Date of Award

1-1-2017

Degree Name

Master of Science (MS)

Department

Civil and Environmental Engineering

Advisor(s)

Shobha K. Bhatia

Second Advisor

Ashok S. Sangani

Keywords

Capillary flow test, Dewatering, Dry sieving test, Filtration, Geotextiles, Soil retention

Subject Categories

Engineering

Abstract

For the last four decades, geotextiles have been used extensively for the purpose of separation, filtration, drainage and soil reinforcement. The basic criteria that impact the behavior of a geotextile filter are soil retention, permeability, and clogging potential. The ability of a geotextile filter to fulfill these requirements depends on the pore sizes and pore size distribution. There are numerous techniques to measure the pore sizes of a geotextile, but not all of them are widely accepted. In the USA, two standard methods of measuring the largest pore size of a geotextile have been accepted, the Dry sieving test (ASTM D4751) and the Capillary flow test (ASTM D6767). Despite of the several drawbacks of the dry sieving test, including trapping of glass beads inside the geotextiles and electrostatic effects, many filtration criteria are designed based on the apparent opening size (AOS, O95). On the other hand, the capillary flow test provides a complete pore size distribution along with the largest pore size (bubble point, O98) of a geotextile, but this method is not typically used in design.

The main objectives of this study are to: 1) perform calibration of the Capillary flow test device (Geo Pore Pro, GPP-1001A) to access the accuracy of the test; 2) establish correlations between bubble point (O98) and AOS (O95) for woven and non-woven geotextiles; and 3) evaluate the role of pore size distribution in the performance of geotextiles using 1-D filtration tests (Falling-head test) and Pressurized 2-D tests.

To achieve these objectives, more than 700 capillary flow tests were performed using Geo Pore Pro (GPP-1001A) manufactured by Porous Materials, Inc. 20 woven geotextiles, 29 non-woven, and 2 composite geotextiles were used in the study. From Capillary flow test, O10, O15, O50, O85, O90, O95 and O98 were measured. From the calibration test, it was found that the for some thin metallic plates and membranes Capillary flow test provides 16% - 23% larger pore size than the

actual pore size. To establish a correlation between Bubble point (O98) and AOS (O95), the outliers were removed and a good correlation (R2 = 78%) was established for all geotextiles. A decreasing trend of Bubble point (O98) was found with the increasing mass per unit area for both needle punched and heat bonded non-woven geotextiles. However, no such trend was found for woven geotextiles. 1-D filtration tests were performed with 3 different water contents (232.56%, 400% and 882.35%) and it was found that piping rate increases with the decreasing water content in slurry (232.56% - 882.35%) and degree of clogging decreases with the increasing pore sizes (both O50 andO98). In the Pressurized 2-D tests, since flocculated slurry was used, instead of soil retention and piping rate, flow rate was the main issue. Therefore, flow ratio (a ratio of radial flow and axial flow) was calculated for all geotextiles and it was found that needle punched non-woven geotextiles showed some decreasing trend of flow ratio with the increasing permeability of clean geotextiles.

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Open Access

Available for download on Friday, August 16, 2019

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Engineering Commons

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