An Evaluation of the Bubble Point Method for Determining Pore Size Distributions of Nonwoven Geotextiles

Abstract

Nonwoven geotextiles are commonly used in soil filtration applications. A geotextile filter must retain soil particles, while allowing permeability to water and being resistant to clogging. Geotextile filter performance is related to the pore sizes of the geotextile. Therefore, knowledge of the size of geotextile pores is necessary for filtration design. The most common method for evaluating geotextile pore size is the AOS test, which uses a single number that only reflects the larger pore sizes of the geotextile. Methods for measuring all of the pore sizes of a geotextile and determining the distribution of pore sizes have been studied in recent years. Among these methods is the capillary flow porometry method, known commonly in the geotextile field as the bubble point method or test, which has been standardized by ASTM International as method D6767. This thesis presents a study of the bubble point method and related observations by the author. Methods for quantifying geotextile pore structure are discussed, along with a detailed description of bubble point method theory and background. A review of the contact angle, an important parameter needed to calculate pore size, is presented. A detailed description of a bubble point testing apparatus developed at Auburn University is presented and the procedure used to conduct the bubble point test is discussed. An automated spreadsheet for reducing bubble point test data is described. The results of multiple bubble point tests performed on a nonwoven geotextile are presented along with various statistical analyses. The influence of three parameters used to calculate pore size (i.e., the contact angle, the capillary constant, and surface tension) are examined. Residual fluid is investigated as a source of error for pore size distributions determined using the bubble point method.