5. Roads on weak subgrade, geotechnical considerations

This chapter will focus mainly on the issues engineers face when building and maintaining roads on weak subgrades, and especially on peat. In this chapter we will mainly use material that has already been published in the ROADEX eLearning package “Roads on peat”.

5.1. General

Most gravel and forest roads are heavy haulage roads, ie heavy trucks regularly use them. Despite this there are usually major limitations with funding when designing these roads and these leads to challenges with the structures on weak subgrade soils. For instance, many gravel roads and forest roads have been built floating on peat which brings geotechnical issues in the management of these road sections

5.2 Compressive soils, road on peat

Discussion about compressive soils and especially about peat

5.3. Behaviour of peat, geotechnical risk management

Discussion what is consolidation, compression, lateral displacement and settlement. Also what is the difference between slow and fast consolidation, the effects of seasonal frost and discussions about the special geotechnical risk considerations of roads built on peat.

5.4. Survey and monitoring techniques

A brief summary of different survey and monitoring techniques of gravel and forest roads including desk study, visual inspections, sampling and probing, GPR, laser scanner, 3d accelerometer and video techniques.

5.5. Construction structures

This chapter will mainly focus on structures resting on peat and soil replacement only when the peat under the road is very thin. Discussion also about timber grillages and steelgrid structures as well as when to use geotextiles. Also description of winter roads, ie roads built on frozen peat.

5.6. Maintenance and renovation of roads resting on peat

This chapter will briefly discuss about the issues needed to be aware of when planning and executing maintenance and renovation operations on gravel road sections resting on compressive soils.