Study On Dynamic Behaviors Of Recently Deposited Soils And Characteristics Of Site Seismic Effect For Deep Soft Sites

Quaternary sediment is thicker for lower area of Yangtze River, and layered structure of soils is obvious. There are potential intermediate strong earthquake at this area in the late ten years, so it is valuable for study and engineering application to research dynamic behaviors of recently deposited soils and characteristics of deep soft site seismic effect.In the dissertation it's analyzed that the test results of free vibration column apparatus on 275 undisturbed recently deposited soil samples for lower area of the Yangtze River including mucky silty soil clay, clay, silty clay, silly clay and silt interbedded strata, silt, fine sand and coarse sand , which are from Nanjing , ChangZhou et al 15 cities. The variation rules about relation between dynamic shear modulus ratio G/Gmax versus shear strain amplitude y and damping ratio versus shear strain amplitude Y for 7 types of soils above mention are presented. Because this systemic research on recently deposit soils of this area is original in our country, this dissertation's research findings can be reference for seismic safety evaluation of engineering sites in this area.In this dissertation Taft earthquake record, El Centra earthquake record and Northridge earthquake record are regarded as input ground motions, and their acceleration peak value are adjusted as 0.35m/s , 0.70 m/s and 0.98 m/s . So it's analyzed that site seismic effect of 54 cases for 6 typical deep soft sites which are from NanJing, YanCheng, ChangZhou , TaiZhou, QiDong, ShangHai in the lower area of the Yangtze River , and the effect of site condition , frequency characteristics of input ground motion and its strength on site seismic effect are discussed , then some rules have been generalized. In addition, in this dissertation the effect of interbedded strata on earthquake response for deep soft sites is discussed.The effect of soft soil layer on earthquake ground motion parameter has been taken into account for engineers. Based on three true sites' data from NanJing, YanCheng , ShangHai, 65 site profiles are created. In the dissertation three acceleration record above mention are considered as input earthquake ground motion ,and their acceleration peak value are also adjusted as 0.35m/s2 , 0.70 m/s2and 0.98 m/s2.Then in this dissertation seismic responses of 555 cases for 65 different site profiles are respectively analyzed. Through analyzing the calculation results, some rules of the thickness of soft superficial soils and the depth and thickness of soft interlayer on the effect of site amplification are drawn out.For sites of much deep bedrock, when we analyze site seismic effect we can think a shallower soil layer as the location of earthquake ground motion input or not, and the analyze results can't influence on the site seismic safety evaluation. The problem above mention has been interesting for engineers. In view of this subject, in this dissertation two typical deep soft site are selected from ShangHai and TianJin, then several soil layer locations of different depths and shear wave velocity are regarded as the location for earthquake ground motion input, and seismic effects of 90 cases for different site profiles are analyzed. At last the results of site seismic effect are researched and compared, and some valuable conclusions are preliminarily drawn out.