CO FLAP PUW16(1) FINAL PTM Appendix C Geotech Report rev.pdf

SUBMITTED TO:

HDR Engineering, Inc.

1670 Broadway, Suite 3400 Denver, Colorado 80202

BY:

Shannon & Wilson, Inc.

1321 Bannock St. Suite 200 Denver, Colorado 80204

(303) 825-3800 www.shannonwilson.com

GEOTECHNICAL DESIGN REPORT

CO FLAP PUW16(1)

S. Nichols Road

PUEBLO WEST, COLORADO

February 2020 Shannon & Wilson No: 102814-001

CO FLAP PUW16(1)

S. Nichols Road

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CONTENTS

1 Introduction

2 Project and Site Description

3 Subsurface Explorations and Laboratory Testing

3.1 Field Investigation

3.2 Geotechnical Laboratory Testing

4 Subsurface Conditions

4.1 Regional Geology

4.2 Subsurface Conditions

4.3 Groundwater

5 Geologic Hazard Evaluation

5.1 Seismic Hazards

5.2 Swelling/Collapsible Soils

5.3 Corrosion

6 Geotechnical Recommendations

6.1 Nichols Road Trail Pedestrian Bridge Over Union Pacific Railroad

6.1.1 Cast in Place Spread Footings

6.1.2 Geosynthetic Reinforced Soil Abutment-Integrated Bridge System Foundation System

6.2 Wing Walls and Lateral Earth Pressures

6.3 Bridge Approach Embankments

6.4 Pavement Recommendations

6.4.1 Design Methodology

6.4.2 Subgrade Moisture Treatment

6.4.3 Traffic Loading

6.4.4 Subgrade Soils

6.4.5 Full Depth Reclamation

6.4.6 Recommended Pavement Sections

7 Construction Considerations

7.1 Site Preparation

7.2 Earthwork and Grading

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7.2.1 Excavation

7.2.2 Subgrade Preparation and Proof Rolling

7.2.3 Low Permeable Import Fill

7.2.4 Fill Placement, Moisture Conditioning and Compaction

7.3 Paving Materials

8 Closure

9 References

Exhibits Exhibit 4-1: Existing Segment Pavement and Subgrade Conditions Exhibit 5-1: Seismic Design Ground Motion Parameters Exhibit 6-1: Recommended Abutment Spread Footing Bearing Resistance Design Parameters Exhibit 6-2: Recommended Abutment Spread Footing Lateral Resistance Design Parameters Exhibit 6-3: Recommended Retaining Wall Bearing Resistance Design Parameters Exhibit 6-4: Recommended Retaining Wall Lateral Earth Pressure Design Parameters Exhibit 6-5: Recommended Pavement Sections Exhibit 7-1: Recommended Materials for Pavements

Figures Figure 1: Vicinity Map Figure 2: Site and Exploration Plan Figure 3: Recommended Surcharge Loading for Temporary and Permanent Walls

Appendices Appendix A: Subsurface Explorations Appendix B: Laboratory Test Results Appendix C: Exploration Photographs Appendix D: Pavement Design Calculations Important Information

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ACRONYMS

AADT Annual Average Daily Traffic AASHTO American Association of State Highway and Transportation Officials ACI American Concrete Institute CDOT Colorado Department of Transportation ESAL 18-kip Equivalent Single Axle Loading FDR Full Depth Reclamation FP-14 Federal Standard Specifications for Construction of Roads and

Bridges on Federal Highway Projects, FP-14 FHWA Federal Highway Administration g Gravity GRS-IBS Geosynthetic Reinforced Soil Abutment-Integrated Bridge System HACP Hot Asphalt Concrete Pavement HDR HDR Engineering, Inc.

HMA Hot Mix Asphalt H:V Horizontal to Vertical ISRM International Society for Rock Mechanics LL Liquid Limit LTPP Long Term Pavement Performance LRFD Load and Resistance Factor Design MC Modified California NMAS Nominal Maximum Aggregate Size OD Outside Diameter PDDM Federal Lands Highway Project Development and Design Manual PG Performance Grade PI Plasticity Index PL Plastic Limit psf Pounds per Square Foot psi Pounds per Square Inch PWMD Pueblo West Metropolitan District sec. Seconds SPT Standard Penetration Test SS Split-Spoon Sampler UPRR Union Pacific Railroad USCS Unified Soil Classification System USGS United States Geological Survey UTBC Untreated Base Course vpd Vehicles per Day

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1 INTRODUCTION

This report summarizes the results of our subsurface exploration and laboratory testing program and presents geotechnical design recommendations and construction considerations for the proposed S. Nichols Road Improvements Project (the Project) in Pueblo West, Colorado. Our services were completed in general accordance with our Task Order Agreement No. 011/10001000041620 with HDR Engineering, Inc. (HDR) dated June 7, 2019. Our conclusions and recommendations in this report are based on:

The limitations of our approved scope, schedule, and budget described in our contract;

Our understanding of the Project and information provided by HDR;

Subsurface conditions observed in the borings at the time our explorations were completed; and

The results of testing performed on samples collected from the explorations.

The objective of our geotechnical studies was to provide recommendations and construction considerations, as presented herein, for the proposed pedestrian bridge and pavement areas.

The authorized scope of services was based on this objective and this report should not be used for other purposes without Shannon & Wilson’s review. If a service is not specifically indicated in this report, do not assume that it was performed.

2 PROJECT AND SITE DESCRIPTION

The Project is located in Pueblo West, Colorado, north of the Lake Pueblo State Park (Figure 1). The existing topography of the Project is generally flat along S. Nichols Road. Both S.

Nichols Road and W. McCulloch Boulevard are currently pavement with hot asphalt concrete pavement (HACP) and consist of two travel lanes (a single lane in each direction).

Refer to Figure 2 for a project map.

This Project includes one segment of a multi-modal Nichols Road Trail alignment that will connect the Lake Pueblo State Park to the existing Pueblo West Metropolitan District (PWMD) trail systems. The proposed roadway improvements consist of reconstructing and widening the pavement of S. Nichols Road from the existing roadway bridge over the Union Pacific Railroad (UPRR) to W. McCulloch Boulevard along with adjustments to the roadway longitudinal profile near (raising grades 1 to 2 feet) near the UPRR Bridge overpass. The S.

Nichols Road and W. McCulloch Boulevard intersection will also be widened to incorporate an eastbound right turn lane and a westbound left turn lane. North of W. McCulloch

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Boulevard, improvements will be made to the Nichols Ranch Trail, an unpaved 'dirt trail' extending north from S. Nichols Road. We understand that no geotechnical analysis is required for the Nichols Ranch Trail improvements, but at the request of HDR, two geotechnical explorations were completed along these proposed trail improvements.

As part of the new trail project, a pedestrian bridge will be constructed crossing the existing UPRR tracks. The UPRR corridor consists of a single track and possible future tracks located approximately 20 feet on each side of the existing track centerline (approximately 17 feet below the native ground surface). The proposed pedestrian bridge will consist of an approximately 160-foot long, single span bridge over the UPRR right-of-way extents. The centerline of the proposed pedestrian bridge will be located approximately 30 feet west of the existing S. Nichols Road Bridge (approximately at the toe of the existing bridge approach fill). We understand the bridge will consist of a prefabricated single span bridge founded on shallow foundations. Also, we understand that the pedestrian bridge approach embankment fill heights will be on the order of 10 feet and supported by wing walls at the bridge abutments. The approach embankments are anticipated to be graded a 4 horizontal to 1 vertical (4H:1V) side slopes.

Based on our review of the bridge design plans for the existing S. Nichols Road Bridge (U.S., Bureau of Reclamation, 1969), the existing single span bridge is founded on 8.5-foot-wide spread footings at the abutment structurally connected to 11.5-foot-wide wingwalls founded at elevation 4,949.0 feet (presumably on bedrock).

3 SUBSURFACE EXPLORATIONS AND LABORATORY

TESTING

3.1 Field Investigation

Shannon & Wilson conducted a field exploration program on August 12, 2019, to explore subsurface conditions along the Project. The subsurface exploration program consisted of drilling and sampling eleven borings (designated SW-01 through SW-11). The locations of the borings are shown in Figure 2.

Appendix A presents a discussion of the drilling and sampling procedures used to complete the borings. Appendix A also presents the individual exploration logs and an explanation of the symbols and terminology used. Photographs of the drilling locations are included in Appendix C.

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3.2 Geotechnical Laboratory Testing

Geotechnical laboratory tests were completed on selected samples retrieved from the borings to estimate index and engineering properties. Index tests included natural water content, grain size analysis, percent fines, and Atterberg limits. Engineering properties tests included corrosion, swell/collapse, and R-Value. Laboratory test results and a discussion of the testing procedures are included in Appendix B. The natural water content, fines content, and Atterberg limits are also shown on the individual boring logs included in Appendix A.

4 SUBSURFACE CONDITIONS

4.1 Regional Geology

In the Pueblo area, the mapped geologic formations are the Pierre Shale, Niobrara Limestone, Carlile Shale, Greenhorn Limestone, Graneros Shale and the Dakota Sandstone, all of which are Cretaceous in age (Scott, 1964; Scott, 1972). In the Project vicinity, the down-cutting from the Arkansas River created steep bluffs that expose bedrock, as well as alluvial deposits. Surficial soils in the Arkansas River Valley generally are alluvial deposits that can be at least 50-feet-thick.

4.2 Subsurface Conditions

Borings SW-01 and SW-02 were drilled at the UPRR Pedestrian Bridge and encountered silty and clayey sand and sandy clay to a depth of 8 feet. Bedrock consisted of 2 feet of weathered shale/claystone overlaying fresh Niobrara Formation shale to the termination depth of approximately 21 feet in each boring.

Borings SW-03 through SW-09 were drilled within S. Nichols Road and generally encountered medium stiff to very stiff, lean clay with sand to sandy lean clay. Exhibit 4-1 summarizes the subsurface conditions. No existing untreated base course (UTBC) or subgrade treatment was observed. Moderately weathered to completely weathered, extremely weak claystone was encountered in borings SW-03 through SW-07 at varying depths (4 to 9 feet below the existing roadway grade). Borings SW-08 through SW-11 encountered similar subsurface conditions consisting of very soft to very stiff, lean clay subsurface conditions along the proposed trail route. Bedrock was not encountered in those borings to the drilling termination depth.

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Exhibit 4-1: Existing Segment Pavement and Subgrade Conditions

Boring

HMA

Thickness (inches)

Subgrade Material

[AASHTO M145] Boring

HMA

Thickness (inches)

Subgrade Material

[AASHTO M145]

SW-03 3.0 A-6 SW-07 2.5 A-6

SW-04 3.0 A-6 SW-08 3.0 A-6

SW-05 3.0 A-6 SW-09 7.0 A-6

SW-06 3.0 A-6

NOTES:

AASHTO = American Association of State Highway and Transportation Officials; HMA = Hot Mix Asphalt

The explorations were performed to evaluate geotechnical soil conditions at the Project site.

Our observations are specific to the locations, depths, and times noted on the logs and may not be applicable to all areas of the site. No amount of explorations or testing can precisely predict the characteristics, quality, or distribution of subsurface and site conditions.

Potential variation includes, but is not limited to:

The conditions between explorations may be different.

The passage of time or intervening causes (natural and manmade) may result in changes to site and subsurface conditions.

If conditions different from those described herein are encountered during construction, we should review our description of the subsurface conditions and reconsider our conclusions and recommendations.

4.3 Groundwater

Groundwater was not encountered in any of our borings during drilling; however, fluctuations of groundwater levels at the site depend on many factors, including seasonal variations, local precipitation, and flood events. Nevertheless, groundwater is not anticipated to affect the design or construction of the Project.

5 GEOLOGIC HAZARD EVALUATION

5.1 Seismic Hazards

The closest fault to the site is the Ute Pass fault zone is located approximately 26 miles to the northwest. The most recent confirmed prehistoric deformation is estimated to be sometime in the mid to late Quaternary, or within the last 750,000 years. Based on this information and relatively low long-term slip rates, it appears that these faults are relatively inactive

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(USGS, 2019a). Therefore, in our opinion, the potential for ground surface fault rupture on these faults is low.

Liquefaction can occur in loose, saturated, cohesionless soils when subjected to earthquake ground shaking. Based on the subsurface conditions encountered at the project site, it is our opinion that the potential for liquefaction is low.

Using the American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design (LRFD) Bridge Design Specifications (AASHTO, 2017) criteria, and based on subsurface conditions encountered in our borings (assuming that similar conditions are present from the maximum depth of our boring to a depth of 100 feet), Site Class C is recommended for the proposed pedestrian bridge.

Ground motion parameters were determined for the project site using the United States Geological Survey (USGS) Web Application (USGS, 2019b) and procedures recommended by AASHTO (2017). Exhibit 5-1 presents recommended seismic design ground motion parameters.

Exhibit 5-1: Seismic Design Ground Motion Parameters

Design Parameter Value

Peak Ground Acceleration1 (PGAB) 0.055 g

Site Class C

Short-period Spectral Acceleration, SS 0.121 g

Long-period Spectral Acceleration, S1 0.037 g

Site Factor, FPGA 1.2

Site Factor, Fa 1.2

Site Factor, FV 1.7

Peak Design Spectral Acceleration, AS 0.066 g

Short-period Design Spectral Acceleration, SDS 0.145 g

Long-period Design Spectral Acceleration, SD1 0.064 g

TO 0.088 sec.

TS 0.448 sec.

NOTES:

PGAB = peak ground acceleration for a site underlain by Site Class B soil (soft rock).

g = gravity; sec. = seconds

5.2 Swelling/Collapsible Soils

Swell susceptible clay soil and bedrock are common in Colorado. In addition, collapsible soils can also exist in Colorado. To assist us in determining the swell and collapse potential

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102814-001 February 2020 and along the roadway alignment, we reviewed a published geologic map of potentially swelling soil and rock of the Pueblo Canon City Area developed by Hart (1974). The map indicates that the Project area generally has low swell potential and no indication of windblown sand or silt deposits along the S. Nichols Road alignment.

To further evaluate the roadway subgrade soil for both swell and collapse potential, we performed five swell/collapse tests on native clay subgrade soil and two tests on the weathered shale/claystone. The swell test results on the overburden soils generally indicated low collapse when wetted under a surcharge load. One of the swell tests completed on the weathered shale/claystone sample (boring SW-02, sample S-1A) indicated 1.8% swell with a corresponding swell pressure of approximately 2,500 pounds per square foot (psf). Based on Colorado Department of Transportation (CDOT) guidelines (2019a) for pavements, the 1.8% swell is considered medium swell potential. The second swell test on weathered shale/claystone (boring SW-02, sample S-2A) indicated 1.4 collapse, but this drive sample of the shale bedrock was noted to be disturbed from the sampling and extraction methods. Based on the above, it is our opinion that there is a low potential for swell and collapse to occur at the site and the design of the project does not need to consider the potential for swell/collapse provided the recommendations in this report are followed (Sections 6 and 7).

5.3 Corrosion

The clay soil and bedrock materials in Colorado area can be corrosive to substructure elements. To assist in estimating the corrosion potential at the site, samples of sandy lean clay were tested for pH, resistivity, water soluble sulfates, and chlorides. The results are presented in Table B-1 in Appendix B.

The resistivity measured in the samples ranged from 837 to 2,882 ohm-centimeters. Based on correlations developed by Roberge (2012), these values suggest an extremely corrosive to highly corrosive subsurface.

The concentration of water-soluble sulfates measured in the samples ranged from 0.007% to 0.307% by weight (70 to 3,070 parts per million). Based on classifications as defined by American Concrete Institute (ACI) ACI-318-19 (ACI, 2019), these test results suggest a negligible to severe degree of sulfate attack on concrete exposed to site soils (exposure class S2). Based on standard construction specifications prepared by CDOT, these test results correspond to Class 2 requirements for sulfate resistance (CDOT, 2019b).

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6 GEOTECHNICAL RECOMMENDATIONS

6.1 Nichols Road Trail Pedestrian Bridge Over Union Pacific Railroad

As discussed in Section 2.0, we understand the proposed pedestrian bridge will consist of a prefabricated, single span bridge founded on shallow foundations. Cast in place spread footings and a geosynthetic reinforced soil abutment-integrated bridge system (GRS-IBS) foundation system are under consideration for the pedestrian bridge crossing. In our opinion, both foundation types are feasible for the bridge based on the subsurface conditions encountered at the site.

6.1.1 Cast in Place Spread Footings

Borings SW-01 and SW-02, which were completed at the south and north abutment, respectively, indicate that approximately 8 feet of sandy lean clay/clayey sand overlies 2 feet of the moderately weathered shale/claystone and the fresh shale bedrock. Based on the consistency of the sandy lean clay and relative density of the clayey sand encountered in the borings, we recommend that the foundation bear on very stiff, sandy lean clay, medium dense clayey sand, or weathered shale/claystone below elevation 4,959 feet.

Exhibit 6-1: Recommended Abutment Spread Footing Bearing Resistance Design Parameters

Abutment Dimensions

Estimated1

Service Limit State

Settlement

Estimated1

Service Limit State

Loading

Nominal Bearing

Resistance

Strength Limit State

Bearing Resistance

Factor

Service and Extreme Event

Limit State Bearing

Resistance Factor

14 feet x 8 feet (min.) 3/4 inch 3,000 psf 12,200 psf 0.45 1.0

NOTES:

The estimated service limit state loading is proportional to the estimated service limit state settlement value.

The above nominal bearing resistance assumes that the footing is embedded at least 3 feet and that there is a flat bench in front of the footing for a distance of at least 16 feet (twice the footing width). For structures founded on shallow foundations, lateral loads from wind, seismic, retained fill, and other loads may be resisted by frictional resistance along the base of the footing and passive pressures in front of the footing. Refer to Exhibit 6-2 for our recommended lateral resistance design parameters.

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Exhibit 6-2: Recommended Abutment Spread Footing Lateral Resistance Design Parameters

Design Parameter Value

Nominal Coefficient of Friction for Sliding on Clay/Sand 1 0.53/0.67

Strength Limit State Resistance Factor for Sliding on Clay/Sand 2 0.85/0.80

Extreme Event Limit State Resistance Factor for Sliding 1.0

Nominal Passive Earth Pressure3 300 pcf

Resistance Factor for Passive Earth Pressures 3 0.50

Extreme Event Limit State Resistance Factor for Passive Earth Pressure 3 1.0

NOTES:

Value assumes cast-in-place concrete. If the concrete is precast, the provided value should be multiplied by a factor of 0.80. To use the values for "sand" the footing should be founded at least 12 inches of UTBC.

Sliding resistance factor based on AASHTO (2017), Table 10.5.5.2.2-1. To use the values for "sand" the footing should be founded at least 12 inches of UTBC.

Passive pressure should be ignored in the upper 3 feet.

pcf = pounds per cubic foot

6.1.2 Geosynthetic Reinforced Soil Abutment-Integrated Bridge System Foundation System

We recommend designing GRS-IBS abutments based on the criteria developed in the Federal Highway Administration (FHWA) Design and Construction Guidelines of GRS-IBS manual (FHWA, 2018). We recommend the following be used for a GRS-IBS foundation system:

The GRS-IBS abutments should have a 'reinforced soil foundation' directly below the GRS abutment that is founded at elevation 4,959 feet or lower.

The service limit state loading for the bridge should be limited to 4,000 psf and the GRS- IBS abutment dimensions should be at least 6 feet by 14 feet.

The nominal bearing resistance at the base of the GRS-IBS abutment should be limited to 11,500 psf for the above conditions.

Based on discussions with HDR, we understand that GRS-IBS foundation system was evaluated, but the cast-in-place spread footing system is preferred.

6.2 Wing Walls and Lateral Earth Pressures

We understand that the eastern wing will be orientated parallel to the UPRR right-of-way boundary and the western wing will be oriented parallel to the trail. For wing walls supported by cast-in-place spread footings, Exhibit 6-3 provides our recommended bearing resistance design parameters.

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Exhibit 6-3: Recommended Retaining Wall Bearing Resistance Design Parameters

Retaining Wall Footing

Dimensions

Estimated1

Service Limit State

Settlement

Estimated1

Service Limit State

Loading

Nominal Bearing

Resistance

Strength Limit State

Bearing Resistance

Factor

Service and Extreme Event

Limit State Bearing

Resistance Factor

3 feet (min.) 1/2 inch 2,000 psf 9,200 psf 0.45 1.0

NOTES:

The estimated service limit state loading is proportional to the estimated service limit state settlement value.

min. = minimum

The lateral earth pressures on the pedestrian bridge abutment and wing walls depend on many factors, including surcharge loads, the soil type, drainage provisions, and whether or not the top of the wall can yield or deflect laterally/rotate during and after excavation.

Where walls are free to deflect, they can be designed for the active condition. Where a deflection greater than 0.001 times the height of the wall (0.001H) cannot occur, walls should be designed for at-rest conditions. Active and at-rest earth pressures provided in Exhibit 6-4 assume the walls are backfilled with properly compacted Structural Backfill in accordance with Section 704.04 of Federal Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14 (FP-14) in a 1H:1V zone extending upward from the base of the wall from a point 1.5 feet behind the wall.

Exhibit 6-4: Recommended Retaining Wall Lateral Earth Pressure Design Parameters

Design Parameter Value

Retaining Wall Backfill Material Structural Backfill (FP-14 Section 704.04)

Total Unit Weight 135 pcf

Effective Friction Angle 34 degrees

Cohesion 0 psf

Active Earth Pressure Coefficient, KA 0.28

Equivalent Fluid Density for Active Conditions 38 pcf

At-Rest Earth Pressure Coefficient, KO 0.44

Equivalent Fluid Density for At-Rest Conditions 60 pcf

The parameters provided in Exhibit 6-4 assume a free-draining backfill condition. As such, it will be important to control surface water and reduce its potential to infiltrate into the ground around the abutment and retaining walls. Surface water behind wing walls should not be allowed to discharge directly into the backfill materials. In addition, water should not be allowed to discharge or pond around walls and weep holes should be incorporated into the walls. A geotextile should be placed behind weep holes to reduce the potential for soil loss.

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Surcharge loads from motor vehicles/traffic and construction equipment will induce additional lateral loads on retaining walls. The pressures provided in Exhibit 6-4 do not account for surcharge loads. Lateral loads due to various types of surcharges may be calculated by multiplying the surcharge by the active or at-rest earth pressure coefficients.

The earth pressure coefficients are also shown in Exhibit 6-4. Surcharge loads should be applied as recommended on Figure 3.

Lateral loads exerted on retaining walls should be resisted by the frictional resistance along the base of the footing and passive pressures in front of the footing. Refer to Exhibit 6-2 for our recommended lateral resistance design parameters.

6.3 Bridge Approach Embankments

We evaluated the geometry of the proposed fills for the pedestrian bridge approach embankments. In our opinion, the proposed 4H:1V side slopes will provide a minimum global stability factor of safety value of 1.3.

Settlement of the embankments may occur after construction, from both the self-weight of the fill and the increased stresses onto the existing embankment fill and the underlying soils from the embankment widening. If a clayey sand or lean clay fill material is used as embankment fill, the time required for the self-weight settlement can occur over several weeks to months after the initial fill placement. If granular soils are used, the self-weight settlement typically occurs as the fill is placed. We recommend that the approach embankment for fill heights greater than 3 feet consist of Unclassified Borrow as specified in Section 704.06 of FP-14, but we recommend that the maximum particle size of the fill be limited to 3 inches. For this material, we anticipate that the embankments may settle on the order of ½ inch at the tallest part of the embankment. In general, the magnitude of settlement will be proportional to the height and width of fill that is placed.

In addition, due to the proximity of the newly placed fill to the existing bridge structure, there is a potential for the weight of the proposed embankment fill to affect the subsurface soils below the existing bridge structure. Borings SW-01 and SW-02 encountered bedrock at a depth of 8 feet (from the base of the existing bridge approach embankment). Assuming a horizontal bedrock elevation and the proposed bridge being approximately 20 feet from the existing bridge abutment, we anticipate that the estimated settlement at the existing bridge structure will be less than ¼ inch.

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6.4 Pavement Recommendations

Performance of a pavement system depends on the pavement material and thicknesses, subgrade strength, traffic loads and repetitions, design life, and subgrade drainage characteristics. The following sections discuss each of these aspects as they relate to the project.

6.4.1 Design Methodology

Our pavement design and results are based on the design procedures presented in the 1993 AASHTO Guide for the Design of Pavement Structures with guidance from the U.S.

Department of Transportation and FHWA Federal Lands Highway Project Development and Design Manual (PDDM), dated March 2008, and the CDOT Pavement Manual (2019a).

Pavement design inputs and calculations are presented in Appendix D. We understand the pavement rehabilitation/reconstruction is considered a 3R project.

6.4.2 Subgrade Moisture Treatment

As indicated in Section 5.2, the volume change potential of the subgrade material is low (either from swell or collapse). As such, we recommend a minimum moisture treatment thickness of 12 inches blow the pavement subgrade in widening locations (areas where the existing roadway is not currently paved).

6.4.3 Traffic Loading

Shannon & Wilson were provided traffic data from the following sources:

The Project ‘Initial Vetting Summary' submitted by PWMD (2019), A limited traffic count study (approximately 9 hour long) provided by HDR in August 2019 at S. Nichols Road and W. McCulloch Boulevard intersection that included truck percentages (Highland Data Collection, LLC., 2019), and

A 7-day traffic count study performed by PWMD in July 2019 at the intersection of W.

Bella Casa Drive and S. Nichols Road and the intersection of W. McCulloch Boulevard and W. Caliente Drive that also included the percentage of large vehicles (PWMD, undated).

The data traffic counts for the above documents is provided in our Pavement Design Calculation Package (located in Appendix D). For our pavement analysis, we utilized the data from the 7-day traffic study, specifically:

A two-way annual average daily traffic (AADT) value of 2,980 vehicles per day (vpd) on W. McCulloch Boulevard with 3.6% large vehicles; and

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A two-way AADT of 2,871 vpd with 3.5% large vehicles on S. Nichols Road.

From discussions with HDR, we assumed the following to develop the design traffic loading (20-year design life 18-kip equivalent single axle loading [ESAL]):

A traffic volume annually compounded growth rate of 2% (for the projected traffic loading), and

The 'large vehicle' component of the PWMD traffic study consisted of entirely of single unit two axle trucks (FHWA Vehicle Classification No. 5).

Using the above traffic loading and assumptions, we estimated ESAL values of 296,000 and 307,000 for W. McCulloch Boulevard and S. Nichols Road, respectively. For design, of both W. McCulloch Boulevard and S. Nichols Road, assume a value of 307,000 ESALs.

6.4.4 Subgrade Soils

The subgrade strength for the project was evaluated by using Hveem stabilometer (R-value) test results bulk subgrade taken from borings SW-03 and SW-07. The R-value test results were 6.9 and 14.1, respectively. To estimate the design subgrade strength, a correlation from R-value to resilient modulus developed by CDOT and provided in the 2020 M-E Pavement Design Manual (2019a). Section 11.3.2.1.1 of the PDDM indicates to use the average resilient modulus (an approximate R-value of 10) in design. Using the CDOT correlation, we used a design resilient modulus value of approximately 6,500 pounds per square inch.

6.4.5 Full Depth Reclamation

Full depth reclamation (FDR) of the existing pavement was initially scoped for the Project.

The FDR process consists of pulverization of the existing pavement and mixing the HACP material with the underlying layer. Exhibit 4-1 indicates the existing HACP is approximately 3 inches for much of the alignment and the underlying layers consist of native A-6 subgrade material. Although a shallow FDR pavement section (an FDR thickness of approximately 4 inches is feasible), mixing the FDR material with cohesive material is not recommended. Further, based on discussions with HDR, supplementing the FDR material with imported UTBC will result in too high of an overall grade raise for much of the S.

Nichols Road alignment. As such, FDR is not recommended for this project.

6.4.6 Recommended Pavement Sections

Using the PDDM procedures and the parameters outlined in Appendix D and our recommended pavement section is summarized in Exhibit 6-5.

Exhibit 6-5: Recommended Pavement Sections

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Location Recommended Pavement Section

S. Nichols Road 5 inches HACP over 8 inches of UTBC

W. McColloch Boulevard 5 inches HACP over 8 inches of UTBC

7 CONSTRUCTION CONSIDERATIONS

The applicability of the design parameters in Section 6 and 7 is contingent on good construction practice. Poor construction techniques may alter conditions from those upon which our recommendations are based, and therefore result in poor performance. Our analyses assume that this project will be constructed according to FP-14 (FHWA, 2014) standards. The following sections provide additional construction considerations for this project.

7.1 Site Preparation

We recommend that brush and other vegetation be cleared, and roots and stumps be removed from previously undisturbed areas to be graded. Any existing surficial topsoil and soil containing organics should be stripped and removed from areas proposed for new construction. The depth of this removal is anticipated to vary, but generally be less than 2 inches. Topsoil and organic-rich soils are not considered suitable for reuse as fill and should be removed from the site or stockpiled for reuse in revegetation.

7.2 Earthwork and Grading

Earthwork, including site preparation, embankment construction, placement of fill, and subgrade preparation, should conform to the requirements provided in Division 200 of FP- 14.

7.2.1 Excavation

The soil materials can likely be excavated using conventional excavating equipment, such as a rubber-tired backhoe or tracked hydraulic excavator. In some project areas very shallow shale bedrock was encountered. We do not anticipate blasting will be required for rock excavation where this shale is encountered. However, excavation in fresh rock could be slow at times and require the use of hydraulic excavators and dozers with ripper attachments.

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7.2.2 Subgrade Preparation and Proof Rolling

In pavement areas, the subgrade should be prepared in accordance with FP-14 Section 204, which includes the use of compression-type rollers. All existing HACP paving materials should be removed. The exposed subgrade should be scarified to a depth of 6 inches and the scarified surface compacted. The compacted surface should then be proof-rolled with a fully-loaded, tandem-axle, 10-yard dump truck or equivalent. Areas that are identified as being loose, soft, or yielding during proof-rolling should be compacted in place or removed until dense and unyielding subgrade is exposed, then reconditioned or replaced with a low permeable import fill (as described in Section 7.2.3). If loose, soft or yielding soils are encountered after overexcavating 2 feet, a geogrid (Tensar biaxial grid BX1200, Tensar triaxial TX5, or equivalent product) should be installed at the base of the excavation before backfilling with a low permeable import fill. Care should be taken during proof-rolling and subgrade preparation to avoid disturbing subgrade soils and supporting soils that will remain in place, as they can rut and pump under repeated construction traffic. The final subgrade surface should be sloped to promote positive drainage and kept free of water at all times. Leaving the subgrade elevation high until final grading begins is a means to reduce the potential for disturbance to the final subgrade materials.

In wall areas, after the subgrade is excavated to the required depth, the subgrade should be probed to determine its suitability.

All subgrades should be protected from drying or wetting in excess of what is required to achieve the specified compaction requirements.

7.2.3 Low Permeable Import Fill

Low permeable imported fill should consist of soil that is free of organics, contaminants, debris, and rock fragments larger than 3 inches; contains between 20% and 40% fines; has a plasticity index of less than 20; and is non-swell susceptible (swell of less than 0.5% when wetted under a surcharge load of 300 psf). This material should have a minimum R-value of

10. It should be noted that as the amount of fines (portion of soil particles passing a U.S.

Standard No. 200 sieve, based on the minus ¾-inch fraction) increases, soil becomes more sensitive to small changes in moisture content, and adequate compaction becomes more difficult to achieve. Import fill should be compacted to a dense and unyielding condition meeting the relative compaction requirements of described in Section 7.2.4.

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7.2.4 Fill Placement, Moisture Conditioning and Compaction

Fill material should be placed in horizontal lifts and be compacted to a dense and unyielding condition. Subgrade preparation, moisture treatment, and compaction should be conducted in accordance with Section 204 of the FP-14 with the following modifications:

Structural Backfill should be moisture treated to within 2% of optimum moisture content and compacted to at least 95% of the maximum dry density, as determined by AASHTO T180.

Due to swell soil potential, existing onsite soils or other cohesive soils (AASHTO classification A-2-6, A-2-7, A-4, A-6, and A-7-6 soils) should be moisture treated between optimum and 2% over optimum moisture content and compacted to at least 95% of the maximum dry density, as determined by AASHTO T99.

The subgrade and fill should not be allowed to dry out during overexcavation and fill placement or the potential for swell and the possible magnitude of swell will increase. This will require wetting and remixing exposed lifts at the beginning of each day. Fill soils composed of on-site clay fill will need to be placed in a highly controlled state. While it is important to place soils above the optimum moisture content to control swell, soils placed wet of optimum are prone to pumping and yielding from construction activities. The Contractor will need to carefully control the movement of equipment around the site and minimize the passage of equipment over the fill area, particularly if the unpaved, exposed subgrade is used as a haul road for the project. Even with these precautions, compaction of the fill will be difficult and extra working should be anticipated. Fill placement and compaction testing should be monitored on a full-time basis to assist in this process.

7.3 Paving Materials

The following exhibit summarizes our recommendations for pavement material selection.

All specification sections reference the FP-14 (FHWA, 2014). Based on the Project estimated paving quantities, we understand that the HACP material will utilize FP-14 Section 303, which uses the local department of transportation mix design. Exhibit 8-1 below reflects a CDOT mix designs (2019b) for the HACP.

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Exhibit 7-1: Recommended Materials for Pavements

Material Specification Additional Requirements/Comments

UTBC Section 301 Use Gradation C, D, or E

HACP Section 403 (FP-14) using CDOT Section 401

(2019b)

Top Lift: CDOT Grade SX (1/2-inch NMAS) Lower Lift: CDOT Grade S (3/4-inch NMAS) PG Binder: PG 64-22, Gyratory Number (N): 75

NOTES:

NMAS = Nominal Maximum Aggregate Size

The binder selection procedure is based on the anticipated pavement temperatures, traffic patterns, and local availability. The PDDM specifies the use of software developed by the FHWA Long Term Pavement Performance (LTPP) Bind (2019) to determine an appropriate binder for a 95% reliability performance for both high and low temperature ranges.

Appendix D provides the output from the LTPP Bind software which indicates that a performance grade (PG) 64-22 binder for all lifts of HACP at the required reliability.

For the top lift of HACP, we recommend a lift thickness range between 1½ and 3 inches. For the lower lift, we recommend lift thicknesses range between 2¼ and 3½ inches. Based on the anticipated traffic loading and the elevation of the site, we recommend a Superpave design gyratory number (N) of 75 be used for mix design of the pavement. In addition, a tack coat should be placed between subsequent lifts if the underlying lift is left uncovered for greater than 24 hours.

8 CLOSURE

This report has been prepared for the exclusive use of HDR and Central Federal Lands Highway Division for the purpose of providing geotechnical recommendations for the S.

Nichols Road Improvements project. This geotechnical design report should not be used without our approval if any of the following occurs:

Assumptions stated in this report have changed.

Project details change or new information becomes available such that our analyses and recommendations may be affected.

A substantial period of time has passed since the date of this report.

If any of these occur, we should be retained to review the applicability of our analyses and recommendations.

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Within the limitations of scope, schedule and budget, the analyses, conclusions and recommendations presented in this report were prepared in accordance with generally accepted professional geotechnical and geological principles and practice in this area at the time this report was prepared. We make no other warranty, either express or implied.

Shannon & Wilson has prepared “Important Information about Your Geotechnical Report,” to assist you and others in understanding the use and limitations of our reports.

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9 REFERENCES

American Concrete Institute (ACI), 2019, Building Code Requirements for Structural

Concrete and Commentary, Farmington Hills, Mich., ACI 318-19.

American Association of State Highway and Transportation Officials (AASHTO), 1993, AASHTO guide for design of pavement structures: Washington, D.C., AASHTO, 2 v.

American Association of State Highway and Transportation Officials (AASHTO), 2017, AASHTO LRFD Bridge Design Specifications, Customary U.S. units, 8th edition:

Washington, D.C., American Association of State Highway and Transportation Officials.

Colorado Department of Transportation (CDOT), 2019a, 2020 M-E Pavement Design Manual, available at https://www.codot.gov/business/designsupport/matgeo/manuals/pdm.

CDOT, 2019b, Standard Specifications for Road and Bridge Construction. Available at:

http://www.coloradodot.info/business/designsupport/construction-specifications.

Highland Data Collection, LLC., 2019, Pueblo West Turning Movement Counts, Nichols Road & McCulloch Blvd PM, dated August 9, 2019.

Hart, S.S., 1974, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado: Colorado Geological Survey, Pueblo - Canon City Area, Colorado, 4 sheets.

Pueblo West Metropolitan District (PWMD), 2019a, Traffic Count Study, Nichols and Bella Casa, Traffic Report from July 18 through July 25, 2019.

PWMD, 2019b, Traffic Count Study, McCulloch and Caliente, Traffic Report from July 9 through July 16, 2019.

PWMD, undated, Central Federal Lands Highway Division Initial Vetting Summary, Project Name: CO FLAP PUW16(1) Nichols Road, Applicate Agency: Pueblo West Metro District.

Roberge, P.R., 2012, Handbook of Corrosion Engineering, Second Edition: McGraw-Hill, New York, New York.

Scott, G.R., 1964, Geology of the Northwest and Northeast Pueblo Quadrangles, Colorado:

U.S. Geological Survey, Miscellaneous Geologic Investigations Map I-408, scale 1:24,000.

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Scott, G.R., and Wobus, R.A., 1973, Reconnaissance Geologic Map of Colorado Springs and vicinity, Colorado: U.S. Geological Survey Miscellaneous Field Studies Map MF- 482.

Federal Highway Administration (FHWA), 2019, LTPP InfoPave: Tools: LTPPBind Online, accessed August 20, 2019, available at:

https://infopave.fhwa.dot.gov/Tools/LTPPBindOnline.

FHWA, 2018, Design and Construction Guidelines for Geosynthetic Reinforced Soil Abutments and Integrated Bridge Systems. Publication No. NHWA-HRT-17-080.

FHWA, 2014, Federal Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects, FP-14 English Units: U.S. Department of Transportation and Federal Highway Administration.

FHWA, 2008, Federal Lands Highway Project Development and Design Manual (PDDM):

U.S. Department of Transportation and Federal Highway Administration.

Available from: http://flh.fhwa.dot.gov/resources/manuals/pddm/.

U.S. Bureau of Reclamation, 1969, Fryingpan-Arkansas Project -- Colorado, Pueblo Reservoir, D.&R.G.W. railroad relocation, Sta. 474+00, County Road Overpass:

Plan-Elevation-Section, sheet 382-D-459, and County Road overpass abutments, sheet 382-D-460.

U.S. Geological Survey (USGS), 2019a, Earthquake Hazards, Faults, Quaternary Fault and Fold Database of the United States, accessed October 23, 2019. Available from:

https://www.usgs.gov/natural-hazards/earthquake-hazards/faults?qt-science_support_page_related_con=4#qt-science_support_page_related_con

USGS, 2019b, Seismic Design Web Service Documentation, AASHTO, 2009 AASHTO Guide Specification (USGS-2009). Available from:

https://earthquake.usgs.gov/ws/designmaps/

RECOMMENDED SURCHARGE

LOADING FOR TEMPORARY AND

PERMANENT WALLS

Fi le

: I :\E

F\ D

EN

\1

0s \1

C

FL

C

O N ic ho ls \D ra fti ng \F ig ur es \1

4-

Fi g 3_

Su rc ha rg e.

dw g

D at e:

0-

-2

A ut ho r:

kw h

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FIG. 3

For m ≤ 0.4: H = 0.28 (psf) (see Note 3)

W al l

PLAN VIEW

2.0

1.5

D ep th F ac to r, Z/

B

1.0

0.0

0.5

W al l

Z

Wall Line

UNIFORM SURCHARGE

EARTH BERM

(see Note 4)

Note:

H z=nH

Bottom of Excavation x = mH

Point Load in Pounds

H (psf) H (psf)

ELEVATION VIEW

x = mH

H

Bottom of Excavation

W al l z=nH Line Load in Pounds/Foot

B) LATERAL PRESSURE DUE TO LINE LOAD

i.e. NARROW CONTINUOUS FOOTING

PARALLEL TO WALL

C) LATERAL PRESSURE DUE TO STRIP LOAD

R ig id W al l

W al l

W al l

A) LATERAL PRESSURE DUE TO POINT LOAD

i.e. SMALL ISOLATED FOOTING OR WHEEL LOAD

D) LATERAL PRESSURE DUE TO EARTH BERM

OR UNIFORM SURCHARGE

Bottom of Excavation

Bottom of Excavation

E) LATERAL PRESSURE DUE

TO ADJACENT FOOTING

(see Notes 5 and 6)

0 0.5 1.0

L

B

NOTES

1. Figures are not drawn to scale.

2. Applicable surcharge pressures should be added to appropriate permanent wall lateral earth and water pressure.

3. If point or line loads are close to the back of the wall such that m 0.4, it may be more appropriate to model the actual load distribution (i.e., Detail E) or use more rigorous analysis methods.

4. See text for recommended K values.

5. The stress is estimated on the back of the wall at the center of the length, L, of loading.

6. The estimated stress is based on a Poisson's ratio of 0.5.

W al l

Bearing Pressure q (psf)

Ip, Influence Factor

H = 2(Ip) qs

Lateral Footing Pressure on Wall

(derived from NAVFAC DM 7.02, 1986; and Sandhu, Earth Pressure on Walls Due to Surcharge, 1974)

(derived from Poulos and Davis, Elastic Solutions for Soil and Rock Mechanics, 1974; and Terzaghi and

Peck, Soil Mechanics in Engineering Practice, 1967)

(NAVFAC DM 7.02, 1986)

(AASHTO LRFD Bridge Design Specifications, 2017)

(NAVFAC DM 7.2, 1986)

Point Load in Pounds

= Unit Weight of Earth Berm

Bearing Pressure

Earth Berm

H = Lateral Pressure in radians

ELEVATION VIEW

(see Note 3) (see Note 3) qs

L 2B

Qp

H2 n2

(0.16 + n2)3

For m > 0.4: H = 1.77 (psf) Qp

H2 m2n2

(m2 + n2)3

Qp

H

'H = H cos2 (1.1 ) (psf)

'H 'H

For m ≤ 0.4: H = 0.20 (psf) (see Note 3) Ql

H n

(0.16 + n2)2

For m > 0.4: H = 1.28 (psf) Ql

H m2n

(m2 + n2)2

QlQp

≤ 33° Hs ≤ 15 Feet

(K)( )(Hs) 2H

Hs

H = (K)qs (see Note 4) qs (psf)

H = [ - sin cos ( + 2 )] (psf)2q

L

= 0.25 = 0.5

= 1

H

L 2B

L 2B

L 2B

CO FLAP PUW 16(1)

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Appendix A: Subsurface Ex plorations

Appendix A

Subsurface Explorations

CONTENTS

A.1 Introduction ........................................................................................................................... A-1

A.2 Explorations ........................................................................................................................... A-1

A.2.1 Soil and Rock Classification System...................................................................... A-1

A.2.2 Split Spoon Sampling .............................................................................................. A-1

A.2.3 Modified California Test and Sampling................................................................ A-2

A.2.4 Bulk Sampling .......................................................................................................... A-2

Figures Figure A-1: Soil Description and Log Key Figure A-2 Rock Classification and Log Key Figure A-3 through A-13: Log of Borings SW-01 through SW-11

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A.1 INTRODUCTION

Shannon & Wilson’s field exploration program was conducted on August 12, 2019, and consisted of drilling 11 borings designated SW-01 through SW-11 at the locations shown on Figure 2. A second mobilization occurred on January 30, 2020, to obtain additional samples from boring SW-02. Photographs of boring locations are provided in Appendix C. The methods used to conduct the field exploration program are described below.

A.2 EXPLORATIONS

The borings were coordinated (including subcontractor coordination, utility locates, and traffic control) and observed by Shannon & Wilson. Individual boring logs are presented in Figure A-3 through A-13. These exploration logs represent our interpretation of the contents of the field logs and results of select laboratory testing. The borings were drilled by Entech Engineering, Inc. of Colorado Springs, Colorado (under subcontract to Shannon & Wilson) using a SIMCO 2800 HT truck mounted drill rig. The borings were advanced with 4-inch diameter solid-stem augers to depths of up to 20 feet. On completion of drilling, borings located in the roadway were backfilled with flow-fill and an asphalt patch. Borings outside the roadway were backfilled with cuttings.

A.2.1 Soil and Rock Classification System

During exploration, our representative collected samples and prepared field logs of the explorations. Soil classification for this project was based on ASTM Designation: D2487, Standard Practice for Classification of Soils for Engineering Purposes (Unified Soil Classification System), and ASTM Designation: D2488, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure). The Unified Soil Classification System is summarized in Figure A-1.

Bedrock was encountered in some of the borings on site. Using the International Society for Rock Mechanics (ISRM) classification of rock strength, the rock resembles a medium strength rock. The ISRM rock classification is summarized in Figure A-2.

A.2.2 Split Spoon Sampling

Disturbed samples were obtained in the borings by driving a 2-inch outside diameter (OD), 1.375-inch inside diameter split-spoon sampler (SS) a distance of 12 inches with a 140-pound hammer free-falling a distance of 30 inches. An automatic hammer system was used to

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