Design Fundamentals for Local Roads & Streets 2016 SD Asphalt Conference Dr. Richard Reid, PE – SD State University Ken Skorseth – SDLTAP – SD State University
Key Design Fundamentals – Presentation Overview • Determining Why Local Roads and Streets are Failing at an Increasing Rate • Planning and Prioritizing Future Work on Local Roads/Streets • Design Considerations for Rehabilitation or New Construction Projects • Control Quality of Materials and Construction
• Commitment to Maintenance in the Future
Why Local Roads and Streets are Failing? • So many roads and streets are old – at end of life cycle • Designed/built to a different standard. • Blotter surfacing on six inches of base? • Two to three inches of HMA on six inches of base? • Geometry and materials
• Changes in traffic type and volume demand better design • Increased traffic in growing areas. • Decreasing traffic in rural areas, but much heavier traffic.
• Budgets are constrained – inadequate maintenance!
Why Local Roads and Streets are Failing – Age!
Road surface is >35 yrs old – end of useful life
Why Local Roads and Streets are Failing – Obsolete Design!
Great changes in loads on public roads
Amazing increase in major crop yields – Five season average shown here in five central SD counties Source: SDDOT - SHRP2 Agricultural Freight Data Improvement Study (page 60)
It’s not just agriculture
Why Local Roads and Streets are Failing – Budget Constraints! Source: SD2008-11 Executive Summary 2008 Local Roads Needs Study
Why Local Roads and Streets are Failing – Budget Constraints (Con’t)
Source: SD2008-11 Executive Summary 2008 Local Roads Needs Study
Planning and Prioritizing Future Work on Local Roads/Streets • Options: 1. Revert some paved roads to unpaved surfaces
2. Do minimum maintenance only on low priority routes 3. Rehabilitate or Reconstruct 4. New Construction
Focus of today’s presentation
Planning and Prioritizing Future Work on Local Roads/Streets (Con’t) • Keys to Planning and Prioritizing: • Get an accurate average daily traffic (ADT) • Estimate or determine average daily truck traffic (ADTT) • SDDOT generally estimates 12% on local roads if no known counts
• Try to determine future growth or change in traffic • Road classification – i.e., local road, residential street, rural minor collector, rural major collector, urban minor arterial, urban principal arterial ---• Is the road/street serving commercial or agribusiness access?
Design Considerations for Rehabilitation or New Construction Projects • Be sure to evaluate causes of existing distresses! • Key Considerations in Good Design: • Good Drainage – ditch or curb and gutter
Site evaluation issues Design issues
• Grade separation • Subgrade condition (possible use of geotextiles if wet and weak?) • Adequate base thickness and quality • Surface selection
Design Consideration Drainage??
Design Consideration Drainage improvement needed on curb prior to rehabilitation project
Design Consideration Drainage improvement needed on rural section prior to rehabilitation project
Design Consideration Grade Separation - Urban
Design Consideration Grade Separation & Subgrade Condition - Urban
Design Consideration Grade Separation & Subgrade Condition - Urban
Design Consideration Grade Separation & Subgrade Construction - Urban
Design Consideration Drainage and Grade Separation- Rural
Design Consideration Subgrade Condition – Rural Rehab
Structural Component • Thickness • SDDOT Rural Road Design, Maintenance and Rehabilitation Guide • Blotter (use Gravel Road Thickness Design table) • Pavement
• Materials – Use SDDOT Standard Specifications • Quality Control
Design Considerations - Adequate base thickness for Blotter Surfacing
Up to 25 heavy trucks per day on a Low subgrade strength condition requires base aggregate thickness of 11.5 inches
Source: SDDOT Rural Road Design, Maintenance and Rehabilitation Guide
Design Considerations - Adequate base thickness for AC pavement Up to 50 heavy trucks per day on a Low subgrade strength condition requires base thickness of 12 inches under 6.5 inches of asphalt pavement
Source: SDDOT Rural Road Design, Maintenance and Rehabilitation Guide
Some Performance Contrasts Failure in one year!
Photo taken in 2008
Blotter constructed in Hand Co in 1965!
Result of ignoring good base thickness design on minor arterial
Distress less than one year after construction
Over 50% serious distress and failure in five years
County major collector with adequate base thickness – This road is 25 yrs old
Commercial Access Rd – 25 yrs performance Construction History: Subgrade Improvement Eight inches base course Four inches of HMA Aggressive maintenance after construction Designed for ADTT ≈ 20 Medium subgrade support condition
City of Pierre, SD Constructed in 2009. Performance has been good thus far.
Blotter or Otta Seals – Works with deep base
Base Thickness Data: • 8 inches of base course aggregate meeting SDDOT spec • 4 inches of milled asphalt • 2 inches of base course placed just prior to Otta seal (final 2 inches not used on entire section) 33
Control Quality of Materials and Construction • Key factors for success: • Specify materials meeting standard specifications (SDDOT or AASHTO) • Do material testing prior to and during construction • Control quality of construction – inspection and documentation
SDDOT Standard Specifications
Section 882
Aggregates for Asphalt Concrete (Hot-mixed Asphalt Pavement) SDDOT Standard Specifications – Section 880
Aggregates for Asphalt Concrete (Hot-mixed Asphalt Pavement) SDDOT Standard Specifications – Section 880 Con’t
SDDOT Standard Spec of HMA Binder • SHRP Performance Graded Asphalt Binders • PG 58-28 (used very little by SDDOT, a lot on local projects – be careful with this)
• PG 58-34 • PG 64-28 • PG 64-34 • PG 70-28 • PG 70-34
A local project using local funds only with no clear spec – No one seemed to know what aggregate spec or what binder spec was being used! One of the colder parts of the state – pavement has cracked prematurely – why?
Quality Control – Aggregate Sampling at Source
Belt sampling aggreagate at the time of production
Project site control of base aggregate
Windrow sampling on site
Field check on coarse/fine aggregate split (#4 Sieve)
Full sieve analysis and other tests have to be done in a lab
Commitment to Maintenance in the Future • Any surface type requires maintenance – don’t build what you can’t maintain! • Is the agency committed to and has budget to perform: • Crack sealing on asphalt pavements • Seal coat maintenance on both pavements and blotters/otta seals – generally on five to seven year intervals on pavement, four to six year intervals on blotters. • Fog seals over seal coats can extend intervals by one to two years • Patching – needed as pavement ages
Crack Sealing – Good Maintenance Practice
County Seal Coat Operation
Closing information from a recently completed project by Alyssa Clemen, a graduate student in Civil Engineering at SDSU
Evaluation of Existing Pavements
Recent study conducted to evaluate performance of existing pavements • • • •
Determine condition of fourteen pavements Establish design and maintenance history Sample and characterize materials Estimate traffic volumes
Compare thickness and material properties to an accepted design and material specification Determine which parameters led to success or failure
SDSU
Evaluation Parameters
Average Daily Traffic (ADT) Average Daily Truck Traffic (ADTT) Age of Construction Maintenance History Surface • Type • Surface Condition • Surface Thickness
Base • • • •
Thickness Gradation Plasticity Index Moisture Content
Dynamic Cone Penetration (DCP) Resistance
Subgrade Moisture Content SDSU
Evaluation of Existing Pavements
Harding County, SD: Route 867 (Camp Crook Road) Bowman County, ND: 154th Avenue Miner County, SD: South Rail Road Street Miner County, SD: Rail Road Street (Canova) Aurora County, SD: 262nd Street (Stickney) Aurora County, SD: 389th Avenue (Plankinton) Deuel County, SD: 311 (Astoria)
Codington County, SD: Old Highway 81 (Watertown) Clay County, SD: Saginaw Road Lincoln County, SD: 135 (Canton) Pennington County, SD: Rockerville Road (Rockerville) Pennington County, SD: Bombing Range Road (Scenic) Brown County, SD: Highway 14 (Aberdeen) Brown County, SD: Highway 17 (Aberdeen) SDSU
Evaluation of Existing Pavements
SDSU
Condition Table 5.1: Surface Condition Assessment Summary
Poor
Average
Good
Harding – Hwy 867
Deuel – Hwy 311 original
Lincoln – Hwy 135
Bowman – 154th Ave
Aurora – W. 262nd St (Stickney)
Miner – Rail Road St
Beadle – Broadland Rd
Pennington – Rockerville Rd
Deuel – Hwy 311 rehab
Aurora – E. 262nd St (Stickney)
Brown – Hwy 17
Codington – Old Hwy 81
Pennington – Bombing Range Rd
Aurora – 386th Ave (Plankinton)
Brown – Hwy 14 Clay – Saginaw Ave
SDSU
Condition Examples
Poor – Clay County
Average – Deuel County
Good – Miner County
SDSU
Thickness Comparison Thickness Comparison
0
0.5 0.75
1
1
1
1.25 3 4
1.75 2.75
3
3.5
2.25
3.25 3.25
5 5
6
6.75
6.5 6.25 8.5
7.6
6 6
6.5
Depth (in)
10
9
8
10.5 1
5.6
4.4
6.5 5
6.25
6.25 5.25
7
10.75 11.5 3.5 1.25 11.75
5.4
8
3
15
5 20
9
8
15
Poor
Average
Good
25 Pavement
Base with Asphalt Emulsion
Base
Subbase
SDSU
Table 6.4: Comparison to Rural Road Guide Design
Condition
Poor
Average
Good
County
Road
Base Meets State Spec
Adequate Thickness
Regular Maintenance
Harding
867
No
Yes
< 1 yr
Bowman
154 Ave
No
Yes
< 1 yr
Beadle
Broadland Rd
Yes
No
No
Aurora
E. Stickney
No
No
No
Pennington
Bombing Range Rd
No
No
No
Brown
Hwy 14
N/A
No
Yes
Clay
Saginaw Ave
Yes
No
No
Deuel
Hwy 311 - org
Yes
No
Yes
Aurora
W. Stickney
No
No
?
Pennington
Rockerville Road
No
No
Yes
Brown
Hwy 17
Yes
No
Yes
Aurora
386th Ave
Yes
No
?
Lincoln
Hwy 135
Yes
No
Yes
Miner
Rail Road St
No
Yes
Yes
Deuel
Hwy 311 - rehab
Yes
No
Yes
Codington
Old Hwy 81
Yes
Yes
Yes
SDSU
Conclusions
The SD Rural Roads Design, Maintenance & Rehabilitation Guide is valid if the following parameters exist: • Proper layer thickness is used • Material quality is enforced • Pavement is maintained
SDSU
Summary Thickness
Base Specification
Regular Maintenance
Performance
X
X
X
Good Poor
X X X
X
X
Avg. (some good)
X
Good ?
SDSU
