Interpretation of Creep Properties of Geogrid Under Simulated Seismic Event Condition by SIM(Stepped Isothermal Method) Test
- Han-Yong Jeon (Inha University)
- Document ID
- International Society of Offshore and Polar Engineers
- The 28th International Ocean and Polar Engineering Conference, 10-15 June, Sapporo, Japan
- Publication Date
- Document Type
- Conference Paper
- 2018. International Society of Offshore and Polar Engineers
- simulated seismic event, SIM test, long-term creep behavior, creep, Geogrid
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- 9 since 2007
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Usually, the lifetimes of geogrid are assessed as the long-term creep behavior which causes shape deformation and collapse of the slopes and embankments. During an earthquake, the structure is subjected to additional loads, which may influence the creep characteristics of the reinforcement. The SIM (stepped isothermal method) 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. In this paper, two simulated seismic event related to SIM tests were performed, one with a simulated seismic event at 23°C step, the other tests carried out after 79°C step. Creep strain decreased after seismic event cause of recovery force, then strain increased again. After same conditions of seismic event in different times were applied, strain finally overlapped.
For assessing the long-term tensile deformation of geogrid, 10% creep strain has been used as critical value but, there is no basic theory or empirical data to 10% creep strain (Cho, Lee, Cazzuffi, Jeon 2006; Farrag, Shirazi, 1997;Farrag 1998). In real 10% is relatively big one that of allowable long-term strain in reinforced earth wall. Another criteria for creep related properties of geogrid, is creep rupture strength (Allen, 2005; Koo, Kim 2005). Creep rupture in geogrid shows brittle tendency because of rapid loading rate in test procedure. Besides each improper aspect, creep factors for long-term allowable strength from each criterion are different each other. Also these 2 characteristics never are able to explaining the long-term deformation of geogrid. So it is required that the replacement method to explain the long-term deformation (Jones, Clarke 2007). The isochronous creep curve was used to define the relation between creep strain and allowable strength. In the isochronous curve at given time, we can read the allowable strength at allowable creep strain. The allowable strain gets from specification by directors or manufacturers. The allowable creep strain can be various according to its facing batter, facing type and critical aspect. Otherwise, the required service lifetime of geogrid used for reinforcement of soil structure varies according to the sensitivity of the environmental conditions (Den Hoedt, 1986; Hsieh, Wu, Lin, Hsieh, 2000). This service lifetime implies that the functional engineering properties of the geogrid should remain within acceptable limits during the required service life. Usually, the lifetime of geogrid are assessed as the long-term creep behavior which causes shape deformation and collapse of the soil structure (Tatsuoka, Kongkitkul, 2007). In this study, the creep behavior of geogrid was evaluated by the stepped isothermal method (SIM). For the engineering design perspective, the creep reduction factor was determined from the creep rupture and limited strain. As an accelerated creep test, 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 soil structure, on the long-term strength of geogrid. Two simulated seismic event related to the SIM tests were performed, one with a simulated seismic event at 23°C step, the other tests carried out after 79°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. The second was to quantitatively calculate creep reduction factor considering seismic event and to reflect this in the design property.
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