BSM Geotechnical Report - Amendment 0003.pdf

REPORT C OVER PAGE

Geotechnical Engineering Report

WAPA Vehicle Maintenance Facility

Bismarck, North Dakota

August 25, 2020

Terracon Project No. M2205057

Prepared for:

Burns & McDonnell

Centennial, CO

Prepared by:

Terracon Consultants, Inc.

Bismarck, ND

Terracon Consultants, Inc. 1805 Hancock Drive, PO Box 2084 Bismarck, ND 58502-2084

P (701) 258 2833 F (701) 258 2857 terracon.com

REPORT C OVER LETTER TO SIGN

Burns & McDonnell

9785 Maroon Circle, Ste 400

Centennial, CO 80112

Attn: Mr. Utkarsh Pandey, P.E., S.E.

P: (303) 362 2338

E: upandey@burnsmcd.com

Re: Geotechnical Engineering Report

WAPA Vehicle Maintenance Facility

700 N Bismarck Expressway

Bismarck, North Dakota

Terracon Project No. M2205057

Dear Mr. Pandey:

We have completed the Geotechnical Engineering services for the above referenced project. This study was performed in general accordance with Terracon Proposal No. PM2205057 dated June

17, 2020. 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.

Chad A. Cowley, P.E. Alex L. Sprunk, P.E.

Department Manager Project Engineer

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REPORT TOPICS

INTRODUCTION

SITE CONDITIONS

PROJECT DESCRIPTION

GEOTECHNICAL CHARACTERIZATION

GEOTECHNICAL OVERVIEW

EARTHWORK

SHALLOW FOUNDATIONS

SEISMIC CONSIDERATIONS

FLOOR SLABS

LATERAL EARTH PRESSURES

PAVEMENTS

CORROSIVITY

GENERAL COMMENTS

FIGURES

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

GeoReport 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

SUPPORTING INFORMATION

Note: Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

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INTRODUCTION

Geotechnical Engineering Report

WAPA Vehicle Maintenance Facility

700 N Bismarck Expressway

Bismarck, North Dakota

INTRODUCTION

This report presents the results of our subsurface exploration and geotechnical engineering services performed for the proposed Vehicle Maintenance Facility to be located at 700 N Bismarck

Expressway in Bismarck, North Dakota. 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

■ Lateral earth pressures ■ Pavement design and construction

The geotechnical engineering Scope of Services for this project included the advancement of two test borings to depths of approximately 31 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 and/or as separate graphs in the Exploration Results section.

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 700 N Bismarck Expressway in Bismarck, North

Dakota

Latitude: 46.8132° N, Longitude: 100.7315° W (approximate)

See Site Location

Existing

Improvements Mass graded, existing buildings, parking and drive areas

WAPA Vehicle Maintenance Facility ■ Bismarck, North Dakota

August 25, 2020 ■ Terracon Project No. M2205057

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Item Description

Current Ground

Cover Asphalt paved parking lot

Existing Topography The site is relatively level with an elevation change of approximately one foot between our borings.

PROJECT DESCRIPTION

Our understanding of the project conditions is as follows:

Item Description

Information Provided Information used to develop our project understanding was provided to us through phone and email communication with Burns & McDonnell

Proposed Structures

The project includes a single-story pre-engineered metal building with a footprint of about 8500 square feet. The building will be slab-on-grade

(non-basement).

Finished Floor Elevation 1667.5

Maximum Loads

(provided by BMcD)

■ Columns: 50 kips (provided by BMcD)

■ Walls: 3 kips per linear foot (klf) (assumed)

■ Slabs: 125 pounds per square foot (psf) (assumed)

Grading Based on the FFE as described above, we anticipate up to 2 feet of fill will be required to develop final grade.

Below-Grade Structures None

Free-Standing Retaining

Walls None

Pavements

We anticipate both rigid (concrete) and flexible (asphalt) pavement sections are being considered.

Anticipated traffic is as follows:

■ Autos/light trucks: 100 vehicles per day

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

■ Tractor-trailer trucks: <50 vehicle per week

The pavement design period is 20 years.

GEOTECHNICAL CHARACTERIZATION

We have developed a general characterization of the subsurface conditions based upon our review of the subsurface exploration, laboratory data, geologic setting and our understanding of the project. This characterization, termed GeoModel, forms the basis of our geotechnical calculations and evaluation of site preparation and foundation options. Conditions encountered at

Responsive ■ Resourceful ■ Reliable 3 each exploration point are indicated on the individual logs. The individual logs can be found in the

Exploration Results section and the GeoModel can be found in the Figures section of this report.

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

Model Layer Layer Name General Description

1 Surface 7 to 8 inches of asphalt over 6 to 7 inches of aggregate base

2 Fill Sand – various amounts of silt and clay, brown to dark brown

3 Clay 1

Lean Clay – various amounts of sand, dark brown to brown, soft to medium stiff, waterbearing seams of sand at approximately 10 feet below grade

4 Clay 2 Fat Clay – brownish gray to grayish brown, very soft to medium stiff, laminations of silt

5 Sand Sand – various amounts of silt, brown to gray, very loose to loose, fine to medium grained, waterbearing

The boreholes were observed while drilling and after completion for the presence and level of groundwater. The water levels observed in the boreholes can be found on the boring logs in

Exploration Results, and are summarized below.

Boring Number Approximate Depth to

Groundwater while Drilling (feet)

Approximate Depth to

Groundwater after Drilling (feet)

B-1 10 20

B-2 10 24

1. Below ground surface.

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 proposed structures can be supported on a spread footing foundation system bearing on structural fill, provided the recommendations presented herein are implemented in design and construction phases. The Shallow Foundations section addresses support of the structures on

Responsive ■ Resourceful ■ Reliable 4 structural fill. The Floor Slabs section addresses slab-on-grade support of the structures.

Additional site preparation recommendations including subgrade improvement and fill placement are provided in the Earthwork section.

The near surface, medium plasticity lean clay could become unstable with typical earthwork and construction traffic, especially after precipitation events. The effective drainage should be completed early in the construction sequence and maintained after construction to avoid potential issues. 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 Earthwork section.

As discussed in the Geotechnical Characterization, undocumented fill was encountered in the borings to approximate depths of four to five feet. This undocumented fill may be variable in consistency, density and moisture, and therefore may have the potential to increase or decrease in volume with variations in moisture content. Furthermore, 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.

Therefore, we recommend completely removing any undocumented fills encountered at this site and replacing them with a structural fill, as outlined in the Earthwork section.

Based on our field measurements the ground water level is on the order of 9 to 10 feet below existing grades. In clayey soils, the groundwater seepage in open excavations should be controllable with sump pumping.

The Pavements section addresses the design of pavement systems.

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

EARTHWORK

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

Site Preparation

As noted in Geotechnical Characterization, our borings encountered existing fill to depths ranging from about 4 to 5 feet, which correlates to elevation 1662 when referenced to existing on-

Responsive ■ Resourceful ■ Reliable 5 site buildings. We have no records to indicate the degree of control or placement methods of the fill, so we consider it undocumented. This undocumented fill may be variable in consistency, density and moisture. We recommend completely removing these soil conditions below the proposed foundation systems and floor slabs and placing a properly compacted structural fill. The structural fill should meet the requirements as outlined in Fill Material Types and Fill

Compaction Requirements. The on-site materials appear suitable for reuse as a structural fill.

Prior to placing fill, all existing pavement and undocumented fill should be removed from the building footprint. We estimate an excavation depth on the order of 4 to 5 feet (elev. 1662) below floors will be needed to remove the existing fill. In order to reduce the potential for detrimental settlement, we recommend extending the excavation to approximately 6 to 7 feet below existing grade (elev. 1660) below foundation areas followed by the replacement with structural fill.

Excavations to this level should provide a uniform depth of controlled fill below the foundation elements. The excavations for structural elements should be observed by the Geotechnical

Engineer prior to the placement of structural fill. The structural fill should meet the requirements as outlined in Fill Material Types and Fill Compaction Requirements.

If the owner is willing to accept risk of differential movement and elects to construct the pavements on the existing fill, the following protocol should be followed. The existing soils can be removed to a minimum of 24 inches beneath proposed pavement sections. The exposed subgrade should then be scarified and recompacted to a minimum depth of 12 inches. A structural fill meeting the material requirements outlined below should be placed at a minimum in the upper 24 inches beneath the proposed pavement sections.

As previously discussed, the groundwater table is estimated at 9 to 10 feet below existing grades.

If groundwater is encountered, it may be necessary to place an initial rock layer with a thickness of approximately 12 inches in order to obtain conditions on which the structural fill can be placed.

The rock should be angular and should not exceed three inches in any dimension. We further recommend placing a geotextile separation fabric in the bottom of the excavation which should extend up each side of the excavation a sufficient distance to wrap around the top of the rock.

The rock should be surface compacted prior to wrapping the top and placement of structural fill.

Fill Material Types

Fill required to achieve design grade should be classified as structural fill and general fill.

Structural fill is material used below, or within 10 feet of structures, pavements or constructed slopes. General fill is material used to achieve grade outside of these areas. Earthen materials used for structural fill should meet the following material property requirements:

On-site soils free of vegetation, organic matter and other deleterious materials or low volume change import materials approved by Terracon may be used as fill/backfill material on the site.

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In general, imported materials meeting the properties presented below should be acceptable for use on the site. However, imported soils should be evaluated and approved by the geotechnical engineer prior to delivery to the site.

Fill Type 1, 2

USCS Classification Acceptable Parameters

Cohesive Soils

CL, CL-ML

100% Passing 2-inch sieve

LL < 40

Granular Soils

SW, SW-SM, SW-SC,

SP, SP-SM, SP-SC,

SM, SC

All: 100% Passing 2-inch sieve

SM Only: Less than 20% Passing #200 sieve

1. The on-site soils typically appear suitable for use as fill, however they should be tested prior to placement to ensure they meet the recommendations for structural fill as outlined above.

2. Structural fill is material used below, or within 10 feet of structures, pavements or constructed slopes.

3. On-site materials can be reworked and reused under structural elements in accordance with the following recommendations: CL soils with a liquid limit greater than 40 and less than 50 should not be used within 2 feet of foundation elements; if the liquid limit exceeds 50, the CH (high plasticity) soils should not be used in the structural footprint. While silts can be used as general fill, they can be difficult to compact. Silts should not be used as structural fill.

Fill Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift

Thickness

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

6 inches in loose thickness when hand-guided equipment (i.e. jumping jack or plate compactor) is used

Same as Structural fill

Minimum

Compaction

Requirements

95% of max. - below footings, above footings, below floor slabs, and finished pavement subgrade

90% of max.

Water Content

Range

Granular: As required to work the material and achieve minimum compaction requirements

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

As required to achieve min.

compaction requirements

Same as Structural fill

High plasticity cohesive:

0 to +4% of optimum

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Item Structural Fill General Fill

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

2. High plasticity cohesive fill should not be compacted to more than 100% of standard Proctor maximum dry density.

Utility Trench Backfill

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

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

Grading and Drainage

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

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

Earthwork Construction Considerations

Shallow excavations, for the proposed structure, are anticipated to be accomplished with conventional construction equipment. Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of floor slabs. Construction traffic over the completed subgrades should be avoided. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, Responsive ■ Resourceful ■ Reliable 8 or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

The groundwater table could affect over-excavation efforts, especially for over-excavation and replacement of lower strength soils. A temporary dewatering system consisting of sumps with pumps could be necessary to achieve the recommended depth of over-excavation.

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

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

Construction Observation and Testing

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

Monitoring should include documentation of adequate removal of vegetation and topsoil, proofrolling, and mitigation of areas delineated by the proofroll 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 should be performed for every 50 linear feet of compacted utility trench backfill.

In areas of foundation excavations, the bearing subgrade should be evaluated under the direction of the Geotechnical Engineer. If unanticipated conditions are encountered, the Geotechnical

Engineer should prescribe mitigation options.

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

SHALLOW FOUNDATIONS

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

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Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing pressure

1,500 psf (foundations bearing within structural fill)

Required Bearing Stratum

Over-excavation of fill and soft soils and placement of a structural fill, minimum 24 inches (as described in

Earthwork)

Minimum Foundation Dimensions Columns: 30 inches

Continuous: 18 inches

Ultimate Coefficient of Sliding Friction

0.30 (native clay)

0.40 (granular material)

Minimum Embedment below

Finished Grade

Exterior footings in unheated areas: 72 inches

Exterior footings in heated areas: 60 inches

Interior footings in heated areas: 12 inches

Estimated Total Settlement from

Structural Loads

Less than about 1 inch

Estimated Differential Settlement 2, 6

About 1/2 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.

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. 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.

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

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 115 pcf should be used for the backfill.

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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.

As discussed in Earthwork, the undocumented fills and soft clays encountered at the anticipated footing depth should be removed to a minimum of 24 inches. The over-excavation should then be backfilled up to the footing base elevation, with lean concrete or structural fill placed as recommended in the Earthwork section. This is illustrated in the following sketches.

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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 and the International Building Code (IBC).

Based on the soil properties encountered at the site and as described on the exploration logs and results, it is our professional opinion that the Seismic Site Classification is E. Subsurface explorations at this site were extended to a maximum depth of 30 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.

FLOOR SLABS

The subgrade soils are comprised of undocumented fill. We recommend removing the existing fill as described in the Earthwork section and replacing it with a properly-compacted structural fill.

Design parameters for floor slabs assume the requirements for Earthwork have been followed.

Specific attention should be given to positive drainage away from the structure and positive drainage of the aggregate base beneath the floor slab.

Floor Slab Design Parameters

Item Description

Floor Slab Support

Minimum 6 inches of free-draining (less than 8% passing the U.S. No.

200 sieve) crushed aggregate or sand compacted to at least 95% of

ASTM D 698.

2, 3

This can be considered as part of the structural fill underneath the floor slabs.

Structural fill placed beneath floor slabs should meet the fill criteria as outlined in Earthwork

Estimated Modulus of

Subgrade Reaction

100 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.

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Item Description

3. Free-draining granular material should have less than 8 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.

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.

Settlement of floor slabs supported on existing fill materials cannot be accurately predicted, but could be larger than normal and result in some cracking. Mitigation measures, as noted in the

Earthwork section, are critical to the performance of floor slabs. In addition to the mitigation measures, the floor slab can be stiffened by adding steel reinforcement, grade beams and/or post-tensioned elements.

Floor Slab Construction Considerations

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

The Geotechnical Engineer should 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.

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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.

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

Lateral Earth Pressure Design Parameters

Earth Pressure

Condition

Coefficient for

Backfill Type

Equivalent Fluid

Density (pcf)

Surcharge

Pressure, p1 (psf)

Earth Pressure, p2 (psf)

Active (Ka) Granular - 0.36

Cohesive - 0.49

(0.36)S

(0.49)S

(40)H

(65)H

At-Rest (Ko) Granular - 0.53

Cohesive - 0.66

(0.53)S

(0.66)S

(60)H

(85)H

Passive (Kp) Granular – 2.77

Cohesive - 2.04

(320)H

(265)H

Applicable conditions to the above table include:

■ For active earth pressure, wall must rotate about base, with top lateral movements of

0.002 H to 0.004 H, where H is wall height.

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■ For passive earth pressure, wall must move horizontally to mobilize resistance.

■ Uniform, horizontal backfill, compacted to at least 95 percent of the ASTM D 698 maximum dry density.

■ Uniform surcharge, where S is surcharge pressure.

■ Loading from heavy compaction equipment is not included.

■ No hydrostatic pressures acting on wall.

■ No dynamic loading.

■ No safety factor is included in these values.

■ Ignore passive pressure in frost zone.

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 and 60 degrees from vertical for the active and passive cases, respectively.

If walls are planned as part of the project, our geotechnical engineer should be contacted with additional information to determine if supplemental foundation preparation and drainage provisions are required for design.

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 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.

Based on the planned grading, we anticipate the onsite soils will be utilized in subgrade construction. A California Bearing Ratio (CBR) has been determined on a composite blend of material encountered in borings B-1 and B-2 from an approximate depth of one to four feet below existing grade. This material was compacted at about 96 percent of the standard proctor maximum dry density at about optimum moisture. The moisture-density relationship test and CBR are presented in the Exploration Results section.

Pavement Design Parameters

A subgrade CBR of 7 was used for the AC pavement designs, and a modulus of subgrade reaction of 150 pci was used for the PCC pavement designs. The values were empirically derived based

Responsive ■ Resourceful ■ Reliable 15 upon our experience with the describe soil type subgrade soils and our understanding of the quality of the subgrade as prescribed by the Site Preparation conditions as outlined in

Earthwork. A modulus of rupture of 580 psi was used for pavement concrete.

Pavement design recommendations for this project have been based on procedures outlined in the AASHTO Guide for Design of Pavement Structures, 1993, coupled with publications by the

Asphalt Institute and the American Concrete Institute on the design of parking lots and our local experience. Pavement design input parameters and resulting pavement sections are provided in the following table:

Pavement Thickness Design Parameters

Input Parameter Flexible (asphalt) Rigid (concrete)

Reliability 85% 85%

Initial Serviceability 4.2 4.5

Terminal Serviceability 2.0 2.5

Standard Deviation 0.45 0.35

Drainage 1.0 1.0

Design ESAL Value:

Anticipated Traffic 630,000 1,100,000

Pavement Section Thicknesses

The following table provides options for AC and PCC Sections:

Asphaltic Concrete Design Thickness (inches)

Traffic Area Asphalt Surface Asphalt Base

Aggregate Base

Total Thickness

Parking/Drive 2.0 4.5 6.0 12.5

Portland Cement Concrete Design Thickness (inches)

Traffic Area Portland Cement

Concrete

Aggregate Base Total Thickness

Parking/Drive 7.0 6.0 13.0

1. NDDOT Superpave FAA41.

2. 4000 psi at 28 days, for inch maximum slump and 5.0% to 7.0% air-entrained, 6 sack minimum mix. PCC pavements are recommended for trash container pads and any other areas subjected to heavy wheel loads and/or turning traffic.

3. NDDOT Class 5 Aggregate Base or Salvage Base Course in accordance with NDDOT Section 817

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Pavement Drainage

Pavements should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. In addition, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the granular subbase.

Due to frost susceptible soils and the possibility of perched groundwater, consideration should be given to installing a pavement subdrain system to control subgrade moisture, improve stability, and improve long term pavement performance.

We recommend minimum thicknesses of free-draining granular material (aggregate base) be placed beneath the pavements as outlined in the Pavement Section Thicknesses section. The use of a free draining granular base will also reduce the potential for frost action. We recommend pavement subgrades be crowned at least 2 percent, to promote the flow of water towards the subdrains, and to reduce the potential for ponding of water on the subgrade.

The subdrains should be hydraulically connected to the free-draining granular base layer.

Subdrains should be sloped to provide positive gravity drainage to reliable discharge points such as the storm water detention basin. Periodic maintenance of subdrains is required for long-term proper performance.

The pavement surfacing and adjacent sidewalks should be sloped to provide rapid drainage of surface water. Water should not be allowed to pond on or adjacent to these grade supported slabs, since this could saturate the subgrade and contribute to premature pavement or slab deterioration.

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:

Responsive ■ Resourceful ■ Reliable 17

■ 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.

CORROSIVITY

The table below lists the results of laboratory soluble sulfate, soluble chloride, and pH testing.

The values may be used to estimate potential corrosive characteristics of the on-site soils with respect to contact with the various underground materials which will be used for project construction.

Corrosivity Test Results Summary

Boring Sample Depth

(feet)

Soluble Sulfate

(ug /g)

Soluble Chloride

(ug /g) pH

B-1 & B-2 2.5-5 131 3.84 8.3

Results of soluble sulfate testing indicate samples of the on-site soils tested possess negligible sulfate concentrations when classified in accordance with Table 4.3.1 of the ACI Design Manual.

Concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. To improve sulfate resistance of concrete in severe sulfate exposure when Type V cement is not available, the following should be considered:

■ Use of Type I-II modified cement for sulfate resistance

■ Cement should have a tricalcium aluminate content of not more than 8%.

■ Concrete mixture should contain at least 20% Class F fly ash.

■ Provide air-entrainment of 4% to 7% by volume.

■ Lower the water to cement ratio to 0.4 to 0.45.

Composite samples were obtained from the depths as shown in the table below and were tested for soil resistivity. The results are presented in the table below.

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Resistivity Test Results Summary

Boring(s) Sample Depth

(feet) Composite Soil Type

Soil Resistivity

(ohm-cm)

B-1 & B-2 2.5-5 Clayey Sand 3,700

Resistivity results indicate the soil samples tested have moderate corrosive potential to buried ferrous metal pipes. Evaluation of the resistivity test results follows the guidelines of J.F. Palmer, “Soil

Resistivity Measurements and Analysis”, Materials Performance, Volume 13, January 1974. The table below outlines the guidelines for soil resistivity versus corrosion potential.

Corrosion Potential of Soil on Steel

SOIL RESISTIVITY (ohm-cm) CORROSION POTENTIAL

0 to 1,000 Very High

1,000 to 2,000 High

2,000 to 5,000 Moderate

> 5,000 Mild

If corrosion of buried metal is critical, it should be protected using a non-corrosive backfill, wrapping, coating, sacrificial anodes, or a combination of these methods, as designed by a qualified corrosion engineer.

For protection against corrosion to buried metals, we recommend an experienced corrosion engineer be retained to design a suitable corrosion protection system for underground metal structures or components.

GENERAL COMMENTS

Our analysis and opinions are based upon our understanding of the project, the geotechnical conditions in the area, and the data obtained from our site exploration. Natural variations will occur between exploration point locations or due to the modifying effects of construction or weather.

The nature and extent of such variations may not become evident until during or after construction.

Terracon should be retained as the Geotechnical Engineer, where noted in this report, to provide observation and testing services during pertinent construction phases. If variations appear, we can provide further evaluation and supplemental recommendations. If variations are noted in the absence of our observation and testing services on-site, we should be immediately notified so that we can provide evaluation and supplemental recommendations.

Our Scope of Services does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of

Responsive ■ Resourceful ■ Reliable 19 pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken.

Our services and any correspondence or collaboration through this system are intended for the sole benefit and exclusive use of our client for specific application to the project discussed and are accomplished in accordance with generally accepted geotechnical engineering practices with no third-party beneficiaries intended. Any third-party access to services or correspondence is solely for information purposes to support the services provided by Terracon to our client.

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

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

Site safety, and cost estimating including, excavation support, and dewatering requirements/design are the responsibility of others. If changes in the nature, design, or location of the project are planned, our conclusions and recommendations shall not be considered valid unless we review the changes and either verify or modify our conclusions in writing.

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FIGURES

Contents:

GeoModel

Note: All attachments are one page unless noted above.

1,635

1,640

1,645

1,650

1,655

1,660

1,665

1,670

E L

E V

A T

IO

N

M

S L

(f ee t)

WAPA Vehicle Maintenance Facility Bismarck, North Dakota Terracon Project No. M2205057

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

Numbers adjacent to soil column indicate depth below ground surface.

NOTES:

B-1 B-2

GEOMODEL

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

Groundwater levels are temporal. The levels shown are representative of the date and time of our exploration. Significant changes are possible over time.

Water levels shown are as measured during and/or after drilling. In some cases, boring advancement methods mask the presence/absence of groundwater. See individual logs for details.

First Water Observation

Second Water Observation

Lean Clay - various amounts of sand, dark brown to brown, soft to medium stiff, waterbearing seams of sand at approximately 10 feet below grade

Fat Clay - browinsh gray to grayish brown, very soft to medium stiff, laminations of silt4

Sand - various amounts of silt, brown to gray, very loose to loose, fine to medium grained, waterbearing5

LEGEND

Asphalt

Aggregate Base Course

Fill

Lean Clay with Sand

Sandy Lean Clay

Fat Clay

Poorly-graded Sand with Silt

Silty Sand

Model Layer Layer Name General Description

1 7 to 8 inches of asphalt over 6 to 7 inches of aggregate base

Sand - various amounts of silt and clay, brown to dark brown2

Clay 1

Clay 2

Sand

Surface

Fill

1.2

11.5

15.5

1.2

ATTACHMENTS

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 1 of 2

EXPLORATION AND TESTING PROCEDURES

Field Exploration

Number of Borings Boring Depth (feet) Location

2 30 Building footprint

Boring Layout and Elevations: Terracon personnel provided the boring layout based on a site plan provided by Burns & McDonnell. Coordinates were obtained with a handheld GPS unit

(estimated horizontal accuracy of about ±10 feet) and approximate elevations at the boring locations were measured to the nearest ½ foot and referenced to a temporary benchmark (See

Exploration Plan). If elevations and a more precise boring layout are desired, we recommend borings be surveyed following completion of fieldwork.

Subsurface Exploration Procedures: We advanced the borings with a track-mounted rotary drill rig using continuous flight augers. Samples were obtained at 2½-foot intervals in the upper 15 feet of each boring and at intervals of 5 feet thereafter using thin-walled and split-barrel sampling procedures. In the thin-walled tube sampling procedure, a thin-walled, seamless steel tube with a sharp cutting edge was pushed hydraulically into the soil to obtain a relatively undisturbed sample.

In the split-barrel sampling procedure, a standard 2-inch outer diameter split-barrel sampling spoon was driven into the ground by a 140-pound automatic 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 Test (SPT) resistance value. The SPT resistance values, also referred to as N-values, are indicated on the boring logs at the test depths.

We observed and recorded groundwater levels during drilling and sampling. For safety purposes, all borings were backfilled with auger cuttings after their completion. Pavements were patched with cold-mix asphalt and/or pre-mixed concrete, as appropriate.

The sampling depths, penetration distances, and other sampling information was recorded on the field boring logs. The samples were placed in appropriate containers and taken to our soil laboratory for testing and classification by a Geotechnical Engineer. Our exploration team prepared field boring logs as part of the drilling operations. These field logs included visual classifications of the materials encountered during drilling and our interpretation of the subsurface conditions between samples. Final boring logs were prepared from the field logs. The final boring logs represent the

Geotechnical Engineer's interpretation of the field logs and include modifications based on observations and tests of the samples in our laboratory.

Laboratory Testing

The project engineer reviewed the field data and assigned laboratory tests to understand the engineering properties of the various soil strata, as necessary, for this project. Procedural

Responsive ■ Resourceful ■ Reliable EXPLORATION AND TESTING PROCEDURES 2 of 2 standards noted below are for reference to methodology in general. In some cases, variations to methods were applied because of local practice or professional judgment. Standards noted below include reference to other, related standards. Such references are not necessarily applicable to describe the specific test performed.

■ ASTM D2216 Standard Test Methods for Laboratory Determination of Water (Moisture)

Content of Soil and Rock by Mass

■ ASTM D7263 Standard Test Methods for Laboratory Determination of Density (Unit

Weight) of Soil Specimens

■ ASTM D4318 Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of

Soils

■ ASTM D1140 Standard Test Methods for Determining the Amount of Material Finer than

No. 200 Sieve in Soils by Washing

■ ASTM D2166/D2166M Standard Test Method for Unconfined Compressive Strength of

Cohesive Soil

■ ASTM D698 Standard Test Methods for Laboratory Compaction Characteristics of Soil

Using Standard Effort

■ ASTM D1883 Standard Test Method for California Bearing Ratio (CBR) of Laboratory-

Compacted Soils

The laboratory testing program often included examination of soil samples by an engineer.