A wave flume experiment for studying erosion mechanism of revetments using geotextiles

摘要

Unfavorable erosion to a revetment can affect the stability of the bank and may jeopardize the safety of adjacent structures, thus improvement work is needed to increase the stability of the revetment as well as reducing the possibility of failure. The use of geotextiles as a protection material for banks is not only environmentally friendly, but also stable in the long run. However, improper design of geotextiles may cause considerable loss of soil, which might result in failure. The actual flow behavior in revetments using geotextiles is rather complicated and can be categorized into three zones, namely, the uni-direc-tional flow zone, the cyclic flow zone, and the tangential flow zone. In this study, a wave flume experiment was performed on model revetments using two kinds of geotextiles as the filter material to prevent erosion induced by cyclic flows. Soil migration behaviors were monitored. Furthermore, two kinds of cover blocks, riprap and concrete blocks, were carefully placed on the revetments in order to avoid puncture and abrasion of geotextiles during construction of revetments. The main purpose of this study is to elucidate the erosion control and filtration performance of soil-geotextile filtration systems under wave action. Two nonwoven needle punched geotextiles were tested. The geotextiles both have the same characteristic opening size, but have a different number of constrictions and different structures. One is a thin double-layer nonwoven material consisting of continuous filaments and the other is a thick one-layer nonwoven material consisting of short fibers.rnThe test result reveals that two different erosion mechanisms occur during wave action. The cyclic wave loadings triggered higher excess pore-water pressure in the upper part of the model and resulted in soil collapse. The geotextile with a higher number of constrictions produced more serious collapse than that with a lower one. At the middle part of the revetments, soil was eroded by the up-and-down drag force of the flow along the bank. In this zone, the thick geotextile displayed better performance in retarding the drag force on the soil surface. In addition, the opening size and thickness of the geotextile as well as the coverage condition provided by the geotextile were the key factors controlling soil erosion.