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HomeMy WebLinkAboutSCHOOLSIDE PARK - BDR240009 - SUBMITTAL DOCUMENTS - ROUND 3 - Geotechnical (Soils) Report (2) CTL|Thompson, Inc. Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County – Colorado Cheyenne, Wyoming and Bozeman, Montana Bacon Park Improvements Timberline Road and Zephyr Road Fort Collins, Colorado Prepared for: City of Fort Collins Park Planning & Development P.O. Box 580 215 North Mason Street Fort Collins, Colorado 80522-0580 Attention: Jennifer Torrey Project No. FC10837.001-125 April 10, 2024 GEOTECHNICAL INVESTIGATION Table of Contents Scope 1 Summary Of Conclusions 1 Site Conditions 2 Previous Investigation 3 Proposed Construction 3 Investigation 3 Subsurface Conditions 4 Groundwater 4 Geologic Hazards 4 Expansive Soils 5 Seismicity 5 Site Development 6 Fill Placement 6 Excavations 7 Over-Excavation 7 Foundations 8 Footings 9 Reinforced Concrete Mat 10 Below Grade Areas 10 Floor Systems 10 Exterior Flatwork 12 Pavements 12 Pavement Selection 13 Subgrade and Pavement Materials and Construction 14 Pavement Maintenance 14 Water-Soluble Sulfates 14 Surface Drainage 15 Construction Observations / Additional Services 16 Geotechnical Risk 16 Limitations 16 FIGURE 1 – LOCATIONS OF EXPLORATORY BORINGS FIGURE 2 – SUMMARY LOGS OF EXPLORATORY BORINGS APPENDIX A – RESULTS OF LABORATORY TESTING APPENDIX B – SAMPLE SITE GRADING SPECIFICATIONS APPENDIX C – PAVEMENT CONSTRUCTION RECOMMENDATIONS APPENDIX D – PAVEMENT MAINTENANCE PROGRAM CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 1 Scope This report presents the results of our Geotechnical Investigation for the proposed Bacon Park with shade structures, restrooms, playground, basketball court, and parking lot in Fort Collins, Colorado (Figure 1). The purpose of this 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-24-0014) dated January 12, 2024. Evaluation of the property for the presence of potentially hazardous materials was not included in our work scope. This report was prepared from data developed during field exploration, field and laboratory testing, engineering analysis, and our experience. This report includes a description of subsurface conditions found in our exploratory borings and discussions of site development as influenced by geotechnical considerations. Our opinions and recommendations regarding design criteria and construction details for site development, floor systems, slabs-on-grade, pavements, and drainage are provided. This report was prepared for the exclusive use of the City of Fort Collins Park Planning & Development 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 borings generally consisted of sandy clay. Bedrock was not encountered in any of the four borings during this investigation. Testing indicates the clay is expansive. 2. Groundwater was measured at approximate depths ranging from 14 to 18 feet in three borings during drilling. When measured several days later, groundwater was encountered at depths of 13 to 16½ feet in four borings. Groundwater levels may fluctuate seasonally and rise in response to precipitation, irrigation, changes in land-use, and water levels in the nearby Mail Creek Ditch. Existing groundwater levels are not expected to affect site development. 3. We judge there is a low risk of heave on this site upon post-construction wetting. The presence of expansive soils constitutes a geologic hazard. There is a risk that slabs-on-grade will experience heave or settlement and be damaged. We believe the recommendations presented in this report will help control the risk of damage; they will not eliminate that risk. Over-excavation is a ground improvement technique that can be considered to reduce potential movements to tolerable levels. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 2 4. Some movement of slab-on-grade floors should be anticipated. Based on the measured swell, we estimate potential heave of 1½ inches or less. If the owner cannot accept the risks of potential movements, over-excavation can be selected to reduce potential movements. Alternatives are discussed in this report. 5. Surface drainage should be designed, constructed, and maintained to provide rapid removal of surface runoff away from the proposed structures. Conservative irrigation practices should be followed to avoid excessive wetting. 6. Samples of the subgrade soils generally classified as AASHTO A-7, with a group index of 6. For the parking lot, we recommend 4 inches of asphalt over 8 inches of aggregate base course. Thicker sections are recommended for areas with heavier traffic. Pavement subgrade will need to be stabilized to mitigate high-swelling soils. Site Conditions The site is located north of Zephyr Road and on the east side of South Timberline Road, at Bacon Park in Fort Collins, CO (Figure 1). The vacant 6-acre lot slopes down gradually to the southeast. There is a house located on the north end of the property. Mail Creek Ditch forms the northeastern boundary of the property. At the time of our drilling, overlot grading was at or near finished grade. The ground has been stripped of any vegetation. Google Earth historical aerial photos indicate the property was previously developed with a farmstead and support structures, with a crop field to the south (Photo 1). The farmland has been vacated and earthwork for the proposed park has begun. Photo 1 – Google Earth Aerial Photo, June 2021 CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 3 Previous Investigation CTL|Thompson performed a Geotechnical Investigation for improvements to the Mail Creek Trail under CTL|Thompson Project No. FC10837.000-125, dated July 24, 2023. That report was reviewed in preparation for writing this report. Proposed Construction We understand the proposed improvements will include shaded picnic structures with concrete slab floors, restrooms, playground, basketball court, and a parking lot. No below grade construction is planned. A paved parking lot and access drive(s) are planned, and buried utilities will be constructed. We anticipate minimal additional site grading will be necessary. A general layout of the planned improvements is provided below. Development Plan Investigation The field investigation included drilling and sampling four exploratory borings at the approximate locations presented on Figure 1. The borings were drilled to depths of approximately 20 to 25 feet using 4-inch diameter continuous-flight augers and a truck-mounted drill rig. Drilling CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 4 was observed by our field representative who logged the soils, estimated groundwater levels, and obtained samples for laboratory tests. Summary logs of the exploratory borings, including results of field penetration resistance tests and a portion of laboratory test data, are presented on Figure 2. Soil 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, 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 borings generally consisted of sandy clay. The clay was medium stiff to stiff based on the results of field penetration resistance tests. Bedrock was not encountered in any of the borings. Samples of the clay soils tested indicated nil to 3.4 percent swell when wetted under applied approximate overburden pressures. Further descriptions of the subsurface conditions are presented on our boring logs and in our laboratory test results. Groundwater Groundwater was estimated at depths ranging from 14 to 18 feet in three borings during drilling. When measured several days later, water was measured at depths of 13 to 16½ feet in all four borings. Groundwater levels may fluctuate seasonally and rise in response to precipitation, landscape irrigation, changes in land-use, or changes in water levels in the nearby Mail Creek Ditch. Geologic Hazards Our investigation addressed potential geologic hazards, including expansive soils and seismicity, that should be considered during planning and construction. None of these hazards considered will preclude the proposed construction. The following sections discuss each of these geologic hazards and associated development concerns. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 5 Expansive Soils Expansive soils are present at the site which constitutes a geologic hazard. There is a risk that ground heave will damage slabs-on-grade and foundations. The risks associated with swelling soils can be mitigated, but not eliminated, by careful design, construction, and maintenance procedures. We believe the recommendations in this report will help control risk of slab damage; they will not eliminate that risk. 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 soils 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 𝑣̅𝑠, 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 700 and 1,000 feet per second. We judge a Seismic Site Classification of D. The field penetration test results along with the empirical estimates imply that shear-wave velocity seismic tests to directly measure 𝒗̅𝒔 could result in a better Seismic Site Classification. The subsurface conditions indicate low susceptibility to liquefaction from a materials and groundwater perspective. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 6 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. Fill should be compacted to a dry density of at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Fill depths greater than 15 feet should be evaluated by CTL|T to recommend appropriate compaction specifications. Clay soils should be moistened between optimum and 3 percent above optimum moisture content. The fill should be moisture-conditioned, placed in thin, loose lifts (8 inches or less) and compacted as described above. We should observe placement and compaction of fill during construction. Fill placement and compaction should not be conducted when fill material is frozen. CTL|Thompson should observe placement and compaction of fill during construction. 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. Water and sewer lines are often constructed beneath areas where improvements are planned. Compaction of trench backfill can have a significant effect on the life and serviceability overlying structures. We recommend trench backfill be moisture conditioned and compacted as described above. Placement and compaction of backfill should be observed and tested by a representative of our firm during construction. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 7 Excavations We believe the soil penetrated in our exploratory borings can generally be excavated with conventional, heavy-duty excavation equipment. 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. The contractor’s “competent person” is responsible to identify the soils and/or rock encountered in excavations and refer to OSHA standards to determine appropriate slopes and safety measures. Based on our investigation and OSHA standards, we believe the clay soils may classify as Type C. 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. Over-Excavation Relatively higher swelling clay materials were found in areas that have not been modified by construction activity. Potential ground heave could be as much as 1 to 2 inches with typical post-construction wetting. If these movements cannot be tolerated, over-excavation should be considered. If the risk of movement of footing foundations needs to be reduced, we recommend over-excavating to a uniform depth of at least 4 feet below foundations and floors to reduce potential heave to generally acceptable levels and provide more uniform support conditions. The existing soils are suitable for re-use as new fill from a geotechnical standpoint, provided it is moisture conditioned and compacted. Over-excavation should extend at least 5 feet outside the lateral extent of foundations. Provided that the over-excavation fill is low swelling, we estimate potential movements of about 1-inch or less are probable, provided excessive wetting does not occur. Differential movements should also be substantially reduced, as the fill is expected to act as a buffer or cushion, and distribute heave more evenly, should it occur. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 8 In order for the over-excavation procedure to be performed properly, close control of fill placement to specifications is required. Over-excavation fill should be placed to the criteria presented in Fill Placement. Our field representative should observe and test compaction of fill during placement. Over-excavation has been used along the Colorado Front Range area with satisfactory performance for the large majority of the sites where this ground modification method has been completed. We have seen isolated instances where settlement of over-excavation fill has led to damage to buildings supported on shallow foundations. In most cases, the settlement was caused by wetting associated with poor surface drainage and/or poorly compacted fill placed at the horizontal limits of the over-excavation. Special precautions should be taken for compaction of fill at corners, access ramps and edges of the over-excavation due to equipment access constraints. The contractor should have the appropriate equipment to reach and compact these areas. The excavation contractor should be chosen based on experience with over-excavation and processing high moisture content clay fills and have the necessary mixing and compaction equipment. The contractor should provide a construction disc to break down fill materials. The operation will be relatively slow. Soil clods should be broken down to about 3 inches or less. The excavation slopes should meet OSHA, state, and local safety standards. We recommend at least 12 inches of over-excavation, moisture-conditioning, and re- compaction below pavements to reduce potential heave and improve performance. The over- excavation can be extended beneath the adjacent sidewalks and improvements, if desired. Foundations Our investigation indicates sandy clay soils are present at the anticipated foundation levels and are likely to influence the performance of foundations. Shallow foundations, such as footings and reinforced concrete mats, are commonly used for the planned type of structures supported on the site soils encountered. The clayey materials exhibit expansive characteristics that present a risk of movement if soil wetting occurs. The risk of foundation movement can be reduced as discussed in Over- Excavation. Provided over-excavation is performed as recommended, we believe footing foundations can be used for the structures. Footing foundations designed to maintain a minimum dead load can be considered for the proposed construction provided the potential movement can be tolerated. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 9 Design criteria for shallow foundations developed from analysis of field and laboratory data and our experience are presented below. Footings 1. Footings should be constructed on undisturbed natural soils and/or properly compacted fill (see Fill Placement). All existing, uncontrolled fill (if encountered) 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. If a reduction in the risk of potential movements is desired, spread footing foundations can be constructed on an over-excavation. The over-excavation should be arranged according to the Over-Excavation section of this report. The fill should be placed as described in Fill Placement. 3. Footings should be designed for a net allowable soil pressure of 3,000 psf and a minimum dead load pressure of 1,000 psf. The soil pressure can be increased 33 percent for transient loads such as wind or seismic loads. 4. If needed to meet the minimum dead load criteria, a continuous void with minimum 4-inch thickness should be placed below grade beams, between pads to concentrate the load of the structures on the footing pads. 5. 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. 6. 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. 7. 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. 8. Exterior footings should be protected from frost action. We believe 30 inches of frost cover is appropriate for this site. 9. 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. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 10 10. 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 a net allowable soil pressure of 3,000 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 borings. Below Grade Areas No below grade areas are planned for the structures. For this condition, perimeter drains are not usually constructed. If any portion of a floor will be below exterior grade, or a crawl space is planned, we should be contacted to provide recommendations for foundation drains. Floor Systems Some movement of slab-on-grade floors should be anticipated. Conventional slab-on- grade floors can be used after over-excavation, provided the risk of heave and distress is acceptable. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 11 The risk of potential movement of slab-on-grade floors can be reduced by over-excavating below the floors and replacing the excavated soils as moisture conditioned fill or imported, non- expansive fill. Fill should be placed according to Fill Placement. More heave or settlement may occur if excessive wetting occurs. We have estimated the potential movements based on swell testing performed during this investigation and our experience. Based on the measured swell, we estimate potential heave of up to 1½ inches at the ground surface if no soil modification is undertaken. Potential heave can be reduced to ½ to 1-inch if 4 feet of over-excavation is performed. If the owner elects to use slab-on-grade construction and accepts the risk of movement and associated damage, we recommend the following precautions for slab-on-grade construction at this site. These precautions can help reduce, but not eliminate, damage or distress due to slab movement. 1. Slabs should be separated from exterior walls and interior bearing members with a slip joint that allows free vertical movement of the slabs. This can reduce cracking if some movement of the slab occurs. 2. Slabs should be placed directly on properly moisture conditioned, well-compacted fill. The 2021 International Building Code (IBC) requires a vapor retarder between the base course or subgrade soils and the concrete slab-on-grade floor, including PTS. The merits of installation of a vapor retarder below floor slabs depend on the sensitivity of floor coverings and building use to moisture. A properly installed vapor retarder (10 mil minimum) is more beneficial below concrete slab-on-grade floors where floor coverings, painted floor surfaces or products stored on the floor will be sensitive to moisture. The vapor retarder is most effective when concrete is placed directly on top of it, rather than placing a sand or gravel leveling course between the vapor retarder and the floor slab. The placement of concrete on the vapor retarder may increase the risk of shrinkage cracking and curling. Use of concrete with reduced shrinkage characteristics including minimized water content, maximized coarse aggregate content, and reasonably low slump will reduce the risk of shrinkage cracking and curling. Considerations and recommendations for the installation of vapor retarders below concrete slabs are outlined in Section 5.2.3.2 of the 2018 report of American Concrete Institute (ACI) Committee 302, “Guide for Concrete Floor and Slab Construction (ACI 302.1R- 15)”. 3. The use of slab-bearing partitions should be minimized. If used, they should be designed and constructed with a minimum 1½-inch space to allow for slab movement. Differential slab movements may cause cracking of partition walls. If the void is provided at the top of partitions, the connection between the slab- supported partition and foundation-supported walls should be detailed to allow differential movement. Doorways, in-wall utility connections, wall partitions perpendicular to the exterior wall or walls supported by foundations should be detailed to allow for vertical movement. Interior perimeter framing and finishing should not extend onto slabs-on-grade, or if necessary, should be detailed to allow for movement. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 12 4. Underslab plumbing should be eliminated where feasible. Where such plumbing is unavoidable, it should be thoroughly pressure tested for leaks prior to slab construction and be provided with flexible couplings. Pressurized water supply lines should be brought above the floors as quickly as possible. 5. Plumbing and utilities that pass through the slabs should be isolated from the slabs and constructed with flexible couplings. Utilities, as well as electrical and mechanical equipment should be constructed with sufficient flexibility to allow for movement. 6. HVAC or other mechanical systems supported by the slabs (if any) should be provided with flexible connections capable of withstanding at least 3 inches of movement. 7. The American Concrete Institute (ACI) recommends frequent control joints in slabs to reduce problems associated with shrinkage cracking and curling. To reduce curling, the concrete mix should have a high aggregate content and a low slump. If desired, a shrinkage compensating admixture could be added to the concrete to reduce the risk of shrinkage cracking. We can perform a mix design or assist the design team in selecting a pre-existing mix. Exterior Flatwork We recommend exterior flatwork and sidewalks be isolated from foundations to reduce the risk of transferring heave, settlement, or freeze-thaw movement to the structure. One alternative 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 building, rather than tying the slabs directly into the building 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. Pavements The project will include a paved parking lot and access drive(s). The performance of pavements is dependent upon the characteristics of the subgrade soil, traffic loading and frequency, climatic conditions, drainage, and pavement materials. We drilled four exploratory borings and conducted laboratory tests to characterize the subgrade soils, which consisted of sandy clay. The subgrade soils classified as A-7 soils with a group index of 6, in accordance with AASHTO procedures. The subgrade soil will likely provide fair to poor support for new pavement. If fill is needed, we have assumed it will be soils with similar or better characteristics. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 13 Traffic loading of a parking lot can be estimated based on type of usage and number of parking spaces. We understand traffic will primarily consist of lightly loaded passenger vehicles. Delivery and garbage truck traffic is anticipated to be minor and possibly isolated to certain areas of the parking lot. We envision that a member of the design team that ultimately configures the parking and access drive(s) will select the locations for which the different pavement sections will be used. Flexible hot mix asphalt (HMA) over aggregate base course (ABC) is likely planned for pavement areas. Rigid Portland cement concrete (PCC) pavement should be used for trash enclosure areas and where the pavement will be subjected to frequent turning of heavy vehicles. Our designs are based on the AASHTO design method and our experience. Using the criteria discussed above we recommend the minimum pavement sections provided in the following table. RECOMMENDED PAVEMENT SECTIONS Classification Hot Mix Asphalt (HMA) + Aggregate Base Course (ABC) Portland Cement Concrete (PCC) Parking Area 4" HMA + 8" ABC 6" PCC Access Drives / Heavy Traffic Areas 4" HMA + 8" ABC 6" PCC Trash Enclosures - 6" PCC Pavement Selection Composite HMA/ABC pavement over a stable subgrade is expected to perform well at this site based on the recommendations provided. HMA provides a stiff, stable pavement to withstand heavy loading and will provide a good fatigue resistant pavement. However, HMA does not perform well when subjected to point loads in areas where heavy trucks turn and maneuver at slow speeds. PCC pavement is expected to perform well in this area; PCC pavement has better performance in freeze-thaw conditions and should require less long-term maintenance than HMA pavement. The PCC pavement for trash enclosures should extend out to areas where trash trucks park to lift and empty dumpsters. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 14 Subgrade and Pavement Materials and Construction The design of a pavement system is as much a function of the quality of the paving materials and construction as the support characteristics of the subgrade. The construction materials are assumed to possess sufficient quality as reflected by the strength factors used in our design calculations. Moisture treatment criteria and additional criteria for materials and construction requirements are presented in Appendix C. Pavement Maintenance Routine maintenance, such as sealing and repair of cracks, is necessary to achieve the long-term life of a pavement system. We recommend a preventive maintenance program be developed and followed for all pavement systems to assure the design life can be realized. Choosing to defer maintenance usually results in accelerated deterioration leading to higher future maintenance costs, and/or repair. A recommended maintenance program is outlined in Appendix D. Excavation of completed pavement for utility construction or repair can destroy the integrity of the pavement and result in a severe decrease in serviceability. To restore the pavement top original serviceability, careful backfill compaction before repaving is necessary. Water-Soluble Sulfates Concrete in contact with soil can be subject to sulfate attack. We measured water-soluble sulfate concentrations of below detectable limits (<0.01 percent) in two samples. 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. Additional sulfate testing is recommended during the design-level phase. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 15 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. 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. We recommend a minimum slope of 5 percent in the first ten feet outside foundations in landscaped areas. Backfill around CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 16 foundations should be moisture treated and compacted as described in Fill Placement. Roof drains should be directed away from buildings. Downspout extensions and splash blocks should be provided at discharge points, or roof drains should be connected to solid pipe discharge systems. We do not recommend directing roof drains under buildings. 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 the City of Fort Collins, 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 CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 17 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 borings were spaced to obtain a reasonably accurate picture of subsurface conditions at this site. The borings are representative of conditions encountered only at the location drilled. Subsurface variations not indicated by our borings 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. CTLTHOMPSON, INC. James Pettus, E.I.T. R.B. “Chip” Leadbetter, III, PE Staff Geotechnical Engineer Senior Engineer 04.11.2024 TH-5 TH-7 TH-6 TH-1 TH-8 TH-3 TH-4 TH-2 Ti m b e r l i n e R o a d Spruc e C r e e k D r i v e ZEPHYR RD. S. T I M B E R L I N E R D . SITE E. TRILBY RD. KECHTER RD. MAIL C R E E K D I T C H LEGEND: INDICATES APPROXIMATE LOCATION OF EXPLORATORY BORING FROM PREVIOUS INVESTIGATION (FC10837.000-125) INDICATES APPROXIMATE LOCATION OF EXPLORATORY BORING FROM THIS INVESTIGATION TH-1 TH-1 CITY OF FORT COLLINS BACON PARK CTL I T PROJECT NO. FC10837.001-125 FIGURE 1 Locations of Exploratory Borings VICINITY MAP (FORT COLLINS, COLORADO) NOT TO SCALE 175'87.5' APPROXIMATE SCALE: 1" = 175' 0' 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 9/12 9/12 6/12 12/12 16/12 WC=19.8DD=106SW=0.4 WC=19.4DD=107SW=0.4SS=<0.01 WC=19.8DD=106SW=0.4 WC=19.4DD=107SW=0.4SS=<0.01 TH-5 9/12 7/12 9/12 13/12 14/12 12/12 WC=18.6DD=108SW=1.4 WC=28.4DD=89-200=60 WC=16.7DD=113SW=1.9 WC=18.6DD=108SW=1.4 WC=28.4DD=89-200=60 WC=16.7DD=113SW=1.9 TH-6 11/12 10/12 5/12 8/12 12/12 WC=18.2DD=109SW=0.4SS=<0.01 WC=20.2DD=111SW=0.1 WC=20.4DD=107LL=41 PI=26-200=79 WC=18.2DD=109SW=0.4SS=<0.01 WC=20.2DD=111SW=0.1 TH-7 13/12 6/12 8/12 10/12 10/12 WC=12.1DD=110SW=3.4 WC=15.5DD=113SW=1.5 WC=18.4DD=112SW=1.8-200=69 WC=12.1DD=110SW=3.4 WC=15.5DD=113SW=1.5 WC=18.4DD=112SW=1.8-200=69 TH-8 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. CLAY, SANDY, MOIST TO VERT MOIST, MEDIUM STIFF TO STIFF, BROWN, RED (CL) 1. 3. LEGEND: DE P T H - F E E T THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS AND CONCLUSIONS IN THIS REPORT. NOTES: WATER LEVEL MEASURED ON FEBRUARY 27, 2024 INDICATES MOISTURE CONTENT (%). INDICATES DRY DENSITY (PCF). INDICATES SWELL WHEN WETTED UNDER OVERBURDEN PRESSURE (%). INDICATES PASSING NO. 200 SIEVE (%). INDICATES LIQUID LIMIT. INDICATES PLASTICITY INDEX. INDICATES UNCONFINED COMPRESSIVE STRENGTH (PSF). INDICATES SOLUBLE SULFATE CONTENT (%). 2. DE P T H - F E E T WATER LEVEL MEASURED AT TIME OF DRILLING. Summary Logs of Exploratory Borings THE BORINGS WERE DRILLED ON FEBRUARY 19, 2024 USING 4-INCH DIAMETER CONTINUOUS-FLIGHT AUGERS AND A TRUCK-MOUNTED DRILL RIG. FIGURE 2 WC DD SW -200 LL PI UC SS - - - - - - - - CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPENDIX A RESULTS OF LABORATORY TESTING Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=106 PCF From TH - 5 AT 2 FEET MOISTURE CONTENT=19.8 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=107 PCF From TH - 5 AT 4 FEET MOISTURE CONTENT=19.4 % CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPLIED PRESSURE -KSF CO M P R E S S I O N % E X P A N S I O N Swell Consolidation FIGURE A-1 CO M P R E S S I O N % E X P A N S I O N -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 10 1001.0 0.1 1.0 10 100APPLIED PRESSURE -KSF -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING Test Results Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=108 PCF From TH - 6 AT 4 FEET MOISTURE CONTENT=18.6 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=113 PCF From TH - 6 AT 14 FEET MOISTURE CONTENT=16.7 % CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPLIED PRESSURE -KSF CO M P R E S S I O N % E X P A N S I O N Swell Consolidation FIGURE A-2 CO M P R E S S I O N % E X P A N S I O N -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 10 1001.0 0.1 1.0 10 100APPLIED PRESSURE -KSF -4 -3 -2 -1 0 1 2 3 NO MOVEMENT DUE TO WETTING Test Results Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=109 PCF From TH - 7 AT 4 FEET MOISTURE CONTENT=18.2 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=111 PCF From TH - 7 AT 19 FEET MOISTURE CONTENT=20.2 % CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPLIED PRESSURE -KSF CO M P R E S S I O N % E X P A N S I O N Swell Consolidation FIGURE A-3 CO M P R E S S I O N % E X P A N S I O N -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 10 1001.0 0.1 1.0 10 100APPLIED PRESSURE -KSF -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING Test Results Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=110 PCF From TH - 8 AT 2 FEET MOISTURE CONTENT=12.1 % CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPLIED PRESSURE -KSF CO M P R E S S I O N % E X P A N S I O N Swell Consolidation Test Results FIGURE A-4 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 1.0 10 100 Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=113 PCF From TH - 8 AT 4 FEET MOISTURE CONTENT=15.5 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=112 PCF From TH - 8 AT 14 FEET MOISTURE CONTENT=18.4 % CITY OF FORT COLLINS BACON PARK CTL | T PROJECT NO. FC10837.001-125 APPLIED PRESSURE -KSF CO M P R E S S I O N % E X P A N S I O N Swell Consolidation FIGURE A-5 CO M P R E S S I O N % E X P A N S I O N -4 -3 -2 -1 0 1 2 3 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 10 1001.0 0.1 1.0 10 100APPLIED PRESSURE -KSF -4 -3 -2 -1 0 1 2 3 NO MOVEMENT DUE TO WETTING Test Results PASSING WATER- MOISTURE DRY LIQUID PLASTICITY APPLIED NO. 200 SOLUBLE DEPTH CONTENT DENSITY LIMIT INDEX SWELL*PRESSURE SIEVE SULFATES BORING (FEET)(%)(PCF)(%)(PSF)(%)(%)DESCRIPTION TH-5 2 19.8 106 0.4 500 CLAY, SANDY (CL) TH-5 4 19.4 107 0.4 500 <0.01 CLAY, SANDY (CL) TH-6 4 18.6 108 1.4 500 CLAY, SANDY (CL) TH-6 9 28.4 89 60 CLAY, SANDY (CL) TH-6 14 16.7 113 0.0 1,800 CLAY, SANDY (CL) TH-7 2 20.4 107 41 26 79 CLAY, SANDY (CL) TH-7 4 18.2 109 0.4 500 <0.01 CLAY, SANDY (CL) TH-7 19 20.2 111 0.1 2,400 CLAY, SANDY (CL) TH-8 2 12.1 110 3.4 500 CLAY, SANDY (CL) TH-8 4 15.5 113 1.5 500 CLAY, SANDY (CL) TH-8 14 18.4 112 0.0 1,800 69 CLAY, SANDY (CL) SWELL TEST RESULTS* TABLE A-I SUMMARY OF LABORATORY TESTING ATTERBERG LIMITS Page 1 of 1 * NEGATIVE VALUE INDICATES COMPRESSION. CITY OF FORT COLLINS BACON PARK CTL|T PROJECT NO. FC10837.001-125 APPENDIX B SAMPLE SITE GRADING SPECIFICATIONS CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 B-1 SAMPLE SITE GRADING SPECIFICATIONS 1. DESCRIPTION This item shall consist of the excavation, transportation, placement, and compaction of materials from locations indicated on the plans, or staked by the Engineer, as necessary to achieve building site elevations. 2. GENERAL The Geotechnical Engineer shall be the Owner's representative. The Geotechnical Engineer shall approve fill materials, method of placement, moisture contents and percent compaction, and shall give written approval of the completed fill. 3. CLEARING JOB SITE The Contractor shall remove all trees, brush and rubbish before excavation or fill placement is begun. The Contractor shall dispose of the cleared material to provide the Owner with a clean, neat appearing job site. Cleared material shall not be placed in areas to receive fill or where the material will support structures of any kind. 4. SCARIFYING AREA TO BE FILLED All topsoil and vegetable matter shall be removed from the ground surface upon which fill is to be placed. The surface shall then be plowed or scarified to a depth of 8 inches until the surface is free from ruts, hummocks, or other uneven features, which would prevent uniform compaction by the equipment to be used. 5. COMPACTING AREA TO BE FILLED After the foundation for the fill has been cleared and scarified, it shall be disked or bladed until it is free from large clods, brought to the proper moisture content and compacted to not less than 95 percent of maximum dry density as determined in accordance with ASTM D 698 or AASHTO T 99. 6. FILL MATERIALS On-site materials classifying as CL, SC, SM, SW, SP, GP, GC, and GM are acceptable. Fill soils shall be free from organic matter, debris, or other deleterious substances, and shall not contain rocks or lumps having a diameter greater than three (3) inches. Fill materials shall be obtained from the existing fill and other approved sources. 7. MOISTURE CONTENT Fill materials shall be moisture treated. Clay soils placed below the building envelope should be moisture-treated to between optimum and 3 percent above optimum moisture content as determined from Standard Proctor compaction tests. Clay soil placed exterior to the building should be moisture treated between optimum and 3 percent above optimum moisture content. Sand soils can be moistened to within 2 percent of optimum moisture content. Sufficient laboratory compaction tests shall be performed to determine the optimum moisture content for the various soils encountered in borrow areas. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 B-2 The Contractor may be required to add moisture to the excavation materials in the borrow area if, in the opinion of the Geotechnical Engineer, it is not possible to obtain uniform moisture content by adding water on the fill surface. The Contractor may be required to rake or disk the fill soils to provide uniform moisture content through the soils. The application of water to embankment materials shall be made with any type of watering equipment approved by the Geotechnical Engineer, which will give the desired results. Water jets from the spreader shall not be directed at the embankment with such force that fill materials are washed out. Should too much water be added to any part of the fill, such that the material is too wet to permit the desired compaction from being obtained, rolling and all work on that section of the fill shall be delayed until the material has been allowed to dry to the required moisture content. The Contractor will be permitted to rework wet material in an approved manner to hasten its drying. 8. COMPACTION OF FILL AREAS Selected fill material shall be placed and mixed in evenly spread layers. After each fill layer has been placed, it shall be uniformly compacted to not less than the specified percentage of maximum dry density. Fill materials shall be placed such that the thickness of loose material does not exceed 8 inches and the compacted lift thickness does not exceed 6 inches. Fill placed under foundations, exterior flatwork and pavements should be compacted to a minimum of 95 percent of maximum standard Proctor dry density (ASTM D698). Compaction, as specified above, shall be obtained by the use of sheepsfoot rollers, multiple-wheel pneumatic-tired rollers, or other equipment approved by the Engineer. Compaction shall be accomplished while the fill material is at the specified moisture content. Compaction of each layer shall be continuous over the entire area. Compaction equipment shall make sufficient trips to ensure that the required dry density is obtained. 9. COMPACTION OF SLOPES Fill slopes shall be compacted by means of sheepsfoot rollers or other suitable equipment. Compaction operations shall be continued until slopes are stable, but not too dense for planting, and there is no appreciable amount of loose soil on the slopes. Compaction of slopes may be done progressively in increments of three to five feet (3' to 5') in height or after the fill is brought to its total height. Permanent fill slopes shall not exceed 3:1 (horizontal to vertical). 10. DENSITY TESTS Field density tests shall be made by the Geotechnical Engineer at locations and depths of his choosing. Where sheepsfoot rollers are used, the soil may be disturbed to a depth of several inches. Density tests shall be taken in compacted material below the disturbed surface. When density tests indicate that the dry density or moisture content of any layer of fill or portion thereof is below that required, the particular layer or portion shall be reworked until the required dry density or moisture content has been achieved. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 B-3 11. SEASONAL LIMITS No fill material shall be placed, spread, or rolled while it is frozen, thawing, or during unfavorable weather conditions. When work is interrupted by heavy precipitation, fill operations shall not be resumed until the Geotechnical Engineer indicates that the moisture content and dry density of previously placed materials are as specified. 12. NOTICE REGARDING START OF GRADING The contractor shall submit notification to the Geotechnical Engineer and Owner advising them of the start of grading operations at least three (3) days in advance of the starting date. Notification shall also be submitted at least 3 days in advance of any resumption dates when grading operations have been stopped for any reason other than adverse weather conditions. 13. REPORTING OF FIELD DENSITY TESTS Density tests performed by the Geotechnical Engineer, as specified under "Density Tests" above, shall be submitted progressively to the Owner. Dry density, moisture content and percent compaction shall be reported for each test taken. APPENDIX C PAVEMENT CONSTRUCTION RECOMMENDATIONS CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-1 SUBGRADE PREPARATION Moisture Treated Subgrade (MTS) 1. The subgrade should be stripped of organic matter, scarified, moisture treated and compacted to the specifications stated below in Item 2. The compacted subgrade should extend at least 3 feet beyond the edge of the pavement where no edge support, such as curb and gutter, are to be constructed. 2. Sandy and gravelly soils (A-1-a, A-1-b, A-3, A-2-4, A-2-5, A-2-6, A-2-7) should be moisture conditioned near optimum moisture content and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). Clayey soils (A-6, A-7-5, A-7-6) should be moisture conditioned between optimum and 3 percent above optimum moisture content and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). 3. Utility trenches and all subsequently placed fill should be properly compacted and tested prior to paving. As a minimum, fill should be compacted to 95 percent of standard Proctor maximum dry density. 4. Final grading of the subgrade should be carefully controlled so the design cross-slope is maintained and low spots in the subgrade that could trap water are eliminated. 5. Once final subgrade elevation has been compacted and tested to compliance and shaped to the required cross-section, the area should be proof-rolled using a minimum axle load of 18 kips per axle. The proof-roll should be performed while moisture contents of the subgrade are still within the recommended limits. Drying of the subgrade prior to proof-roll or paving should be avoided. 6. Areas that are observed by the Engineer that have soft spots in the subgrade, or where deflection is not uniform of soft or wet subgrade shall be ripped, scarified, dried, or wetted as necessary and recompacted to the requirements for the density and moisture. As an alternative, those areas may be over-excavated and replaced with properly compacted structural backfill. Where extensively soft, yielding subgrade is encountered; we recommend a representative of our office observe the excavation. Chemically Stabilized Subgrade (CSS) 1. Utility trenches and all subsequently placed fill should be properly compacted and tested prior to subgrade preparation. As a minimum, fill should be compacted to 95 percent of standard Proctor maximum dry density. 2. The subgrade should be stripped of organic matter and should be shaped to final line and grade. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-2 3. The contractor or owner’s representative should have a mix design performed in general accordance with ASTM D 558 using the actual site soils and the approved stabilizing agent (lime, fly ash or a combination of lime and fly ash). Scheduling should allow at least five weeks for the mix design to be completed prior to construction. 4. High calcium quicklime should conform to the requirements of ASTM C 977 and ASTM C 110. Dolomitic quicklime, magnesia quicklime with magnesium oxide contents in excess of 4 percent, or carbonated quicklime should not be used. 5. Fly ash should consist of Class C in accordance with ASTM C 593 and C 618. 6. All stabilizing agents should come from the same source as used in the mix design. If the source is changed, a new mix design should be performed. 7. Stabilizing agents should be spread with a mechanical spreader from back of curb to back of curb for detached sidewalks or back of walk to back of walk for attached sidewalks, where applicable. 8. The subgrade should be mixed to the specified depth and at the specified concentration until a uniform blend of soil, stabilizing agent and water is obtained and the moisture content is at least 2 percent (for fly ash) and 3 percent (for lime) above the optimum moisture content of the design mixture (ASTM D 558). 9. If lime is used, a mellowing period of up to seven days may be required following initial mixing. Once the pH of the mixture is 12.3 or higher and the plasticity index is less than 10, the soils shall again be mixed and moisture conditioned to at least 3 percent over optimum moisture content and compacted to at least 95 percent of the mixture’s maximum dry density (ASTM D 558). Up to seven additional days may be required for curing prior to paving. The treated surface shall be kept moist or sealed with emulsified asphalt. Traffic should not be allowed on the surface during the mellowing and curing periods. 10. If fly ash is used, the mixture should be moisture conditioned to at least 2 percent over optimum moisture content and compacted to at least 95 percent of the mixture’s maximum dry density (ASTM D 558) within 2 hours from the time of initial fly ash mixing. 11. If a lime/fly ash combination is used, the lime should be mixed first and allowed to mellow as indicated for lime treatment in item 9. Following the mellowing period, the fly ash should be added, moisture conditioned and compacted as indicated above within 2 hours of initial fly ash mixing. 12. Samples of loose, blended stabilizing agent/soil mixture should be sampled by a representative of CTL Thompson, Inc. for compressive strength testing (ASTM D 1663) to determine compliance (optional) when full credit for the FASS layer is used in the pavement thickness design. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-3 13. Batch tickets should be supplied to the owner or owner’s representative with the application area for that batch to determine compliance with the recommended proportions of fly ash to soil. 14. The subgrade should be re-shaped to final line and grade. 15. The subgrade should be sealed with a pneumatic-tire roller that is sufficiently light in weight so as to not cause hairline cracking of the subgrade. 16. Mixing of the fly ash, lime, or lime/fly ash treated subgrade should not occur if the temperature of the soil mixture is below 40oF. 17. We recommend a minimum of 2 days curing prior to paving. The surface of the stabilized area should be kept moist during the cure period by periodic, light sprinkling if needed. Strength gains will be slower during cooler weather. Traffic should not be permitted on the treated subgrade during the curing period. The subgrade should be protected from freezing or drying at all times until paving. 18. The treated areas will gain greater strength if they are allowed to cure for 1 to 3 days prior to paving. Construction traffic on the treated subgrade prior to pavement section construction should be limited and the subgrade should be protected from freezing or drying at all times until paving. 19. Placement, mixing and compaction of stabilized subgrade should be observed and tested by a representative of our firm. PAVEMENT MATERIALS AND CONSTRUCTION Aggregate Base Course (ABC) 1. A Class 5 or 6 Colorado Department of Transportation (CDOT) specified ABC should be used. A reclaimed concrete pavement (RCP) alternative which meets the Class 5 or 6 designation and design R-value/strength coefficient is also acceptable. Blending of recycled products with ABC may be considered. 2. Bases should have a minimum Hveem stabilometer value of 72, or greater. ABC, RAP, RCP, or blended materials must be moisture stable. The change in R-value from 300-psi to 100-psi exudation pressure should be 12 points or less. 3. ABC or RCP bases should be placed in thin lifts not to exceed 6 inches and moisture treated to near optimum moisture content. Bases should be moisture treated to near optimum moisture content and compacted to at least 95 percent of standard Proctor maximum dry density (ASTM D 698, AASHTO T 99). CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-4 4. Placement and compaction of ABC or RCP should be observed and tested by a representative of our firm. Placement should not commence until the underlying subgrade is properly prepared and tested. Hot Mix Asphalt (HMA) 1. HMA should be composed of a mixture of aggregate, filler, hydrated lime, and asphalt cement. Some mixes may require polymer modified asphalt cement or make use of up to 20 percent reclaimed asphalt pavement (RAP). A job mix design is recommended and periodic checks on the job site should be made to verify compliance with specifications. 2. HMA should be relatively impermeable to moisture and should be designed with crushed aggregates that have a minimum of 80 percent of the aggregate retained on the No. 4 sieve with two mechanically fractured faces. 3. Gradations that approach the maximum density line (within 5 percent between the No. 4 and 50 sieves) should be avoided. A gradation with a nominal maximum size of 1 or 2 inches developed on the fine side of the maximum density line should be used. 4. Total void content, voids in the mineral aggregate (VMA), and voids filled should be considered in the selection of the optimum asphalt cement content. The optimum asphalt content should be selected at a total air void content of approximately 4 percent. The mixture should have a minimum VMA of 14 percent and between 65 percent and 80 percent of voids filled. 5. Asphalt cement should meet the requirements of the Superpave Performance Graded (PG) Binders. The minimum performing asphalt cement should conform to the requirements of the governing agency. 6. Hydrated lime should be added at the rate of 1 percent by dry weight of the aggregate and should be included in the amount passing the No. 200 sieve. Hydrated lime for aggregate pretreatment should conform to the requirements of ASTM C 207, Type N. 7. Paving should be performed on properly prepared, unfrozen surfaces that are free of water, snow, and ice. Paving should only be performed when both air and surface temperatures equal, or exceed, the temperatures specified in Table 401-3 of the 2006 Colorado Department of Transportation Standard Specifications for Road and Bridge Construction. 8. HMA should not be placed at a temperature lower than 245oF for mixes containing PG 64-22 asphalt, and 290oF for mixes containing polymer- modified asphalt. The breakdown compaction should be completed before the HMA temperature drops 20oF. 9. Wearing surface course shall be Grading S or SX for residential roadway classifications and Grading S for collector, arterial, industrial, and commercial roadway classifications. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-5 10. The minimum/maximum lift thicknesses for Grade SX shall be 1½ inches/2½ inches. The minimum/maximum lift thicknesses for Grade S shall be 2 inches/3½ inches. The minimum/maximum lift thicknesses for Grade SG shall be 3 inches/5 inches. 11. Joints should be staggered. No joints should be placed within wheel paths. 12. HMA should be compacted to between 92 and 96 percent of Maximum Theoretical Density. The surface shall be sealed with a finish roller prior to the mix cooling to 185oF. 13. Placement and compaction of HMA should be observed and tested by a representative of our firm. Placement should not commence until approval of the proof rolling as discussed in the Subgrade Preparation section of this report. Subbase, base course, or initial pavement course shall be placed within 48 hours of approval of the proof rolling. If the Contractor fails to place the subbase, base course, or initial pavement course within 48 hours or the condition of the subgrade changes due to weather or other conditions, proof rolling and correction shall be performed again. Portland Cement Concrete (PCC) 1. Portland cement concrete should consist of Class P of the 2021 CDOT - Standard Specifications for Road and Bridge Construction specifications for normal placement. PCC should have a minimum compressive strength of 4,500 psi at 28 days and a minimum modulus of rupture (flexural strength) of 650 psi. Job mix designs are recommended and periodic checks on the job site should be made to verify compliance with specifications. 2. Portland cement should be Type II “low alkali” and should conform to ASTM C 150. 3. Portland cement concrete should not be placed when the subgrade or air temperature is below 40°F. 4. Concrete should not be placed during warm weather if the mixed concrete has a temperature of 90°F, or higher. 5. Mixed concrete temperature placed during cold weather should have a temperature between 50°F and 90°F. 6. Free water should not be finished into the concrete surface. Atomizing nozzle pressure sprayers for applying finishing compounds are recommended whenever the concrete surface becomes difficult to finish. 7. Curing of the Portland cement concrete should be accomplished by the use of a curing compound. The curing compound should be applied in accordance with manufacturer recommendations. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 C-6 8. Curing procedures should be implemented, as necessary, to protect the pavement against moisture loss, rapid temperature change, freezing, and mechanical injury. 9. Construction joints, including longitudinal joints and transverse joints, should be formed during construction, or sawed after the concrete has begun to set, but prior to uncontrolled cracking. 10. All joints should be properly sealed using a rod back-up and approved epoxy sealant. 11. Traffic should not be allowed on the pavement until it has properly cured and achieved at least 80 percent of the design strength, with saw joints already cut. 12. Placement of Portland cement concrete should be observed and tested by a representative of our firm. Placement should not commence until the subgrade is properly prepared and tested. APPENDIX D PAVEMENT MAINTENANCE PROGRAM CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 D-1 MAINTENANCE RECOMMENDATIONS FOR FLEXIBLE PAVEMENTS A primary cause for deterioration of pavements is oxidative aging resulting in brittle pavements. Tire loads from traffic are necessary to "work" or knead the asphalt concrete to keep it flexible and rejuvenated. Preventive maintenance treatments will typically preserve the original or existing pavement by providing a protective seal or rejuvenating the asphalt binder to extend pavement life. 1. Annual Preventive Maintenance a. Visual pavement evaluations should be performed each spring or fall. b. Reports documenting the progress of distress should be kept current to provide information on effective times to apply preventive maintenance treatments. c. Crack sealing should be performed annually as new cracks appear. 2. 3 to 5 Year Preventive Maintenance a. The owner should budget for a preventive treatment at approximate intervals of 3 to 5 years to reduce oxidative embrittlement problems. b. Typical preventive maintenance treatments include chip seals, fog seals, slurry seals and crack sealing. 3. 5 to 10 Year Corrective Maintenance a. Corrective maintenance may be necessary, as dictated by the pavement condition, to correct rutting, cracking, and structurally failed areas. b. Corrective maintenance may include full depth patching, milling and overlays. c. In order for the pavement to provide a 20-year service life, at least one major corrective overlay should be expected. CITY OF FORT COLLINS BACON PARK CTLT PROJECT NO. FC10837.001-125 D-2 MAINTENANCE RECOMMENDATIONS FOR RIGID PAVEMENTS High traffic volumes create pavement rutting and smooth polished surfaces. Preventive maintenance treatments will typically preserve the original or existing pavement by providing a protective seal and improving skid resistance through a new wearing course. 1. Annual Preventive Maintenance a. Visual pavement evaluations should be performed each spring or fall. b. Reports documenting the progress of distress should be kept current to provide information of effective times to apply preventive maintenance. c. Crack sealing should be performed annually as new cracks appear. 2. 4 to 8 Year Preventive Maintenance a. The owner should budget for a preventive treatment at approximate intervals of 4 to 8 years to reduce joint deterioration. b. Typical preventive maintenance for rigid pavements includes patching, crack sealing and joint cleaning and sealing. c. Where joint sealants are missing or distressed, resealing is mandatory. 3. 15 to 20 Year Corrective Maintenance a. Corrective maintenance for rigid pavements includes patching and slab replacement to correct subgrade failures, edge damage, and material failure. b. Asphalt concrete overlays may be required at 15 to 20 year intervals to improve the structural capacity of the pavement.