Fiber Reinforced Sandy Slopes under Groundwater Return Flow

Abstract

The instability of earthen embankments caused by subsurface flow draining out of the banks has been a major concern. In an effort to prevent embankment failures, tension resisting synthetic fibers may be an effective additive to increase their mechanical properties such that drainage does not cause failure. In this study, triaxial compression tests measured the increase in peak deviatoric stress with increase in fiber content and length. In addition, laboratory lysimeter experiments (total of eight experiments) were conducted on sandy slopes reinforced with polypropylene (PP) fiber using two different fiber lengths (6 and 12mm) and gravimetric fiber contents (0.3 and 1.0%) under two different constant piezometric head boundary conditions (25 and 50cm) maintained in the water reservoir of the lysimeter. Fiber-reinforced sand was compacted in the lysimeter to obtain a 45 degrees slope with dimensions of 55cm height, 20cm width, and 100cm base length. The only experiment that experienced seepage erosion by particle mobilization under 25-cm water pressure head boundary condition was the sand slope reinforced with fiber length and content of 6mm and 0.3%, respectively. The increase in the water pressure head boundary condition to 50cm resulted in small-scale sapping of slopes reinforced with 0.3% fiber content, independent of the fiber length. For slopes reinforced with 1.0% fiber content, sapping did not occur, only erosion of sand particles caused by seepage was observed. A slope stability analysis reflected the favorable effect of fiber inclusion, as the increased effective cohesion increased the factor of safety of slopes.