3. Geotech Report_Hiawatha Gardens Additions_FINAL 222-157_.pdf

Geotechnical Engineering Report Hiawatha Gardens Additions 10 Old Man’s Trail Manitou Springs, Colorado GEG Project No. 222-157

April 27, 2023

Copyright 2023 Granite Engineering Group, Inc.

All Rights Reserved

ONLY THE CLIENT OR ITS DESIGNATED REPRESENTATIVES MAY USE THIS DOCUMENT

AND ONBLY FOR THE SPECIFIC PROJECT THAT THIS REPORT WAS PREPARED FOR.

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A Report Prepared for:

Mr. Dole Grebenik, P.E., City Engineer City of Manitou Springs 606 Manitou Avenue Manitou Springs, Colorado 80829

GEOTECHNICAL ENGINEERING REPORT

HIAWATHA GARDENS ADDITIONS

10 OLD MAN’S TRAIL

MANITOU SPRINGS, COLORADO

GEG PROJECT NO. 222-157

April 27, 2023

Prepared by:

Hai Ming Lim, PE Project Manager

Xuhui Chang Senior Engineer

GRANITE ENGINEERING GROUP, INC.

3927 Van Teylingen Dr.

Colorado Springs, CO 80917 Phone: 719-716-9009

4-27-23

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Table Of Contents

1. INTRODUCTION

GENERAL

PROJECT INFORMATION

PURPOSE AND SCOPE

2. SUBSURFACE EXPLORATION

FIELD EXPLORATION

LABORATORY TESTING

3. SITE AND SUBSURFACE CONDITIONS

SITE CONDITIONS

GEOLOGIC SETTING

SUBSURFACE CONDITIONS

GROUNDWATER

4. CONSTRUCTION RECOMMENDATIONS

GEOTECHNICAL FEASIBILITY

CONSTRUCTION CONSIDERATIONS

4.2.1 Site Preparation and Grading

4.2.2 Excavation and Trench Construction

4.2.3 Structural Fill Requirements

4.2.4 Compaction Requirements

4.2.5 Utility Trench Backfill

4.2.6 Drainage Considerations

4.2.7 Construction in Wet or Cold Weather

4.2.8 Corrosion Potential and Concrete Type

5. FOUNDATION DESIGN RECOMMENDATIONS

5.1 POSSIBLE FILL MATERIALS AND SUBGRADE PREPARATION

5.2 SHALLOW FOOTINGS

5.3 INTERACTION BETWEEN NEW AND EXISTING STRUCTURES

5.4 FLOOR SLAB DESIGN AND CONSTRUCTION

EXTERIOR SLABS

SEISMICITY

6. PAVEMENT THICKNESS RECOMMENDATIONS

ANTICIPATED PAVEMENT SUBGRADE

DESIGN TRAFFIC

CONCRETE PAVER PAVEMENT THICKNESS DESIGN

ASPHALT AND CONCRETE PAVEMENT THICKNESS DESIGN

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PAVEMENT MATERIALS

6.5.1 Base Course

6.5.2 Hot Mix Asphalt

6.5.3 Portland Cement Concrete

7. LIMITATIONS

List Of Figure

FIGURE 3-1. GEOLOGIC MAP

List Of Tables

TABLE 4-1 IMPORTED STRUCTURAL FILL CRITERIA

TABLE 4-2 SUBGRADE PREPARATION AND FILL PLACEMENT CRITERIA

TABLE 4-3. ANALYTICAL TEST RESULTS

TABLE 4-4. RESISTIVITY AND CORROSIVITY CATEGORIES

TABLE 5-1. DESIGN ACCELERATION FOR SHORT PERIODS

TABLE 6-1. RECOMMENDED MINIMUM CONCRETE PAVER SURFACING PAVEMENT THICKNESS

TABLE 6-2. RECOMMENDED MINIMUM PAVEMENT SECTIONS

List Of Appendices

FIGURE A-1: SITE LOCATION PLAN .....................................................................................................................A

FIGURE A-2: BORING LOCATION PLAN ..............................................................................................................A

KEY TO BORING LOGS............................................................................................................................................ B

BORING LOGS ........................................................................................................................................................... B

LABORATORY TEST RESULTS ............................................................................................................................. C

PAVEMENT DEISGN OUTPUTS ............................................................................................................................ D

Hiawatha Gardens Additions GEG Project No. 222-157 Manitou Springs, Colorado April 27, 2023

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1. INTRODUCTION

General

Granite Engineering Group, Inc. (GEG) has completed the subsurface exploration and geotechnical engineering evaluation for the proposed additions to the existing Hiawatha Gardens located at 10 Old Man’s Trail in Manitou Springs, Colorado. The general location of the project site is presented on Figure A-1, Site Location Plan in Appendix A.

This report includes our recommendations related to the geotechnical aspects of the project design and construction. Conclusions and recommendations presented in this report are based on the subsurface information encountered at the locations of our exploration, preliminary information provided to us, and the provision and requirements outlined in the Limitations section of this report.

Project Information

Based on information provided to us, it is our understanding that the part of the existing building has been demolished except Structure 1 which remained after the removal of the portion of the existing building. The proposed additions include a new bathroom and a plaza at the location of the removed structures. The exact location of the additions is not known at this time, but it is estimated that it will be on the north side of the existing building.

The additions also include a parking lot and dumpster pad and apron. Based on our conversation with the city, we understand that the parking lot will be used by passenger cars and pickups with occasional buses. For the purpose of our pavement design, we have assumed that the design traffic consists of 100 passes of passenger cars, 50 passes of pickups, and 1 pass of bus per day. For dumpster pad and apron, we have assumed 1 pass of dumpster truck per day in addition to the parking lot traffic.

Grading plans were also not available at the time of preparing this report; and it was assumed the final grade of the additions will match that of the existing building.

If the type of construction is to vary significantly from the above descriptions, GEG should be notified immediately in order to re-evaluate our recommendations, if required. Once the final design such as grading plan is established, GEG should be allowed to review the engineering recommendations.

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Purpose and Scope

The purpose of our study was to evaluate the subsurface conditions at the locations of the proposed construction and provide associated geotechnical engineering recommendations for the design and construction of the proposed additions.

This report has been prepared in general accordance with our approved proposal for geotechnical engineering services, dated September 21, 2022. Our scope of services consisted of the following:

• Review available mapped geology at the site.

• Arrange for the underground utility locate.

• Conduct a subsurface exploration to evaluate the subsurface conditions. The subsurface exploration included two (2) borings to approximately 16 feet below the existing ground surface (bgs) in the proposed addition area. The approximate boring locations are shown on

Figure A-2, Boring Location Plan in Appendix A.

• Perform laboratory testing on soil samples obtained from the subsurface exploration to evaluate engineering characteristics.

• Prepare a report that presents the results of encountered site and subsurface conditions, laboratory testing, geotechnical engineering analyses, geotechnical feasibility, design and recommendations for the proposed structure foundation system, pavement thickness design, and earthwork.

The conclusions and recommendations presented herein are based on our limited site explorations and the subsurface conditions encountered at our boring locations during the time of our exploration. Our findings, conclusions, and recommendations should not be extrapolated to other areas of the site or used for other projects without our prior review. Additionally, they should not be used if the site has been altered or if more than three (3) years has elapsed since the date of our final report without our prior review to determine if they remain valid.

2. SUBSURFACE EXPLORATION

Field Exploration

Our field exploration program consisted of advancing a total of two (2) borings at the project site as shown on Figure A-2, Boring Location Plan in Appendix A.

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The boring locations were established in the field by GEG personnel by using a hand-held GPS unit with accuracy of approximately 10 feet. The boring locations should be considered accurate only to the degree implied by the method used to define them.

The borings were advanced with a rubber track ATV mounted CME-55 drill rig equipped with 4-inch diameter, solid-stem, continuous-flight augers. The borings were drilled to approximately 16 feet bgs in the planned building addition area.

Continuously sampling was performed to the terminated depths. Samples were collected by driving a standard penetration test (SPT) or Modified California (MC) split barrel samplers into the strata with a 140-pound hammer falling 30-inches.

The SPT is a 1.375-inch I.D. standard split barrel sampler performed in accordance with ASTM

D1586. The Modified California (MC) sampler is a 2.5-inch O.D., 2.0-inch ID (1.95-inch ID with liners), split barrel sampler with internal liners, performed in accordance with ASTM D3550. The blows required to drive the SPT sampler the final 12-inches are known as the SPT N-value. The

MC Sampler “Penetration Resistance” refers to the sum of all blows required to drive the sampler the drive length of the final 12 inches or portion thereof. The SPT N-value and the MC penetration resistance represent the consistency or relative density of the strata.

The boring logs along with the key to the logs are presented in Appendix B.

Laboratory Testing

Representative soil samples were selected for laboratory testing that was completed in accordance with industry standards and consistent with local practice. Laboratory soil testing included:

• Description and identification of soils (visual-manual procedure)

• Natural moisture;

• Gradation analysis;

• Atterberg limits;

• Analytical tests including water soluble sulfates and chlorides; soil resistivity; pH.

Laboratory tests are shown on the boring logs and in the Laboratory Summary in Appendix C.

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3. SITE AND SUBSURFACE CONDITIONS

Site Conditions

The site is located at 10 Old Man’s Trail in Manitou Springs, Colorado. The existing building except

Structure 1 has been demolished. The existing building was surrounded by asphalt parking. There are trees on the south side of the existing building. The site is in a commercial area.

Geologic Setting

Review of the “Geologic Map of the Manitou Springs Quadrangle, El Paso and Teller Counties, Colorado, 2003” indicates that the site is located within Alluvium two (Qa2). Alluvium two consists of dark yellow to dark brown, poorly to moderately sorted, poorly consolidated clay, silt, sand, gravel, and rare boulders. The geologic unit mapped at the project site is presented in Figure 3-

1. The WebSoil Survey provided by Natural Resources Conservation Service (NRCS) indicates that the surficial soil at the site is the Fortwingate-Rock outcrop complex consisting of loam, clay, weathered and un-weathered bedrock.

Figure 3-1. Geologic Map

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Subsurface Conditions

The borings encountered possible fill consisting of sand with varying amounts of silt and clay at the surface and extending to approximately 3.5 feet bgs. Below the possible fill, clayey sand and silty clayey sand were encountered and extended to depths of about 7 to 9 feet bgs and underlain by poorly graded sand with silt to the boring termination depths of about 16 feet. The sandy soils were maroon in color and very loose to dense, generally loose to medium dense, in relative density.

The boring logs in Appendix B present detailed results of the subsurface exploration.

Groundwater

Groundwater was measured during drilling and immediately after boring completion. Groundwater was encountered at a depth of approximately 8 feet in both borings during our field exploration.

Cave-in was observed at a depth of about 9 feet in both borings after boring completion.

Groundwater observations are representative of conditions at the time of our field exploration, and therefore may not be indicative of groundwater levels at other times of the year or at other locations across the site. Groundwater conditions may fluctuate with seasonal precipitation, site grading and improvements, and local irrigation practices.

4. CONSTRUCTION RECOMMENDATIONS

Geotechnical Feasibility

Subsurface conditions encountered at the site during the field exploration did not find conditions that would preclude the construction of the project as planned provided the conclusions and recommendations presented in the following sections are incorporated into the project design.

The recommendations submitted herein are based, in part, upon data obtained from our subsurface exploration. The nature and extent of subsurface variations that may exist at the proposed project site will not become evident until construction. If variations appear evident, then the recommendations presented in this report should be evaluated. In the event that any changes in the nature, design, or location of the proposed project are planned, the conclusions and recommendations contained in this report will not be considered valid unless the changes are reviewed, and our recommendations modified in writing.

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Construction Considerations

4.2.1 Site Preparation and Grading

Site preparation and earthwork operations should be performed in accordance with applicable codes, safety regulations and other local, state, or federal guidelines. Earthwork on the project should be observed and evaluated by GEG. The evaluation of earthwork should include observation and testing of subgrade preparation, foundation bearing soils and other geotechnical conditions exposed during project construction.

Areas within the limits of construction should be stripped and cleared of surface vegetation, topsoil, and any debris. All surface and subsurface features from past site use should be removed full depth. Stripped materials consisting of vegetation, organic materials and debris should be wasted from the site or used to revegetate landscaped areas after completion of grading operations. Exposed surfaces should be free of mounds and depressions in order to promote uniform compaction.

Following initial stripping and grading, all exposed areas which will receive fill or support structures, once properly cleared, should be scarified to a minimum depth of 8 inches, moisture conditioned, and compacted according to Section 4.2.4 of this report. Following any required undercutting and moisture conditioning, and prior to placement of structural fill, it is recommended that the subgrade be proof rolled. Proof rolling of the subgrade aids in identifying soft or disturbed areas. Soft and unsuitable areas identified by proof rolling should be undercut and replaced with structural fill. Proof rolling can be accomplished through use of a loaded, tandem-axle dump truck or similar equipment providing an equivalent subgrade loading.

Suitable structural fill should be placed to design grade as soon as practical after reworking the subgrade to avoid moisture changes in the underlying soils. Fill material should be placed on a horizontal plane and placed in loose lifts not to exceed 8 inches thick, unless otherwise accepted by GEG. The moisture content and compaction of subgrade soil and structural fill should be maintained until slab construction.

Based upon the subsurface conditions encountered, subgrade soils exposed during construction are anticipated to be relatively stable. However, the stability of the subgrade may be affected by precipitation, repetitive construction traffic and other factors. If unstable conditions are encountered or develop during construction, stability may be improved by scarifying and drying the subgrade soils. Over excavation of wet zones and replacement with structural fill or crushed

7 | P a g e rock may be necessary. If areas are found to be unsuitable for re-work, additional stabilization will be required. If additional stabilization is required, GEG should be contacted to evaluate the conditions in the field, and a suitable stabilization method can be provided. In addition, any soft and/or wet areas exposed during the excavation may need to be stabilized prior to the placement of new fill to create a stable, firm construction platform. A typical stabilization method may include utilizing gravel with the combination of geo-grid (e.g. Tensar TX160) to create a stable base.

Other stabilization methods may also be appropriate.

4.2.2 Excavation and Trench Construction

Excavations into the on-site soils will encounter a variety of conditions. All excavations must comply with the applicable local, State, and Federal safety regulations, and particularly with the excavation standards of the Occupational Safety and Health Administration (OSHA).

Construction site safety, including excavation safety, is the sole responsibility of the Contractor as part of its overall responsibility for the means, methods, and sequencing of construction operations. GEG recommendations for excavation support is provided for the Client’s sole use in planning the project, in no way do they relieve the Contractor of its responsibility to construct, support, and maintain safe slopes. Under no circumstances should the following recommendations be interpreted to mean that GEG is assuming responsibility for either construction site safety or the Contractor’s activities.

We believe the existing fill and native soil encountered at this site will classify as a Type C material, using OSHA criteria. OSHA requires that unsupported cuts be no steeper than 1½H:1V for Type C material for unbraced excavations up to 20 feet in height. In general, we believe that these slope ratios will be temporarily stable under unsaturated conditions. Flattened slopes may be required if excavations encounter groundwater, or the slopes will be exposed for an extended period of time. Please note that the Contractor’s OSHA-qualified “competent person” must make the actual determination of soil type and allowable sloping in the field.

The soils encountered by the proposed excavations may vary significantly across the site. The preliminary classifications presented above are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should confirm that similar conditions exist throughout the proposed area of excavation.

As a safety measure, it is recommended that all vehicles and soil piles be kept to a lateral distance equal to at least the depth of the excavation from the crest of the slope. The exposed slope face

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4.2.3 Structural Fill Requirements

Based on our laboratory test results, the on-site sandy soils may be utilized as structural fill placed beneath shallow foundations and slabs on-grade elements provided that they are properly over-excavated, moisture conditioned and compacted. Additional imported structural fill, if required, should consist of non-expansive granular material meeting the following criteria:

Table 4-1 Imported Structural Fill Criteria

Gradation Requirements

Standard Sieve Size Percent Passing

2 inches 100

No. 200 10 – 30

Plasticity Requirements (Atterberg Limits)

Liquid Limit 30 or less

Plasticity Index 6 or less

We recommend that a qualified representative of GEG visit the site during excavation and during placement of the structural fill to confirm the soils exposed in the excavations are consistent with those encountered during our subsurface explorations and that proper foundation subgrade preparation and placement are performed.

All fill placed on this site should be compacted according to the recommendations in Section 4.2.4 of this report. Fill to be placed at this site during leveling/grading operations should be placed under controlled conditions. A sample of any imported fill material, if required, should be submitted to GEG for approval and testing at least 3 days prior to stockpiling at the site.

4.2.4 Compaction Requirements

Fill materials should be placed in horizontal lifts compatible with the type of compaction equipment being used, moisture conditioned, and compacted in accordance with the criteria shown in Table

4-2.

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Table 4-2 Subgrade Preparation and Fill Placement Criteria

Fill Location Material Type Percent

Compaction (ASTM Method)

Moisture Content

Foundation and Floor Slab Subgrade Soils

On Site Sand Soils/Imported Structural Fill

95 minimum

(ASTM D1557)

± 2 % of OMC

Trench Backfill On Site Sand Soils/Imported Structural Fill

92 minimum

(ASTM D1557)

± 2 % of OMC

Aggregate Base (ABC) Imported CDOT Class

6 ABC

95 minimum

(ASTM D1557)

± 2 % of OMC

OMC= Optimum Moisture Content determined from Proctor Test

Fill should be placed in level lifts not exceeding 8-inches in loose thickness and compacted to the specified percent compaction to produce a firm and unyielding surface. If field density tests indicate the required percent compaction has not been obtained, the fill material should be reconditioned as necessary and re-compacted to the required percent compaction before placing any additional material.

4.2.5 Utility Trench Backfill

On-site soils may be utilized as backfill material in utility trenches provided the backfill is essentially free of plant matter, organic soil, debris, trash, other deleterious matter and rock particles larger than 2-inches. Backfill should be placed in lifts of 8-inches or less in loose thickness and compacted with appropriate trench equipment. Utility trench backfill should be compacted as recommended in Section 4.2.4 of this report.

4.2.6 Drainage Considerations

Positive drainage should be provided during construction and maintained throughout the life of the proposed project. Proper design of drainage should include prevention of ponding water on or immediately adjacent to the structures. Surface features that could retain water in areas adjacent to the structures should be eliminated. Backfill against any kind of structures and in utility line trenches should be well compacted and free of all construction debris to reduce the possibility of moisture infiltration and migration. Concentrated runoff should be avoided in areas susceptible to erosion and slope instability. Slopes and other stripped areas should be protected against erosion by re-vegetation or other methods.

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4.2.7 Construction in Wet or Cold Weather

Grading fill, structural fill or other fill should not be placed on frosted or frozen ground, nor should frozen material be placed as fill. Frozen ground should be allowed to thaw or be completely removed prior to placement of fill. A good practice is to cover the compacted fill with a “blanket” of loose fill to help prevent the compacted fill from freezing.

Concrete and asphalt structures should not be constructed on frozen soil. Frozen soil should be completely removed from beneath the concrete elements, or thawed, scarified and re-compacted.

The amount of time passing between excavation or subgrade preparation and placing concrete should be minimized during freezing conditions to prevent the prepared soils from freezing.

Blankets, soil cover, or heating as required may be utilized to prevent the subgrade from freezing.

4.2.8 Corrosion Potential and Concrete Type

Analytical testing was completed on a composite sample from Boring B-1 at depth of 3.5 feet below surface. The test results are presented in Appendix C and are summarized in Table 4-3.

Table 4-3. Analytical Test Results

Sample Materials Water Soluble

Sulfates, % Water Soluble Chlorides, % pH Resistivity, ohm.cm

B-1 @ 3.5’ Silty Clayey

Sand

0.0289 0.0077 8.0 1,522

The concentration of water-soluble sulfates measured in the sample that was tested was 0.0289 percent. This concentration of water-soluble sulfates represents a Class 0 degree of sulfate attack on concrete exposed to the existing foundation soils. The degree of sulfate attack is based on a range of Class 0 (negligible) to Class 3 (very severe) as described in the American Concrete

Institute (ACI) Standard 201.2R, “Guide to Durable Concrete”.

Results of soluble sulfate testing indicate that ASTM C150 Type I or II cement should be specified for all project concrete on and below grade.

The pH and electrical resistivity were also tested for the sample of the existing foundation soils from the geotechnical borings. Test results measured a pH value of 8.0, and resistivity measurement had a value of 1,522 ohm-centimeters for the soil sample that was tested.

Corrosion of buried metal is an electrochemical process in which the amount of metal loss due to corrosion is directly proportional to the flow of electrical current (DC) from metal into the soil. As

1 1 | P a g e resistivity decreases, the corrosivity of the soil increases. The following table provides a correlation between soil resistivity and corrosivity towards ferrous metal.

Table 4-4. Resistivity and Corrosivity Categories

Resistivity in Ohm-centimeters Corrosivity Category

0 to 1,000 Severely Corrosive

1,000 to 2,000 Corrosive

2,000 to 10,000 Moderately Corrosive

Greater than 10,000 Mildly Corrosive

Based on the laboratory resistivity test results, the existing soils are anticipated to be corrosive to unprotected iron or steel pipe. A qualified corrosion engineer should review this data to determine the appropriate corrosion protection measures at the site.

5. FOUNDATION DESIGN RECOMMENDATIONS

The site appears suitable for the proposed construction based upon geotechnical conditions encountered in the borings. Based on subsurface exploration and laboratory test results, and the geotechnical engineering analyses, we recommend that the proposed building additions be supported on a spread footing foundation system bearing on the existing sand soils or properly compacted structural fill. Design and construction details for the recommended foundation system are given for Allowable Stress Design (ASD).

5.1 Possible Fill Materials and Subgrade Preparation

Possible fill consisting of sand with varying amounts of silt and clay was encountered at the surface. The possible fill materials are similar to the native soils at the site, and we believe these are the materials associated with construction of the demolished building or prepared after a portion of the existing building was removed. The possible fill materials appeared to be compacted but no records were available. Subgrade preparation and proof rolling as described in Section

4.2.1 should be performed prior to the construction of foundation system.

5.2 Shallow Footings

The proposed building additions may be supported on shallow spread and strip footings, that are founded in the existing sand soils or properly compacted structural fill. Shallow foundations founded in the described materials should be designed using the maximum allowable bearing pressures of 2,500 psf and 2,000 psf for spread footings and strip wall footings, respectively. The

1 2 | P a g e recommended allowable bearing pressures are based on a factor of safety (F.O.S.) of approximately three (3) with respect to shear failure of the foundation bearing materials. A one third increase in the allowable bearing pressure may be used for the maximum allowable bearing pressure for temporary loading conditions including wind or seismic conditions.

Lateral capacity of the footings may be derived from passive resistance along the vertical face of the footings, and friction between the bottom of the footings and the foundation soils. An allowable passive resistance using an equivalent fluid pressure of 180 pcf (F.O.S. of 2) may be used for the design. An allowable coefficient of friction of 0.25 (F.O.S. of 1.5) between the bottom of the footings and the native soil/structural fill can be used for the sliding. We recommend upper 3 feet of the soils to be neglected in the passive resistance calculations.

Continuous wall footing should have a minimum width of 18 inches, and isolated spread footings should have a minimum width of 30 inches.

All exterior footings and footings founded in the unheated portions of the structure should be supported at a minimum of 30 inches below the final exterior grade to provide protection against frost penetration. Interior footings should bear a minimum of 12 inches below finished grade.

Finished grade is the lowest adjacent exterior grade for perimeter footings and floor level for interior footings.

Footings should be proportioned to reduce differential foundation movement. Proportioning on the basis of equal total movement is recommended; however, proportioning to relative constant dead load pressure will also reduce differential movement between adjacent footings. Total movement is estimated to be on the order of 1 inch or less. Differential movement is anticipated to be on the order of ½ to ¾ of the estimated total movement. Additional foundation movements could occur if water from any source infiltrates the foundation soils, therefore, proper drainage should be provided in the design and during construction.

Footings, foundations, and masonry walls should be reinforced as necessary to reduce the potential for distress caused by differential foundation movement. The use of joints at openings or other discontinuities and at periodic intervals on long masonry walls is recommended.

Foundation excavations should be observed by the geotechnical engineer or engineer’s representative. If the soil conditions encountered differ significantly from those presented in this report, supplemental recommendations will be required.

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5.3 Interaction Between New and Existing Structures

Care should be taken not to disturb the bearing soils beneath the existing building foundations. It is recommended that, where possible, excavations below existing footings not extend below an imaginary plane extending out and down from the outside edge of existing footings at a slope of approximately 2H:1V. Even with these criteria, excavations that extend below the level of existing foundations should be backfilled the same day they are excavated. Where this is impractical, shoring or underpinning of existing foundations may be required.

Some overlap in stress distribution from new and existing footings may occur, which may cause minor movement of the existing footings and supported structures. Maintaining a clear distance at least equal to the width of the new column spread footings between the edges of the new and existing footings could significantly reduce this risk. Connections between the new and existing structures should be designed to allow for the anticipated differential movement including but not limited to installation of construction joints.

5.4 Floor Slab Design and Construction

The floor slab subgrade soils have a low plasticity and are loose to medium dense. Floor slabs constructed on these soils are anticipated to have a low risk of movement, less than 1 inch.

Conventionally reinforced slab-on-grade is feasible for this project, provided that floor slab subgrade is prepared per the recommendations in Section 4.2.1 of this report.

For structural design of concrete slabs-on-grade, a modulus of subgrade reaction of 100 pounds per cubic inch (pci) may be used for floors supported on properly prepared native sand soils or structural fill. If a higher modulus of subgrade reaction is required, consideration could be given to constructing the floor slab section on a granular base course.

Additional floor slab design and construction recommendations are as follows:

• Landscaped irrigation and roof run-off should be minimized or eliminated adjacent to the foundation system and the buildings.

• Positive separations and/or isolation joints should be provided between slabs and all foundations, columns, or utility lines to allow independent movement.

• Control joints should be provided in slabs to control the location and extent of cracking.

• Interior trench backfill placed beneath slabs should be compacted in accordance with recommended specifications outlined herein.

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• In areas subjected to normal loading, a minimum 2-inch layer of sand over 6-inch of aggregate base course should be placed beneath interior slabs. For heavy loading, re-evaluation of slab and/or base course thickness may be required.

• If moisture-sensitive floor coverings are used on interior slabs, consideration should be given to the use of vapor barriers to minimize potential vapor rise through the slab.

• Floor slabs should not be constructed on frozen subgrade.

• Other design and construction considerations, as outlined in Section 302.1 R of the "ACI Design Manual", are recommended.

Exterior Slabs

Subgrade preparation for exterior slabs-on-grade and flatwork should also be performed per the recommendations in Section 4.2.1 of this report. The anticipated movement of foundation soils is less than 1 inch.

Seismicity

Based upon the geologic setting, subsurface soil conditions, liquefaction potential at this site is estimated to be low. The subsurface soil profiles correspond with Site Class D of the 2015 IBC.

The intermediate values from 2015 IBC used to obtain the design parameters are provided below.

Table 5-1. Design Acceleration for Short Periods

SS Fa

SMS

(SMS = FaSs)

SDS

(SDS = 2/3 SMS)

0.191 1.6 0.305 0.203

S1 Fv

SM1

(SM1 = FvS1)

SD1

(SD1 = 2/3 SM1)

0.063 2.4 0.15 0.1

SS = The mapped spectral accelerations for short periods (U.S. Geological Survey Web Page, 2019) Fa = Site coefficient from Table 1613.5.3(1), 2015 IBC SMS = The maximum considered earthquake spectral response accelerations for short periods SDS = 5-percent damped design spectral response acceleration at short periods

S1 = The mapped spectral accelerations for 1-second period (U.S. Geological Survey Web Page, 2019) Fv = Site coefficient from Table 1613.5.3(2), 2015 IBC SM1 = The maximum considered earthquake spectral response accelerations for 1-second period SD1 = 5-percent damped design spectral response acceleration at 1-second period

6. PAVEMENT THICKNESS RECOMMENDATIONS

The pavement thickness design was performed in general accordance with the AASHTO 1993 pavement design guidelines.

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Anticipated Pavement Subgrade

Based on the results of the borings, the pavement subgrade materials are anticipated to consist of clayey sand and silty clayey sand (AASHTO classification A-2-4). Based on the material types encountered, an R-value of 30 was estimated. Design Resilient Modulus (Mr) was calculated based on available correlations between R-value and resilient modulus. A Mr value of 6,849 psi and a modulus of subgrade reaction (K) value of 100 pci were used for the pavement thickness design.

Design Traffic

As discussed previously, GEG has assumed that the design traffic consists of 100 passes of passenger cars, 50 passes of pickups, and 1 pass of bus per day for the proposed parking lot.

For dumpster pad and apron, GEG has assumed 1 pass of dumpster truck per day in addition to the parking lot traffic.

Based on those assumptions, ESALs of 3,960 for Portland cement concrete (PCC) pavement and

3,883 for hot mix asphalt (HMA) pavement were used for a 20-year design life for the parking lot.

For the dumpster pad and apron, ESALs of 30,924 were used.

Concrete Paver Pavement Thickness Design

It is our understanding that the planned parking lot may be designed as a concrete paver surfacing lot. Since discrete concrete pavers do not have much interlock between them, they are not anticipated to provide much structure support to traffic and were not treated as a structure component of the pavement structure. Therefore, the pavement design was based on the gravel surfacing pavement design methodology included in the AASHTO 1993.

A serviceability loss of 1.0 and a maximum rutting depth of 1 inch were used in the gravel surfacing pavement design.

Based on the subgrade soils, anticipated traffic, and specified performance criteria we have provided the following concrete paver surfacing pavement thickness recommendations presented in Table 6-1.

Table 6-1. Recommended Minimum Concrete Paver Surfacing Pavement Thickness

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Pavement Area Recommended Minimum Pavement Section

Parking Lot

- 3-inch Concrete Paver

- 11.0 inches of CDOT Class 6 ABC 1

- 8.0 inches of Compacted Subgrade or

- 3-inch Concrete Paver

- 8.0 inches of CDOT Class 6 ABC 1

- a layer of Tensar TX-160 or equivalent

- 8.0 inches of Compacted Subgrade

1. Properly prepared subgrade in accordance with Section 4.2 of this report.

The performance of pavements will be affected by the drainage provided. We recommend pavement surfaces and subgrades be provided with cross-slope of at least 1 percent to move water off pavement.

Asphalt and Concrete Pavement Thickness Design

The proposed parking lot may also be designed as either PCC or HMA pavement. We recommend

PCC be placed in trash/dumpster areas or other areas where large/heavy trucks frequently stop or turn.

Recommended pavement sections are presented below in Table 6-2.

Table 6-2. Recommended Minimum Pavement Sections

Pavement Area Minimum HMA

Design Thickness

Minimum Portland Cement Concrete (PCC) Design

Thickness

Parking Lot

- 4.0 inches HMA

- 6.0 inches Aggregate Base

- 8.0 inches of Compacted

Subgrade

- 5.0 inches PCC

- 6.0 inches Aggregate Base

- 8.0 inches of Compacted

Subgrade

Dumpster Pad and Apron NA

- 6.0 inches PCC

- 6.0 inches Aggregate Base

- 8.0 inches of Compacted

Subgrade

Pavement Materials

6.5.1 Base Course

We recommend Coarse Aggregate Type Class 6 to be used for the aggregate base materials.

The material should be placed in a uniform layer without segregation of size and compacted in

1 7 | P a g e loose lifts not to exceed 8-inches. The material should be compacted as recommended in Section

4.2.4 of this report.

6.5.2 Hot Mix Asphalt

Hot mix asphalt materials, placement procedures, and testing should follow The Pike Peak Region

Asphalt Specification. We recommend PG 58-28 HMA binder with Grading S or SX aggregate, and gyration of 50.

6.5.3 Portland Cement Concrete

The Portland Cement Concrete (PCC) shall conform to the requirements for Portland Cement

Concrete Pavement, have a minimum 28-day flexural strength of at least 650 pounds per square inch (psi), and have a required minimum 28-day compressive strength of 4,000 psi.

7. LIMITATIONS

The findings and recommendations presented in this report are based upon data obtained from borings, field observations, laboratory testing, our understanding of proposed construction, and other sources of information referenced in this report. It is possible that subsurface conditions may vary between or beyond the locations explored. If subsurface conditions are encountered during construction that differ from those described herein, we should be notified immediately in order that a review may be made and any supplemental recommendations provided. If the scope of the proposed construction, including the proposed loads or structural locations, changes from that described in this report, the conclusions and recommendations contained in this report are not considered valid unless the changes are reviewed, and the conclusions of this report are modified or approved in writing, by GEG.

This report was prepared in in a manner consistent with that level of care and skill ordinarily exercised by other members of GEG’s profession practicing in the same locality, under similar conditions and at the date the services are provided. GEG makes no other representation, guarantee, or warranty, express or implied, regarding the services, communication (oral or written), report, opinion, or instrument of service provided.

The scope of services for this subsurface exploration and geotechnical report did not include environmental assessments or evaluations regarding the presence or absence of wetlands or hazardous substances in the soil, surface water, or groundwater at this site.

1 8 | P a g e

The recommendations provided in this report are based on the assumption that an adequate program of tests and observations will be conducted by GEG during the construction phase in order to evaluate compliance with our recommendations. The scope of our services did not include any environmental assessment or exploration for the presence of hazardous or toxic materials in the soil, surface water, groundwater or air, on, below or around this site.

This report may be used only by the Client and the registered design professional in responsible charge and only for the purposes stated for this specific engagement within a reasonable time from its issuance, but in no event later than three (3) years from the date of the report.

Appendix A

FIGURE A-1: SITE LOCATION PLAN

FIGURE A-2: BORING LOCATION PLAN

PROJECT NO. 222-157

DRAWN: 11/12/2022

DRAWN BY: XC

CHECKED BY: HML

FILE NAME:

SITE LOCATION PLAN

FIGURE

A-1Hiawatha Gardens Additions 10 Old Mans Trail

Manitou Springs, CO222-157

Project Site

PROJECT NO. 222-157

DRAWN: 11/12/2022

DRAWN BY: XC

CHECKED BY: HML

FILE NAME:

BORING LOCATION PLAN

FIGURE

A-2Hiawatha Gardens Additions 10 Old Mans Trail

Manitou Springs, CO222-157

B-1

B-2

Appendix B

KEY TO BORING LOGS

BORING LOGS

Project Number: 222-157

Hiawatha Gardens Additions

Lithology Symbols(see Boring Logs for complete descriptions)

Fill USCS Clayey Sand USCS Clayey Sand USCS Poorly-graded Sand with Silt

Lab Test Standards Other Lab Test Abbreviations pH Soil pH (AASHTO T289-91) S Water-Soluble Sulfate Content (AASHTO T290-91, ASTM D4327)

Chl Water-Soluble Chloride Content (AASHTO T291-91, ASTM D4327)

S/C Swell/Consolidation (ASTM D4546) UCCS Unconfined Compressive Strength (ASTM D2166) R-Value Resistance R-Value (ASTM D2844) DS (C) Direct Shear cohesion (ASTM D3080) DS (phi) Direct Shear friction angle (ASTM D3080) Re Electrical Resistivity (AASHTO T288-91) PtL Point Load Strength Index (ASTM D5731)

Notes

Moisture Content ASTM D2216 Dry Density ASTM D7263 Sand/Fines Content ASTM D421, ASTM C136, ASTM D1140

Atterberg Limits ASTM D4318 AASHTO Class. AASHTO M145, ASTM D3282

USCS Class. ASTM D2487 (Fines = % Passing #200 Sieve Sand = % Passing #4 Sieve, but not passing #200 Sieve)

Modified California Sampler (2.5 inch OD, 2.0 inch ID)

Standard Penetration Test

(ASTM D1586)

Sample Types

Legend for Symbols Used on Borehole Logs

Project:

2. The Modified California sampler used to obtain samples is a 2.5-inch OD, 2.0-inch ID (1.95-inch ID with liners), split-barrel sampler with internal liners, as per ASTM D3550. Sampler is driven with a 140-pound hammer, dropped 30 inches per blow.

3. "ER" for the hammer is the Reported Calibrated Energy Transfer Ratio for that specific hammer, as provided by the drilling company.

1. "Penetration Resistance" on the Boring Logs refers to the uncorrected N value for SPT samples only, as per ASTM D1586. For samples obtained with a Modified California (MC) sampler, drive depth is 12 inches, and "Penetration Resistance" refers to the sum of all blows. Where blow counts were > 50 for the 3rd increment (SPT) or 2nd increment (MC), "Penetration Resistance" combines the last and 2nd-to-last blows and lengths; for other increments with > 50 blows, the blows for the last increment are reported.

20.0

21.0

A-2-4 (0)

SC

A-2-4 (0)

SC-SM

6.4

7.8

3-5-7

3-2-2

3-7-5

2-2-2

2-1

2-6

2-3-4

6-4-6

1-10-7

4-6-18

20-27-16

0.0 - 3.5 ft. Possible Fill: CLAYEY SAND, minor clay lenses, maroon, damp to moist, medium dense to loose.

3.5 - 7.0 ft. SILTY CLAYEY SAND, maroon, damp to moist, medium dense to very loose.

7.0 - 16.0 ft. POORLY GRADED SAND, with silt, maroon, wet, loose to dense.

Bottom of Hole at 16.0 ft.

Groundwater Levels:

Logged By: J. Shekoski

Final By: HML

Symbol Depth Date

Weather Notes: Sunny & Cool

Inclination from Horiz.: Vertical

8.0 ft 10/20/22

Night Work:

Boring Began: 10/20/2022

Boring Completed: 10/20/2022

Drilling Method(s): Solid-Stem Auger (4" OD)

Driller: Vine Laboratories

Drill Rig: CME 55 Rubber Track

Hammer Type: Automatic (hydraulic), ER: 80%

Total Depth: 16.0 ft

Ground Elevation:

Coordinates: Lat: 38.8583 Long: -104.9099

Location: Manitou Springs, CO

PAGE

Project Number: 222-157

Atterberg Limits

Boring No.: B-1

Li qu id Li m it

S am pl e

T yp e/ A dv an ce m en t M et ho d

Hiawatha Gardens Additions 10 Old Mans Trail, Manitou Springs, CO

E le va tio n (f ee t)

D ep th (f ee t)

F in es C on te nt

P la st ic ity In de x

Project Name:

AASHTO

& USCS

Classifi-cations

Field Notes and

Other Lab Tests

B O

R

IN

G L

O G

2-

M

A N

IT

O

U H

IA

W

A T

H A

G A

R D

E N

S .G

P J

G E

G B

O R

IN

G

L O

G S

T E

M P

LA

T

E .G

D T

G E

G L

IB

R

A R

Y

-3 -2

.G

LB

1/

/2

M oi st ur e C on te nt

D ry

D en si ty

(p cf

)Blows per 6 in

P en et ra tio n

R es is ta nc e

Li th ol o gy

Soil Samples

Material Description

24.0

31.0

A-2-4 (0)

SC-SM

A-2-4 (0)

SC

4.6

6.2

11-8-7

10-9-8

2-3-4

3-4-2

3-2-2

3-2

2-2

5-8-5

3-4-2

26-16-16

4-8-16

0.0 - 3.5 ft. Possible Fill: SILTY CLAYEY SAND, minor clay lenses, maroon, damp to moist, medium dense.

3.5 - 9.0 ft. CLAYEY SAND, maroon, damp to moist, loose.

9.0 - 16.0 ft. POORLY GRADED SAND, with silt, maroon, wet, loose to dense.

Bottom of Hole at 16.0 ft.

Groundwater Levels:

Logged By: J. Shekoski

Final By: HML

Symbol Depth Date

Weather Notes: Sunny & Cool

Inclination from Horiz.: Vertical

8.0 ft 10/20/22

Night Work:

Boring Began: 10/20/2022

Boring Completed: 10/20/2022

Drilling Method(s): Solid-Stem Auger (4" OD)

Driller: Vine Laboratories

Drill Rig: CME 55 Rubber Track

Hammer Type: Automatic (hydraulic), ER: 80%

Total Depth: 16.0 ft

Ground Elevation:

Coordinates: Lat: 38.85831 Long: -104.90965

Location: Manitou Springs, CO

PAGE

Project Number: 222-157

Atterberg Limits

Boring No.: B-2

Li qu id Li m it

S am pl e

T yp e/ A dv an ce m en t M et ho d

Hiawatha Gardens Additions 10 Old Mans Trail, Manitou Springs, CO

E le va tio n (f ee t)

D ep th (f ee t)

F in es C on te nt

P la st ic ity In de x

Project Name:

AASHTO

& USCS

Classifi-cations

Field Notes and

Other Lab Tests

B O

R

IN

G L

O G

2-

M

A N

IT

O

U H

IA

W

A T

H A

G A

R D

E N

S .G

P J

G E

G B

O R

IN

G

L O

G S

T E

M P

LA

T

E .G

D T

G E

G L

IB

R

A R

Y

-3 -2

.G

LB

1/

/2

M oi st ur e C on te nt

D ry

D en si ty

(p cf

)Blows per 6 in

P en et ra tio n

R es is ta nc e

Li th ol o gy

Soil Samples

Material Description

Appendix C

LABORATORY TEST RESULTS

B-1 2.0~3.5 SPT 6.4 20.0 26 18 8 A-2-4(0) SC

B-1 3.5~5.0 SPT 7.8 21.0 24 18 6 A-2-4(0) SC-SM

B-2 2.0~3.5 SPT 4.6 24.0 22 16 6 A-2-4(0) SC-SM

B-2 3.5~5.0 SPT 6.2 31.0 26 16 10 A-2-4(0) SC

Summary of Laboratory Test Results

Water Soluble Sulfate

% Swell (+) / Consolidation (-) R-ValueDepth

(ft)

Atterberg Classification

LL

Project No: 222-157

Fines < #200

AASHTOPISample

Type Boring

No.

Sand

(%) USCS

Gravel > #4

Sample Location Gradation psf

Natural Dry

Density (pcf)

Natural Moisture Content pH

Unconf.

Comp.

Strength

Project Name:Hiawatha Gardens Additions, 10 Old Mans Trail, Manitou Springs, CO

PL

Page 1 of 1 Date: 2022-11-12Rev 09/18

0 20 40 60 80 100

PI

Passing #200

ATTERBERG LIMITS

Date: 11/12/2022

CH or OH

LL PL

USCS Sample Description

CLAYEY SAND(SC)

SILTY, CLAYEY SAND(SC-SM)

SILTY, CLAYEY SAND(SC-SM)

CLAYEY SAND(SC)

B-1

B-1

B-2

B-2

BOREHOLE DEPTH

2.0

3.5

2.0

3.5

AASHTO

Class.

Project No. 222-157

P

LA

S T

IC

IT

Y I

N D

E X

Drawn By: Lab

Checked By: PM

ML or OL

"U " L

IN

E

"A " L

IN

E

CL or O L

CL-ML MH or OH

LIQUID LIMIT

A-2-4(0)

A-2-4(0)

A-2-4(0)

A-2-4(0)

Hiawatha Gardens Additions 10 Old Mans Trail, Manitou

Springs, CO

0.0010.010.1110100

3/4 3/8 3 10024 16 301 2006 10 501/2

U.S. SIEVE NUMBERS HYDROMETER

Drawn By: Lab

B-1

B-1 fine

SAND

mediumcoarsefine

Checked By: PM

LL

20.0

21.0

24.0

31.0

BOREHOLE DEPTH

%Fines

%Clay%Gravel

USCS

Classification

AASHTO

Classification PI

PL

%Silt%Sand

GRAIN SIZE IN MILLIMETERS

GRAVEL

coarse

COBBLES

SC

SC-SM

SC-SM

SC

2.0

3.5

2.0

3.5

A-2-4(0)

A-2-4(0)

A-2-4(0)

A-2-4(0)

Hiawatha Gardens Additions 10 Old Mans Trail, Manitou

Springs, CO

Project No. 222-157

P E

R C

E N

T F

IN

E

R B

Y W

E

IG

H T

SIEVE ANALYSIS

SILT OR CLAY

Date: 11/12/2022

U.S. SIEVE OPENING IN INCHES

1403 4 20 406 601.5 8 14

Appendix D

PAVEMENT DEISGN OUTPUTS

WinPAS 12 Pavement Thickness Design According to

1993 AASHTO Guide for Design of Pavements Structures American Concrete Pavement Association

Traffic Input by Day Annual Growth Rate 0.00 percent Design Life 20 years Terminal Serviceability 2.0 Directional Distribution 0.00 percent Estimated Structural Number 2.0 Design Lane Distribution 0.00 percent Estimated Rigid Thickness 5.00 inches Design Lane

Traffic Factor Traffic Input by

10 Old Man's Trail, Manitou Springs, CO Parking Lot Hiawatha Gardens Additions

ESAL Data by Vehicle Type

Vehicle Axle Load Axle Type Number

2.00 Single

2.00 0.00

Single Single 100

2.00 4.00 0.00

Single Single Single 50

6.00 14.00

0.00

Single Single Single 1

NumberAxle TypeAxle LoadVehicle

0.00 Single

0.00 0.00

Single Single

0.00 0.00 0.00

Single Single Single 0

0.00 0.00 0.00

Single Single Single

0.00 0.00

Single Single 0

Total Rigid ESALs Total Flexible ESALs3,960 3,883

Project Name:

Route:

Location:

Owner/Agency:

Design Engineer:

Thursday, April 6, 2023 2:45:12PM Engineer: XC

WinPAS 12

1993 AASHTO Guide for Design of Pavements Structures American Concrete Pavement Association

Traffic Input by Day Annual Growth Rate 0.00 percent Design Life 20 years Terminal Serviceability 2.0 Directional Distribution 0.00 percent Estimated Structural Number 2.0 Design Lane Distribution 0.00 percent Estimated Rigid Thickness 6.00 inches Design Lane

Traffic Factor Traffic Input by

10 Old Man's Trail, Manitou Springs, CO Dumpster Pad and Apron Hiawatha Gardens Additions

ESAL Data by Vehicle Type

Vehicle Axle Load Axle Type Number

2.00 Single

2.00 0.00

Single Single 100

2.00 4.00 0.00

Single Single Single 50

6.00 14.00

0.00

Single Single Single 1

NumberAxle TypeAxle LoadVehicle

20.00 Single

35.00

0.00 Tandem

Single

0.00 0.00 0.00

Single Single Single 0

0.00 0.00 0.00

Single Single Single

0.00 0.00

Single Single 0

Total Rigid ESALs Total Flexible ESALs30,924 24,409

Project Name:

Route:

Location:

Owner/Agency:

Design Engineer:

Thursday, April 6, 2023 2:53:51PM Engineer: XC

WinPAS

1993 AASHTO Guide for Design of Pavements Structures American Concrete Pavement Association

Flexible Design Inputs

Project Name:

Route:

Location:

Owner/Agency:

Design Engineer:

Flexible Pavement Design/Evaluation

Structural Number Total Flexible ESALs Reliability Overall Standard Deviation percent Terminal Serviceability Initial Serviceability Subgrade Resilient Modulus

Layer Pavement Design/Evaluation

Layer Material

Layer Coefficient

Drainage Coefficient

Layer Thickness

Layer

SN

Hiawatha Gardens Additions Parking Lot 10 Old Man's Trail, Manitou Springs, CO

0.00 3,883 90.00

0.44

6,849.00 4.50 2.00 psi

Asphalt Cement Concrete 0.44 1.00 4.00 1.76 Graded Stone Base 0.12 1.00 6.00 0.72

SN 2.48

Thursday, April 6, 2023 2:46:26PM Engineer:XC

1993 AASHTO Guide for Design of Pavements Structures American Concrete Pavement Association

Rigid Design Inputs

Hiawatha Gardens Additions Parking Lot 10 Old Man's Trail, Manitou Springs, CO

Rigid Pavement Design/Evaluation

Concrete Thickness Total Rigid ESALs Reliability Overall Standard…