This document summarizes a presentation on analyzing bearing capacity at road edges to reduce heavy truck crashes. It notes that unstable road edges pose a serious safety risk for heavy vehicles. Road edge deformation is common and costly to repair. The Danish method for analyzing edge bearing capacity is being updated and harmonized into a Nordic method, with the goal of impacting road design codes and projects in Nordic countries to improve safety by preventing edge deformation.

1. BEARING CAPACITY AT THE PAVEMENT SIDE
- THE NVF/NRA ANALYSIS METHOD
Presenter: Johan Granlund, Vectura
Co-authors: Jan M Jansen, Danish Road Directorate
Sebastian Pettersson, Oden Enterprise

2. Outline
Unstable road edges is a serious heavy truck crash risk.
Road edge deformation is common and repair is costly.
Low bearing capacity at edge neglected by road design codes.
Updating the Danish method.
Impact on national design codes and road projects.
Harmonizing into a Nordic method in NVF report 04/2012.

3. Heavy vehicles
are extra susceptible to lateral forces
The crash type where
most truck drivers are
injured is the rollover.
Higher C.o.G. makes the
vehicle prone to lateral
forces. [NVF report 02/11].
[Source: Volvo Trucks crash investigation]
Crashes with
severely injured truck
drivers / passengers
Typical number of truck rollovers:
• Norway: 200 per year
• Finland: 200 per year
• Sweden: 650 per year [Source: Insurance-companies IF & LF]
Photo: Volvo Trucks

4. Roll-related lateral buffeting
at road edge deformations
This is what lateral buffeting looks like, Rd 331 in Sweden:
Photo: J Granlund
Lateral buffeting is extremely hazardous on ice-slippery roads,
as it can trigger vehicle (or driver) to develop a skid.

5. Roll-related lateral buffeting
at road edge deformations
Roadex IV project (Finland):
Truck ride sensors recorded
lateral buffeting up to 0.5 – 0.7 G
at many edge damages.
Reference: Cargo latches are
designed for 0.7 G.
Photo: J Granlund

6. Road edge deformation is common
and the repair is costly
On roads with narrow shoulders, deterioration typically
starts in the outer wheelpath and at the pavement edge.
Damage modes include rutting, cracking and
roughness/warpiness.
Edge slump is a significant problem on the road networks
in the Nordic countries (less of a problem in Denmark).
The problem of weak edges has been given much focus in
Finland, Sweden and Norway [Gullberg, Lehtipuu,
Lampinen, Mork, Aksnes, Weydahl, Granlund and others].
Approximately 10 % of the budget for maintenance of
paved roads is spent on repair of edge deformations.

7. Analysis of bearing capacity
close to the road edge
Denmark implemented an edge analysis method decades ago.
Based on classic geotechnology; Terzaghi and Vesic.
With regular 0.25 m shoulder, the outer wheelpath may have as
little as 45 % of the b.c. at the road center.
Sweden has updated the method:
• References to Eurocode 7 ”Geotechnical Design”.
• New figures.
• Parameter sensitivity test.
• Application cases.

8. Road edge bearing capacity
Key parameters:
• Slope towards ditch.
• Shoulder width.
• Depth of ditch / Embankment.
• Pavement bearing capacity
(at the road center).
Access road provides lateral support:
 No highway edge deformation;
Compare with the 7 cm deep depression just in
front of the access road (Note exploded truck tyre).
Denmark: Wide shoulder provides lateral support.Photo: J Granlund

9. Impact on design codes and road projects
The method is derived from the Danish ”Vejregler” codes.
C/B-analysis of widening roads being made in the Norwegian
Durable Roads programme.
Immediate impact on the design of Pajala Iron Ore Express
road in Sweden; A 90 ton high-capacity truck every 7´th min.
Finland and Iceland recognize common problems with weak
road edges, and lack analysis method up until now.
E6 at Stortjønna, Norway:
The narrow road section forced
oncoming truck to park on the tiny
shoulder, to avoid mirror crash.
Photo: Johan Granlund

10. Summary
Unstable road edges is a serious heavy truck crash risk.
Road edge deformation is common and repair is costly.
Edge bearing capacity neglected by road design codes.
Updating the Danish method.
Impact on national design codes and road projects;
Harmonizing into a Nordic method in NVF report 04/2012.