The influence of bentonite extrusion on shear strength of GCL/geomembrane interface

A series of shear strength tests of needle-punched geosynthetic clay liner (GCL)/textured geomembrane interface were conducted at normal stresses ranging from 10 to 400 kPa. The geomembrane was in contact with the woven geotextile of GCL. One half of the tests were carried out on prehydrated GCL samples at low normal stress (about 1 kPa), whereas the other half on non-prehydrated samples. The prehydrated samples exposed during shearing to normal stresses of 100 kPa and above demonstrated bentonite extrusion to the area in contact with geomembrane, which was visible to the naked eye. The bentonite extruded was quantified by introducing an extrusion coefficient. The quantity of the bentonite extruded increased with an increase in normal stress, and lubrication of the contact area with bentonite resulted in reduced shear strength. Finally, the testing showed that for tests carried out on prehydrated samples at lower shear rates, lower contact shear strengths were obtained and more extensive bentonite extrusion to the contact area was observed.