Study on Subgrade Settlement Characteristics After Widening Project of Highway Built on Weak Foundation

Generally, the maximum differential settlement appears at the overlapping area of existing and new road pavement after highway widening project. However, lots of longitudinal cracks and other kinds of distresses were found on the existing pavement after the widening project of Guangsan Highway. The field investigation was carried out to find out the reason that the large settlement appeared on existing lanes induced by the weak foundation under the existing lanes, which leaded the cracks observed on the existing pavement. In addition, numerical method was adopted to verify this explanation. The parameter sensitivities were studied to discuss the characteristics of subgrade settlement after the highway widening project. Factors considered include different layouts of cement-fly ash-gravel (CFG) piles, different strengths of CFG piles and different filling materials of new embankment. The results showed that the settlement of pavement became larger when the existing road has weaker foundation. The maximum settlement on the ground surface shifts toward the new embankment when the foundation of existing road has higher strength. The lightweight filling material was proved to have advantage in reducing the settlement of the existing embankment.