Study Of Isolating Character For Sand Gravel Cushion

Sand gravel cushion is a kind of ground cushion treatment, it is widely applied because of its low cost. It works by choosing appropriate gravel, scree, talus decries, coarse sand, medium sand, then ram them to be closely knitted. The sand gravel cushion can increase the bearing capacity of weak groundwork. It has widely use because of its good compact character, water permeability, high shearing strength and low deformation.The basement is treated as rigid in common seismic design, the dynamic character of the whole structure is decided by only the superstructure, and the infection of basement and foundation soil is neglected, in this way, the structure be calculated is quite different from its actual performance. So a finite calculating model considers the combined activate of basement soil, sand gravel cushion, basement and superstructure was taken in this paper, in order to study the infection on the anti-seismic ability of superstructure that brought on by sand gravel cushion.Basic isolation is the vibration isolation technique which has the most developed theory, and the most extensive use. Basic isolation mainly works by setting a reliable isolating zone between the basement and the structure, in order to reduce the fundamental frequency and prolong the fundamental period to keep the structure away from the main frequency band of the earthquake which carries the most energy, and in this way, the earthquake energy that transfers into the superstructure can be reduced. At the same time, the basic isolation systems use some dissipating equipments to reduce structure displacement, in this way, all the structure dynamic response can be reduced, and the structure and the establishment in it can be safe when earthquake occurred.In this paper, the definition of sand gravel underlayer and the researching actuality of combined activate are introduced at the very first. Then, the isolating mechanism of combined activate of sand gravel underlayer with foundation soil and superstructure is analyzed based on the basic isolation theory. Then, set up 2 finite element models using the numericalanalysis program ANSYS, one takes the combined activate into consideration, and the other not. At last, analyze the different time-history dynamic response of 2 model2, summarize the characteristics of the seismic response for combined activate system, and analyze the isolating effect of the combined activate system.The results shows that the fundamental frequency of the model which takes the combined activate into consideration reduced evidently, and the fundamental period prolonged evidently. The structural displacement of this model is partly carried by the underlayer and the foundation soil, so most stories' deformation of superstructure are evidently reduced, but the deformation at the bottom is magnified. The acceleration response was reduced in all the floors. So we get the result that, when considering the combined activate of sand gravel underlayer with foundation soil and superstructure, the seismic response of most floors can be evidently reduced.