LOAD-STRAIN-DISPLACEMENT RESPONSE OF GEOSYNTHETICS IN MONOTONIC AND CYCLIC PULLOUT

Mobilization of the pullout resistance of geosynthetics in monotonic a nd cyclic modes is described from both displacement- and load-controll ed tests performed at normal stresses in the range 4-17 kPa. The tests were performed on three geogrids and two geomembranes embedded nearly 1.0 m in a uniformly graded sand. Results for load-controlled tests a t a constant rate of 0.25 kN/(m.min(-1)), followed by several series o f load cycles of increasing amplitude, are compared with displacement- controlled tests at a constant rate of 0.5 mm/min. In general the geog rids behave as an equivalent textured sheet. Pullout behaviour, and es pecially the incremental displacement mobilized at cyclic loads close to the maximum resistance, is found to vary with type of geogrid. In o nly one case was cyclic pullout resistance of a grid found to exceed t he monotonic resistance. A comparison of the cyclic and monotonic resp onse yields a constant ratio of pullout resistance at large displaceme nt, but one which is not unique to a particular specimen. Cyclic strai ns of decreasing amplitude are mobilized along a test specimen, with m ost of the necessary relative displacement occurring close to the load ed end and the embedded end showing little response.