| The earthquake as a natural disaster suddenly happens which may do great harm to human life and property and may cause many geological disasters and therefore the slope support related to earthquakes is brought out because of many mountains and frequent earthquakes in our country. The stability of supporting structures of the highway engineering under earthquake is of great significance with more roads being built in mountain areas or even in highly seismic regions and fractured zones if necessary when the strategy of developing the West is implemented.The influence of the earthquake on the slope (sliding slope) is a complicated dynamic process. And the stability analysis is based on the pseudo-static method in the existing standard aseismatic design of road engineering (JTJ004-89) which can't assess the earthquake trend quantificationally. The dynamic analysis theory based on earthquake responses is the trend of this subject. There may be a transition between the static and dynamic methods which needs further research. Combined with the Dujiangyan-Wenchuan road in highly seismic regions of Wenchuan earthquake, this thesis analyzes the natural vibration frequencies of shoulder supportings of gravity retaining walls with the finite element software ANSYS.The contrastive study on seismic performances of four types of gravity retaining walls is conducted by the software FLAC based on the numerical analysis method of dynamic finite difference. There are three failure modes of the retaining wall:the wall is declining outwards along the construction joints and dislocated; the wall swells out and cracks in its longitudinal direction. Four types of gravity retaining walls namely weighing gravity mode and retaining walls with wall back inclining upwards, wall back inclining downwards and straight wall back, are designed by lizheng software whose supporting effects are the same under static loads and all are stable in earthquakes with the magnitude of 7,8 and 9. Their dynamic responses in earthquakes with different magnitudes are compared and analyzed by FLAC to decide which type is the best in its seismic effect. The research makes sense both in theories and in practice by designers to select the right types of retaining walls with better seismic performance when considering the earthquake reaction.The research contents and findings are as follows: 1,The first three frequencies and their corresponding vibration shapes are derived based on the modal analysis of 20 cutting gravity retaining walls on Dujiangyan-Wenchuan road by ANSYS. It is found that the first three failure vibration shapes are consistent with three failure modes of retaining walls namely sliding failure, overturning failure and dislocation in transverse direction. Then the failure frequency of retaining walls can be forecast and optimized to avoid the low frequency since the earthquake frequency is low.2,The basic law of dynamic properties is that the natural vibration frequency of the model reduces and the damping ratio increases with the increase of the retaining wall height. The natural vibration frequency is sensitive as a factor influencing the model that can fully disclose the change of the model's microscopic features.3,The gravity retaining walls are mostly used walls that can be classified into four types according to their wall back forms. The seismic performance of the gravity retaining walls, usually not taken into consideration by designers, is analyzed by FLAC 3D. Five aspects after the earthquake, the shear strain increment (the plastic strain zone), the X displacements of the wall top and bottom (perpendicular to the retaining wall direction), the residual stress on the top of the wall (soil stress) and the maximum acceleration on the back of the wall, are compared and analyzed and the comparation results agree well with results derived from Lizheng software which indicates that the seismic performance of the retaining wall with the wall back inclining downwards is the best, those of the weighing retaining wall, the retaining wall with a straight wall back and retaining wall with the wall back inclining upwards comes second, third and the last. As a result, the retaining wall with the wall back inclining downwards is advised to be selected as a priority in retaining wall designs in earthquake areas.4,The seismic performance of the retaining wall changes obviously and the comparative factors differ more as the increase of the earthquake magnitude. |
