Rate-dependent load-strain behaviour of geogrid arranged in sand under plane strain compression

A number of previous experimental studies showed that polymer geogrid reinforcement as well as sand exhibit significantly rate-dependent behaviour. The viscous properties of polymer geogrids and Toyoura sand were independently evaluated by changing stepwise the strain rate as well as performing sustained loading and load/stress relaxation tests during otherwise monotonic loading in, respectively, tensile loading tests and drained plane strain compression (PSC) tests. The viscous properties of the two types of material were separately formulated in the same framework of non-linear three-component rheology model. The viscous response of geogrid-reinforced sand in PSC is significant, controlled by viscous properties of geogrid and sand. Local strain distributions in the reinforced sand specimen were evaluated by photogrametric analysis and used to determine the time history of the tensile strain in the geogrid. The time history of tensile load activated in the geogrid during sustained loading of reinforced sand specimen was deduced by analysing the measured time history of geogrid strain by the non-linear three-component model. It was found that the tensile load in the geogrid reinforcement arranged in a sand specimen subjected to fixed boundary loads could decrease with time. In that case, the possibility of creep rupture of geogrid is very low.