04_Appendix A_Geotechnical Report_Hwy 9 Sidewalks Improvements_25946.pdf

Colorado Regional Office: 7108 South Alton Way, Building B • Centennial, CO 80112 Arizona • Colorado • Idaho • Texas • Utah Phone 303-220-0300 • www.cesareinc.com

GEOTECHNICAL STUDY

Frisco Highway 9 Sidewalk

Frisco, Colorado

Prepared for:

Mr. Eric Lee JR Engineering, LLC

7200 South Alton Way, Suite C400 Centennial, CO 80112

Project No. 23.5043.A November 10, 2023

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 i

GEOTECHNICAL STUDY

Frisco Highway 9 Sidewalk

Frisco, Colorado

Prepared for:

Mr. Eric Lee JR Engineering, LLC

7200 South Alton Way, Suite C400 Centennial, CO 80112

Project No. 23.5043.A November 10, 2023

Prepared by: Reviewed by:

Jason A. Inskeep, P.E. Darin R. Duran, P.E.

Project Engineer Southwest Colorado Office Manager/

Senior Principal - Colorado

11/13/23

CMT TECHNICAL SERVICES - COLORADO

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 ii

TABLE OF CONTENTS

1. PURPOSE

1.1 GENERAL

1.2 SCOPE OF SERVICES

2. SUMMARY OF FINDINGS AND CONCLUSIONS

3. SITE CONDITIONS

4. PROPOSED CONSTRUCTION

5. GEOLOGIC CONDITIONS

5.1 SURFICIAL DEPOSITS

6. FIELD EXPLORATION

7. LABORATORY TESTING

8. SUBSURFACE CONDITIONS

9. GEOTECHNICAL CONSIDERATIONS

9.1 SITE PREPARATION

10. RETAINING WALLS

10.1 SLOPE STABILITY

10.1.1 DURING CONSTRUCTION

10.1.2 POST-CONSTRUCTION

10.2 LATERAL EARTH PRESSURES

10.3 EXCAVATIONS

10.4 STRUCTURAL FILL/BACKFILL SOIL

10.5 IMPORT FILL

10.6 SUBSURFACE DRAINAGE

10.7 SURFACE DRAINAGE

11. SOIL CHEMICAL TESTING

11.1 SULFATE EXPOSURE

12. GEOTECHNICAL RISK

13. LIMITATIONS

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TABLES

TABLE 7.1. Laboratory Testing Performed TABLE 10.1. Material Parameters Used in Global Stability Analysis and Determination of Lateral Earth Pressures TABLE 10.2. Lateral Earth Pressures and for Onsite Material TABLE 10.3. Allowable Slope Configuration for Onsite Material TABLE 10.4. Compaction Specifications TABLE 10.5. Import Fill Specifications

FIGURES

VICINITY MAP ................................................................................................................... FIGURE 1 EXPLORATION PLAN (1) ................................................................................................... FIGURE 2 EXPLORATION PLAN (2) ................................................................................................... FIGURE 3

APPENDICES

FIELD EXPLORATION ................................................................................................... APPENDIX A LABORATORY TESTING ................................................................................................ APPENDIX B

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COMMON ABBREVIATIONS AND ACRONYMS

AASHTO ......... American Association of State Highway and Transportation Officials ABC ................ aggregate base course ACI ................ American Concrete Institute ADA ............... Americans with Disabilities Act ADSC ............. International Association of Foundation Drilling AI .................. Asphalt Institute APM .............. asphalt paving material ASCE .............. American Society of Civil Engineers ASTM ............. American Society for Testing and Materials AWWA ........... American Water Works Association bgs................. below ground surface CDOT ............. Colorado Department of Transportation CBR ................ California Bearing Ratio CFR ................ Code of Federal Regulations CGS ................ Colorado Geological Survey CKD ............... cement of kiln dust stabilized subgrade CMU ............... concrete masonry unit CTB ................ cement treated base course deg ................ degree EDLA .............. equivalent daily load application em ................. edge moisture variation distance EPS ................ expanded polystyrene ESAL .............. equivalent single axle loads f’c .................. specified compressive strength of concrete at the age of 28 days Fa ................... seismic site coefficient FHWA ............ Federal Highway Administration FS .................. factor of safety FV ................... seismic site coefficient GSA ................ global stability analysis GVW .............. gross vehicle weight IBC ................ International Building Code ICC-ES ........... International Code Council Evaluation Services, Inc.

IRC ................ International Residential Code kip ................. 1,000 pounds-force km ................. kilometer LTS ................ lime treated subgrade MDD .............. maximum dry density mg/L ............. milligrams per liter MGPEC ........... Metropolitan Government Pavement Engineers Council mm ................ millimeter Mr .................. resilient modulus MSE ............... mechanically stabilized earth mV ................. millivolts NAPA ............. National Asphalt Pavement Association NDESIGN ........... design gyrations OMC ............... optimum moisture content

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OSHA ............. Occupational Safety and Health Administration OWTS ............ onsite wastewater treatment system PCA ................ Portland Cement Association PCC ................ portland cement concrete pcf ................. pounds per cubic foot pci .................. pounds per cubic inch pH .................. power of hydrogen psf ................. pounds per square foot psi .................. pounds per square inch PT .................. post-tension RAP ................ recycled asphalt pavement Ss ................... mapped spectral accelerations for short periods UBC ............... Uniform Building Code USGS ............. United States Geological Survey

Geotechnical-Engineering Report Important Information about This

Subsurface problems are a principal cause of construction delays, cost overruns, claims, and disputes.

While you cannot eliminate all such risks, you can manage them. The following information is provided to help.

The Geoprofessional Business Association (GBA) has prepared this advisory to help you – assumedly a client representative – interpret and apply this geotechnical-engineering report as effectively as possible. In that way, you can benefit from a lowered exposure to problems associated with subsurface conditions at project sites and development of them that, for decades, have been a principal cause of construction delays, cost overruns, claims, and disputes. If you have questions or want more information about any of the issues discussed herein, contact your GBA-member geotechnical engineer.

Active engagement in GBA exposes geotechnical engineers to a wide array of risk-confrontation techniques that can be of genuine benefit for everyone involved with a construction project.

Understand the Geotechnical-Engineering Services Provided for this Report Geotechnical-engineering services typically include the planning, collection, interpretation, and analysis of exploratory data from widely spaced borings and/or test pits. Field data are combined with results from laboratory tests of soil and rock samples obtained from field exploration (if applicable), observations made during site reconnaissance, and historical information to form one or more models of the expected subsurface conditions beneath the site. Local geology and alterations of the site surface and subsurface by previous and proposed construction are also important considerations. Geotechnical engineers apply their engineering training, experience, and judgment to adapt the requirements of the prospective project to the subsurface model(s). Estimates are made of the subsurface conditions that will likely be exposed during construction as well as the expected performance of foundations and other structures being planned and/or affected by construction activities.

The culmination of these geotechnical-engineering services is typically a geotechnical-engineering report providing the data obtained, a discussion of the subsurface model(s), the engineering and geologic engineering assessments and analyses made, and the recommendations developed to satisfy the given requirements of the project. These reports may be titled investigations, explorations, studies, assessments, or evaluations.

Regardless of the title used, the geotechnical-engineering report is an engineering interpretation of the subsurface conditions within the context of the project and does not represent a close examination, systematic inquiry, or thorough investigation of all site and subsurface conditions.

Geotechnical-Engineering Services are Performed for Specific Purposes, Persons, and Projects, and At Specific Times Geotechnical engineers structure their services to meet the specific needs, goals, and risk management preferences of their clients. A geotechnical-engineering study conducted for a given civil engineer will not likely meet the needs of a civil-works constructor or even a different civil engineer. Because each geotechnical-engineering study is unique, each geotechnical-engineering report is unique, prepared solely for the client.

Likewise, geotechnical-engineering services are performed for a specific project and purpose. For example, it is unlikely that a geotechnical-engineering study for a refrigerated warehouse will be the same as one prepared for a parking garage; and a few borings drilled during a preliminary study to evaluate site feasibility will not be adequate to develop geotechnical design recommendations for the project.

Do not rely on this report if your geotechnical engineer prepared it:

• for a different client;

• for a different project or purpose;

• for a different site (that may or may not include all or a portion of the original site); or

• before important events occurred at the site or adjacent to it;

e.g., man-made events like construction or environmental remediation, or natural events like floods, droughts, earthquakes, or groundwater fluctuations.

Note, too, the reliability of a geotechnical-engineering report can be affected by the passage of time, because of factors like changed subsurface conditions; new or modified codes, standards, or regulations; or new techniques or tools. If you are the least bit uncertain about the continued reliability of this report, contact your geotechnical engineer before applying the recommendations in it. A minor amount of additional testing or analysis after the passage of time – if any is required at all – could prevent major problems.

Read this Report in Full Costly problems have occurred because those relying on a geotechnical-engineering report did not read the report in its entirety. Do not rely on an executive summary. Do not read selective elements only. Read and refer to the report in full.

You Need to Inform Your Geotechnical Engineer About Change Your geotechnical engineer considered unique, project-specific factors when developing the scope of study behind this report and developing the confirmation-dependent recommendations the report conveys.

Typical changes that could erode the reliability of this report include those that affect:

• the site’s size or shape;

• the elevation, configuration, location, orientation, function or weight of the proposed structure and the desired performance criteria;

• the composition of the design team; or

• project ownership.

As a general rule, always inform your geotechnical engineer of project or site changes – even minor ones – and request an assessment of their impact. The geotechnical engineer who prepared this report cannot accept responsibility or liability for problems that arise because the geotechnical engineer was not informed about developments the engineer otherwise would have considered.

Most of the “Findings” Related in This Report Are Professional Opinions Before construction begins, geotechnical engineers explore a site’s subsurface using various sampling and testing procedures. Geotechnical engineers can observe actual subsurface conditions only at those specific locations where sampling and testing is performed. The data derived from that sampling and testing were reviewed by your geotechnical engineer, who then applied professional judgement to form opinions about subsurface conditions throughout the site. Actual sitewide-subsurface conditions may differ – maybe significantly – from those indicated in this report. Confront that risk by retaining your geotechnical engineer to serve on the design team through project completion to obtain informed guidance quickly, whenever needed.

This Report’s Recommendations Are Confirmation-Dependent The recommendations included in this report – including any options or alternatives – are confirmation-dependent. In other words, they are not final, because the geotechnical engineer who developed them relied heavily on judgement and opinion to do so. Your geotechnical engineer can finalize the recommendations only after observing actual subsurface conditions exposed during construction. If through observation your geotechnical engineer confirms that the conditions assumed to exist actually do exist, the recommendations can be relied upon, assuming no other changes have occurred. The geotechnical engineer who prepared this report cannot assume responsibility or liability for confirmation-dependent recommendations if you fail to retain that engineer to perform construction observation.

This Report Could Be Misinterpreted Other design professionals’ misinterpretation of geotechnical-engineering reports has resulted in costly problems. Confront that risk by having your geotechnical engineer serve as a continuing member of the design team, to:

• confer with other design-team members;

• help develop specifications;

• review pertinent elements of other design professionals’ plans and specifications; and

• be available whenever geotechnical-engineering guidance is needed.

You should also confront the risk of constructors misinterpreting this report. Do so by retaining your geotechnical engineer to participate in prebid and preconstruction conferences and to perform construction-phase observations.

Give Constructors a Complete Report and Guidance Some owners and design professionals mistakenly believe they can shift unanticipated-subsurface-conditions liability to constructors by limiting the information they provide for bid preparation. To help prevent the costly, contentious problems this practice has caused, include the complete geotechnical-engineering report, along with any attachments or appendices, with your contract documents, but be certain to note conspicuously that you’ve included the material for information purposes only. To avoid misunderstanding, you may also want to note that “informational purposes” means constructors have no right to rely on the interpretations, opinions, conclusions, or recommendations in the report. Be certain that constructors know they may learn about specific project requirements, including options selected from the report, only from the design drawings and specifications. Remind constructors that they may perform their own studies if they want to, and be sure to allow enough time to permit them to do so. Only then might you be in a position to give constructors the information available to you, while requiring them to at least share some of the financial responsibilities stemming from unanticipated conditions. Conducting prebid and preconstruction conferences can also be valuable in this respect.

Read Responsibility Provisions Closely Some client representatives, design professionals, and constructors do not realize that geotechnical engineering is far less exact than other engineering disciplines. This happens in part because soil and rock on project sites are typically heterogeneous and not manufactured materials with well-defined engineering properties like steel and concrete. That lack of understanding has nurtured unrealistic expectations that have resulted in disappointments, delays, cost overruns, claims, and disputes.

To confront that risk, geotechnical engineers commonly include explanatory provisions in their reports. Sometimes labeled “limitations,” many of these provisions indicate where geotechnical engineers’ responsibilities begin and end, to help others recognize their own responsibilities and risks. Read these provisions closely. Ask questions.

Your geotechnical engineer should respond fully and frankly.

Geoenvironmental Concerns Are Not Covered The personnel, equipment, and techniques used to perform an environmental study – e.g., a “phase-one” or “phase-two” environmental site assessment – differ significantly from those used to perform a geotechnical-engineering study. For that reason, a geotechnical-engineering report does not usually provide environmental findings, conclusions, or recommendations; e.g., about the likelihood of encountering underground storage tanks or regulated contaminants. Unanticipated subsurface environmental problems have led to project failures. If you have not obtained your own environmental information about the project site, ask your geotechnical consultant for a recommendation on how to find environmental risk-management guidance.

Obtain Professional Assistance to Deal with Moisture Infiltration and Mold While your geotechnical engineer may have addressed groundwater, water infiltration, or similar issues in this report, the engineer’s services were not designed, conducted, or intended to prevent migration of moisture – including water vapor – from the soil through building slabs and walls and into the building interior, where it can cause mold growth and material-performance deficiencies.

Accordingly, proper implementation of the geotechnical engineer’s recommendations will not of itself be sufficient to prevent moisture infiltration. Confront the risk of moisture infiltration by including building-envelope or mold specialists on the design team.

Geotechnical engineers are not building-envelope or mold specialists.

Copyright 2019 by Geoprofessional Business Association (GBA). Duplication, reproduction, or copying of this document, in whole or in part, by any means whatsoever, is strictly prohibited, except with GBA’s specific written permission. Excerpting, quoting, or otherwise extracting wording from this document is permitted only with the express written permission of GBA, and only for purposes of scholarly research or book review. Only members of GBA may use this document or its wording as a complement to or as an element of a report of any kind.

Any other firm, individual, or other entity that so uses this document without being a GBA member could be committing negligent or intentional (fraudulent) misrepresentation.

Telephone: 301/565-2733 e-mail: info@geoprofessional.org www.geoprofessional.org

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 1

1. PURPOSE

1.1 GENERAL

CMT Technical Services - Colorado (CMT) performed a geotechnical study for the proposed tiered retaining walls to be located on the western side of Colorado State Highway 9 (SH 9) and south of the intersection with Lagoon Drive in Frisco, Colorado. The study was made to characterize existing subsurface conditions at the site and assist in determining design criteria for planning, removal of existing and construction of new retaining walls, and other pertinent geotechnical issues. Information gathered during the field exploration and laboratory testing is summarized in Figures 1 through 3 and Appendices A and B. CMT’s opinions and recommendations presented in this report are based on data generated during this field exploration, laboratory testing, and its experience.

1.2 SCOPE OF SERVICES

The scope of services performed is detailed in CMT’s Proposal Agreement No. S230901 which was executed on September 11, 2023.

2. SUMMARY OF FINDINGS AND CONCLUSIONS

This section is intended as a summary only and does not include design details. The report should be read in its entirety and utilized for design.

Three borings to depths of about 20.5 to 25.5 feet and two 7 foot deep exploratory pits completed at the site indicated that the stratigraphy behind the wall included about 1.0 feet of topsoil over about 18.4 to 21.3 feet of fill composed of silty sand with cobbles and boulders. Clay with sand was encountered at about 19 feet in Boring B-1. Native silty sand was encountered below the fill to the terminal depths explored. Groundwater was not encountered during the exploration.

The seismic Site Class is D.

Undocumented fill was encountered to depths up to 22 feet. If fill is encountered beneath the proposed walls, it should be removed and replaced with structural fill.

Analysis of the post-construction condition, assuming the use of a Redi Rock block gravity/precast modular block wall system of the dimensions shown in the drawings, indicated the proposed construction met minimum criteria for global stability.

Good surface drainage should be established and positive drainage away from the walls and other site improvements should be provided during construction and maintained throughout its service life.

3. SITE CONDITIONS

The site is located on the western side of State Highway (SH) 9 and south of the intersection with Lagoon Drive in Frisco, Colorado. A vicinity map is shown in Figure 1. A rockery wall located at the site will be removed for construction of the proposed tiered gravity wall system. The site is bound by SH 9 to the east and the recreation (rec) path to the west. A two lane roadway and residential structures are about 35 feet from the back of the existing wall. The site slopes gently from north to south along the alignment of the proposed wall. The drawings, “Highway 9 Retaining Wall and Sidewalks,” dated August 17, 2023, by JR Engineering (the drawings), Sheets 10 and 11 indicated that the batter/slope of the existing wall face ranged from about 45 to 56 degrees from the horizontal.

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The existing rockery wall appeared to consist of dry stacked boulders and is one boulder thick with unknown embedment depth. Based on observations, the existing rockery wall is likely a slope protection measure and does not act as a wall. Borings and test pits were made near the back of the rockery wall and the exploration did not reveal an existing gravel drainage layer or filter. No additional information on the design or construction of the existing rockery wall was contained in the documentation provided to CMT.

Vegetation onsite consisted of trees, shrubs, weeds, and grasses; both in the retained zone and growing in the wall face. No bodies of water or bedrock outcrops were observed onsite and groundwater was not encountered during subsurface exploration.

Photo 1. View looking north at the rockery wall and vegetation onsite.

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Photo 2. View looking south at the northern end of the rockery wall.

Photo 3. View looking south from about midpoint of the northern reach of the rockery wall. The rockery appeared to have a base layer of embedded stone.

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4. PROPOSED CONSTRUCTION

CMT understands that the rockery wall will be replaced with gravity concrete block retaining walls (Redi-Rock or similar). The retaining wall provides grade separation between the rec path and the sidewalk along the western side of SH 9. Preliminary retaining wall plans were provided by the Client.

The project includes a two-tiered northern wall and a single-tiered southern wall. At the northern wall, the lower tier will be up to 7.5 feet tall, the upper tier up to 9 feet tall, and a total wall height of up to 16 feet. The northern wall varies in height along the alignment with the tallest section in the approximate middle of the wall. The southern wall will be up to 6 feet tall.

For this study, CMT assumed that the intended wall is a Redi-Rock block gravity wall system as shown on Sheets 38 and 39 of the drawings. CMT understands that the wall design has not been completed as of the date of this report. All recommendations provided in this report are only applicable to the wall design shown in the drawings provided. Deviations from those drawings would require further review. Recommendations made in this report are for feasibility purposes only; ultimately the wall designer’s specifications supersede any recommendations made herein and recommendations made in this document should not be used as final design recommendations or specifications.

5. GEOLOGIC CONDITIONS

5.1 SURFICIAL DEPOSITS

EXHIBIT 1. “Geologic Map of the Eastern Half of Vail 30’ x 60’ Quadrangle, Eagle, Summit, and Grand Counties, Colorado,” by Kellogg, Shroba, Premo, and Bryant (2011).

Site

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The “Geologic Map of the Eastern Half of Vail 30’ x 60’ Quadrangle, Eagle, Summit, and Grand Counties, Colorado”, prepared for the USGS by Kellogg, Shroba, Premo, and Bryant, dated 2011, indicates that surficial deposits onsite likely consist of:

“Qtp - Till of Pinedale glaciation (Upper Pleistocene)”

6. FIELD EXPLORATION

Subsurface conditions were explored on September 28, 2023 by drilling three borings at the locations indicated in Figures 2 and 3. Borings were drilled 20.5 to 22.5 feet deep. Two shallow (7 feet deep) exploratory pits were also excavated near B-1 and B-3. Graphical logs of the subsurface conditions observed, locations of sampling, and further explanation of the exploration are presented in the boring logs contained in Appendix A.

Photo 4. View looking north at drilling of Boring B-3.

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Photo 5. View looking south at Exploratory Pit EP-2.

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Photo 6. View looking down and south at Exploratory Pit EP-2 and spoils pile.

7. LABORATORY TESTING

CMT personnel returned samples obtained during field exploration to its laboratory where professional staff visually classified them and assigned testing to selected samples to evaluate pertinent engineering properties. Large scale direct shear testing was subcontracted to Advanced Terra Testing. Laboratory tests performed are listed in Table 7.1. Further discussion of laboratory testing and the laboratory test results are presented in Appendix B.

TABLE 7.1. Laboratory Testing Performed Laboratory Test To Evaluate

Grain size analysis Grain size distribution for classification purposes.

Atterberg limits Soil plasticity for classification purposes.

Standard Proctor Moisture/density relationship of compacted soil.

Water soluble sulfate content Potential corrosivity of the soil on cementitious material.

Large scale direct shear testing Drained shearing strength of soil.

8. SUBSURFACE CONDITIONS

CMT’s borings and exploratory pits encountered:

About 0.75 to 1.0 of topsoil.

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Fill consisting of sand with varying amounts of clay, silt, gravel, cobbles, and boulders to depths of 19 to 22 feet.

Clay with sand at about 19 feet in Boring 1.

Overburden soil consisting of silty sand to about 19 feet in Boring B-1 and to the terminal depth explored in Boring B-2.

Measured N-values in Boring B-3 were low, between about 2 and 7 for 12 inches, from a depth of about 14 feet to the terminal depth explored.

Groundwater was not encountered to the maximum depth of exploration (25.5 feet) at the time of drilling/excavation. Borings were backfilled at the completion of the last groundwater check. A more complete description of the subsoil and groundwater conditions encountered is shown in Appendix A.

These observations represent conditions at the time of field exploration and may not be indicative of other times or other locations. Groundwater can be expected to fluctuate and can be influenced by variations in seasons, weather, precipitation, drainage, vegetation, landscaping, irrigation, leakage of water and/or wastewater systems, etc., both onsite and offsite. Discontinuous zones of perched water may exist or develop within the overburden material, especially during spring snowmelt. CMT’s field explorations were performed during the fall when groundwater levels are usually lowest.

Groundwater levels may be higher in the spring and early summer.

9. GEOTECHNICAL CONSIDERATIONS

9.1 SITE PREPARATION

Demolition of the existing walls should include removing all boulders and smaller chinking material that make up the existing rockery.

The existing fill encountered in Boring B-3 is loose/soft and may be prone to settlement. The existing structure has been in service for several years. A pseudo equilibrium or steady state condition has likely developed over time. This steady state condition may be disrupted with new construction and post-construction settlement may occur.

If settlement of the wall is not acceptable, the following options are recommended to mitigate some potential settlement and increase bearing capacity:

The fill may be entirely removed from below the foundation level and replaced as properly compacted structural fill.

The fill may be removed to a depth of 3 feet and replaced with reinforced structural fill.

CMT recommends placing structural fill in compacted 1 foot thick lifts with a layer of geogrid between each lift. Settlement of the existing fill may still occur, but the structural fill with geogrid will reduce the risk of differential movement.

Chemical grouting of the subgrade.

10. RETAINING WALLS

The proposed precast modular block wall (PMB) walls will be founded on silty sand material. The PMB walls should be designed in accordance with the following criteria:

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a) A minimum embedment depth of 1 foot.

b) The base of the wall should be designed for a maximum allowable soil bearing pressure of 2,000 psf based upon dead load plus full live load.

c) All soft or loose soil beneath footing areas should be stabilized using one of the methods indicated in 9.1 SITE PREPARATION.

d) All foundation excavations should be observed to determine if bearing conditions are consistent with those assumed to develop CMT’s recommendations.

Additionally, it is recommended that compaction of backfill within 3 feet of the back of the wall be conducted with hand operated equipment and lightweight equipment at distances greater than 3 feet from the back of the wall.

10.1 SLOPE STABILITY

10.1.1 During Construction

The during construction condition model geometry was based on the requirements for placement of the proposed bearing pads and wall geometries shown on Sheets 10, 11, 38, and 39 of the drawings.

The locations modeled were selected based on the design height of the wall and the height of retained fill. Slope stability analysis results indicated the slope of the excavation should be no greater than 1.7H:1V. With this configuration, the during construction condition FS is about 1.30. The minimum recommended FS for short term conditions is 1.3. The analysis assumed there was no seepage into the excavation and that groundwater was maintained well below the excavation. Construction during dry times of the year is recommended and the contractor is responsible for dewatering and maintaining a safe and stable excavation as stated in section 10.3 EXCAVATIONS.

EXHIBIT 2. Locations of modeled cross sections, borings, and exploratory pits.

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EXHIBIT 3. Construction condition stability analysis, FS=1.30

10.1.2 Post-Construction

Analysis of the post-construction condition, assuming the use of a Redi Rock block gravity/precast modular block wall system of the dimensions shown in the drawings, indicated the proposed construction met minimum criteria for global stability. The results of the analyses are not applicable to other facings or wall configurations/types and the wall designer is responsible for final global and internal stability of the designed wall.

Loose soil was encountered in Boring B-3 that is inconsistent with other borings. The extents of this material is not clear; however, CMT’s borings indicated that this is an exception rather than the normal condition at the site. The stability analysis assumes the removal and replacement of the upper 3 feet of the loose material and replacement with properly compacted gravel. If another method of stabilizing the subgrade, such as chemical grouting, is used, the stabilization measures should be designed to provide at least the same depth of remediation.

Groundwater was not encountered during the field exploration. CMT anticipates that infiltration could become an issue if appropriate drainage is not provided for the proposed walls.

Analyses indicated that the post-construction condition for the proposed wall sections met criteria for long term stability with an FS of 1.54. The minimum recommended FS is 1.5.

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EXHIBIT 4. Post-construction FS was about 1.54.

10.2 LATERAL EARTH PRESSURES

Lateral pressures on walls depend on the type of wall, hydrostatic pressure behind the wall, type of backfill material, and allowable wall movements. CMT recommends drain systems be constructed behind walls to reduce the potential for hydrostatic pressures to develop. Where anticipated/permissible wall movements are greater than 0.5% of the wall height, lateral earth pressures can be estimated for an "active" condition. Where anticipated/permissible wall movement is less than approximately 0.5% of the wall height or wall movement is constrained, lateral earth pressures should be estimated for an "at rest" condition. Recommended lateral earth pressures for onsite material are provided in Table 10.1 and are based on the wall geometry shown in the drawings and are not applicable to other configurations.

The recommended values for lateral earth pressures provided in Table 10.1 are given in terms of an equivalent unit weight. The equivalent unit weight multiplied by the depth below the top of the

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 12 ground surface is the horizontal pressure against the wall at that depth. The resulting pressure distribution is a triangular shape. These soil pressures are for the proposed PMB wall indicated in the drawings and account for the wall geometry, backslope, and expected back cut (see Section 10.1 SLOPE STABILITY) and fill (CDOT Class 1 with minimum drained shearing strength of 34 degrees), no surcharge loading or hydrostatic pressures. If these criteria cannot be met, CMT should be contacted for additional criteria. The coefficients of sliding resistance are valid for PMB wall design indicated in the drawings and use of crushed angular stone gravel for the bearing pad material.

TABLE 10.1. Material Parameters Used in Global Stability Analysis and Determination of

Lateral Earth Pressures.

Material Unit

Weight (pcf)

Internal Friction Angle

(deg) Cohesion

(psf) Coefficient of Friction with

Concrete Upper silty sand 130 35 60 0.41 Lower silty sand 125 26 60 0.31 Leveling pad 130 34 10 0.55 Class 1 fill 130 34 50 0.55

TABLE 10.2. Lateral Earth Pressures and for Onsite Material

Portion of Wall

Total at Rest Fluid Weight

Horizontal Component

Vertical Component At Rest* Passive**

Upper 82 50 65 55 450 Lower 56 43 36 55 320

*At rest values provided for information. The values are based on Jaky’s equation which does not account for the wall geometry and may not be applicable for this design.

**Passive earth pressures provided for information only and are not recommended for use based on the design.

10.3 EXCAVATIONS

Conventional earthmoving equipment should be adequate to excavate the onsite soil. All excavations should be properly sloped and/or braced, and local and federal safety codes observed. Slopes and other areas void of vegetation should be protected against erosion.

It is the contractor’s responsibility to provide safe working conditions and comply with the regulations in OSHA Standards-Excavations, 29 CFR Part 1926. The following guidelines are provided for planning purposes. Sloping and shoring requirements must be evaluated at the time of construction by the contractor’s competent person as defined by OSHA. The geotechnical engineer is NOT the contractor’s “competent person” in any circumstance, including but not limited to, by way of default or delegation. OSHA classifications for various material types and the steepest allowable slope configuration corresponding to those classifications are shown in Table 10.3.

TABLE 10.3. Allowable Slope Configuration for Onsite Material

Material Type

OSHA

Classification Steepest Allowable

Slope Configuration* Silty sand (SM) Type C 1-1/2:1

* Units horizontal to units vertical. The values shown apply to excavation less than 20 feet in height. Conditions can change and evaluation is the contractor’s responsibility.

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The preceding classifications and slope configurations assume that excavations are above the groundwater table, there is no standing water in the excavations, and there is no seepage from the slope into the excavations, unless otherwise specified. The preceding classifications and slope configurations assume that the material in the excavations is not fractured, adversely bedded, jointed, nor left open to desiccate, crack, or slough, and is protected from surface runoff. There are other considerations regarding allowable slope configurations that the contractor is responsible for, including proximity of equipment, stockpiles, and other surcharge loads to the excavation. The contractor’s competent person is responsible for all decisions regarding slope configuration and safety conditions for excavations.

Excavations should not undermine existing foundation systems of structures or infrastructure, unless they are adequately protected. At a minimum, new excavations should not intersect a line drawn using the steepest allowable slope configuration from Table 10.3 down and away from the bottom edge of the existing foundation systems or bottom edge of infrastructure. If this condition cannot be met, shoring or staged excavations may be required. If shoring is required, a condition survey of the adjacent structures is recommended before construction starts and upon completion of construction.

In CMT’s experience, condition surveys include, but may not be limited to, photographs of any distress to adjacent structures.

Permanent slopes should be no steeper than 3:1 and revegetated or otherwise protected from erosion.

10.4 STRUCTURAL FILL/BACKFILL SOIL

The various types of fill anticipated in construction of the wall should be compacted in accordance with the wall designer’s specifications which supersede the recommendations contained in this document. Where fill/backfill soil is necessary, suitable onsite inorganic soil may be used. At this site, unsuitable material is defined as topsoil, organics, trash, ash, frozen material, hard lumps and clods, claystone, and particles larger than 6 inches. Existing onsite fill material can be reused for structural fill/backfill, provided it is free of unsuitable material. If unsuitable material is encountered in the existing fill, it must be removed before the existing fill can be reused as fill/backfill. Recommendations for fill/backfill placement are:

a) Clods and lumps shall be broken down to a maximum size of 6 inches. Pieces larger than 6 inches shall be removed from the fill/backfill.

b) Fill/backfill material should be placed in loose lifts and compacted in accordance with Table 10.4.

c) Maximum loose lift thickness shall be 8 inches, depending on the type of equipment used to apply compactive effort and shall be reduced if the specified compaction cannot be obtained with the equipment used.

d) Fill/backfill should not be placed if material is frozen or if the placement surface is frozen.

e) Fill/backfill material should be placed and spread in horizontal lifts of uniform thickness in a manner that avoids segregation.

f) Placement surface should be kept free of standing water, debris, and unsuitable material during placement and compaction of fill/backfill material.

g) Fill/backfill maximum allowable particle size is 6 inches. Do not incorporate oversize

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 14 material in the fill/backfill that is incapable of being broken down by the equipment and methods being employed to process and compact the fill/backfill. Process and compact material in the lift, as necessary, to produce the specified fill/backfill characteristics. If oversize particles remain in the lift after processing and compacting, remove oversize material to produce a fill/backfill within specified requirements.

h) Fill placement and compaction should be observed and tested on a full-time basis by a representative of CMT. At a minimum the subgrade should be tested in accordance with jurisdictional requirements.

TABLE 10.4. Compaction Specifications

Fill Location Material Type

(General)

AASHTO

Classification

Material Thickness

(ft)

Moisture Content

Relative Compaction (%)*and

Compaction Standard

Foundation Subgrade and Structural Fill**

Granular material that is clean to silty

A-1, A-2-4, A-2-5, A-3, A-4, A-5 <15 +/-2% of

OMC

>90% Modified Proctor

(ASTM D1557)

or >98% Standard Proctor

(ASTM D698)

Fine grained material and granular material with plastic fines

A-2-6, A-2-7 A-6, A-7 <15

0% to +3% of

OMC

90% Modified Proctor

(ASTM D1557)

or >98% Standard Proctor

(ASTM D698)

Fill in nonstructural areas (e.g., landscaping)

Granular material that is clean to silty

A-1, A-2-4, A-2-5, A-3, A-4, A-5 <15 +/-2% of

OMC

>95%*

Standard Proctor

(ASTM D698)

Fine grained material and granular material with plastic fines

A-2-6, A-2-7 A-6, A-7 <15

0% to +3% of

OMC

>95%* Standard Proctor

(ASTM D698)

* If fill thickness greater than 15 feet is planned, additional requirements may apply.

** The foundation subgrade, bearing/leveling pad, fill directly behind the wall face, and drainage aggregate should be compacted in accordance with the wall designers specifications.

10.5 IMPORT FILL

Material imported for structural fill should be tested and approved for use onsite by the project geotechnical engineer prior to hauling to the site. Proctor, remolded swell, and classification tests should be conducted to determine if the fill meets required specifications. Fill material should be well graded, low permeable material meeting the specifications in Table 10.5.

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TABLE 10.5. Import Fill Specifications Soil Parameter Specification

Maximum particle size 3 inch Percent finer than No. 200 sieve 20% to 40% Liquid limit 20% to 40% Plasticity index 8% to 15% Swell potential under anticipated loads less than 1%*

* Upon inundation, when remolded to 97% maximum dry density at 1% below the optimum moisture content per ASTM D698 at a surcharge pressure of 100 psf.

10.6 SUBSURFACE DRAINAGE

Groundwater was not encountered during this study; however, groundwater loading may be higher at other times. Drainage behind the wall should be provided according to the manufacturers and/or wall designers’ recommendations. Placement and compaction of drainage aggregate should be in accordance with the wall designers’ specifications. A geosynthetic separation or graded granular filter layer is recommended for use between the retained existing fill/native material and the wall block/drainage aggregate placed at the back of the wall to prevent migration of finer soil and the creation of voids behind the wall.

10.7 SURFACE DRAINAGE

Good drainage and surface water management is important. Performance of site improvements, such as foundations, floors, hardscape, and pavement are often adversely affected by failing to establish and/or maintain good site drainage. Grades should be adjusted to provide positive drainage away from the wall. Additional surface drainage considerations should be in accordance with the wall block manufacturer and/or the wall designers’ guidance.

11. SOIL CHEMICAL TESTING

11.1 SULFATE EXPOSURE

Water soluble sulfate contents of 0.05% were measured on samples of sand with silt. Results are summarized in Appendix B. The PCA publication, Design and Control of Concrete Mixtures 2002 and the ACI publication. Building Code Requirements for Structural Concrete and Commentary consider this range negligible for water soluble sulfate exposure.

12. GEOTECHNICAL RISK

The concept of risk is an important aspect of any geotechnical study. The primary reason for this is that the analytical methods used by geotechnical engineers are generally empirical and must be tempered by engineering judgment and experience, therefore, the solutions or recommendations presented in any geotechnical study should not be considered risk free, and more importantly, are not a guarantee that the interaction between the soil and the proposed construction will perform as predicted, desired, or intended. The engineering recommendations presented in the preceding sections constitute CMT’s best estimate of those measures that are necessary to help the structure perform in a satisfactory manner based on the information generated during this study, training, and experience in working with these conditions.

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 16

13. LIMITATIONS

This document has been prepared as an instrument of service for the exclusive use of JR Engineering, LLC for the specific application to the project as discussed herein and has been prepared in accordance with geotechnical engineering practices generally accepted in the state of Colorado at the date of its preparation. No warranties, either expressed or implied, are intended or made. This document should not be assumed to contain information that is sufficient for other purposes or to satisfy the needs of other parties.

The findings of this study are valid as of the date of its preparation. Changes in the conditions of a property can occur with the passage of time, whether due to natural processes or the works of people on this or adjacent properties. Standards of practice evolve in engineering and changes in applicable or appropriate standards may occur, whether a result from legislation or the broadening of knowledge. Accordingly, the findings of this study may be invalidated wholly or partially by changes outside of CMT’s control, therefore, this study is subject to review and should not be relied upon without such review after a period of 3 years.

In the event that changes, including but not limited to, the nature, type, design, size, elevation, or location of the project or project elements as outlined in this report are made, the conclusions and recommendations contained in this report shall not be considered valid unless CMT reviews the changes and either confirms or modifies the conclusions of this report in writing.

CMT should be retained to review final plans and specifications that are developed for proposed construction to judge whether the recommendations presented in this report and any addenda have been appropriately interpreted and incorporated in the project plans and specifications as intended.

The exploration locations for this study were selected to obtain a reasonably accurate depiction of underground conditions for design purposes and these locations are often modified based on accessibility and the presence of underground or overhead utility conflicts. Variations from the soil conditions encountered are possible. These variations may necessitate modifications to CMT’s design recommendations, therefore, CMT should be retained to observe subsurface conditions, once exposed, to evaluate whether they are consistent with the conditions encountered during CMT’s exploration and that the recommendations of this study remain valid. If parties other than CMT perform these observations and judgements, they must accept responsibility to judge whether the recommendations in this report remain appropriate.

CMT’s scope of services for this report did not include either specifically, or by implication, any environmental assessment of the site or identification of contaminated or hazardous material or conditions. Additionally, none of the services performed in connection with this study were designed or conducted for the purpose of mold prevention. Proper implementation of the recommendations conveyed in this report will not, of itself, be enough to prevent mold from growing in or on the structures involved.

23.5043.A Frisco Hwy 9 Sidewalk Report 11.10.23 17

At a minimum, CMT should be retained during construction to observe and/or test:

completed excavations.

placement and compaction of fill.

proposed import or onsite fill material.

CMT offers many other construction observations, materials engineering, and testing services and can be contacted to discuss further.

Site

FIGURE 1

Vicinity Map

PROJECT NO:

PROJECT NAME:

23.5043

Frisco Highway 9 Sidewalk

DRAWN BY: CHECKED BY:MSR RSG

DWG DATE: REV. DATE:

W:\2023\Silverthorne\23.5043.A Frisco Highway 9 Wall and Sidewalks\Drafting\ACAD\23.0901 HWY 9 PROPOSAL.dwg 9/29/2023 12:19 PM

0 500' 1000'

1" = APPROX. 500'

N

BACKGROUND IMAGE FROM GOOGLE EARTH

09.29.23

SITE BOUNDARY

LEGEND:

B-1

B-3

B-2

EP-1

EP-1

FIGURE 2

Exploration Plan (1)

PROJECT NO:

PROJECT NAME:

23.5043

Frisco Highway 9 Sidewalk

DRAWN BY: CHECKED BY:MSR RSG

DWG DATE: REV. DATE:

0 80' 160'

1" = APPROX. 80'

N

W

\S ilv er th or ne

\2 3.

.A F ris co

H ig hw ay

W al l a nd S id ew al ks

\D ra fti ng

\A

CA

D\

.0

HW

Y

PR

OP

OS

AL

.d w g 9/

/2

:2

PM

LEGEND:

BACKGROUND IMAGE FROM GOOGLE EARTH

B-1

EP-1

BORING NUMBER AND LOCATION

EXPLORATORY PIT NUMBER AND

LOCATION

SITE BOUNDARY

09.29.23

B-1 B-2 B-3 EP-2EP-1

CDOT ROW

FIGURE 3

Exploration Plan (2)

PROJECT NO:

PROJECT NAME:

23.5043

Frisco Highway 9 Sidewalk

DRAWN BY: CHECKED BY:MSR RSG

DWG DATE: REV. DATE:

W:\2023\Silverthorne\23.5043.A Frisco Highway 9 Wall and Sidewalks\Drafting\ACAD\23.0901 HWY 9 PROPOSAL.dwg 9/29/2023 12:20 PM

0 40' 80'

1" = APPROX. 40'

N

BACKGROUND IMAGE BY J.R. ENGINEERING

LEGEND:

B-1 BORING NUMBER AND LOCATION

09.29.23

CDOT ROW

EP-1 EXPLORATORY PIT NUMBER AND

LOCATION

APPENDIX A

Field Exploration

23.5043 Frisco Hwy 9 Field Exploration App A 1

FIELD EXPLORATION

At this site, samples of the subsoil were obtained using a split spoon sampler which was driven into the soil by dropping a 140-pound hammer through a free fall of 30 inches.