Shear strength of HDPE geomembrane/geosynthetic clay liner interfaces

A study of interface shear strengths between smooth and textured high densi ty polyethylene (HDPE) geomembranes (GMs) and a woven/nonwoven needle-punch ed geosynthetic clay liner (GCL) is presented. Tests were performed using a large direct shear machine capable of measuring peak and large displacemen t (200 mm) shear strengths. The failure surface was located at the GM/GCL i nterface for all tests conducted, corresponding to a normal stress range of 1-486 kPa. Small positive pore pressures were measured for all interfaces at peak shear strength. Thus, the practice of preparing failure envelopes u sing total normal stress, instead of effective normal stress, appears to be conservative. Interface shear strengths for textured GMs placed against th e nonwoven side of the GCL were higher than those corresponding to the wove n side. By comparison, differences in peak shear strength for laminated and coextruded GM interfaces were relatively less. Limited tests showed that p eak and large displacement shear strengths were independent of displacement rate and dependent on the shear direction of the GM. The quantity of extru ded bentonite at the interfaces generally increased with normal stress and was less for nonwoven geotextile interfaces than for woven geotextile inter faces. Implications of the findings to the testing of GM/GCL interfaces and the characterization of GM/GCL interface shear strength are discussed.