Ron Munro DEALING WITH BEARING CAPACITY PROBLEMS ON LOW VOLUME ROADS CONSTRUCTED ON PEAT Including case histories from roads projects within the ROADEX Partner Districts THIS PROJECT IS BEING PART- FINANCED BY THE EUROPEAN UNION European Regional Development Fund DEALING WITH BEARING CAPACITY PROBLEMS ON LOW VOLUME ROADS CONSTRUCTED ON PEAT INCLUDING CASE HISTORIES FROM ROADS PROJECTS WITHIN THE ROADEX PARTNER DISTRICTS December 2004 Ron Munro The Highland Council PREFACE This Report is a final report of the Phase 2 ‘Understanding and Analysis’ section of the EU ROADEX II Project and aims to give an insight into the state of the art of road construction and road maintenance for roads constructed across peat in the Northern Periphery of Europe. It will concentrate particularly on the current practices for road construction over peatlands in the four specific Partner Areas of the EU Roadex Project i.e. Troms County in Norway, the Districts of Keski-Suomi and Lapland in Finland, the Region Norr of Sweden and the Highland Area of Scotland. In addition, where appropriate, the report will also refer to relevant peat related experiences being carried out elsewhere in the world where these are considered apposite to the report. The report was written following discussions and meetings with engineers across the Partner areas. The author would like to thank Aarno Valkeisenmäki, Hannu Keralampi, Timo Saarenketo, Jorma Immonen and Martti Eerola from Finland, Karl Melby, Stein Stokkebø, Tor Erik Frydenlund, Roald Aabøe, Kjetil Vollan, Even Øiseth and Inge Hoff from Norway, Peter Carlsten, Johan Ullberg and Gunnar Zweifel from Sweden and Alistair Gilchrist, Frank MacCulloch, Hugh Mackay, Ken Wiseman, Richard Evans, Douglas Bremner and Willie Watt from Scotland for their help and input into the report. The report was written by Ron Munro of The Highland Council Transport, Environmental & Community Services. Mika Pyhähuhta of Laboratorio Uleåborg designed the graphic layout and Garry Smith of The Highland Council prepared many of the graphic images. Virpi Halttu, Teen Mackay and Janet Mackintosh assisted in the production of the report by typing, drafting and editing the various versions. Finally the author would like to thank the ROADEX II Steering Committee for its encouragement and guidance in this work. Copyright ©2004 Roadex II Project All rights reserved. Roadex II Lead Partner: The Highland Council, Transport, Environmental & Community Service, HQ, Glenurquhart Road, Inverness IV3 5NX Scotland, Project co-ordinator: Mr. Richard Evans. CONTENTS PREFACE ................................................................................................................................................... 5 CONTENTS ................................................................................................................................................ 6 ABSTRACT ................................................................................................................................................ 1 1 THE ROADEX II PROJECT................................................................................................................. 1 2 BACKGROUND...................................................................................................................................... 3 2.1 INTRODUCTION ................................................................................................................................. 3 2.2 HISTORY............................................................................................................................................. 3 2.3 THE PRESENT SITUATION.................................................................................................................. 4 3 PEAT ........................................................................................................................................................ 5 3.1 INTRODUCTION.................................................................................................................................. 5 3.2 FORMATION OF PEAT ........................................................................................................................ 5 3.2.1 “The Wetland Succession” ..........................................................................................................................6 3.2.2 Mires, Fens and Bogs in the Northern Periphery.........................................................................................6 3.3 THE CLASSIFICATION OF PEAT ...................................................................................................... 10 3.4 PEAT CHARACTERISTICS & PROPERTIES...................................................................................... 12 3.4.1 Introduction................................................................................................................................................12 3.4.2 Peat characteristics and properties .............................................................................................................12 3.4.3 Summary of properties...............................................................................................................................13 4 BEHAVIOUR OF PEAT ...................................................................................................................... 14 4.1 INTRODUCTION................................................................................................................................14 4.2 CONSOLIDATION & SETTLEMENT.................................................................................................. 14 4.2.1 Primary consolidation................................................................................................................................14 4.2.2 Secondary compression .............................................................................................................................15 5 GROUND INVESTIGATIONS & LABORATORY TESTS ............................................................ 17 5.1 INTRODUCTION................................................................................................................................17 5.2 GROUND INVESTIGATIONS.............................................................................................................. 17 5.2.1 Ground investigation methods in peat .......................................................................................................17 5.2.2 Ground investigation methods in the ROADEX partner areas ..................................................................22 5.3 LABORATORY TESTING ................................................................................................................... 22 6 EMBANKMENTS OVER PEAT.........................................................................................................24 6.1 INITIAL CONSIDERATIONS .............................................................................................................. 24 6.2 BEARING CAPACITY........................................................................................................................ 24 6.3 STABILITY ........................................................................................................................................ 25 6.4 SETTLEMENT ................................................................................................................................... 25 6.4.1 Methods of prediction of settlement ..........................................................................................................26 7 GEOTECHNICAL RISK MANAGEMENT ...................................................................................... 30 7.1 INTRODUCTION................................................................................................................................30 7.2 THE PRELIMINARY GEOTECHNICAL INVESTIGATION.................................................................. 31 7.3 THE GEOTECHNICAL REPORT......................................................................................................... 31 7.4 THE GEOTECHNICAL FEEDBACK REPORT...................................................................................... 32 7.5 THE GEOTECHNICAL RISK REGISTER............................................................................................. 32 8 TYPES OF CONSTRUCTION ............................................................................................................ 34 8.1 INTRODUCTION................................................................................................................................34 8.2 AVOIDANCE...................................................................................................................................... 34 8.3 PEAT EXCAVATION.......................................................................................................................... 35 8.4 PEAT REPLACEMENT....................................................................................................................... 36 8.5 PEAT DISPLACEMENT...................................................................................................................... 37 8.5.1 Progressive displacement...........................................................................................................................38 8.5.2 Partial excavation.......................................................................................................................................40