HomeMy WebLinkAbout17 - Design Report - Rosa Way - Pavement PAVEMENT DESIGN REPORT
ROSA WAY
Prepared for:
Rosa Construction, Inc.
125 Central Avenue, Bozeman, MT 59718
Prepared by:
r
Engineering and Surveying Inc.
1091 Stoneridge Drive • Bozeman, MT 59718
Phone (406) 587-1115 • Fax (406) 587-9768
www.chengineers.com • info@chengineers.com
In
r,
Project Number: 16723.1 �, EJR"
April 2017
PAVEMENT DESIGN FOR LOCAL STREETS WITHIN SUBDIVISION
PUBLIC RIGHT-OF-WAY SOIL CONDITIONS
On June 7 and 8, 2004, two test holes were excavated by SK Geotechnical with a hollow stein
auger drill rig in the vicinity of the proposed future roadway to be known as Rosa Way. The
subsurface conditions in the vicinity of the interior roadway generally consist of an upper soil
horizon of an 11 to 24-inch layer of organic clay with sand and roots. This layer was noted as
being of low plasticity,dark brown and rather soft. Below the topsoil and root zone a 2 to 2.6 foot
thick layer of lean clay with sand was encountered. This layer was described as having a medium
plasticity, some roots, dark brown in color, moist to wet and soft. The layer was also labeled
alluvium in the boring log. Underlying the above layer a poorly graded gravel with sand was
encountered. This layer is described as being a fine to coarse-grained, dark olive brown, water
bearing dense alluvium. Groundwater was also encountered at depths ranging from 2.5' to 4 feet
below the ground surface.
Laboratory tests were performed on the silty-clay material below the topsoil to estimate the
California Bearing Ratio (CBR) and are provided in the geotechnical report from 2002 submitted
by Allied Engineering for Laurel Glen Subdivision. The CBR determined by Allied in this report
is approximately 3. Although the CBR reported in 2002 was observed in the subdivision to the
west it is assumed that soils on the Rosa Apartments site are similar. The CBR value used for this
report, however, is 1.0, which is a conservative estimate based on previous field experience of
C&H Engineering while working on adjacent subdivisions.
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.I (MS-1). The design shall be based on a minimum 20-year
Design Report-Page 2 of 6
performance period traffic volume, with the minimum design lane based on a minimum of 50,000
ESAL.
According to a recent traffic study conducted by Abelin Traffic services, the estimated traffic
generated by full build-out of Rosa Apartments is expected to be approximately 1290 vehicle trips
per day(VPD) during the average weekday. Rosa Way is a proposed public roadway to be located
in a public utility and access easement. This roadway contains 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. 1290 VPD was used in this calculation, however, in reality the actual trips on Rosa Way
may be much less as there is likely to be equal usage of the east and west entrances to the site and
as such the actual vehicle trips could be assumed to be half of the above estimation. 1290 VPD
was chosen as a conservative number for the purposes of designing this roadway section.
Average daily traffic per lane equates to 1290/2 = 645 vehicles per lane per day (vplpd), which
equates to 645 vplpd x 365 days/year=235,425 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 230,717 cars per lane per year, and 4,709
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)
0.0002*2 =
Passenger Car 230,717 29.78 687,0737 7,126
0.0004
Design Report-Page 3 of
2 axle/6 tire 4,709 29.78 140,219 0.08+.08=0.16 22,435
truck/bus
Total ESAL 25,183
The calculated estimate of the equivalent 18,000 lb Single Axle Load (ESAL) =25,183
The calculated ESAL is less than the minimum 50,000 ESAL design requirement. Therefore,
ESAL=50,000 shall be used for all calculations.
For this report, a CBR= 1 was used to give a more conservative sub-base thickness based on field
experience gained by C and H Engineering during construction of adjacent subdivisions.
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 CBR""' (United States Anny Waterway Experiment Station)
MR=2,550 CBR"" (Transport&Research Laboratory, England)
With CBR= 1.0
MR= 1,500 CBR= 1,500 (1) = 1,500 psi
MR= 5,409 CBR0-"1 = 5,409 (1)0.7 11 = 5,409 psi
MR=2,550 CBR0.64=2,550 (If64 =2,550 psi
Use most conservative value= 1,500 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.
Design Report-Page 4 of 6
Structural Number Equation(EQ 1):
to APSI
log W18 = ZRSo + 9.36[log(SN+ 1)] - 0.20+ g .7 + 2.32logMR - 8.07
0.40+ 1094
(SN+ 1)5.19
Variables:
1. ESAL(W18) = 50,000
2. Level of Reliability(ZR)_-0.841 used for Local Roads based on 80%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 nonnal 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 nonnally allowed to deteriorate to 2.0. The
resulting difference in the initial to final indexes is the total serviceability loss.
5. Soil Resistance Modulus (MR) = 1,500 psi
Solution: using(EQ1), the SN for Local Streets = 3.91
Pavement Design Equation(EQ2):
SN = a1D1 + a2D2M2 + a3D3M3 I
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)
Design Report-Page 5 of 6
2. Drainage Coefficients: m2 = 1.00 (good drainage 5-25%)
m3 = 1.00 (good drainage> 25%)
% of time base & sub-base will approach saturation
3. Layer Depth Assumptions: Dr = 3"for Local Streets
D2= 6" for Local Streets
Solution: using the values given for D1 and D2, and solving(EQ2), D3 = 12.22" for Local Streets
Use a standard street sub-base section of 6"on the Local Streets. This results in an asphalt section
of 3", a base course of 6", and sub-base course of 15" for the Local Streets.
Design Report-Page 6 of 6
Project# 16723.1
Title: Rosa Way-Local Roads
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
Wl$ (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
dPSI Serviceability loss over design life
MR Soil Resistence Modulus of subgrade soil
EQ 1: log APSI
log W1B= ZRSo+ 9.36[log(SN+ 1)]— 0.20+ 2.7 1094 + 2.32►ogMR— 8.07
0.40+ SN+ 1 s.iv
Equivalent Single Axle Load
ADT
Peak A.M.
Peak P.M.
Total 1290
AYT 235425 (per lane)
Assumptions:
2 %of AYT Consisting of Heavy Trucks
4 %over 20 Years Growth Rate
Lb/Axle 2000 for cars
Lb/Axle 10000 fortrucks
Initial SN 5 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 230716.50 29.78 6870737 0.0004 2748
2 Axle/6 Tire
Truck 4708.50 29.78 140219.13 0.16 22435
Total ESAL 25183 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(%)= 80 (local)
ZR= -0.841
Standard Deviation(So)
So=1 0.49
Serviceability Loss(APSI)
Road Type vs.TSI
Present Serviceability Index(PSI)= 4.2 Highways 3.0
Terminal Serviceability Index(TSI)= 2.0 Arterials 2.5-3.0
Local Roads 2.0
APSI 2.2
Resistance Modulus(MR)
CBR 1lDetermined on basis of soil analysis
MR= 1500 Shell Oil Co. (Should not be used for CBR>10)
MR= 5409.00 U.S.Army Waterway Experimentation Station
MR= 2550.00 Transport&Research Laboratory,England
Use most conservative value of the three methods to calculate MR C_1500.00
Structural Number(SN)
SN= I 3.504382263 Calculated by EQ 1
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
al,a2,a3 structural layer coefficients of wearing surface,base,and subbase
M2,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
Di= 3 Assumed(in inches)
D2= 6 Assumed(in inches)
Solve for D3 12.22