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Home My WebLink About18 - Design Report - Flanders Mill - Local Streets PAVEMENT DESIGN REPORT FLANDERS MILL SUBDIVISION LOCAL STREETS Prepared for: Flanders Mill, LLC 235 Greenhills Ranch Road, Bozeman, MT 59718 Prepared by: C&H Engineering and Surveying, Inc. 1091 Stoneridge Drive, Bozeman, MT 59718 (406) 587-1115 MARKA. r � Project Number: 14500 January 2018 PAVEMENT DESIGN REPORT—FLANDERS MILL SUBDIVISION LOCAL STREETS WITHIN SUBDIVISION PUBLIC RIGHT-OF-WAY SOIL CONDITIONS 19 Test holes were excavated across the proposed subdivision using a backhoe on August 24, 2013. The subsurface conditions consist of approximately 12 inches of an organic topsoil of low plasticity (OL) underlain by a layer of sandy lean silty-clay (CL). Poorly graded gravel with sand and cobbles (GP) followed the sandy lean silty-clay. Additionally, groundwater is present in the gravel. Penetration tests were performed on the sandy lean silty-clay material below the topsoil to estimate the California Bearing Ratio (CBR). The estimated CBR is then obtained by the equation Qc = 3.3(CBR), or CBR = Qc/3.3, with Qc being the cone index. With the average measured value of the cone index being 12.23, we have CBR= 12.23/3.3 = 3.71. A conservative value for the CBR of 2 was used for this report to provide for possible inconsistencies that may be found in the soils during construction, and the approximate testing methods used. The Standard Test Method for CBR (California Bearing Ratio) of Soils in Place, based on ASTM Designation D 4429-4, requires complex and specialized equipment, the expense of which is not warranted for the local streets with low projected use. STREET DESIGN Criteria for design: Bozeman Municipal Code, Section 38.24.060 and City of Bozeman Design Standards and Specifications Policy, Addendum No. 4, Section IV.G: pavement thickness design will be based on the current AASHTO Guide for Design of Pavement Structures, or the current Asphalt Institute Manual Series No.1 (MS-1). The design shall be based on a minimum 20 year performance period traffic volume, with the minimum design lane based on a minimum of 50,000 ESAL. According to the Traffic Impact Study (TIS) prepared for the subdivision by Marvin and Associates, the estimated traffic after subdivision build-out is expected to be approximately 1,800 vehicle trips per day on Flanders Mill Road during the average weekday. This value was the maximum traffic value listed for Local Streets in the TIS and was used for the design criteria for Local Streets in this report. All of the local streets in the proposed subdivision contain two driving lanes (one in each direction) so the number of trips per day is divided in half to calculate the ESAL value for each lane. Average daily traffic per lane equates to 1800/2 = 900 vehicles per lane per day (vplpd), which equates to 900 vplpd x 365 days/year=328,500 vehicles per lane per year. The following assumptions were made while calculating the Total ESAL: 2% of the AYT will consist of heavy trucks or buses Growth rate =4% over 20 years 2000 lb axle load for cars, and 10,000 lb axle load for trucks. 2 axles per vehicle Based on 2% of the traffic being trucks/buses, this yields 321,930 cars per lane per year, and 6,570 trucks/buses per lane per year at full build out. Traffic Estimate for Local Streets within Subdivision Vehicle Type Vehicles Growth Design Vehicles ESAL Factor Design per year Factor (20 years) ESAL (4%,20yrs) Passenger Car 321,930 29.78 9,587,075 0.0003*2=0.0006 5,752 2 axle/6 tire 6,570 29.78 195,655 0.1 18*2=0.236 46,174 truck/bus Total ESAL 51,927 The calculated estimate of the equivalent 18,000 lb Single Axle Load(ESAL) = 51,927 The calculated ESAL is greater than the minimum 50,000 ESAL design requirement. Therefore, ESAL=51,927 shall be used for all calculations. According to the California Bearing Ratio (CBR) Test (ASTM-D 1883/AASHTO T193) performed by C&H Engineering Inc., the CBR used for the subgrade soil is 2.0. CBR can be related to the subgrade Resilient Modulus Mx by the following: (Sec. 3.5.4, Highway Engineering Handbook, McGraw Hill, 1996) Subgrade Resilient Modulus MR(psi): MR= 1,500 CBR(Shell Oil Co.) This value used by Asphalt Institute. Mx= 5,409 CBR0."1 (United States Army Waterway Experiment Station) MR=2,550 CBRo.61 (Transport& Research Laboratory, England) With CBR=2.0 MR= 1,500 CBR= 1,500 (2.0) = 3,000 psi MR= 5,409 CBRo.711 = 5,409 (2.0)0.711 = 8,854.2 psi MR=2,550 CB o.6a=2,550 (2.0)0.64= 3,973.74 psi Use most conservative value=3,000 psi USING THE AASHTO METHOD OF FLEXIBLE PAVEMENT DESIGN The AASHTO method utilizes a value known as the Structural Number (SN) which relates the below variables to the wear surface,base, and sub-base depths. Structural Number Equation(EQ 1): to OPSI log W18 = ZRSo + 9.36[log(SN + 1)] — 0.20 + g .7 + 2.32 log MR — 8.07 0.40 + 1094 (SN + 1)5.19 Variables: 1. ESAL (W18) = 51,927 2. Level of Reliability (Zx) _ -1.282 for Local Streets used for Local Streets based on 90% reliability from Part 1, Table 4.1, and Part II, Table 2.2, AASHTO Guide. Level of reliability is based on the cumulative percent of probability of reliability with a standard normal distribution. 3. Standard Deviation(So) =0.49 for flexible pavements. See Part I, Sec. 4.3, AASHTO Guide. The standard deviation is the statistical error in the estimates for future values within the formula. Typical values range from 0.40-0.50 for flexible pavements,with a value of 0.49 used to ensure a conservative solution. 4. Serviceability Loss (OPSI) =2.2 for Local Streets. The designed allowable deterioration of the roadway is represented by the serviceability loss. A new road is usually assigned a serviceability index of 4.2 and the final index is based on the type of roadway. Local streets are normally allowed to deteriorate to 2.0. The resulting difference in the initial to final indexes is the total serviceability loss. 5. Soil Resistance Modulus (Mx) = 3,000 psi Solution: using(EQ1),the SN for Local Streets = 2.98 Pavement Design Equation (EQ2): FSN = a1D1 + a2D2M2 + a3D3M3 1. Layer Coefficients: al = 0.44 (Hot-mix asphalt concrete) a2=0.14 (Base Course - 1 '/2" minus crushed gravel) a3 = 0.11 (Sub-base Course - 6" minus crushed stone) 2. Drainage Coefficients: 1112 = 1.00 (good drainage 5-25%) 1113 = 1.00 (good drainage> 25%) % of time base & sub-base will approach saturation 3. Layer Depth Assumptions: Di = 3" for Local Streets D2=6" for Local Streets Solution: using the values given for Di and D2, and solving(EQ2), D3 = 7.49" for Local Streets Use a standard street sub-base section of 9" on the Local Streets. This results in an asphalt section of 3", a base course of 6", and sub-base course of 9" for the Local Streets. Project# 14500 Title: Flanders Mill Subdivision-Local Streets To solve for minimum required Sub-Base depth,we first need to calculate the Structural Number(SN). Calculating SN can be accomplished by formula or graphically(AASHTO Guide for Design of Pavement Structures) Required Values For SN Calc W16 (ESAL) Equivalent Single Axle Load R(%) Probability serviceability will be maintained over the design life(R is used for graphical solution) ZR Probability serviceability used in numerical solutions(Equated to R by table below) So Standard Deviation in estimates for ESAL,typically 0.30-0.50 APSI Serviceability loss over design life MR Soil Resistence Modulus of subgrade soil APSI EQ 1: lag iop W1B=ZRSo+9.36[log(SN+1)]—0.20+ 4 +2.32 log MR—8.07 0.40+ SN+1 s,19 Equivalent Single Axle Load ADT 1800 Peak A.M. Peak P.M. Total 1 1800 AYT 328500 (per lane) Assumptions: 2 %of AYT Consisting of Heavy Trucks 4 %over 20 Years Growth Rate Lb/Axle 2000 for cars Lb/Axle 10000 for trucks Initial SN 3 AASHTO tables for ESAL Factor are based on SN and above listed axle loads Vehicle Type Vehicles Per Year Growth Factor Design Vehicles ESAL Factor Design ESAL (4%,20 years) (20 years) Passenger Car 321930 29.78 9587075 0.0006 5752 2 Axle/6 Tire Truck 6570 29.78 195654.60 0.236 46174 Total ESAL 51927 or Use Minimum Value of 50,000 Level of Reliability(R and ZR) R to ZR Conversion Chart R ZR 90 -1.2820 95 -1.6450 97.5 -1.9675 99 -3.0800 R(%)= 90 (Conservative estimate) ZR= -1.282 Standard Deviation(So) So=10.49 Serviceability Loss(OPSI) Road Type vs.TSI Present Serviceability Index(PSI)= 4.2 Highways 3.0 Terminal Serviceability Index(TSI)= 2.0 Arterials Local Roads 2.0 APSI=j 2.2 Resistance Modulus(MR) CBR E 2�Determined on basis of soil analysis MR= 3000 Shell Oil Co. (Should not be used for CBR>10) MR= 8854.20 U.S.Army Waterway Experimentation Station MR= 3973.74 Transport&Research Laboratory,England Use most conservative value of the three methods to calculate MR 3000.00 Structural Number(SN) SN= 2.983466997 Calculated by EQ i Once SN is determined,the thickness of the wearing surface,base,and subbase layers can be determined by EQ 2. EQ 2: SN=a1D1+a2D2M2+a3D3M3 I al,a2,a3 structural layer coefficients of wearing surface,base,and subbase M21 M3 drainage coefficients of base and subbase Dl,D2,D3 thickness of wear surface,base,and subbase in inches Structural Layer Coefficients(a) Pavement Component Coeffiecient Wearing Surface Sand-mix asphaltic concrete 0.35 Hot-mix asphaltic concrete 0.44 Base Crushed Stone 0.14 Dense-graded crushed stone 0.18 Soil cement 0.2 Emulsion/aggregate-bituminous 0.3 Portland cement/aggregate 0.4 Lime-pozzolan/aggregate 0.4 Hot-mix asphaltic concrete 0.4 Subbase Crushed Stone 0.11 a,= 0.44 (Hot-mix asphaltic concrete) a2= 0.14 (1 1/2"Minus crushed gravel) a3= 0.11 (6"Minus crushed stone) Drainage coefficients(M) M2= 1.00 Good Drainage M3= 1.00 Good Drainage Layer Thickness Dl= 3 Assumed(in inches) D2= 6 Assumed(in inches) Solve for D3= 7.49