| Summary: | 碩士 === 國立宜蘭大學 === 土木工程學系碩士班 === 105 === Earthquakes bring damages to slopes and affect their safety. Therefore, geosynthetic reinforced soil retaining structures (GRSRS) are used commonly in geotechnical engineering to strengthen slopes. The features of GRSRS contain easy construction, short project duration, and high resistance to stress and earthquake. Consequently, conventional gravity retaining structures are thus being gradually replaced by GRSRS. In order to understand the seismic response of GRSRS influenced by earthquake, this study uses actual recorded seismic data from an earthquake monitoring system for the GRSRS built in FoGuang University. The seismic response simulation is then followed by employing the finite element program PLAXIS dynamic analysis. The predicted results of the seismic analysis show that the maximum acceleration increases with the elevation of the slope during the earthquake. The predicted results provide the ratios of the maximum accelerations for the top layer and middle layer to the bottom layer as 2.0 and 1.4, which is only about 4% difference between the monitored data and simulation predictions.
This study attempts to explore the effects of earthquakes on GRSRS with the aid of dynamic numerical simulation. The boundary conditions and material damping are discussed comprehensively. This study implements the finite element program PLAXIS to simulate the seismic responses of the geosynthetic reinforced slope. Since the reflection of seismic input wave may affect the dynamic simulation, boundary conditions provided in PLAXIS must be able to simplify and ensure the calculation accuracy. Applicable boundary conditions for the geosynthetic reinforced slope may be retrieved using the free-field and viscous boundaries for the dynamic simulation analysis to enhance the accuracy. Furthermore, it is necessary to apply appropriate material damping for dynamic response analysis if one wants to analyze the loss of energy correctly in the soil mass. Otherwise, the whole geosynthetic reinforced slope system will continue to produce vibration. In the PLAXIS finite element program, the soil damping method is considered by Rayleigh Damping. Rayleigh damping makes the soil more realistic and the simulation results more accurate under seismic conditions.
The seismic monitored data of this study are the actual information and make the dynamic predicted results of the numerical simulation for geosynthetic reinforced slope practical. It is suggested to conduct the dynamic simulation process with free field boundary and 5.5% damping ratio in PLAXIS. Based on the predicted results obtained from the seismic simulation, it is found that the maximum acceleration on surface area of the geosynthetic reinforced slope is obviously enlarged with the elevation increasing during earthquake. However, inside the reinforced area as well as the inner part of soil layer, the seismic amplification behavior with height is significantly reduced.
|
|---|
