Large scale direct shear tests of soil/PET-yarn geogrid interfaces: Fid-Bau Portal

Large scale direct shear tests of soil/PET-yarn geogrid interfaces

Liu, Chia-Nan / Ho, Yu-Hsien / Huang, Jian-Wen

The interface shear strength of soil against geosynthetic is of great interest. This study conducts a series of large scale direct shear tests to investigate the interface shear strength of different soils (sand, gravel, and latente) against PET-yarn geogrids of various tensile strengths, percent open area, and aperture patterns. First, the appropriateness of different set-ups of a lower shearing box is examined. It reveals that a lower box which is filled with the test soil and is of the same size as the upper box is more suitable for testing the soil/geogrid interface. The test results show that the soil/PET-yarn geotextile interface has significantly lower shear strength than soil strength. The ratio of shear strength soil/PET-yarn geotextile interface to internal shear strength of soil is about 0.7-0.8 for Ottawa sand and for latente, and it is about 0.85-0.95 for gravel. On the other hand, the soil/geogrid interface has higher shear strength. The ratio of shear strength soil/PET-yarn geogrid interface to internal shear strength of soil is about 0.9-1.05. The interface shear test results of PET-yarn geogrid against different soils are compared with the test results predicted by a classical model for analyzing the applicability of the classical model. Further, a simple model is proposed herein to estimate the bearing resistance provided by the transverse ribs of geogrid. It shows this component to be about 0-15% when PET-yarn geogrid is against Ottawa sand or laterite, while it is smaller when the PET-yarn geogrid is against gravel.