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Home My WebLink AboutSW1200501_SW Report_20201109 DESIGN REPORT STORMWATER MANAGEMENT PLAN Fairview Elementary School Car Rider Road/School Expansion Buncombe County, North Carolina April 2020 _________________________________________ Scott E. Burwell, PE NC Professional Engineer No. 039177 McGill Associates, P.A. 55 Broad Street Asheville, NC 28801 License Number C-0459 APRIL 2020 REVISED AUGUST 2020 REVISED NOVEMBER 2020 QspkfduTjuf 1 of 1 Total 2602726027 Whole Site Area (sf) Post-Development Built Upon Area Summary (sf) Impervious (Proposed Road)Impervious (existing)Total 669 54796148 10/28/2020 Runoff coefficient \[(storm runoff (in)/ storm rainfall(in)\] unitlessImpervious Fraction \[impervious portion of drainage area (ac)/ drainage area (ac)\], unitlessVolume of Runoff for the design storm (cf)Design storm rainfall depth (in)Watershed area (acres) 0.236 0.2624 cu.ft. 1 572 0.60 NCDEQ Stormwater Design ManualPart B, Simple Method for Runoff Volume0.05+0.9*Ia =DA-IMP/DA6148/26027=3630 * Rd * Rv * A Stormwater Runoff Volume Calculation Bio Cell #1Reference:Simple Method (Proposed Conditions)Rv =Ia =V=Rd =A =V min.= P:\\2019\\19.00154-BuncombeBOE-Fairview Elem Car Rider Lane\\Design\\Calcs\\Stormwater\\20-1030 Resubmittal\\Simple Method Runoff Volume-Cell 1_10-28-20 1 of 1 Total 101495101495 Whole Site Area (sf) Post-Development Built Upon Area Summary (sf) Impervious (Proposed Road)Impervious (Existing)Total 4046 1499419040 10/28/2020 Runoff coefficient \[(storm runoff (in)/ storm rainfall(in)\] unitlessImpervious Fraction \[impervious portion of drainage area (ac)/ drainage area (ac)\], unitlessVolume of Runoff for the design storm (cf)Design storm rainfall depth (in)Watershed area (acres) 0.187 0.2183 cu.ft. 1 2.33 1847 NCDEQ Stormwater Design ManualSection B, Simple Method for Runoff Volume0.05+0.9*Ia =DA-IMP/DA19040/101495=3630 * Rd * Rv * A Stormwater Runoff Volume Calculation - Bio Cell #2Reference:Simple Method (Proposed Conditions)Rv =Ia =V=Rd =A =V min. = P:\\2019\\19.00154-BuncombeBOE-Fairview Elem Car Rider Lane\\Design\\Calcs\\Stormwater\\20-1030 Resubmittal\\Simple Method Runoff Volume-Cell 2_10-28-20 Stage Storage Calculations Project #:19.00154 Project Name:Fairview Elementary Car Rider Road Date:8/6/2020 By:N Sawyer Basin Name:Bio Retention Cell #1 Contour ElevationContour Area (sf)Depth (ft)Incremental Volume (cf)Cumulative Volume (cf) 23061463.65N/AN/AN/A 23072021.5411742.601742.60 23082635.9712328.764071.35 Minimum Volume Required for Design Storm of 1" = 572 cu.ft. or 33% of the actual volume at 12" of ponding. 12" x 33% = 3.96" or .33' Elevation of the 1" design storm = 2306.33 Buncombe Co. Pre vs Post 1 yr, 24 hour event, Volume to be treated = 1099 cu.ft. or 63% of the actual volume at 12" of ponding. 12" x 63% = 7.56" or .63' Elevation of the treated volume = 2306.63 Sfwjtfe22.16.3131 Stage Storage Calculations Project #:19.00154 Project Name:Fairview Elementary Car Rider Road Date:8/6/2020 By:N Sawyer Basin Name:Bio Retention Cell #2 Contour ElevationContour Area (sf)Depth (ft)Incremental Volume (cf)Cumulative Volume (cf) 22702793.6N/AN/AN/A 22713471.5613132.583132.58 22724206.0713838.826971.40 Minimum Volume Required for Design Storm of 1" = 1847 cu.ft. or 58% of the actual volume at 12" of ponding. 12" x .58% = 6.96" or .58' Elevation of the 1" design storm = 2270.58 Buncombe Co. Pre vs Post 1 yr, 24 hour event, Volume to be treated = 3048 cu.ft. or 97% of the actual volume at 12" of ponding. 12" x 97% = 11.64" or .97' Elevation of the treated volume = 2270.97 Sfwjtfe22.16.3131 duration) duration)duration)duration) min minminmin 5 555 yr, yr,yr,yr, SoilCQ10Q25Q50Q100 (10(25(50(100 NOAANOAANOAANOAA Packed FromFromFromFrom (>7%)Bare Steep Soil, coefficients Heavy runoff 7%)0.15 7%)0.2 (2 (2 (>7%)0.3 (>7%)0.2 (<2%)0.15 (<2%)0.1 FlataverageSteep FlatAverage (in/hr)9.44Taken Steep (in/hr)6.88Taken(in/hr)7.9Taken(in/hr)8.66Taken Soil,Soil,Soil, IǤķƩƚƌƚŭǤ Soil,Soil, Soil, Areas0.35 Soil0.6 intensity Areas0.15 intensityintensityintensity SandySandyHeavyHeavyHeavy Inclined1Flat0.9Sandy Packed Year YearYearYear aĻƷŷƚķ DescriptionrationalUnimprovedAsphalt0.95Concrete0.95Brick0.85Roofs,Roofs,Lawns,Lawns,LawnsLawns,Lawns,Lawns,BareWooded102550100 wğƷźƚƓğƌ 5źƷĭŷ (sf)ImperviousWoodedLawns, area 0.6026019422300198860.6132.522.893.173.461.46635613482277653231400.2702.713.113.413.720.4620008170012421706600.3461.091.261.381.501.0947617462404299300.3632.733.143.443.751.6973833632412426626700.353 4.124.735.185.650.08331400033140.6000.310.360.400.430.16700700070070.6000.660.760.840.91 (acres)total area #1#2 Basin (east) (west) (north) DitchDitch (middle) #3 #1 #4 #2 Ditch Skimmer Ditch Ditch Ditch TemporaryTemporary Permanent Permanent Ditchtotal Permanent Permanent 4/13/2020 NLC 19.00154By:Date: Geotechnical Engineering Exploration and Analysis Proposed Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and 3 1355 Charlotte Highway Fairview, North Carolina Prepared for: Buncombe County Schools Asheville, North Carolina Prepared by: Gentry Geotechnical Engineering, PLLC. Asheville, North Carolina May 20, 2020 Gentry Project Number 20G-0124-01 May 20, 2020 Buncombe County Schools 175 Bingham Road Asheville, North Carolina 28806 Attention: Mr. Clark Wyatt Subject:Geotechnical Engineering Exploration and Analysis Proposed Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and 3 1355 Charlotte Highway Fairview, North Carolina Gentry ProjectNo. 20G-0124-01 Gentry NC Engineering License No. P-1170 Dear Mr. Wyatt: As requested, Gentry Geotechnical Engineering, PLLC (Gentry) conducted a Geotechnical Engineering Exploration and Analysesfor the proposed project. The accompanying report describes the services that were conducted for the project and it provides geotechnical-related findings, conclusions and recommendations that were derived from those services. We sincerely appreciate the opportunity to provide geotechnical consulting services for the proposed project. Please contact the undersigned if there are questions concerning the report or if we may be of further service. Respectfully submitted, GENTRY GEOTECHNICAL ENGINEERING, PLLC William T. Gentry III, P.E. Principal Engineer NC License #33927 TABLE OF CONTENTS GEOTECHNICAL ENGINEERING EXPLORATION AND ANALYSES PROPOSED FAIRVIEW ELEMENTARY CAR RIDER IMPROVEMENTS AND BUILDING ADDITIONS PHASE 2 AND 3 1355 CHARLOTTE HIGHWAY FAIRVIEW, NORTH CAROLINA GENTRY PROJECT NUMBER 20G-0124-01 Section No.DescriptionPage No. 1.0SCOPE OF SERVICES..................................................................................................1 2.0 SITE DESCRIPTION.......................................................................................................1 3.0 PROJECT DESCRIPTION.............................................................................................1 4.0 GEOTECHNICAL SUBSURFACE EXPLORATION PROGRAM............................2 5.0 GEOTECHNICAL LABORATORY SERVICES..........................................................3 6.0 MATERIAL CONDITIONS..............................................................................................3 6.1. Surface Materials...............................................................................................3 6.2. Residual Soils.....................................................................................................3 7.0 GROUNDWATER CONDITIONS..................................................................................4 8.0 CONCLUSIONS AND RECOMMENDATIONS..........................................................4 8.1. Seismic Design Considerations.....................................................................4 8.2. Building Foundation Recommendations.....................................................4 8.3. Floor Slab Recommendations........................................................................5 8.4. Pavement Recommendations.........................................................................6 8.5. Generalized Site Preparation Recommendations.....................................8 8.6. Generalized Construction Considerations..................................................9 8.7. Recommended Construction Materials Testing Services....................10 8.8. Basis of Report.................................................................................................10 ATTACHMENTS: Test Boring Location Plan Records of Subsurface Exploration (11Pages) Reference Notes for Boring Logs GEOTECHNICAL ENGINEERING EXPLORATION AND ANALYSES PROPOSED FAIRVIEW ELEMENTARY CAR RIDER IMPROVEMENTS AND BUILDING ADDITIONS PHASE 2 AND 3 1355 CHARLOTTE HIGHWAY FAIRVIEW, NORTH CAROLINA GENTRY PROJECT NUMBER 20G-0124-01 1.0 SCOPE OF SERVICES This report provides the results of the Geotechnical Engineering Exploration and Analysesthat Gentry Geotechnical Engineering, PLLC (“Gentry”)conducted regarding the proposed development. The Geotechnical Engineering Exploration and Analysesincluded several separate, but related, service areas referenced hereafter as the Geotechnical Subsurface Exploration Program, Geotechnical Laboratory ServicesandGeotechnical Engineering Services. The scope of each service area was narrow and limited, as directed by our client and in consideration of the proposed project. The scope of each service area is briefly explained later. Geotechnical-related recommendations for design and construction of the foundation,ground- bearing floor slab for the proposed buildingsand pavement areasare provided in this report. Site preparation recommendations arealso given; however, those recommendations are only preliminary since the means and methods of site preparation will largely depend on factors that were unknown when this report was prepared. Those factors include the weather before and during construction, subsurface conditions that are exposed during construction, and finalized details of the proposed development. 2.0 SITE DESCRIPTION The site consists of the existing Fairview Elementary School buildings and grounds. The car rider improvement will be constructed across open, mildly slopingmowed grounds with a wooded area on the east side of the buildings. The Phase 2 building addition consisted ofmildly sloping mowed grounds and the Phase 3 building addition consisted of an existing outdoor basketball court. The north bio-retention pond consisted of a flat gravel area, the south bio-retention area was in moderately sloping grounds near the cul-de-sac. The overall site is bordered by Charlotte Highway to the north, Jeffery Lane to the south, school grounds to the east and Oak Hill Lane to the west. 3.0 PROJECT DESCRIPTION It is understood that the car rider improvements will consist of approximately 976 linear feet of a 22 feet wide asphaltic concrete driveway with curb and gutter. The car rider pavement is anticipated to be subjected to mostly automobile traffic and occasional/limited bus and heavy truck traffic.We understand that the preferred asphaltic concrete pavement section would consist of 2 inches of S9.5B or C surface course over 2 inches of I19.0C binder course over 8 inches of ABC stone for longevity. Dependent upon bids and budget, the binder course may be eliminated. Grading operations for the car rider driveway will generally consist of 1 to 2 feet of cut and 1 foot of fill. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage2 Two bio-retention cells are planned for storm water management.The existing ground surface elevation for the north bio-retention cell was 2273.0 feet with a planned bottom of media elevation of 2268.0 feet and finished grade of 2270.0 feet. Therefore, the bio-retention cell will be about 5 feet deep to the bottom of the media and 3 feet deep to finished grade. The existing ground surface elevation for the south bio-retention cell was 2313.0 feet with a planned bottom of media elevation of 2304.0 feet and finished grade of 2306.0 feet. Therefore, the bio-retention cell will be about 9 feet deep to the bottom of the media and 7 feet deep to finished grade. In addition, we understand that Phase 2and Phase 3building additions are planned. The existing grades for the Phase 2 building range from 2310.0 feet to 2318.0 feet with a planned finished floor elevation of 2308.0 feet and assumed finished subgrade elevation of about 2307.0 feet. Therefore, approximately 3 to 11 feet of cut will be required to achieve the finished subgrade elevation. The existing grades for the Phase 3 building were 2295.5 feet with a planned finished floor elevation of 2296.5 feet and assumed finished subgrade elevation of about 2295.5 feet. Therefore, little to no grading is anticipated to achieve the finished subgrade elevation. The building additions are planned to consist of single-story masonry structures with conventional wood-truss or bar-joist roof system. The structure is anticipated to be supported by bearing walls and/or columns with maximum loads estimated at 2,000 pounds per lineal foot for walls and 25 kips for columns. The floor is expected to support a maximum 100 pounds per square foot live load. 4.0 GEOTECHNICAL SUBSURFACE EXPLORATION PROGRAM The scope of the Geotechnical Subsurface Exploration Program included evaluating the subsurface conditions by performing 11soil test borings. The drilling company, Jordan Environmental, performedthegeotechnical test borings at the site on April 28, 2020. The soil borings were completed using a Track Mounted Diedrich D50 drill rig with a 2 1/4" ID Hollow Stem Auger. The soil test borings ranged in depth from 5 to 50 feet. Building Addition Phase 2 and 3 soil test boring numbersB-1, B-2 and B-4 were drilled to 20 feet deep and B-3 was drilled to 50 feet deepfor seismic site classification purposes. The car rider driveway and bio-retention cell borings were drilled to depths ranging from 5 to 15 feet deep.The approximate test boring locations are shown on theattachedTestBoring Location Plan. The ground elevations at the test borings were determined as part of the Geotechnical Subsurface Exploration Programby estimating the ground surface elevation based on the topographic survey provided to us by McGill Associates, P.A. The test boring elevations are noted on the Records of Subsurface Exploration, which are logs of the test borings. The test boring elevations are considered accurate within about two feet. Samples were collected from the test borings, at certain depths, using a split-barrel sampler during Standard Penetration Testing (SPT). Immediately after sampling, select portions of the SPT samples were transferred from the sampler to clean jars that were labeled at the sitefor identification. The retained samples were transported to Gentrys’ geotechnical laboratory as part of the Geotechnical Subsurface Exploration Program. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage3 5.0 GEOTECHNICAL LABORATORY SERVICES Samples thatwere retainedatthesitewereclassifiedbyageotechnicalengineerusingthe descriptivetermsandparticle-size criteria, and by using the Unified Soil Classification System (ASTM D 2488-75) asageneral guide. The classifications are shown on the Records of Subsurface Exploration,along withhorizontallinesthatshowsupposeddepthsofmaterial change.Field-relatedinformationpertaining to the test borings is also shown on the Records of SubsurfaceExploration.The natural moisture content and percent fines of select soil samples was performed to aid in soil classification and estimating engineering properties of the site soils. The laboratory test results are shown in Table 1 below. Table 1 -LABORATORY TEST RESULTS Test Boring No.Depth Percent Finer Moisture USCS Soil (ft)than No. 200 Content (%)Classification Sieve (%) B-23.5-5.042.219.5SM B-38.5-10.060.044.0ML B-48.5-10.058.042.0ML B-58.5-10.052.331.0ML B-56-7.555.132.0ML B-101-2.572.331.0ML B-111-2.543.412.0SM 6.0 MATERIAL CONDITIONS Since material sampling at the test borings was discontinuous, it was necessary for Gentry to suppose conditions between sample intervals. The supposed conditions at the test borings are briefly discussed in this section and are described in detail on the Records of Subsurface Exploration. Also, the conclusions and recommendations in this report are based on the supposed conditions. 6.1.Surface Materials The surface material consisted of either 2 to 3 inches of grass root mat and sandy silt topsoil, no topsoil or 8 inches of gravel at B-11. 6.2.Residual Soils Below the surface materials, the soils generally consisted of loose to firmreddish brown, orange, tan and orange, tan and gray or brown, moist to very moist, micaceous, sandy siltswith silty sand layersto at least 50 feet, the maximum depth exploredthat we classified as residual soils.There were some very loose near surface residual soils in the car rider driveway borings B-8 and B-9. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage4 7.0 GROUNDWATER CONDITIONS Groundwater was measured at a depth of 15 feet (Elevation 2280.5 feet) in B-3 and 17 feet (Elevation 2278.5 feet) in B-4, but was not encountered in the remaining soil test borings. It should be noted that ground water levels may fluctuate several feet with seasonal and rainfall variations andwith changes in the water level in adjacent drainage features. Normally, the highest groundwater levels occur in late winter and spring and the lowest levels occur in late summer and fall. 8.0 CONCLUSIONS AND RECOMMENDATIONS 8.1.Seismic Design Considerations A soil site class Dis recommended for seismic design. By definition, site class is based on the average properties of subsurface materials to a depth of 100 feet below the ground surface. Since 100-foot test borings were not requested or authorized for the project, it wasnecessary to estimate the site class based onthe information obtained fromthe 50 feet deep soil test boring,subsequent calculations, presumed area geology, Section 1613.3.2 Site Class Definitions of the 2018North Carolina State Building Code and Chapter 20, Table 20.3-1 Site Classification of ASCE 7. 8.2.Building Foundation Recommendations Based on the assumed structural loads, provided finished floor elevations, provided bottom of footing elevationsand the test boringfindings, a foundation designed using a 2,000 psf maximum, net, allowable soil bearing capacity is recommended for the proposed structures.Strip footing pads are recommended to be at least 18 inches wide and isolated column pads are recommended to be atleast 24 inches wide for geotechnical considerations,regardless of the calculated foundation bearing stress.Foundation walls are assumed to be built of reinforced cast-in-place concrete or areinforced masonry wall system. It is understood that specific foundation details including footing dimensions, reinforcing, and other parameters will be constructed per the most recent edition of the North Carolina State Building Codeor specified by theproject architect or project structural engineer. We recommend footings have a minimum 24-inch foundation depth for stability and frost action concerns. Therefore, footings for foundation walls and columns of the proposed structure are recommended to bear at least 24 inches belowthe finished ground grade. The foundation analysis was conducted assuming that the foundations will bear at about 24 inches below the exterior ground surface. Foundation excavations are recommended to be dug with a smooth-edge backhoe bucket to develop a relatively undisturbed bearing grade. A toothed bucket will likely disturb foundation- bearing soil more than a smooth-edge bucket, thereby making soil at the excavation base more susceptible to saturation and instability, especially during adverse weather. It is critical that contractors protect foundation support soil and foundation construction materials (concrete, reinforcing, etc.). In addition, engineeredfill is recommended to be placed and compacted in Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage5 benched excavations along foundation walls immediately after the foundation walls are capable of supporting lateral pressures from backfill, compaction, and compaction equipment. Earth- formed footing construction techniques will likely be feasible considering thatsilty sand to sandy silt was above the estimated foundation bearing elevations at the test borings. Foundation Support Soil Requirements Footing pads are recommended to be directly and entirely supported by suitable-bearing residual soil. Based on the recommended 2,000 psf bearing capacity, the average corrected N-value (determined from SPTs and correlated from other in-situ tests)is recommended to be at least 5 based upon a 2,000 psf maximum bearing capacity. Suitable bearing residual soils for foundation support are anticipated to be available at the provided bottom of footing elevations in Project Description and shown on the attached Test Boring Location Plan. It is further recommended that the strength characteristics of soil within the entire foundation influence zone (determined byGentryduring construction) meet or exceed the recommended values, unless Gentry approves lesser values. It is recommended that Gentryevaluate foundation support soil using appropriate means and methods immediately before foundation construction. The purpose of the recommended evaluation is to confirm that the foundation will be properly supported and confirm that the support soil is similar to the conditions described on the Records of Subsurface Exploration. In the event that another firm performs the recommended foundation elevation, Gentrymust be notified if the composition or strength characteristics of foundation support soil differ from those shown on the Records of Subsurface Exploration. Soil that is within a foundation influence zone but does not meet the recommended allowable bearing capacity (described above), or is otherwise unsuitable, is recommended to be replaced. Unsuitable bearing material could be replaced with engineered fill, such as No. 57 stone.It is recommended that Gentry provide specific recommendations pertaining to soil over-excavation and replacement at the time of constructionincluding the need for wrapping the stone in a geotextile fabric. As an option to soil replacement, strip footings could be stepped or thickened to extend through unsuitable bearing materials. It is recommended that a structural engineer or architect should provide specific details of stepped or thickened footings. Estimated Foundation Settlement The post-construction total and differential settlements of foundations designed and constructed based on this report are estimated to be a maximum of about 1 and 1/2 inch, respectively. The post-construction angular distortion is estimated to be a maximum of about 1/480 across a distance of 20 feet or more. 8.3.Floor Slab Recommendations With proper sub-grade preparation, it is expected that site soil will be suitable for floor slab support. Engineered fill that is selected, placed, and compacted according to this reportcould Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage6 also support a concrete slab.It is understood that the specific floor slab thickness, reinforcing, joint details and other parameters will be constructed per the most recent edition of the North Carolina State Building Codeor specified by the project architect or project structural engineer. A minimum 4-inch-thick base course is recommended to be directly below the floor slab to serve as a capillary break and help develop uniform support. It is recommended that the base course consist of free-draining aggregate. It is recommended that Gentrytest and approve base course aggregate before it is placed. Depending on aggregate gradation, a geotextile might need to be below the base course. A minimum 10-mil vapor retarder is recommended to be directly below the base course throughout the entire floor area. If the base course has sharp, angular aggregate, protecting the retarder with a geotextile (or by other means) is recommended. It is recommended that a structural engineer or architect specify the vapor retarder location with careful consideration of concrete curing and the effects of moisture on future flooring materials. Estimated Floor Slab Settlement The post-construction total and differential settlements of an isolated floor slab constructed in accordance with this report are estimated to be a maximum of -inch, respectively. 8.4.Pavement Recommendations Based ondiscussions with Mr. Clark Wyatt with Buncombe County Schools and Mr. Scott Burwell, P.E. with McGill Associates, P.A., it is understood that the car rider driveway will have light duty traffic consisting of primarily passenger vehicles with occasional bus/heavy truck traffic. We understand that the preferred asphaltic concrete pavement section would consist of 2 inches of S9.5B or C surface course over 2 inches of I19.0C binder course over 8 inches of ABC stone for longevity. Dependent upon bids and budget, the binder course may be eliminated. The recommended light duty section is for automobiles, with occasional bus/heavy truck traffic. We have also provided a heavy-duty truck section based on 50,000 equivalent single axle loads (ESALs) and a 20-year design life.The heavy-duty section would also meet the preferred longevity pavement section if budget allows. It is recommendedthattheprojectownerconfirmthatthetrafficvolumesareappropriate.If requested,Gentrywillprovidesupplementalpavementrecommendationsbaseduponother trafficconditionsifthetraffic volumes are notappropriate. A California Bearing Ratio (CBR) test is used to determine soil support parameters forpavement design.SinceaCBRtestwasnotauthorizedforthisproject,itwasnecessaryforGentryto estimateaCBRvaluebasedonthesoiltestboringsinordertogivepavement recommendations. The following pavement sections are based on an estimated CBR value of 5. Engineered fill that is placed in proposed pavement areas is recommended to have aCBR value equaltoorgreaterthan5andthefillisrecommendedtobeplacedandcompactedperthis report. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage7 Areas of subgrade stabilization and/or overexcavation up to 2 feet may be neededin the vicinity of B-8 and B-9 where surficial very loose soils were encountered. Other areas may also require subgrade stabilization and/or overexcavation especially ifthesubgrade is subjected to construction traffic disturbance or construction occurs duringadverse weather conditions.Use of a geogrid, coarse crushed aggregate or chemicallymodified subgrade may be needed to stabilize the subgrade, or a geotextile, thickened base course ora subbase course may be needed to prevent or reduce the intrusion of the subgrade soil intothe base course material. The need for stabilization, overexcavation or reduction of the intrusionof the subgrade soil into the base course should be determined by a representative ofthe Geotechnical Engineer based on the conditions duringconstruction. TABLE 2 RECOMMENDED PAVEMENT SECTIONS Section Thickness (Inches) North Carolina DOT Light Duty Heavy Duty Material Specifications (Automobile (Truck Drive Drive Lane) Lane) Asphalt Concrete Surface Course 22Section 610 SF9.5B or C Asphaltic Concrete Binder Course _2Section 610 I19.0C Aggregate Base Section 520, Table 1005-1 88 CourseABC Stone Note: The recommendedlight duty automobile drive lane section should not be used where buses or heavy trucks will travelother than occasionally. If the light duty automobile drive lane section is subjected to buses and heavy truck trafficmore than occasionally, increased pavement maintenance and premature pavement failure should be expected. Theasphalt and base course should meet the material properties and be placed and compacted inaccordance with the North Carolina DOTspecifications. A minimum 5-inch-thick Portland cement concrete pavement with a minimum 4-inch-thick compacted aggregate base course is recommended for use in low-stress areas. A minimum 6- inch-thick Portland cement concrete pavement with a minimum 4-inch-thick compacted aggregate base course is recommended for use in high-stress areas such as at entrance/exit aprons, trash enclosure, and in areas where buses or heavy trucks will turn or will be parked. Materials and construction procedures for concrete pavement are recommended to be per North Carolina DOT Standard Specifications Section 700 and 710. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage8 The pavement recommendations assume that the pavement sub-grade will be prepared perthis report, the base course will be properly drained, and Gentry will monitor pavementconstruction. TheasphaltpavementwasdesignedbasedonAASHTOdesignparametersforatwenty-year designperiod.Pavementmaintenancealongwithamajorrehabilitationafterabout8to10 yearsshouldbeexpected.Localcodesmayrequirespecifictestingtodeterminesoilsupport characteristics and/or minimum pavement section thickness might berequired. 8.5.Generalized Site Preparation Recommendations This section deals with site preparation including preparation of foundation, floor slab,pavement and engineered fill areas. The means and methods of site preparation will greatly depend on the weather conditions before and during construction, the subsurface conditions that are exposed during earthwork operations, and the finalized details of the proposed development. Therefore, only generalized site preparation recommendations are given. Clearing, Grubbing and Stripping Surface vegetation, topsoil with adverse organic content, and otherwise unsuitable bearing materials are recommended to be removed from the proposed building footprint, pavementsand other structural areas. Clearing, grubbing and stripping should extend at least several feet beyond proposed development areas, where feasible. When the geotechnical soil test borings were performed, the topsoil was about 2 to 3 inches thick. Those topsoil thicknesses could be used on a preliminary basis to estimate topsoil stripping quantities. However, since topsoil may be thinner or thicker away from the test borings, the actual stripping quantity may be more or less than estimated. It might be beneficial to stockpile stripped topsoilon the site for later use in landscape areas. Proof-Rolling and Fill Placement After the recommended clearing, grubbing, and stripping, and once the site is cut (lowered) as needed, the sub-grade is recommended to be proof-rolled with a fully-loaded, tandem-axle dump truck or other suitable construction equipment to help locate unstable soil based on sub-grade deflection caused by the wheel loads of the proof-roll equipment. Theentire site is recommended to be proof-rolled and, where feasible, proof-rolling should extend at least several feet beyond development areas. It is recommended that Gentryobserve proof-roll operations and evaluate the sub-grade stability based on those observations. Soil that yields excessively or ruts during proof-rolling, or shows other signs of instability, is recommended to be replaced with engineered fill. As an option to replacement, unsuitable soil could be scarified to a sufficient depth (likely 6 to 12 inches, or more), moisture-conditioned (uniformly moistened or dried), and compacted to the required in-place density. Unsuitable soil could also be modified with hydrated lime or Portland cement, or mechanically stabilized with coarse aggregate and/or geosynthetics (geogrids, geotextiles, etc.). It is recommended that Gentryprovide specific soil improvement recommendations based on the conditions during construction. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage9 The site is recommended to be raised, where necessary, to the planned finished grade with engineered fill immediately after the sub-grade is confirmed to be stable and suitable to support the proposed site improvements. Engineered fill should have a maximum liquid limit of 50, maximum plasticity index of 25, a maximum fines content of 50 percent, a maximum organic content of 5 percent and be fee of deleterious or otherwise unsuitable material. Engineered fill is recommended to be placed in uniform, relatively thin layers (lifts). It is recommended that engineered fill slopes be placed no steeper than 2H:1V and be properly benched into the existing soils.Fill slopes steeper than 2H: 1V should be reinforced with geogrid and designed by a professional engineer.Each layer of engineered fill is recommended to be compacted to at least 95 percentof the fill material’s maximum dry density within 3 percent of the optimum moisture content as determined by The Standard Proctor Compaction test (ASTM D698). Engineered fill that does not meet the density and water content requirements is recommended tobe replaced or scarified to a sufficient depth (likely 6 to 12 inches, or more), moisture- conditioned, and compacted to the required density. A subsequent lift of fill should only be placed after Gentryconfirms that the previous lift was properly placed and compacted. Sub-grade soil may need to be recompacted immediately before construction since equipment traffic and adverse weather may reduce soil stability. Use of Site Soil as Engineered Fill Site soil that does not contain adverse organic content, deleterious materials,or fines content greater than 50 percent, maximum liquid limit of 50 and maximum plasticity index of 25 (15 preferred), could be used as engineered fill.The majority of the near surface soils consisted of sandy silts with greater than 50 percent fines and will likely not be suitable for re-use as engineered fill. If construction is during adverse weather (discussed in the following section), drying site soil will likely not be feasible. In that case, aggregate fill (or other fill material with a low water-sensitivity) will likely need to be imported to the site. 8.6.Generalized Construction Considerations Adverse Weather Site soil is very moisture sensitive and will become unstable when exposed to adverse weather such as rain, snow, and freezing temperatures. Therefore, it might be necessary to remove or stabilize the upper 6 to 12 inches (or more) of soil due to adverse weather, which commonly occurs during late fall, winter, and early spring. At least some over-excavation and/or stabilization of unstable soil should be expected if construction is during or after adverse weather. Based on the test borings, extensive over-excavation is not expected to be needed if construction is during and afterfavorable, dry weather. Because site preparation is weather dependant, bids for site preparation, and other earthwork activities, are recommended to be based on the time of year that construction will be conducted. In an effort to protect soil from adverse weather, the site surface is recommended to be smoothly graded and contoured during construction to divert surface water away from construction areas. Foundation construction should begin immediately after suitable support is confirmed. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage10 Dewatering Groundwater was measured at a depth of 15 feet (Elevation 2280.5 feet) in B-3 and 17 feet (Elevation 2278.5 feet) in B-4, but was not encountered in the remaining soil test borings. However, groundwater was not encountered within anticipated depths that would affect foundation or pavement construction. Some dewatering might be needed during construction due to precipitation or if perched water is encountered. Water that accumulatesin construction areas is recommended to be removed from excavations and other construction areas, along with unstable soil as soon as possible. Filtered sump pumps, drawing water from sump pits excavated in the bottom of construction trenches, will likely be adequate to remove water that collects in shallow excavations. Excavated sump pits should be fully-lined with a geotextile and filled with open-graded, free-draining aggregate. Excavation Stability Excavations through silty sand and sandy silt residual soils should be no steeper than 1H:1V for short term conditions and no steeper than 1.5H:1V for long term conditions.Excavations may cave during construction, especially if granular soil is encountered. Excavations are recommended to be made in accordance with current OSHA excavation and trench safety standards, and other applicable requirements. Sides of excavations might need to be sloped or braced to maintain or develop a safe work environment. Temporary shoring must bedesigned according to applicable regulatory requirements. Contractors are responsible for excavation safety. 8.7.Recommended Construction Materials Testing Services This report was prepared assuming that Gentry will performConstruction Materials Testing (“CMT”) services during construction of the proposed development.In general, CMT services are recommended (and expected) to at least include observation and testing of: foundation, floor slab, concreteand other construction materials.It might be necessary for Gentryto provide supplemental geotechnical recommendations based on the results of CMT services and provided specific details of the project. 8.8.Basis of Report This report is based on Gentryproposal No. 20P-099, which is dated April 21, 2020 and authorized by Buncombe County Schools Purchase Order No. 621726671 dated April 24, 2020. The actual services for the project varied somewhat from those described in the proposal because of the conditions that were encountered while performing the services and in consideration of the proposedproject. This report is strictly based on the project description given earlier in this report. Gentrymust be notified if any part of the project description is not accurate so that this report can be amended, if needed. This report is based on the assumption that the structure will be designed and constructed according to the building code that governs construction at the site. Proposed Fairview Elementary Car Rider Improvements andMay 20, 2020 Building Additions Phase 2 and 3 –1355 Charlotte HighwayGentry Project No. 20G-0124-01 Fairview, North CarolinaPage11 The conclusions and recommendations in this report are based on supposed subsurface conditions as shown on the Records of Subsurface Exploration.Gentrymust be notified if the subsurface conditions that are encountered during construction of the proposed development differ from those shown on the Records of Subsurface Explorationbecause this report will likely need to be revised. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-1 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2310.0Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Phase 2 Building Addition, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Loose to firm, orange, very moist, micaceous, sandy SILT (Residual)SS8SPT = Standard Penetration Test 5SS11 Loose to firm, tan-orange, very moist, micaceous, sandy SILT (Residual)SS8 10SS14 Loose to firm, grey, very moist, micaceous, sandy SILT (Residual) 15SS18 Loose, tan-orange-black, very moist, micaceous, sandy SILT (Residual) 20SS7 Boring terminated at 20 feet. No groundwater encountered. Cave in at 17.5 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-2 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2318.0Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Phase 2 Building Addition, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Loose to firm, orange-brown, very moist, micaceous, sandy SILT (Residual)SS5SPT = Standard Penetration Test 5SS12 Loose, tan-grey, very moist, micaceous, sandy SILT (Residual) SS6 10SS5 Firm to very firm, grey-brown, moist, micaceous, silty, fine to medium SAND (Residual) 15SS29 Firm, tan-white, moist, micaceous, silty, fine to medium SAND (Residual) 20SS17 Boring terminated at 20 feet. No groundwater encountered. Cave in at 14.5 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-3 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2295.5Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Phase 3 Building Addition, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks No root mat or topsoilSS - Split Spoon Sample Very Loose to loose, red-brown, very moist to wet, micaceous, sandy SILT (Residual)SS6SPT = Standard Penetration Test 5SS4 SS5 10SS7 15SS8 Loose to firm, tan-grey, very moist, micaceous, silty, fine to medium SAND (Residual) 20SS7 25SS16 30SS23 Very firm, brown, moist, micaceous, silty, fine to medium SAND (Residual) 35SS27 Loose, grey to orange, very moist, micaceous, sandy SILT (Residual) 40SS9 Firm to very firm, grey, very moist, micaceous, sandy SILT (Residual) 45SS18 Very firm, grey, moist, micaceous, silty, fine to medium SAND (Residual) 50SS30 Boring terminated at 50 ft. Groundwater at 15 ft. Cave in at 30 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-4 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2295.5Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Phase 3 Building Addition, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks No root mat or topsoilSS - Split Spoon Sample Firm, orange, moist, micaceous, silty, fine to medium SAND (Residual)SS13SPT = Standard Penetration Test Loose, orange-black, very moist to wet, micaceous, sandy SILT (Residual) 5SS7 SS7 10SS5 15SS7 20SS5 Boring terminated at 20 feet. Groundwater encountered at 17 feet. Cave in at 18 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-5 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2273.0Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:North Bio-Retention Cell, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks No root mat or topsoilSS - Split Spoon Sample Loose to very loose, orange to tan-orange, very moist, micaceous, sandy SILT (Residual)SS8SPT = Standard Penetration Test 5SS3 Loose, grey black, very moist, micaceous, sandy SILT (Residual)SS10 Loose, tan-grey, very moist, micaceous, sandy SILT (Residual) 10SS5 Boring terminated at 10 feet. No groundwater encountered. Cave in at 8 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-6 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2313.0Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:South Bio-Retention Cell Near Cul-De-Sac, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Very loose to loose, red-orange, very moist, micaceous, sandy SILT (Residual)SS5SPT = Standard Penetration Test 5SS4 SS5 10SS5 Loose, red-orange-black, moist, micaceous, silty SAND (Residual) 15SS7 Boring terminated at 15 feet. No groundwater encountered. Cave in at 11.5 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-7 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2322.3Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Car Rider Driveway, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Loose to firm, tan-orange-grey, moist, micaceous, sandy SILT (Residual)SS8SPT = Standard Penetration Test 5SS12 Boring terminated at 5 feet. No groundwater encountered. Cave in at 3 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-8 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2333.5Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Car Rider Driveway, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Very loose, tan-orange-grey, moist, micaceous, sandy SILT (Residual)SS3SPT = Standard Penetration Test Loose, orange-grey, very moist, micaceous, sandy SILT (Residual) 5SS7 Boring terminated at 5 feet. No groundwater encountered. Cave in at 3 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-9 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2326.2Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Car Rider Driveway, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 3 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Very loose, orange-tan, moist, micaceous, sandy SILT (Residual)SS3SPT = Standard Penetration Test Loose, tan-orange-grey, moist, micaceous, sandy SILT (Residual) 5SS6 Boring terminated at 5 feet. No groundwater encountered. Cave in at 3 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-10 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2320.2Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Car Rider Driveway, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 2 inches of root mat and sandy silt topsoilSS - Split Spoon Sample Loose, red-orange, very moist, micaceous, sandy SILT (Residual)SS9SPT = Standard Penetration Test 5SS9 Loose, orange-tan-black, very moist, micaceous, sandy SILT (Residual)SS10 Boring terminated at 7.5 feet. No groundwater encountered. Cave in at 5.5 ft after augers removed. GENTRY GEOTECHNICAL ENGINEERING, PLLC Record of Subsurface Exploration Boring:B-11 Project Name:Fairview Elementary Car Rider Improvements and Building Additions Phase 2 and Phase 3Elevation:2305.5Date:April 28, 2020 1355 Charlotte Highway, Fairivew, NC 28730 Location:Car Rider Driveway, See Boring Location PlanProject No.20G-0124-01 Driller:Baker Jordan, Jordan Environmental, LLC, Track Mounted Diedrich D-50 , 2 1/4" ID Hollow Stem AugerASTM D1586 DescriptionDepthSampleSPT feettypeN-ValueRemarks 8 inches of gravelSS - Split Spoon Sample Loose, tan-grey, moist, micaceous, silty, fine to medium SAND (Residual)SS7SPT = Standard Penetration Test 5SS10 Boring terminated at 5 feet. No groundwater encountered. Cave in at 3.5 ft after augers removed. Drilling and Sampling Abbreviations: Sample/Drilling:In-Situ Tests: SS-Split Spoon SamplerSPT-Standard Penetration Test ST-Shelby Tube SamplerPMT-Pressuremeter Test RC-Rock Core: NX, BX, AXVS-Vane Shear HSA-Hollow Stem AugerDCP-Dynamic Cone Penetrometer Q p-Estimated Unconfined Compressive Strength using Pocket Penetrometer Q u-Estimated Unconfined Compressive Strength using strain-controlled axial load device. Correlation of Penetration Resistances to Soil Properties: Relative Density -Sands, SiltsConsistency Cohesive Soils More than 50% retained onto the No. 200 sieveMore than 50% passing the No. 200 seive Unconfined Compressive SPT-N ValueRelative DensityStrength QSPT-N ValueConsistency p tsf 0-4Very Looseunder 0.250-2Very Soft 5-10Loose0.25-0.503-4Soft 11-20Firm0.50-1.005-8Firm 21-30Very Firm1.00-2.009-15Stiff 31-50Dense2.00-4.0016-30Very Stiff over 50Very Dense4.00-8.0031-50Hard over 8.00over 50Very Hard Gradation Description and Terminology: Major ComponentDescription ofPercent of of SampleSize RangeMinor ComponentsDry Weight BouldersOver 12 inchesTrace1-9 Cobbles12 inches to 3 inchesLittle10-19 Gravel3 inches to No. 4 sieveSome20-34 Coarse3 inches to 3/4 inchesAnd35-50 Fine3/4 inches to No. 4 sieve SandNo. 4 sieve to No. 200 sieve CoarseNo. 4 sieve to No. 10 sieve MediumNo. 10 seive to No. 40 sieve FineNo. 40 seive to No. 200 sieve Silt/ClayPassing No. 200 seive REFERENCE NOTES FOR BORING LOGS