3-Horace Mann Elementary Geotechnical Survey.pdf

Report Cover Page

Northside Elementary

School Geotechnical Engineering Report

November 13, 2025 | Terracon Project No. M1255070

Prepared for:

Fargo Public Schools

700 7th Street South

Fargo, ND 58103

860 9th St NE, Unit K

West Fargo, ND 58078

P (701) 282-9633

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

November 13, 2025

Fargo Public Schools

700 7th Street South

Fargo, ND 58103

Attn: Mr. James Hand, Director of Facilities

P: (701) 446 1023

E: handj@fargo.k12.nd.us

Re: Geotechnical Engineering Report

Northside Elementary School

1025 3rd Street North

Fargo, North Dakota

Terracon Project No. M1255070

Dear Mr. Hand, We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. PM1255070 dated

August 4, 2025. 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

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

Senior Engineer Department Manager

11/13/2025

Northside Elementary School | Fargo, North Dakota

Facilities | Environmental | Geotechnical | Materials i

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

Demolition Site Preparation Subgrade Preparation Excavation Fill Material Types Fill Placement and Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Construction Observation and Testing

Shallow Foundations Design Parameters – Compressive Loads Foundation Construction Considerations

Ground Improvement Floor Slabs

Floor Slab Design Parameters Floor Slab Construction Considerations

Below-Grade Structures Lateral Earth Pressures

Design Parameters Subsurface Drainage for Below-Grade Walls

Pavements General Pavement Comments Pavement Design Parameters Pavement Section Thicknesses Pavement Drainage Pavement Maintenance

Frost Considerations General Comments

Figures GeoModel

Facilities | Environmental | Geotechnical | Materials ii

Attachments

Exploration and Testing Procedures Site Location and Exploration Plans

Exploration and Laboratory Results

Supporting Information

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

Refer to each individual Attachment for a listing of contents.

http://client.terracon.com/

Introduction

This report presents the results of our subsurface exploration and Geotechnical

Engineering services performed for the proposed elementary school to be located at

1025 3rd Street North in Fargo, North Dakota. The purpose of these services was to provide information and geotechnical engineering recommendations relative to:

■ Subsurface soil conditions

■ Groundwater conditions

■ Seismic site classification per IBC

■ Site preparation and earthwork

■ Demolition considerations

■ Foundation design and construction

■ Floor slab design and construction

■ Lateral earth pressure

■ Pavement design and construction

■ Frost considerations

The geotechnical engineering Scope of Services for this project included the advancement of test borings, laboratory testing, engineering analysis, and preparation of this report.

Drawings showing the site and boring locations are shown on the Site Location and

Exploration Plan, respectively. The results of the laboratory testing performed on soil samples obtained from the site during our field exploration are included on the boring logs or as separate graphs in the Exploration and Laboratory Results section.

Project Description

Our final understanding of the project conditions is as follows:

Item Description

Information

Provided

A Request for Proposal (RFP) was provided to Terracon by FPS on July 21, 2025. The RFP included a project overview statement along with an itemized scope of services.

Subsequently, additional project details were provided to

Terracon by FPS via a phone conversation on July 28, 2025. In late October 2025, Icon Architects provided updates loads for the structure.

Item Description

Project

Description

The project includes demolition of the existing Horace Mann

Elementary School and construction of Northside Elementary

School and associated parking lot. The new structure footprint is partially situated in the footprint of the old school structure.

Proposed

Structure

The proposed Northside Elementary School is planned to cover a footprint of approximately 70,000 square feet. It is our understanding the west wing of the proposed structure is planned to be a three-story academic wing. We understand the east wing will primarily feature a gymnasium. We anticipate the central portion of the structure will include a common space and cafeteria/kitchen.

Building

Construction

It is our understanding the preferred construction is precast concrete walls and precast hollow-core planking. We assume slab-on-grade construction. No additional information regarding building construction was provided at the time of this proposal.

Finished Floor

Elevation

We understand the finished floor elevation has not been determined. We anticipate the first floor elevation will be constructed at or slightly above existing grade (within 1 to 2 feet of existing grade) to promote positive drainage away from the structure.

Maximum Loads

Provided and assumed loading conditions are identified below.

Provided:

■ Isolated Column Footings at 3-story area: 200 kips

■ Continuous Wall Footings at 3-story area: 8 to 10 kips per lineal foot (klf)

■ Continuous Wall Footings at gymnasium: 6.5 klf

Assumed:

■ Continuous Wall Footings at single-story area between gymnasium and 3-story area: less than 5 klf

■ Slabs: 150 pounds per square foot (psf)

Grading/Slopes

Based on the assumed finished floor elevation as described above, fills are not expected to exceed 1 to 2 feet to develop final grades around the planned building location. Structural fill placement will be necessary in the footprint of the existing structure as the existing structure includes a basement level which extends approximately 12 to 16 feet below existing grade.

Final slopes are anticipated to be minimal and only to achieve positive drainage from the proposed structures.

Below-Grade

Structures

We are unaware of a planned basement level for the new structure.

Free-Standing

Retaining Walls

Retaining wall structure locations have not been defined. We understand the project may include some short retaining walls.

Pavements

Paved drive lanes and a parking lot will be constructed on the approximate north third of the property. There will also be a paved service drive on the east side of the structure and a paved bus drop on the west side of the structure.

A preferred pavement surfacing has not been identified to us as part of the preliminary information. We assume both asphalt and concrete surfacing are being considered for this project.

Unless information is provided prior to the report, the anticipated ACI traffic categories and daily truck traffic for concrete pavements will be assumed to consist of:

■ Category A: Car parking areas and access lanes, 10 trucks per day

■ Category C: Buses

■ Category E: Garbage or fire truck lanes

Unless information is provided prior to the report, we assume that the traffic classification for asphalt pavements will consist of:

■ Class I: Parking stalls for autos and pickup trucks

■ Class II: Traffic consisting of home delivery trucks, trash pickup

■ Class III: Delivery lanes with up to ten 3-axle trucks per day

The pavement design period is 20 years.

Terracon should be notified if any of the above information is inconsistent with the planned construction, especially the grading limits and maximum anticipated loads, as modifications to our recommendations may be necessary.

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.

Parcel

Information

The project is located at 1025 3rd Street North in Fargo, North

Dakota.

The parcel covers approximately 5 acres.

Latitude: 46.8877° N, Longitude: 96.7823° W

See Site Location

Existing

Improvements

The property is currently occupied by Horace Mann Elementary

School, associated parking and drive areas, playground space and limited exterior structures (fences, lighting, etc.)

Current Ground

Cover

Mix of vegetated earthen cover, pavements, and sand/pea gravel)

Existing

Topography

The site appears to be relatively level. We anticipate the existing grades across the site are within 1 to 2 feet.

Geotechnical Characterization

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

Figures attachment of this report.

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

Model

Layer Layer Name General Description

1 PAVEMENT

Bituminous pavement – ranges in thickness from

7.5 to 8.5 inches (encountered at B-4, B-6, B-7, and B-16)

2 TOPSOIL Fat clay - black (only encountered at B-9 and B-11)

3 CLAY FILL

Fat clay mixture - gray, brown, and black, with occasional sand and gravel

4 SAND FILL

Poorly graded sand with silt or clay and gravel -medium to fine grained, brown to gray

(encountered at B-4, B-6, B-7, and B-16)

Model

Layer Layer Name General Description

MISCELLANEOUS

FILL

Pea gravel and clay mixture - gray and brown (only encountered at B-8)

6 UPPER FAT CLAY

Fat clay - shades of gray and brown, occasional lenses and laminations of silt, mostly mottled, stiff to soft

7 SILT

Silt - brownish gray, very loose to medium dense, seams of fat clay, waterbearing

LOWER FAT

CLAY

Fat clay - gray, stiff to very soft

UPPER GLACIAL

TILL

Sandy lean clay - gray, trace gravel, hard, seams of sand and silt (only encountered at B-5)

LOWER GLACIAL

TILL

Clayey sand - gray, trace gravel, medium to fine grained, very dense (only encountered at B-5)

The boreholes were observed while drilling and after completion for the presence and level of groundwater. While apparent groundwater levels were not observed in the borings while drilling, or for the short duration the borings could remain open, this does not necessarily mean the borings terminated above groundwater. Due to the low permeability of the fat clays encountered in the boring, 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. Based on the moisture condition of the samples encountered in the borings, we anticipate the groundwater level was on the order of 7 to 12 feet below existing grade at the time of our fieldwork.

Groundwater conditions may be different at the time of construction. Groundwater conditions may change because of seasonal variations in rainfall, runoff, and other conditions not apparent at the time of drilling. Long-term groundwater monitoring was outside the scope of services for this project.

Seismic Site Class

The seismic design requirements for buildings and other structures are based on Seismic

Design Category. Site Classification is required to determine the Seismic Design

Category for a structure. The Site Classification is based on the upper 100 feet of the site profile defined by a weighted average value of either shear wave velocity, standard penetration resistance, or undrained shear strength in accordance with Section 20.4 of

ASCE 7 and the International Building Code (IBC). Based on the soil properties observed at the site and as described on the exploration logs and results, our professional opinion is for that a Seismic Site Classification of E be considered for the project. Subsurface explorations at this site were extended to a maximum depth of 135 feet below existing grade. 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 condit ions below the current boring depth.

Geotechnical Overview

Based on the heavy loads anticipated at the three-story portion of the structure and at the gymnasium and the presence of highly compressible glacial lacustrine clays to depths greater than 100 feet, we estimate settlement of shallow foundations will be well in excess of 1 inch total and ½ inch differential (typical structural tolerances). For this reason, we recommend consideration be given to supporting the heavily-loaded portions of the structure on a ground improvement system such as rammed aggregate piers or vibratory stone columns More discussion on these ground improvement systems is included in the Ground Improvement section of this report. Alternatively, deep foundations such as driven piling could be considered for support. Generally speaking, deep driven piling is a less cost effective option.

The lightly-loaded portions of the structure may be supported on shallow spread foundations bearing on structural fill after the removal of all undocumented fill and desiccated fat clays from below foundation and floor slab areas. The Shallow

Foundations section addresses support of the lightly-loaded portions of the structure bearing on structural fill. The Floor Slabs section addresses slab-on-grade support of the structure using overexcavation techniques. 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 at the boring locations conducted within the proposed footprint of the school building to depths ranging from approximately 2 feet to 12 feet below existing grades. A majority of the borings conducted within the footprint encountered fill thicknesses of 2 to 3 feet. Borings B-4 and B-8 encountered greater fill thickness of approximately 12 feet and 6 feet, respectively. 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.

Additionally, at the boring locations conducted within the proposed school footprint, we encountered native fat clay soils which appear to be in a desiccated (dry) condition. The desiccated fat clays were generally found to depths ranging from 4 to 7 feet below existing grades. We anticipate that a greater extent of desiccation may be encountered in the treed area west of the existing school building. These desiccated soils are subject to swelling with increases in water content; therefore, if allowed to remain in place beneath footing and floor areas, there is a greater risk of detrimental building movement associated with swelling soils. To reduce the potential for detrimental building movement associated with swelling soils, we recommend removing the desiccated fat clays to a uniform depth of at least 6 feet below existing grade and replacing them with a structural fill, as outlined in the Earthwork section.

Based on our understanding that the existing school building features a basement level, we anticipate deep fill, as evidenced in boring B-4, will be encountered immediately exterior to the existing school footprint. The existing school building and associated exterior pavements, playground space, etc. will be razed prior to construction of the project. All materials derived from the demolition of the existing structures and pavements, including backfill materials, should be removed from the site, and not be allowed for re-use on site.

At planned pavement areas, primarily near boring locations B-9 through B-14, the subsurface soils encountered consisted of surficial topsoil or fat clay fill to depths ranging from approximately 1 to 2 feet below existing grade. At a minimum, we recommend all topsoil be removed from below planned pavement areas. Support of pavements on or above existing fill materials is discussed in this report. However, even with the recommended construction procedures, an inherent risk remains 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.

Based on condition of the soil samples recovered from the boreholes and laboratory testing, we estimate the groundwater table at the time of our fieldwork was on the order of 7 to 12 feet below existing grade. If groundwater is encountered during earthwork operations, it should be readily controlled by diverting the groundwater to sumps for collection and removal.

The near surface, stiff to medium stiff high plasticity fat clays 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 times 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.

Our opinion of pavement section thickness design has been developed based on our understanding of the intended use, assumed traffic, and subgrade preparation recommended herein using methodology contained in ACI 330 “Guide to Design and

Construction of Concrete Parking Lots” and adjusted with consideration to local practice.

The Pavements section includes minimum pavement component thicknesses.

Expansive soils are present on this site. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these procedures are followed, some movement and (at least minor) cracking in the structure should be anticipated. The severity of cracking and other damage such as uneven floor slabs will probably increase if modification of the site results in excessive wetting or drying of the expansive soils. Eliminating the risk of movement and distress may not be feasible, but it may be possible to further reduce the risk of movement if significantly more expensive measures are used during construction. Some of these options are discussed in this report such as complete replacement of expansive soils.

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

Earthwork

Earthwork is anticipated to include demolition, 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.

Demolition

The proposed building will be constructed within the footprint of the existing school building which will need to be demolished, as well as exterior sidewalks, pavements, utilities, and playground features. Materials derived from the demolition of any existing structures and pavements should be removed from the site, and not be allowed for use on site.

We recommend existing foundations, slabs, utilities, and exterior backfill be removed from within the proposed building footprint and at least 5 feet beyond the outer edge of new foundations.

For areas outside the proposed building footprint and foundation bearing zones, existing foundations, floor slabs, and utilities should be removed where they conflict with proposed utilities, retaining walls, and pavements. In such cases, existing foundations, floor slabs, and utilities should be removed to a depth of at least 2 feet below the affected utility or design pavement subgrade elevation.

Site Preparation

Prior to placing fill, existing vegetation, topsoil, and root mats should be removed.

Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas.

Mature trees are located within or near the footprint of the proposed building, which will require removal at the onset of construction. Tree root systems can remove substantial moisture from surrounding soils. Where trees are removed, the full root ball and all associated dry and desiccated soils should be removed. The soil materials which contain less than 5 percent organics can be reused as general fill provided the material is moisture conditioned and properly compacted.

Where fill is placed on existing slopes steeper than 5H:1V, benches should be cut into the existing slopes prior to fill placement. The benches should have a minimum vertical face height of 1 foot and a maximum vertical face height of 3 feet and should be cut wide enough to accommodate the compaction equipment. This benching will help provide a positive bond between the fill and natural soils and reduce the possibility of failure along the fill/natural soil interface.

Subgrade Preparation

We recommend that undocumented fill soils and desiccated native fat clay soils encountered within the footprint of the proposed structure be removed to a uniform minimum depth of 6 feet below existing grades followed by replacement with structural fill. Structural fill placed beneath the entire footprint of the foundations should extend horizontally a minimum distance of 2/3 times the depth of structural fill or 16 inches, whichever is greater, beyond the outside edge of footings. As previously discussed, greater fill depths are anticipated exterior to the existing school building due to the presence of a basement level. These undocumented fill soils should also be removed from below the proposed school footprint followed by replacement with structural fill.

The near-surface materials anticipated to be developed as excavation spoils are not considered suitable for reuse as structural fill.

As noted in Geotechnical Characterization, borings B-10 and B-12 through B-14 encountered previously placed fill to an approximate depth of 2 feet below existing grade. We have no records to indicate the degree of control, and consequently, the fill as-is is considered unreliable for support of pavements. If the owner elects to construct pavements on existing fill, the following protocol should be followed. If the owner elects to construct pavements on the existing fill, the following protocol should be followed.

The existing soils can be removed to a minimum of 18 inches beneath proposed pavement sections. The exposed subgrade should then be scarified and recompacted to a minimum depth of 12 inches. A structural fill or fills meeting the material requirements outlined below should be placed at a minimum in the upper 18 inches beneath the proposed pavement sections.

Once the planned subgrade elevation has been reached, the entire pavement area should be proofrolled with an adequately loaded vehicle such as a fully-loaded tandem-axle dump truck. The proofrolling should be performed under the observation of the

Geotechnical Engineer or representative. Areas excessively deflecting under the proofroll should be delineated and subsequently addressed by the Geotechnical Engineer. Such areas should be undercut and replaced with either new structural fill or suitable, existing on-site materials. Excessively wet or dry material should either be removed or moisture conditioned and recompacted.

Based upon the subsurface conditions determined from the geotechnical exploration, subgrade soils exposed during construction are anticipated to be relatively workable;

however, the workability of the subgrade may be affected by precipitation, repetitive construction traffic or other factors. If unworkable conditions develop, workability may be improved by scarifying and drying.

Excavation

The natural soils are susceptible to disturbance during construction. Therefore, we recommend excavating be performed by a backhoe with a smooth cutting surface. Any natural soils which become disturbed beneath footing and floor areas should be removed and replaced with a well-compacted structural fill

Fill Material Types

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

Structural fill is typically material used below structures and pavements. General fill is material used to achieve grade outside of these areas.

Reuse of On-Site Soil: Excavated on-site soil may be selectively reused as structural fill below pavements and exterior backfill of the building in landscape areas and general fill below other landscaping areas. On-site fat clays, once properly moisture conditioned may be reused as structural fill within the existing school basement area up to an elevation 5 below footings and floor slabs.

Material property requirements for on-site soil for use as general fill and structural fill are noted in the table below:

Property General Fill Structural Fill

Composition Free of deleterious material Free of deleterious material

Maximum particle size 6 inches

(or 2/3 of the lift thickness) 2 inches

Fines content Not limited Not limited

Plasticity Not limited Plasticity index of less than 55

GeoModel Layer

Expected to be Suitable1 2 through 6 3 and 6

1. Based on subsurface exploration. Actual material suitability should be determined in the field at time of construction.

Imported Fill Materials: Imported fill materials should meet the following material property requirements. Regardless of its source, compacted 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.

Soil Type 1

USCS

Classification

Acceptable Parameters

(for Structural Fill)

High Plasticity

Cohesive (only for pavement areas)

CH

Plasticity index of less than 55

100% passing 2-inch sieve

Granular

SP, SP-SM, SP-

SC, SW, SW-SM,

SW-SC, SM, SC

All: 100% passing 2-inch sieve

Less than 20% passing No. 200 sieve

(SM only)

Non-Frost

Susceptible (NFS) 2

SW, SP

100% passing 1-inch sieve

Less than 5% passing No. 200 sieve

1. Structural and general fill should consist of approved materials 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.

Fill Placement and 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

4 to 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 1,2,3

98% of max. below foundations and within 1 foot of finished pavement subgrade

95% of max. above foundations, below floor slabs, and more than 1 foot below finished pavement subgrade

95% of max. for high plasticity cohesive soils placed as structural fill within existing basement area

90% of max.

Water Content

Range

Granular: as required to achieve min.

compaction requirements

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

Same as structural fill

Same as structural 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.

3. If the granular material is a coarse sand or gravel, or of a uniform size, or has a low fines content, compaction comparison to relative density may be more appropriate. In this case, granular materials should be compacted to at least

70% relative density (ASTM D 4253 and D 4254). Materials not amenable to density testing should be placed and compacted to a stable condition observed by the Geotechnical Engineer or representative.

Utility Trench Backfill

Any soft or unsuitable materials encountered at the bottom of utility trench excavations should be removed and replaced with structural fill or bedding material in accordance with public works specifications for the utility to be supported. This recommendation is particularly applicable to utility work requiring grade control and/or in areas where subsequent grade raising could cause settlement in the subgrade supporting the utility.

On-site materials are considered suitable for backfill of utility and pipe trenches from 1 foot above the top of the pipe to the final ground surface, provided the material is free of organic matter and deleterious substances.

Trench backfill should be mechanically placed and compacted as discussed earlier in this report. Compaction of initial lifts should be accomplished with hand-operated tampers or other lightweight compactors.

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 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

Upon completion of filling and grading, care should be taken to maintain the subgrade water content prior to construction of grade-supported improvements such as floor slabs and pavements. Construction traffic over the completed subgrades should be avoided.

The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. Water collecting over or adjacent to construction areas should be removed. If the subgrade freezes, desiccates, saturates, or is disturbed, the affected material should be removed, or the materials should be scarified, moisture conditioned, and recompacted prior to floor slab construction.

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.

Excavations or other activities resulting in ground disturbance have the potential to affect adjoining properties and structures. Our scope of services does not include review of available final grading information or consider potential temporary grading performed by the contractor for potential effects such as ground movement beyond the project limits. A preconstruction/ precondition survey should be conducted to document nearby property/infrastructure prior to any site development activity. Excavation or ground disturbance activities adjacent or near property lines should be monitored or instrumented for potential ground movements that could negatively affect adjoining property and/or structures.

Construction Observation and Testing

The earthwork efforts should be observed by the Geotechnical Engineer (or others under their direction). Observation should include documentation of adequate removal of surficial materials (vegetation, topsoil, undocumented fill, desiccated fat clays, and pavements), evaluation and remediation of existing fill materials, as well as proofrolling and mitigation of unsuitable areas delineated by the proofroll.

Each lift of compacted fill should be tested, evaluated, and reworked, as necessary, as recommended by the Geotechnical Engineer prior to placement of additional lifts. Each lift of fill should be tested for density and water content 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. Where not specified by local ordinance, one density and water content test should be performed for every 100 linear feet of compacted utility trench backfill and a minimum of one test performed for every 12 vertical inches of compacted backfill.

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

Geotechnical Engineer. If unanticipated conditions are observed, the Geotechnical

Engineer should prescribe mitigation options.

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

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 of lightly loaded building sections (wall loads less than 5 kips per lineal foot).

Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing

Pressure 1, 2

2,000 psf

Required Bearing Stratum

Structural fill extending to undisturbed native fat clays

Minimum Foundation Dimensions Columns: 30 inches

Continuous: 18 inches

Ultimate Passive Resistance

(equivalent fluid pressures) 390 pcf (granular backfill)

Sliding Resistance

0.35 allowable coefficient of friction -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, 7

About ½ 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. Additional geotechnical consultation will be necessary if higher loads are anticipated.

3. Unsuitable or desiccated fat clays should be overexcavated and replaced per the recommendations presented in 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. Assumes no hydrostatic pressure.

5. Can be used to compute sliding resistance where foundations are placed on suitable soil/materials. Frictional resistance for granular materials is dependent on the bearing pressure which may vary due to load combinations. For fine-grained materials, lateral resistance using cohesion should not exceed ½ the dead load.

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 noted for equivalent-loaded foundations and bearing elevation as measured over a span of 50 feet.

Foundation Construction Considerations

As noted in Earthwork, the footing excavations should be evaluated under the observation 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 before foundation concrete is placed.

As discussed in Earthwork, desiccated high plasticity clays and undocumented fills encountered beneath the anticipated building footprint. The dry fat clays (both native and fill), if left in below footings, will be susceptible to increases in water content by means of capillary action over time which could result in detrimental foundation movement associated with swelling of the clays. In an effort to reduce the risk of detrimental movement, we recommend these unsuitable soils be removed from below the building footprint to a uniform depth of 6 feet below existing grade. If the extent of desiccation is found to extend below this level, the excavation should be extended deeper to remove the desiccated native fat clays. The over-excavation should then be backfilled up to the footing base elevation, with structural fill placed as recommended in the Earthwork section.

Overexcavation for structural fill placement below footings should be conducted as shown below. The overexcavation should be backfilled up to the footing base elevation, with structural fill placed, as recommended in the Earthwork section.

Differential settlement between the building sections supported on ground improvement elements and the section not supported on ground improvement is anticipated to approach ½ to ¾ inch. Settlement joints in the foundation and flexible partitions should be considered to accommodate this differential movement. If this differential settlement is unacceptable, consideration should be given to supporting all building sections on ground improvement elements.

Ground Improvement

The heavily loaded sections of the building (three-story area and gymnasium) can be supported on the lower strength native soils encountered at the site if ground improvement methods such as rammed aggregate piers or vibratory stone columns are utilized.

A rammed aggregate pier or vibratory stone column consists of a stone-filled column constructed by excavating a cylindrical hole and backfilling it with crushed stone placed in lifts and applying a high degree of compactive effort resulting in stone filled piers. The aggregate pier/stone column construction process not only results in a rigid stone-filled column that lends support to structures, it also helps to densify the soils surrounding the pier.

We understand if ground improvement is utilized for support of portions of the school building, the ground improvement design firm will be the geotechnical engineer of record for these foundations. As such, the design firm should provide the necessary design parameters for the planned foundation system including, but not limited to, net allowable bearing capacity, settlement estimates and foundation-specific earthwork recommendations. Based on our past experience with ground improvement in the Fargo area, we estimate ground improvement could provide an improved net allowable bearing on the order of 3,000 to 4,000 psf.

Minimum foundation depth for frost protection should be in accordance with local design practice, which is 60 inches for footings in heated areas and 72 inches for footings in unheated areas. The owner or structural engineer should verify that all aspects of the ground improvement design and performance are within the design tolerance of the structures.

Floor Slabs

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

The subgrade soils are comprised of undocumented fill soils and underlying desiccated high plasticity clays exhibiting the potential to swell with increased water content.

Construction of floor slabs, combined with the removal of trees, and revising site drainage creates the potential for gradual increased water contents within the clays.

Increases in water content will cause the clays to swell and damage the floor slab. To reduce the swell potential to less than about 1 inch, the soils (fill and native) located within 6 feet of existing grade should be removed and replaced with an approved granular structural fill as recommended in Earthwork.

Floor Slab Design Parameters

Item Description

Floor Slab

Support1

A minimum 6 inches of free draining (less than 5% passing the

No. 200 sieve) aggregate is recommended to be provided directly below floor slabs. This should be considered part of the recommended granular structural fill thickness beneath the floor slab areas.

Subgrade prepared and compacted as recommended in

Earthwork

Estimated Modulus of Subgrade

Reaction 2

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.

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

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

Below-Grade Structures

We understand below-grade structure such as stormwater detention chambers may be installed below the future green space south of the school or beneath the planned parking lot north of the school. We assume the chamber system will be similar to the

StormTech® system. Based on the soil conditions encountered in the borings and laboratory testing completed on collected samples, a net allowable bearing pressure of

2,000 psf may be used for design of the underground stormwater detention chamber system.

Lateral Earth Pressures

Design Parameters

Structures, such as short retaining walls, 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 in the diagram below. Active earth pressure is commonly used for design of free-standing cantilever retaining walls and assumes wall movement. The “at-rest” condition assumes no wall movement and is commonly used for basement walls, loading dock walls, or other walls restrained at the top. The recommended design lateral earth pressures do not include a factor of safety and do not provide for possible hydrostatic pressure on the walls (unless stated).

Lateral Earth Pressure Design Parameters

Earth

Pressure

Condition 1

Coefficient for

Backfill Type 2

Surcharge

Pressure 3 p1 (psf)

Equivalent Fluid Pressures

(psf) 2,4

Unsaturated 5 Submerged 5

Active (Ka) Granular - 0.33

Cohesive - 0.53

(0.33)S

(0.53)S

(40)H

(60)H

(80)H

(90)H

At-Rest (Ko) Granular - 0.50

Cohesive - 0.69

(0.50)S

(0.69)S

(60)H

(80)H

(90)H

(100)H

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

Lateral Earth Pressure Design Parameters

Earth

Pressure

Condition 1

Coefficient for

Backfill Type 2

Surcharge

Pressure 3 p1 (psf)

Equivalent Fluid Pressures

(psf) 2,4

Unsaturated 5 Submerged 5 pressure, wall must move horizontally to mobilize resistance. Fat clay or other expansive soils should not be used as backfill behind the wall.

2. Uniform, horizontal backfill, with a maximum unit weight of 120 pcf for cohesive soils and 120 pcf for granular soils.

3. Uniform surcharge, where S is surcharge pressure.

4. Loading from heavy compaction equipment is not included.

5. To achieve “Unsaturated” conditions, follow guidelines in Subsurface Drainage for Below-Grade Walls below. “Submerged” conditions are recommended when drainage behind walls is not incorporated into the design.

Backfill placed against structures should consist of granular soils or low plasticity cohesive soils. For the granular values to be valid, the granular backfill must extend out and up from the base of the wall at an angle of at least 45 degrees from vertical for the active case.

Footings, floor slabs or other loads bearing on backfill behind walls may have a significant influence on the lateral earth pressure.