Differential Settlements of Embankment Treated by Cement Fly-Ash Gravel Pile and Sheet Pile in Freeway Extension Constructions

The differential settlement between the newly built embankment and the old one is becoming a serious problem in the extension construction of roadways in some areas. To solve this problem, cement fly-ash gravel (CFG) piles are used to control settlements because of their simple construction. Sheet piles, which are mainly used in railway subgrade construction, can provide greater load performance and reduce settlement. The main objectives of this study were (1) to compare the settlement-controlling performance of sheet piles and CFG piles and (2) to evaluate the application of sheet piles to highway extension engineering. To compare the treatment effect, a case study was conducted. The settlements occurring at the instrumented locations were periodically monitored through the embedded settlement plates and horizontal inclinometers. The settlements in the construction processes were continuously observed. It was found that the settlement rate in the sheet-pile area lessened after surface construction, and the settlement was much smaller than that in the CFG-pile area, even though the initial settlement in the sheet-pile area was larger than that in the CFG-pile area before surface construction. The results suggest that the sheet pile has a significant effect on total and differential settlement control in extension construction. The insights in differential settlement indicate that the sheet pile could improve the subgrade bearing capacity and strengthen the stability of the embankment. Sheet piles could be one of the favorable ground-improvement methods to treat the settlement in highway extension constructions when the construction time and deformation are strictly restricted. (C) 2017 American Society of Civil Engineers.