Erosion stability of punctured geotextile filters subjected to cyclic wave loadings—a laboratory study

Abstract

The alternating flow through the geotextile filter creates a cyclic flow regime quite unlike the uni-directional flow that has been extensively studied. Most of the filter design criteria and codes are based on tests from uni-directional flow conditions, which may not truly reflect the cyclic flow of in situ tidal conditions. A new laboratory apparatus has been used to investigate the influence of the hydraulic conditions on the behavior of soil-geotextile interaction and the stability of the coastal revetment system. This apparatus is capable of simulating cyclic flow conditions normal to the soil-geotextile interface. In this study, a series of tests were conducted with geotextile specimens with pre-cut L-shaped holes of different size, to simulate the punctured holes on the geotextile filter caused by installation damage. Various overburden pressures (0, 25, 110 kPa) and different periods of wave (2, 5, 7, 10 s) and different geotextiles, nonwoven (NW1, NW2) and woven (W1), were employed in this tests series. Results show that a given geotextile, with holes up to a certain critical size, can still perform satisfactorily if soil arching can be fully developed. It will be stable under certain cyclic wave load of a specific wave period. The geotextile filter with punctured holes can form a stable filter, and the presence of punctured holes in the geotextile filter does not imply failure of the revetment system if they are smaller than the critical size. The critical size of the pre-cut hole, before the filtration function was impaired, was found to be a function of the geotextile properties, wave period, cycles of wave load applied on to the soil for a given soil type under retention.