A Study on Geotextile—Sand Interface Behavior Based on Direct Shear and Triaxial Compression Tests

Abstract

The effect of shear box size, geotextile type and properties and sand grain shape and size on the sand–geotextile interaction was investigated experimentally by conducting interface tests with conventional (100 mm) and large-scale (300 mm) direct shear boxes. Triaxial compression tests were also conducted on reinforced sand samples in order to evaluate the effectiveness of a methodology developed for obtaining interface friction coefficient values. Four uniform sands, one with subangular grains and three with rounded grains of different sizes were tested in dry and dense condition. Seven nonwoven polypropylene geotextiles of various types and properties and seven woven geotextiles with or without apertures were used in the tests. The conventional shear box is satisfactory for testing materials like those used in the present investigation because it gave comparable interface friction coefficient values to those obtained by the large-scale shear box. The sand–geotextile interaction behavior depends on the surface characteristics of the geotextiles and the interlocking of sand grains in geotextile apertures. The rounded shape and decrease in size of sand grains more effectively mobilize the soil–geotextile interface friction. The results of triaxial compression tests are in quantitative and qualitative agreement with the results of direct shear tests, for geotextiles without apertures. The friction efficiency for geotextiles with apertures obtained from triaxial compression tests attains a maximum value for an aperture ratio (aperture size of geotextile / mean grain size of sand) value approximately equal to 1.9, in agreement with the results of other studies.