Direct relaxation method to calculate stresses induced by gravel particles in a geomembrane

A new method, direct stress relaxation, was developed, verified and applied to calculate local geomembrane stress from local strain induced by gravel particles. The method utilizes the fading memory concept whereby the deformation path is taken to have a minor effect on stress if strains remain constant for some time before calculating stress. The method requires a geomembrane time-dependent material model, test time and final local strain to calculate stress. The method was tested against, and was in good agreement with, stresses from finite element models simulating physical tests. The new method was applied to analyse the deformed shape of a geomembrane from a physical test with coarse gravel above a geomembrane to examine new insights into local stresses gained from protection layer testing. Local strains were deduced from the deformed shape using thin plate theory and strains were converted to local stress by the direct stress relaxation method. The local stress results showed that different major tensile strain can develop under different major and minor local stresses. The new direct stress relaxation method now provides the ability to calculate local stress in addition to just strain, which may be used to unlock new insights into local stress rupture.