Exhibit I - Geotechnical Engineering Study_(REVISED 10-06-23).pdf

GEOTECHNICAL ENGINEERING STUDY

PROPOSED FIRE STATION #01 AND HEALTH CLINIC

UPPER PINE FIRE PROTECTION

BAYFIELD, COLORADO

Revised on October 6, 2023

PREPARED FOR:

Bruce Evans

(970) 884-9508 bevans@upperpinefpd.org

PROJECT NO. 58023GE

mailto:bevans@upperpinefpd.org

Project No. 58023GE Revised on October 6, 2023

Table of Contents

1.0 REPORT INTRODUCTION

1.1 Proposed Construction

2.0 FIELD STUDY

2.1 Site Description and Geomorphology

2.2 Subsurface Soil and Water Conditions

3.0 LABORATORY STUDY

4.0 FOUNDATION RECOMMENDATIONS

4.1 Shallow Foundation System Concepts

4.1.1 Spread Footings

4.1.2 General Shallow Foundation Considerations

5.0 RETAINING STRUCTURES

6.0 SUBSURFACE DRAIN SYSTEM

7.0 CONCRETE FLATWORK

7.1 Interior Concrete Slab-on-Grade Floors

7.1.1 Capillary and Vapor Moisture Rise

7.1.2 Slab Reinforcement Considerations

7.2 Exterior Concrete Flatwork Considerations

7.3 General Concrete Flatwork Comments

8.0 CONSTRUCTION CONSIDERATIONS

8.1 Fill Placement Recommendations

8.1.1 Natural Soil Fill

8.1.2 Granular Compacted Structural Fill

8.1.3 Deep Fill Considerations

8.2 Excavation Considerations

8.2.1 Excavation Cut Slopes

8.3 Utility Considerations

8.4 Exterior Grading and Drainage Comments

8.5 Landscaping Considerations

8.6 Soil Sulfate and Corrosion Issues

8.7 Radon Issues

8.8 Mold and Other Biological Contaminants

9.0 PAVEMENT SECTION THICKNESS DESIGN RECOMMENDATIONS

9.1 Traffic Estimates

9.2 Asphalt Pavement Design Recommendations

9.3 General Asphalt Pavement Recommendations

9.4 Portland Cement Concrete Pavement Recommendations

10.0 CONSTRUCTION MONITORING AND TESTING

11.0 CONCLUSIONS

12.0 LIMITATIONS

FIELD STUDY RESULTS ...................................................................................................... Appendix A Log of Test Borings LABORATORY TEST RESULTS ........................................................................................ Appendix B Sieve and Atterberg Limit Test Results Swell-Consolidation Test Results California Bearing Ratio (CBR) Test Results Modified Proctor Test Resutls

Revised October 6, 2023

1.0 REPORT INTRODUCTION

This report presents our geotechnical engineering recommendations for the proposed Fire Station #01 and Health Clinic to be located on Lot 1 Bayfield Center, TBD Sower Drive in Bayfield, Colorado. This report was requested by Mr. Bruce Evans, Upper Pine River Fire Protection District and was prepared in accordance with our proposal dated July 11, 2023, Proposal No.

23273P.

As outlined within our proposal for services for this project the client is responsible for appropriate distribution of this report to other design professionals and/or governmental agencies unless specific arrangements have been made with us for distribution.

Geotechnical engineering is a discipline which provides insight into natural conditions and site characteristics such as; subsurface soil and water conditions, soil strength, swell (expansion) potential, consolidation (settlement) potential, and often slope stability considerations. The information provided by the geotechnical engineer is utilized by many people including the project owner, architect or designer, structural engineer, civil engineer, the project builder and others. The information is used to help develop a design and subsequently implement construction strategies that are appropriate for the subsurface soil and water conditions, and slope stability considerations.

We are available to discuss any aspect of this report with those who are unfamiliar with the recommendations, concepts, and techniques provided below.

This geotechnical engineering report is the beginning of a process involving the geotechnical engineering consultant on any project. It is imperative that the geotechnical engineer be consulted throughout the design and construction process to verify the implementation of the geotechnical engineering recommendations provided in this report. Often the design has not been started or has only been initiated at the time of the preparation of the geotechnical engineering study. Changes in the proposed design must be communicated to the geotechnical engineer so that we have the opportunity to tailor our recommendations as needed based on the proposed site development and structure design.

The following outline provides a synopsis of the various portions of this report;

Sections 1.0 provides an introduction and an establishment of our scope of service.

Sections 2.0 and 3.0 of this report present our geotechnical engineering field and laboratory studies Sections 4.0 through 7.0 presents our geotechnical engineering design parameters and recommendations which are based on our engineering analysis of the data obtained.

Section 8.0 provides a brief discussion of construction sequencing and strategies which may influence the geotechnical engineering characteristics of the site. Ancillary information such as some background information regarding soil corrosion and radon considerations is also presented as general reference.

Section 9.0 presents our pavement section recommendations.

Section 10.0 provides our general construction monitoring and testing recommendations.

Sections 11.0 and 12.0 provides our conclusions and limitations.

The data used to generate our recommendations are presented throughout this report and in the attached figures.

All recommendations provided within this report must be followed in order to achieve the intended performance of the foundation system and other components that are supported by the site soil.

1.1 Proposed Construction

Architectural details and grading plans were not available at the time of this report. We understand the proposed construction will likely be an approximately 21,000 ft², single story fire station and health clinic supported by a steel reinforced concrete foundation system. A possible mezzanine structure would be located in the fire truck bay on the north end of the proposed construction, and the health clinic would be located on the south end. Grading for the structure is assumed to be relatively minor with cuts of approximately 3 to 5 feet below the adjacent ground surface. We assume relatively light foundation loadings, typical of the proposed type of construction.

When final building location, grading and loading information have been developed, we should be notified to re-evaluate the recommendations presented in this report.

2.0 FIELD STUDY

2.1 Site Description and Geomorphology

The approximate 2.68-acre project site was vacant at the time of our field study. The site is relatively flat, with a slight slope towards the west. The Pine River has influenced the geology of the project area, with river terrace deposits of gravel and cobble, overlain by loess (wind-blown) deposits. There were several underground utility lines that run across the building site orientated north-south. This site is bordered by a commercial lot to the north, Sower Drive to the east, Bayfield Center Drive to the south, and County Road 501 to the west.

2.2 Subsurface Soil and Water Conditions

We advanced six structural test bores and three pavement test bores for a combined total of nine test borings in the vicinity of the proposed structure and parking lot. A schematic showing the approximate boring locations is provided below as Figure 1. The logs of the soils encountered in our test borings are presented in Appendix A.

Figure 1: Locations of Exploratory Borings. Adapted from SDP Plans.

The schematic presented above was prepared using notes and field measurements obtained during our field exploration and is intended to show the approximate test boring locations for reference purposes only.

The subsurface conditions encountered in our test borings consisted of a medium stiff to hard lean clay with sand (CL) from the ground surface down to 9 to 15 feet throughout the project site.

In TB-3, we encountered a gravelly lean clay with sand (CL) from 9 to 13 feet. Underlying the CL soils, we encountered a gravelly clay with sand and cobbles which was drilled to a maximum depth explored of 19 feet, where practical auger refusal occurred on cobbles. Auger drilling refusal was also encountered at 17 feet in TB-6.

Free subsurface water was encountered at a depth of approximatley 15 feet in TB-1 and 13 feet in TB-6 below the adjacent ground surface during drilling. We suspect that the subsurface water elevation and soil moisture conditions will be influenced by snow melt and/or precipitation and local irrigation.

The logs of the subsurface soil conditions encountered in our test borings are presented in Appendix A. The logs present our interpretation of the subsurface conditions encountered in the test borings at the time of our field work. Subsurface soil and water conditions are often variable across relatively short distances. It is likely that variable subsurface soil and water conditions will be encountered during construction. Laboratory soil classifications of samples obtained may differ from field classifications.

TB-1

TB-2

TB-3 TB-4

TB-5

TB-6

PB-1

PB-2

PB-3

3.0 LABORATORY STUDY

The laboratory study included tests to estimate the strength, swell and consolidation potential of the soils tested. We performed the following tests on select samples obtained from the test borings.

The laboratory test results are provided in Appendix B.

• Moisture Content and Dry Density

• Sieve Analysis (Gradation)

• Atterberg Limits, Liquid Limit, Plastic Limit and Plasticity Index

• Swell Consolidation Tests

• Moisture Content Dry Density Relationship Test

• California Bearing Ratio Test

A synopsis of some of our laboratory data for some of the samples tested is tabulated below.

Sample Designation

Percent Passing

#200 Sieve

Atterberg Limits

LL/PI

Moisture Content (percent)

Dry Density

(PCF)

Estimated Load-Back

Swell Pressure

(PSF)

Swell or Consolidation

Potential

TB-1 @ 0-4’ 72 28/11 2.9 - - -

TB-1 @ 4’ - - 6.7 106.0 1,600

1.4

(% under 500 psf load)

TB-2 @ 2’ - - 5.3 105.5 1,110

2.1

(% under 100 psf load)

TB-3 @ 9-14’ 57 39/24 6.7 - - -

TB-4 @ 2’ - - 6.2 106.3 1,880

2.9

(% under 100 psf load)

TB-6 @ 0-4’ 83 32/14 5.8 - - -

TB-6 @ 4’ - - 8.4 106.7 1,920

2.1

(% under 500 psf load)

Bulk Subgrade 76 30/13 6.5 - - -

*NOTES:

1. We determine the swell pressure as measured in our laboratory using the graphically estimated load-back swell pressure method.

4.0 FOUNDATION RECOMMENDATIONS

There are two general types of foundation system concepts, “deep” and “shallow”, with the designation being based on the depth of support of the system. We have provided a discussion of viable foundation system concepts for this project below. The choice of the appropriate foundation system for the project is best made by the project structural engineer or project architect. We should be contacted once the design choice has been made to provide consultation regarding implementation of our design parameters.

Deep foundation system design concepts which include isolation of shallow components including floor systems from shallow soils are less likely to experience post-construction movement due to volume changes in the site soil. Deep foundation system design concepts may be viable for this project; however, we anticipate that only a shallow foundation system design is being considered at this time. We are available to develop deep foundation design parameters if desired.

4.1 Shallow Foundation System Concepts

Subsurface data indicate that lean clay with sand (CL) will likely be the predominant soil type encountered beneath shallow foundations. Based on the laboratory analysis, the soils encountered in our borings were found to have a low to moderate swell/expansion potential. The anticipated soils at the foundation level are considered suitable for shallow foundation support.

There are numerous types of shallow foundation systems and variants of each type. Shallow foundation system concepts discussed below include:

• Spread Footings (continuous) and stem walls

The integrity and long-term performance of each type of system is influenced by the quality of workmanship which is implemented during construction. It is imperative that all excavation and fill placement operations be conducted by qualified personnel using appropriate equipment and techniques to provide suitable support conditions for the foundation system.

4.1.1 Spread Footings

A spread footing foundation system consists of a footing which dissipates, or spreads, the loads imposed from the stem wall (or beam) from the structure above. The soil samples tested from the anticipated support elevations in our test borings had a measured swell pressure of up to about 1,920 pounds per square foot and a swell potential magnitude of up to about 2.9 percent under a 100 pound per square foot surcharge load. The owner must understand that regardless of the expansive soil mitigation design concepts presented below, if the swell pressure generated by the expansive soil on this site exceeds the minimum dead load which is imposed by the spread footing or other structural components, and the expansive site soils become wetted, uplift of the foundation system and other structural components is highly likely. Drilled piers, or other deep foundation system design will provide the least likelihood of post construction movement associated with soil volume changes.

The actual magnitude of the potential uplift of the foundation system depends on the volume (or depth) of the support soils which become moistened after construction. It is difficult to predict the amount of soil which will become moistened after construction, some theories suggest that with time the entire soil mantle may become moistened. Based on our experience in the area we feel that it is possible for at least 3 to 4 feet of soil below the footings to be influenced by subsurface moisture. Based on the assumed depth of moistened soil, laboratory test data, and the soil characteristics we estimate that the magnitude of the potential uplift associated with swelling of the expansive support soil materials may be in the range of about 1 to 1¼ inches. If the entire soil mantle becomes moistened the total potential uplift may be higher than 1 ¼ inch. Proper surface and subsurface drainage and placement of compacted structural fill under the foundation will minimize the potential for the entire soil mantle to become moistened. The project structural engineer or architect should determine if the potential uplift is tolerable for the proposed structure on this project site.

Uplift associated with swelling soils occurs only where the foundation support soils have been exposed to water; therefore, the uplift may impose shear stresses in the foundation system. The magnitude of the imposed shear stress is related to the swell pressure of the support soil, but is difficult to estimate. Properly designed and constructed continuous spread footings with stem walls (or beams) have the ability to distribute the forces associated with swelling of the support soil. The rigidity of the system helps reduce differential movement and associated damage to the overlying structure. Swelling of the soil supporting isolated pad footings will result in direct uplift of the columns and structural components supported by the columns. Damage to the structure due to this type of movement can be severe. If possible, we recommend that isolated pad footings be avoided and that the foundation system be designed as rigid as is reasonably possible. If isolated pad footings are used, we should review the foundation plan.

High foundation dead load, careful preparation of the support soils, placement of granular compacted structural fill, careful placement and compaction of stem wall backfill and positive surface drainage adjacent to the foundation system all help reduce the influence of swelling soils on the performance of the spread footing foundation system.

We recommend that the footings be designed with a high dead load and supported by a layer of moisture conditioned and compacted natural soil which is overlain by a layer of compacted structural fill material. This concept is outlined below:

• The foundation excavation should be excavated to at least 18 inches below the proposed footing support elevation.

• The natural soils exposed in the bottom of the excavation should be scarified to a depth of about 6 to 8 inches

• The scarified soil should be thoroughly moisture conditioned to about 2 percent above the laboratory determined optimum moisture content and then compacted.

• After completion of the compaction of the moisture conditioned natural soil an 18 inch thick layer of granular aggregate base course structural fill material should be placed, moisture conditioned and compacted.

• The moisture conditioned natural soil material and the granular soils should be compacted as discussed under the Compaction Recommendations portion of this report below.

• In the absence of structural engineering design and for general geotechnical engineering purposes, we recommend the stem walls be designed to act as beams and reinforced with continuous steel reinforcement, 4 reinforcement bars, 2 top and 2 bottom. Taller walls may require additional reinforcement bar.

• The structural engineer should be contacted to provide the appropriate reinforcement bar diameter and locations.

We recommend that particular attention and detail be given to the following aspects of the project construction for this lot;

• A subsurface drain system should be installed adjacent to the structure foundation system.

Concepts for a subsurface drain system are presented in Section 6.0 of this report.

• The landscaping drainage concept provided in Section 8.5 below is imperative for this site to limit the moisture available to the foundation bearing soils.

• The exterior foundation backfill must be well compacted and moisture conditioned to above optimum moisture content. Recommendations for exterior foundation backfill are provided later in this report.

We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. Topographic conditions on the site may influence the ability to install a subsurface drain system which promotes water flow away from the foundation system. The subsurface drain system concept is discussed under the Subsurface Drain System section of this report below.

The footing embedment is a relatively critical, yet often overlooked, aspect of foundation construction. The embedment helps develop the soil bearing capacity, increases resistance of the footing to lateral movement and decreases the potential for rapid moisture changes in the footing support soils, particularly in crawl space areas. Interior footing embedment reduces the exposure of the crawl space support soils to dry crawl space air. Reduction in drying of the support soil helps reduce downward movement of interior footings due to soil shrinkage.

All footings should have a minimum depth of embedment of at least one 1 foot. The embedment concept is shown below.

Spread footings located away from sloped areas may be designed using the allowable gross bearing capacity information tabulated below.

Minimum Depth of Embedment (Feet)

Continuous Footing Design Capacity (psf)

Isolated Footing Design Capacity (psf)

1 1,700 Not Recommended 2 1,900 Not Recommended 3 2,100 Not Recommended

We recommend a minimum dead load of 500 psf be maintained where possible. The bearing capacity values tabulated above may be increased by 20 percent for transient conditions associated with wind and seismic loads. Snow loads are not transient loads.

The bearing capacity values above were based on footing placed directly on the natural soils and on a continuous spread footing width of 1.5 feet. Larger footings and/or footings placed on a blanket of compacted structural fill will have a higher design soil bearing capacity. Development of the final footing design width is usually an iterative process based on evaluation of design pressures, footing widths and the thickness of compacted structural fill beneath the footings. We should be contacted as the design process continues to re-evaluate the design capacities above based on the actual proposed footing geometry.

The settlement of the spread footing foundation system will be influenced by the footing size and the imposed loads. We estimated the total post construction settlement of the footings based on our laboratory consolidation data, the type and size of the footing. Our analysis below assumed that the highest bearing capacity value tabulated above was used in the design of the footings. The amount of post construction settlement may be reduced by placing the footings on a blanket of compacted structural fill material.

The estimated settlement for continuous footing with a nominal width of about 1½ to 2½ feet are tabulated below.

Thickness of Compacted Structural Fill (feet)

Estimated Settlement (inches)

0 ¾ - 1 B/2 ½ - ¾ B ¼ - ½

B is the footing width

The estimated settlement for continuous footing with a nominal width of about 4 to 6 feet are tabulated below with 18 inches of structural fill.

Thickness of Compacted Structural Fill (feet)

Estimated Settlement (inches)

B/2 ¼ - ½ B About ¼

B is the footing width

The compacted structural fill should be placed and compacted as discussed in the Construction Considerations, “Fill Placement Recommendations” section of this report, below. The zone of influence of the footing (at elevations close to the bottom of the footing) is often approximated as being between two lines subtended at 45 degree angles from each bottom corner of the footing.

The compacted structural fill should extend beyond the zone of influence of the footing as shown in the sketch below.

A general and simple rule to apply to the geometry of the compacted structural fill blanket is that it should extend beyond each edge of the footing a distance which is equal to the fill thickness.

We estimate that the footings designed and constructed above will have a total post construction settlement of about 1 inch or less. We estimate that the differential settlement may be about 1 to 1 ¼ inch.

All footings should be support at an elevation deeper than the maximum depth of frost penetration for the area. This recommendation includes exterior isolated footings and column supports. Please contact the local building department for specific frost depth requirements.

The post construction differential settlement may be reduced by designing footings that will apply relatively uniform loads on the support soils. Concentrated loads should be supported by footings that have been designed to impose similar loads as those imposed by adjacent footings.

Under no circumstances should any footing be supported by more than 3 feet of compacted structural fill material unless we are contacted to review the specific conditions supporting these footing locations.

The design concepts and parameters presented above are based on the soil conditions encountered in our test borings. We should be contacted during the initial phases of the foundation excavation at the site to assess the soil support conditions and to verify our recommendations.

4.1.2 General Shallow Foundation Considerations

Some movement and settlement of any shallow foundation system will occur after construction.

Movement associated with swelling soils also occurs occasionally. Utility line connections through and foundation or structural component should be appropriately sleeved to reduce the potential for damage to the utility line. Flexible utility line connections will further reduce the potential for damage associated with movement of the structure.

5.0 RETAINING STRUCTURES

We understand that laterally loaded walls will be constructed as part of this site development.

Lateral loads will be imposed on the retaining structures by the adjacent soils and, in some cases, additional surcharge loads will be imposed on the retained soils from vehicles or adjacent structures. The loads imposed by the soil are commonly referred to as lateral earth pressures. The magnitude of the lateral earth pressure forces is partially dependent on the soil strength characteristics, the geometry of the ground surface adjacent to the retaining structure, the subsurface water conditions and on surcharge loads.

The site soils have a measured swell pressure of 1,920 pounds per square foot. A 1,920 pound per square foot swell pressure will exert approximately 15,360 pounds of force per lineal foot for a wall that retains 8 feet of soil. Due to the expansive nature of the site soils we do not recommend that the natural clay soils be used for retaining wall backfill. The retaining walls may be designed using the equivalent fluid pressure values for imported granular soil that are tabulated below.

Type of Lateral Earth Pressure Level Granular Soil Backfill (pounds per cubic foot/foot)

Active 35 At-rest 55 Passive 460

Allowable Coefficient of Friction

0.45

The granular soil that is used for the retaining wall backfill may be permeable and may allow water migration to the foundation support soils. There are several options available to help reduce water migration to the foundation soils, two of which are discussed here. An impervious geotextile layer and shallow drain system may be incorporated into the backfill, as discussed in Section 9.5, Landscaping Considerations, below. A second option is to place a geotextile filter material on top of the granular soils and above that place about 1½ to 2 feet of moisture conditioned and compacted site clay soils. It should be noted that if the site clay soils are used volume changes may occur which will influence the performance of overlying concrete flatwork or structural components.

The values tabulated above are for well drained backfill soils. The values provided above do not include any forces due to adjacent surcharge loads or sloped soils. If the backfill soils become saturated the imposed lateral earth pressures will be significantly higher than those tabulated above.

The granular imported soil backfill values tabulated above are appropriate for material with an angle of internal friction of 35 degrees, or greater. The granular backfill must be placed within the retaining structure zone of influence as shown below in order for the lateral earth pressure values tabulated above for the granular material to be appropriate.

If an open graded, permeable, granular backfill is chosen it should not extend to the ground surface. Some granular soils allow ready water migration which may result in increased water access to the foundation soils. The upper few feet of the backfill should be constructed using an impervious soil such as silty-clay and clay soils from the project site, if these soils are available.

The 55 degree angle shown in the figure above is approximately correct for most clay soils. The angle is defined by 45 + (φ/2) where “φ” if the angle of internal friction of the soil.

Backfill should not be placed and compacted behind the retaining structure unless approved by the project structural engineer. Backfill placed prior to construction of all appropriate structural members such as floors, or prior to appropriate curing of the retaining wall concrete, may result in severe damage and/or failure of the retaining structure.

6.0 SUBSURFACE DRAIN SYSTEM

We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. Exterior retaining structures may be constructed with weep holes to allow subsurface water migration through the retaining structures. Topographic conditions on the site may influence the ability to install a subsurface drain system which promotes water flow away from the foundation system. The subsurface drain system concept is discussed under the Subsurface Drain System section of this report below.

A drain system constructed with a free draining aggregate material and a 4 inch minimum diameter perforated drain pipe should be constructed adjacent to retaining structures and/or adjacent to foundation walls. The drain pipe perforations should be oriented facing downward.

The system should be protected from fine soil migration by a fabric-wrapped aggregate which surrounds a rigid perforated pipe. We do not recommend use of flexible corrugated perforated pipe since it is not possible to establish a uniform gradient of the flexible pipe throughout the drain system alignment. Corrugated drain tile is perforated throughout the entire circumference of the pipe and therefore water can escape from the perforations at undesirable locations after being collected. The nature of the perforations of the corrugated material further decreases its effectiveness as a subsurface drain conduit.

The drain should be placed at each level of excavation and at least 12 inches below lowest adjacent finish floor or crawlspace grade. The drain system pipe should be graded to surface outlets or a sump vault. The drain system should be sloped at a minimum gradient of about 2 percent, but site geometry and topography may influence the actual installed pipe gradient. Water must not be allowed to pool along any portion of the subsurface drain system. An improperly constructed subsurface drain system may promote water infiltration to undesirable locations. The drain system pipe should be surrounded by about 2 to 4 cubic feet per lineal foot of free draining aggregate. If a sump vault and pump are incorporated into the subsurface drain system, care should be taken so that the water pumped from the vault does not recirculate through pervious soils and obtain access to the basement or crawl space areas. An impervious membrane should be included in the drain construction for grade beam and pier systems or other foundation systems such as interrupted footings where a free pathway for water beneath the structure exists. A generalized subsurface drain system concept is shown below.

There are often aspects of each site and structure which require some tailoring of the subsurface drain system to meet the needs of individual projects. Drain systems that are placed adjacent to void forms must include provisions to protect and support the impervious liner adjacent to the void form. We are available to provide consultation for the subsurface drain system for this project, if desired.

Water often will migrate along utility trench excavations. If the utility trench extends from areas above the site, this trench may be a source for subsurface water within the proposed basement or crawl space. We suggest that the utility trench backfill be thoroughly compacted to help reduce the amount of water migration. The subsurface drain system should be designed to collect subsurface water from the utility trench and direct it to surface discharge points.

7.0 CONCRETE FLATWORK

We anticipate that both interior and exterior concrete flatwork will be considered in the project design. Concrete flatwork is typically lightly loaded and has a limited capability to resist shear forces associated with uplift from swelling soils and/or frost heave. It is prudent for the design and construction of concrete flatwork on this project to be able to accommodate some movement associated with swelling soil conditions.

The soil samples tested have a measured swell pressure of about 1,920 pounds per square foot and a magnitude swell potential of about 2.9 percent under a 100 pound per square foot surcharge load. Due to the measured swell potential and swell pressure, interior floors supported over a crawl space are less likely to experience movement than are concrete slabs support on grade. The following recommendations are appropriate for garage floor slabs and for interior floor slabs if the owner is willing to accept the risk of potential movement beyond normal tolerances.

7.1 Interior Concrete Slab-on-Grade Floors

A primary goal in the design and construction of concrete slab-on-grade floors is to reduce the amount of post construction uplift associated with swelling soils, or downward movement due to consolidation of soft soils. A parallel goal is to reduce the potential for damage to the structure associated with any movement of the slab-on-grade which may occur. There are limited options available to help mitigate the influence of volume changes in the support soil for concrete slab-on-grade floors, these include:

• Preconstruction scarification, moisture conditioning and re-compaction of the natural soils in areas proposed for support of concrete flatwork, and/or,

• Placement and compaction of granular compacted structural fill material

Damage associated with movement of interior concrete slab-on-grade floor can be reduced by designing the floors as “floating” slabs. The concrete slabs should not be structurally tied to the foundations or the overlying structure. Interior walls or columns should not be supported on the interior floor slabs. Movement of interior walls or columns due to uplift of the floor slab can cause severe damage throughout the structure. Interior walls may be structurally supported from framing above the floor, or interior walls and support columns may be supported on interior portions of the foundation system. Partition walls should be designed and constructed with voids/slip joints at the bottom of the wall or the top of the wall, to allow independent movement of the floor slab. This concept is shown below.

KileyBaham Highlight Damage associated with movement of interior concrete slab-on-grade floor can be reduced by designing the floors as “floating” slabs. The concrete slabs should not be structurally tied to the foundations or the overlying structure.

KileyBaham Highlight Interior walls or columns should not be supported on the interior floor slabs.

KileyBaham Highlight artition walls should be designed and constructed with voids/slip joints at the bottom of the wall or the top of the wall

KileyBaham Highlight Pa

KileyBaham Highlight nterior walls may be structurally supported from framing above the floor, or interior walls and support columns may be supported on interior portions of the foundation system.

KileyBaham Callout confirm with struct we are supporting from structure above

The sketch above provides a concept. If the plans include isolation of the partition walls from the floor slab, the project architect or structural engineer should be contacted to provide specific details and design of the desired system.

Due to the expansive nature of the soils tested we do not recommend that interior floor slabs in finished areas be considered unless the owner thoroughly understands the implications of movement of these structural components. The recommendation provided below provides a soil conditioning strategy if the owner wishes to pursue construction of concrete floor slabs.

If the owner chooses to construct the structure with concrete slab-on-grade floors, the floors should be supported by a layer of granular structural fill overlying the processed natural soils.

Interior concrete flatwork, or concrete slab-on-grade floors, should be underlain by scarification, moisture conditioning and compaction of about 6 inches of the natural soils followed by placement of at least 18 inches of compacted granular structural fill material that is placed and compacted as discussed in the Construction Considerations, “Fill Placement Recommendations” section of this report, below.

The above recommendations will not prevent slab heave if the expansive soils underlying slabs-on-grade become wet. However, the recommendations will reduce the effects if slab heave occurs.

All plumbing lines should be pressure tested before backfilling to help reduce the potential for wetting. The only means to completely mitigate the influence of volume changes on the performance of interior floors is to structurally support the floors over a void space. Floors that are suspended by the foundation system will not be influenced by volume changes in the site soils.

The suggestions and recommendations presented in this section are intended to help reduce the influence of swelling soils on the performance of the concrete slab-on-grade floors.

KileyBaham Line

KileyBaham Line

KileyBaham Callout not our condition, needs to be confirmed with struct. clarify if we need soils report amended to reflect our conditions

KileyBaham Highlight Due to the expansive nature of the soils tested we do not recommend that interior floor slabs in finished areas be considered unless the owner thoroughly understands the implications of movement of these structural components. The recommendation provided below provides a soil conditioning strategy if the owner wishes to pursue construction of concrete floor slabs.

KileyBaham Highlight moisture conditioning and compaction of about 6 inches of the natural soils followed by placement of at least 18 inches of compacted granular structural fill material that is placed and compacted as discussed in the Construction Considerations

KileyBaham Highlight However, the recommendations will reduce the effects if slab heave occurs.

7.1.1 Capillary and Vapor Moisture Rise

Capillary and vapor moisture rise through the slab support soil may provide a source for moisture in the concrete slab-on-grade floor. This moisture may promote development of mold or mildew in poorly ventilated areas and may influence the performance of floor coverings and mastic placed directly on the floor slabs. The type of floor covering, adhesives used, and other considerations that are not related to the geotechnical engineering practice will influence the design. The architect, builder and particularly the floor covering/adhesive manufacturer should be contacted regarding the appropriate level of protection required for their products.

Comments for Reduction of Capillary Rise

One option to reduce the potential for capillary rise through the floor slab is to place a layer of clean aggregate material, such as washed concrete aggregate for the upper 4 to 6 inches of fill material supporting the concrete slabs.

Comments for Reduction of Vapor Rise

To reduce vapor rise through the floor slab, a moisture barrier such as a 6 mil (or thicker) plastic, or similar impervious geotextile material is often be placed below the floor slab. The material used should be protected from punctures that will occur during the construction process.

There are proprietary barriers that are puncture resistant that may not need the underlying layer of protective material. Some of these barriers are robust material that may be placed below the compacted structural fill layer. We do not recommend placement of the concrete directly on a moisture barrier unless the concrete contractor has had previous experience with curing of concrete placed in this manner. As mentioned above, the architect, builder and particularly the floor covering/adhesive manufacturer should be contacted regarding the appropriate level of moisture and vapor protection required for their products.

7.1.2 Slab Reinforcement Considerations

The project structural engineer should be contacted to provide steel reinforcement design considerations for the proposed floor slabs. Any steel reinforcement placed in the slab should be placed at the appropriate elevations to allow for proper interaction of the reinforcement with tensile stresses in the slab. Reinforcement steel that is allowed to cure at the bottom of the slab will not provide adequate reinforcement.

7.2 Exterior Concrete Flatwork Considerations

Exterior concrete flatwork includes concrete driveway slabs, aprons, patios, and walkways. The desired performance of exterior flatwork typically varies depending on the proposed use of the site and each owner’s individual expectations. As with interior flatwork, exterior flatwork is particularly prone to movement and potential damage due to movement of the support soils. This movement and associated damage may be reduced by following the recommendations discussed under interior flatwork, above. Unlike interior flatwork, exterior flatwork may be exposed to frost heave, particularly on sites where the bearing soils have a high silt content. It may be prudent to

KileyBaham Highlight 4 to 6 inches of fill

KileyBaham Highlight material supporting the concrete slabs.

KileyBaham Callout not required, we will provide

KileyBaham Highlight We do not recommend placement of the concrete directly on a moisture barrier unless the concrete contractor has had previous experience with curing of concrete placed in this manner.

KileyBaham Callout contrary to ACI 302 remove silt soils from exterior flatwork support areas where movement of exterior flatwork will adversely affect the project, such as near the interface between the driveway and the interior garage floor slab. If silt soils are encountered, they should be removed to the maximum depth of frost penetration for the area where movement of exterior flatwork is undesirable.

If some movement of exterior flatwork is acceptable, we suggest that the support areas be prepared by scarification, moisture conditioning and re-compaction of about 6 inches of the natural soils followed by placement of at least 12 inches of compacted granular fill material. The scarified material and granular fill materials should be placed as discussed under the Construction Considerations, “Fill Placement Recommendations” section of this report, below.

It is important that exterior flatwork be separated from exterior column supports, masonry veneer, finishes and siding. No support columns, for the structure or exterior decks, should be placed on exterior concrete unless movement of the columns will not adversely affect the supported structural components. Movement of exterior flatwork may cause damage if it is in contact with portions of the structure exterior.

It should be noted that silt and silty sand soils located near the ground surface are particularly prone to frost heave. Soils with high silt content have the ability to retain significant moisture.

The ability for the soils to accumulate moisture combined with a relatively shallow source of subsurface water and the fact that the winter temperatures in the area often very cold all contribute to a high potential for frost heave of exterior structural components. We recommend that silty soils be removed from the support areas of exterior components that are sensitive to movement associated with frost heave. These soils should be replaced with a material that is not susceptible to frost heave. Aggregate road base and similar materials retain less water than fine-grained soils and are therefore less prone to frost heave. We are available to discuss this concept with you as the plans progress.

Landscaping and landscaping irrigation often provide additional moisture to the soil supporting exterior flatwork. Excessive moisture will promote heave of the flatwork either due to expansive soil, or due to frost action. If movement of exterior slabs is undesirable, we recommend against placement of landscaping that requires irrigation. The ground surfaces near exterior flatwork must be sloped away from flatwork to reduce surface water migration to the support soil.

Exterior flatwork should not be placed on soils prepared for support of landscaping vegetation.

Cultivated soils will not provide suitable support for concrete flatwork.

7.3 General Concrete Flatwork Comments

It is relatively common that both interior and exterior concrete flatwork is supported by areas of fill adjacent to either shallow foundation walls or basement retaining walls. A typical sketch of this condition is shown below.

Settlement of the backfill shown above will create a void and lack of soil support for the portions of the slab over the backfill. Settlement of the fill supporting the concrete flatwork is likely to cause damage to the slab-on-grade. Settlement and associated damage to the concrete flatwork may occur when the backfill is relatively deep, even if the backfill is compacted.

If this condition is likely to exist on this site it may be prudent to design the slab to be structurally supported on the retaining or foundation wall and designed to span to areas away from the backfill area as designed by the project structural engineer. We are available to discuss this with you upon request.

8.0 CONSTRUCTION CONSIDERATIONS

This section of the report provides comments, considerations and recommendations for aspects of the site construction which may influence, or be influenced by the geotechnical engineering considerations discussed above. The information presented below is not intended to discuss all aspects of the site construction conditions and considerations that may be encountered as the project progresses. If any questions arise as a result of our recommendations presented above, or if unexpected subsurface conditions are encountered during construction we should be contacted immediately.

8.1 Fill Placement Recommendations

There are several references throughout this report regarding both natural soil and compacted structural fill recommendations. The recommendations presented below are appropriate for the fill placement considerations discussed throughout the report above.

All areas to receive fill, structural components, or other site improvements should be properly prepared and grubbed at the initiation of the project construction. The grubbing operations should include scarification and removal of organic material and soil. No fill material or concrete should be placed in areas where existing vegetation or fill material exist.

We observed evidence of previous site use and existing man-placed fill during our field work. We encountered man-placed fill in our test borings. We suspect that man-placed fill and subterranean structures may be encountered as the project construction progresses. All existing fill material should be removed from areas planned for support of structural components. Excavated areas and subterranean voids should be backfilled with properly compacted fill material as discussed below.

8.1.1 Natural Soil Fill

Any natural soil used for any fill purpose should be free of all deleterious material, such as organic material and construction debris. Natural soil fill includes excavated and replaced material or in-place scarified material. Due to the expansive characteristics of the natural soil we do not recommend that it be used as fill material for direct support of structural components. The natural soils may be used to establish general site elevation. Our recommendations for placement of natural soil fill are provided below.

• The natural soils should be moisture conditioned, either by addition of water to dry soils, or by processing to allow drying of wet soils. The proposed fill materials should be moisture conditioned to between about optimum and about 2 percent above optimum soil moisture content. This moisture content can be estimated in the field by squeezing a sample of the soil in the palm of the hand. If the material easily makes a cast of soil which remains in-tact, and a minor amount of surface moisture develops on the cast, the material is close to the desired moisture content. Material testing during construction is the best means to assess the soil moisture content.

• Moisture conditioning of clay or silt soils may require many hours of processing. If possible, water should be added and thoroughly mixed into fine grained soil such as clay or silt the day prior to use of the material. This technique will allow for development of a more uniform moisture content and will allow for better compaction of the moisture conditioned materials.

• The moisture conditioned soil should be placed in lifts that do not exceed the capabilities of the compaction equipment used and compacted to at least 90 percent of maximum dry density as defined by ASTM D1557, modified Proctor test.

• We typically recommend a maximum fill lift thickness of 6 inches for hand operated equipment and 8 to 10 inches for larger equipment.

• Care should be exercised in placement of utility trench backfill so that the compaction operations do not damage underlying utilities.

• The maximum recommended lift thickness is about 6 to 8 inches. The maximum recommended rock size for natural soil fill is about 3 inches. This may require on-site screening or crushing if larger rocks are present. We must be contacted if it is desired to utilize rock greater than 3 inches for fill materials.

8.1.2 Granular Compacted Structural Fill

Granular compacted structural fill is referenced in numerous locations throughout the text of this report. Granular compacted structural fill should be constructed using an imported commercially produced rock product such as aggregate road base. Many products other than road base, such as clean aggregate or select crusher fines may be suitable, depending on the intended use. If a specification is needed by the design professional for development of project specifications, a material conforming to the Colorado Department of Transportation (CDOT) “Class 6” aggregate road base material can be specified. This specification can include an option for testing and approval in the event the contractor’s desired material does not conform to the Class 6 aggregate specifications. We have provided the CDOT Specifications for Class 6 material below.

Grading of CDOT Class 6 Aggregate Base-Course Material Sieve Size Percent Passing Each Sieve

1 inch 100 ¾ inch 95-100

#4 30-65 #8 25-55

#200 3-12 Liquid Limit less than 30

All compacted structural fill should be moisture conditioned and compacted to at least 90 percent of maximum dry density as defined by ASTM D1557, modified Proctor test. Areas where the structural fill will support traffic loads under concrete slabs or asphalt concrete should be compacted to at least 95 percent of maximum dry density as defined by ASTM D1557, modified Proctor test.

Although clean-screened or washed aggregate may be suitable for use as structural fill on sites with sand or…