J03a Georeport Pryor Clinic Expansion Construction.pdf

Report Cover Page

Pryor Health Center -

Foundation Improvements Geotechnical Engineering Report

November 27, 2024 | Terracon Project No. 26245031

Prepared for:

K.F. Davis Engineering Inc.

530 La Gonda Way, Suite E

Danville, California 94526

2110 Overland Avenue, Suite 124

Billings, Montana 59102

P (406) 656-3072

Terracon.com

Facilities | Environmental | Geotechnical | Materials

Report Cover Letter to Sign

November 27, 2024

K.F. Davis Engineering Inc.

530 La Gonda Way, Suite E

Danville, California 94526

Attn: Lesa Durham, President

P: (925) 743-8884

E: lesa.durham@KFDE.com

Re: Geotechnical Engineering Report

Pryor Health Center - Foundation Improvements

148 Pryor Gap Road

Pryor, Montana

Terracon Project No. 26245031

Dear Ms. Durham:

We have completed the scope of Geotechnical Engineering services for the above referenced project in general accordance with Terracon Proposal No. P26245031 dated

July 18, 2024 and subsequent signed Work Order #172-24-22, signed September 19, 2024. This report presents the findings of the subsurface exploration and provides geotechnical recommendations concerning earthwork and the design and construction of foundations 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

Hudson Dorian, E.I.T. Matthew D. Hoffmann, P.E.

Field Engineer Principal | Office Manager https://na3.documents.adobe.com/verifier?tx=CBJCHBCAABAA0vJRr7NqxTlCRT9-ikNGjQ0w3g7dQfP1 https://na3.documents.adobe.com/verifier?tx=CBJCHBCAABAA0vJRr7NqxTlCRT9-ikNGjQ0w3g7dQfP1

Pryor Health Center - Foundation Improvements | Pryor, Montana

Facilities | Environmental | Geotechnical | Materials i

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

Demolition Site Preparation Subgrade Preparation Existing Fill Excavation Soil Stabilization 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 Design Parameters – Overturning and Uplift Loads Construction Adjacent to Existing Building Foundation Construction Considerations

Micropile Foundations Micropile Design Pile Load Testing Micropile Construction Considerations

Below-Grade Structures Lateral Earth Pressures

Design Parameters Subsurface Drainage for Below-Grade Walls

Frost Considerations General Comments

Figures GeoModel

Attachments

Facilities | Environmental | Geotechnical | Materials ii

Exploration and Testing Procedures Photography Log

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/ http://client.terracon.com/

Facilities | Environmental | Geotechnical | Materials 1

Introduction

This report presents the results of our subsurface exploration and Geotechnical

Engineering services performed for the proposed renovations of the Pryor Health Clinic at 148 Pryor Gap Road in Pryor, Montana. 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

■ Dewatering considerations

■ Foundation design and construction

■ Lateral earth pressure

■ 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 and as separate graphs in the Exploration Results section.

Project Description

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

Item Description

Information

Provided

On July 3, 2024, Ms. Lesa Durham of KFDE submitted a request for proposal through email, including a general description of the planned development and a set of civil and structural drawings for the planned additions.

Facilities | Environmental | Geotechnical | Materials 2

Project

Description

The project includes a series of improvements to the Pryor

Health Center: a revision to the entryway; a new elevator pit, the existing foundation to be reinforced/supported with micropiles where the existing foundation is anticipated to be undermined by the addition of the elevator pit; a new set of attic access stairs on the eastern face of the structure; and a replacement air conditioner (AC) unit pad to the north of the building. Based on the site plan drawings, the new entryway is planned to be slab-on-grade with continuous footings, the attic-access stairway supported on isolated and continuous footings, the new AC unit pad is to be slab-on-grade, and the elevator pit is to be slab-on-grade.

Finished Floor

Elevation

The finished floor elevations were not provided. The finished floor elevation of the entrance improvements is assumed to be no more than 1 to 2 feet from existing grade, matching that of the existing structure. The finished floor elevation of the elevator pit is planned to be on the order of 4 feet below the existing basement slab, and approximately 13 feet below existing grade.

Maximum Loads

Anticipated foundation loads were not provided. In the absence of information provided by the design team, we have used the following loads in estimating settlement based on our experience with similar projects.

■ Columns: 50 kips

■ Walls: 3 kips per linear foot (klf)

■ Mats/Slabs: 150 pounds per square foot (psf)

Estimated design loads for the proposed micropiles (MP 1 to 4) were provided by the client, as follows (maximum loads, accounting for dead, live, and snow loading).

■ MP 1: 22.7 kips

■ MP 2: 64.7 kips

■ MP 3: 27.3 kips

■ MP 4: 24.2 kips

Grading/Slopes Proposed finished grade elevation for the additions is anticipated to be the same as the current structure.

Below-Grade

Structures

The existing structure features a basement. In the proposed additions, an elevator pit with sump basin is planned to extend below the existing floor of the basement, with a floor elevation 4 feet below the floor elevation of the basement slab.

Facilities | Environmental | Geotechnical | Materials 3

Free-Standing

Retaining Walls None stated, assumed to be outside of scope of services.

Pavements None stated, assumed to be outside of scope of services.

Building Code 2021 IBC

Terracon should be notified if any of the above information is inconsistent with the planned construction, 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.

Item Description

Parcel

Information

The project is located at 148 Pryor Gap Road in Pryor, Montana.

The project includes three areas of interest, on the northern, eastern and southern sides of the Pryor Health Center.

Latitude/Longitude (approximate) 45.42833°N, 108.53683°W

See Site Location

Existing

Improvements

The project improvements are within the grounds of the Pryor

Health Center, adjacent to the existing main structure, paved parking lots, and landscaped areas.

Current Ground

Cover Exterior concrete flatwork and/or landscaped grass and foliage.

Existing

Topography

The property slopes gently towards the northeast, towards a drainage ditch, with an overall elevation change up to 4 feet within the working area around the structure.

Facilities | Environmental | Geotechnical | Materials 4

Geology

Based on the Montana Bureau of Mines and Geology (MBMG)

Geologic Map of the Bridger Quadrangle1, the site sits within an alluvial fan deposit, characterized by poorly-sorted deposits of gravel, sand, silt, and clay, with variable thickness. An excerpt is provided below.

1. Lopez, D.A., 2000, Geologic map of the Bridger 30' x 60' quadrangle, Montana: Montana

Bureau of Mines and Geology Geologic Map 58, 1 sheet, scale 1:100,000.

We also collected photographs at the time of our site visits. Representative photos are provided in our Photography Log.

Geotechnical Characterization

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

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

Facilities | Environmental | Geotechnical | Materials 5

Model

Layer Layer Name General Description

Surficial

Materials

Asphalt, base course and topsoil encountered depending on boring location; Borings B-1 and B-2 we advanced through asphalt pavement, B-3 in a landscaped area.

2 Fill Lean clay with gravel encountered in Boring B-1 over organic clay, grey-brown to black-brown.

3 Clay Clay soils with variable gravel and sand content, encountered at all three boring locations.

4 Organic Clay

Organic clay soil, grey-brown to black-brown, roots throughout with an organic odor, encountered within 5 feet of ground surface at Borings B-1 and B-2 (trace).

Sand and

Gravel

Sand and Gravel soils with variable fines content, tan-brown to red-brown to grey-tan, loose to dense above

30 feet below ground surface, then very dense.

The borings were advanced dry using the hollow-stem auger (HSA) drilling technique that allowed short term groundwater observations to be made while drilling.

Groundwater was encountered between 7 to 10 feet below ground surface (bgs), from

4,060 to 4,063 feet elevation above mean sea level (MSL). Groundwater conditions may be different at the time of construction due to 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 D be considered for the project. Subsurface explorations at this site were extended to a maximum depth of 50.5 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.

Facilities | Environmental | Geotechnical | Materials 6

Corrosivity

The table below lists the results of laboratory soluble sulfate, electrical resistivity, 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)

Soil

Description

Soluble

Sulfate

Electrical

Resistivity

(Ω-cm) pH

B-1 3 - 5 Lean Clay 0.0035 1,500 8.1

Results of soluble sulfate testing can be classified in accordance with ACI 318 – Building

Code Requirements for Structural Concrete. Numerous sources are available to characterize corrosion potential to buried metals using the parameters above.

ANSI/AWWA is commonly used for ductile iron, while threshold values for evaluating the effect on steel can be specific to the buried feature (e.g., piling, culverts, welded wire reinforcement, etc.) or agency for which the work is performed. Imported fill materials may have significantly different properties than the site materials noted above and should be evaluated if expected to be in contact with metals used for construction.

Consultation with a NACE certified corrosion professional is recommended for buried metals on the site.

Mapping by the NRCS includes qualitative severity of corrosion to concrete and steel.

Based on this source, the near-surface materials are rated “Moderate” for corrosion to concrete and “High” for corrosion of steel.

Geotechnical Overview

Our geotechnical exploration was conducted for the proposed renovations to the IHS

Pryor Health Center building in Pryor, Montana. Three borings were advanced to depths between 16.5 and 50.5 feet bgs. The original location of the borings, shown in the proposal, had to be adjusted for practical access; this most affected Boring B-1, which had to be moved from beside the existing clinic to the parking lot. As-drilled boring locations are shown in the attached Exploration Plan. This report addresses the geotechnical recommendations for the proposed micropile foundation system that will support the portion of the existing foundation for the construction of the elevator pit, and the shallow foundation system to be used for the new entryway, elevator pit, attic access stairway, and the replacement foundation pad for the air conditioner units.

Facilities | Environmental | Geotechnical | Materials 7

The subsurface generally consisted of alluvial soils in moderately thick (2-5 feet) layers, overlying dense gravel extending to the maximum depth of exploration, as stated in the

Geotechnical Characterization section.

We believe a micropile foundation system will be feasible at this site, bearing into the very dense gravel soils, discussed in further detail in the Micropile Foundations section. We also believe that the exterior improvements (entryway, attic stairs, AC unit pad) can be supported on shallow foundation systems as proposed. Both are conditional to the implementation of our recommendations in the design and construction phases of this project.

In the vicinity of the proposed attic staircase (east of the existing structure) weak sandy clay soils are anticipated to be present at the planned bearing elevation. It is recommended that these soils be overexcavated to more reliable gravel with clay and sand, with engineered fill used to backfill up to bearing elevation, discussed in the

Subgrade Preparation section.

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 engineered 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 and floor slabs.

Demolition

The proposed additions will be constructed within and adjacent to the existing Pryor

Health Clinic building. The current entryway will be significantly modified, requiring the removal of the existing ramp and stairway. It is assumed that the existing foundation of the ramp and stairway will be excavated out prior to construction of the replacement features. The attic access stairway will be constructed in the location of existing sidewalk slabs, which will need to be removed.

The basement of the structure will need to be significantly adjusted for the new elevator pit, requiring cutting of the existing floor slab and removal of soils beneath existing footings to the planned bearing elevation of the elevator pit slab. It has been assumed that measures will be implemented to provide the necessary support to the structure

Facilities | Environmental | Geotechnical | Materials 8 before this process begins, which may include the installation of the proposed micropiles in conjunction with other temporary measures to prevent undermining of the existing structure foundations.

Any utilities within the proposed location of the additions will need to be removed prior to construction. It has been assumed that a more detailed survey of the existing utility lines is included in the pre-construction planning.

Site Preparation

Prior to placing fill, existing vegetation, topsoil, root mats, exterior slabs, asphalt pavement, and existing fill should be removed. Complete stripping of the topsoil should be performed in the proposed building and parking/driveway areas.

Subgrade Preparation

For the proposed elevator pit and column footing slab, it is anticipated that the elevation for the bottom of the elevator pit slab will be within the layer of silty gravel with sand, which sits over a layer of silty sand with gravel. It is recommended that this soil be scarified to a minimum depth of 12 inches and recompacted to a minimum of 98% of the maximum dry density, as determined by ASTM D689.

During our subsurface exploration, groundwater was encountered around 10 feet bgs

(4,063 feet MSL) in the parking lot directly in front of the clinic building. Based on the plan drawings, it was estimated that the floor of the basement was 9 feet below ground surface of the parking lot, and that the bottom of the existing footings were approximately 11 feet bgs. We recommend a minimum 3 feet of vertical separation between the bottom of new footings and the groundwater table, in order to prevent increased settlement and softening of bearing surface. At the time of report preparation, it was unknown how the existing clinic building mitigated the proximity of groundwater to the estimated bearing elevation, either through an impermeable perimeter boundary, a sump and pump system, or by other means. Whatever means are currently in place should be evaluated and adjusted in respect to accommodate the new lowest bearing elevation of the structure, the bottom of the elevator pit slab. The contractor should be prepared to perform construction dewatering for construction of at least the elevator pit, depending on the groundwater table at time of construction. Based on groundwater elevation, the use of waterstop at construction joints and waterproofing membrane attached to foundation walls below groundwater elevation should be considered.

For the proposed new entryway, three distinct bearing elevations were proposed according to the site plans; the ramp and stairway, the ‘landing’, and the covered extension. The ramp and stairway will bear at approximately at 4,069.5 feet MSL, the landing will bear at approximately 4,065 feet MSL, and the covered extension will bear

Facilities | Environmental | Geotechnical | Materials 9 at approximately 4,063 feet MSL. Based on Boring B-1, the ramp and stairway are anticipated to bear onto medium stiff clay, the landing onto dense, poorly graded gravel with clay and sand, and the covered extension onto medium dense, silty gravel with sand. In the boring location, organic clays were encountered near the anticipated bearing elevation of the ramp and stairway, denoted by a specific, sharp odor and black coloration. We do not recommend that footings bear on or over organic clay deposits; if this soil is encountered during excavation in the planned location of a foundation element, it should be removed to the depth of the next reliable bearing stratum and replaced with Structural Fill. As much of the new construction in this vicinity will take place within previously developed areas, it is not considered likely that organic soils will be encountered, but precaution should still be taken.

For the proposed attic access stairs, based on the nearby Boring B-2, the foundation footings are anticipated to bear into lean clay, at approximately 4,067 feet MSL. This soil is anticipated to cause a larger degree of settlement due to consolidation; although the loading is anticipated to be low, the soil is not heavily consolidated. Since this layer was only found to be 2.5 feet thick onsite, we recommend this soil be overexcavated to the depth of the poorly graded gravel with clay and sand beneath and replaced with

Structural Fill.

For the proposed AC pad, it is anticipated that the slab-on-grade foundation will bear approximately 1 foot below existing grade, within the near-surface clayey gravel or sandy lean clay (based on the nearby Boring B-3). Although these strata appeared reasonably stiff during the site investigation, their clay content may pose a risk of shrink-swell movement, leading to damage of the slab. Thus, it is recommended that these soils be overexcavated down to the depth of the clayey gravel with sand or poorly graded gravel with clay and sand, approximately 4 to 5 feet bgs, which are anticipated to be less susceptible to shrink and swell movements.

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

Structural Fill soils should then be placed to the proposed design grade and the moisture content and compaction of subgrade soils should be maintained until foundation construction. Structural Fill placement should follow the recommendations included in the Earthwork Construction Considerations section.

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.

Facilities | Environmental | Geotechnical | Materials 10

Existing Fill

As the elevator pit is planned to be constructed within the footprint of the existing health clinic building, it is anticipated that engineered fill materials, if previously used below the slab and/or footings of the existing health clinic building, may be encountered in the process of excavation to the planned bearing elevation of the elevator pit. These materials may be reused as engineered fill for the new construction, following review by the Geotechnical Engineer provided they meet the gradation criteria referenced in the

Fill Material Types section of this report. Even if the existing engineered fill met the criteria when placed during the initial construction, the fill should be reevaluated;

infiltration of fines into the material or mixing of the soils during excavation may alter the gradation of the material, and thus its suitability as engineered fill. If reuse is in consideration, excavated existing engineered fill should be properly sorted and stored separately from the natural subgrade soils.

Excavation

We anticipate that excavations for the proposed construction can be accomplished with conventional earthmoving equipment. The bottom of excavations should be thoroughly cleaned of loose soils and disturbed materials prior to backfill placement and/or construction.

The largest obstacle to excavation for this rehabilitation project will be the limited space available in the basement of the clinic. It was not known at the time of report preparation how much the existing clinic building would be modified or deconstructed for the renovations (i.e. how much vertical space will be available, how equipment can be conveyed into the basement of the structure, etc.). For this reason, arrangements should be made for the use of smaller, hand-propelled excavation and compaction equipment. Proper engineering controls, administrative controls, and personal protective equipment should be in place if gas-powered equipment is to be used in the basement area, in accordance with the Occupational Safety and Health Association (OSHA) 29 CFR, Subpart S “Underground Construction, Caissons, Cofferdams, and Compressed Air”, Subpart D, “Occupational Health and Environmental Controls”, and Subpart AA, “Confined spaces in Construction”, as applicable.

Soil Stabilization

To reduce potential settlement of structures due to loose or soft subgrade soils, soil improvement or stabilization methods can be implemented. Methods of subgrade improvement, as described below, could include scarification, moisture conditioning and recompaction, removal of unstable materials and replacement with granular fill (with or without geosynthetics), and chemical stabilization. The appropriate method of improvement, if required, would be dependent on factors such as schedule, weather, the

Facilities | Environmental | Geotechnical | Materials 11 size of area to be stabilized, and the nature of the instability. More detailed recommendations can be provided during construction as the need for subgrade stabilization occurs. Performing site grading operations during warm seasons and dry periods would help reduce the amount of subgrade stabilization required.

If the exposed subgrade is found to be unstable by the geotechnical engineer, it could be stabilized using one of the methods outlined below.

■ Scarification and Recompaction - It may be feasible to scarify, dry, and recompact the exposed soils. The success of this procedure would depend primarily upon favorable weather and sufficient time to dry the soils. Stable subgrades likely would not be achievable if the thickness of the unstable soil is greater than about 1 foot, if the unstable soil is at or near groundwater levels, or if construction is performed during a period of wet or cool weather when drying is difficult.

■ Structural Fill - The use of Structural Fill gravel is a common procedure to improve subgrade stability. Typical undercut depths would be expected to range from about 24 to 48 inches below finished subgrade elevation, but recommended depth is dependent on site conditions and anticipated loading. The use of high modulus geotextiles (i.e., engineering fabric or geogrid) could also be considered after underground work such as utility construction is completed. Equipment should not be operated above the fabric or geogrid until one full lift of Structural

Fill is placed above it. The maximum particle size of granular material placed over geotextile fabric or geogrid should not exceed 1-1/2 inches.

■ Chemical Modification - Improvement of subgrades with portland cement or class C fly ash could be considered for improving unstable soils. Chemical modification should be performed by a pre-qualified contractor having experience with successfully stabilizing subgrades in the project area on similar sized projects with similar soil conditions. Results of chemical analysis of the additive materials should be provided to the geotechnical engineer prior to use. The hazards of chemicals blowing across the site or onto adjacent property should also be considered. Additional testing would be needed to develop specific recommendations to improve subgrade stability by blending chemicals with the site soils. Additional testing could include, but not be limited to, determining the most suitable stabilizing agent, the optimum amounts required, the presence of sulfates in the soil, and freeze-thaw durability of the subgrade.

Further evaluation of the need and recommendations for subgrade stabilization can be provided during construction as the geotechnical conditions are exposed.

Facilities | Environmental | Geotechnical | Materials 12

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 5 feet horizontally of structures, 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 engineered fill, provided they meet the gradation requirements stated in this section. Portions of the on-site soil have an elevated fines content and will be sensitive to moisture conditions

(particularly during seasonally wet periods) and may not be suitable for reuse when above optimum moisture content.

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)

3 inches

Fines content Not limited Less than 12% Passing No. 200 sieve

Plasticity Not limited Maximum plasticity index of 10

GeoModel Layer

Expected to be Suitable1 1, 2, 3, 5 5

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.

Facilities | Environmental | Geotechnical | Materials 13

Soil Type 1

USCS

Classification

Acceptable Parameters (for Structural

Fill)

Structural Fill

GW, GP, SW, SP,

and dual (GM/SM) symbols

Below foundation elevation, below slab areas, and as replacement backfill

Crushed Base

Course

Montana Public

Works Standard

Specifications

(MPWSS), 7th Ed, Section 02235, ¾ or

1-½ inch minus

Leveling course below slabs and above

Structural Fill

Non-Frost

Susceptible Fill

(NFS)

GP, GW, SP, SW

Below exterior flatwork critical to project to mitigate frost-action

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.

Additional geotechnical consultation should be provided prior to use of uniformly graded gravel on the site.

2. Structural Fill, defined as imported aggregate, should meet the following criteria outlined below:

Gradation Percent Finer by Weight (ASTM C136)

1 ½”

No. 4 ............................................................................................ 30-60

No. 200 ..................................................................................... 12 (max)

Liquid Limit ................................................................................ 25 (max)

Plastic Index ............................................................................... 10 (max)

3. Non-Frost Susceptible Fill should have no more than 5 percent passing the No.

200 sieve

Facilities | Environmental | Geotechnical | Materials 14

Fill Placement and Compaction Requirements

Structural and general fill should meet the following compaction requirements.

Item Structural Fill General Fill

Maximum Lift

Thickness

8 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

98% of max. below foundations and interior floor slabs

95% of max. above foundations

92% of max.

Water Content

Range

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

Granular: -3% to +3% of optimum

As required to achieve min.

compaction requirements

1. Maximum density and optimum water content as determined by the standard

Proctor test (ASTM D 698).

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

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

Utility Trench Backfill

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 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.

Trench excavation should not be conducted below a downward 2:1 projection from existing foundations without engineering review of shoring requirements and geotechnical observation during construction.

On-site materials, with the exception of the organic clay layer (GeoModel layer 4) are considered suitable for backfill of utility and pipe trenches from 1 foot above the top of

Facilities | Environmental | Geotechnical | Materials 15 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. Where trenches are placed beneath slabs or footings, the backfill should satisfy the gradation and plasticity index requirements of engineered fill discussed in this report. Flooding or jetting for placement and compaction of backfill is not recommended.

For low permeability subgrades, utility trenches are a common source of water infiltration and migration. Utility trenches penetrating beneath foundation footings 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 (MPWSS 7th Ed. Section 02222) 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 additions during and after construction and should be maintained throughout the life of the structure. Water retained next to the footings of the additions 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 and the footings of any new additions to the structure.

Exposed ground should be sloped and maintained at a minimum 5% away from the building and additions for at least 10 feet beyond the perimeter of the additions. Locally, flatter grades may be necessary to transition ADA access requirements for flatwork.

After construction and landscaping have been completed, final grades should be verified to document effective drainage has been achieved. Grades around the structure should also be periodically inspected and adjusted, as necessary, as part of the structure’s maintenance program. Where paving or flatwork abuts the structure or additions, a maintenance program should be established to effectively seal and maintain joints and prevent surface water infiltration.

Facilities | Environmental | Geotechnical | Materials 16

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 grade-supported improvements such as 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, 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 overexcavation efforts, especially for overexcavation and replacement of lower strength soils. A temporary dewatering system consisting of sumps with pumps may be necessary to achieve the recommended depth of overexcavation depending on groundwater conditions at the time of construction and any current dewatering measures in place. The design and implementation of a temporary dewatering system is the sole responsibility of the contractor.

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

Facilities | Environmental | Geotechnical | Materials 17 surficial materials (vegetation, topsoil, 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, until approval has been received from the Geotechnical Engineer prior to placement of additional lifts. 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

Primarily, the geotechnical concerns for this project focus on minimizing potential for differential settlement between the existing health clinic building and any new additions planned. For the elevator pit, it is understood that this will be mitigated by the use of micropiles, the performance of which will depend on the final design of the micropiles and proper execution of the installation process, which are recommended to be installed firmly bearing into the very dense gravel layer encountered near 4,042 feet MSL. The exterior additions will be reliant on shallow foundations, bearing onto near-surface sand and gravel soils. The performance of these additions will be dependent on quality earthwork operations (excavation and preparation of the subgrade, along with use of replacement Structural Fill as recommended) and construction of the foundation elements. Based on a review of the design drawings provided by the client, we believe that the proposed use of shallow foundations will be suitable for the planned additions.

We recommend the use of the design parameters stated in the following table, provided that the recommendations in the Earthwork section are incorporated.

Design Parameters – Compressive Loads

Item Description

Maximum Net Allowable Bearing

Pressure 1, 2, 3

3,000 psf – strip and isolated spread foundations bearing upon Structural Fill extending to properly-prepared native sand and gravel soils

500 psf – slab-on-grade/mat foundations bearing upon Structural Fill extending to

Facilities | Environmental | Geotechnical | Materials 18 properly-prepared native sand and gravel soils

(i.e. AC pad)

Minimum Foundation

Dimensions Per IBC 1809.7

Ultimate Passive Resistance

(equivalent fluid pressures)

280 pcf (Native Clay)

440 pcf (Native Sand)

460 pcf (Native Gravel)

500 pcf (Structural Fill)

Sliding Resistance

0.45 allowable coefficient of friction - granular material

Minimum Embedment below

Finished Grade

Exterior footings in unheated areas: 42 inches

Interior footings in heated areas: 24 inches

Estimated Total Settlement from

Structural Loads

Less than about 3/4 inches

Estimated Differential

Settlement 2, 7

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. Values assume that exterior grades are no steeper than 20% within 10 feet of structure.

2. Values provided are for maximum loads noted in Project Description. Additional geotechnical consultation will be necessary if higher loads are anticipated.

3. Unsuitable or soft soils 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.

Design Parameters – Overturning and Uplift Loads

Shallow foundations subjected to overturning loads should be proportioned such that the resultant eccentricity is maintained in the center-third of the foundation (e.g., e < b/6, Facilities | Environmental | Geotechnical | Materials 19 where b is the foundation width). This requirement is intended to keep the entire foundation area in compression during the extreme lateral/overturning load event.

Foundation oversizing may be required to satisfy this condition.

Uplift resistance of spread footings can be developed from the effective weight of the footing and the overlying soils with consideration to the IBC basic load combinations.

Construction Adjacent to Existing Building

We understand that, inherently, some of the planned additions are to be built directly adjacent to the existing structure; specifically, the new entryway and attic access stairway. Differential settlement between the new foundation elements and the existing hospital building, and associated flatwork, is expected to approach the magnitude of the total settlement of the addition. Expansion joints should be provided between the existing building and the proposed additions to accommodate differential movements between previous and new construction.

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

It was noted that several of the planned foundation elements will directly abut the existing foundation, based on the design drawings. It is understood that the slab for the new covered entryway will be pinned into the existing foundation with a smooth dowel, utilizing the foundational support of the existing structure. With proper jointing, it is anticipated that this design will properly accommodate the anticipated differential movement. The attic access stairs appear to bear on new footings, separate to the existing structure, but bearing directly adjacent to the existing foundation wall. The design drawings do not indicate if these are to be pinned to the existing structure. Even

Item Description

Average Soil Moist Unit Weight 120 pcf

Soil Effective Unit Weight 1 58 pcf

Soil weight included in uplift resistance

Soil included within the prism extending up from the top perimeter of the footing at an angle of 20 degrees from vertical to ground surface

1. Effective (or buoyant) unit weight should be used for soil above the foundation level and below a water level. The high groundwater level should be used in uplift design as applicable.

Facilities | Environmental | Geotechnical | Materials 20 though the anticipated axial loads are comparatively low for this addition, the existing foundation wall should be evaluated for resistance to the additional lateral earth pressure imposed by the footing.

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/reconditioned before foundation concrete is placed.

Sensitive soils exposed at the surface of footing excavations may require surficial compaction with hand-held dynamic compaction equipment prior to placing Structural

Fill, steel, and/or concrete. Should surficial compaction not be adequate, construction of a working surface consisting of either crushed stone or a lean concrete mud mat may be required prior to the placement of reinforcing steel and construction of foundations.

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.

Micropile Foundations

It is understood that the currently planned means of providing support to potentially undermined footings around the elevator pit is though the use of four micropiles. The benefit of a micropile system is the smaller diameter (less than 12 inches) of the advancing system (typically an auger, driven or vibrating tooling such as a down-the-

Facilities | Environmental | Geotechnical | Materials 21 hole hammer, or rotary drilling system) used to clear space for the micropiles, potentially allowing for easier drilling through the upper gravel strata (compared to larger drilled shafts). The equipment utilized for micropile construction also allows for closer construction activities in closer proximity to existing foundations/structures than typical drilled shaft units as well as some units have low-head capabilities specific to working in existing structures/basements. Micropiles are installed by a specialty contractor that will also at times provide design of their systems.