23.5059 Marina Cafe Site Report 02.20.24.pdf

Colorado Regional Office: 7108 South Alton Way, Building B • Centennial, CO 80112 Arizona • Colorado • Idaho • Texas • Utah

Phone 303-220-0300 • www.cmttechnicalservices.com

GEOTECHNICAL STUDY

Marina Café Site Dillon, Colorado

Prepared for:

Mr. Dan Burroughs Town of Dillon

P.O. Box 8 Dillon, CO 80435-0008

Project No. 23.5059 February 20, 2024

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GEOTECHNICAL STUDY

Marina Café Site Dillon, Colorado

Prepared for:

Mr. Dan Burroughs Town of Dillon

P.O. Box 8 Dillon, CO 80435-0008

Project No. 23.5059 February 20, 2024

Prepared by: Reviewed by:

Richard S. Greeley, P.E. William H. Koechlein, P.E.

Project Engineer Senior Consultant

02/20/24

CMT TECHNICAL SERVICES - COLORADO

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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

5.2 BEDROCK

6. FIELD EXPLORATION

7. LABORATORY TESTING

8. SUBSURFACE CONDITIONS

9. GEOTECHNICAL CONSIDERATIONS

9.1 DOCUMENTED FILL

9.1.1 PENETRATION TESTING

9.1.2 EXPENDABLE POINT PENETROMETER TESTING

9.1.3 REVIEW OF PHOTOGRAPHIC DOCUMENTATION

9.2 MOISTURE SENSITIVE SOIL

9.3 POTENTIALLY UNSTABLE SLOPE

10. FOUNDATION RECOMMENDATIONS

10.1 SPREAD FOOTINGS

11. LATERAL EARTH PRESSURES

11.1 FOUNDATION WALLS

12. INTERIOR FLOORS

12.1 SLAB-ON-GRADE CONSTRUCTION DETAILS

12.2 STRUCTURALLY SUPPORTED FLOORS

13. EXTERIOR FLATWORK

13.1 OVERHANGING ROOFS

14. EXCAVATIONS

15. STRUCTURAL FILL/BACKFILL SOIL

15.1 IMPORT FILL

16. SUBSURFACE DRAINAGE

17. SURFACE DRAINAGE

18. SOIL CHEMICAL TESTING

18.1 SULFATE EXPOSURE

18.2 SOIL CORROSIVITY

19. GEOTECHNICAL RISK

20. LIMITATIONS

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TABLES

TABLE 7.1. Laboratory Testing Performed TABLE 11.1. Lateral Earth Pressures and Coefficients of Sliding Resistance for Onsite Material 14 TABLE 14.1. Allowable Slope Configuration for Onsite Material TABLE 15.1. Compaction Specifications TABLE 15.2. Import Fill Specifications TABLE 18.1. Summary of Soil Chemical Test Results

FIGURES

VICINITY MAP ................................................................................................................... FIGURE 1 BORING LOCATION PLAN ................................................................................................. FIGURE 2 TYPICAL EXTERIOR PERIMETER DRAIN FOOTINGS/SLAB ON GRADE FLOOR ................ FIGURE 3

APPENDICES

FIELD EXPLORATION ................................................................................................... APPENDIX A LABORATORY TESTING ................................................................................................ APPENDIX B VAPOR BARRIERS ........................................................................................................ APPENDIX C

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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 ............. Association of Drilled Contractors 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 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:

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

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1. PURPOSE

1.1 GENERAL

CMT Technical Services - Colorado (CMT) performed a geotechnical study for the proposed café building to be located on Marina Drive in Dillon, Colorado. The study was made to characterize existing subsurface conditions at the site and assist in determining design criteria for planning, site development, foundation systems, interior floor systems, exterior flatwork, surface and subsurface drainage adjacent to structures, and to present other pertinent geotechnical issues. Information gathered during the field exploration and laboratory testing is summarized in Figures 1 through 3 and Appendices A through C. 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. S231006 which was executed on November 28, 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.

Borings B-1 through B-4 were completed in or near the area of the proposed building.

These borings typically encountered about 6 to 15 feet of fill, underlain by silty sand with varying amounts of gravel, underlain by weathered and competent shale bedrock. Boring B-5 was completed at the toe of the slope and subsurface conditions consisted of gravelly sand with silt to a depth of 5 feet, underlain by sandy clay to a depth of 9 feet, underlain by weathered shale bedrock.

Fill soil with moderate plasticity was encountered. The fill was tested for its swell/consolidation potential. The results indicated that the fill soil has a nil potential to swell and low potential to consolidate.

CMT evaluated the adequacy of the fill for foundation support of the proposed Marina Café building. CMT evaluated the fill by penetration testing, expendable point penetrometer (EPP) testing, and review of documentation of fill construction provided by the Town of Dillon (TOD).

o Penetration test results indicated the fill is typically medium dense to dense (sands) and very stiff to hard (clay). No test indicated loose or soft fill.

o EPP testing largely agreed with the penetration test results in the borings. No test indicated loose or soft fill.

o Photographic documentation and the description of the project details from the TOD indicated adequate placement of the fill.

The proposed café may be founded on conventional spread footings or pad type footings bearing on the existing fill or on new, controlled, structural fill below frost depth.

Potential settlement of the fill has likely been realized to a significant degree, but it is unknown if there is potential for additional settlement after new construction is complete.

To reduce the potential for movement of the slabs-on-grade, existing fill should be removed to a depth of 2 feet below floor slabs and replaced as structural fill.

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CMT understands that the building may be constructed on or near the crest of the slope.

Details of the proposed construction and the location of the building relative to the slope may affect the stability of the slope. Once plans have progressed, CMT should be contacted to provide a global slope stability analysis (GSA) for the critical section of the slope.

Good surface drainage should be established and positive drainage away from the structures, pavement, and other site improvements should be provided during construction and maintained throughout the life of the proposed structures. Below grade areas, such as basements and crawlspaces, should be provided with an exterior perimeter subsurface drainage system.

3. SITE CONDITIONS

The site is located on Marina Drive in Dillon, Colorado. A vicinity map is shown in Figure 1. The site currently has no vertical structures. A dock and several concrete blocks are being stored onsite. The site was part of a regrading project in 2012 which included fill placements up to about 15 feet deep.

The site is bound by Marina Drive to the north, the marina and boat ramp to the east, a steep slope and Dillon Reservoir to the south, and a recreation (rec) path and Marina Park Playground to the west. Topography of the site is gently sloping but the adjacent slope would be considered steep with a grade change of about 18 feet (south) which is up to about 30 degrees.

The ground surface is typically bare. Snow covered the ground surface at the time of the field exploration. Vegetation on the slope consists of grasses and weeds and vegetation below the slope is native grasses, weeds, and bushes. Dillon Reservoir is about 130 feet south of the site and 35 feet lower in elevation. No outcrops were observed onsite.

Photo 1. View looking south at the site and Dillon Reservoir.

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Photo 2. View looking west at the site.

Photo 3. View looking east at the slope below the site.

4. PROPOSED CONSTRUCTION

CMT understands that the Arapahoe Café structure may be moved from 626 Lake Dillon Drive to the site. Alternatively, a new structure may be built. Site improvements include a deck/patio area, potential crawlspace/basement, and a potential retaining wall. The foundation and/or

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crawlspace/basement excavations are estimated to be about 3 to 10 feet deep. CMT anticipates that changes to existing site grades will be limited to about 3 feet of cut and/or fill to achieve final surface grades.

5. GEOLOGIC CONDITIONS

5.1 SURFICIAL DEPOSITS

The “Geologic Map of the Dillon Quadrangle, Summit and Grand Counties, Colorado” prepared for the USGS by Kellogg, dated 2002, indicates that surficial deposits onsite likely consist of:

Older outwash gravel (middle or lower Pleistocene).

5.2 BEDROCK

The “Geologic Map of the Dillon Quadrangle, Summit and Grand Counties, Colorado” prepared for the USGS by Kellogg, dated 2002, indicates that bedrock onsite likely consists of:

Dakota sandstone.

Pierre shale.

6. FIELD EXPLORATION

Subsurface conditions were explored on December 18 and 19, 2023 by drilling five borings at the locations indicated in Figure 2. Borings were drilled 20.5 to 31 feet deep. The elevation of the borings was interpolated from a topographic map provided by TOD.

Additionally, the fill was evaluated using an expendable point penetrometer. The penetrometer was advanced in two locations adjacent to each boring (B-1 through B-4). The cone was advanced by repetitive blows from the 140 pound automatic hammer attached to the drill rig. 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 west at drilling of B-3.

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Photo 5. View looking at cone penetrometer testing.

Photo 6. View looking east at drilling of B-5 at the toe of the slope.

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. Laboratory tests performed are listed in Table 7.1. Further

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discussion of laboratory testing and the laboratory test results are presented in Appendix B. Results of corrosivity testing are presented in Section 18. SOIL CHEMICAL TESTING.

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.

Swell/consolidation Effect of wetting and loading on the soil.

Proctor (standard) Moisture/density relationship of compacted soil.

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

Direct Shear Shear strength of the soil.

pH, water soluble chloride content, redox, and resistivity Potential corrosivity of the soil to metal.

8. SUBSURFACE CONDITIONS

CMT’s borings encountered:

In Borings B-1 through B-4:

o Fill consisting of clayey sand and sandy clay with gravel to depths of 6 to 15 feet.

o Overburden soil consisting of silty sand with gravel to gravelly beneath the fill to depths of 20 to 25 feet.

o Native clay below the sand in B-1 to a depth of 23 feet.

o Weathered shale at depths from 20 to 25 feet to depths of 29 feet to maximum depths explored of 31 feet.

o Shale bedrock beneath the weathered shale in B-1 and B-4 to the maximum depths explored of 31 feet.

o No groundwater.

In Boring B-5:

o Gravelly sand with silt to a depth of 5 feet.

o Sandy clay below the sand to a depth of 9 feet.

o Weathered shale below the clay to the maximum depth explored of 20.5 feet.

o No groundwater.

With the exception of the fill, the subsurface conditions encountered in CMT’s borings are reasonably consistent with those described in Section 5. GEOLOGIC CONDITIONS. These observations represent conditions at the time of field exploration and may not be indicative of other times or other locations.

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Photo 7. View looking at plastic debris encountered at a depth of 12 feet in B-3 indicating fill soil.

Photo 8. View looking at shale encountered in B-4.

9. GEOTECHNICAL CONSIDERATIONS

9.1 DOCUMENTED FILL

CMT understands that the fill soil was placed in 2012 during a grading project. Full time compaction testing was provided by the Town of Dillon (TOD) (Mr. Ned West). Mr. West communicated the

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following to CMT via email correspondence:

The source of the fill material was the excavation area for the Marina Parking Lot project.

Cesare Inc. (CMT formerly known as) provided the geotechnical report for the Marina Parking Lot project and native subsurface conditions typically consisted of sandy clay, clayey sand, and claystone. Fill material encountered consisted of silty sand, clayey sand with gravel, sandy gravel with clay, and clayey sand with gravel.

The material was blended prior to placement and moisture was added, as needed.

The material was placed in relatively uniform lifts of 6 to 8 inches.

Compaction equipment consisted of a rex style sheepsfoot compactor with blade (rex).

Proof rolls were observed with the mine haul truck loads and compaction equipment.

Three to four density tests were conducted with a nuclear gauge, per lift.

Standard Proctor was used with specification of 95% of maximum dry density and +/-2% of optimum moisture.

Proof rolls were also observed after weather events and at the top of the hill.

The embankment fill was completed in the Fall 2012 and roadway construction started in the Spring 2013.

CMT understands compaction test results were recorded during placement of the fill but have since been misplaced. The TOD provided photographs of the project but was unable to provide documentation of the compaction testing. Refer to Photos 9 through 15 provided by the TOD of placement of the embankment fill.

Photo 9. View looking west at bench with topsoil removed.

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Photo 10. View looking at moisture conditioning and compaction efforts with a sheepsfoot compactor, smooth drum compactor, and water truck.

Photo 11. View looking west at rex style sheepsfoot compactor compacting the embankment.

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Photo 12. View looking east at haul truck to the south and TOD truck with nuclear gauge box in the bed.

Photo 13. View looking south at rex spreading haul truck dumps into lifts.

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Photo 14. View looking north at rex and TOD truck with nuclear gauge box in bed.

Photo 15. View looking east at preparation for roadway construction.

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CMT was tasked with evaluating the adequacy of the fill for foundation support of the proposed Marina Café building. CMT evaluated the fill by standard penetration testing, expendable point penetrometer (EPP) testing, and review of photographic documentation of fill construction provided by the TOD.

9.1.1 Penetration Testing

Modified California and standard split spoon samplers were driven into the soil by dropping a 140 pound hammer through a free fall of 30 inches. The number of blows required for the sampler to penetrate 12 inches gives an indication of the relative stiffness of cohesive soil, relative density of non-cohesive soil, and relative hardness of sedimentary bedrock material encountered. Penetration tests were performed at an interval of 2 feet in the fill material. Penetration test results indicated the fill was typically medium dense to dense (sands) and very stiff to hard (clay). No tests were indicative of loose or soft fill. Penetration test results are presented on the boring logs in Appendix A.

9.1.2 Expendable Point Penetrometer Testing

Expendable point penetrometer testing was performed in two locations adjacent to each boring where fill was encountered. A cone with a 60 degree point was attached to the drilling rods and lowered to the testing start depth of 3 feet. The cone was driven into the soil by dropping a 140 pound hammer through a free fall of 30 inches. The number of blows to advance the cone was recorded every 6 inches until the cone had advanced past the depth of fill. Test results are provided in Appendix A.

EPP testing largely agreed with the penetration test results in the borings. No tests were indicative of loose or soft fill.

9.1.3 Review of Photographic Documentation

CMT reviewed the 95 photographs provided by the TOD taken between August 28 and October 2, 2012. Compaction equipment and nuclear gauge density test equipment was seen in the photographs. Photograph documentation indicated controlled placement of the fill.

9.2 MOISTURE SENSITIVE SOIL

Fill soil with moderate plasticity was encountered. The clay soil encountered was sandy and contained gravel. The fill was tested for its swell/consolidation potential. During the tests, the samples were loaded to about 500 to 1,000 psf before being inundated with water. The results indicated that the fill soil has a nil potential to swell and low potential to consolidate. The test results are consistent with our experience with a moisture conditioned and replaced fill material.

9.3 POTENTIALLY UNSTABLE SLOPE

Construction plans are currently preliminary. CMT understands that the building may be constructed on or near the crest of the slope. The slope is stable in its current condition. Details of the proposed construction and the location of the building relative to the slope may affect the stability of the slope.

Once plans have progressed, CMT should be contacted to provide a global slope stability analysis (GSA) for the critical section of the slope.

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10. FOUNDATION RECOMMENDATIONS

10.1 SPREAD FOOTINGS

The proposed café may be founded on conventional spread footings or pad type footings bearing on the existing fill or on new, controlled, structural fill below frost depth in accordance with the following design recommendations:

a) A frost depth of 40 inches should be assumed for this area (Summit County Building Inspection Department Matrix).

b) Footings should be designed for a maximum allowable soil bearing pressure of 2,000 psf based on dead load plus full live load.

c) Continuous footings should have a minimum width of 18 inches and isolated pad type footings a minimum dimension of 24 inches. Using the soil pressure recommended above, CMT estimates the maximum settlement for the structure will be on the order of 1 inch, with differential settlement potentially on the order of 0.5 inches. Footings should be proportioned as much as practicable to reduce differential settlement.

d) Steel reinforcement for continuous concrete foundation walls should be designed to span localized settlements over a distance of 10 feet.

e) All soft or loose soil beneath footing areas should be redensified in place, or removed and replaced with properly compacted structural fill, suitable flow fill, or concrete prior to placement of footing concrete. All footing excavations should be observed by a CMT representative prior to concrete placement to determine if bearing conditions are consistent with those assumed to develop its recommendations.

11. LATERAL EARTH PRESSURES

11.1 FOUNDATION WALLS

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 11.1.

The recommended values for lateral earth pressures provided in Table 11.1 are given in terms of an equivalent unit weight. The equivalent unit weight multiplied by the depth below the top of the 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 horizontal backfill with no surcharge loading or hydrostatic pressures. If these criteria cannot be met, CMT should be contacted for additional criteria.

The unfactored or ultimate coefficients of sliding resistance between concrete and bearing soil are provided in Table 11.1.

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TABLE 11.1. Lateral Earth Pressures and Coefficients of Sliding Resistance for Onsite Material

Backfill Material Type

Equivalent Unit Weight (pcf)

Coefficient of Sliding

Resistance Active At Rest Passive Backfill soil, no hydrostatic pressure 40 60 360 0.55

Exterior retaining walls such as MSE or rockery walls can be addressed under separate cover should the need arise.

12. INTERIOR FLOORS

The existing manmade fill was placed in 2012. Potential settlement of the fill has likely been realized to a significant degree, but it is unknown if there is potential for additional settlement after new construction is complete. To reduce the potential for movement of the slabs-on-grade, existing fill should be removed to a depth of 2 feet below floor slabs. Acceptable existing fill material or a suitable, offsite material should be moisture conditioned and compacted in accordance with Section 15.

STRUCTURAL FILL/BACKFILL SOIL. If movement of the interior floors cannot be tolerated, structural floors should be considered.

12.1 SLAB-ON-GRADE CONSTRUCTION DETAILS

Slab-on-grade cracking can result from compression of the supporting soil and also from concrete curing stresses. If slab-on-grade floors are chosen, CMT recommends that design and construction of all interior slab-on-grade floors incorporate the following considerations and precautions. These details will not reduce the amount of movement but are intended to reduce potential damage should some settlement of the supporting subgrade take place. The ACI Committee 302, “Guide for Concrete Floor and Slab Construction (ACI 302.R-96)” should be consulted regarding methods/techniques to reduce the occurrence of concrete shrinkage cracks and other potential issues associated with concrete finishing and curing.

a) A vapor barrier is recommended beneath concrete slabs-on-grade that will support equipment sensitive to moisture or will be covered with wood, tile, carpet, linoleum, or other moisture sensitive or impervious coverings. Location of the vapor barrier should be in accordance with recommendations provided by ACI 302.2R-06, “Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials.” Further discussion of vapor barriers is presented in Appendix C.

b) Plumbing beneath slabs should be eliminated, where practicable. Where such plumbing is unavoidable, it should be thoroughly pressure tested during construction for leaks prior to slab placement.

c) Backfill in utility trenches beneath slabs should be compacted as specified in Section 15.

STRUCTURAL FILL/BACKFILL SOIL.

d) Plumbing and utilities that pass through the slab should be isolated from the slabs.

12.2 STRUCTURALLY SUPPORTED FLOORS

A floor system that is supported by the foundation system and has an air or void space (typically a crawlspace) below the floor so that it is not in contact with the underlying soil/bedrock material is

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considered a structurally supported or structurally suspended floor. If potential movement of slab-on-grade floors and associated cracking/distress are not considered tolerable by the owner, developer, architect, or structural engineer for any reason, a structurally supported floor should be provided.

There are design and construction issues associated with structurally supported floors that must be considered, such as ventilation and lateral loads. Where structurally supported floors are installed, the minimum required air space depends on the material used to construct the floor. Building codes require a clearance space of at least 18 inches above exposed soil if untreated wood floor components are used. Where other support material is used, a minimum clearance space of 8 inches is recommended. This minimum clearance space should be maintained between any point on the underside of the floor system (including beams and plumbing) and the surface of the exposed soil.

The minimum clearance between the crawlspace ground surface and the structural floor members and suspended plumbing should be constructed to meet minimum code or recommended clearances.

Where structurally supported floors are used, utility connections, including water, gas, air duct, and exhaust stack connections to floor supported appliances should be capable of absorbing some deflection of the floor. Plumbing that passes through the floor should ideally be hung from the underside of structural floor and not lay on the bottom of the excavation. This configuration may not be achievable for some parts of the installation. It is prudent to maintain the minimum clearance space below all plumbing lines. If trenching below the lines is necessary, CMT recommends sloping these trenches so they discharge to the foundation drain. Penetrations through the foundation wall should allow for at least 4 inches of clearance and/or be provided with flexible connections. The ground surface below the structurally supported floor should be sloped to the perimeter drain.

Control of humidity in crawlspaces is important for indoor air quality and performance of wood floor systems. An engineering professional with expertise in the design and construction of crawlspace humidity control should be contacted.

13. EXTERIOR FLATWORK

Flatwork supported on foundation wall backfill may settle and crack if the backfill is not properly moisture conditioned and compacted.

Exterior flatwork should be isolated from the structures. Exterior flatwork should be expected to move, although measures can be incorporated into construction to limit the movement or effects of the movement. CMT recommends flatwork not be doweled into structure foundations, but rather supported on a haunch to limit settlement. The haunch should extend the full length of the slab.

Exterior flatwork, such as driveways and sidewalks, are normally constructed as slabs-on-grade.

Porches and patios are increasingly constructed as structurally supported slabs, which in CMT’s opinion, is the most positive means of keeping slabs from moving and adversely affecting the operation of doors or means of egress. CMT recommends that landings and slabs at egress doors, as well as porches and patios, be constructed as structurally supported elements, if potential movement cannot be tolerated.

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Simple decks that are not integral to the structure and can tolerate foundation movement can be constructed with less substantial foundations. A short pier or footing bottomed below frost depth can be used if movement is acceptable and if acceptable by local building requirements. Use of deeper foundation elements can reduce potential movement. Footings or short piers should not be underlain by wall backfill due to risk of settlement. Inner edges of decks may be constructed on haunches and detailed such that movement of the deck foundations will not cause distress to the structure.

13.1 OVERHANGING ROOFS

Porches, patios, or decks with overhanging roofs that are integral to the structure, such that foundation movement cannot be tolerated, should be constructed with the same foundation type as the structure.

14. EXCAVATIONS

Conventional earthmoving equipment should be adequate to excavate the onsite soil. Excavation into the underlying bedrock is not anticipated. 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. If temporary shoring is required, a contractor specializing in design and construction of shoring should be contacted.

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 14.1.

TABLE 14.1. Allowable Slope Configuration for Onsite Material

Material Type

OSHA

Classification Steepest Allowable

Slope Configuration* Onsite fill and native granular soil Type B 1:1

* 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.

The classifications and slope configurations in Table 14.1 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 above 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 are 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.

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Permanent slopes should be no steeper than 2:1 and revegetated or otherwise protected from erosion.

15. STRUCTURAL FILL/BACKFILL SOIL

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, 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) Fill/backfill material should be placed in loose lifts and compacted in accordance with Table 15.1.

b) Maximum loose lift thickness shall be 12 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.

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

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

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

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

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TABLE 15.1. Compaction Specifications

Fill Location Material Type

(General)

AASHTO

Classification

Moisture Content

Relative Compaction

Compaction

Standard

Structural fill (under foundations)

Granular material that is clean to silty

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

OMC >98%*

Standard Proctor

(ASTM D698)

Fine grained material and granular material with plastic fines

A-2-6, A-2-7 A-6, A-7

0% to +3% of OMC >98%*

Standard Proctor

(ASTM D698)

Structural fill (under slabs and flatwork)

Granular material that is clean to silty

A-1, A-2-4, A-2-5, A-3, A-4, A-5 +/-3% 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

0% to +3% of OMC >95%*

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 N/A >90%*

Standard Proctor

(ASTM D698)

Fine grained material and granular material with plastic fines

A-2-6, A-2-7 A-6, A-7

+/-2% of

OMC >90%*

Standard Proctor

(ASTM D698)

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

15.1 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 and classification tests should be conducted to determine if the fill meets required specifications. Fill material should be well graded meeting the specifications in Table 15.2.

TABLE 15.2. Import Fill Specifications Soil Parameter Specification

Maximum particle size 3 inch Percent finer than No. 200 sieve 10% to 20% Liquid limit 30% maximum Plasticity index 15% maximum

16. SUBSURFACE DRAINAGE

Groundwater was not encountered during this study. If a crawlspace or basement is included, however, it will be excavated into relatively impervious material. This creates a depression around the structure that is backfilled with soil.