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Soil/geotextile filtration behavior under dynamic conditions of cyclic flow and vibration Hameiri, Avikam

Abstract

An evaluation of soil internal stability and soil/geotextile filtration compatibility for different types of loading conditions is important for the proper use and extension of empirically based design procedures. Static conditions like those found in earth dams and vertical drains, are characterized by steady flow. Dynamic conditions can, however, be present in some situations, for example under revetments due to hydraulic disturbance and under railways due to physical mechanical disturbance. To better understand the filtration performance of nonwoven geotextiles under dynamic conditions, this experimental study was undertaken. An existing permeation (Gradient Ratio) device was modified to perform tests with vibration. In addition, a new automatic cyclic Gradient Ratio device with a computerized control system was designed and commissioned to perform tests with cyclic flow. Forty-one combinations of four nonwoven geotextiles with narrow, wide, or gap-graded model soils were examined in testing. The reconstituted model soils were composed of glass bead fractions in the range between coarse silt and fine sand. The test program was conducted under a hydraulic gradient of four, and involved multi-stage tests. In the vibration tests, an initial stage of unidirectional flow was imposed and followed by a dynamic stage that involved physical disturbance using controlled energy blows at a frequency of 3 FIz. In cyclic flow tests the initial unidirectional flow was followed by reversing the direction of flow at frequencies of 0.2 Hz and 0.02 Hz, under both confined (av=25 kPa) and unconfined (ov=0 kPa) conditions. The results of each test were interpreted from the measurements of flow rate, water head distribution along the sample length, visual observations both during and after testing, and the weight and gradation of the particles that passed through the geotextile. Reflecting on existing design criteria and previous research work, the analysis and conclusions address issues of internal stability and soil geotextile compatibility under both static and dynamic conditions.

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