HomeMy WebLinkAboutAppendix F - Pavement Design
PAVEMENT DESIGN REPORT
FLANDERS MILL SUBDIVISION
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
Project Number: 13067
April 2014
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 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 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
per year
Growth
Factor
(4%,20yrs)
Design Vehicles
(20 years)
ESAL Factor Design
ESAL
Passenger Car 321,930 29.78 9,587,075 0.0003*2=0.0006 5,752
2 axle/6 tire
truck/bus
6,570 29.78 195,655 0.118*2=0.236 46,174
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 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)
MR = 2,550 CBR0.64 (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 CBR0.64 = 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 (EQ1):
Variables:
1. ESAL (W18) = 51,927
2. Level of Reliability (ZR) = -1.282 for Local Streets used for Local Streets based on 90%
reliability from Part I, Table 4.1, and Part II, Table 2.2, AASHTO Guide.
log𝑊18 =𝑍𝑅𝑆𝑂+9.36[log(𝑆𝑁+1)]−0.20 +log ∆𝑃𝑆𝐼2.70.40 +1094(𝑆𝑁+1)5.19 +2.32 log 𝑀𝑅−8.07
Level of reliability is based on the cumulative percent of probability of reliability with a
standard normal distribution.
3. Standard Deviation (S0) = 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 (ΔPSI) = 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 (MR) = 3,000 psi
Solution: using (EQ1), the SN for Local Streets = 2.98
Pavement Design Equation (EQ2):
1. Layer Coefficients: a1 = 0.44 (Hot-mix asphalt concrete)
a2 = 0.14 (Base Course - 1 ½" minus crushed gravel)
a3 = 0.11 (Sub-base Course - 6" minus crushed stone)
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: D1 = 3” for Local Streets
D2 = 6” for Local Streets
Solution: using the values given for D1 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.
𝑆𝑁=𝑎1𝐷1 +𝑎2𝐷2𝑀2 +𝑎3𝐷3𝑀3
PAVEMENT DESIGN REPORT – FLANDERS MILL SUBDIVISION
COLLECTOR/ARTERIAL ROADS (BAXTER, OAK, AND FERGUSON)
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 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 Collector/Arterial Streets to be constructed with this subdivision in the TIS
and was used for the design criteria for Collector/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 trucks/buses, 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
per year
Growth
Factor
(4%,20yrs)
Design Vehicles
(20 years)
ESAL Factor Design
ESAL
Passenger Car 545,493 29.78 16,244,782 0.0003*2=0.0006 9,747
2 axle/6 tire
truck
11,132 29.78 331,510 0.118*2=0.236 78,236
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)
MR = 2,550 CBR0.64 (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 CBR0.64 = 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 (EQ1):
Variables:
1. ESAL (W18) = 87,983
2. Level of Reliability (ZR) = -1.645 used for Arterials and Collectors based on 95%
reliability from Part I, Table 4.1, and Part II, Table 2.2, AASHTO Guide.
log𝑊18 =𝑍𝑅𝑆𝑂+9.36[log(𝑆𝑁+1)]−0.20 +log ∆𝑃𝑆𝐼2.70.40 +1094(𝑆𝑁+1)5.19 +2.32 log 𝑀𝑅−8.07
Level of reliability is based on the cumulative percent of probability of reliability with a
standard normal distribution.
3. Standard Deviation (S0) = 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 (ΔPSI) = 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 and collector roads such as Oak St., Ferguson Ave, and Baxter Ln 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., Ferguson Ave., and Baxter Ln. SN = 3.60
Pavement Design Equation (EQ2):
1. Layer Coefficients: a1 = 0.44 (Hot-mix asphalt concrete)
a2 = 0.14 (Base Course - 1 ½" minus crushed gravel)
a3 = 0.11 (Sub-base Course - 6" minus crushed stone)
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: D1 = 4” for Oak, Ferguson and Baxter
D2 = 6” for Oak, Ferguson and Baxter
𝑆𝑁=𝑎1𝐷1 +𝑎2𝐷2𝑀2 +𝑎3𝐷3𝑀3
Solution: using the values given for D1 and D2, and solving (EQ2), D3 = 9.12” for Oak St.,
Ferguson Ave., and Baxter Ln.
Use a conservative value of 12” for the sub-base section D3. This results in final values used for
this design of 4 inches of asphalt, 6 inches of 1” minus road mix, and 12 inches of 6” minus
gravel for Oak St., Ferguson Ave., and Baxter Ln. to meet or exceed the structural requirement.
Project #13067
Title:Flanders Mill Subdivision
W18 (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)
S0 Standard Deviation in estimates for ESAL, typically 0.30-0.50
ΔPSI Serviceability loss over design life
MR Soil Resistence Modulus of subgrade soil
EQ 1:
Equivalent Single Axle Load
ADT 3474
Peak A.M.7
Peak P.M.9
Total 3050
AYT 556625 (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
(4%, 20 years)
Design Vehicles
(20 years)ESAL Factor Design ESAL
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
Required Values For SN Calc
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)
log𝑊𝑊18 =𝑍𝑍𝑅𝑅𝑆𝑆𝑂𝑂+9.36 log 𝑆𝑆𝑆𝑆+1 −0.20+log∆𝑃𝑃𝑆𝑆𝑃𝑃2.70.40+1094𝑆𝑆𝑆𝑆+1 5.19 +2.32log𝑀𝑀𝑅𝑅−8.07
Level of Reliability (R and ZR)
R ZR
90 -1.2820
95 -1.6450
97.5 -1.9675
99 -3.0800
R (%) = 95 (Conservative estimate)
ZR = -1.645
Standard Deviation (S0)
S0 =0.49
Serviceability Loss (ΔPSI)
4.2 Highways 3.0
2.5 Arterials 2.5-3.0
Local Roads 2.0
ΔPSI =1.7
Resistance Modulus (MR)
CBR 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 = 3.602795748 Calculated by EQ 1
Road Type vs. TSI
Present Serviceability Index (PSI) =
Terminal Serviceability Index (TSI) =
R to ZR Conversion Chart
EQ 2:
a1, a2, a3 structural layer coefficients of wearing surface, base, and subbase
M2, M3 drainage coefficients of base and subbase
D1, D2, D3 thickness of wear surface, base, and subbase in inches
Structural Layer Coefficients (a)
Coeffiecient
0.35
Hot-mix asphaltic concrete 0.44
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
Crushed Stone 0.11
a1 =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
Subbase
Pavement Component
Sand-mix asphaltic concrete
Wearing Surface
Base
Once SN is determined, the thickness of the wearing surface, base, and
subbase layers can be determined by EQ 2.
𝑆𝑆𝑆𝑆=𝑎𝑎1𝐷𝐷1 +𝑎𝑎2𝐷𝐷2𝑀𝑀2 +𝑎𝑎3𝐷𝐷3𝑀𝑀3