HomeMy WebLinkAbout18 - Design Report - Flanders Mill - Arterial & Collector PAVEMENT DESIGN REPORT
FLANDERS MILL SUBDIVISION
ARTERIAL/COLLECTOR 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
cn.
A. ; c
Project Number: 14500
January 2018
PAVEMENT DESIGN REPORT—FLANDERS MILL SUBDIVISION
COLLECTOR/ARTERIAL ROADS (OAK)
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
Q,=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 with the
conservative value for the CBR being used.
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 3,050
vehicle trips on Oak Street during the average weekday. This value was the maximum traffic value
listed for Arterial Streets to be constructed with this subdivision in the TIS and was used for the
design criteria for Arterial Streets in this report.
All of the roads 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 3050/2 = 1525 vehicles per lane per day (vplpd), which equates to
1525 vplpd x 365 days/year= 556,625 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 trucksibuses,this yields 545,493 cars per year per lane,and 11,132
trucks per lane per year at full build out.
Traffic Estimate for Arterial/Collector Roads Surrounding Subdivision
Vehicle Type Vehicles Growth Design Vehicles ESAL Factor Design
per year Factor (20 years) ESAL
(4%,20yrs)
Passenger Car 545,493 29.78 16,244,782 0.0003*2=0.0006 9,747
2 axle/6 tire 11,132 29.78 331,510 0.118*2=0.236 78,236
truck
Total ESAL 87,983
The calculated estimate of the equivalent 18,000 lb Single Axle Load (ESAL) = 87,983
The calculated ESAL is greater than the minimum 50,000 ESAL design requirement. Therefore,
ESAL=87,983 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 for the subgrade soil is 2.0.
CBR can be related to the subgrade Resilient Modulus MR 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.
MR= 5,409 CBR0.711 (United States Army Waterway Experiment Station)
Mx=2,550 CBRo.64 (Transport& Research Laboratory, England)
With CBR=2.0
MR= 1,500 CBR= 1,500 (2.0) =3,000 psi
MR= 5,409 CBR0.711 = 5,409 (2.0)0-711 = 8,854.2 psi
MR=2,550 CBRo.64=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):
tog APSI
log W18 = ZRSo + 9.36[log(SN + 1)] — 0.20 + 2.7 1094 + 2.32 log MR — 8.07
0.40 + (SN + 1)1.19
Variables:
1. ESAL (W18) = 87,983
2. Level of Reliability (ZR) = -1.645 used for Arterials based on 95% reliability from Part I,
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) = 1.7 used for Arterials and Collectors.
See Part II, Sec. 2.2, AASHTO Manual. 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 roads
such as the interior roads of the subdivision are normally allowed to deteriorate to 2.0.
Arterial roads such as Oak St. are normally allowed to deteriorate to 2.5. The resulting
difference in the initial to final indexes is the total serviceability loss.
5. Soil Resistance Modulus (MR) = 3,000 psi
Solution: using (EQ1), the SN for Oak St. SN= 3.60
Pavement Design Equation(EQ2):
SN = a1D1 + a2D2M2 + a3D3M3
1. Layer Coefficients: a1 =0.44 (Hot-mix asphalt concrete)
az = 0.14 (Base Course - 1 %" minus crushed gravel)
a3 = 0.11 (Sub-base Course- 6" minus crushed stone)
2. Drainage Coefficients: Ma= 1.00 (good drainage 5-25%)
M3 = 1.00 (good drainage>25%)
% of time base & sub-base will approach saturation
3. Layer Depth Assumptions: Di =4" for Oak
Dz = 6" for Oak
Solution: using the values given for D1 and Dz, and solving (EQ2), D3 = 9.12 ' for Oak Street.
CONCLUSION
A conservative value of 18 inches will be used for sub-base section D3 for Oak Street. This results
in 4 inches of asphalt, 6 inches of 1" minus road mix, and 18 inches of 6" minus gravel for Oak
Street. Sanderson Stewart Engineering proposed a similar Oak Street section for their design east
of Flanders Mill Subdivision. However, they specified an 18-inch section of 3" minus gravel for
the sub-base, instead of 6"minus gravel.
Project# 14500
Title: Flanders Mill Subdivision-Collector and Arterial 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
Wie (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
EQ 1: APSI
log WiB=ZRSo+9.36Dog(SN+1)]—0.20+ log Ol 94 +2.32logMR—8.07
0.40+ SN+1 s1
Equivalent Single Axle Load
ADT 3474
Peak A.M. 7
Peak P.M. 9
Total 3050
AYT _ 5566251(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 545493 29.78 16244767 0.0006 9747
2 Axle/6 Tire
Truck 11133 29.78 331525.85 0.236 78240
Total ESAL 87987 or Use Minimum Value of 50,000
Level of Reliability(R and ZR)
R to ZRConversion Chart
R ZR
90 -1.2820
95 -1.6450
97.5 -1.9675
99 -3.0800
R(%)= 95 (Conservative estimate)
ZR= -1.645
Standard Deviation(So)
So= 0.49
Serviceability Loss(APSI)
Road Type vs.TSI
Present Serviceability Index(PSI)= 4.2 Highways 3.0
Terminal Serviceability Index(TSI)= 2.5 Arterials 2.5-3.0
Local Roads 2.0
APSI
Resistance Modulus(MR)
CBR 21 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= I 3.602795748 Calculated by EQ 1
Once SN is determined,the thickness of the wearing surface,base,and 1
subbase layers can be determined by EQ 2. JI
EQ 2: SN=a1D1+a2.D7Mz+a3D3M3
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
Lim e-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
D1= 4 Assumed(in inches)
D2= 6 Assumed(in inches)
Solve for D3= 9.12