| China is a mountainous and earthquake-prone country, and problems caused by seismic slope response are prominent. During the'May 12'Wenchuan earthquake in 2008, tens of thousands of secondary geological hazards were triggered in a mountain area, causing great loss. After the earthquake, most researchers oriented their work on source mechanism, hazard formation mechanism, or hazard risk management and assessment, however, research on seismic slope response was limited. Post-earthquake survey indicates that, dynamic slope deformation and failure mostly occurred in hard rocks, with the pronounced response in the special parts of valley slopes like crest and the transition part between two slope angles. Macroscopically qualititive knowledge of seismic slope response has reached a basic agreement at home and abroad. Due to the limited earthquake recordings, however, in addition to the complicated influence factors, it is to early to get a systematic understanding of the seismic slope response laws from the time and space angles, let alone guide the engineering practice. With gradually entering into the seismically active period on a world scale, study on seismic slope response is bound to have great significance in theory and practice.On the background of'May 12'Wenchuan earthquake, the present paper aims to explore the seismic slope response characteristics and laws to some extent by means of a physical model. The main work and results are as follows:(1) Simulating the typical rock structures of slopes in the Wenchuan earthquake region, two conception models with combinational structures of hard rock overlying soft rock and soft rock overlying hark rock were designed to perform the large scale shaking table test with a geometric scale of 1:100. Through a secquence of preparation work on determing similitude relations , sensor arrangement, input motions and a loading scheme, a set of design plan has been established applicable to the horizontal layered combinational slopes. (2) Throgh exicating models at the bottom with input waves of different types, vibrating directions and intensities, the macro deformation and failure characteristics of models havd been observed, meanwhile, the characteristics related with the input parameters have been analyzed. The failure mechanism shows that, the hard material overlying soft material model failed in a collapse, while the other one failed in a landslide with the'tension-shear'mechanical process.(3) A total of 101 loading conditions had been completed in this test. Through large amounts of accelerometers in the interior and on the surface of each model slope, about 6000 time history recordings in horizontal and vertical components had been obtained. Afterwords, the absolute peak acceleration (PGA) and its amplification relative to shaking table soleplate were calculated for each recording. By comparing these values, the dynamic response laws of two model slopes in horizontal and vertical components were analyzed, and the effect of input parameters on the response laws were also explored by the single factor analysis method.Results show well the nonlinear amplification effect along increasing elevations, and the differences in responses between two componts were also reflected obviousely. Futhermore, input waves having different spectrum features caused different response laws; excitation in a combination direction generated stronger response than in a single direction; when excitated in real waves, the response intensity in two components tended to decrease.(4) Finally, Fourior transformations are conducted on accerleration recordings. Then two Fourior spectrum ratios are calculated to explore the transfer features of models at different elevations for waves. The two ratios well indicate the foundamental frequencies of two models. Moreover, the spectrum ratios of horizontal components of the surface to the table soleplate (input motion) confirm the nonlinear seismic response of models in their upper parts as the input motion is intensified. |
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