This report forms part of Task 2 of the SEACAP 19 programme. It is concerned with the behaviour of engineered roads with only the natural soil as surfacing (ENS roads). The objective is to define the conditions under which an earth surface is a reasonable choice of road surface type to use. A review of the subject was carried out earlier (Technical Paper No 2.1, 'Behaviour of engineered natural surfaced roads' [see separate output]) the purpose of which was to identify the principal factors on which the performance of an earth road depends so that a field survey of actual performance in Cambodia could be designed to record values of the important variables and to help define critical limits. This report outlines the field survey that was undertaken and the results of a comprehensive analysis of behaviour.
The study has illustrated the complexity of performance of ENS roads and highlighted the reasons why deriving general specifications has proved elusive. It has confirmed the need for locally derived flexible specifications that are relevant to the local materials and the road tasks. The results of the study have been encouraging and have indicated that, with longer term monitoring, the outstanding questions can be resolved.