Dynamic stress study in pavement subgrade under a major highway in Hong Kong

Flexible pavements are relatively thick in Hong Kong. Their thicknesses are generally designed to be at least 300 mm, generally due to high traffic volume. The design is based on the fatigue failure concept of the main structural layer (i.e. roadbase) after a prolonged number of traffic passages and, in turn, it is highly related to the stress levels being experienced in the pavement layers, including the subgrade. This paper presents the data collected on the dynamic stresses of the subgrade layer by soil pressure gauges under a major highway in Hong Kong. The results illustrate that the vertical stresses are in the range of 0.5 to 5kPa. These correspond well to the theoretical analysis results obtained by the software mePADs, by using the typical properties of the pavement layers. Subsequently, horizontal stresses at the bottom of the roadbase were also estimated. These fundamental findings provide an important yardstick for the review of design and analysis for fatigue life of flexible pavements in Hong Kong.