Particle breakage has a significant impact on the mechanical properties of soils and has drawn continuous concerns among researchers. This study aims to deepen the current understanding on the particle breakage phenomenon through insights of high frequency acoustic emission (AE) signals. Two series of physical model pile tests were performed with AE instrumentation, using two different materials: silica sand and coral sand. The AE signals were digitalized continuously throughout the tests with a sampling interval of 0.5 μs (2 Mps), which enabled the signals with a maximum frequency of 1 MHz to be captured, and the AE signals with a frequency higher than 100 kHz were interpreted to be associated with particle breakage mechanism. Results show that the high frequency AE (i.e., particle breakage) occurred throughout the tests. An initial period of rapid rising and a following period of relatively stable high frequency AE signals were observed in all tests. Based on AE characteristics, the extent of particle breakage was found to be related to the material property, the pile penetration depth, and the ground density. In general, silica sand was found to be more emissive, although coral sand was more prone to break, and the dense ground was more emissive and more prone to break than the loose ground. In conclusion, the asymptotic evolving trend is suggested for simplified estimation of particle breakage during the pile penetration process.

Geotextile filters have gained extensive applications in geotechnical and geoenvironmental drainage systems. Despite of the abundant research about geotextiles filtering coarse-grained soils, there is little experimental study on the performance of geotextiles filtering fine-grained soils. Since clogging and blinding of geotextiles are more likely to occur in clayey soils, a complex filtration performance of the filters is expected, posing great challenges to the long-term durability of the filtration system. In this research, long-term permeability tests were conducted on silty clay filtrated by three types of nonwoven needle-punched geotextiles. Comprehensive results regarding the permeability evolution, soil retention and clogging behavior were obtained. Interior clogging behavior of the geotextile was checked after the tests by means of scanning electron microscopy. Significant reduction around two orders of magnitude from 10⁻⁸ m/s to 10⁻¹⁰ m/s was observed in the permeability coefficient of the silty clay-geotextile system after 90 days of seepage flow. The influence of filtration opening size of the geotextile was obviously noticed in the initial permeation process, while the thickness played an increasingly important role at the later stage. Geotextile with the larger thickness and smaller filtration opening size had more soil retention and poorer filtration performance. In addition, a theoretical equation relating permeability coefficient and filtration opening size of nonwoven geotextile under clogged condition was proposed.

To avoid serious clogging and loss of drainage capacity, which puts the underground structure at risk of anti-floating failure, the buried drainage filter must be equipped with a nonwoven geotextile layer. In this scenario, nonwoven geotextiles are subjected to normal compressive stress, which can cause changes in geotextile porosity and structure, affecting the filtration behavior of the geotextile filter. In this paper, in order to evaluate the filtration compatibility of the soil–geotextile system, gradient ratio (GR) tests were performed under a hydraulic gradient of 1.0 using a specially designed gradient ratio filtration device capable of applying normal stress. In total four nonwoven geotextiles and two types of soil were used. The results of the gradient ratio filtration tests were discussed in terms of GR values, the permeability of the soil–geotextile system, and the amount of fines retained in geotextiles. It was shown that under a larger normal compressive stress, the GR value would also increase, while the permeability coefficient of the soil–geotextile system decreased. The filtration responses to various soil–geotextile combinations differed under normal compressive stress. A thick nonwoven geotextile with a small filtration opening size exhibited poor filtration performance while benefiting soil retention. Fines retention was influenced by geotextile thickness, soil type, and normal compressive stress magnitude. In addition, for nonwoven geotextiles filter fine-grained soil under normal compressive stress, the test results indicated that anticlogging design criteria should be improved.