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HomeMy WebLinkAboutBANNER HEALTH MEDICAL CAMPUS - PDP - PDP130003 - SUBMITTAL DOCUMENTS - ROUND 1 - GEOTECHNICAL (SOILS) REPORT2390 South Lipan Street Denver, CO 80223 phone: (303) 742-9700 fax: (303) 742-9666 email: kadenver@kumarusa.com www.kumarusa.com Office Locations: Denver (HQ), Colorado Springs, Fort Collins, and Frisco, Colorado GEOTECHNICAL ENGINEERING STUDY AND PAVEMENT THICKNESS DESIGN PROPOSED HARMONY ROAD MEDICAL CENTER SOUTHEAST CORNER OF HARMONY ROAD AND LADY MOON DRIVE FORT COLLINS, COLORADO DRAFT Prepared By: Reviewed By: Joshua L. Barker, P.E. Project Engineer _____________________________ James A. Noll, P.E. President Prepared For: Atwell, LLC 3033 East First Avenue, Suite 415 Denver, Colorado 80206 Attention: Ms. Anna Rasiak and Banner Health 1441 North 12th Street Phoenix, Arizona 85006 Attention: Mr. Kip Edwards, Vice President Development & Construction Project No. 12-1-490 November 15, 2012 Revised November 21, 2012 TABLE OF CONTENTS SUMMARY ................................................................................................................................ 0 PURPOSE AND SCOPE OF WORK .......................................................................................... 2 PROPOSED CONSTRUCTION ................................................................................................. 2 SITE CONDITIONS ................................................................................................................... 3 FIELD EXPLORATION .............................................................................................................. 3 SUBSURFACE CONDITIONS ................................................................................................... 4 LABORATORY TESTING .......................................................................................................... 5 GEOTECHNICAL CONSIDERATIONS ...................................................................................... 6 FOUNDATION RECOMMENDATIONS...................................................................................... 8 FOUNDATION WALLS AND RETAINING STRUCTURES........................................................14 FLOOR SLABS .........................................................................................................................14 SITE SEISMIC CRITERIA .........................................................................................................18 EXCAVATION CONSIDERATIONS ..........................................................................................18 SITE GRADING ........................................................................................................................19 SURFACE DRAINAGE .............................................................................................................22 UNDERDRAINS ........................................................................................................................23 PAVEMENT DESIGN ................................................................................................................24 DESIGN AND CONSTRUCTION SUPPORT SERVICES .........................................................27 LIMITATIONS ...........................................................................................................................28 FIG. 1 - LOCATIONS OF EXPLORATORY BORINGS FIG. 1 A – APPROXIMATE BEDROCK SURFACE CONTOURS FIG. 2 through 5 – LOGS OF EXPLORATORY BORINGS FIG. 6 – LEGEND AND NOTES FIGS. 5 through 19 - SWELL-CONSOLIDATION TEST RESULTS FIGS. 20 and 21 – GRADATION TEST RESULTS FIG. 22 – LABORATORY RESISTIVITY RESULTS FIG. 23 – HVEEM STABILOMETER TEST RESULTS FIG. 24 – MOISTURE-DENSITY RELATIONSHIPS TABLE I - SUMMARY OF LABORATORY TEST RESULTS APPENDIX A – DARWIN™ PAVEMENT THICKNESS DESIGN OUTPUTS SUMMARY 1. Subsurface conditions at the site were explored by drilling a total of 37 exploratory borings. The borings drilled within the proposed building footprints encountered a thin veneer of topsoil (plowed or rooted zone). The topsoil was underlain by 1 to 2 feet of man-placed fill material in seven of the borings. The topsoil and fill material were underlain by natural lean clay to sandy lean clay, which was in turn underlain by claystone bedrock at depths ranging from approximately 13 to 21.5 feet. The claystone bedrock continued to the explored depths ranging from approximately 20 to 30 feet. A zone of clayey sand with gravel was encountered above the claystone bedrock in 15 of the borings. The clayey sand zone varied in thickness from approximately 3.5 feet to 8 feet. The borings drilled within the proposed pavement areas generally encountered a thin layer of topsoil (plowed or root zone) overlying natural lean clay to lean clay with sand, which continued to the explored depths ranging from approximately 5 to 10 feet. Boring P-3 encountered a thin lens of man-placed fill material below the topsoil. Borings P-7 and P-11 encountered 2 to 7.75 inches of aggregate base course material at the ground surface instead of topsoil. Ground water was encountered in three of the borings at the time of drilling at depths ranging from 15.5 to 20 feet. Subsequent water level measurements made 12 to 14 days later encountered ground water in nineteen of the borings at depths ranging from approximately 15 to 21 feet. 2. The site conditions are favorable for construction of shallow spread footing foundations designed for a minimum dead load pressure and placed on a minimum of 3 feet of properly compacted structural fill material. A concern with shallow foundations arises when basement structures planned to be constructed immediately adjacent to the foundation elements at a later date. Given the planned future development, we propose that structures without basements and are a significant distance from below grade construction, be founded on shallow spread footing foundations. Structures with basements or that are planned to have basements adjacent to the proposed building should be founded on drilled shafts terminating in the bedrock at least 10 feet below the lowest floor level of the proposed building or future addition. Straight-shaft piers drilled into the bedrock used to support the proposed structures may be designed for allowable end-bearing soil pressures of 25,000 psf with allowable side shear equal to 10% of the end bearing pressure for the portion of the pier in bedrock. Piers should also be designed for a minimum dead load pressure of (applied dead load divided by pier cross-sectional area) 15,000 psf. Shallow spread footings used to support the proposed structures bearing on at least 6 feet of properly compacted structural fill material and should be designed for a net allowable bearing pressure of 2,500 psf and a minimum dead load pressure of 1,000 psf. 1. 3. Although the on-site soils and bedrock have a low to high swell potential, we feel a slab on grade floor system may be used at the buildings. It should be understood some slab movement may be experienced should the underlying expansive materials experience wetting. In order to reduce potential floor slab movement, floor slabs should be placed on at least 6-feet of relatively non-expansive fill. The use of imported structural fill or moisture conditioned on-site soils may be considered for use as underslab fill. 1 DRAFT 4. Areas of pavement should be provided with a moisture conditioned and compacted zone to a depth of at least 2 feet below the proposed pavement surface. The proposed pavement thickness designs are presented below: LOCATION Full Depth Asphalt (inches) Asphalt Over Aggregate BASE COURSE (inches) Concrete (inches) Auto Parking 5½ 3½ over 8 5 Drives/Fire Lanes 6 4 over 8 7 Cinquefoil Lane N/A 5½ over 11 8 Kumar & Associates, Inc. 2 DRAFT PURPOSE AND SCOPE OF WORK This report presents the results of a geotechnical engineering study and pavement thickness design for the proposed health care facility to be located on the southeast corner of Harmony Road and Lady Moon Drive in Fort Collins, Colorado. The project site is shown on Fig. 1. The study was conducted in accordance with the scope of work in our Proposal No. P-12-555 to Atwell, LLC dated October 17, 2012 and revised October 23, 2012. A field exploration program consisting of exploratory borings was conducted to obtain information on subsurface conditions. Samples of the soils and bedrock obtained during the field exploration were tested in the laboratory to determine their classification and engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundations, floor slabs, and site pavements. The results of the field exploration and laboratory testing are presented herein. This report has been prepared to summarize the data obtained during this study and to present our conclusions and recommendations based on the proposed construction and the subsurface conditions encountered. Design parameters and a discussion of geotechnical engineering considerations related to construction of the proposed structures are included in the report. PROPOSED CONSTRUCTION Based on the site plan provided, the construction of the facility is to be multi-phased in nature with the first phase to generally consist of a one-story health center, a two-story diagnostic and treatment facility, and a three-story hospital. The alignment of Cinquefoil Lane will be constructed for the initial phase, along with paved access drives and parking lots. La Fever Drive will be constructed in the future. Future construction will include an addition to the three- story hospital building, an addition to the health center building, expansion of the two-story diagnostic and treatment facility, and a central plant/receiving building structure. A stand alone medical office building is planned for the future at the southwest corner of the site. Expansion of the paved surface areas will also occur in the future. Portions of the 3-story hospital along with the future hospital additions will be provided with below grade basements constructed on the order of about 18 feet below the proposed structure. Kumar & Associates, Inc. 3 DRAFT A proposed site grading plan was not available at the time of this report preparation. Based on the existing topography at the site, we assume cuts and fills of 5 feet or less will occur to achieve the final ground surface elevations. If the proposed construction varies significantly from that described above or depicted in this report, we should be notified to reevaluate the recommendations provided in this report. SITE CONDITIONS At the time of drilling, the site was largely an undeveloped agricultural field that had a slight slope downward to the south and east. The west side of the site had numerous deciduous trees planted as part of an old farmstead. There was a single family residence and several outbuildings located along the west side of the site approximately 1,350 feet south of Harmony Road. A fenced storage lot was located near the southwest corner of the site. The site was bounded on the north by Harmony Road, on the west by Lady Moon Drive, on the south by the future alignment of La Fever Drive and on the east by Cinquefoil Lane. Harmony Road and Lady Moon Drive were paved with asphalt at the time of drilling. Cinquefoil Lane was rough graded and consisted of a gravel surface drive lane for a portion of the northern end of the alignment. An approximate difference in elevation of about 8 to 10 feet occurs across the site. The site was crossed from west to east by several irrigation ditches that were up to about 3 feet deep. FIELD EXPLORATION The field exploration for the project was conducted between October 31 and November 2, 2012. Thirty-seven (37) exploratory borings were drilled across the site as part of this study. One boring was drilled within the proposed footprint of the future 1-story medical office building, six borings were drilled within the proposed footprint of the 1-story health center and associated future addition, seven borings were drilled within proposed footprint of the 2-story diagnostic and treatment building, seven borings were drilled within the proposed 3-story Phase II hospital building footprint, four borings were drilled within the proposed future phase 2-story D&T and CUP building footprints, and twelve borings were drilled across the site in various areas of pavement. The borings were made to explore the subsurface conditions at the site at the general locations shown on Fig. 1. The boring locations and elevations were field located by the Kumar & Associates, Inc. 4 DRAFT client. The borings were drilled to depths ranging from 5 to 25 feet at the direction of the proposed facility owner. The borings were advanced into the overburden soils with 4-inch diameter continuous flight augers. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the soils and bedrock materials were taken with a 2-inch I.D. modified California sampler. The sampler was driven into the various strata with blows from a 140-pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D 1586. Penetration resistance values, when properly evaluated, indicate the relative density or consistency of the soils. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figs. 2 through 5. The legend and associated explanatory notes are also provided on Fig. 6. Measurements of the water level were made in the borings by lowering a weighted tape measure into the open hole shortly after completion of drilling and 12 to 14 days later. SUBSURFACE CONDITIONS Building Areas: The borings drilled within the proposed building footprints encountered a thin veneer of topsoil (plowed or rooted zone). The topsoil was underlain by 1 to 2 feet of man- placed fill material in seven of the borings. The topsoil and fill material were underlain by natural lean clay to sandy lean clay, which was in turn underlain by claystone bedrock at depths ranging from approximately 13 to 21.5 feet. The claystone bedrock continued to the explored depths ranging from approximately 20 to 30 feet. A zone of clayey sand with gravel was encountered above the claystone bedrock in 15 of the borings. The clayey sand zone varied in thickness from approximately 3.5 feet to 8 feet. The man-placed fill materials appeared to be manipulated on-site clayey materials. The natural clayey overburden soils were fine to coarse grained with occasional gravel, stiff to very stiff consistency (based on blow count data) and light brown to brown. The clayey sand was coarse grained with frequent gravel, medium dense and light brown to brown. The claystone bedrock was fine to medium grained, firm to very hard and light brown to brown to brownish gray. Ground water was encountered in three of the borings at the time of drilling at depths ranging from 15.5 to 20 feet. Subsequent water level measurements made 12 to 14 days later encountered ground water in nineteen of the borings at depths ranging from approximately 15 to Kumar & Associates, Inc. 5 DRAFT 21 feet. Water levels may fluctuate with time, and may fluctuate upward after wet weather and landscape irrigation. Pavement Areas: The borings drilled within the proposed pavement areas generally encountered a thin layer of topsoil (plowed or root zone) overlying natural lean clay to lean clay with sand, which continued to the explored depths ranging from approximately 5 to 10 feet. Boring P-3 encountered a thin lens of man-placed fill material below the topsoil. Borings P-7 and P-11 encountered 2 to 7.75 inches of aggregate base course material at the ground surface instead of topsoil. The man-placed fill materials appeared to be manipulated on-site clayey materials. The natural clayey overburden soils were fine to coarse grained with occasional gravel, stiff to very stiff consistency and light brown to brown. Ground water was not encountered in the borings at the time of drilling. Bedrock Topography: The competent bedrock surface ranged in elevation from 4937 to 4968 feet and appeared to slope gently down towards the south and west. A bedrock surface contour map is provided on Fig. 1A. LABORATORY TESTING The samples obtained from the exploratory borings were visually classified in the laboratory by the project engineer and samples were selected for laboratory testing. Laboratory testing included index property tests, such as moisture content (ASTM D 2216), dry unit weight, percent passing the No. 200 sieve (ASTM D 1140), liquid and plastic limits (ASTM D 4318), and percent water soluble sulfates. Swell-consolidation tests (ASTM D 4546, Method B) were conducted on samples of the soil and bedrock to determine the compressibility or swell characteristics under loading and when submerged in water. Results of the laboratory testing program are shown adjacent to the boring logs, Figs. 2 through 5, plotted on Figs. 7 through 24 and are summarized in the attached Summary of Laboratory Test Results, Table I. Swell consolidation testing, presented on Figs. 6 through 19, indicate samples of the lean clay generally exhibit a low to high swell potential when tested under a constant surcharge of 200 psf or 1,000 psf. The claystone bedrock exhibited low to high swell potential under similar conditions. A single sample tested indicated low consolidation potential, Kumar & Associates, Inc. 6 DRAFT although we believe this was the result of sample disturbance and is not indicative of the on-site materials. Water Soluble Sulfates: The concentration of water soluble sulfates measured in samples obtained from the exploratory borings was less than 0.02%. This concentration of water soluble sulfates represents a Class 0 level of severity for exposure in accordance with the guidelines presented in ACI 201. The guidelines have severity levels for potential exposure of Class 0 through Class 3. We recommend that all concrete on the site meet the criteria presented in ACI 201 for Class 0 sulfate resistance. Buried Metal Corrosion: Samples of the overburden soils were tested in the laboratory to evaluate soil electrical resistivity, chloride content, and pH characteristics. The tests were conducted in accordance with procedures in Appendix A of AWWA C-105, American Waterworks Association publication. Results are presented on Fig. 22 and in Table I. The test results indicated minimum electrical resistivities ranging from 1,190 to 2,000 ohm-cm. Based on the Ductile Iron Pipe Research Association (DIPRA) handbook, the lower resistance material would classify as potentially corrosive. At a minimum, buried metal utilities should be protected with a polyethylene encasement. The chloride contents of the samples tested was 0.03 and the pH varied between 8.1 and 8.4. We recommend a qualified corrosion engineer review the information presented in consideration of corrosion protection for buried metal. GEOTECHNICAL CONSIDERATIONS The site is generally consists of a low to high swelling clay overburden soil overlying a low to high swelling claystone bedrock. Several samples of the clay soils possessed low moisture content and low dry density indicating a potential for collapse as shown on Fig. 19. The swell potential of the overburden soils is generally the result of low in-situ moisture conditions and high dry density values. We performed a swell-consolidation test on a sample remolded to approximately 95% of the standard Proctor maximum dry density near the optimum moisture content. The remolded sample indicated low swell potential when wetted under a 200-psf surcharge pressure. This indicates that the on-site soils, exclusive of claystone, are generally Kumar & Associates, Inc. 7 DRAFT suitable for use as structural fill below footing foundations and floor slabs. Swelling soils frequently become problematic for shallow foundations, floor slabs, and pavement structures placed directly on the soils in their natural state. Heaving movements of the foundations, floor slabs and pavement structures at a minimum can produce a range of effects ranging from aesthetical issues such as dry wall cracking to structural issues that could require costly repairs to the foundations and building walls. A table presenting theoretical heaving movements is presented in the Floor Slabs section of this report. Swelling materials are only problematic if the natural moisture content of the soils and bedrock are allowed to fluctuate. Subexcavating and replacing the clayey materials below the proposed foundations, floor slabs or pavement structures is a common method of mitigating the swell potential of the clayey soils. We recommend that the on-site soils and bedrock be subexcavated, moisture conditioned and properly compacted to a depth of at least 6 feet below the proposed floor slab subgrade elevation to mitigate heaving movements. The site conditions are feasible for construction of shallow spread footing foundations designed for a minimum dead load pressure and placed on a minimum of 6 feet of properly compacted structural fill material. The spread footings appear to be feasible for the health center and its future expansion, as well as the future office building. A concern with shallow foundations arises when basement structures planned to be constructed immediately adjacent to the foundation elements at a later date. Significant shoring and underpinning would likely be required to construct a deep excavation adjacent to a building founded on spread footing foundations. Given the planned future development, structures without basements or that are a significant distance from below grade construction (a minimum of 20 feet away) may be founded on spread footing foundations. Structures with basements or that are planned to have basements adjacent to the proposed building should be founded on drilled shafts terminating in the bedrock at least 10 feet below the lowest floor level of the proposed building or future addition. Buildings adjacent to deep basement that are founded on drilled shafts will be less susceptible to movements due to construction of below grade structures and will have the benefit of requiring less shoring efforts during excavation and construction of the future phases. Kumar & Associates, Inc. 8 DRAFT FOUNDATION RECOMMENDATIONS As discussed above, structures with below grade basement structures or structures that will be constructed adjacent to buildings with below grade basements should be founded on straight shaft drilled piers. Other free-standing structures without basements or away from structures with basements may be founded on shallow spread footings placed on a minimum of 6 feet of properly compacted structural fill material. Drill Pier Foundation: The design and construction criteria presented below should be observed for a straight-shaft drilled pier foundation system. The construction details should be considered when preparing project documents. 1. Piers should be designed for an allowable end bearing pressure of 25,000 psf and a side shear of 2,500 psf. Bedrock encountered within 5 feet of the proposed floor elevation surface should not be included in the design for side shear or minimum penetration. Uplift due to structural loadings on the piers can be resisted by using 75% of the allowable skin friction value plus an allowance for pier weight. 2. Piers should also be designed for a minimum dead load pressure of 15,000 psf based on pier end area only. Application of dead load pressure is the most effective way to resist foundation movement due to swelling soils. However, if the minimum dead load requirement cannot be achieved and the piers are spaced as far apart as practical, the pier length should be extended beyond the minimum bedrock penetration and minimum length to mitigate the dead load deficit. This can be accomplished by assuming one-half of the skin friction given above acts in the direction to resist uplift caused by swelling soil near the top of the pier. The owner should be aware of an increased potential for foundation movement if the recommended minimum dead load pressure is not met. 3. Piers should penetrate at least three pier diameters or 10 feet into the bedrock, whichever is greater. Based on the depth to bedrock encountered in the borings, a minimum pier length of 20 feet is recommended. Both requirements for minimum pier length and minimum bedrock penetration should be met. 4. Piers should be designed to resist lateral loads using a modulus of horizontal subgrade reaction of 30 tcf in the natural clay and in properly compacted structural fill, and 200 tcf in bedrock. These modulus values are for a long 1-foot diameter pier and must be Kumar & Associates, Inc. 9 DRAFT corrected for pier size. Alternatively, the lateral capacity of the piers may be analyzed using LPILE computer programs and the parameters provided in the following table. The strength criteria provided in the table are for use with these software applications only and may not be appropriate for other usages: Material C φ γ ks kc Є50 Soil Type Natural Clay and Clayey Fill 750 0 120 500 200 0.007 1 Bedrock 8,000 0 125 2,000 800 0.004 1 c Cohesion intercept (pounds per square foot) φ Angle of internal friction (degrees) γ Total unit weight (pounds per cubic foot) ks Initial static modulus of horizontal subgrade reaction (pounds per cubic inch) kc Initial cyclic modulus of horizontal subgrade reaction (pounds per cubic inch) Є50 Strain at 50 percent of peak shear strength Soil Types: 1. Stiff clay without free water (Reese) 5. Closely spaced piers may require appropriate reductions of the lateral and axial capacities. Reduction in lateral load capacity may be avoided by spacing the piles at least 6 piers diameters (center to center) in the direction parallel to pile loading, and 2.5 diameters in the direction perpendicular to loading. For axial loading, the piers should be spaced a minimum of 3 diameters center to center. More closely spaced piers should be studied on an individual basis to determine the appropriate reduction in axial and lateral load design parameters. If the recommended pier spacings cannot be achieved, we recommend the load- displacement curve (p-y curve) for an isolated pier be modified for closely spaced piers using p-multipliers to reduce all the p values on the curve. With this approach, the computed load carrying capacity of the pier in a group is reduced relative to the isolated pier capacity. The modified p-y curve should then be reentered into the LPILE software to calculate the pier deflection. It should be noted that the reduction for the leading pier, the pier leading the direction of movement of the group, is less that that for the trailing piers. We recommend p-multipliers of 0.6 and 1.0 for pier spacing of 3 and 6 diameters, respectively, for the leading pier, and 0.4 and 1.0 for 3 and 6 diameter spacings, respectively, for the trailing piers. Reduction factors for spacings between 3 and 6 diameters may be obtained by linear interpolation. It will be necessary to determine the Kumar & Associates, Inc. 10 DRAFT load distribution between the piers that attains deflection compatibility because the leading pier carries a higher proportion of the group load and the pier cap prevents differential movement between the piers. 6. A minimum 4-inch void should be provided beneath the grade beams to concentrate pier loadings and to separate the expansive soil from the grade beams. Absence of a void space will result in a reduction in dead load pressure, which could result in upward movement of the foundation system. A void should also be provided beneath necessary pier caps. 7. Piers should be reinforced their full length with at least one No. 5 reinforcing rod for each 18 inches of pier perimeter to resist tension created by the swelling materials. 8. A minimum pier diameter of 12 inches is recommended to facilitate proper cleaning and observation of the pier hole. The pier length-to-diameter ratio should not exceed 30. 9. Bedrock penetration in all pier holes should be roughened artificially to assist the development of peripheral shear stress between the pier and the bedrock. The roughening should be installed with a grooving tool in a pattern considered appropriate by the geotechnical engineer. Horizontal grooves at 1 to 2-foot centers or helical grooves with a 1 to 2-foot pitch are acceptable patterns. The specifications should allow the geotechnical engineer to eliminate the requirements for pier roughening if it appears their installation is not beneficial. This could occur if a rough surface is provided by the drilling process or if the presence of water and/or weakly cemented materials results in a degradation of the pier hole during the roughening procedure. 10. Based on the results of our field exploration, laboratory testing and our experience with similar, properly constructed drilled pier foundations, we estimate pier settlement will be low. Generally, we estimate the settlement of a pier 2 to 3 feet in diameter will be approximately ½ to 1-inch when designed according to the criteria presented herein. The settlement of closely spaced piers will be larger and should be studied on an individual basis. Kumar & Associates, Inc. 11 DRAFT 11. The presence of water during construction of piers could require the use of temporary casing or dewatering equipment in the pier holes to control water infiltration. The requirements for casing and dewatering equipment can sometimes be reduced by placing concrete immediately upon cleaning and observing the pier hole. In no case should concrete be placed in more than 3 inches of water. 12. When water and/or drilling slurry is present outside the casing, care should be taken that concrete of sufficiently high slump is placed to a sufficiently high elevation inside the casing to prevent intrusion of the water and/or slurry into the concrete when the casing is withdrawn. 13. The drilled shaft contractor should mobilize equipment of sufficient size and operating condition to achieve the required bedrock penetration. 14. Care should be taken that the pier shafts are not oversized at the top. Mushroomed pier tops can reduce the effective dead load pressure on the piers. 15. Pier holes should be properly cleaned prior to the placement of concrete. 16. Concrete used in the piers should be a fluid mix with sufficient slump so it will fill the void between reinforcing steel and the pier hole. We recommend a concrete slump in the range of 5 to 8 inches be used. 17. Concrete should be placed in piers the same day they are drilled. The presence of water or caving soils may require that concrete be placed immediately after the pier hole is completed. Failure to place concrete the day of drilling will normally result in a requirement for additional bedrock penetration. 18. The field exploration did not encounter weak to non-cemented sandstone below the bedrock surface, but have been encountered at other locations in the area. If present, these materials may cave during the drilling process and casing in the bedrock may be required to complete the piers. Zones of caving material should not be included in the required length of penetration and the pier length should be increased an amount equal to the length of caving material. In general, no allowance for skin friction is given in Kumar & Associates, Inc. 12 DRAFT cased portions of the bedrock. However, if a significant quantity of the bedrock is being cased, we can evaluate the possibility of reduced skin friction values in the cased bedrock. 19. A representative of the geotechnical engineer should observe pier drilling operations on a full-time basis to assist in identification of adequate bedrock strata and monitor pier construction procedures. Shallow Spread Footings: The design and construction criteria presented below should be observed for a spread footing foundation system. The construction details should be considered when preparing project documents. 1. Footings placed on a minimum of 6 feet of properly compacted structural fill material should be designed for an allowable soil bearing pressure of 3,000 psf. The allowable bearing pressure may be increased by 1/3 for transient loadings. The footings should also be designed for a minimum dead load pressure of 1,000 psf. In order to satisfy the minimum dead load pressure and minimum footing width criteria, it may be necessary to concentrate loads by using a grade beam and pad or similar foundation design. If this system is used, a void should be provided beneath the grade beams between pads. 2. Based on experience, we estimate total settlement for footings designed and constructed as discussed in this section will be approximately 1 inch. Differential settlements across the building are estimated to be approximately ½ to ¾ of the total settlement. 3. Spread footings should have a minimum footing width of 16 inches for continuous footings and of 24 inches for isolated pads. 4. Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below the exterior grade is typically used in this area. 5. The lateral resistance of a spread footing placed on properly compacted structural fill material will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to Kumar & Associates, Inc. 13 DRAFT sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.3. Passive pressure against the sides of the footings can be calculated using an equivalent fluid unit weight of 175 pcf. The above values are working values. Compacted fill placed against the sides of the footings to resist lateral loads should be a nonexpansive material. Fill should be placed and compacted to at least 95% of the standard Proctor maximum dry density at a moisture content as listed in the Site Grading section of this report. 6. Continuous foundation walls should be reinforced top and bottom to span an unsupported length of at least 10 feet. 7. Areas of loose or soft material and/or deleterious substances encountered within the foundation excavation should be removed and the footings extended to adequate natural bearing material. As an alternate, the loose or soft material and/or deleterious substances may be removed and replaced with nonexpansive fill material and compacted as listed in the Site Grading section of this report. New fill should extend down from the edges of the footings at a 1 horizontal to 1 vertical projection. 8. The results of our field exploration indicate existing fill may be encountered in foundation excavations below the proposed foundation bearing elevations. The existing fill material should be removed and the footings extended to adequate natural bearing material. As an alternate, the loose or soft material and/or deleterious substances may be removed and replaced with nonexpansive fill material and compacted as listed in the Site Grading section of this report. New fill should extend down from the edges of the footings at a 1 horizontal to 1 vertical projection. 9. Care should be taken when excavating the foundations to avoid disturbing the supporting materials. 10. The natural soils may pump or deform excessively under heavy construction traffic as the excavations approach footing levels. Construction equipment should be selected to avoid this difficulty. The movement of vehicles over proposed foundation areas should be restricted. Kumar & Associates, Inc. 14 DRAFT 11. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement. FOUNDATION WALLS AND RETAINING STRUCTURES Structures which are laterally supported and can be expected to undergo only a moderate amount of deflection should be designed for an at-rest lateral earth pressure computed on the basis of an equivalent fluid unit weight of 65 pcf for backfill consisting of the on-site fine-grained soils and 55 pcf for backfill consisting of imported granular materials meeting CDOT Class I Structure Backfill criteria. Cantilevered retaining structures which can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of 45 pcf for backfill consisting of the on-site fine-grained soils and 36 pcf for backfill consisting of imported granular materials meeting CDOT Class I Structure Backfill criteria. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent buildings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. Compacted fill placed against the sides of the below grade structure to resist lateral loads should be a non-expansive, material. Fill should be placed and compacted to at least 95% of the standard Proctor maximum dry density at a moisture content as presented in the Site Grading section of this report. Care should be taken not to over-compact the backfill around below- grade structures since this could cause excessive lateral pressure on the walls. FLOOR SLABS Floor slabs present a difficult problem where moderately expansive materials are present near floor slab elevation because sufficient dead load cannot be imposed on them to resist the uplift pressure generated when the materials are wetted and expand. The most positive method to avoid damage as a result of floor slab movement is to construct a structural floor above a well- Kumar & Associates, Inc. 15 DRAFT vented crawl space. The floor would be supported on grade beams and piers the same as the main structure. Based on the moisture-volume change characteristics of the materials encountered, we believe slab-on-ground construction may be used, provided the risk of distress resulting from slab movement is accepted by the owner. The following discussion presents estimates of slab heave for different wetting depth scenarios to aid in the floor system decision making process. Floor slab movement risk can be mitigated to a certain degree by providing a zone of non- to low-swelling, relatively impervious fill directly beneath the slab. Heave estimate calculations can be useful in evaluating the relative effectiveness of varying the thickness of a select underslab fill layer. However, such calculations can not address the uncertainty in the potential depth and degree of wetting that may occur under a floor slab, or the variability of swell potential across a site, which is frequently erratic. We have performed calculations to demonstrate the potential for slab movement if the underslab soils should be thoroughly wetted to significant depth below the depth of the select fill layer. The following table presents estimates of potential heave based on the results of swell- consolidation tests using test and analysis methods generally accepted in the Colorado Front Range. Both depth of wetting and depth of select fill were considered as variables in the analysis. ALTERNATIVE SLAB HEAVE IN INCHES 10 feet of wetting 15 feet of wetting 20 feet of wetting No Treatment 4.1 5.6 6.9 3 Feet of M/C 2.7 4.2 5.6 8 Feet of M/C 1.0 2.5 3.5 The heave estimate calculations demonstrate that significant heave should be expected if wetting of the underslab soils occurs to significant depth below the bottom of the select fill layer. However, our experience indicates that the large majority of similar structures underlain by similar subsoils do not experience extreme moisture increases in the underslab soils to significant depth provided that good surface drainage is designed, constructed, and maintained, and that good irrigation practices are followed. Wetting can also occur as a result of unforeseeable influences such as plumbing breaks, or in some cases even due to off-site influences depending on geologic conditions. Kumar & Associates, Inc. 16 DRAFT Considering the above discussion, we believe slab-on-grade construction may be used for the project, provided that the risk of distress is recognized and accepted by the owner, and the following measures are taken to reduce the damage which could result from movement should the underslab materials be subjected to excessive moisture increases. The intent of our recommendations is to provide for a condition where there is a good chance slab heave movements will not exceed 1 inch and it is unlikely they will exceed 2 inches unless extreme wetting is allowed. Barring unforeseen events, we do not believe extreme wetting is likely to occur if the surface and subsurface drainage and irrigation recommendations presented in this report are followed. It is also very important to provide the recommended isolation between the structure and the slab-on-grade floors to reduce damage in the event that heaving occurs. We recommend the existing expansive soils and bedrock be subexcavated to a depth of at least 6 feet below the bottom of the floor slab elevations. Use of the on-site materials as structural fill is discussed in the Site Grading section of this report. All fill materials for support of floor slabs should be placed and compacted according to the criteria presented in the Site Grading section of this report. An underdrain should be constructed at the base of the nonexpansive fill zone when the zone is excavated into the claystone bedrock to prevent development of perched water in the fill. This drain should be designed in accordance with recommendations in the Underdrain System of this report. The following measures should be taken to reduce damage which could result from movement should the underslab materials be subjected to moisture changes. 1. Floor slabs should be placed at least 6 feet of moisture-controlled fill obtained from on- site sources as discussed in the Site Grading section of this report. At the planned floor level, the existing grade is such that some overexcavation is anticipated to be required at most locations. 2. The placement of the 6-foot layer of moisture conditioned fill will not eliminate the potential for slab movement, but should reduce the movement by either removing a portion of the expansive materials or providing a surcharge on the expansive materials, also reducing the amount of heave that can occur. Based on theoretical calculations, Kumar & Associates, Inc. 17 DRAFT which consider the swell potential of the soils and anticipated depth of wetting, we feel that floor slabs constructed as discussed in this section will be less than 1-inch. 3. The lean clay soils, if used as moisture conditioned fill will be represented by a modulus of subgrade reaction estimated at 125 psi/inch for interior slabs. 4. Floor slabs should be separated from all bearing walls and columns with expansion joints, which allow unrestrained vertical movement. 5. Interior non-bearing partitions resting on floor slabs should be provided with slip joints, preferably at the bottom of the walls, so if the slabs move, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards, stairways and doorframes. Slip joints, which will allow at least 2 inches of vertical movement are recommended. If slab bearing masonry block or steel stud partitions are constructed, the slip joints will have to be placed at the tops of the walls. If slip joints are provided at the tops of walls and the floors move, it is likely the partition walls will show signs of distress, such as cracking. An alternative, if masonry block walls or other walls without slip joints at the bottoms are required, is to found them on footings and grade beams and construct the slabs independently of the foundation. If slab bearing partition walls are required, distress may be reduced by connecting the partition walls to the exterior walls using slip channels. Floor slabs should not extend beneath exterior doors or over foundation grade beams, unless saw cut at the beam after construction. 6. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Joint spacing is dependent on slab thickness, concrete aggregate size, and slump, and should be consistent with recognized guidelines such as those of the Portland Cement Association (PCA) or American Concrete Institute (ACI). The joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. 7. If moisture-sensitive floor coverings will be used, mitigation of moisture penetration into Kumar & Associates, Inc. 18 DRAFT the slabs, such as by use of vapor barrier, may be required. If an impervious vapor barrier is used, special precautions will be required to prevent differential curing problems, which could cause the slab to curl. ACI 302.1R addresses this topic. 8. All plumbing lines should be tested before operation. Where plumbing lines enter through the floor, a positive bond break should be provided. Flexible connections should be provided for slab-bearing mechanical equipment. The precautions and recommendations itemized above will not prevent the movement of floor slabs if the underlying expansive materials are subjected to alternate wetting and drying cycles. However, the precautions should reduce the damage if such movement occurs. SITE SEISMIC CRITERIA The soil profile is expected to consist of compacted moisture conditioned fill and/or natural clay overlying claystone bedrock. The overburden materials will generally classify as International Building Code (IBC) Site Class D. The underlying bedrock generally classifies as IBC Site Class B or C. Based on our experience with similar subsurface profiles along the Front Range area, we recommend a design soil profile of IBC Site Class C. Based on the subsurface profile, and site seismicity, liquefaction is not a design consideration. EXCAVATION CONSIDERATIONS We assume that the site excavations will be constructed by generally over-excavating the side slopes to a stable configuration where enough space is available. All excavations should be constructed in accordance with OSHA requirements, as well as state, local and other applicable requirements. The claystone bedrock generally classify as OSHA Type A soil, and the fill materials and natural overburden clay soils generally classify as OSHA Type B soils. Some of the granular soils encountered above the claystone bedrock will classify as OSHA Type C soil. In our opinion, excavation of the on-site materials should be possible with conventional excavation equipment. Some of the soils near the ground surface or the claystone bedrock may require excavation equipment provided with ripper teeth to loosen the soils. Kumar & Associates, Inc. 19 DRAFT SITE GRADING Cut and Fill Slopes: We do not anticipate significant cut and fill slopes on this project. Due to the flatness of ground surface slopes, no signs of major slope instability were noted in the existing slopes during our field investigation. Major stability problems are not anticipated if site grading is carefully planned and cuts and fills do not exceed approximately 20 feet in height. Permanent unretained cuts in the overburden soils, above the ground water level and less than 20 feet in height may be constructed at 3 horizontal to 1 vertical. The risk of slope instability will be significantly increased if seepage is encountered in cuts. Based on the planned grading and ground water levels measured in the borings, we do not anticipate seepage will be encountered. However if it is encountered, a stability investigation should be conducted to determine if the seepage will adversely affect the cut. Fills up to 20 feet in height can be constructed if the fill slopes do not exceed 3 horizontal to 1 vertical (3:1) and the fills are properly compacted and drained. The ground surface underlying all fills should be carefully prepared by removing all organic matter, scarification to a depth of 8 inches and compacting the surface to provide a uniform base for fill placement. Fill placed on slopes exceeding 4:1 should be benched into the slope. Good surface drainage should be provided around all permanent cuts and fills to direct surface runoff away from the slope faces. Fill slopes, cut slopes and other stripped areas should be protected against erosion by revegetation or other methods. No formal stability analyses were performed to evaluate the slopes recommended above. Published literature and our experience with similar cuts and fills indicate the recommended slopes should have adequate factors of safety. If a detailed stability analysis is required, we should be notified. Fill Considerations: The on-site clay soils are suitable for reuse as fill under slabs and pavement subgrades. Fill placed slab support should be placed with careful moisture control as discussed later in this section. Uniform moisture conditions in fill obtained from on-site sources placed for slab support will be important in reducing the swell potential of the compacted fill. In order to obtain uniform moisture in the fill, a moistening and mixing program will need to be developed during the initial stages of site grading. The existing moisture content of the clay soils appears to be well under the assumed optimum moisture content. Recommendations are Kumar & Associates, Inc. 20 DRAFT presented in the report regarding material properties, degree of compaction and moisture control. We recommend the on-site materials used as fill be mixed thoroughly with construction equipment, such as a mixer/reclaimer to break up clumps of soil and add water to obtain a homogeneous mixture. The use of a disc may be considered, but the effectiveness of this mixing process should be evaluated at the time of fill placement. Material Specifications: The following material specifications are presented for fills on the project site. A geotechnical engineer should evaluate the suitability of all proposed fill materials to be used on the site prior to placement. Fill Beneath Buildings and Parking Lots: The on-site overburden soils, exclusive of claystone bedrock, are suitable for re-use as structural fill below spread footing foundations, floor slabs and pavement structures. Imported structural fill, if required, for use under footings or slabs should meet the following criteria: Percent Passing No. 200 Sieve Less than 75% Liquid Limit Less than 35 Plasticity Index Less than 20 Swell Potential < 2% at 200 psf surcharge at optimum moisture content Foundation Wall Backfill (Interior and Exterior Backfill): On-site soils or approved imported soils meeting the criteria presented above may be used for foundation wall backfill. Utility Trench Backfill: Material excavated from the utility trenches may be used for backfill provided it does not contain unsuitable material or particles larger than 4 inches. Other Fill Material: All fill material should be a non-expansive soil free of vegetation, brush, sod and other deleterious substances and should not contain rocks or particles having a diameter of more than 4 inches. If grading is performed during times of freezing weather, the fill should not contain frozen materials and if the subgrade is allowed to freeze, all frozen material should be removed prior to additional fill placement or footing, slab or pavement construction. Base Course: Base course placed in conjunction with pavements should consist of material meeting the requirements of CDOT Class 5 or 6 base course. Kumar & Associates, Inc. 21 DRAFT Compaction Specifications: We recommend the following compaction criteria be used on the project: 1. Compaction of all on-site soil fill materials placed under building foundations and floor slabs should be placed at moisture contents between 0 and +3% of the optimum moisture content (ASTM D 698) for fine grained fill. Any imported granular fill material should be placed within 2% of the optimum moisture content and cohesive fill placed within pavement or non-building areas should be placed within -1 to +3% of the optimum moisture content. Recommended compaction specifications for this project, based on percentage of maximum density are presented in the following table: Area Percentage of Maximum Standard Proctor Density (ASTM D 698/ AASHTO T-99) Percentage of Maximum Modified Proctor Density (ASTM D 1557, AASHTO T-180) Beneath Footings and Foundation Elements 98 N/A Beneath Floor Slabs and Parking Lots 95 N/A Utility Trenches 95 N/A Parking Lots/Drives 95 N/A Aggregate Base Course N/A 95 Dewatering: Site grading required to prepare the structure foundations for basement levels will generally require grading consisting of temporary cuts up to about 20 feet. Excavations are expected to be impacted by the presence of ground water. Prior to excavation, we recommend a dewatering plan be developed and implemented by the contractor. An open cut interceptor drain outside the structures may be considered, but may require frequent maintenance during construction. Excavation below the ground water should be avoided, as caving of the side slopes and disturbance of the bearing surface may occur, unless adequately dewatered. We suggest the ground water level be lowered to at least 2 feet below the base of the required excavation prior to achieving the final grade. The fine grained soils are expected to be unstable under trafficking by construction equipment. It is likely that any wet clayey material in this area will require Kumar & Associates, Inc. 22 DRAFT removal and replacement with a compacted granular fill prior to slab construction. In order to reduce disturbance of the foundation materials during construction, we recommend the contractor consider a thick layer of gravel to provide a stable working platform. Reuse of excavated granular soils, if any, may be considered. We assume that the lower level excavations will be constructed by overexcavating the slopes to a stable configuration rather than using a temporary retaining system. We recommend temporary excavation slopes in the soils be constructed no steeper than 2 horizontal to 1 vertical. Seepage of ground water in cut slopes may require that the slopes be flattened for safety purposes. Temporary shoring will most likely be required for excavations constructed below the ground water level. Pumps located within the excavation may still be required to provide sufficiently dry dewatered working conditions. SURFACE DRAINAGE Proper surface drainage is very important for acceptable performance of the structures during construction and after the construction has been completed. Drainage recommendations provided by local, state and national entities should be followed based on the intended use of the facility. The following recommendations should be used as guidelines and changes should be made only after consultation with the geotechnical engineer. 1. Excessive wetting or drying of the foundation and slab subgrade(s) should be avoided during construction. 2. Exterior backfill should be adjusted to near optimum moisture content (generally ±2% of optimum unless indicated otherwise in the report) and compacted to at least 95% of the ASTM D 698 (standard Proctor) maximum dry density. 3. Care should be taken when compacting around the foundation walls and underground structures to avoid damage to the structure. Hand compaction procedures, if necessary, should be used to prevent lateral pressures from exceeding the design values. 4. The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 Kumar & Associates, Inc. 23 DRAFT inches in the first 10 feet in unpaved areas. Site drainage beyond the 10-foot zone should be designed to promote runoff and reduce infiltration. A minimum slope of 3 inches in the first 10 feet is recommended in the paved areas. These slopes may be changed as required for handicap access points in accordance with the Americans with Disabilities Act. 5. The upper 1 to 2 feet of the backfill should be relatively impervious material compacted as above to limit infiltration of surface runoff. 6. Ponding of water should not be allowed in backfill material or in a zone within 10 feet of the foundation walls whichever is greater. 7. Roof downspouts and drains should discharge well beyond the limits of all backfill. 8. Excessive landscape irrigation should be avoided within 10 feet of the foundation walls. As discussed under Floor Slabs, if slab-on-grade floors are used, the risk could be significantly reduced by eliminating landscape irrigation within about 15 feet of buildings and limiting irrigation elsewhere on side, provided good surface drainage is provided. 9. Plastic membranes should not be used to cover the ground surface adjacent to foundation walls. UNDERDRAINS We recommend that the buildings with basements be protected by a multi-drain system. The upper drain system should consist of a perimeter underdrain system at an elevation just below the bottom of the basement level slab and a geocomposite wall drain placed exterior to the walls. The intent of the perimeter drain is to collect possible surface water infiltration and perched water levels that may have accumulated on top of relatively impervious layers in the upper bedrock zones. The geocomposite wall drain is to be installed to reduce potential for hydrostatic buildup. We recommend a geocomposite drain board such as the Miradrain 6000 series be used. Also, the geocomposite drain board should allow flow rates of at least 15 gallons per minute per foot of board. The upper level perimeter drain should be constructed with the high point at least 6 inches below the bottom of the floor slab sloping at least ½ percent to an outlet or sump. The Kumar & Associates, Inc. 24 DRAFT geocomposite wall drain should be connected to the upper level perimeter drain system. Lateral drains should be installed below the floor slab spaced on maximum 50-foot centers. The upper perimeter drain including laterals should consist of 4-inch diameter, rigid perforated plastic pipe constructed at a minimum slope of ½%. The lower drain system should consist of a 4-inch diameter pipes. The pipes should be covered with at least 6 inches of CDOT #67 coarse aggregate which in turn are wrapped with filter fabric. A lower drain system should consist of a perimeter drain placed no higher than the interface of the material located at the bottom of the zone of subexcavation and the underlying bedrock. An additional, drain system will be required for construction dewatering purposes. The construction dewatering requirements are discussed in another section of this report. Both permanent underdrain systems should be sloped to a sump or multiple sumps where water can be removed by pumping or gravity drainage. Standby pump capacity should be provided in the event of pump failure. We also believe an overdesigned pump capacity is desirable in the event ground water conditions change. PAVEMENT DESIGN A pavement section is a layered system designed to distribute concentrated traffic loads to the subgrade. Performance of the pavement structure is directly related to the physical properties of the subgrade soils and traffic loadings. Soils are represented for pavement design purposes by means of a resilient modulus value for flexible pavements and a modulus of subgrade reaction for rigid pavements. Both values are empirically related to strength. Pavement design procedures are based on strength properties of the subgrade and pavement materials assuming stable, uniform conditions. Certain soils, such as those encountered on this site, are potentially expansive and require additional precautions be taken to provide for adequate pavement performance. Expansive soils are problematic only if a source of water is present. If those soils are wetted, the resulting movements can be large and erratic. Therefore, pavement design procedures address expansive soils only by assuming they will not become wetted. Proper surface drainage is essential for adequate performance of pavement on these soils. Kumar & Associates, Inc. 25 DRAFT Subgrade Materials: Based on the field and laboratory studies, tested samples of the subgrade materials at the site classify as A-6 and A-7-6 with group indices ranging from 3 and 26 in accordance with the American Association of State Highway and Transportation Officials (AASHTO) classification. These soils are generally considered to provide fair to poor subgrade support. An R-value performed on the overburden soils resulted in an R-value of 9. Using correlation calculations presented by the Colorado Department of Transportation, this value correlates to a subgrade resilient modulus (MR) of 3,448 psi. Design Traffic: Actual traffic conditions for this project were unavailable at the time of report preparation. Therefore, we have estimated traffic loading conditions based on experience with similar facilities. We have assumed that the traffic loading conditions for auto parking areas will be represented by an Equivalent Daily Load Application (EDLA) of 5 and combined truck/auto areas (drives/fire lanes) will be represented by and EDLA of 10, resulting in Equivalent Single Axle Load’s (ESALs)of 36,500 and 73,000 respectively. The proposed Cinquefoil Lane and La Fever roadways were assumed to classify as a Local: Industrial/Commercial roadway in accordance with the Larimer County Urban Area Street Standards. This roadway classification indicates that an EDLA of 50 be used, which corresponds to an ESAL value of 365,000. If traffic loading conditions are different from that described, we should be notified to re-evaluate the recommendations presented herein. Pavement Thickness Design: A pavement thickness design was performed using DARWINTM, a proprietary pavement design and analysis computer program which uses 1993 AASHTO pavement design guidelines. Pavement design input parameters are based on the Larimer County Urban Area Street Standards design guidelines. Based on the subgrade soils encountered or anticipated, we recommend the following pavement sections for consideration: LOCATION Full Depth Asphalt (inches) Asphalt Over Aggregate BASE COURSE (inches) Concrete (inches) Auto Parking 5½ 3½ over 8 5 Drives/Fire Lanes 6 4 over 8 7 Cinquefoil Lane N/A 5½ over 11 8 The Larimer County Urban Area Street Standards design guidelines do not allow construction of full depth asphalt sections on public roadways. Therefore, the Cinquefoil Drive pavement thickness recommendations presented above do not include a full depth asphalt pavement Kumar & Associates, Inc. 26 DRAFT thickness option. Composite and full depth pavement sections are allowed for private pavement facilites. Flexible Pavement Materials: Flexible pavements should meet the requirements presented in the Larimer County Urban Area Streets Standards with respect to grading and compaction. A mix design should be submitted for approval, prior to placement. Rigid Pavements: All concrete should be based on a mix design established by a qualified engineer. The design mix should consist of aggregate, Portland cement, water and additives which will meet the requirements of CDOT Class P concrete or the recommendations presented below. The fine and coarse aggregate should conform to AASHTO M-6, M-43 and M-80. Cement should be Portland cement conforming to AASHTO M-85 and all additives should be approved by a qualified engineer. The concrete should have a modulus of rupture of third point loading of 650 psi. Normally, a concrete with a 28-day compressive strength of 4,200 psi should develop this modulus of rupture value. Concrete should be air entrained with approximately 6% air and should have a minimum cement content of 6 sacks per cubic yard. Maximum allowable slump will depend on the method of placement but should not exceed 4 inches. The concrete should contain joints not greater than 12 feet on centers. The joints should be hand formed, sawed or formed by premolded filler. The joints should be at least ¼ of the slab thickness. Expansion joints should be provided at the end of each construction sequence and between the concrete slab and adjacent structures. Expansion joints where required, should be filled with a ½-inch thick asphalt impregnated fiber. Concrete should be cured by protecting against loss of moisture, rapid temperature changes and mechanical injury for at least three days after placement. Drainage: The collection and diversion of surface drainage away from paved areas is extremely important to the satisfactory performance of pavement. Surface drainage design should provide for the removal of water from paved areas and prevent the wetting of the subgrade soils. Subgrade Preparation: All pavement areas should be provided with a zone of moisture conditioned and properly compacted fill material to a depth of at least 2 feet below the proposed Kumar & Associates, Inc. 27 DRAFT subgrade elevation. Material criteria and compaction requirements are presented in the Site Grading section of this report. Within 48 hours prior to placing the pavement section, the entire subgrade area should be thoroughly scarified and will mixed to a depth of at least 12 inches, adjusted to a moisture content within 0 to plus 3 percentage points of optimum and compacted to 95% of the maximum standard Proctor dry density (ASTM D 698). The moisture content may need to be near the lower end of the moisture range to provide for stability. The pavement subgrade should be proofrolled with a heavily loaded pneumatic-tired vehicle. Pavement design procedures assume a stable subgrade. Areas that deform excessively under heavy wheel loads are not stable and should be removed and replaced to achieve a stable subgrade prior to paving. The on-site cohesive soils and bedrock may be unstable under construction traffic when moisture conditioned to the range indicated above. Alternatives for chemical stabilization associated with providing a stable paving platform as well as contribution to the pavement substructure section can be provided upon request. Drainage: The collection and diversion of surface drainage away from paved areas is extremely important for the satisfactory performance of pavement. Drainage design should provide for the removal of water from paved areas and prevent the wetting of the subgrade soils. DESIGN AND CONSTRUCTION SUPPORT SERVICES Kumar & Associates, Inc. should be retained to review the project plans and specifications for conformance with the recommendations provided in our report. We are also available to assist the design team in preparing specifications for geotechnical aspects of the project, and performing additional studies if necessary to accommodate possible changes in the proposed construction. We recommend that Kumar & Associates, Inc. be retained to provide observation and testing services to document that the intent of this report and the requirements of the plans and specifications are being followed during construction, and to identify possible variations in subsurface conditions from those encountered in this study so that we can re-evaluate our recommendations, if needed. Kumar & Associates, Inc. 28 DRAFT LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering practices in this area for exclusive use by the client for design purposes. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings at the locations indicated on Fig. 1, and the proposed type of construction. This report may not reflect subsurface variations that occur between the exploratory borings, and the nature and extent of variations across the site may not become evident until site grading and excavations are performed. If during construction, fill, soil, rock or water conditions appear to be different from those described herein, Kumar & Associates, Inc. should be advised at once so that a re-evaluation of the recommendations presented in this report can be made. Kumar & Associates, Inc. is not responsible for liability associated with interpretation of subsurface data by others. JLB/jw cc: book, file Kumar & Associates, Inc.