Attachment E- Geotech Report.pdf

GEOSCIENCES & ENGINEERING

7290 South Fraser Street Centennial, Colorado 80112-4286 Phone: 303-337-0338 Fax: 303-337-0247

GEOTECHNICAL REPORT FOR

FOUNDATION AND PAVEMENT DESIGN

North Monroe Avenue Bridge Replacement City of Loveland, Larimer County, Colorado

Short Elliot Hendrickson (SEH), Inc.

Mr. Parsa Kolahi, P.E.

Bridge Project Manager 2000 Colorado Center Drive, Suite 6000

Denver, CO 80222

February 10, 2025

Prepared For

Geotechnical Report for Foundation and Pavement Design (G22.2010.000) North Monroe Avenue Bridge Replacement, City of Loveland, Larimer County, Colorado Page ii

TABLE OF CONTENTS

Page

1.0 PURPOSE AND SCOPE

2.0 PROPOSED CONSTRUCTION

3.0 SITE CONDITIONS

4.0 SITE GEOLOGY

5.0 SUBSURFACE EXPLORATION

6.0 SUBSURFACE CONDITIONS

7.0 LABORATORY TESTING

8.0 FOUNDATION RECOMMENDATIONS

8.1 DRIVEN H-PILES

8.2 DRILLED SHAFTS (CAISSONS)

8.3 DEEP FOUNDATION LATERAL CAPACITY PARAMETERS

9.0 SEISMIC DESIGN PARAMETERS

10.0 EARTH PRESSURES

11.0 SITE GRADING AND EXCAVATIONS

12.0 PAVEMENT DESIGN RECOMMENDATIONS

12.1 PAVEMENT MATERIALS AND SUBGRADE RECOMMENDATIONS

13.0 LIMITATIONS

FIGURES, TABLES, AND APPENDICES

FIGURE 1 LOCATIONS OF EXPLORATORY BORINGS

FIGURE 2 FENCE DIAGRAM OF EXPLORATORY BORINGS

FIGURE 3 LEGEND AND NOTES FOR EXPLORATORY BORINGS

FIGURES 4 AND 5 GRADATION TEST REPORTS

FIGURES 6 AND 7 SWELL-COMPRESSION TEST RESULTS

FIGURE 8 R-VALUE TEST REPORT

FIGURES 9 AND 10 UNCONFINED COMPRESSIVE STRENGTH TEST RESULTS

TABLE 1 SUMMARY OF LABORATORY TEST RESULTS

TABLE 2 SUMMARY OF LABORATORY CHEMICAL TEST RESULTS

APPENDIX A INDIVIDUAL LOGS OF EXPLORATORY BORINGS

APPENDIX B M-E PAVEMENT DESIGN PRINTOUTS

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1.0 PURPOSE AND SCOPE

This report presents the results of a subsurface exploration and pavement design conducted for the North

Monroe Avenue Bridge Replacement Project in the City of Loveland, Larimer County, Colorado. A subsurface exploration was conducted to obtain information on soil, bedrock, and groundwater conditions. The soil and bedrock samples collected were visually classified, and selected samples were laboratory tested to evaluate the engineering properties. The results of the field and laboratory testing programs were evaluated to develop geotechnical recommendations for the design and construction of the proposed replacement structure and associated pavement.

The subsurface exploration and foundation recommendations are based on the 2022 Colorado Department of

Transportation (CDOT) Standard Specifications for Road and Bridge Construction (CDOT Standard Specifications) and the American Association of State Highway Transportation Officials (AASHTO) Load and Resistance Factor

Design (LRFD) Bridge Design Specifications (9th Edition, 2020) (AASHTO LRFD Specifications). The pavement design for the approach pavement is in accordance with the 2021 Larimer County Urban Area Street Standards (Larimer County Specifications), as referenced by the City of Loveland.

This report has been prepared to summarize the data and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations related to design of the proposed structure and pavements are included. Environmental considerations related to hazardous material are beyond the scope of this study. The subsurface exploration and analyses were conducted in general accordance with Geocal, Inc.’s (Geocal) agreement with SEH, Inc. (SEH), dated February 25, 2022.

2.0 PROPOSED CONSTRUCTION

Based on information provided by SEH, we understand that the existing bridge carrying County Road 13E

(North Monroe Avenue) over Dry Creek (CDOT Structure #: LR13E-0.3-24E) will be replaced with a new single-span bridge. We understand that the dimensions of the new bridge are not known as of this report and are pending per the results of a structure selection report. The new bridge is expected to be supported by driven piles or drilled shafts. Portions of the approach roadways are expected to be reconstructed to accommodate the new bridge structure. We anticipate the pavement on the bridge deck and at the approaches to remain asphalt pavement.

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Excluding the fill material needed for the backfill material behind the wingwalls and abutments, cut and fill depths are expected to be nominal and less than two feet. If the scope of the proposed construction changes significantly from that described, this office should be notified to re-evaluate the recommendations contained in this report.

3.0 SITE CONDITIONS

The project area is situated along North Monroe Avenue approximately a quarter mile north of the intersection with East 37th Street near the southwest corner of Horseshoe Lake. The bridge carries traffic along North Monroe Avenue over Dry Creek, which is an east-flowing stream that drains into Horseshoe Lake. The neighborhood surrounding the project area includes primarily single-family housing surrounded by deciduous trees.

North Monroe Avenue is a two-lane, approximately 25-foot-wide, asphalt roadway. The existing bridge, constructed in 1937, is identified in the most recent bridge inspection report as structurally defective as evidenced by observed defects in the deck, superstructure, and substructure. Transverse and longitudinal cracks were observed along the bridge deck pavement during the field work. A general view of the asphalt roadway along the bridge deck is shown in Figure A.

Figure A: General view of bridge deck looking south

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4.0 SITE GEOLOGY

The following sub-regional scale geologic and surficial soil mapping documents, supplemented by Geocal’s field observations, were referenced to provide the framework for subsurface soils, bedrock, and groundwater characterizations:

1) Crosby, E.J., and Hansen, W.R. (1982). Environmental Geology of the Front Range Urban Corridor and Vicinity, Colorado. Geological Survey Professional Paper 1230.

2) Colton, R.B. (1978). Geologic Map of the Boulder-Fort Collins-Greeley Area, Front Range Urban Corridor, Colorado: Miscellaneous Investigations Map I-855-G. Scale 1:100,000.

3) Robson, S.G. et al. (2000). Geohydrology of the Shallow Aquifers in the Fort Collins-Loveland Area, Colorado: Hydrologic Investigations Atlas HA-746B. Scale 1:50,000.

The project site is situated in the Colorado Piedmont physiographic province denoted as Piedmont uplands with topography characterized as low-rolling uplands (1). The local area is characterized by subdued topography consisting of hills and channels. Irregularities in the bedrock surface are often covered by eolian silt and sand, however, the bedrock outcrops occasionally. The local topographic relief is to the south and east, oriented towards Horseshoe Lake and the Big Thompson River.

Surficial Soils: Original (pre-construction) natural, surficial soil has been mapped as Holocene-Age Piney

Creek Alluvium (2). The Piney Creek Alluvium is described as generally consisting of dark gray sand and gravel containing organic matter. The alluvial deposits in the project area are indicated to be less than 20 feet thick (3). The published maps do not denote artificial fill as being present at the project site; however, the existing bridge and roadway construction at the site are indicative of fill placement. This is evidenced by the artificial fill we encountered in our borings. If encountered during construction, the artificial fill is expected to vary in both thickness and composition.

Bedrock Strata: The bedrock at the project site is mapped as the upper shale member of the Pierre Shale.

The bedrock is noted as consisting of gray concretionary silty shale (2). Bedrock is noted as outcropping on the south and east sides of Horseshoe Lake but is not exposed at the project site.

Groundwater: Groundwater is indicated on the published maps as being less than 20 feet below existing grades (3). The water table depth is expected to fluctuate seasonally due to the weather and the hydrologic connection with Horseshoe Lake.

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5.0 SUBSURFACE EXPLORATION

The subsurface exploration was conducted on March 10, 2023, and consisted of drilling four (4) borings at the approximate locations shown on Figure 1, Locations of Exploratory Borings. Borings B-1 and B-2 were drilled for bridge foundation information (one boring near each existing abutment) to depths of approximately 44 feet. Borings P-1 and P-2 were drilled for pavement design information (one boring in each approach to the existing bridge) to depths of approximately 10 feet. The four (4) borings were drilled through the existing pavement of North Monroe Avenue. The borings were drilled with a Central Mine Equipment (CME)-75, truck-mounted drill rig equipped with both 8¼-inch outside-diameter (O.D.) hollow-stem augers and 4-inch diameter solid-stem augers.

Soil and bedrock samples were collected from the borings using a nominal 2-inch inside-diameter (I.D.)

California spoon sampler (ASTM D3550) and a 1⅜-inch I.D. Standard Penetration Test (SPT) split barrel sampler (ASTM D1586). Penetration resistance values, when properly evaluated, indicate the relative density or consistency of the soils or bedrock hardness. Below a depth of one foot, the samples were obtained at approximately five-foot intervals continuing to the total depths of the borings. Disturbed bulk samples of auger cuttings were collected from about one foot to five feet below grade for each boring. A representative of Geocal logged the borings and collected the samples. The borings were backfilled with imported sand and were patched with cold-patch asphalt that was compacted in lifts to a thickness of nine inches or to the thickness of the existing asphalt, whichever was thicker.

Logs of the subsurface conditions encountered, including depths at which samples were collected, penetration resistance values, and depths to groundwater are shown on Figure 2, Fence Diagram of Exploratory Borings. Descriptions of the materials encountered and notes regarding the symbols used are shown on Figure 3, Legend and Notes for Exploratory Borings. Individual boring logs are presented in Appendix A.

6.0 SUBSURFACE CONDITIONS

The four (4) borings were drilled through the existing pavement of North Monroe Avenue. The pavement sections encountered are summarized in the following table:

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Bridge Approach Boring No. Hot Mix Asphalt (HMA) Pavement Thickness (in)

South P-1 11 B-1 6

North P-2 6 B-2 7

Aggregate base course (ABC) was not encountered below the pavement sections in our borings. Artificial fill was encountered in our borings to depths ranging from approximately two feet to four feet beneath existing grades. The artificial fill encountered in our bridge borings (Borings B-1 and B-2) was more clayey than the fill encountered in our pavement borings (Borings P-1 and P-2) and consisted of medium stiff, light brown to gray clay that had a medium plasticity and was very calcareous. Medium dense, mottled brown and white, sandy soil with variable amounts of silt, clay, and fine gravel was encountered in the artificial fill in Borings P-1 and P-2.

Natural soil generally consisting of soft to stiff, light brown to gray, lean clay with variable amounts of fine sand was encountered below the artificial fill in our borings. The natural soil generally had a medium plasticity, but lenses of high plasticity clay were encountered within the natural soil. Bedrock pertaining to the upper member of the Pierre Shale was encountered in our bridge borings (Borings B-1 and B-2) at a depth of approximately 30 feet below existing grades. The bedrock encountered was generally hard to very hard, dark gray, and laminated (fissile texture).

The top approximately five feet of the bedrock surface was slightly weathered. Groundwater was encountered during drilling in Borings B-1 and B-2 at a depth of approximately 17 feet beneath existing grades. Groundwater levels can be expected to fluctuate with varying seasonal and weather conditions and with the water level in Horseshoe Lake.

7.0 LABORATORY TESTING

Laboratory tests conducted on selected samples consisted of gradation, Atterberg limits (liquid and plastic limits), swell-compression, unconfined compressive strength (UCS), R-value, and chemical tests including water-soluble sulfates, water-soluble chlorides, pH, and laboratory resistivity. Laboratory test results are presented on Figures 4 through 10 and are summarized in Table 1, Summary of Laboratory Test Results. The chemical test results are summarized in Table 2, Summary of Laboratory Chemical Test Results. Testing was conducted in general accordance with local practice and applicable American Society for Testing and Materials (ASTM) standards.

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Gradation and Atterberg Limits: Soils were classified according to the AASHTO Classification System and the Unified Soil Classification System (USCS, ASTM D-2487). These systems are based on index property tests, including Liquid Limit (ASTM D-423), Plastic Limit (ASTM D-424) and grain size distribution (ASTM D-422).

Results of the Atterberg limits tests and gradation tests are presented on Figures 4 and 5.

The gradation and Atterberg limits test results indicate that the soils tested were predominantly lean clays

(CL) with variable amounts of sand, silty sand (SM), and silty, clayey sand with gravel (SC-SM). AASHTO classifications for the sandy soils tested included A-2-4 and A-4. AASHTO classifications for the clayey soils tested included A-6 and A-7-6 with Group Indices ranging from 9 to 19. The Atterberg limit tests indicate that the clayey soils may have expansion potential. In general, these classifications provide qualitative information on the suitability of the subgrade materials for pavement or foundation support.

Swell-Compression Test: Swell-compression tests (ASTM D 4546) were conducted on samples of lean clay to evaluate compressibility or swell characteristics under loading and wetting. The samples were placed in an odometer ring between porous discs, and an initial pressure of either 200 pounds per square foot (psf), 500 psf, or 1,000 psf was applied, depending on the depth from which the sample being tested was collected. After stabilization, the samples were submerged, and the percent volume change measured. Incremental loading was then applied, and the volume change monitored until deformation practically ceased under each load. The swell-compression test results are shown on Figures 6 and 7. The samples tested had swell pressures ranging from 0 psf to 1,300 psf and corresponding volume changes ranging from 0% to 0.5%. The results indicate a low swell potential for the samples tested. The samples of clay also exhibited low to moderate compressibility under increased loading and wetting.

Resistance R-value: The R-value is a measure of the soil’s ability to transfer traffic loading laterally. Test results are shown on Figure 8 for the bulk sample collected from the top approximate five feet of Boring P-1. The sample of artificial fill from Boring P-1 classified as a silty sand with gravel (AASHTO A-4(0)) and had an R-value of

62. This result indicates that the sample tested exhibited good strength for support of pavements.

Unconfined Compressive Strength: This test is a measurement of the compressive strength of a sample under axial loading without lateral confinement, providing a quantitative strength comparison to Standard Penetration Test results. Samples of shale bedrock were prepared by trimming the samples at right angles to the samples’ axis.

A load was applied axially and continuously to each sample to produce a constant rate of deformation. The axial strain and stress were measured and plotted to provide a peak strength value. The test results are shown on Figures 9 and 10. The samples of shale bedrock tested from Boring B-1 at 39 feet and B-2 at 34 feet had unconfined compressive strength values of 15 kips per square foot (ksf) and 12.2 ksf, respectively.

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Water-Soluble Sulfates: The water-soluble sulfate test is a measurement of the potential degree of sulfate attack on concrete exposed to the onsite soils and bedrock. Sulfate solutions react with tri-calcium aluminate hydrate, which is a constituent of Portland Cement Concrete, forming sulfo-aluminate with an accompanying substantial volume expansion causing cracking. Sulfate expansion problems will typically exist when the soils have sulfate concentrations in excess of 0.10%. The severity of potential exposure is based on a range of Class 0 (negligible) to Class 3 (severe) as presented in Table 601-2 of Section 601.04 Sulfate Resistance of the CDOT Standard Specifications. As shown in Table 2, water-soluble sulfate concentrations generally ranged from ‘Not Detected’ to 0.18% for the samples tested. The test results indicate that a Class 1 Severity of Sulfate Exposure is applicable for concrete exposed to the onsite soils.

Buried Metal Corrosion Potential: Electrical resistivity, pH, and water-soluble chloride tests were conducted on selected samples to help evaluate the potential degree of attack on buried metal (corrosion of piles).

These limited test results are presented in Table 2. Section 10.7.5 of the AASHTO LRFD Specifications provides guidance on determining whether the soil/site conditions could be indicative of a potential pile deterioration or corrosion situation. The two samples tested had electrical resistivity values of 1,100 ohm-cm and 1,000 ohm-cm, water-soluble chloride contents of 0.0207% to 0.0174%, and pH values of 7.8 and 7.5. Based on the results of the chemical testing of the onsite soil, the site conditions should be considered to have an increased potential for pile deterioration because of corrosion. A corrosion specialist should be consulted to evaluate the corrosive potential of the site and to provide recommendations for increasing the resistance of the steel placed in the ground to corrosion and deterioration.

8.0 FOUNDATION RECOMMENDATION

Based on the proposed construction and the subsurface conditions encountered, a deep foundation system consisting of driven piles or drilled shafts, bearing in the underlying bedrock may be used for support of the bridge structure. Wingwalls should be supported by the same foundation type used to support the bridge abutments.

Recommendations for these deep foundation types are provided in the following sections.

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8.1 Driven H-piles

Recommendations presented in this section are generally based on the CDOT LRFD Bridge Design Manual (CDOT BDM) and the American Association of State Highway Transportation Officials (AASHTO) Load and

Resistance Factor Design (LRFD) Bridge Design Specifications (9th Edition, 2020) (AASHTO LRFD Specifications), the subsurface data obtained, our experience, and local geotechnical engineering practice. Installation of driven piles should be in accordance with Section 502 – Piling of the CDOT Standard Specifications and applicable Standard Special Provisions.

1) Piles should consist of heavy steel H-sections driven to refusal in the underlying shale bedrock. H-piles driven to refusal in the underlying shale bedrock may be designed for the combined side shear and end bearing Nominal capacity of 38 kips per square inch (ksi) times the cross-sectional area pile for Grade 50 steel. A resistance factor of 0.65 should be applied per Table 10.5.5.2.3-1 of the AASHTO LRFD Specifications, assuming that the driving criteria for the piles is established by dynamic testing of at least two piles per site condition or abutment.

2) H-piles are anticipated to encounter practical refusal within approximately five feet of the bedrock surface, at an approximate elevation of 4,945 feet although some variation in the bedrock surface elevation and penetration should be expected.

3) Pile groups will require appropriate reductions of the axial capacities based on the effective envelope of the pile group. For axial and uplift, this reduction can be avoided by spacing the piles no closer than three diameters from center-to-center. Piles spaced closer than three diameters should be evaluated on an individual basis to establish the appropriate reduction in the design parameters.

4) Settlement of the properly constructed H-piles bearing in bedrock is expected to be on the order of ½ inch or less.

5) Lateral parameters are provided in Section 8.3 – Deep Foundation Lateral Capacity Parameters. Additional resistance to horizontal forces may be provided with battered piles. The vertical and horizontal components of the load will depend on the batter inclinations. Batter should not exceed 1:4 (horizontal to vertical) inclination as per the CDOT BDM. Pre-drilling of the bedrock may be needed if additional lateral capacity is needed.

6) Pile protection should be included for all piles driven into bedrock per the CDOT BDM.

7) Uplift resistance should be limited to the soil/pile interface and side shear friction above the bedrock penetration. The α-method (Section 10.7.3.8.6b of the AASHTO LRFD Specifications) was used to calculate a nominal (average) side shear friction value of 160 psf for the clayey soils encountered at the site.

The side shear friction value should be assumed to start at depth of three feet below the ground surface and increase linearly then remain constant to the bedrock surface. No side shear capacity should be assumed for the top five feet of the pile to account for surface disturbance and frost action. A Resistance Factor of

0.25 (based on using the α-method) should be applied to the nominal value for uplift resistance as indicated in Table 10.5.5.2.3-1 of the AASHTO LRFD Specifications. Pile and pile cap weights may be included in dead weight resistance to uplift forces.

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8) Refusal criteria should be determined during construction using the Pile Driving Analyzer (PDA) in accordance with Section 502 of the CDOT Standard Specifications.

9) The pile driving contractor should provide the results of a GRLWeap drivability analysis for the pile driving equipment proposed for use, and the type of pile in accordance with the CDOT Standard Specifications prior to pile driving operations.

10) The pile driving operation should be observed by Geocal personnel on a full-time basis. Piles should be observed and checked for buckling, crimping, and alignment in addition to recording penetration resistance and general pile driving operations. Because the bridge is located close to a residential neighborhood, pile driving operations should be monitored for noise and vibration and completed in a manner to minimize the disturbance to the nearby structures and residents.

8.2 Drilled Shafts (Caissons)

Drilled shafts should be drilled into and supported by the underlying competent, shale bedrock. Competent bedrock is defined as bedrock having an N-value of 50 blows per 6 inches (50/6) of penetration or less. The N-value is determined by a 140-pound hammer falling 30 inches onto the subgrade. Drilled shafts should be installed in accordance with Section 503 of the 2022 CDOT Standard Specifications. The following design and construction details should be observed.

1) Drilled shafts should be designed for the following Nominal values in kips per square foot (ksf):

Nominal Unit Tip Resistance (ksf) Nominal Unit Side Shear Resistance (ksf)

67.5 2.4

These values were calculated in accordance with Section 10.8.3.5.1 of the AASHTO LRFD Specifications (total stress method for unit tip resistance and the α-method for unit side resistance). A drilled shaft diameter of two feet was assumed for calculations. The upper five feet of the drilled shaft should be ignored when calculating the nominal shaft side resistance to account for the effects of seasonal moisture changes, potential scour, disturbance during construction, and low lateral stresses from freshly placed concrete. The following resistance factors, based on Table 10.5.5.2.4-1 of the AASHTO LRFD Specifications, should be applied for design:

Resistance Factor Applied To

0.45 Side Shear Resistance

0.40 Tip Resistance

0.35 Uplift Resistance

The above tip resistance and side resistance capacities are for foundation support provided by competent shale bedrock. Any weathered bedrock encountered during construction at the bedrock surface is expected to grade to competent bedrock. At least the upper three feet of the bedrock surface should be assumed to be weathered. Drilled shafts may require the use of mud slurry during installation, which could leave the soils at the final concrete/soil interface coated with mud. Therefore, potential side shear capacity from the overburden soils should not be used during design.

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2) Section 10.6 of the CDOT BDM indicates that drilled shafts used to support bridges should have a minimum diameter of 24 inches. Drilled shafts should penetrate a minimum distance of 10 feet into competent bedrock for the capacities presented in Item #1 of this section to be valid. These are geotechnical parameters. Greater penetration depths may be needed based on the structural requirements.

3) Settlement of properly constructed drilled shafts bearing in competent bedrock is expected to be on the order of ½ inch or less.

4) The minimum spacing requirements between drilled shafts should be three diameters from center-to-center.

At this spacing, no reduction in the axial design parameters is required. Drilled shafts grouped less than three diameters center-to-center should be studied on an individual basis to evaluate the appropriate reduction in axial capacity.

5) Lateral capacity analysis parameters are presented in Section 8.3 – Deep Foundation Lateral Capacity

Parameters of this report.

6) Drilled shaft holes should be properly cleaned prior to placement of reinforcing steel or concrete. A maximum length to diameter ratio of 25 is recommended to facilitate cleaning and observation of the shaft hole.

7) Concrete utilized in the drilled shafts should be a fluid mix with sufficient slump so it will fill the voids between reinforcing steel and the shaft hole. Section 503.05 of the CDOT Standard Specifications indicates that the concrete used in the construction of drilled shafts should be Class BZ. For Class BZ concrete, Table 601-1 of the CDOT Standard Specifications indicates that a slump in the range of six inches to nine inches is required.

8) The presence of groundwater in the exploratory borings and the presence of soils with potential for caving indicates that casing and/or mud slurry methods will be needed to reduce water infiltration and to stabilize the walls of drilled shafts during construction. If water cannot be removed, or if it is impractical to remove the water prior to placement of concrete, then concrete should be placed using an approved tremie method.

Concrete placement should occur after the hole has been well cleaned. In no case should concrete be placed through more than two inches of water.

9) If casing is used, a sufficient head of concrete should be maintained inside the casing during casing removal to help prevent voids being formed in the concrete. The concrete level should not be allowed to rise during casing removal. If it becomes apparent that voids may have formed during shaft installation, the contractor should be required to perform non-destructive tests to evaluate the continuity and integrity of the shafts.

Tests may include sonic echo tests or other tests.

10) Bedrock penetration should be measured down from the bottom of the casing or top of competent bedrock, whichever is the lower elevation and as determined by a qualified observer.

11) Concrete should be placed in drilled shafts the same day they are drilled. The presence of water and/or caving soils will likely require the concrete to be placed immediately after the drilled shaft hole is completed.

Failure to place concrete the day of drilling will result in bedrock degradation and a requirement for additional penetration. The amount of additional penetration will be a function of how long the hole is left open and whether water accumulates during the inactive period. If the drilled shaft is left open overnight, this office should be contacted for evaluation of additional penetration requirements.

12) The drilling contractor should mobilize equipment of sufficient size and operating condition to penetrate the materials and to achieve the required penetration.

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13) Care should be taken to prevent forming mushroom shapes at the top of the drilled shafts. The use of Sonotubes® of the appropriate shaft diameter and/or mud slurry may be needed at the top.

14) Installation of drilled shafts should be observed by a representative of Geocal to verify bedrock penetration, placement of reinforcing steel, and condition of the bottom and sides of the holes prior to placement of concrete.

8.3 DEEP FOUNDATION LATERAL CAPACITY PARAMETERS

The following recommendations are provided for the structural engineer using the computer program LPILE for the lateral load analysis. Resistance to lateral loads should be assumed zero above the elevation represented by three feet below the proposed final grade due to potential loss of support from frost penetration, scour, or other shallow ground disturbances. We anticipate that the designer will determine the scour depth. The following recommendations are provided for a lateral capacity analysis using the LPILE Plus 6.0 computer program.

Lateral Capacity Parameters for Deep Foundations

Material Type (p-y Curve Model Type)

Total Unit Weight

(pcf)

Cohesion Cu

(psf)

Friction angle (deg) k-static (pci) k-cyclic (pci) ε50

Artificial Fill (Sand, Reese) 120 -- 30 90 -- -- Artificial Fill (Stiff Clay, Reese) 120 1,000 -- 500 200 0.007

Soft Clay (Matlock) 105 250 -- 30 -- 0.02 Stiff Clay (Reese) 120 1,000 -- 500 200 0.007

Bedrock (Stiff Clay w/out Free Water) 135 7,500 -- 2,000 800 0.004 ε50 = strain at 50% of peak strength.

The unit weight of water should be subtracted from the total unit weight for the submerged condition.

Reductions in lateral capacity for loading perpendicular to the line of shafts or piles will not be required if center-to-center spacing of five shaft/pile diameters or more between adjacent drilled shafts or piles is maintained.

LPILE uses p-multipliers to account for reduced capacity of closely spaced drilled shafts or piles for loading in either direction. The following data is from Article 10.7.2.4 of the AASHTO LRFD Specifications. A sketch of the loading and how the rows are referenced is also shown below.

P-Multipliers for Drilled Shaft / Driven Pile Foundations

Center-to-Center Spacing in Direction of Loading

P-multiplier for LPILE

Row 1 Row 2 Row 3 and Higher

3B 0.80 0.40 0.30 5B 1.00 0.85 0.70

B = Diameter of Shaft or Pile

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9.0 SEISMIC DESIGN PARAMETERS

The subsurface conditions encountered at the project area consist generally of lean clay with variable amounts of silt, sand, and gravel. Shale bedrock was encountered below the natural soils at a depth of approximately 30 feet and extended to the maximum depths explored in our borings. Based on the American Society of Civil Engineers (ASCE) Standard 7-16 requirements and considering the composition and thickness of the natural soils as well as the penetration test results, a Seismic Site Class D (Stiff Soil) should be used for design. The following Seismic Site Class D factors should be utilized for design:

Approximate Latitude (degrees): 40.43372988 Approximate Longitude (degrees): -105.06789843 Peak Ground Acceleration (PGA): 0.102 Spectral Acceleration Coefficient at 0.2 Second Period (Ss): 0.190 Spectral Acceleration Coefficient at 0.1 Second Period (S1): 0.056 Site Factor (FPGA): 1.6 Site Factor (Fa): 1.6 Site Factor (Fv): 2.4 Modified Peak Ground Acceleration (As): 0.162 Modified Spectral Acceleration Coefficient at 0.2 Second Period (SDS): 0.203 Modified Spectral Acceleration Coefficient at 0.1 Second Period (SD1): 0.089

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10.0 EARTH PRESSURES

We have assumed that wingwalls will be cast-in-place concrete and supported by the same foundation type as the bridge abutments. Retaining structures, such as wingwalls, which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for lateral earth pressures based on the "at-rest" earth pressure condition. Cantilevered or gravity retaining structures which rotate and/or deflect sufficiently to mobilize the internal soil strength of the wall backfill may be designed for the "active" earth pressure condition. The following ultimate earth pressure coefficients are recommended for imported CDOT Class 1 Structure Backfill material. Fine grained soils (i.e., clays and silts) produce excessive earth pressures on walls and are not recommended for use as structure backfill. The onsite soil generally consists of lean clay with variable amounts of sand. This soil is not recommended for use as structure backfill. The following values assume placement and compaction in accordance with the CDOT Standard Specifications:

Material Active (Ka) At-Rest (Ko) Passive (Kp) γT – Total Unit Weight (pcf) Φ - Friction Angle (deg) Class 1 0.28 0.44 3.53 135 34

For granular backfill, lateral wall movements or rotation equal to 1% of the wall height is typically required to develop the full active case, whereas lateral movement equal to at least 2% of the wall height is normally required to establish full passive resistance. Suitable factors of safety should be applied to the above ultimate values to limit strain needed to reach ultimate strength, particularly in the case of passive resistance where large strains are needed to mobilize resistance. Imported material should meet Class 1 Structure Backfill grading requirements. A sufficient number of laboratory tests such as gradation should be performed during construction to confirm that backfill material meets the grading requirements. Natural borrow sources often have wider grading variability than plant mixes and will require that more frequent tests be done.

Equivalent fluid unit weights may be taken as follows:

Above groundwater: γeq = γT x Ka,o,p Below groundwater: γeq = (γT – 62.4) x Ka,o,p where: γT = soil total unit weight Ka,o,p = appropriate earth pressure coefficient

The above parameters are for a horizontal backfill and no surcharge loading. Retaining structures should be designed for appropriate surcharge pressures such as from traffic, etc. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on retaining structures. An underdrain

North Monroe Avenue Bridge Replacement, City of Loveland, Larimer County, Colorado Page 14 of 20 should be provided to help reduce unbalanced hydrostatic pressure buildup unless the wall is designed to accommodate the additional pressure.

Structure backfill should be placed and compacted in accordance with the CDOT Standard Specifications for structure backfill. Care should be taken not to over-compact the backfill or use large equipment adjacent to the wall because this could cause excessive lateral wall loading. Settlement of wall backfill is estimated at approximately 1% to 2% of the total wall height. Most of that settlement should occur during construction assuming CDOT Class 1 Structure Backfill material is used, and the base of the backfill and embankment area is prepared in accordance with Section 11.0 – Site Grading and Excavations.

11.0 SITE GRADING AND EXCAVATIONS

The onsite soils generally consisted of lean clay with variable amounts of silt, sand, and gravel. Excavation of the onsite soil should be possible with conventional heavy-duty equipment. The re-use of onsite materials will be a function of where the material is taken from and what the intended use is. Existing vegetation, debris and deleterious materials should be stripped and removed from all proposed pavement and fill areas. Exposed surfaces should be free of mounds and depressions which could prevent uniform compaction. Fill should be placed and compacted according to CDOT Standard Specifications. The existing onsite soil is not suitable for use as Engineered Fill for support of pavements and for common embankments as it may contain high plasticity clays and compressible soil.

Therefore, the onsite soil should be removed and replaced with Engineered Fill that will have to be imported from off site.

Permanent fill slopes up to 15 feet high should be constructed no steeper than 3H:1V (horizontal to vertical) grade provided the fills are properly compacted and drained. The ground surface underlying proposed fills should be carefully prepared by removing all organic matter and oversized material (greater than six inches maximum dimension), scarifying to a depth of eight inches, and re-compacting in accordance with the CDOT Standard Specifications. Settlement of properly compacted embankments constructed of material similar to that encountered onsite should be on the order of 1% to 2% of the embankment height (depending on the embankment materials selected).

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Proper surface drainage should be provided around all permanent cuts to direct surface runoff away from the cut face. Cut slopes and other stripped areas should be protected against erosion by re-vegetation or other methods. Cut slopes up to 10 feet high should be possible provided the slopes do not exceed 3H:1V and if seepage is not encountered. No formal stability analyses were performed to evaluate the slopes recommended above.

Published literature and our experience with similar cuts and fills indicate the recommended slopes have adequate factors of safety. If seepage is encountered, we should be advised for further evaluations.

During construction, excavations will be particularly susceptible to localized instabilities if seepage is encountered, and the contractor should be aware of potential groundwater, excavation stability, and safety for workers. The onsite soil can be classified as Type C per the Occupational Safety and Health Administration (OSHA) requirements. Sloped excavations should conform to applicable OSHA regulations, and the contractor should assume responsibility for excavations that are safe for workers.

Dewatering: Groundwater was encountered at an approximate depth of 17 feet below existing grades in the bridge borings drilled on North Monroe Avenue. Depending on the depth of excavation, seasonal conditions, and water level in Horseshoe Lake and Dry Creek, groundwater may be encountered in excavations. If excavations are conducted during the spring and early summer months, the contractor may need to be prepared with sufficient equipment to accommodate a rapid rise of water level. The contractor should anticipate that groundwater flow rates into excavations that are below the groundwater level will be high and that unstable conditions could exist. The contractor may need to install appropriate well points on either side of the excavation to maintain stability.

12.0 PAVEMENT DESIGN RECOMMENDATIONS

A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade without overstressing the subgrade soils. Performance of the pavement structure is a function of several factors including but not limited to the physical properties of the supporting soils, traffic loadings, and drainage. The pavement recommendations presented in this report are based on the AASHTO mechanistic-empirical design methodology (M-E Design) as presented in the 2021 CDOT Pavement Design Manual (CDOT PDM) and the 2022 Manual Addendum, as referenced in the Larimer County Specifications. We have assumed that Hot Mix Asphalt (HMA) pavement is preferred for the roadway to be consistent with the existing pavement type.

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The AASHTOWare M-E Pavement Design Software Version 2.3.1 was used to develop pavement thickness designs. The M-E Design software calculates pavement responses such as stress, strain, and deflection under axle loads and climatic conditions, and calculates the accumulated damage over the design analysis period. The procedure empirically relates calculated damage over time to pavement distresses and smoothness based on performance of actual projects in Colorado. Performance verification forms the basis of the acceptance or rejection of a trial design evaluated using the M-E Design software. A successful design is one where the selected performance criteria threshold limits are satisfied at their chosen levels of reliability at the end of the design life, or the minimum age to the first rehabilitation. The performance criteria and reliability factors are selected based on the functional classification of the roadway.

Performance Criteria: The following performance criteria for flexible pavement were used, based on a classification of ‘Minor Arterial (Two Lane)’, per the City of Loveland 2040 Full Buildout Street Plan, for the North Monroe Avenue.

Climate: CDOT has a database of climatic data from 42 weather stations across Colorado. The project site is in the City of Loveland, Larimer County, Colorado. For design, weather data from the closest available weather stations in the City of Fort Collins, Colorado was used.

Design Traffic Loading: The Annual Average Daily Traffic (AADT), and the truck traffic distribution of

North Monroe Avenue, were obtained from the traffic study provided to us by the client. The 20-year growth factor for the section is assumed based on the growth factor of North Garfield Avenue, which is a major arterial that runs in north-south direction and is approximately a half mile west of North Monroe Avenue. The M-E Design methodology considers the Annual Average Daily Truck Traffic (AADTT) and the growth rate to quantify traffic loading to pavements over the design period. The growth rates were calculated based on the assumed growth factor. The AADTT is converted from the AADT and the truck traffic distribution. Using the given AADT values and the truck traffic rate, we calculated the following opening day AADTT values in 2024 and the equivalent growth rate:

Flexible Pavement Performance Criteria North Monroe Avenue

Reliability (%) 90 Initial IRI (in/mile) 59.8 Terminal IRI (in/mile) 200 AC top-down fatigue cracking (ft/mile) 3,000 AC bottom-up fatigue cracking (% lane area) 25 AC thermal cracking (ft/mile) 1,500 Permanent deformation – total pavement (in) 0.80 Permanent deformation – AC only (in) 0.65

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Roadway AADTT Growth rate North Monroe Avenue (North of East 37th Street) 188 1.00% North Monroe Avenue (South of Sundisk Drive) 177 1.00%

A CDOT Cluster 2 truck traffic distribution was used for the roadways, with two distinct peaks of Class 5 and

Class 9 vehicles and Class 9 vehicles are predominant.

Subgrade Soil Strength: The subgrade soil encountered in our borings generally consisted of lean clay with variable amounts of silt, sand, and gravel (AASHTO A-6). However, an R-value test was conducted on a sample of artificial fill that classified as silty sand with gravel (AASHTO A-4(0)). An R-value of 62 was obtained for the sample. However, as the soil in the other borings classified as generally clayey, the R-value of 62 from the onsite fill is not representative of most of the onsite soil that would be supporting the pavement. Therefore, for pavement design, an R-value of 15 was used for design as this value is more representative of an A-6 soil. An R-value of 15 corresponds to a resilient modulus of 7,247 pounds per square inch (psi), based on Equation 4-1 of the CDOT PDM.

Pavement Thickness Recommendations: The M-E pavement design software was used to design the pavement sections of the project. The following composite pavement sections Hot Mix Asphalt (HMA) pavement over ABC with the subgrade R-Values of 15 used in the design. The six-inch-thick aggregate base course (ABC) below the pavement is modeled as a non-stabilized layer of crushed gravel with a resilient modulus of 21,000 psi, based on the limiting modulus criteria presented in Figure 5.2 of the CDOT PDM. The first pages of the M-E pavement design software printouts are included in Appendix B. Full reports and/or design files may be provided upon request.

Roadway Hot Mix Asphalt (HMA)

Pavement Thickness (in) Aggregate Base Course

(ABC) Thickness (in) North Monroe Avenue

(North of East 37th Street) 5½ 6

North Monroe Avenue (South of Sundisk Drive) 5½ 6

However, Table 10.1 – Flexible Pavement Design Criteria of the Larimer County Standards indicates that for roadways classified as ‘two-lane arterials’, the minimum asphalt section is 7½ inches of HMA over 11½ inches of ABC. Our calculated design is thinner than the minimum pavement section established by the Larimer County Specifications. Therefore, we recommend following the HMA and ABC thickness recommendations contained in the Larimer County Specifications.

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12.1 PAVEMENT MATERIALS AND SUBGRADE RECOMMENDATIONS

Hot Mix Asphalt (HMA) Pavement: HMA pavement materials should consist of a bituminous plant mix composed of a mixture of aggregate and bituminous material that meets the requirements of a job-mix formula established by a qualified engineer in accordance with the CDOT Standard Specifications. The binder types were determined using the LTPPBind software, and gyrations were determined based on the anticipated traffic loading.

The following mix types are recommended for this project:

Top Lift: SX(100) PG 76-28 Lower Lifts: S(100) PG 64-22

The design was run using a 100-gyration mix; however, a 75-gyration mix may also be used for design if requested by the City of Loveland. Grading SX has a finer aggregate gradation and is recommended for the top lift.

This layer may help reduce surface water penetration and oxidation of the HMA surface, which in turn may help reduce long-term maintenance. The lift thickness should not exceed four times the nominal aggregate size of asphalt mix (NMAS).

Aggregate Base Course (ABC): ABC material should meet specifications in accordance with Class 6 ABC requirements in accordance with Section 703.03 of the CDOT Standard Specifications and have a minimum R-value of 78. The material should be placed and compacted in accordance with Section 304 of the CDOT Standard Specifications. The ABC should also be included below the sidewalks.

Subgrade Preparation: Artificial fill consisting predominantly of lean clay with variable amounts of sand with isolated areas of silt sand with gravel was encountered in our borings within the top five feet of the existing pavement. Debris was not encountered within the artificial fill in the exploratory borings; however, artificial fills can vary in thickness and composition and may include debris, organics, high plasticity clays, etc. which are not suitable for pavement support. Some of the existing granular soil may be suitable for pavement support; however, during roadway construction, the pavement subgrade should be checked thoroughly for debris, high plasticity clays, vegetation, or other deleterious material that may exist within the existing artificial fill. Soil encountered that contains deleterious or otherwise unsuitable material should be removed to a minimum depth of two feet below the base of the proposed pavement and replaced with Engineered Fill. The determination of the quality of the existing artificial fill and its potential reuse may need to be determined during construction.

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New Engineered Fill needed for support of the pavements should have similar or better strength characteristics with an AASHTO classification of A-6 or better, and a minimum R-value of 15. The Engineered Fill material should be placed and compacted in accordance with Section 203.07 of the CDOT Standard Specifications.

Granular soils are not recommended in the pavement subgrade without a filter separator layer and edge drains to collect and divert water away from the pavement. If swelling soils are encountered during construction, the upper two feet of the subgrade soils should be moisture conditioned and recompacted, based on Table 4.9 – Treatment of

Expansive Soils of the CDOT PDM. The top two feet of the subgrade soils supporting new pavements should be excavated, moisture conditioned to within -1% to +3% of optimum moisture content and compacted to at least 95% of the maximum standard Proctor dry density (AASHTO T-99).

Proof Roll: Prior to placing the pavement section including ABC, the upper eight inches of subgrade should be uniformly scarified and blended, moisture conditioned, and compacted as specified.