When severe, water ponds in the ruts and steering is affected creating safety problems. Subgrade failures are bearing capacity failures in the layers underlying the BST and base. Shoulder Disintegration refers to the disintegration of the BST surface starting at the shoulder edge and progressively working inwards. Potholes refer to shallow failures in BST or base course as opposed to the subgrade failures mentioned above which are more deeply seated. Patching refers to the amount of patching already carried out on the section.
Distortions refer to uneven aggregate embedment leading to a washboard surface.
Streaking refers to longitudinal streaks in the BST where there is uneven embedment of the aggregate in the longitudinal direction. Sections generally are never longer than 10 kms and are always different for BST classes, or BST age. There are many criteria that impact on the life of BST and the decision when to rip it up and replace it. The following shows average life of BST by class based on 2 different BCI criteria. These costs do not include the aggregates another 20 - 25 per m should be added for this purpose.