1240LN21R0001GeotechRpt.pdf

10020 E. Knox Avenue, Suite 200 Spokane, WA 99206 Phone.509.891.1904 Fax.509.891.2012 www.stratageotech.com

October 22, 2018 File: SP18164A

Deborah A. Johnston, P.E.

Vice President – Industrial Group Leader Morrison-Maierle 1055 Mount Avenue Missoula, Montana 59801 Email: djohnston@m-m.net

RE: GEOTECHNICAL REPORT

Wise River Helipad

65600 MT-43

Wise River, Montana

Greetings Deborah:

Strata, Inc. (STRATA) is pleased to present this geotechnical engineering report for the Wise River Helipad to be located at 65600 MT-43 in Wise River, Montana. The purpose of this geotechnical engineering report was to explore the subsurface conditions within the development area and provide geotechnical opinions and recommendations to assist project planning, design, and construction. We accomplished our geotechnical services referencing our authorized proposal signed on October 8, 2018.

The following report provides geotechnical recommendations for earthwork activities, shallow foundation design, concrete slab-on-grade floors, lateral earth pressures, based on the conditions we encountered and observed.

The geotechnical recommendations presented herein must be read and implemented in its entirety. Portions of this report cannot be relied upon individually without the supporting text or other pertinent sections and associated attachments or appendices. Construction success will depend, in part, on the design team and contractor adhering to the report recommendations, the contractor executing good construction practices, and the owner and/or contractor providing the necessary construction monitoring, testing, and geotechnical consultation to verify the work is completed as recommended herein. We recommend that STRATA be retained to provide monitoring, testing, and geotechnical consultation to verify that the report recommendations are followed during final design and construction. If STRATA is not retained to provide geotechnical continuity, STRATA cannot be responsible for designer or contractor errors, omissions, or report misinterpretations; and your selected firm shall become the engineer-of-record for administering these recommendations.

We appreciate the opportunity to continue to work with Morrison-Maierle and the design team on this project.

Please do not hesitate to contact us if you have any questions or comments.

Sincerely, STRATA

Jerry Weed, EIT-OR Ben Vance, P.E.

Staff Engineer Engineering Manager

JW/BV/cm http://www.stratageotech.com/

Geotechnical Report

Wise River Helipad

PREPARED FOR:

Deborah A. Johnston, P.E.

Vice President – Industrial Group Leader Morrison-Maierle

1055 Mount Avenue Missoula, Montana, 59801

PREPARED BY:

STRATA, A Professional Services Corporation

10020 E. Knox Avenue, Suite 200 Spokane, Washington 99206 Telephone (509) 891-1904

October 22, 2018

© 2018 by Strata, Inc. All rights reserved.

TABLE OF CONTENTS

Page

INTRODUCTION

PROJECT UNDERSTANDING

Proposed Construction

FIELD AND LABORATORY EVALUATION

Site Exploration

Subsurface Conditions Laboratory Testing

GEOTECHNICAL OPINIONS AND RECOMMENDATIONS

General Project Considerations Discussion Earthwork

Site Preparation Site Stripping Test Pit Remediation Establishing Subgrades

Excavation Characteristics Soil Product Specifications Required Compaction Wet Weather, Wet Soil Construction and Over-Excavations

Shallow Foundation Design Design Parameters Seismicity Foundation Drainage

Concrete Slab-On-Grade Floors Moisture Protection

Lateral Earth Pressures Site Grading Considerations

ADDITIONAL RECOMMENDED SERVICES

Geotechnical Design Continuity Plan and Specification Review Geotechnical Observation During Construction

EVALUATION LIMITATIONS

REPORT TABLES & FIGURES

Table 1. Soil Fill Specifications and Allowable Use

Table 2. Required Soil Products for Designated Project Areas

Table 3. Seismic Response Criteria

Figure 1: Vapor Retarder Flowchart

Table 4. Static Equivalent Fluid Pressures (EFP)

REPORT PLATES AND APPENDICES

Plate 1: Exploration Site Plan Plate 2: Foundation and Wall Drain Schematic Appendix A: Unified Soil Classification System (USCS) & Subsurface Exploration Appendix B: Laboratory Testing

© 2017 by Strata, A Professional Services Corporation. All rights reserved.

Geotechnical Report Wise River Helipad

INTRODUCTION

The purpose of this geotechnical report was to assess subsurface soil conditions within the proposed project area and to prepare geotechnical recommendations to assist final design and construction document development. This report represents the deliverable associated with the authorized proposal signed October 8, 2018. The following summary describes the authorized scope of service:

1. Coordinated exploration with Morrison-Maierle and the U.S.F.S Ranger Station to delineate exploration schedules, locations, utility issues, cleanup expectations, site access issues, and other exploration-specific considerations.

2. Coordinated exploration with the U.S.F.S Ranger Station to help locate utilities and reduce the potential for damage to existing utilities.

3. Performed subsurface exploration at the site by coordinating with a backhoe operator to excavate three exploratory test pits at the site extending 9.0- to 10.5- feet beneath the existing ground surface (bgs) and loosely backfilled each test pit approximately level with the ground surface following exploration. Refer to this report’s Test Pit Remediation section for recommendations regarding test pit remediation during construction.

4. Visually described and classified the soil encountered, referencing the American Society for Testing and Materials International (ASTM) Test Designation D2488, and obtained select soil samples for laboratory testing.

5. Performed laboratory testing on select soil samples obtained during exploration, referencing ASTM test standards.

6. Reviewed conceptual design project plans, subsurface conditions, laboratory test results, the proposed construction, conducted geotechnical analyses, and provided geotechnical recommendations to assist project design and construction for the following:

• Earthwork;

• Shallow foundation design;

• Concrete slab-on-grade floors;

7. Prepared and provided this geotechnical report deliverable for project design team review including exploration logs, laboratory test results, and a site plan illustrating exploration locations.

PROJECT UNDERSTANDING

STRATA bases the project understanding on discussions with Deborah A Johnston, P.E. with

Morrison-Maierle, and a cursory review of the following documents:

• An MS Word document that you emailed to us that was a marked-up aerial photograph that detailed the proposed hanger, warehouse, bunkhouse, and drain field locations;

• A Google Earth Keyhole Markup Language (.kml) provided by you that showed the project location;

Wise River Helipad – Wise River, Montana

© 2018 by Strata, Inc.. All rights reserved.

• Our subsurface knowledge in the immediate area, and experience with similar construction;

and

• Email correspondence with Mr. Chad Taylor, P.E. and our email and phone conversations with you to date.

STRATA understands Morrison-Maierle and their design team are currently accomplishing final design and developing construction documents for the Wise River Helipad to be constructed at 65600 MT-43 in Wise River, Montana. The site is shown on Plate 1, Exploration Site Plan. The planned development is located within a U.S.F.S. ranger station. The property is bordered on the west, east, and south by undeveloped land and to the north by MT-43.

Proposed Construction

Construction for the Wise River Helipad will generally include the following:

• Main Hanger– Approximately 14,000 square-foot (SF), single-story, above-grade structure supported by shallow foundations with slab-on-grade floors. The building will likely be a pre-engineered structure. Structural loads were not reported at the time of this report. The finished floor elevation is planned to be at 5,732 feet.

• Helipad – Two 900 square-feet (SF) helipads are located immediately east of the hanger building. The helipads will likely consist of an 8-inch thick steel reinforced slab built on grade.

• New Bunkhouse – Approximately 2,300 SF bunkhouse building comprising of standard stick-frame construction. The structure will be built upon shallow foundations and a crawl space.

FIELD AND LABORATORY EVALUATION

Site Exploration

Subsurface conditions were evaluated within the proposed project area by observing three exploratory test pits on October 10, 2018. Test pits were advanced to depths extending 9.0- to 10.5-feet below the existing ground surface. Test pits were advanced using a CAT 430E backhoe equipped with a 2.0-foot wide toothed bucket. Select soil samples were obtained within test pits for laboratory testing and to assist soil classification. Test pits were loosely backfilled and smoothed approximately level with the surrounding ground surface elevation. Test pits are recommended to be located and reviewed by

STRATA during site grading to determine whether additional remediation (i.e. removing backfill and replacing with Structural Fill) is necessary as further discussed in this report’s Test Pit Remediation section.

Plate 1 illustrates approximate exploration locations documented in the field. A STRATA

GeoProfessional visually described, classified, and logged the subsurface conditions encountered during exploration referencing ASTM D2488. Appendix A presents exploratory test pit logs and a

Unified Soil Classification System (USCS) explanation, which should be used to help interpret soil terms used throughout this report and on the exploratory logs.

Subsurface Conditions

Silty Gravel with Sand (topsoil) was encountered at the ground surface in Test Pits TP-1 through TP-

3 to depths extending between 6- and 12-inches beneath the ground surface. Rootlets were observed in all test pits to depths of 2-feet. The soil was generally brown, medium-dense, and moist.

Below the topsoil, we encountered 2 primary subsurface unit(s):

• Glacial Moraine – Well-Graded Gravel with Sand (GP) – Encountered in all exploratory test pits beneath topsoil, extending to test pit termination depths ranging between 4.5- and 10.5-feet BGS; generally light brown medium dense, and moist. Fines content decreased and angular gravel was consistent.

• Glacial Moraine – Well-Graded Sand with Gravel (SP) - Encountered in exploratory test pits TP-1 and TP-2 beneath the (GP) layer, extending to test pit termination depths ranging between 9.0- and 9.5-feet BGS; generally tan, medium dense, and moist. Fines content decreased and angular gravel was consistent with depth.

Groundwater or bedrock was not encountered during exploration. Based on our review of Montana’s

Groundwater Information Center (GWIC) static groundwater levels within the proposed project area are expected to be greater than 62.0-feet below the existing ground surface. Furthermore, well logs indicate bedrock is greater than 100.0-feet below ground surface.

Soil conditions encountered in locations explored were moderately uniform across the site. However, exploratory excavations only allow observation of a relatively small sample of the subsurface conditions at the site. Due to the existing site developments, subsurface variations likely occur beyond our exploration locations, and laterally across the entire site. Such variations will not be apparent until construction and may impact project schedules and costs. Where such variations exist, it may affect the opinions and recommendations presented in this report as well as construction timing and costs, and STRATA must be contacted to review the encountered conditions and recommendations to make any necessary revisions. See General Project Considerations Discussion section of this report for further discussion on variability and risk assessment.

Laboratory Testing

Laboratory testing was performed on select soil samples collected in the field referencing ASTM procedures. Laboratory test results were used to verify soil classification and to estimate soil engineering properties. Exploration logs in Appendix A include index laboratory test results; Appendix

B provides graphical and analytical laboratory test results. Laboratory tests included:

• ASTM D1140 – Test method for the amount of materials in soil finer than No. 200; and

• ASTM C136 - Standard test method for sieve analysis of fine and coarse aggregates.

GEOTECHNICAL OPINIONS AND RECOMMENDATIONS

General Project Considerations Discussion

As summarized herein, several subsurface conditions and considerations have been identified which will impact project construction and should be considered by the project team during final design and also prospective bidding contractors:

• Undocumented fill was encountered within TP-3 evident from an abandoned coaxial cable and isolated wood debris. Due to limited subsurface exploration, and existing site development, there is a moderate-probability that undocumented fill may occur across the site. It is anticipated that the undocumented fill encountered at TP-3 was associated with a utility alignment. Aligned with geotechnical standard-of-care, and to reduce the risk of foundation slab, we recommend all undocumented fill encountered during site preparation and construction be completely removed below footings, foundations, interior floor slabs, and exterior slabs to expose native sands and gravel. If encountered, the undocumented fill may be repurposed as structural fill if it meets the requirements in Table 1.

The following geotechnical recommendations are presented to assist final design and construction document development of the Wise River Helipad to be located 65600 MT-43 in Wise River, Montana.

Geotechnical recommendations are based on experience with similar soil and geologic conditions, findings from field and laboratory evaluation, and understanding of the proposed construction. If development plans change, STRATA recommends to be contacted to review any project modifications relative to recommendations and, if necessary, provide any necessary revisions or modifications.

Additionally, if subsurface conditions exposed during construction are different than what was encountered during exploration, STRATA should be contacted to review recommendations and provide any necessary revisions or modifications.

Earthwork

Site Preparation

Site Stripping

Stripping must extend laterally at least 5.0 feet outside of planned improvement areas. All topsoil containing vegetation and organics must be removed across the site, beneath any planned buildings and structural fill areas. It is estimated that this will require removing and disposing of approximately

6- to 12-inches of soil at the ground surface. However, varying thicknesses of vegetation and organic deposits should be expected. Soil containing vegetation and organics should be disposed off-site or may be reused on-site for landscaping, but may not be re-used as Structural Fill.

Test Pit Remediation

All test pits located beneath the planned building are recommended to be remediated during earthwork construction. Test pits shall be backfilled with either on-site native gravel and sand or imported

Structural Fill meeting the requirements stated in this report’s Soil Product Specifications and Required

Compaction section. STRATA requires all test pits within the proposed construction areas be reviewed by STRATA and the contractor, following site stripping, to determine whether full-depth remediation is necessary based on conditions observed during construction and planned improvements overlying test pit areas.

Establishing Subgrades

Following site stripping, excavating to achieve site grades, and prior to fill placement; prepare subgrades to receive fill, concrete, asphalt, or other site improvements as outlined below:

Slab-on-grade and foundation subgrades:

• Excavation of subgrades should be performed with a smooth bucket to avoid degradation of native material below desired subgrade elevations. All disturbed soil should be recompacted to 95 percent of a modified proctor or proof-rolled under the supervision of the geotechnical engineer of record or designee.

All other subgrades (i.e. exterior hardscapes, pavements & landscape areas):

• Excavation of subgrades should be performed with a smooth bucket to avoid degradation of native material below desired subgrade elevations. All disturbed soil should be recompacted to 95 percent of a modified proctor or proof-rolled under the supervision of the geotechnical engineer of record or designee.

After preparing subgrades, it is the contractor’s sole responsibility to protect subgrades from degradation, freezing, saturation, or other disturbance. Careful construction and earthwork procedures will be critical to achieving adequate subgrade preparation and reducing over-excavation. Specifically, these procedures could include carefully staging equipment and/or stockpiles, routing construction equipment away from subgrades, and implementing aggressive site drainage procedures to help reduce saturating subgrades during wet weather conditions. As stated above, it is the contractor’s responsibility to protect subgrades throughout construction. If a subgrade freezes, it must be recompacted and retested prior to acceptance. Subgrade disturbance that occurs due to the contractor’s means and methods must be repaired at no cost to the owner. STRATA will remain available to consult with the owner, the project team, and the contractor as the project moves forward regarding subgrade preparation procedures.

Excavation Characteristics

The on-site soil is anticipated to be excavated using conventional soil excavation techniques. In general, slopes and excavations must be excavated, shored, or braced in accordance with the

Occupational Safety and Health Administration (OSHA) regulations and local codes. The maximum allowable slope allowed by OSHA is 1.5H:1V. Ultimately, the selected contractor is responsible for site safety and determining appropriate excavations for the conditions and soil types encountered during construction. STRATA accepts no responsibility for temporary excavation stability.

Exploration and laboratory classification indicate the on-site native soil is low moisture sensitive and susceptible to disturbance when moist or wet. Soil disturbance will negatively impact the soil’s performance below slabs, pavement, and foundations. Disturbed and/or uncompacted soil shall not be allowed beneath any structure. Equipment with large tracks, lugs, or having toothed buckets has a significant potential to disturb the site soil following compaction. Rubber-tired transport vehicles should not access prepared subgrades unless the subgrade is sufficiently stiff to allow construction traffic without disturbance. Project earthwork specifications specifically outline that the contractor is required to maintain the subgrade in a compacted condition and protect subgrades from construction traffic disturbance after they have been prepared and meet compaction requirements. Further information can be found in this report’s Wet Weather, Wet Soil Construction and Over-Excavation.

Soil Product Specifications

All fill placed beneath anticipated structures (foundations or slabs) is recommended to consist of

Structural Fill meeting the requirements presented in Table 1. The on-site native well-graded gravel is expected to be suitable for re-use as Structural Fill but will require moisture-conditioning prior to placement. Undocumented fill, if encountered, cannot be re-used as Structural Fill unless approved by the geotechnical engineer of record.

Table 1. Soil Fill Specifications and Allowable Use

Soil Fill Product Allowable Use Material Specifications

Structural Fill1

• Site grading and fill placement

• Foundation wall backfill

• Over-excavations

• Utility trench backfill

Soil must be classified as GP, GM, GW, SP, SM or SW according to the USCS.

Soil may not contain particles larger than 6 inches in median diameter.

Soil must contain less than 3 percent (by weight) of organics, vegetation, wood, metal, plastic or other deleterious substances.

Crushed Surfacing2

• Structural fill uses

• Slab support aggregate

• Pavement section aggregate

Soil meeting requirements stated in Section 9- 03.9(3) – Crushed Surfacing of WSDOT Standards.

Foundation Drain

• Foundation drain backfill

Soil meeting requirements stated in Section 9- 03.12(4) – Gravel Backfill for Drains of WSDOT Standards.

Utility Trench Backfill

• Pipe zone bedding

Soil meeting requirements stated in Section 9- 03.12(3) – Gravel Backfill for Pipe Zone Bedding of WSDOT Standards.

Unsatisfactory Soil

• NONE

Soil classified as CH, MH, OH, OL or PT may not be used at the project site.

Any soil type not maintaining moisture contents within 5 percent of optimum during compaction.

Any soil containing more than 3 percent (by weight) of organics, vegetation, wood, metal, plastic or other deleterious substances.

1. The on-site native well-graded gravel with silt and sand (GW) soil generally meets the intent of our recommendations for Structural Fill.

2. Crushed Surfacing includes both “top course” and “base course” according to WSDOT Standards.

Required Compaction

Table 2 summarizes soil product compaction requirements.

Table 2. Required Soil Products for Designated Project Areas

Project Area Required Soil Product Compaction

Requirement1

Structural fill placed for site grading, undocumented fill removal, building footprint, fill within the bio-infiltration swale and floor slab

Structural Fill 95%

Directly beneath asphalt or concrete pavements, slabs, hardscaped, and sidewalks

Crushed Surfacing 95%

1. Reference ASTM D1557 modified Proctor

Place Soil Fill Products over approved subgrades. Never place Soil Fill Products over frozen, saturated, or soft subgrades. All Soil Fill Products should be moisture-conditioned to near optimum moisture content and be placed in maximum 12-inch-thick loose lifts. If site access precludes the use of large (10 ton or greater) compaction equipment and smaller or lighter equipment is used, a reduction in fill lift thickness and adjustment in compaction effort must be used. The contractor is responsible for selecting compaction equipment suitable for achieving compaction.

Imported or native Structural Fill may be too coarse for conventional Proctor testing if it contains more than 30 percent particles retained on the No. ¾ sieve (i.e., oversize material). If excessive oversized material is present within the imported Structural Fill, oversize material is recommended to be compacted using method specification. Method compaction should occur by applying at least 5 complete passes over the soil using vibratory compaction equipment with a drum energy rating of at least 10 tons. Smaller compaction equipment is not recommended for method compaction. Method compaction should be observed on a full-time basis by STRATA and should achieve a firm/dense, unyielding and interlocking Structural Fill surface. Observations and laboratory testing indicates that the native soil will be classified as oversize material.

Wet Weather, Wet Soil Construction and Over-Excavations

Earthwork construction is strongly recommended to take place during dry weather conditions. In soft or wet soil areas and during wet weather conditions, earthwork contractors must be familiar with the hazards of using rubber-tired equipment, which exerts a point load on the subgrade. Staggering wheel paths, using tracked equipment to traverse exposed subgrades and other techniques are important processes that reduce the potential for subgrade pumping, rutting, and contractor rework. Construction traffic is strongly recommended to be controlled in a manner that reduces traffic directly on the sensitive soil subgrade.

Earthwork should not be performed immediately after rainfall, or until soil can dry sufficiently to allow construction traffic without disturbing the subgrade. Any soil exhibiting pumping, rutting, weaving, or otherwise exhibiting unstable performance is recommended to be moisture-conditioned (typically drying) and recompacted to Structural Fill requirements, or removed. Moisture-conditioning the on-site soil could be difficult. If moisture-conditioning is impractical or may create project delays, the soil should be removed to undisturbed native soil using smooth-blade equipment and Structural Fill placed to desired grades. The “over-excavation” process is recommended to occur as follows:

1. STRATA and/or the selected contractor should identify and delineate unstable subgrade soil conditions. STRATA must review the affected area and provide Morrison-Maierle feedback to help facilitate the over-excavation process.

2. After attempting proper moisture conditioning, remove unstable areas using smooth-blade equipment to a minimum depth of 1.0-foot below the subgrade surface. Extend the over-excavation a minimum of 2.0 feet laterally beyond the delineated unstable area.

3. STRATA shall verify the resulting subgrade following consists of suitable, undisturbed native soil.

4. Place Structural Fill in the over-excavation to desired grades in accordance with the Soil Product Specifications and Required Compaction report sections.

In some instances, a 1.0-foot deep over-excavation may not be sufficient to expose suitable native soil; additional over-excavation depth may be needed. STRATA recommends to be present to observe all over-excavations to verify they have been constructed according to the above criteria, but also to provide immediate on-site feedback and discussion with the project team regarding soft or unsuitable soil conditions to help facilitate the construction schedule.

Shallow Foundation Design

If recommendations are followed, the foundation design criteria presented herein can be applied to project building foundations, assuming the loading conditions stated in the Project Understanding report section are current and accurate. Any foundation for the Wise River Helipad project is recommended to bear on compacted native soil, or Structural Fill placed over compacted native soil prepared per the Earthwork report section. Foundation subgrades are recommended to remain in a compacted condition during foundation preparations, construction of concrete formwork, and reinforcing steel placement. All foundation bearing surfaces should be free of loose soil and debris and be compacted to requirements presented in the Required Compaction report section.

Design Parameters

Based on preparing the foundation bearing soil units as described herein, the following items provide the recommended shallow foundation design parameters:

• Maximum allowable bearing pressure: 3,500 pounds per square foot.

• The allowable bearing capacity may be increased by 1/3 if the loading is transient in nature. The increase in bearing capacity may not be combined with a load factor that reduces the load.

• Requires maintaining drained subgrade conditions via perimeter foundation drainage.

See Site Drainage report section for foundation drainage recommendations.

• Estimated foundation vertical settlement:

• Total settlement: Less than 1.0 inch.

• Differential settlement: Less than 0.5 inches in 30.0-foot horizontal span or between adjacent, differently loaded footings.

• Lateral load resistance:

• Foundation base friction coefficient:

o 0.50 for foundations cast directly on prepared native gravel or Structural Fill soil.

• Passive soil resistance on foundation sides:

o Equivalent fluid pressure: 400 pounds per cubic feet (requires ¾-inch lateral movement to mobilize full resistance).

o Neglect upper 24 inches of wall backfill due to frost action.

• Footing embedment:

• Exterior footings (or footings in non-heated areas) must extend to depths recommended by local building code to help protect against frost action.

Seismicity

Section 1613 in the 2015 International Building Code (IBC) and Chapter 20 in the American Society of Civil Engineers (ASCE) 7-10 outline procedures for evaluating site ground motions and design spectral response accelerations. Based on available soil and geologic data, exploration beneath the site and the project location, a Site Class D is recommended to be utilized as a basis for structural seismic design. The Maximum Considered Earthquake (MCE) maps from the IBC, the National

Earthquake Hazards Reduction Program (NEHRP), and the U.S. Geological Survey (USGS) seismic hazard data (2009) was referenced to develop individual seismic response criteria as presented in

Table 3.

Table 3. Seismic Response Criteria

(N 45.79101 °, W -112.94093°)

Parameter Value (g)

SS - 0.2 Second MCE Spectral Response Acceleration 0.406

S1 - 1.0 Second MCE Spectral Response Acceleration 0.133

SDS - 0.2 Second Design Spectral Response Acceleration (SDS = SMS x 0.667) 0.400

SD1 - 1.0 Second Design Spectral Response Acceleration (SD1 = SM1 x 0.667) 0.201

PGAM - Design Peak Ground Acceleration 0.232

1. Values from 2015 IBC, and 2009 USGS seismic hazard maps, Risk Category I,II,III (low hazard, other, substantial hazard).

Foundation Drainage

Maintaining uniformly drained conditions is critical to long-term foundation system performance.

Foundation drains are recommended to be installed around the building perimeter to route nuisance water away from foundation subgrades to dedicated stormwater disposal areas. Based on the well-drained native soil conditions at the site and the low potential for shallow groundwater (i.e. less than

5.0 feet deep), the design and ownership team may elect to omit foundation drains from proposed improvements. Omitting the drainage system does not pose a great risk of damage to improvements so long as hardscaped surfaces adequately route surface runoff water away from structure subgrades.

Plate 2, Foundation Drain Schematic presents an example of a foundation and wall drainage system.

Concrete Slab-On-Grade Floors

Concrete slab-on-grade floors should be supported by a minimum of 6 inches of Crushed Surfacing meeting the requirements shown in Table 1. The recommendations provided in this section assume compacted Native or Structural Fill subgrades will be prepared per the Earthwork report section.

Crushed Surfacing below slab support should be placed directly over compacted subgrade observed and approved by STRATA, and meeting the requirements specified in this report’s Establishing

Subgrades and Soil Product Specifications sections.

Slabs must be structurally designed for the anticipated use and equipment or storage loading conditions, as applicable. STRATA has not provided slab design as part of the scope of service. Based on correlations to field and laboratory test results, concrete slab design is recommended to utilize an allowable modulus of subgrade reaction (k) of 250 pounds per square inch per inch. To realize the estimated subgrade modulus, drained conditions and a minimum of 6 inches of Crushed Surfacing must be provided.

Moisture Protection

The interior floor slabs may be susceptible to moisture migration caused by subsurface capillary action and vapor pressure. Moisture migration through floor slabs can break down a floor covering, its adhesive, or cause various other floor covering performance problems. Specifically, STRATA has participated in numerous projects where inadequate vapor protection caused significant damage to moisture-susceptible flooring systems. Often, these moisture problems were associated with either no moisture protection below the slab or, alternatively, with improperly sealed sub-slab penetrations that allowed vapor migration and damage to the flooring system. Plumbing penetrations are notoriously problematic for under-slab vapor protection.

Vapor retarders must consist of thick, puncture-resistant polyethylene sheeting placed immediately below the floor slab. An example of this material is Stego Wrap™, a 15-mil retarder. Alternatively, the vapor barrier may be covered with an additional 2-inch-thick layer of clean, coarse sand placed between the aggregate base course and the concrete slab-on-grade floors, if the base material and slabs are placed with a waterproofing system in-place. Vapor barrier installation options are outlined in Figure 1, following.

Figure 1: Vapor Retarder Flowchart (Adapted from Figure 3-1 of ACI 302.1R-04)

Form stakes, piping, or other sub-slab penetrations must never penetrate the vapor retarder. Carefully design and construct any vapor retarder penetrations to reduce vapor transport through such penetrations. Even if these recommendations are used, water vapor migration through the concrete floor slab is still possible. Floor covering should be selected accordingly. Manufacturer's recommendations should be strictly followed. Where vapor retarders are utilized, the flooring and concrete slab contractors, as well as the plastic sheeting manufacturer, should be consulted regarding additional slab cure time requirements and/or the potential for slab curling.

Morrison-Maierle or the U.S. Forest Service may desire to reduce the project budget by omitting a vapor retarder system below the concrete slab-on-grade floors. However, buildings and associated utilities can act as conduits for moisture and water vapor that exists in the soil to migrate vertically.

STRATA recommends you strongly consider the risks of excluding a vapor barrier prior to omitting such a system. Where floor coverings or equipment must be protected from damage by moist floor conditions, installation of a vapor retarder is strongly suggested.

Ultimately, the location of the vapor retarder (if specified) should be carefully considered by Morrison-

Maierle and the design team. ASTM E1643 and American Concrete Institute (ACI) Committee 302 are

2 publications that provide considerations for vapor retarder locations. Studies have shown that decreased water-cement ratios, higher strength concrete, and good construction finishing practices significantly decrease any negative impacts associated with the above options for vapor retarder locations.

Lateral Earth Pressures

The following recommendations apply to horizontal earth pressures against permanent walls and footings that are less than 6-feet tall. Walls taller than 6 feet must be reviewed and recommendations provided separately. Structural Fill must comprise the entire active wedge behind the walls. Any wall should be designed against overturning, sliding, and global wall failure. At-rest lateral earth pressures are recommended to be estimated using the following equivalent fluid pressures (EFP) from Table 4.

Table 4. Static Equivalent Fluid Pressures (EFP)

Rankine Lateral Earth Pressure Case Equivalent Fluid Pressure

(EFP)

Structural Fill in the active zone (Φ = 32°, ɣm = 125 pcf)

At-rest case (no wall movement) 60 pcf

Active case (wall movement away from soil mass) 40 pcf

Passive case (wall movement toward soil mass)* 400 pcf

*Note that mobilizing full passive resistance requires approximately ½-inch of lateral movement.

The recommended EFP assume fully-drained conditions with no hydrostatic forces acting on the wall and Structural Fill backfill throughout the entire active zone. At-rest equivalent earth pressures should be utilized for walls that cannot tolerate movement. The recommended EFP do not incorporate back-slopes. Lateral surcharge pressures due to equipment, slopes, storage loads or other surcharge loads have not been included in the above lateral earth pressure recommendations.

Site Grading Considerations

Runoff from precipitation or snowmelt must be routed away from structures to the practical maximum extent and must not be allowed to infiltrate or be diverted towards slopes, foundations, exterior flatwork, or slab subgrades. Runoff or water migrating along the ground surface must be conveyed away from slopes and structures by an appropriately designed series of ditches, swales, or other surface water management procedures.

The ground surface outside any structure is recommended to be sloped at least 5 percent away for a minimum of 10.0 feet to rapidly convey surface water or roof runoff away from foundations. Site grades beyond 10.0 feet from structures should slope at least 2 percent away and toward acceptable areas, as determined via recommendations and site grading design. Americans with Disabilities Act (ADA) hardscapes may not meet the above site grading recommendations adjacent to structures. ADA-pertinent hardscapes are recommended to be sloped away from structures to the maximum extent practical. The elastomeric sealant is recommended to be considered between hardscapes and foundation walls to reduce moisture infiltration at joints near building structures. Well-designed site drainage and careful final grading will help limit moisture infiltration near the building which will help reduce impacts from frost heave, vapor intrusion to interior spaces, and help improve the long-term performance of such structures.

Stormwater should be routed away from disturbed soil areas and should be disposed of in a suitable location as determined by site grading design. Bio infiltration swales or other infiltration facilities are recommended to be located at least 25.0 lateral feet from any structure or the overflow invert be established a minimum of 1.0 foot below the bottom of the exterior foundation footings.

ADDITIONAL RECOMMENDED SERVICES

Geotechnical Design Continuity

The information contained in this report is based on current development plans provided by Morrison-

Maierle and estimated structural loads. Conditions encountered following the final design of the floor elevation, floor configuration, loading conditions, as well as site geometry, can significantly alter opinions and design recommendations. Specifically, changes in structural design loads and planned site grading may require an additional analysis. STRATA should be contacted if additional exploration is preferred prior to design completion, to observe conditions following demolition, and once final designs are completed to review opinions and design recommendations contained herein.

Plan and Specification Review

STRATA recommends being retained to review geotechnical-related plan and specification sections prior to issuance of the construction documents for bidding. It has been STRATA’s experience that having the geotechnical consultants from the design team review the construction documents reduces the potential for errors and reduces costly changes to the contract during construction.

To maintain STRATA as the engineer-of-record through construction, retain STRATA to verify design parameters and provide construction monitoring that documents site soil conditions and gives you the confidence that report recommendations are incorporated into the grading and foundation construction. Such observation is a critical part of the geotechnical design process and can help reduce the potential for soil engineering or construction-related errors or omissions. Further, material testing and special inspection services are required by local building departments, the IBC, and project specifications. STRATA is available to provide these services.

Geotechnical Observation During Construction

STRATA should be retained to provide construction observation and testing to document the report recommendations have been followed. If for some reason we are not retained to provide the recommended construction observation services, we cannot be responsible for soil engineering-related construction errors or omissions. Providing these services during construction will help to identify potential earthwork and foundation construction issues, thus allowing the contractor to proactively remedy problems and reduce the potential for errors and omissions.

EVALUATION LIMITATIONS

This geotechnical engineering report has been prepared to assist in planning, design, and construction for Morrison-Maierle’s Wise River Helipad to be constructed at 65600 MT-45 in Wise River, Montana.

The scope does not include an engineering evaluation for deep foundations, retaining walls or landscaping. Variation in subsurface conditions may exist between or beyond explorations, which can necessitate changes to the geotechnical recommendations in this report. Also, changes to the planned development can drastically affect provided recommendations. If the improvement plans change from those described herein, STRATA must be notified so that modifications to recommendations may be made with respect to the modified improvements. If unforeseen conditions are encountered during earthwork, STRATA must be afforded the opportunity to review recommendations and provide necessary consultation, revision, or modifications to information contained herein. STRATA recommends being retained to review the final project plans and specifications, to provide geotechnical continuity throughout construction, and to identify any soil variations which could impact provided recommendations.

This report was prepared for the exclusive use of Morrison-Maierle and their project design team, for the specific project referenced herein. STRATA cannot be held responsible for unauthorized duplication or reliance upon this report or its contents without written authorization. The geotechnical recommendations provided herein are based on the premise that an adequate program of tests and observations will be conducted by STRATA during construction in order to verify compliance with provided recommendations and to confirm conditions between exploration locations. Subsurface conditions may vary from the locations explored and the extent of variation may only be known at the time of construction. Where variations occur, it is critical STRATA be afforded the opportunity to modify this report to reflect the site conditions exposed. This acknowledgment is in lieu of all warranties either express or implied.

IMAGE SOURCE: GOOGLE EARTH

APPROXIMATE SCALE - FEET

PROPOSED TEST PIT

LOCATION

LEGEND

TEST PIT LOCATION

SP1615509A PLATE 1

EXPLORATION SITE PLAN

Wise River Helipad - USFS Ranger Station

65600 MT-43

WISE RIVER, MONTANA

SP18164 PLATE 1OCTOBER 26, 2018

PLATE 2 SP17009ASP17095A

Subsurface Exploration Logs

APPENDIX A

UNIFIED SOIL CLASSIFICATION SYSTEM

MAJOR DIVISIONS

GRAVEL

COURSE

GRAINED

SOIL

CLEAN GRAVEL

GRAVEL WITH FINES

CLEAN SAND

SAND WITH FINES

SAND

FINE

GRAINED

SOIL

SILT AND CLAY

LIQUID LIMIT

LESS THAN 50%

SILT AND CLAY

LIQUID LIMIT

GREATER THAN 50%

GRAPHIC

SYMBOL

USCS GROUP

SYMBOL

SOIL DECRIPTION

WELL-GRADED GRAVEL

POORLY-GRADED GRAVEL

SILTY GRAVEL

SILTY GRAVEL WITH SAND

CLAYEY GRAVEL

CLAYEY GRAVEL WITH SAND

WELL-GRADED SAND

POORLY-GRADED SAND

SILTY SAND

CLAYEY SAND

INELASTIC SILT

LEAN CLAY

ORGANIC SILT

ELASTIC SILT

FAT CLAY

PEAT.

ORGANIC CLAY

GW

GP

GM

GC

SW

SP

SM

SC

ML

CL

OL

MH

CH

OH

PT

ABBREVATIONS

BGS - BELOW EXISTING GROUND SURFACE

N.E. - NOT ENCOUNTERED

Client:

Project:

Equipment:

Depth to Groundwater:

Test Pit Number:

Date Excavated:

Bucket Width:

Logged By: Sheet:

E L E

V A

T

IO

N

(F T

D E

P T

H

F

T

L

IT

H O

L O

G Y

S A

M P

L E

IN

E R

V A

L

U S

D A

S O

IL

X T

U R

A

C

A S

S

P

A S

S

IN

G

N O

S

IE

V E

D R

Y

D

N S

IT

(P

F

M O

IS

T

U

N T

E

P O

C K

P

N (T

S F

ADDITIONAL

NOTES

USCS DESCRIPTION

Test pit terminated at 9-feet bgs due to sidewall caving.

TOPSOIL - Silty Gravel with Sand (GM) Medium

Dense, Brown, Wet

Rootlets to 2-feet

-G a llo n

B u lk

ALLUVIUM - Well-Graded Gravel With Sand (GW)

Medium Dense, Light Brown, Wet

Subangular gravel

1.9

ALLUVIUM - Well-Graded Sand With Gravel (SW)

Medium Dense, Tan, Wet

Morrison and Maierle

Wise River (SP18164A)

CAT 416C

N.E.

10/10/2018

36 Inches

JW

Equipment:

Depth to Groundwater:

Test Pit Number:

Date Excavated:

Bucket Width:

Logged By: Sheet:

E L E

V A

T

D E

P T

H

F

T

L

IT

H O

L O

G Y

B L A

N K

P

A S

S

IN

G

N O

V E

D

N S

F

M O

IS

T

U

N T

E

P O

C K

N (T

S F

ADDITIONAL

NOTES

USCS DESCRIPTION

S A

M P

E R

V A

L

Test pit terminated at 9.5-feet bgs due to sidewall caving.

-G a lk

TOPSOIL - Well-Graded Gravel with Silt and Sand

(GW-GM) Medium Dense, Light Brown, Wet

Rootlets to 2-feet

-G a lk

ALLUVIUM - Well-Graded Gravel With Sand (GW)

Medium Dense, Light Brown, Wet

Cobbles up to 6-inches

4.2

ALLUVIUM - Well-Graded Sand With Gravel (SW)

Medium Dense, Tan, Wet

Subangular gravel

Morrison and Maierle

Wise River (SP18164A)

CAT 416C

N.E.

10/10/2018

Equipment:

Depth to Groundwater:

Test Pit Number:

Date Excavated:

Bucket Width:

Logged By: Sheet:

E L E

V A

T

D E

P T

H

F

T

L

IT

H O

L O

G Y

B L A

N K

P

A S

S

IN

G

N O

V E

D

N S

F

M O

IS

T

U

N T

E

P O

C K

N (T

S F

ADDITIONAL

NOTES

USCS DESCRIPTION

S A

M P

E R

V A

L

Test pit terminated at 10.5-feet bgs due to sidewall caving.

TOPSOIL - Silty Gravel with Sand (GM) Medium

Dense, Dark Brown, Wet

Rootlets to 2-feet, coaxial cable and 2x4 debris in top

6-inches

ALLUVIUM - Well-Graded Gravel With Sand (GW)

Medium Dense, Light Brown, Wet Subangular gravel

Morrison and Maierle

Wise River (SP18164A)

CAT 416C

N.E.

10/10/2018

Laboratory Testing Results

APPENDIX B

ASTM D6913

100 10 1 0.1 SOIL GRAIN DIAMETER, millimeters

P E

R C

E N

T P

A S

S

IN

G

Reviewed by:________________________

6" 4" 3" 2.

5"

2" 1.

5"

1" 3/ 4"

1/ 2"

3/ 8"

#4 #8 #1

#1

#2

#3

#4

#5

#6

#1

#2

Inches Screen Sizes

C ob bl es

Coarse Fine

Gravel Sand

FineCoarse

Project: Wise River Helipad - U.S.F.S. Ranger Station Client: Morrison-Maierle File: SP18164A Sample No.: SP1800709 Sample Location: Test Pit TP-2 from 4.0 to 5.0 feet BGS Description: Poorly-graded GRAVEL with Silt and Sand (GP-GM) Date Sampled: October 10, 2018 By: J. Weed Date Tested: October 13, 2018 By: R. Matteson

Laboratory Testing

EVALUATION LIMITATIONS