«Saara Aho, Timo Saarenketo DESIGN AND REPAIR OF ROADS SUFFERING SPRING THAW WEAKENING Executive Summary Design and Repair of Roads Suffering Spring ...»
THIS PROJECT IS BEING PART-FINANCED BY
THE EUROPEAN UNION
EUROPEAN REGIONAL DEVELOPMENT FUND
Saara Aho, Timo Saarenketo
DESIGN AND REPAIR OF ROADS
SUFFERING SPRING THAW WEAKENING
Design and Repair of Roads Suffering Spring Thaw Weakening
EXECUTIVE SUMMARYMarch 2006 Saara Aho Roadscanners Oy Timo Saarenketo Roadscanners Oy
PREFACEThe report that follows is an executive summary of the 2005 ROADEX II report “Managing Spring Thaw Weakening On Low Volume Roads - Problem Description, Load Restriction Policies, Monitoring And Rehabilitation” by Timo Saarenketo and Saara Aho of Roadscanners Oy.
It aims to be a working manual, concentrating on the rehabilitation methods and practices that should be carried out for low volume roads suffering from problems related to seasonal changes, especially spring thaw weakening.
The report is not intended to replace the many excellent reference works and text books available on the subject but it is hoped that the summaries that are outlined will give the reader a greater understanding of the issues and solutions for this recurring seasonal problem.
The report was written by Saara Aho and Timo Saarenketo from Roadscanners Oy, Finland. Ron Munro, project manager of the ROADEX III Project, checked the language. Mika Pyhähuhta of Laboratorio Uleåborg designed the report layout.
The authors would like to thank the ROADEX III Steering Committee for its encouragement and guidance in this work.
Copyright © 2006 Roadex III Project All rights reserved.
ROADEX III Lead Partner: The Swedish Road Administration, Northern Region, Box 809, S-971 25 Luleå. Project co-ordinator: Mr. Krister Palo.
CHAPTER 1. INTRODUCTION
1.1 THE ROADEX PROJECT
1.2 DESIGN AND REPAIR OF ROADS SUFFERING SPRING THAW WEAKENING
CHAPTER 2. THAW WEAKENING – SHORT DESCRIPTION
2.1 FACTORS AFFECTING THAW WEAKENING
2.2 SPRING THAW WEAKENING PHASES
2.3 SPRING THAW WEAKENING SITE CLASSIFICATION
CHAPTER 3. REHABILITATION PROCESS
CHAPTER 4. RESEARCH AND ANALYSIS OF SPRING THAW WEAKENED ROADSECTIONS
4.1 RESEARCH METHODS FOR LOW VOLUME ROADS
4.2 INTEGRATED ANALYSIS OF SURVEY DATA
4.3 OPERATIONS MODEL FOR RESEARCH AND ANALYSIS OF SPRING THAW WEAKENED ROADS........17 CHAPTER 5. SPRING THAW DAMAGE STRENGTHENING
5.2 LIFECYCLE COSTS OF REHABILITATION STRUCTURES
5.3 REHABILITATION STRUCTURES FOR GRAVEL ROADS
5.4 REHABILITATION STRUCTURES FOR PAVED ROADS
5.4.2 Roads with thin pavements – pavement thickness: 20 – 100 mm
5.4.3 Roads with thick pavements - pavement thickness 100 mm
CHAPTER 6. QUALITY ASSURANCE AND FUNCTIONALITY CONTROL OFREHABILITATED ROADS
CHAPTER 7. REFERENCES
Chapter 1. INTRODUCTION
1.1 THE ROADEX PROJECT The ROADEX Project is a technical cooperation between roads organisations across northern Europe that aims to share roads related information and research between the partners.
The Project was started in 1998 as a 3 year pilot co-operation between the roads districts of Finnish Lapland, Troms County of Norway, the Northern Region of Sweden and The Highland Council of Scotland and this was later followed up Figure 1: The Northern Periphery Area and with a second project, ROADEX II, from Roadex II partners 2002 to 2005.
The partners in the ROADEX II Project comprised public road administrations, forestry organizations, forest companies and haulage organizations from regions in the Northern Periphery. These were The Highland Council, Forest Enterprise & The Western Isles Council from Scotland. The Region Nord of The Norwegian Public Roads Administration and The Norwegian Road Haulage Association, The Northern Region of The Swedish Road Administration and The Lappi and Keski-Suomi Regions of The Finnish National Roads Administration. (These latter Finnish Regions also received aid from their local forest industry organisations of Metsähallitus, Lapin Metsäkeskus, Metsäliitto & Stora-Enso.) The goal of the project was to develop ways for interactive and innovative road condition management of low traffic volume roads integrating the needs of local industry, society and roads organisations. 8 formal reports were published together with a project DVD and full copies of all reports are available for download at the ROADEX web site at www.roadex.org.
This Executive Summary report is one of 8 summaries that have been prepared under the direction of the ROADEX III project (2006-2007), a new Project where the named project Partners above were joined by the additional Northern Periphery Partners of the Municipality of Sisimiut, Greenland, The Iceland Public Roads Administration and the Finnish Road Administration Region of Savo-Karjala.
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Chapter 1. INTRODUCTION Page 6
1.2 DESIGN AND REPAIR OF ROADS SUFFERING SPRING
THAW WEAKENINGSeasonal changes, freeze-thaw cycles and the damage they cause are the most significant factors affecting the road condition of northern cold climate road networks in Europe, Asia and North America. Freeze-thaw processes also cause major problems in high elevated areas in countries with warmer climates. In the United States, the AASHO research program studied the appearance of pavement distress during different seasons (White and Goree 1990) and, according to the results, 60% of the distresses appeared during the springtime when the relative amount of traffic was 24%. During the summer time the relative amount of new pavement damage was only 2% when the relative traffic amount was 30%.
Frost damage exhibits in roads as uneven frost heave and longitudinal and transverse cracking, but above all as softening of the road structure and permanent deformation during the thawing period. In the worst scenario driving on these roads can be impossible. Usually thaw weakening damage is the biggest problem on “unbuilt” gravel roads but it also causes major problems on paved roads and especially on weak roads with a surface dressing pavement.
Depending on the scale and scope of the spring thaw weakening problem there are several policies and techniques for managing a road during this weak period. In
general the management tools can be divided into:
1) different maintenance techniques to reduce the effect of spring thaw
2) load restrictions and different tools to minimize the problems caused by these restrictions
3) strengthening weak road sections to the extent that load restrictions can be removed or used only in extreme conditions and
4) co-operation with transportation organizations using heavy vehicles.
Traditionally road administrators have endeavoured to prevent spring thaw damage by implementing load restrictions or even closing the road. The use of spring load restrictions increases the pavement lifetime but at the same time load restriction measures also incur major extra costs for industries using heavy transport vehicles.
For instance in Finland the extra costs to the forest industry, due to spring thaw weakening, has been calculated to be 100 M€, of which 65 M€ comes from public roads (Pennanen and Mäkelä 2003).
Thus, the best and most sustainable solution for managing thaw weakening problems is to strengthen and rehabilitate the weak road sections. However this can, and should, only be done if the road region has enough resources to take appropriate measures that will function over the long term. Major mistakes have been made when road sections have been strengthened using structures that are too weak.
These problems become especially apparent if the road is paved afterwards.
Roadex III The Northern Pheriphery Research
Chapter 1. INTRODUCTION Page 7This report concentrates on presenting the strengthening processes and methods for weak road sections based on the research work done during the ROADEX II – subprojects “Managing Spring Thaw Weakening on Low Volume Roads” (Saarenketo and Aho 2005) and “Permanent Deformation” (Dawson and Kolisoja 2005) and also on the report “Design and Rehabilitation of Spring Thaw Weakened Road Sections” (Aho et al. 2005b) prepared for Finnish Road Administration (Finnra). The goal for this report is to provide a practical guide that addresses the needs of the local roads engineer, designer etc. and presents a systematic step-by-step analytical approach for design and repair of roads suffering spring thaw weakening. A classification system for spring thaw damaged road sections, as well as the basic theory relating on the spring thaw weakening, is also presented providing better understanding the process behind the problems. The report also provides a short review for rehabilitation structures and their suitability for repairing different types of damages.
Finally, the report handles the general aspects relating to the quality assurance and functionality control of the rehabilitated roads.
More policies and techniques for spring thaw weakening management are discussed in ROADEX II project report “Managing Spring Thaw Weakening on Low Volume Roads” written by Saarenketo and Aho (2005).
Chapter 2. Thaw Weakening – Short Description
1 FACTORS AFFECTING THAW WEAKENINGThe term “spring thaw weakening” has different meanings in different languages. In general, spring thaw weakening can be defined as a decrease in the bearing capacity of a road during the period in which the frozen layers of the road thaw during the spring. Launonen et al. (1995) listed the following factors as being necessary for the
appearance of spring thaw weakening:
• the road and/or subgrade freezes
• the material is frost susceptible
• the freezing front has enough water available
• during the thawing period the water, released by the melting segregation ice, stays in the road structure or subgrade soil, thus weakening the structure
• the road is subject to loads during the thawing period.
If any one of these factors is absent there is no risk of spring thaw damage. In countries with warmer climates (e.g.. Scotland) frost thaw weakening is usually related to weakening of the road after daily freeze-thaw cycles. The processes behind thaw weakening are described in more detail in the ROADEX II project report “Managing Spring Thaw Weakening on Low Volume Roads” (Saarenketo and Aho 2005).
The factors affecting the development of thaw weakening can be divided into loading, environmental and design related factors as presented in Table 2.1. The design related factors are the local factors related to the location of the road and its surroundings that have an influence on frost action, on the amount of frost heave and on the dissipation of melting water. All of the factors presented in Table 2.1 have some effect on their own and combine with the others to jointly increase their influence. Maintenance measures and the bearing capacity of the road shoulders can also affect the degree of difficulty of spring thaw damage in addition to seasonal effects.
2.2 SPRING THAW WEAKENING PHASES The ROADEX II spring thaw monitoring results identified four different time phases for spring thaw weakening with unique features requiring separate classifications.
These occur in a chronological order and the need for load restrictions, for instance, in each phase is strongly dependent on the increase, or lack of it, in moisture content
and stiffness of the road during the previous period. The four phases are:
1) the freeze-thaw cycles phase,
2) the surface thaw weakening phase,
3) the structural thaw weakening phase and
4) the subgrade thaw weakening phase.
A common factor in all of these phases is cryo suction. A potential fifth category, with similar bearing capacity problems, could be the autumn heavy rain season, although during this season, freezing is not a factor in the weakening process. In Scotland, and in other countries with warmer climates, the main problem is not spring thaw weakening but the repeated freeze-thaw cycles that occur daily during the winter. In those areas the freeze-thaw cycles phase is usually the only phase present.
The four spring thaw weakening phases are presented in greater detail in the ROADEX II report “Managing Spring Thaw Weakening on Low Volume Roads”. They can be used in monitoring and communication terminology to describe the status of spring thaw and they can also be used in the decision making process for the implementation, or removal, of load restrictions. Also, as a part of the rehabilitation design and problem analysis, it is important to identify the particular phases that are causing the problems. This is an important factor in determining the appropriate repair methods.
Roadex III The Northern Pheriphery Research
Chapter 2. Thaw Weakening – Short Description Page 10
2.3 SPRING THAW WEAKENING SITE CLASSIFICATIONThe ROADEX II report “Managing Spring Thaw Weakening on Low Volume Roads” (Saarenketo and Aho 2005) proposes a system of classifying spring thaw damage sites, and their causes, by means of topographical and subgrade conditions and
damage descriptions. The criteria used are:
• subgrade soil
• topography of road and its surroundings
• severity of damages
• frequency of damages Each class considered is sub-divided into three (I-III) subclasses depending on the
severity and frequency of the damages. The subclasses are: