Comparison of strength and deformation of geomembranes at uniaxial and biaxial tension: Fid-Bau Portal

Comparison of strength and deformation of geomembranes at uniaxial and biaxial tension

Sainov, M. P.

Geomembrane used as a seepage control facility of an embankment dam operates in conditions of complicated stress state. They do not correspond to conditions of the standard methodology of uniaxial tensile tests. It may be also a case when a geomembrane is in conditions of biaxial tension. In order to estimate the effect of the type of stress state on strength and deformation of geomembranes we performed the tests of two types of geomembranes (made of PVC and HDPE). They were conducted according to «Burst test» pattern, when extension of the geomembrane specimen is reached due to pressure applied on its surface. The obtained results were compared with the results of experiments fulfilled by the other authors. First of all, there were compared the results of studies fulfilled in China. During these studies the geomembrane specimens were tested directly at biaxial tension («Biaxial test»). Comparison showed a good agreement of the results of geomembrane tests performed by the patterns «Burst test» and «Biaxial test». At biaxial tension the yield stress of HDPE geomembranes is approximately 16 МPа, and of those made of PVC it is approximately 6.5 МPа. It is, as a rule, 20÷40% more than at uniaxial tension. However, it should be taken into account that at biaxial tension the geomembrane modulus of linear deformation also increases. At the initial section of tensioning the geomembrane modulus of linear deformation at biaxial tension is approximately 3 times as much as during the standard methodology of uniaxial tensile tests. Thus, the type of stress state has variable effect on strength and deformation of geomembranes; its effect may be ambiguous. Therefore, at analysis of spatial stress-strain state of a dam with a geomembrane it is not correct to use the results of standard uniaxial tensile tests.