Large-Scale Shaking Table Test Data Analysis And The Dynamic Response Law Of Steep Stratified Slope

The response law of slopes under dynamic loading is the key for analysis of slopedynamic instability mechanism. The ‘5.12’ Wenchuan earthquake in2008caused tensof thousands of secondary geological hazards, the loss is huge. Geological hazardssurvey after the earthquake shows that Secondary geological hazards caused by theearthquake have a certain relationship with the dynamic characteristics and dynamicresponse rule of slope. This article uses the massive earthquakes secondary hazardstriggered by "5.12" earthquake as the background, aims to study the dynamiccharacteristics and dynamic response rule of steep layered slope. Via the researchacquire the following results:1) In the basis of comprehensive analysis the characteristic of dynamicdeformation and damage of slope induced by5.12earthquake and the main influencefactors of the characteristics of dynamic response, a large-scale shaking table model testof slope with the scale of1:100was designed and performed. According the concernmatter of slope dynamic test and the parameters of the equipment, the similar relation ofexperiment model is deduced, then determine the test model size parameters; bufferlayer laid in the model box and sensors placed in the middle will reduce the boundaryeffect of model box; two different forms of dynamic loading was adopted includeseismic wave and sine waves, and change the vibration parameters of dynamic loads toset up dynamic loading method.2) The signals data collected from shaking table test due to the interference ofnoise and instrument defects contain many harmful composition. Firstly, in order toeliminate the error reasonably, preprocess the original signal data; then conductcorrelation analysis, Fourier transform, classic spectral estimation and transfer functioncalculation to the data which is well dealt to obtain the results needed by follow-up study analysis.3) Using transfer function to identify the dynamic characteristic parameters ofslope, by effect of lithology and slope body structure, the acceleration transfer functioncurve of each slope surface is different. The first natural vibration frequency is obvious,and the difference of first vibration frequency between each measured point is small.After several times of dynamic load, the second order has been strengthened. Vibrationfrequency decrease gradually undulate, and with the amplitude of load increases,vibration frequency reduction range increases, the change of damping ratio of eachslope is different. The dynamic characteristics of the slope are affected by the amplitudeof dynamic loads, previous shake history and the lithology and body structure of slope.4) The PGA amplification coefficient is used to study dynamic accelerationresponse rule of slope. The horizontal and vertical acceleration dynamic response rulesof different slope surface is different. Upward along the slope surface, the horizontaland vertical PGA amplification coefficient is rising. Under the effect of seismic wave,PGA amplification coefficient curve is more undulate, the dynamic response is stronger.The PGA amplification coefficient of the slope surface changes rhythmic. Themaximum of vertical PGA amplification coefficient is less than the maximum ofhorizontal PGA amplification coefficient. PGA amplification coefficient in the verticaldirection of the slope body increases in linear. Along horizontal direction of the slopebody, from the surface to internal, the PGA amplification coefficient decrease, andchanges rhythmic. The effect of amplitude of dynamic loading on the slope dynamicresponse distribution regular is little.5) Seismic wave propagation in slope body, the response acceleration time-historyis changed compared to the input. The vertical incident SV waves occur reflection andrefraction in medium; generate new types of reflection and refraction P wave. Spectrumcomposition of seismic wave would change, the component near slope vibrationfrequency is amplified and other composition is reduced. Along with the slope dynamicload increased, the seismic wave energy can only be strengthened in the lower,narrower frequency range.6) Based on the shaking test of slope model, FLAC3D numerical simulation isadopted; use sine wave as dynamic loading, draw PGA amplification coefficient isolineof slope under different amplitude, frequency of dynamic loading and lithology.Through the analysis can obtain dynamic response law as elevation amplification, freeface amplification and rhythm change of PGA amplification coefficient, etc. At thesame time find the influence of amplitude to the slope dynamic response distribution is small, and frequency and lithology of slope have significant influence on the dynamicresponse distribution.