HomeMy WebLinkAbout20 - Design Report - Allison Ph IV - Pavement
PAVEMENT
DESIGN REPORT
FOR:
ALLISON SUBDIVISION
PHASE IV
BOZEMAN, MT
Prepared By:
Madison Engineering
895 Technology Drive, Suite 203
Bozeman, MT 59718
(406) 586-0262
JUNE 2020
ALLISON SUBDIVISION PHASE IV
PAVEMENT DESIGN REPORT
A. General
This design report will provide documentation of design for the proposed roadways for the
development of Allison Subdivision Phase IV (Section 24, Township 02S, Range 5E, Plat J-
608A) located at the intersection of Arnold Street and S. 11th Avenue in Bozeman. The
proposed improvements are anticipated to be constructed during the summer of 2020.
The following references were used in the roadway design:
a. COB Design Standards and Specifications Policy, 2004, Addendum #7
b. AASHTO Guide for Design of Pavement Structures
c. Marvin & Associates Traffic Impact Study March 2019
d. Castle Rock Geotechnical Report and Response Letter April 2020
B. Traffic Volume
The City of Bozeman requires that roadway design be based on at least a 20-year performance
period traffic volume, with a minimum value not less than 50,000 ESALs (Equivalent 18,000-lb
Single Axle Load). The Traffic Impact Study for the project predicted an Average Daily Trips
(ADT) of 1,813 trips. Assuming that 1% of the daily trips constitutes an 18 kip single axle load,
this results in 18 ESALs per day. Over a 20 year period, this equates to 132,000 ESALs,
exceeding the required minimum.
C. Road Section Design
The AASHTO Flexible Pavement Design Procedure was utilized to determine the roadway
sections per the City of Bozeman Standards. The Geotech report and response letter dated April
2020 provided resilience modulus, serviceability indexes, reliability, and standard deviation
values for the proposed roadways. These values were utilized in the flexible pavement design to
provide section thicknesses for pavement, base course, and sub-base course. The results of the
calculations are summarized below:
Roadway
Asphalt Thickness
(in)
Base Course
Thickness (in)
Sub-Base Course
Thickness (in)
Arnold St (Local) 4 6 15
Other Local Streets 3 6 10
Detailed calculations are included in the Appendix. The Geotech report and Response Letter
Dated April 2020 provided alternative section thicknesses, which are summarized below:
The Geotechnical report and Response Letter Dated April 2020 are included separately.
Appendix:
Pavement Calculations
Allison Subdivision Phase 4
Pavement Calculations
6/23/2020
The pavement design is completed using the AASHTO flexible pavement design procedure:
Arnold St
Input:
ADT 1813 (Average Daily Trips from Traffic Impact Study)
ESAL %1 (Percent of trips constituting an ESAL)
Design life 20 years
ESALs 132349 Must be greater than 50,000 for Bozeman Local Streets
CBR NA From Geotech
Mr 3250 psi - Soil resilient modulus - From Geotech
PSI 4.5 From Geotech
TSI 2 From Geotech
∆PSI 2.5 From Geotech
Zr 0 From Geotech
So 0.5 From Geotech
a1 0.44 Asphalt - from geotech
a2 0.14 Base Course - from geotech
a3 0.11 Sub-Base Course - from geotech
D1 4 in - Asphalt Thickness
D2 6 in - Base Thickness
D3 15 in - Sub-Base Thickness
M2 1 Well Drained
M3 1 Well Drained
Calculations:
SN 4.25
LHS eqn 4.7 5.12
RHS eqn 4.7 6.56
RHS > LHS OK Proposed Section is greater than required (LHS)
Other Local Streets
Input:
ADT 1813 (Average Daily Trips from Traffic Impact Study)
ESAL %1 (Percent of trips constituting an ESAL)
Design life 20 years
ESALs 132349 Must be greater than 50,000 for Bozeman Local Streets
CBR NA From Geotech
Mr 3250 psi - Soil resilient modulus
PSI 4.5 From Geotech
TSI 2 From Geotech
∆PSI 2.5 From Geotech
Zr 0 From Geotech
So 0.5 From Geotech
a1 0.44 Asphalt - from geotech
a2 0.14 Base Course - from geotech
a3 0.11 Sub-Base Course - from geotech
D1 3 in - Asphalt Thickness
D2 6 in - Base Thickness
D3 10 in - Sub-Base Thickness
M2 1 (well drained)
M3 1 (well drained)
Calculations:
SN 3.26
LHS eqn 4.7 5.12
RHS eqn 4.7 5.74
RHS > LHS OK Proposed Section is greater than required (LHS)