Abstract: Under load, the differential displacement of dam body/abutment at the peripheral joints of high geomembrane-faced rockfill dam (GFRD) causes the PVC geomembrane to be in a state of large deformation and tension. Indoor stress relaxation test was conducted on PVC geomembrane to investigate its mechanical properties under large deformation after differential displacement stabilizes. The change of tension at initial elongations of 50%, 80%, and 125% was monitored. According to analysis results of the test data, the stress relaxation law of PVC geomembrane was described respectively with generalized Maxwell and fractional order models. The advantages and disadvantages of the two models were compared and analyzed. Results suggest that the fractional order model can more accurately describe and predict the stress relaxation performance of PVC geomembrane in long-term uniaxial tensile deformation state at surrounding joints of GFRD. The accuracy was verified by using long-term stress relaxation test data. After stress relaxation, elongation at break of samples attenuates greatly. Engineering measures are recommended to ensure the safety of anti-seepage geomembrane structure during design and construction.

Key words: high GFRD, stress relaxation, PVC geomembrane, peripheral joints, Maxwell model, fractional order model, geomembrane structure design