Stduy On Response Law And Deformation Mechanism Of Talus Slope Under Eathequake Action

The western of China is located on the Eurasian plate, where tectonic activities are intense at the global activity time of the earthquake, eg. The earth has been in a seismically active period for the past few years, and frequent earthquakes have caused vast geologic hazards. The talus slopes widely distributed in the Qinghai-Tibet Plateau has endangered people living there because strong earthquakes break the stability of talus slopes. After the Wenchuan Earthquake, more studies are focusing on dynamic characteristics of the rock slope under earthquake action, while less are concerning the talus slope. Therefore, it’s very valuable to intensively study on the dynamic response and deformation mechanism of the talus slope under earthquake action.The talus slope in front of the left dam of Zippingpu hydraulic project is 17 km away from the seismic center of the Wenchuan Earthquake. The Long-term stability and deformation monitoring equipment was buried inside the talus slope to monitor the deformation throughout the comprehensive improvement and Wenchuan Earthquake, which resulted in valuable first-hand data. Taking the effect from the Wenchuan Earthquake to the talus slope in front of the dam for example, using on-site investigation and data analysis, this paper analyzed the regional geological background, engineering geological properties, pre-earthquake instability mode, and deformation before and after the earthquake of the talus slope. By analyzing the clinograph deformation-replacement and hole depth relation curve, this paper analyzed stability of the talus slope in front of the dam before and after the earthquake. By introducing mathematical statistics method, this paper carried out filtering processing and multiple regression analysis for the data monitored before and after the earthquake, and explored the law and characteristics of major factors and the time sequence model. Using the shaking table experiment and FLAC3 D numerical simulation, this paper studied the response of talus slope in front of the left dam under the Wenchuan Earthquake action. Major results and conclusions are as follows:(1) By a comparison of data changes monitored before and after the earthquake, this paper evaluated the stability of talus slope using correlation analysis, integrity index, destructive index, and fractal theory. The result suggests that displacement and deformation of the talus slope in front of the dam is consistent in the vectorial direction. After the Wenchuan Earthquake, the integrity of the talus slope in front of the dam decreased along with the decrease of elevation of monitoring points. At the same time, the Hurst index reflected the same decrease law.(2) According to the correlation analysis, the talus slope was disorderly arranged before the earthquake, and became orderly arranged after the earthquake. This paper analyzed major factors of the talus slope before and after the earthquake and built up the quantitative relation between the deformation displacement and major factors. The multiple regression analysis indicated that the Wenchuan Earthquake lightened the impact of the time effect and water level in the reservoir to the deformation and displacement, but enhanced the effect to amount of rainfall. Using the time series analysis, this paper built up a deformation time-distance ARIMA model for the talus slope in front of the dam before and after the earthquake.(3) By geological modeling talus slope, this paper performed simulation calculation of dynamic numerical under calculated fluid-structure interaction. The maximal and minimum principal stress monitoring points of the surface monitoring points are changing as an “E” shape along with the change of elevation, the PGA amplification factor is in an “S” shape, and increase of the displacement of the surface monitoring points presents a “small-big-small” trend along with increase of the elevation. In the vertical direction, the maximal and minimum principal stress monitoring points of the surface monitoring points present a non-linear decreasing relation along with the change of elevation; the PGA amplification factor increases obviously along with increase of the elevation; and the displacement of the monitoring points presents an increasing trend along with increase of the elevation. When there is water stored in the reservoir, the pore stress increases sharply on the sliding surface under earthquake action.(4) Using the shaking table experiment, on the basis of full comparison and selection of similar materials, scale, and measurement etc., this paper carried out shaking table experiments for three situations, i.e., half-reservoir, full-reservoir and empty-reservoir. The result disclosed dynamic response mechanisms for different types of seismic waves, the phenomenon of deformation and destruction for talus slope, and the evolution mechanism. Conclusions obtained from the experiment result include the following:(1)The talus slope has obvious free surface amplification effect and elevation amplification effect. The PGA amplification factor of the talus slope is obviously larger than that of the bed rock. The PGA amplification factors in different frequency spectrums are consistent, that is, Maoxian wave is the largest, followed by 15 Hz sine wave, 10 Hz sine wave and 5Hz sine wave. In the same horizontal level, the closer to slope, the more obvious the PGA amplification effect is, and the larger the enlargement range is.(2)The PGA amplification factors at each monitoring point reflects the response level of the talus slope under the earthquake action. The PGA amplification factors decrease when the shaking intensity increases, which indicates that the response level of the talus slope is decreasing gradually.(5) In the half-reservoir, full-reservoir and empty-reservoir situations, the deformation, destruction and evolution mechanisms are different. The empty-reservoir model is crack-shear damage mechanism, and the instability motion is of push type, while half-reservoir and full-reservoir models are plastic flow-tensile crack damage mechanism, and the instability motion is of pull type.(6) For the talus slope beside the reservoir with water, due to the excess pore water pressure and the inertial force caused by earthquake action, the pore water pressure increased at the moment of the earthquake, which resulted in an instant increase of deformation and the liquefaction degree of the talus slope. The talus slope soaked in water collapsed at first, followed by further landslide and destabilization failure. For the talus slope beside the reservoir without water, the granular space developed and accumulated due to the cyclic load from the earthquake wave, and the soft layer in the talus slope collapsed completely because of sudden shake, which resulted in landslides and collapses.