A commonly observed feature on roads in tropical countries is the presence of long cracks running parallel to the edge of the pavement. The mode of development of such cracks has been studied on an experimental road at the east African agriculture and forestry research organization's estate at Muguga, Kenya. Measurements were made of the horizontal and vertical movements of the soil surface resulting from moisture changes. It was found that cracks occur along a line between the zone where there is a seasonal fluctuation of moisture content and the zone of more static conditions further under the pavement. It is suggested that the lateral shrinkage of the soil under the shoulder and edge of the road causes the systematic cracks to develop at the wet/dry interface in the subgrade. This interface is generally within 2 to 3 feet of the edge of the pavement and within the zone most frequently trafficked by the nearside wheels of road vehicles. The cracks provide an easy path for water to enter the road structure, hence such shrinkage cracking probably plays an important part in the behaviour of roads in tropical countries. (Author/publisher)
Abstract