Study On The Characteristics Of Predominant Period Evolution Of Blown Sand Reclamation Ground In The Beibu Gulf

As an important place for the Beibu Gulf heavy chemical industry base,cargo port,terminal and urban construction,the blown sand reclamation ground is the key target of disaster prevention and mitigation.Differences in ground condition factors such as marine soft soil layer and sandy soil layer properties,topography,groundwater level and external condition factors such as ground motion and engineering construction with different periodic components and amplitudes induce "drift" in the predominant period of the site.This paper conducts on-the-spot investigation,collection of site survey data and determines the relevant parameters of the site soil layer by means of laboratory tests.The MATLAB programming is used to calculate the viscoelastic artificial boundary parameters and the equivalent nodal force of wave which are introduced into the dynamic analysis of the site.The ABAQUS two-dimensional numerical simulation method is used to study the evolution characteristics of the predominant period in the Beibu Gulf blown sand reclamation ground from different angles under different factors and provided practical reference for the seismic fortification of similar sites.The main research work and results are as follows:(1)Through modal analysis,time history analysis and orthogonal experiment,the characteristics of the predominant period evolution of the blown sand reclamation ground under the change of ground conditions are studied.The analysis results show that the natural vibration period and the predominant period of the site are in a short-cycle direction with the consolidation degree of the marine soft soil layer,the relative compactness of the blown sand layer and the depth of the groundwater table,and in a long-cycle direction with the increase in the thickness of the soft soil layer and the blown sand layer.Among them,the thickness variation of marine soft soil layer has the most significant influence on the evolution of the predominant period of the site,and the influence of the relative compactness of the sand layer is the least.(2)The characteristics of the predominant period evolution of the blown sand reclamation ground under different periodic components and amplitude of ground motions were studied.The results show that the site has different high-frequency suppression and low-frequency amplification effects on the ground motion of different periodic components.The site response is the strongest under the long-period ground motion,and the characteristic period of acceleration response spectrum of the site surface shows a different degree of increasing trend with the increase of the characteristic period of the input ground motion response spectrum.This kind of field is prone to the resonance effect of "ground motion-site-long period structure”with long-period ground motion.As the amplitude of the ground motion increases,the nonlinearity of the soil in the site increases,and the predominant period of the site develops toward the long-term direction.(3)Through the“Soak-Loading" linkage test and indoor geotechnical test,the physical and mechanical parameters of the soft soil layer and the blown sand layer under different preload pressures were obtained,and the numerical simulation analysis of different preloading and consolidation conditions was carried out.The results show that the predominant period of the site decreases with the increase of the preloading reinforcement degree.As the preload strength of the stack increases,not only does the reduction of predominant period of the site trend become more pronounced,but the site category changes.The preloading reinforcement treatment of the site can effectively reduce the dynamic response of the site under far-field long-term ground motion.