Dynamic Response Of Embankment Under Seismc Excitations

The primary seismic hazard investigation of Wenchuang earthquake shows the highway subgrades of meizoseismal areas are heavily damaged. The main destructional forms include the lateral deformation of the embankment, the vertical sinkage, the tension craking in vertical and horizontal direction, subgrade sliding failure, the subgrade separating, the inclining and damage of the shoulder retaining wall. The slope unstability by earthquakes can cause devastating damage to the lifeline and hinder the the rescue work which will greatly affect the earthquake reconstuction. The smoothness of transportation passages in highly seismic regions is the emphasis to be considered. Studies on seismic hazard control techniques of highway slopes are very necessary based on the subgrades and slope engineering of mountainous roads in view of the construction of railways and roads in highly seismic regions, so that some reference can be worked out for the future earthquake resistant design of subgrade engineering.The research contents of the thesis are as follows:1.comparing slope model with layered soil model experiments by shaking table, also reinforced layered soil model with layered soil model experiments..The influence of slope shapes and reinforcement measures on the transfer of earthquake wave is discussed. It is found that compared with layered soil, the amplitude magnification coefficient of seismic acceleration will increase by 30% in slope with free face; It can be seen that the reinforcement measures can greatly weaken the amplification effect of the soil to the earthquake wave.compared with layered soil, the amplitude magnification coefficient of seismic acceleration in reinforced layered soil can be reduced by 20%.2.The conclusion is drawn that the part from the upper middle to the shoulder of the slope is the easiest to be damaged and become unstable which is the key point to be considered based on discussions on the dynamic properties of the slope models subjecting to the earthquake. The self-vibrating frequency of the soil can be reduced by the soil internal damage and more closer to the predominant frequency which may enhance the amplification of the soil to the earthquake wave with the increase of the vibration times and amplitudes of the earthquake.As a result, loss assessments of the geotechnical engineering even that are not seriously damaged in appearance should be done and decide whether to take strengthening measures or not.3.The acceleration responses and its mechanism, displacement responses and the influence of the embankment on the frequency spectrum of earthquake wave of embankments with heights of 10m to 40m in regions of different earthquake intensities are studied based on the elastic-plastic theory of FLAC3D. There are three different forms of the maximum horizontal acceleration amplification coefficients of embankments with different heights:the coefficient increases monotonically as the embankment height increases(when the embankment height is less than 10m), the coefficient increases→reduces→increases as the embankment height increases (when the embankment height is more than 20m) and the transitional form between the two mentioned above(when the embankment height is more than 10m and less than 20m). The formation mechanisms of the three different forms are therefore discussed in view of the reflection superposition of the earthquake wave and the damping effect of the soil to the earthquake wave. It is found that the embankment itself can obviously absorb the high frequency component of the earthquake wave(more than 10HZ) except the low frequency component(less than 10HZ). A conclusion reaches that the embankment engineering is less sensitive to the hypocenter distance(the earthquake intensity is usually in reverse proportional to the hypocenter distance) than other engineerings that are sensitive to the high frequency component of the earthquake wave.4. The embankment settlements of shaking table tests under earthquake and the influence of the earthquake intensity and the slope shapes on the embankment settlements are both discussed. The subgrade settlement is directly related to the earthquake intensity and the settlement becomes obviously large when earthquake intensity reaches a certain value while the settlement under the earthquake of lesser magnitude is very little. In most cases, the settlement of the embankment model with free surfaces is more than that of the subgrade model. The settlement of embankment models under earthquake is mainly composed of the soil compression deformation and the horizontal deformation while the settlement of subgrade models is mainly the soil compression deformation. The experimental data show that the final settlement of the embankment is 12.4% more than that of the subgrade. The conclusion comes out that the settlement of embankments is mainly the soil compression deformation caused by the earthquake before the embankment collapses.