web-based format. Orange Bold text in the report indicates a referenced section heading. The PDF version also includes hyperlinks which direct the reader to that section and clicking on the logo 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 with Rock and Unified Soil Classification System) http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report Air National Guard Building Addition

631 Minuteman Drive St. Paul, Minnesota

Terracon Project No. MP175151 October 9, 2018

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed building addition to be located at 631 Minuteman Drive in St.

Paul, Minnesota. The purpose of these services is to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil and rock conditions ■ Foundation design and construction

■ Groundwater conditions ■ Floor slab design and construction

■ Site preparation and earthwork ■ Pavement design and construction

■ Excavation considerations ■ Frost considerations

The geotechnical engineering scope of services for this project included the advancement of two test borings to depths ranging from approximately 7 to 10 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.

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.

Item Description

Parcel Information

The project is located at the existing Minnesota Air National Guard facility in the Minneapolis/St. Paul International airport with address of 631 Minuteman Drive in St. Paul, Minnesota.

Latitude/Longitude 44.8895° / -93.2043° (approximate) See Site Location

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Item Description Existing Improvements

The area of the proposed building expansion is currently a paved parking lot located to the south of the existing building.

Current Ground Cover Asphalt/concrete paved parking lot.

Existing Topography Detailed site topography plans were not provided. We assume the site is relatively level.

PROJECT DESCRIPTION

Our initial understanding of the project was provided in our proposal and was discussed in the project planning stage. A period of collaboration transpired since the project was initiated, and our final understanding of the project conditions is as follows:

Item Description

Information Provided Stanley Consultants provided an aerial photograph showing an outline of the proposed construction area and noting that the building expansion will be located in the parking lot to the south of the existing building.

Proposed Structure The project includes a single-story building with a footprint of about 3,500 square feet. The building will be slab-on-grade (non-basement).

Finished Floor Elevation Not available at this time; assumed to match existing structure.

Maximum Loads

■ Columns: 40 kips maximum

■ Walls: 4 kips per linear foot maximum

■ Slabs: 125 pounds per square foot maximum

Grading/Slopes Around 1 to 2 feet of fill will likely be required to develop final grade.

Below Grade Structures None anticipated.

Free-Standing Retaining Walls None anticipated.

Pavements n Paved driveway and parking will be constructed adjacent to this addition.

n No information regarding anticipated vehicle axle configurations, weights or traffic volumes was provided, but assumed to be light to medium volume semi-trailer truck traffic with mostly smaller trucks.

n Standard-duty pavements subjected to primarily light passenger vehicle (gross weight less than 4 tons) traffic, and the occasional delivery truck traffic, with design traffic less than 50,000 ESALs*.

n Heavy-duty pavement subjected to less than 100,000 ESALs* (equivalent to about 5 fully-loaded semi-truck passes per day for a 20-year design life).

* Equivalent 18,000-pound single axle loads based on 20-year design.

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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. The following page provides a general representation of characterization.

The geotechnical characterization as described below 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 (feet) Material Description Consistency/Density

Surface 5 inches Asphalt Pavement N/A

Boring B-1 – 4 feet Boring B-2 – 6 feet

Existing fill - Sandy lean clay N/A

Boring B-1 – 7 feet Boring B-2 – 9 feet

Clayey sand Medium dense

8-foot termination depth of Boring B-1

10-foot termination depth of Boring B-2

Limestone N/A

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

Groundwater was not observed in the remaining borings while drilling, or for the short duration the borings could remain open. However, this does not necessarily mean the borings terminated above groundwater, or the water levels summarized above are stable groundwater levels. Due to the low permeability of the soils encountered in the borings, a relatively long period may be necessary for a groundwater level to develop and stabilize in a borehole. Long term observations in piezometers or observation wells sealed from the influence of surface water are often required to define groundwater levels in materials of this type.

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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 be higher or lower than the levels indicated on the boring logs. The possibility of groundwater level fluctuations should be considered when developing the design and construction plans for the project.

GEOTECHNICAL OVERVIEW

The near surface, soils could become unstable with typical earthwork and construction traffic, especially after precipitation events. Drainage provisions should be implemented early in the construction sequence and maintained after construction to avoid ponding of water near buildings and pavements. If possible, the grading should be performed during the warmer and drier time of the year. If grading is performed during the winter months, an increased risk for possible undercutting and replacement of unstable subgrade will persist. Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Site Preparation section.

The Shallow Foundations section addresses support of the building bearing on native medium dense clayey sand or engineered fill. The Floor Slabs section addresses slab-on-grade support of the building.

The Pavements section addresses the design of pavement systems.

Support of floor slabs and pavements on or above existing fill materials is discussed in this report.

However, even with the recommended construction procedures, 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 removing the existing fill but can be reduced by following the recommendations contained in this report. To take advantage of the cost benefit of not removing the entire amount of undocumented fill, the owner must be willing to accept the risk associated with building over the undocumented fills following the recommended reworking of the material.

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.

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Recommendations include critical quality criteria as necessary to render the site in the state considered in our geotechnical engineering evaluations for foundations and floor slabs.

Site Preparation

Existing pavement should be removed from the building area. We recommend site stripping, subgrade preparation, and compaction procedures extend at least 5 feet beyond the perimeter of the building, and at least 2 feet beyond the edges of the proposed drive/parking areas.

If subgrades become disturbed by precipitation and/or construction activity, the subgrade should be improved before fill is placed, or before the floor slabs are placed. Stabilization measures are recommended should unstable subgrade conditions develop. Improvement methods are influenced by schedule, weather, the size of the disturbed area, the nature of the disturbance, and the availability of materials and equipment on the site. 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 foot.

■ 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 reinforcement product manufacturer should be verified prior to material purchase/delivery and placement at the site.

We recommend that Terracon be retained to assist in evaluating stripping and exposed subgrades during earthwork so that unsuitable materials, if any, are removed at the time of construction.

After stripping and completing cuts to designated subgrade levels below floor slabs and drive/parking areas, we recommend scarifying the subgrade to a depth of 9 inches, adjusting the moisture contents to recommended levels, and then compacting. It should then be possible to evaluate the stability of the soil subgrade by proofrolling or observing subgrade stability during the compaction process. Sandy soil subgrades should be proofrolled using a smooth drum vibratory roller weighing at least 10 tons. Clay subgrades, as encountered in pavement areas, should be proofrolled with a sheepsfoot roller weighing at least 20 tons. Weak areas detected during proofrolling, as well as zones containing organics and voids resulting from removal of boulders, etc., should be removed and replaced with new structural fill.

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Prior to placing fill in areas to receive fill, the subgrade should be proofrolled in the presence of a Terracon geotechnical representative. Proofrolling aids in providing a firm base for compaction of fill and delineating soft, or disturbed areas that may exist below subgrade level. Unsuitable areas observed at this time should be improved by scarification and recompaction or by undercutting and replacement with structural fill. Proofrolling may be accomplished with a fully loaded, tandem-axle, dump truck with a minimum gross weight of 25 tons or other equipment providing an equivalent subgrade loading.

Fill Material Types

Structural fill should meet the following material property requirements:

Fill Type 1 Soil Classification Acceptable Location for Placement

On-site soils SC, SC

■ Below floor slabs 3, 4

■ Below foundations if placed during mass grading on stable subgrades

■ Below gravel drive/parking areas

Imported granular material 4

GW, GP, GM, GC,

GP-GM, GW-GMSW,

SP, SM, SC,

SW-SM, SP-SM

■ Below foundations in overexcavations

■ Below grade-supported floor slabs (granular soils should contain <15% passing No. 200 sieve)

■ Backfill around structures

■ Free-draining zones below slabs (if containing

<6% passing No. 200 sieve)

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

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. 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.

3. If low plasticity fine-grained soils are planned for use as structural fill, by our definition, these materials should have a liquid limit of 45 or less and a plasticity index of 25 or less (ASTM D 4318).

4. Use of fine-grained soils is recommended to be limited to more than 12 inches below floor slabs.

5. Specific material requirements will need to be satisfied based on the intended use.

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

Fill Compaction Requirements

Structural fill should meet the following compaction requirements.

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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

Minimum Compaction Requirements 1, 2

98% of max. below foundations and within 3 feet of gravel drive/parking area subgrades 95% of max. above foundations, below floor slabs, and more than 3 feet below finished gravel drive/parking area subgrades

Water Content

Range 1 P200>20%: -1% to +3% of optimum P200<20%: -3% to +3% of optimum

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. Consideration can be given to compacting all fill below drive/parking areas to 95% during mass grading.

Immediately prior to paving, we recommend that the subgrade below these areas be rough-graded as needed, and then scarified and recompacted. We recommend this process include scarifying the subgrade to a depth of about 8 inches, moisture conditioned to within the recommended water content range, and compacting the scarified soil to at least 98%. Scarified soils which cannot be recompacted to this degree should be undercut and replaced with stable material.

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

Utility Trench Backfill

All trench excavations should be made with sufficient working space to permit construction, including backfill placement and compaction. If utility trenches are backfilled with relatively clean granular material, they should be capped with either paving or at least 12 inches of cohesive fill to reduce the infiltration and conveyance of surface water through the trench backfill.

Grading and Drainage

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

Finished grading slopes should promote drainage away from the building and parking/drive areas.

We recommend final grades for seeded and landscaped areas be sloped at least 5 percent within 10 feet around the building. 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 in lawn areas more than 5 feet from the buildings. Exterior slabs or sidewalks installed adjacent to the building should slope away from the building at a grade of 2% or more.

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Overwatering of grass or landscaping vegetation is a significant source of water and should be avoided near the building. Sprinkler heads should be adjusted to miss the exterior building walls.

Automated watering systems should be programmed to not run after natural rain events, and to not overwater. Any utility leaks should be promptly repaired. Lining the bottom of irrigated planter areas along the buildings with an impermeable moisture barrier and installing tile lines leading to gravity outlets or sump pits and pumps, would also help to control surface water that infiltrates into these features.

Earthwork Construction Considerations

Shallow excavations, for the proposed structure, are anticipated to be accomplished with conventional construction equipment.

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

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

If precipitation occurs immediately prior to or during construction, the near-surface soils could increase in moisture content and become more susceptible to disturbance. Construction activity should be monitored and should be curtailed if the construction activity is causing subgrade disturbance. A Terracon representative can help with monitoring and developing recommendations to avoid subgrade disturbance.

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

Construction staging should provide drainage of surface water and precipitation away from the building and parking/drive 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.

As a minimum, all temporary excavations should be sloped or braced as required by Occupational Safety and Health Administration (OSHA) regulations to provide stability and safe working conditions. Construction site safety is the sole responsibility of the contractor who controls the means, methods, and sequencing of construction operations. All excavations should comply with applicable local, state and federal safety regulations, including the current OSHA Excavation and Trench Safety Standards.

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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 monitored by a Terracon representative. 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 and evaluated by a Terracon representative. Areas of failing tests should be reworked as necessary.

In areas of foundation excavations, the bearing subgrade should be evaluated by a Terracon representative. In the event that unanticipated conditions are encountered, Terracon should prescribe mitigation options.

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

SHALLOW FOUNDATIONS

It is our opinion that the proposed building can be supported on spread footings bearing on native soils or on granular structural fill extending to suitable native soils. Overexcavations used to remove unsuitable native soils should be performed 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

Item Description Maximum Net Allowable Bearing pressure 1, 2 3,000 psf

Minimum Foundation Dimensions Columns: 30 inches Continuous: 18 inches

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Item Description

Ultimate Passive Resistance 4

(equivalent fluid pressures) 290 pcf (granular backfill)

Ultimate Coefficient of Sliding Friction 5 0.40 (granular material)

Minimum Embedment below

Finished Grade 6

Exterior footings in unheated areas: 60 inches Exterior footings in heated areas: 42 inches Interior footings in heated areas: 12 inches

Estimated Total Settlement from Structural Loads 2 Less than about 1 inch

Estimated Differential Settlement 2, 7 About 2/3 of total settlement

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. These bearing pressures can be increased by 1/3 for transient loads unless those loads have been factored to account for transient conditions. Values assume that exterior grades are no steeper than 20% within 10 feet of structure.

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

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

Earthwork.

4. Use of passive earth pressures require the sides of the excavation for the spread footing foundation to be nearly vertical and the concrete placed neat against these vertical faces or that the footing forms be removed and compacted structural fill be placed against the vertical footing face.

5. 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.

6. 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.

7. Differential settlements are as measured over a span of 50 feet.

Construction Adjacent to Existing Building

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

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

A typical building addition construction method is to use existing foundations to support additional load from the walls of the new additions. It is possible additional loads on the existing foundations

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Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the direction of the Geotechnical Engineer. The base of all foundation excavations should be free of water and loose soil, prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Care should be taken to prevent wetting or drying of the bearing materials during construction. Excessively wet or dry material or any loose/disturbed material in the bottom of the footing excavations should be removed/reconditioned before foundation concrete is placed.

If unsuitable bearing soils are encountered at the base of the planned footing excavation, the excavation should be extended deeper to suitable soils, and the footings could bear directly on these soils at the lower level or on lean concrete backfill placed in the excavations. This is illustrated on the sketch below.

Over-excavation for structural fill placement below footings should be conducted as shown below.

The over-excavation should be backfilled up to the footing base elevation, with structural fill placed, as recommended in the Earthwork section.

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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.

Floor Slab Design Parameters

Item Description

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

95% of ASTM D 698 3

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

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.

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.

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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.

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 control 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.

Terracon should approve 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

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 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 formulate recommended pavement sections for the proposed facility:

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■ American Concrete Institute (ACI) ACI 330R-08 – Guide for the Design and Construction of Concrete Parking Lots; and

■ Minnesota Asphalt Paving Association (MAPA).

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.

In our opinion, the pavement sections intended for use are suitable for the assumed design traffic stated in Project Description. 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 Pavement Section 1, 2, 3

Standard Duty (Parking and Drive)

5 inches PCC over 4 inches of aggregate base, OR

3½ inches ACC over 8 inches aggregate base

Heavy Duty Parking and Drives

6 inches PCC over 4 inches of aggregate base, OR

4 inches ACC over 9 inches aggregate base

Refuse collection pads, areas for turning and maneuvering delivery trucks and facility entrance aprons

7 inches concrete over 4 inches aggregate base

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 consist of crushed stone that 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 Site Preparation.

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

As part of the layout design of the project we recommend the designer use signs and preventive structures to restrict heavy truck traffic from entering automobile parking areas.

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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.

Pavement Drainage

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 adjacent to the 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.

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. The pavement subgrade should slope toward the subdrain lines.

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

Item Description

Pavement aggregate base A minimum of 4 inches of material meeting the specifications for MnDOT base aggregate is recommended.

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Item Description

Subdrain pipe

■ Minimum 4-inch diameter

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

■ Pipe invert is recommended to be placed 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 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. Maintenance activities are intended to slow the rate of pavement deterioration and to preserve the pavement investment.

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 priority when implementing a pavement maintenance program. Additional engineering observation 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 below 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.

■ Place curb, gutter and/or sidewalk directly on clay subgrade soils rather than on unbound granular base course materials.

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FROST CONSIDERATIONS

The soils on this site are frost susceptible. Frost-susceptible soils can heave upon freezing, resulting in both localized and general heaving of slabs, sidewalks and pavements. This type of heaving can result in trip hazards, impact local drainage, and result in additional pavement and slab deterioration.

We recommend providing surface drainage away from the building and slabs, and toward the site storm drainage system to reduce frost-heave related issues.

In critical exterior slab areas, such as at building entrances, we recommend removing frost-susceptible soils to a depth of at least 5 feet below finished grade and backfilling the excavation with non-frost susceptible (NFS) fill. The bottom of the excavation should be sloped to one or more drains that transmit the water to a suitable outlet. In order to reduce differential movement at transitions, we recommend a 3H:1V or flatter transition from the NFS critical slab area to less-critical areas. This transition helps reduce abrupt heave.

GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications, so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, foundation construction and other earth-related construction phases of the project.

The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur between across the site 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. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided.

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 removing the existing fill but can be reduced by performing additional testing and evaluation.

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The scope of services for this project 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.

This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing.

ATTACH MENTS

ATTACHMENTS

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EXPLORATION AND TESTING PROCEDURES

Field Exploration

Boring Layout and Elevations: The drill crew spotted the boring locations in relation to existing features. We used a handheld GPS equipment with an estimated horizontal accuracy of +/-20 feet to document the boring locations.

Approximate ground elevations at the boring locations were measured to the nearest ½-foot with a surveyor’s rod and level and were referenced to the existing building’s finished floor elevation.

An arbitrary elevation of 100.0 feet was given for this benchmark. The elevations should be considered accurate only to the degree implied by these methods.

If precise locations and elevations are desired, we suggest that the client retain a licensed surveyor to stake the boring locations and provide elevations.

Subsurface Exploration Procedures: The borings were advanced with a truck-mounted drilling rig utilizing continuous hollow stem augers. Representative samples were obtained using split-barrel sampling procedures. In the split-barrel sampling procedure, a standard 2-inch O.D. split-barrel sampling spoon is driven into the ground with an automated 140-pound hammer falling a distance of 30 inches. The number of blows required to advance the sampling spoon the last 12 inches of a normal 18-inch penetration is recorded as the standard penetration resistance value.

These values are indicated on the boring logs at the depths of occurrence. The “N” value is used to estimate the in-situ relative density of cohesionless soils and, to a lesser extent, the consistency of cohesive soils and hardness of rock. The samples were sealed and transported to the laboratory for testing and classification.

Our exploration team prepared field boring logs as part of standard drilling operations. The field logs included sampling depths, penetration distances, and other relevant sampling information.

Field logs also included water level observations, visual classifications of materials encountered during drilling, and our interpretation of subsurface conditions between samples. Typed boring logs included with the report represent the geotechnical engineer's interpretation of the logs, and include modifications based on laboratory observations and tests.

Laboratory Testing

Water content tests (ASTM D2216) were performed on the samples and Passing No. 200 sieve tests (ASTM D1140) were performed on selected samples. The results of these laboratory tests are provided on the boring logs.

The samples were classified in the laboratory based on visual observation and texture (ASTM D2488). Additional laboratory testing could be performed to more accurately classify the samples.

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The soil descriptions presented on the boring logs for native soils are in general accordance with our enclosed General Notes and Unified Soil Classification System (USCS, ASTM D2487). The estimated group symbol for the USCS is also shown on the boring logs, and a brief description of the Unified System is included in this report.

Procedural standards noted above are for reference to methodology in general. In some cases, variations to methods are applied as a result of local practice or professional judgment.

SITE LOCA TION AND EXPLORATI ON PLANS

SITE LOCATION AND EXPLORATION PLANS

SITE LOCATION

Air National Guard Base Addition ■ St. Paul, Minnesota Terracon Project No. MP175151

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY

QUADRANGLES INCLUDE: ST PAUL WEST, MN (1/1/1993) and ST PAUL SW, MN

(1/1/1993).

SITE

EXPLORATION PLAN

Air National Guard Base Addition ■ St. Paul, Minnesota Terracon Project No. MP175151

AERIAL PHOTOGRAPHY PROVIDED BY

MICROSOFT BING MAPS

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT

INTENDED FOR CONSTRUCTION PURPOSES

EXPLORATION RESULTS

EXPLORATION RESULTS

2-2-7 N=9

7-4-6 N=10

50/2"

4.0

7.0

8.0

Approx. 5 inches of asphalt at surface FILL - SANDY LEAN CLAY , trace gravel, light brown & gray

CLAYEY SAND (SC), brown, medium dense

LIMESTONE, light gray, hard

Boring Terminated at 8 Feet

G R

A P

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L O

G

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

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ELEVATION (Ft.)

Surface Elev.: 99.0 (Ft.)

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LOCATION See Exploration Plan

Latitude: 44.8895° Longitude: -93.2046°

Advancement Method:

Hollow-stem Auger

Abandonment Method:

Boring backfilled with auger cuttings upon completion.

13400 15th Ave N Plymouth, MN

Notes:

Project No.: MP175151

Drill Rig: 928

Boring Started: 09-19-2018

BORING LOG NO. B-1

Stanley Consultants, Inc.CLIENT:

Minneapolis, MN

Dri…