Causes of structur
Causes of structural failure
The strength of the subgrade used in road construction doesn’t remain the same throughout its life. It may be higher at times and almost certainly lower at other times. This change in the strength of sub grade , known as “regression” , is the main cause of road structure failure.This regression may be due to any of the following causes.
1- Action of traffic
Repeated wheel loads can cause the compaction and consolidation of aggregate material. Thereby , penetration of road crust into the subgrade or ingress of soft subgrade soil into the base course of the pavement takes place ,figure (I.8), leaving the localized area of the base unsupported . (23)
2- Improper drainage
This is the most important cause of regression. Inadequate drainage causes excess pressure , the soil faces the danger of instability and consolidation problem. Moreover , improper drainage causes an increase of soil water content and thereby a decrease of soil strength results.