The Filtration Mechanism and Micro-Observation of Soil-Geotextile Systems under Cyclic Flows

Abstract

Geotextile filters have been used frequently in revetments for protection of riverbanks, levees, seashores, etc. The filters may be subjected to different flow conditions such as unidirectional or cyclic flows. Besides, the period of flow may vary from short to long due to the fluctuation of water table caused by sea waves, boats, tidal activity, or periodic drawdown of water for irrigation purposes. Due to few literatures on cyclic flow studies, this paper presents the investigation on soil-geotextile filtration mechanisms under long-term cyclic flows using a self-developed apparatus. The soil samples are composed mainly of sand, with 0-20% fines content of silts and clays. The factors taken into account are overburden pressure and cyclic flow periods ranging from long to short, in order to simulate a range of waves. A stereomicroscope is utilized to observe the microstructure of the geotextile filter after testing. The results show that both the overburden pressure and the fine soil content play important roles in the filtration, soil boiling, and settlement behaviors of a soil-geotextile filtration system. Furthermore, the microscopic images of the geotextile show that soil clogging under cyclic flows is not so serious as that under unidirectional flows. Besides, a bridging network can be formed under long-term cyclic flows in the areas near the filter that are not supported by marbles.