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CTL|Thompson, Inc.

Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County – Colorado

Cheyenne, Wyoming and Bozeman, Montana

Power Trail Underpass Fort Collins, Colorado

Prepared for:

Otak 371 Centennial Parkway Suite 210

Louisville, Colorado 80027

Attention:

Dan Beltzer

Project No. FC10823.000-125 Rev 1

June 30, 2023 (Revised June 30, 2023)

GEOTECHNICAL INVESTIGATION

EXHIBIT G

https://ctlthompson.com/ https://ctlthompson.com/denver https://www.ctlthompson.com/fortcollins https://www.ctlthompson.com/coloradosprings https://www.ctlthompson.com/glenwoodsprings https://www.ctlthompson.com/pueblo https://www.ctlthompson.com/summitcounty https://www.ctlthompson.com/cheyenne https://www.ctlthompson.com/bozeman

Table of Contents

OTAK

POWER TRAIL UNDERPASS

CTLT PROJECT NO. FC10823.000-125 rev 1

Scope 1

Summary Of Conclusions 1

Site Conditions 2

Proposed Construction 3

Previous Investigation 3

Investigation 3

Subsurface Conditions 4

Groundwater 4

Geologic Hazards 4

Seismicity 4

Site Development 5

Fill Placement 5 Excavations 7 Permanent Cut and Fill Slopes 7 Bracing 8 Dewatering 8

Foundations 9

Footings 9 Reinforced Concrete Mat 10 Drilled Shafts Socketed in Bedrock 11

Retaining Walls 14

Cantilever and MSE Walls 16 Soldier Pile Walls 16 Sheet Pile Walls 17 Laterally Loaded Sheet Piles 18

Wall and Box Drains 19

Flatwork 20

Water-Soluble Sulfates 20

Surface Drainage 22

Construction Observations / Additional Services 22

Geotechnical Risk 22

Limitations 23

EXHIBIT G

Table of Contents

CTLT PROJECT NO. FC10823.000-125

FIGURE 1 – LOCATION OF EXPLORATORY BORING

FIGURE 2 – SUMMARY LOG OF EXPLORATORY BORING

APPENDIX A – RESULTS OF LABORATORY TESTING

APPENDIX B – SAMPLE SITE GRADING SPECIFICATIONS

Scope

This report presents the results of our Geotechnical Investigation for the proposed box culvert underpass in Fort Collins, Colorado (Figure 1). The purpose of the investigation was to evaluate the subsurface conditions and provide geotechnical design and construction criteria for the project. The scope was described in a Service Agreement (No. FC-21-0611) dated November

17, 2021. Evaluation of the property for the presence of potentially hazardous materials was not included in our work scope.

The report was prepared from data developed during field exploration, field and laboratory testing, engineering analysis, and our experience. The report includes a description of subsurface conditions found in our exploratory boring and discussions of site development as influenced by geotechnical considerations. Our opinions and recommendations regarding design criteria and construction details for site development, foundations, lateral earth loads, pavements, and drainage are provided. The report was prepared for the exclusive use of OTAK and your team in design and construction of the proposed improvements. If the proposed construction differs from descriptions herein, we should be requested to review our recommendations. Our conclusions are summarized in the following paragraphs.

Summary Of Conclusions

1. Strata encountered in our boring generally consisted of sandy clay fill, sandy clays, and clayey sands over claystone bedrock. Claystone bedrock was encountered at a depth of approximately 28 feet and extended to the maximum depth explored.

Testing indicates the clay is not expansive.

2. Groundwater was measured at an approximate depth of 19 feet during drilling.

Groundwater levels may fluctuate seasonally and rise in response to precipitation, irrigation, and changes in land-use. Existing groundwater levels are not expected to significantly affect site development.

3. Footing or mat foundations placed on natural, undisturbed soil and/or properly compacted fill are recommended for the proposed construction. Design and construction criteria for foundations are presented in the report.

4. Some movement of slabs-on-grade should be anticipated. Based on the measured swell, we estimate potential heave of less than one inch.

5. Surface drainage should be designed, constructed, and maintained to provide rapid removal of surface runoff away from the proposed structure. Conservative irrigation practices should be followed to avoid excessive wetting.

Site Conditions

The site is located on Harmony Road near Innovation Drive in Fort Collins, Colorado

(Figure 1). The Union Pacific railroad crosses Harmony Road to the east of the project location and an electrical substation exists directly to the north. The site is relatively flat with a slight slope in the southward direction. The planned underpass construction will cross below the existing six lane Harmony Road. The area of the project exhibits mature development with commercial structures and significant subsurface utilities with landscaping consisting of grass turf, maintained beds, and trees.

Google Earth historical aerial photos indicate the project area has been relatively static since 1999 other than Harmony Road was widened from 4 to 6 lanes in early 2012.

Google Earth Aerial Photo, May 2023

Proposed Construction

We understand the proposed structure will be an underpass structure to connect Power

Trail across (below) Harmony Road. We understand this improvement will be constructed as a box culvert using cut and cover construction methods. Retaining walls and wing walls will be used at each end for grade transition. We anticipate surface grading changes will be minimal outside of the grade transition walls at each end of the box culvert.

Previous Investigation

A preliminary engineering report for this project was prepared by Lithos Engineering

(Project No. 18034, dated November 16, 2018). The report provided project scoping information and an evaluation of construction options for the underpass. The data, evaluations, and recommendations presented in that report were reviewed in preparation of this report.

Investigation

The field investigation included drilling and sampling one exploratory boring at the approximate location presented on Figure 1. The boring was drilled to a depth of approximately

30 feet using 4-inch diameter continuous-flight augers, and a truck-mounted drill rig. Drilling was observed by our field representative who logged the soils and bedrock and obtained samples for laboratory tests. A summary log of the exploratory boring, including results of field penetration resistance tests and a portion of laboratory test data, is presented as Figure 2.

Soil and bedrock samples obtained during drilling were returned to our laboratory and visually examined by our geotechnical engineer. Laboratory testing was assigned and included moisture content, dry density, swell-consolidation, particle-size analysis, Atterberg limits, unconfined compression, and water-soluble sulfate concentration. Swell-consolidation test samples were wetted at a confining pressure which approximated the pressure exerted by the overburden soils (overburden pressures). Results of the laboratory tests are presented in

Appendix A and summarized in Table A-I.

Subsurface Conditions

Strata encountered in our exploratory boring generally consisted of 22 feet of sandy clay over 6 feet of clayey sand. Claystone bedrock was encountered at 28 feet to the maximum depths explored. Samples of the clay soils tested indicated 0.1 percent compression to 0.5 percent swell.

Further descriptions of the subsurface conditions are presented on our boring log and in our laboratory test results.

Groundwater

Groundwater was measured at a depth of 19 feet during drilling. Groundwater levels may fluctuate seasonally and rise in response to precipitation, landscape irrigation, or changes in land-use. Groundwater is not currently expected to affect below-grade construction at the site.

Geologic Hazards

Our investigation addressed potential geologic hazards that should be considered during planning and construction. None of these hazards considered will preclude proposed construction. The following section discusses the primary geologic hazard and associated development concerns.

Seismicity

According to the USGS, Colorado’s Front Range and eastern plains are considered low seismic hazard zones. The earthquake hazard exhibits higher risk in western Colorado compared to other parts of the state. The Colorado Front Range area has experienced earthquakes within the past 100 years, shown to be related to deep drilling, liquid injection, and oil/gas extraction.

Naturally occurring earthquakes along faults due to tectonic shifts are rare in this area.

The soil and bedrock at this site are not expected to respond unusually to seismic activity.

The 2021 International Building Code (Section 16.13.2.2) defers the estimation of Seismic Site

Classification to ASCE7-22, a structural engineering publication. The table below summarizes

ASCE7-22 Site Classification Criteria.

ASCE7-22 SITE CLASSIFICATION CRITERIA

Seismic Site Class �̅�𝑠, Calculated Using Measured or Estimated

Shear Wave Velocity Profile (ft/s)

A. Hard Rock >5,000

B. Medium Hard Rock >3,000 to 5,000

BC. Soft Rock >2,100 to 3,000

C. Very Dense Sand or Hard Clay >1,450 to 2,100

CD. Dense Sand or Very Stiff Clay >1,000 to 1,450

D. Medium Dense Sand or Stiff Clay >700 to 1,000

DE. Loose Sand or Medium Stiff Clay >500 to 700

E. Very Loose Sand or Soft Clay ≥500

F. Soils requiring Site Response Analysis See Section 20.2.1

Based on the results of our investigation, the reduced, empirically estimated average shear wave velocity values for the upper 100 feet range between 806 and 952 feet per second with an average value of 887 feet per second. We judge a Seismic Site Classification of D. USGS indicates the following acceleration values for a Site Class D and Risk Categories of I/II/III/IV based on the requirements of the ASCE7-16:

SS = 0.19 g SMS = 0.24 g SDS = 0.16 g

S1 = 0.043 g SM1 = 0.093 g SD1 = 0.062 g

Refraction microtremor (ReMi) testing may indicate lower design acceleration values. The structural engineer should provide comments regarding the potential cost savings between the use of Site Class C and D for these structures. The subsurface conditions generally indicate low susceptibility to liquefaction from a materials and groundwater perspective.

Site Development

Fill Placement

The existing onsite soils are generally suitable for re-use as new fill from a geotechnical standpoint, provided debris or deleterious organic materials are removed. In general, import fill should meet or exceed the engineering qualities of the onsite soils. In addition, particles larger than 3 inches should be broken down or removed. If import material is used, it should be tested and evaluated for approval by CTL|Thompson.

Prior to fill placement, debris, organics/vegetation, and deleterious materials should be substantially removed from areas to receive fill. The surface should be scarified to a depth of at least 8 inches, moisture conditioned and compacted to the criteria below. Subsequent fill should be placed in thin (8 inches or less) loose lifts, moisture conditioned, and compacted. All fill should be placed according to the placement requirements listed in the table below. The fill should be moisture-conditioned, placed in thin, loose lifts (8 inches or less) and compacted as described above. Fill placement and compaction should not be conducted when fill material is frozen.

CTL|Thompson should observe placement and compaction of fill during construction.

SUMMARY OF FILL PLACEMENT REQUIREMENTS

Soil Classification (Unified and AASTO)

Depth of Fill (feet)

Minimum Compaction per Standard Proctor

(ASTM D 698)

Moisture Content From Optimum

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

0 to 15 > 15*

95 % 100 %

+1 to +4 -1 to +2

A-1 through A-5 (except A-2-6 and A-2-7)

CDOT Class 1 Fill

0 to 15 > 15*

95 % 100 %

-2 to +2 -2 to +2

* Portions of the fill deeper than 15 feet below proposed grade.

Site grading in areas of landscaping where no future improvements are planned can be placed at a dry density of at least 90 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Example site grading specifications are presented in Appendix B. The use of claystone as backfill for abutment walls or retaining walls is not encouraged. The claystone is expansive, more likely to compress over time and will result in higher lateral design pressures.

Our experience indicates fill and backfill can settle, even if properly compacted to the criteria above. Factors that influence the amount of settlement are depth of fill, material type, degree of compaction, amount of wetting, and time. The degree of compression of fill under its own weight will likely range from low for granular soils (0.5 percent or less), moderate for clay/sand mixtures (0.7 to 1.5 percent), and too high for highly plastic clay and claystone (1 to 2 percent or more).

Excavations

We believe the soil and bedrock penetrated in our exploratory boring can generally be excavated with conventional, heavy-duty excavation equipment. However, some of the soils are soft and will be displaced if wheeled equipment is used in the excavations. We recommend wheeled traffic not be allowed in the excavations.

Excavations should be sloped or shored to meet local, State, and Federal safety regulations. Excavation slopes specified by OSHA are dependent upon types of soil and groundwater conditions encountered. Based on our investigation and OSHA standards, we believe the soils at this site classify as Type B or Type C soils. Clays and sandy clays would generally classify as Type B and sands as Type C. Type B soils require a maximum slope inclination of 1:1 (horizontal:vertical) in dry conditions. Type C soils require a maximum slope inclination of 1.5:1 in dry conditions. Stockpiles of soils, rock, equipment, or other items should not be placed within a horizontal distance equal to one-half the excavation depth, from the edge of excavation. Excavations deeper than 20 feet should be braced, or a professional engineer should design the slopes.

Wind and water erosion is more likely with disturbed conditions expected during construction and may need to be addressed due to municipal regulation. The erosion potential will decrease after construction if proper grading practices, surface drainage design, and re-vegetation efforts are implemented.

Permanent Cut and Fill Slopes

We recommend permanent cut and fill slopes be designed with a maximum inclination of

3:1 (horizontal to vertical). Where fills will be placed on slopes exceeding 20 percent (5:1) the slope should be benched. Structures should be setback from the top or bottom of cut and fill slopes. If site constraints (property boundaries and streets) do not permit construction with recommended slopes, we should be contacted to evaluate the subsurface soils and steeper slopes. If increased resistance to erosion is desired, the soils can be stabilized using turf reinforcement matting. Seeding should also be used to reduce erosion.

Bracing

Bracing may be necessary for some of the excavations. Bracing systems could include driven sheet piling, soldier piles and lagging, and others. Lateral loading of bracing depends on the depth of excavation, slope of excavation above the bracing, soil stockpiles and other surface loads, hydrostatic pressures, and allowable movement.

For bracing allowed to move enough to mobilize the strength of the soils with associated settlement and cracking of the ground surface, “active” earth pressure conditions are appropriate for design. If movement is not tolerable, “at rest” earth pressures are appropriate. Equivalent fluid densities and L-Pile design values for lateral design are provided in the Lateral Earth Pressure section later in the report. Hydrostatic pressure and surcharge loads should be accounted for, where applicable.

The OSHA construction standard provides recommendations for timber bracing. We are also available to assist further with bracing design if desired. Bracing and/or slopes for excavations greater than 20 feet should be designed by a registered professional engineer.

Dewatering

Groundwater was encountered in our boring approximately 19 feet below the existing ground surface in the area of the planned crossing. Groundwater depths can vary with season and, depending on the time of construction, could be higher than measured in our boring. Based on current groundwater levels, we do not anticipate the planned excavations will encounter saturated soil and/or groundwater. If groundwater levels rise, compromised soil conditions may be encountered.

Underpass structures that will extend below groundwater (even if only seasonally) should consider permanent dewatering systems to prevent water collecting on the walking surface.

Drains may be needed along walls and/or under the box floor to collect and dispose of water.

Permanent drains are typically encouraged to be constructed to use gravity and outlet downhill of planned structures. These drain structures may also provide construction dewatering if installed first.

Construction excavations within approximately 2 feet of groundwater should consider temporary dewatering prior to and/or during construction. Dewatering within a few feet of the groundwater surface can usually be accomplished using a series of trenches and sumps. Deeper penetrations below the groundwater surface may require more comprehensive systems. The sumps should be several feet below the bottom of the excavation to pump water down through the soil rather than up through the bottom of the excavation. Pumping water up through the base of the excavation will likely result in destabilization of the base of the excavation. The ground surface surrounding the excavation should be sloped to direct runoff away from the excavation.

Foundations

We understand the underpass will likely be constructed as a concrete box structure. Box structures are typically constructed as shallow or mat foundations which are acceptable for this site. If spread footing foundations are not able to support the anticipated loads, deep foundations, such as drilled shafts, should be considered.

Wing walls will likely cantilever concrete walls or block walls. Generally, footing foundations should be acceptable for wall structures. If retaining walls, including wing walls, are integral with crossing structures, we recommend they be constructed on a similar foundation. If they are not integral with the structure and free to rotate, they may be founded on a different foundation type.

We understand this structure will be designed using LRFD methods. A resistance factor of 0.45 to 0.55 is commonly applied for shallow foundation design using LRFD methods. Factored bearing capacity is determined as qr= Φb qnn where Φb is the resistance factor and qnn is the unfactored bearing capacity. Design criteria for footing or mat foundations developed from analysis of field and laboratory data and our experience are presented below.

Footings

1. Footings should be constructed on natural, undisturbed soils or properly compacted fill (see Fill Placement). All existing, uncontrolled fill should be removed from under footings and within one footing width around footings and replaced with properly compacted fill. Any soft, loose, or poorly compacted fill is present in footing excavations, or are the result of the excavation/forming process, should be removed and recompacted or stabilized.

2. Footings should be designed for an ultimate (unfactored) soil pressure of 6,000 psf. The soil pressure can be increased 33 percent for transient loads such as wind or seismic loads.

3. We anticipate footings designed using the soil pressure recommended above could experience 1-inch of movement. Differential movement of ½- inch should be considered in the design.

4. Footings should have a minimum width of at least 12 inches. Foundations for isolated columns should have minimum dimensions of 16 inches by 16 inches. Larger sizes may be required depending on loads and the structural system used.

5. The soils beneath footing pads can be assigned an ultimate coefficient of friction of 0.4 to resist lateral loads. The ability of grade beam or footing backfill to resist lateral loads can be calculated using a passive equivalent fluid pressure of 250 pcf. This assumes the backfill is densely compacted and will not be removed.

Deflection of grade beams is necessary to mobilize passive earth pressure; we recommend a factor of safety of 2 for this condition. Backfill should be placed and compacted to the criteria in Fill Placement.

6. Exterior footings should be protected from frost action. We believe 30 inches of frost cover is appropriate for this site.

7. Foundation walls and grade beams should be well reinforced both top and bottom.

We recommend reinforcement sufficient to simply span 10 feet. The reinforcement should be designed by a structural engineer.

8. The completed foundation excavations should be observed by a representative of our firm to confirm subsurface conditions are as anticipated. Our representative should observe and test moisture and compaction of the fill and backfill.

9. Excessive wetting of foundation soils during and after construction can cause heave, or softening and consolidation, of foundation soils and result in footing movements. Proper surface drainage around the buildings is critical to control wetting.

Reinforced Concrete Mat

1. Reinforced concrete mat foundations should be constructed on natural, undisturbed soil and/or properly compacted fill or fill placed for an over-excavation as described in the SITE DEVELOPMENT section of this report. The reinforced concrete mat foundation should be designed for an ultimate (unfactored) soil pressure of 6,000 psf. The soil pressure can be increased 33 percent for transient loads such as wind or seismic loads.

2. Reinforced slabs are typically designed using a modulus of subgrade reaction. We recommend use of a modulus of 75 pounds per square inch per inch of deflection (pci).

3. The soils beneath mat foundations can be assigned an ultimate coefficient of friction of 0.4 to resist lateral loads. The ability of foundation backfill to resist lateral loads can be calculated using a passive equivalent fluid pressure of 250 pcf. This assumes the backfill is densely compacted and will not be removed. Backfill should be placed and compacted to the criteria in the Fill Placement section of the report. A moist unit weight of 120 pcf can be assumed for natural soils and compacted fill. These values are considered ultimate values and appropriate factors of safety should be used. Typically, a factor of safety of 1.5 is used for sliding and 1.6 for lateral earth pressure.

4. The edges of the mats should be thickened or turned down for structural strength and frost protection.

5. Materials beneath the mat foundation should be protected from frost action. We believe 30 inches of frost cover is appropriate for this site.

6. We should be retained to observe the completed excavations to confirm whether the subsurface conditions are similar to those found in our boring.

Drilled Shafts Socketed in Bedrock

Drilled shafts socketed in bedrock are usually designed to account for the nominal end bearing (tip) resistance plus the nominal side resistance along the shaft, neglecting the side resistance within the potential scour depth and the depth of shrinkage cracking. We recommend that the minimum shaft lengths be determined by referring to Section 10.8 of the AASHTO LRFD

Bridge Design Manual, 9th Edition. A summary of nominal end and side shear resistance are provided below. These criteria were developed from analysis of field and laboratory data and our experience. The foundation elements should be sized considering the side and end bearing resistances in the following table.

GEOTECHNICAL

DRILLED SHAFT AXIAL RESISTANCE

Subsurface Strata Ultimate

End Pressure (psf)

Ultimate Side Shear

(psf)

Clay and Sand Not an End Bearing Stratum Ignore Above Scour Line

Bedrock Claystone 50,000 5,000

The static shaft lengths and minimum bedrock penetration should be determined by the structural engineer considering the factored loads and ultimate (nominal) end pressure and side shear values provided in the table above. The recommended values were developed based on our experience and referencing CDOT Report No. CDOT-DTD-R-2003-6, Improvement of the

Geotechnical Axial Design Methodology for Colorado’s Drilled Shafts Socketed in Weak Rocks, dated July 2003. The 2003 CDOT report provides recommendations for the use of an updated

Colorado SPT-based (UCSB) design method, in which the nominal tip and side resistance of a drilled shaft in sedimentary bedrock is proportional to the driven sampler penetration resistance, i.e., N-value. The following tabulated resistance factors should be applied by the structural engineer.

LRFD STATIC ANALYSIS

RESISTANCE FACTORS

DRILLED SHAFTS

Subsurface Material Resistance Type Static Resistance Factor

(phi)

Bedrock Claystone Side 0.60

End/Tip 0.55

It can be beneficial to verify the axial resistance of drilled shafts by static load testing. Side resistance and end resistance values obtained from load tests allow use of a higher resistance factor. A higher resistance factor can result in shorter foundation lengths to resist axial loads than those predicted from static analysis methods. The table below includes the resistance factors from load testing of drilled shafts (AASHTO LRFD Bridge Design Specifications, 9th Edition).

LRFD LOAD TEST

RESISTANCE FACTORS

DRILLED SHAFTS

Method of Capacity Determination (Load Tests)

Resistance Factor (phi)

Static Load Test, Compression 0.7

Static Load Test, Tension 0.6

We recommend the following design and construction criteria be incorporated into the construction documents.

1. The ultimate end and side shear pressures presented in the table should be appropriately factored by the structural engineer to be used for design.

2. Scour depths will impact the design of foundations. The side resistance along the foundation segment within the depth of scour should be ignored.

3. Side resistance should be ignored in the upper 3 feet below the top of shaft due to the potential for soil shrinkage away from the shaft and the subsequent loss in geotechnical resistance.

4. Shafts should have a minimum bedrock socket length of 5 feet. Longer shafts may be necessary based on structural and scour considerations.

5. Shafts should be reinforced their full length and the reinforcement should extend an adequate distance into abutment walls and shaft caps. More reinforcement may be required for structural considerations. The structural engineer should design the steel reinforcement.

6. Shaft drilling should produce shafts with relatively undisturbed bedrock exposed.

Excessive remolding and caking of bedrock on shaft walls must be removed. The bedrock surface along the shaft walls should be rough or roughened.

7. Shafts should have a center-to-center spacing of at least three pier diameters for a single row of shafts and four diameters for a multiple-row group, or they should be designed as a group for vertical loading conditions. Shafts aligned in the direction of lateral forces should have a center-to-center spacing of at least six pier diameters. Reduction factors for closely-spaced piers are provided in later paragraphs.

8. Shafts should be cleaned prior to placement of concrete. Groundwater was encountered during our investigation and will likely be found during installation of drilled piers. Temporary casing may be necessary where groundwater and granular soil are present. We anticipate the use of casing at the north abutments at both roadways. If excessive water develops (more than about 3 inches at time of placement), the holes may require pumping or underwater concrete placement.

Concrete should not be placed by free-fall in shaft holes containing more than 3 inches of water. If less than 3 inches of water is in the bottom of the shaft and concrete placement by free-fall is desired, the structural engineer should specify the maximum free-fall distance.

9. Concrete should be on-site and placed in the shaft holes immediately after the holes are drilled, cleaned, and observed and reinforcing steel is set. Concrete placed in pier holes should have a slump of 6 inches ( 1 inch) to promote proper consolidation and reduce arching of concrete on the reinforcement, casing, and sides of the piers.

10. Some shaft-drilling contractors use casing with an O.D. equal to the specified shaft diameter. This practice results in a shaft diameter less than specified. The shaft design and specifications should consider the alternatives. If full-size casing is desired (I.D. of casing equal to specified pier diameter) it should be clearly specified. If the design considers the potential reduction in diameter, then the specifications should include a tolerance for a smaller diameter for cased piers.

11. Some movement of drilled shaft foundations should be anticipated to mobilize the skin friction. We estimate the movement will be on the order of ¼ to ½-inch.

Differential movement between adjacent shafts may equal total movement.

12. Installation of drilled shafts should be observed by a representative of our firm to identify the bearing strata, confirm the subsurface conditions are as anticipated from our borings, and observe contractor’s installation procedures.

Retaining Walls

We understand retaining walls and/or wing walls will be associated with the trail and underpass structures. Retaining walls that are not integral with the underpasses would be free to rotate sufficiently to mobilize the strength of the backfill and can be designed for the "active" earth pressure. If the walls are integral with the underpasses and cannot rotate, they should be designed for the "at rest" earth pressure. Equivalent fluid densities for lateral design are provided in the Lateral Earth Pressures section below. Unbalanced hydrostatic pressure behind a wall caused by differential water levels across the wall can be relieved by providing weep holes through the walls or drains behind the walls. Weep holes may cause staining on the visible surface of the wing walls; therefore, we suggest using drains such as discussed below.

If retaining walls are integral with the underpass or abutments, they should be founded on a similar foundation system. Foundation recommendations and construction criteria are presented in the Foundations section of this report. A drain should be provided behind all walls, both cantilever and soldier pile. Additional information and recommendations are provided in the

Wall and Box Drains section.

Abutment Walls

Abutment walls will be restrained at the bottom by the foundations and should not rotate enough to apply load to the bridge; therefore, we recommend designing the abutments using an

“at-rest” pressure. Vehicle surcharges above the abutments will add to the lateral earth pressures and should be calculated by the structural engineer. Appropriate LRFD load factors should be applied to the lateral earth pressures.

Thermal movement (expansion and contraction) of the bridge girders can deflect abutments and result in lateral earth pressures on the abutments that can engage the passive resistance. Thermal movement and the resulting pressures on abutment walls should be considered in the design. Ideally, the structural engineer should detail the girder-abutment connection to absorb this movement so that additional pressure will not be subjected on to the abutment walls. The passive resistance can be used to evaluate backfill resistance to girder expansion.

Cantilever and MSE Walls

Site retaining walls, such as cast-in-place (CIP) concrete or mechanically stabilized earth

(MSE), can be constructed on footing foundations, however, some movement is possible for footings constructed on expansive soil. For mechanically stabilized earth (MSE) wall design, we recommend using a friction angle of 25 degrees and no cohesion for the retained soil. We recommend an imported granular soil be used as backfill within the reinforced zone behind the walls.

Walls may be subjected to lateral loading. Lateral loads are dependent on the height and type of wall, backfill configuration, and backfill type. For purposes of design, we have assumed backfill will consist of onsite soils. Lateral design values are presented in Lateral Earth Pressures.

If imported granular soil is used, it should have properties meeting the requirements of CDOT

Class 6 Road Base when used as backfill, the equivalent fluid density can be reduced to 35 pcf.

These values are for dry conditions. We recommend appropriate hydrostatic pressure be included in the design. Drains should be installed to help control hydrostatic pressures as presented in

Wall and Box Drains.

The top 2 feet of exterior backfill behind walls should be clayey soils to reduce water infiltration. Backfill behind retaining walls should be placed in thin, loose lifts; moisture conditioned and compacted. Settlement on the order of 1 to 2 percent of the backfill depth may occur;

improvements constructed over backfill should be designed to perform considering anticipated settlements.

Soldier Pile Walls

Where tall walls or high lateral loads must be accommodated, soldier pile walls are an option provided a soldier pile and lagging system is a suitable alternative for wing walls at this site provided durable lagging materials are selected. For this project, soldier piles are anticipated to be constructed as drilled shafts. Depending on the height of the wall, tie backs may be necessary.

Special techniques may be required for proper installation. Soldier pile construction/installation should follow the Drilled Shaft section.

Sheet Pile Walls

While more commonly employed as a temporary shoring solution, a sheet pile is a suitable alternative for wing walls at this site. We understand the sheet piles may be covered with cast concrete or shotcrete. Depending on the height of the wall and the refusal depth of the piles, tie backs may be necessary. Special techniques may be required for proper installation. Based on the depth to bedrock at this site, we anticipate sheet piles would be installed with a vibratory hammer system.

Lateral Earth Pressures

The lateral loads acting on the underpass walls and wing walls are dependent on the height and type of wall, backfill configuration, and backfill type. For the purposes of this report, we have assumed less than 15 feet of fill will be retained by retaining walls, wing walls, and the underpass structure and the backfill will be onsite or similar soils. If taller retaining walls are necessary for the project, our office should be contacted to evaluate plans and develop recommendations.

All walls should be designed to resist lateral earth pressures that act upon the wall. The following table provides the necessary equivalent fluid pressure values for the backfill soils anticipated at this site. The pressures given do not include allowances for surcharge loads such as sloping backfill, vehicle traffic, or excessive hydrostatic pressure. These values also do not include a factor of safety. Normally, a factor of safety of 1.5 is used for sliding and 1.6 for lateral earth pressure. For design purposes, compacted fill above the box can be considered at 125 pcf.

Loading Condition Equivalent

Hydrostatic Fluid Pressure

Lateral Earth Pressure

Coefficient

Active (A) pcf 50 0.45

At-Rest (o) pcf 65 0.50

Passive (p) pcf 250 2.50

Horizontal Friction Coefficient 0.30

The appropriate load distribution to apply for design depends not only on the soil type, but also on the wall type and restraint. For retaining walls and wing walls that are integral to the underpass and restrained from rotation, the walls should be designed to resist the “at rest” earth pressure. For walls, which are free to rotate to develop the shear strength of the retained soils, such as retaining walls and wing walls not integral to the underpass, the walls should be designed to resist the “active” earth pressure. Resistance to lateral loads can be provided by friction between concrete and soil and/or by “passive” earth pressure. Passive earth pressure should be ignored for the top one foot of soils against the structure since it can be removed easily with time.

The proper application of these loading conditions is the responsibility of the wall designer. Wall backfill should be placed according to the Fill Placement section.

Hydrostatic pressure and surcharge loads should be accounted for, where applicable.

Drains can be installed behind earth retaining structures to minimize hydrostatic pressures exerted on the structures. Recommendations for drain construction are provided in the Wall and

Box Drains section of this report.

Laterally Loaded Sheet Piles

Lateral load analysis of sheet piles can be performed with the software analysis package

LPILE by Ensoft, Inc. We believe this method of analysis is appropriate for sheet piles and soldier piles with a pile length to width ratio of seven or greater, as the p-y models were developed using similar flexible deep foundations. Suggested criteria for LPILE analysis are presented in the following table. While sheet piles are not anticipated to be installed deep enough to interact with bedrock, values for bedrock are provided for completeness.

SOIL INPUT DATA FOR “LPILE”

Soil Type Sand Clay Bedrock p-y Curve Type Reese Sand Mod. Stiff

Clay Weak Rock

Effective Unit Weight Above Water Table

(pcf) 125 120 -

Effective Unit Weight Submerged

(pcf)

62.6 57.6 110

Friction Angle ϕ(degree)

25 - -

Undrained Cohesion c (psf)

-- 1500 10,000

Strain Factor, ε50 or krm

- 0.01 0.0005 p-y Modulus ks (pci)

50 250 -

Uniaxial Compressive

Strength qu (psi)

- - 150

Initial Modulus of Rock Mass

(psi)

- - 2 x 104

RQD

- - 90

Wall and Box Drains

A drain should be provided below the underpass and behind the retaining walls to remove accumulated water. We recommend using a gravel mix consisting of 50 percent fine and 50 percent course concrete aggregate (by weight) for the drain. The drain gravel mix should be placed in at least a 12-inch layer against the walls of the underpasses and behind the retaining walls to within 2 feet of the top of the underpass. Compacted clays should be placed from the top of the drain to the ground surface. At least 6 inches of gravel drain should be placed under the box "mat" or floor and be connected to the drain against the walls. As an alternative to gravel along the walls, an equivalent drain board can be substituted.

We recommend a minimum 3-inch diameter perforated pipe be placed at the bottom of the drain gravel along the retaining walls and underpass walls. The invert of the pipe should be at least 6 inches below the elevation of the floor and sloped slightly to drain. The pipe should extend the full length of the box and wing walls, and drain by gravity to an outfall.

If used, weep holes should be 4 inches in diameter, spaced 10 feet center-to-center at the bottom of the wall. At least two weep holes should be provided per wall at the bottom of the wall.

The back of the weep holes should connect to the drain, be protected from clogging, and be screened to prevent drain materials from falling out of the weep holes. A manufactured drain such as Miradrain could be substituted for the drain sand and gravel. Manufactured drains should be installed following the manufacturer’s recommendations.

Flatwork

We recommend exterior flatwork and sidewalks be isolated from foundations and walls to reduce the risk of transferring heave, settlement, or freeze-thaw movement to the structure. One alternative to maintain surface elevations and not adversely load adjacent structures would be to construct the inner edges of the flatwork on haunches or steel angles bolted to the foundation walls and detailing the connections such that movement will cause less distress to the structure, rather than tying the slabs directly into the foundation. Construction on haunches or steel angles and reinforcing the sidewalks and other exterior flatwork will reduce the potential for differential settlement and better allow them to span across wall backfill. Frequent control joints should be provided to reduce problems associated with shrinkage. Panels that are approximately square perform better than rectangular areas.

Water-Soluble Sulfates

Concrete in contact with soil can be subject to sulfate attack. We measured water-soluble sulfate concentrations of less than 0.01 percent in one sample. As indicated in our tests and ACI

318-19, the sulfate exposure class is Not Applicable or S0. Deviations from the exposure class may occur as a result of additional sampling and testing.

SULFATE EXPOSURE CLASSES PER ACI 318-19

Exposure Classes Water-Soluble Sulfate (SO4) in Soil A

Not Applicable S0 < 0.10

Moderate S1 0.10 to 0.20

Severe S2 0.20 to 2.00

Very Severe S3 > 2.00 A) Percent sulfate by mass in soil determined by ASTM C1580

For this level of sulfate concentration, ACI 318-19 Code Requirements indicates there are no cement type requirements for sulfate resistance as indicated in the table below.

CONCRETE DESIGN REQUIREMENTS FOR SULFATE EXPOSURE PER ACI 318-19

Exposure Class

Maximum Water/

Cement Ratio

Minimum Compressive

Strength (psi)

Cementitious Material Types A

Calcium Chloride

Admixtures

ASTM

C150/ C150M

ASTM

C595/ C595M

ASTM

C1157/ C1157M

S0 N/A 2500 No Type

Restrictions No Type

Restrictions

No Type

Restrictions

No Restrictions

S1 0.50 4000 IIB

Type with

(MS)

Designation

MS

No

Restrictions

S2 0.45 4500 V B Type with

(HS)

Designation

HS

Not

Permitted

S3 Option 1 0.45 4500

V + Pozzolan or

Slag Cement C

Type with

(HS)

Designation plus

Pozzolan or Slag

Cement C

HS +

Pozzolan or

Slag Cement C

Not Permitted

S3 Option 2 0.4 5000 V D Type with

(HS)

Designation

HS

Not

Permitted

A) Alternate combinations of cementitious materials shall be permitted when tested for sulfate resistance meeting the criteria in section 26.4.2.2(c).

B) Other available types of cement such as Type III or Type I are permitted in Exposure Classes S1 or S2 if the C3A contents are less than 8 or 5 percent, respectively.

C) The amount of the specific source of pozzolan or slag to be used shall not be less than the amount that has been determined by service record to improve sulfate resistance when used in concrete containing Type V cement. Alternatively, the amount of the specific source of the pozzolan or slab to be used shall not be less than the amount tested in accordance with ASTM C1012 and meeting the criteria in section 26.4.2.2(c) of ACI 318.

D) If Type V cement is used as the sole cementitious material, the optional sulfate resistance requirement of

0.040 percent maximum expansion in ASTM C150 shall be specified.

Superficial damage may occur to the exposed surfaces of highly permeable concrete, even though sulfate levels are relatively low. To control this risk and to resist freeze-thaw deterioration, the water-to-cementitious materials ratio should not exceed 0.50 for concrete in contact with soils that are likely to stay moist due to surface drainage or high-water tables.

Concrete should have a total air content of 6 percent ± 1.5 percent. We advocate damp-proofing of all foundation walls and grade beams in contact with the subsoils.

Surface Drainage

Performance of foundations, flatwork, and pavements is influenced by changes in subgrade moisture conditions. Carefully planned and maintained surface grading can reduce the risk of wetting of the foundation soils and pavement subgrade. Backfill around foundations should be moisture treated and compacted as described in Fill Placement.

Construction Observations / Additional Services

This project will involve many activities that should be monitored during the construction phase by a geotechnical engineering firm. To provide continuity between design and construction, CTL|Thompson, Inc. should provide these services. Other observations are recommended to review general conformance with design plans. If another firm is selected to provide these services, they must accept responsibility to evaluate whether conditions exposed during construction are consistent with findings in this report and whether design recommendations remain appropriate. When construction schedules and quantities are defined, we can develop an appropriate scope of services and budget for construction observation and materials testing.

Geotechnical Risk

The concept of risk is an important aspect with any geotechnical evaluation, primarily because the methods used to develop geotechnical recommendations do not comprise an exact science. We never have complete knowledge of subsurface conditions. Our analysis must be tempered with engineering judgment and experience. Therefore, the recommendations presented in any geotechnical evaluation should not be considered risk-free. Our recommendations represent our judgment of those measures that are necessary to increase the chances that the structures and improvements will perform satisfactorily. It is critical that all recommendations in this report are followed during construction. Owners or property managers must assume responsibility for maintaining the structures and use appropriate practices regarding drainage and landscaping. Improvements after construction, such as construction of additions, retaining walls, landscaping, and exterior flatwork, should be completed in accordance with recommendations provided in this report and may require additional soil investigation and consultation.

Limitations

This report has been prepared for the exclusive use of Otak, and the design team for the project, to provide geotechnical design and construction criteria for the proposed project. The information, conclusions, and recommendations presented herein are based upon consideration of many factors including, but not limited to, the type of construction proposed, the geologic setting, and the subsurface conditions encountered. The conclusions and recommendations contained in the report are not valid for use by others. Standards of practice evolve in the area of geotechnical engineering. The recommendations provided are appropriate for about three years.

If the proposed construction is not constructed within about three years, we should be contacted to determine if we should update this report.

Our boring was located to obtain a reasonably accurate picture of subsurface conditions at this site. The boring is representative of conditions encountered only at the location drilled.

Subsurface variations not indicated by our boring are possible. We believe this investigation was conducted with that level of skill and care ordinarily used by geotechnical engineers practicing under similar conditions. No warranty, express or implied, is made.

If we can be of further service in discussing the contents of this report, or in the analysis of the influence of subsurface conditions on design of the structures or any other aspect of the proposed construction, please call.

CTLTHOMPSON, INC.

Alex Leadbetter R.B. “Chip” Leadbetter, III, PE Staff Geotechnical Engineer Senior Engineer

TH-1

HARMONY ROAD

IN

N

O

VA

TI

O

N D

R

IV

E

OAKRIDGE DRVE

M cM

U R

R Y

AV

E. E. HARMONY RD.

IN

N

O

VA

TI

O

N D

R

.MONTE CARLO DR.

S

TI

M

BE

R

LI

N E

R D

SITE

LEGEND:

INDICATES APPROXIMATE

LOCATION OF EXPLORATORY

BORING

TH-1

FIGURE 1

Locations of Exploratory Borings

VICINITY MAP

(FORT COLLINS, COLORADO)

NOT TO SCALE

175'87.5'

APPROXIMATE

SCALE: 1" = 175'

0'

OTAK

POWER TRAIL UNDERPASS

CTL I T PROJECT NO. FC10823-125 REV 1

9/12

WC=22.2

DD=102

SW=-0.1

SS=<0.01

8/12

WC=9.0

DD=123

UC=3,465

10/12

WC=21.3

DD=105

LL=36 PI=22

-200=84

10/12

WC=16.7

DD=113

SW=0.5

8/12

9/12

50/8

TH-1

FILL, CLAY, SANDY, MOIST, MEDIUM STIFF, BROWN

(CL)

LEGEND:

SAND, CLAYEY, SLIGHTLY GRAVELLY TO GRAVELLY,

VERY MOIST, LOOSE, BROWN (SC)

CLAY, SLIGHTLY SANDY TO SANDY, MOIST, MEDIUM

STIFF TO STIFF, BROWN (CL)

DRIVE SAMPLE. THE SYMBOL 9/12 INDICATES 9

BLOWS OF A 140-POUND HAMMER FALLING 30 INCHES

WERE REQUIRED TO DRIVE A 2.5-INCH O.D. SAMPLER

12 INCHES.

Boring

NOTES:

THE BORING WAS DRILLED ON MAY 18TH, 2020 USING

4-INCH DIAMETER CONTINUOUS-FLIGHT AUGERS AND

A TRUCK-MOUNTED DRILL RIG.

THESE LOGS ARE SUBJECT TO THE EXPLANATIONS,

LIMITATIONS AND CONCLUSIONS IN THIS REPORT.

3.

WATER LEVEL MEASURED AT TIME OF DRILLING.

1.

2.

Exploratory Summary Log of

FIGURE 2

WC

DD

SW

-200

LL

PI

UC

SS

D E

P T

H

F E

E T

D E

P T

H

F E

E T

INDICATES MOISTURE CONTENT (%).

INDICATES DRY DENSITY (PCF).

INDICATES SWELL WHEN WETTED UNDER

APPROXIMATE OVERBURDEN PRESSURE (%).

INDICATES PASSING NO. 200 SIEVE (%).

INDICATES LIQUID LIMIT.

INDICATES PLASTICITY INDEX.

INDICATES UNCONFINED COMPRESSIVE STRENGTH (psf).

INDICATES SOLUBLE SULFATE CONTENT (%).

CLAYSTONE, SANDY, SILTY, MOIST, HARD, BROWN,

GREY

OTAK

POWER TRAIL UNDERPASS

CTL | T PROJECT NO. FC10823.000-125 REV 1

APPENDIX A

RESULTS OF LABORATORY TESTING

Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT= 102 PCF

From TH - 1 AT 2 FEET MOISTURE CONTENT= 22.2 %

Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT= 113 PCF

From TH - 1 AT 14 FEET MOISTURE CONTENT= 16.7 %

APPLIED PRESSURE - KSF

C O

M P

R E

S S

IO

N

E

X P

A N

S

IO

N

Swell Consolidation

FIGURE A-1

C O

M P

R E

S S

IO

N

E

X P

A N

S

IO

N

-4

-3

-2

-1

REDNUNOSSIPREMNAL COIOTDIDA

TOUENT PREATSN E DSURSOC

GNTIEW T

0.1 10 1001.0

0.1 1.0 10 100

APPLIED PRESSURE - KSF

-4

-3

-2

-1

TNSTAONER CION UNDANSPXE

GINTETWTOP RE DUESSUER

OTAK

POWER TRAIL UNDERPASS

CTL | T PROJECT NO. FC10823-125 REV 1

Sample of CLAY, SANDY (CL) GRAVEL 0 % SAND

From LOT 19, BLOCK 5 AT 24 FEET SILT & CLAY LIQUID LIMIT %

PLASTICITY INDEX %

Sample of SAND, GRAVELLY (SP) GRAVEL 0 % SAND #### %

From LOT 30, BLOCK 5 AT 19 FEET SILT & CLAY % LIQUID LIMIT %

PLASTICITY INDEX %

Gradation

Test Results

0.002

15 MIN.

.005

60 MIN.

.009

19 MIN.

.019

4 MIN.

.037

1 MIN.

.074

*200

.149

*100

.297

*50

0.42

*40

.590

*30

1.19

*16

2.0

*10

2.38

*8

4.76

*4

9.52

3/8"

19.1

3/4"

36.1

1½"

76.2

3"

5"

6"

8"

.001

45 MIN.

CLAY (PLASTIC) TO SILT (NON-PLASTIC)

SANDS

FINE MEDIUM COARSE

GRAVEL

FINE COARSE COBBLES

DIAMETER OF PARTICLE IN MILLIMETERS

25 HR. 7 HR.

HYDROMETER ANALYSIS SIEVE ANALYSIS

TIME READINGS U.S. STANDARD SERIES CLEAR SQUARE OPENINGS

P E

R C

E N

T P

A S

S

IN

G

P E

R C

E N

T R

E T

A

IN

E D

0.002

15 MIN.

.005

60 MIN.

.009

19 MIN.

.019

4 MIN.

.037

1 MIN.

.074

*200

.149

*100

.297

*50

0.42

*40

.590

*30

1.19

*16

2.0

*10

2.38

*8

4.76

*4

9.52

3/8"

19.1

3/4"

36.1

1½"

76.2

3"

5"

6"

8"

.001

45 MIN.

CLAY (PLASTIC) TO SILT (NON-PLASTIC)

SANDS

FINE MEDIUM COARSE

GRAVEL

FINE COARSE COBBLES

DIAMETER OF PARTICLE IN MILLIMETERS

25 HR. 7 HR.

HYDROMETER ANALYSIS SIEVE ANALYSIS

TIME READINGS U.S. STANDARD SERIES CLEAR…