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HomeMy WebLinkAboutSCHOOLSIDE PARK - BDR240009 - SUBMITTAL DOCUMENTS - ROUND 2 - Geotechnical (Soils) Report CTL|Thompson, Inc. Denver, Fort Collins, Colorado Springs, Glenwood Springs, Pueblo, Summit County – Colorado Cheyenne, Wyoming and Bozeman, Montana Mail Creek Trail Improvements Between Timberline Road and Zephyr Road Fort Collins, Colorado Prepared for: CITY OF FORT COLLINS 215 North Mason Street 3rd Floor Fort Collins, Colorado 80522 Attention: Greg Oakes Project No. FC10837.000-125 July 24, 2023 GEOTECHNICAL INVESTIGATION Table of Contents Scope 1 Summary Of Conclusions 1 Site Conditions and Proposed Construction 2 Investigation 3 Subsurface Conditions 3 Groundwater 4 Geologic Hazards 4 Expansive Soils 4 Seismicity 4 Site Development 5 Fill Placement 5 Excavations 6 Foundations 7 Footings 7 Abutments 8 Lateral Earth Pressures 8 Trail Alignment 9 Subgrade and Pavement Materials and Construction 9 Pavement Maintenance 10 Over-Excavation 10 Water-Soluble Sulfates 11 Construction Observations 12 Geotechnical Risk 13 Limitations 13 FIGURE 1 – LOCATIONS OF EXPLORATORY BORINGS FIGURE 2 – SUMMARY LOGS OF EXPLORATORY BORINGS APPENDIX A – LABORATORY TEST RESULTS APPENDIX B – SAMPLE SITE GRADING SPECIFICATIONS APPENDIX C – PAVEMENT CONSTRUCTION RECOMMENDATONS APPENDIX D – PAVEMENT MAINTENANCE PROGRAM CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 1 Scope This report presents the results of our Geotechnical Investigation for the proposed improvements to the Mail Creek Trail in Fort Collins, Colorado. 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-23-0178) dated May 2, 2023. 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 borings and discussions of site development as influenced by geotechnical considerations. Our opinions and recommendations regarding design criteria and construction details for site development and foundations are provided. The report was prepared for the exclusive use of the City of Fort Collins 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 and clayey sand. Weathered sandstone bedrock was encountered in boring TH-3 at approximately 22 feet extending to the maximum depth explored. 2. Groundwater was encountered during drilling at 12 to 13½ feet in two borings. When measured several days later, groundwater was at depths of 9½ to 11½ feet in the same borings. Existing groundwater levels are not expected to affect construction as proposed. 3. The presence of expansive soils constitutes a geologic hazard. There is risk that foundations and pavements will experience heave or settlement and be damaged. We believe that risk is low to moderate. We believe the recommendations presented in this report will help to control risk of damage; they will not eliminate that risk. In some instances, foundations may be damaged. 4. We understand that footing foundations are desired for the proposed pedestrian bridge. Footing foundations are acceptable for the proposed structures provided they are placed on at least 3 feet of over-excavated, moisture treated and properly compacted fill (over-excavation). Design and construction criteria for footing foundations are presented in the report. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 2 5. Samples of the subgrade soils generally classified as A-6 by AASHTO methods. We recommend a minimum section of 5 inches of Portland cement concrete (PCC). Expansive soils were encountered in the upper few feet of our borings. The subgrade will likely provide poor support for the new trail without mitigation. We recommend placing the trail on at least 12 inches of moisture treated and properly compacted fill. 6. Surface drainage should be designed, constructed, and maintained to provide rapid removal of surface runoff away from the proposed trail and foundations. Site Conditions and Proposed Construction The trail alignment is located between Timberline Road and Zephyr Road, along the Mail Creek Ditch, in southeast Fort Collins, Colorado (Figure 1). Bacon Elementary School is to the southwest and the Mail Creek Crossing Subdivision is located to the northeast. The site is relatively flat with groundcover consisting of natural grasses, trees, and weeds. There were fill piles and construction activity to the west of the site. The Mail Creek Ditch was running at the time of our investigation. Image 1: Google Earth Aerial Image 11/8/2019 CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 3 The proposed section of trail alignment will run between Timberline Road and Zephyr Road. It will be comprised of Portland cement concrete. The proposed pedestrian bridge will span the Mail Creek Ditch near borings TH-3 and TH-4 and connect to the trails, and the north and south side of the ditch. Plans for the bridge were unavailable prior to completion of this report but is our understanding, based on conversation with the client, that the abutments are to be placed on footing foundations. 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 10 to 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. Summary logs of the exploratory borings, including results of field penetration resistance tests and a portion of laboratory test data, are presented in on Figure 2. 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, unconfined compressive strength, 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 borings generally consisted of sandy clay and clayey sand. Weathered sandstone bedrock was encountered in boring TH-3 at approximately 22 feet extending to the maximum depth explored. Samples of the sandy clay tested for swell- consolidation exhibited nil to 7.0 percent swell. Particle size analysis indicated fines contents of 31 to 80 percent for the sandy clay and clayey sand. One sample of clay at a depth of 24 feet exhibited 3,100 pounds per square foot of unconfined compressive strength. Atterberg limit tests of the soils within the trail alignment indicated liquid limits of 38 and 40, and plastic indices of 21 and 23. Further descriptions of the subsurface conditions are presented on our boring logs and in our laboratory test results. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 4 Groundwater Groundwater was encountered during drilling at 12 to 13½ feet in two borings. When measured several days later, groundwater was at depths of 9½ to 11½ feet in the same borings. Groundwater levels will fluctuate seasonally and will be affected by the water level in the Mail Creek Ditch. Groundwater is not expected to affect construction of the trail or the pedestrian bridge as proposed. 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 proposed construction. The following sections discuss each of these geologic hazards and associated development concerns. 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 foundations; 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 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 5 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 670 and 707 feet per second with an average value of 689 feet per second. We judge a Seismic Site Classification of DE. 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 = 0.185 g SMS = 0.295 g SDS = 0.197 g S1 = 0.055 g SM1 = 0.132 g SD1 = 0.088 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 6 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. Sand soils used as fill should be moistened to within 2 percent of optimum moisture content. 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. Soft soils were found in our borings. If stabilization is necessary, it can likely be achieved by crowding 1½ to 3-inch nominal size crushed rock into the subsoils until the base of the excavation does not deform by more than about 1-inch when compactive effort is applied. 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. Excavations We believe the soil and bedrock 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 soils classify as Type B soils. Type B soils require a maximum slope inclination of 1:1 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 7 Foundations We understand that footing foundations are desired for the pedestrian bridge abutments. Our investigation indicates low to moderately expansive soil is present at anticipated foundation depths. Footing foundations are acceptable for this site as long as they are placed on a 3-foot mat of over-excavated, moisture treated and re-compacted soil (over-excavation). Design and construction criteria for foundations are presented below. The criteria presented below were developed from analysis of field and laboratory data and our experience. Footings 1. Footings should be constructed on properly compacted fill (see Over-excavation). 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 you are willing to accept risk of potential movements, spread footing foundations can be used if constructed on an over-excavation. The over-excavation should extend at least 3 feet below the foundation subgrade and at least 3 feet beyond the perimeter of the footprint of the structure. The fill should be placed as described in Over-excavation. 3. Soft/loose soils were encountered in our borings. If soft soils are encountered, stabilization can likely be achieved by crowding 1½ to 3-inch nominal size crushed rock into the subsoils until the base of the excavation does not deform by more than about 1-inch when compactive effort is applied. 4. Footings 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. 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. Larger sizes may be required depending on loads and the structural system used. 7. The soils beneath footing can be assigned an ultimate coefficient of friction of 0.5 to resist lateral loads. The ability abutment backfill to resist lateral loads can be calculated using a passive equivalent fluid pressure of 300 pcf. This assumes the backfill is densely compacted and will not be removed. 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 8 9. 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. 10. 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. 11. 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. Abutments Abutment foundations will not be restrained and could rotate enough to apply load to the bridge; lateral earth pressure may need to be considered. Maintenance 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 abutments 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 placed the abutment walls. Passive resistance can be used to evaluate backfill resistance to girder expansion. Lateral Earth Pressures The lateral loads acting on the bridge abutments are dependent on the height and type of foundation, backfill configuration, and backfill type. 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 can be considered at 110 pcf. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 9 Loading Condition Equivalent Hydrostatic Fluid Pressure Lateral Earth Pressure Coefficient Active (A) pcf 35 0.31 At-Rest (o) pcf 60 0.47 Passive (p) pcf 300 3.3 Horizontal Friction Coefficient 0.50 Trail Alignment The performance of pavement is dependent upon the characteristics of the subgrade soil, loading and frequency, climatic conditions, drainage and pavement materials. We drilled two exploratory borings in the area of the trail alignment and conducted laboratory tests to characterize the subgrade soils. Samples of the subgrade soils found in our borings were sandy clay, classifying as A-6 by AASHTO methods. We understand that rigid pavement is preferred for the trail. We recommend a minimum section of 5 inches of Portland cement concrete (PCC) for the trail in anticipation of predominantly pedestrian traffic with occasion maintenance vehicles. If the frequent use of vehicular traffic is expected a minimum thickness of 6 inches of PCC should be used. The subgrade soil is expansive and will likely provide poor support for the new trail without mitigation. We recommend removal, moisture treatment, and recompaction of at least 12 inches of the subgrade soil below the trail. If fill is needed, we expect it will be soils with similar or better characteristics. 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 of this report. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 10 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. Over-Excavation Relatively higher swelling clay materials are present in the upper few feet throughout the site. Potential ground heave could be as much as 2 inches with typical post-construction wetting. We recommend over-excavating to a uniform depth of at least 3 feet below pedestrian bridge foundations to reduce potential heave to acceptable levels and provide more uniform support conditions. For the trail alignment we recommend over-excavation of at least 12 inches of the subgrade below the pavement. Deeper over-excavation on the order of 18 to 24 inches below pavements can be considered for better performance. 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 3 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. 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 structures 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 CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 11 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. Water-Soluble Sulfates Concrete in contact with soil can be subject to sulfate attack. We measured water-soluble sulfate concentrations in three samples, and all were below measurable. 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 12 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. Construction Observations 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 CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 13 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 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 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 14 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. Trace Krausse, EI R.B. “Chip” Leadbetter, III, PE Geotechnical Project Engineer Senior Engineer TH-1 TH-4 TH-3 TH-2 Ti m b e r l i n e R o a d Zephyr Road Spruc e C r e e k D r i v e TI M B E R L I N E R D KECHTER RD TRILBY RD TI L D E N S T SITE ZEPHYR RD. LEGEND: INDICATES APPROXIMATE LOCATION OF EXPLORATORY BORING TH-1 CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTL I T PROJECT NO. FC10837.000-125 FIGURE 1 Locations of Exploratory Borings VICINITY MAP FORT COLLINS, COLORADO NOT TO SCALE 200'100' APPROXIMATE SCALE: 1" = 200' 0' 0 5 10 15 20 25 30 35 40 0 5 10 15 20 25 30 35 40 11/12 9/12 5/12 WC=8.6DD=103SW=2.4SS=<0.01 WC=15.9DD=106LL=40 PI=23-200=77 WC=8.6DD=103SW=2.4SS=<0.01 WC=15.9DD=106LL=40 PI=23-200=77 TH-1 18/12 8/12 4/12 WC=9.7LL=38 PI=21-200=76 WC=10.8-200=80SS=<0.01 WC=9.7LL=38 PI=21-200=76 WC=10.8-200=80SS=<0.01 TH-2 22/12 5/12 4/12 10/12 16/12 WC=9.3DD=120SW=7.0 WC=15.1DD=113-200=31 WC=18.2DD=114SW=0.0 WC=9.3DD=120SW=7.0 WC=15.1DD=113-200=31 WC=18.2DD=114SW=0.0 TH-3 6/12 5/12 7/12 8/12 15/12 13/12 WC=14.2DD=112SW=1.6SS=<0.01 WC=22.7DD=95-200=35 WC=19.0DD=111UC=3,100 WC=14.2DD=112SW=1.6SS=<0.01 WC=22.7DD=95-200=35 TH-4 DRIVE SAMPLE. THE SYMBOL 11/12 INDICATES 11 BLOWS OF A 140-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE A 2.5-INCH O.D. SAMPLER 12 INCHES. CLAY, SANDY, SLIGHTLY MOIST TO WET, MEDIUM STIFF TO VERY STIFF, BROWN, TAN, PINK (CL) 1. 3. LEGEND: WEATHERED SANDSTONE, CLAYEY, MOIST, FIRM, BROWN, GREY DE P T H - F E E T THESE LOGS ARE SUBJECT TO THE EXPLANATIONS, LIMITATIONS AND CONCLUSIONS IN THIS REPORT. NOTES: SAND, CLAYEY, MOIST, LOOSE, RED (SC) 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 JUNE 9TH, 2023 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 MAIL CREEK TRAIL IMPROVEMENTS CTL | T PROJECT NO. FC10837.000-125 WATER LEVEL MEASURED ON JUNE 23, 2023. APPENDIX A LABORATORY TEST RESULTS Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=103 PCF From TH - 1 AT 2 FEET MOISTURE CONTENT=8.6 % CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTL | T PROJECT NO. FC10837.000-125 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-1 -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=120 PCF From TH - 3 AT 2 FEET MOISTURE CONTENT=9.3 % CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTL | T PROJECT NO. FC10837.000-125 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-2 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 EXPANSION UNDER CONSTANT PRESSURE DUE TO WETTING 0.1 1.0 10 100 Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=114 PCF From TH - 3 AT 19 FEET MOISTURE CONTENT=18.2 % Sample of CLAY, SANDY (CL) DRY UNIT WEIGHT=112 PCF From TH - 4 AT 4 FEET MOISTURE CONTENT=14.2 % CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTL | T PROJECT NO. FC10837.000-125 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 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 UNCONFINED PASSING WATER- MOISTURE DRY LIQUID PLASTICITY APPLIED COMPRESSIVE NO. 200 SOLUBLE DEPTH CONTENT DENSITY LIMIT INDEX SWELL*PRESSURE STRENGTH SIEVE SULFATES BORING (FEET)(%)(PCF)(%)(PSF)(PSF)(%)(%)DESCRIPTION TH-1 2 8.6 103 2.4 500 <0.01 CLAY, SANDY (CL) TH-1 4 15.9 106 40 23 77 CLAY, SANDY (CL) TH-2 2 9.7 38 21 76 CLAY, SANDY (CL) TH-2 4 10.8 80 <0.01 CLAY, SANDY (CL) TH-3 2 9.3 120 7.0 500 CLAY, SANDY (CL) TH-3 14 15.1 113 31 SAND, CLAYEY (SC) TH-3 19 18.2 114 0.0 2,400 CLAY, SANDY (CL) TH-4 4 14.2 112 1.6 500 <0.01 CLAY, SANDY (CL) TH-4 9 22.7 95 35 SAND, CLAYEY (SC) TH-4 24 19.0 111 3,100 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 MAIL CREEK TRAIL IMPROVEMENTS CTL|T PROJECT NO. FC10837.000-125 APPENDIX B SAMPLE SITE GRADING SPECIFICATIONS CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 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 MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 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 MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 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 MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 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. 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. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 C-2 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). 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. 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. 8. Curing procedures should be implemented, as necessary, to protect the pavement against moisture loss, rapid temperature change, freezing, and mechanical injury. CITY OF FORT COLLINS MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 C-3 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 MAIL CREEK TRAIL IMPROVEMENTS CTLT PROJECT NO. FC10837.000-125 D-1 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.