Study On The Seismic Amplification Effect On Site With Ground Fissure

Fen-Wei basin is the most serious area of ground fissure formation and disasters in Chinaand world. A great deal of research on ground fissure has been completed and madesubstantial contributions to scientific research and engineering, such as distributionregularities、active characteristics、formation mechanism and precautions. However, there isan absence aspect important to ground fissure research: the ground fissure site earthquakeamplification effect, about which there is little research. Located in Fen-Wei basin whereNeotectonics are strenuous, earthquakes have occurred many times in history and more futureseismic hazard would appear, Xi’an city is a significant study area with much practicalengineering value for ground fissure site amplification effect research basis on the intensivedistributing ground fissures.This essay presents the research on Xi’an ground fissures combining the platformvibrator model tests and numerical analysis to study the characteristics of ground fissure siteearthquake amplification effect. Research has focused on two aspects: the dynamic responsesof ground fissure under earthquake and the influence on site seismic oscillation parametersdue to the existence of ground fissures (earthquake amplification effect). With the early fieldstudy, the research was carried out by laboratory soil properties experiments, theoreticalanalysis, numerical analysis and large-scale physical model tests.To establish the generalized structural model of ground fissures site section in Xi’an city,the related basic geologic information has been collected based on the learning of sectionalstructure and mechanics of ground fissures. Thus, we established the geological structuremodel to obtain the influencing parameters, such as construction of soil layers, relative offsetsbetween upper and lower soil layers, dip angle of ground fissures and depth of false rock basalsurface of soil earthquake response analysis.Consolidated and undrained triaxial tests(CU)on soil of ground fissure field have beenconducted to obtain the soil mechanics parameters for the analysis of influence of siteconditions, especially the soil dynamic properties and responses owing to ground fissure.After calculating the results of triaxial tests, the strength envelope characteristics and dynamic strength parameters of ground fissure field soil based on the Mohr-Coulomb strength criterionwith the dynamic stress strain curve and dynamic strength curve under different radial stress.Moreover, the dynamic shear modulus and damping ratio variation of ground fissure field soilwere fitted to establish the equivalent visco elastic dynamics constitutive model visco elasticdynamics of ground fissure field soil.The element finite software FLAC3D was adopted to analysis the ground fissure siteearthquake amplification effect under earthquake. From the research we can concluded thatthe horizontal layers site and ground fissures field with and without diastrophism all showedamplification effect. And the upper and lower soil layers effect is obvious. The peakacceleration of upper soil layer is higher than the lower and the peak acceleration graduallyincreases as the distance of ground fissures lengthen.The earthquake dynamic platform vibrator model tests of ground fissures site wereconducted in this essay firstly. Based on similarity theory, gravity distortion model with singleground fissure platform vibrator were built. The ground fissures site earthquake responsesdistribution characteristics and effects (stress, strain and acceleration) were obtained by themodel tests. Thus the distribution characteristics of round fissure site earthquake amplificationeffect was calculated to reveal the dynamic responses characteristics and the influences ofground fissures.This study has important theoretical and practical significance for earthquake safety andrationality of urban construction land planning and ground fissures seismic site engineeringfacilities to deepen and expand the field of study of ground fissures in Xi’an city. Meanwhile,the results of the study were also expected to complement the existing norms, and the groundfissure site will be fortified more safely and reasonably.