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A laboratory investigation was conducted to evaluate the applicability of five preparation techniques of fly ash/geotextile specimens for the gradient ratio (GR) test (ASTM D 5101-90). These techniques included the current ASTM method, a modified ASTM method, a vibro-prep technique, a dry preparation, and slurry method. Using the ASTM method for preparation, measured specific discharge and GR across the fly ash-geotextile systems were 8.0×10-4 cm/sec and 1.25, respectively. However, during the placement of the fly ash in the permeameter some intrusion of the particles into the geotextile openings took place. A technique for placing fly ash in the permeameter was modified after ASTM D5101. Using this modified method, the specific discharge and GR were measured to be 6.8x10-4 cm/sec and 0.80, respectively. The specimens prepared using the slurry method exhibited a relatively stable behavior. The specific discharge had an average value of 2.5×10-4 cm/sec after 600 hours of testing. The GR decreased from 1.52 to 1.37 during this period. The extent of piping under different testing conditions was quantified in this investigation. The specimens prepared using dry method exhibited an unsteady behavior and piping was observed to be dominant. Although piping of fine particles through the geotextile system was less than the suggested limit of 0.25 g/cm2 for soils, it is proposed that in the case of fly ash specimens with geotextile, stable systems should be categorized as those with piping rate less than 0.03 g/cm2.
filtration, fly ash, geotextiles, gradient ratio, laboratory, piping, sampling, specific discharge
Assistant Professor, West Virginia University, Morgantown, WV
Graduate Research Assistant, West Virginia University, Morgantown, WV