The residual strength of geosynthetic reinforcement subjected to accelerated creep testing and simulated seismic events

Abstract

All geosynthetic materials used as soil reinforcements creep and it is necessary to obtain data on their creep behaviour before they can be used. During an earthquake the structure is subjected to additional loads, as may be the case with mining subsidence, blast loading or the application of abnormal loads, which may influence the creep characteristics of the reinforcement. The stepped isothermal method (SIM) is a recently developed procedure that is used to predict the long-term creep behaviour of geosynthetics from short-term tests. These tests can typically be performed in one day and use a single specimen, loaded continuously whilst being exposed to a sequence of timed isothermal events of increasing temperature. The development of the SIM Test provides an opportunity to study the effect of simulated seismic events or the influence of other additional loads, occurring at different intervals of the life of the structure, on the long-term strength of geosynthetic reinforcement. This is the subject of the paper. Five simulated seismic SIM Tests were performed, one with a simulated seismic event in each of the 26, 40, and 82 °C temperature steps, with two tests carried out with during the 54 °C step. The reason for varying the time of application of the simulated seismic load was to study the effect of the timing of real life earthquakes. This procedure facilitated the fulfilment of the first primary aim of the research, to assess the SIM as a device for investigating the effect of simulated seismic events on the creep mechanism of geosynthetic reinforcement. With respect to this, the research has shown that for lower temperatures, the SIM procedure can produce satisfactory results. However, at temperatures of 54 °C and above, the SIM procedure described proved unsuccessful for the simulation of seismic events. The second aim was to assess the residual strength of geosynthetic reinforcement subjected to seismic episodes. From the successful simulated seismic SIM Tests, it was found that the residual strengths of the material, after exposure to a seismic loading equivalent to 80% of the ultimate tensile strength of the reinforcement were the same as that of a virgin specimen. It is thought that the unsuccessful seismic SIM Tests illustrate a deficiency on the part of the test, rather than the geosynthetic material being unable to sustain seismic loading later in the design life. This was confirmed by a conventional creep test specimen sustaining a seismic loading at the end of its design life, and retaining its full tensile strength.