Reinvestigation On The Liquefied Sites In The Tangshan Earthquake

Liquefaction is one of the typical damages caused by earthquakes. The liquefaction area in Tangshan Earthquake in China in July 1976 has reached to 2400 KM2, causing a large-scale ground settlement, deformation, sliding, sand boiling and severe damages of the buildings, roads, farmlands and bridges.Some researchers have made a detailed in-situ investigation on the liquefaction damages and took testing of liquefied sites during 1977 to 1979. The obtained data have been used to develop liquefaction criteria of Chinese seismic code. However, the testing equipments employed then were limited in the function. Meanwhile, in recent years, the predictive method of liquefaction worldwide made great progress, and foreign liquefaction predictive methods and China's comparative methods, are also worth studying the issue. Moreover, the present characteristics of the soil in Tangshan area and the situation of this region, which are designed according to the fortification level new generation of zoning mop or are subjected to the same intensity earthquake after 30 years, are crucial and applicable issues to be investigated.In July 2007, we go to the liquefaction sites of Tangshan Earthquake and investigate the scenes again. 23 testing boreholes were selected to conduct SCPT and Vs testes by using international advanced equipments which are quite different with those used 30 years ago. Some salient points can be outlined:(1)In the thesis, the effect factors of liquefaction have been presented, and the common soil in-situ testing methods have been discussed. The liquefaction background of Tangshan Earthquake has been reviewed and summed up. The progress and development trends of liquefaction estimation method of liquefaction have been summed up and analyzed.(2)The liquefied and non-liquefied sites in Tangshan Earthquake have been reinvestigated with CPTU and shear wave velocity test. Comparing the historic and present information, the factors of tip resistance and friction resistance have been given. The shear wave velocity structure of Tangshan region and the relationship between the shear wave velocity and the cone tip resistance in the region have been established.(3)Liquefaction estimation by using the new in-situ CPT data and new methods has been presented. The prediction of liquefaction is given when the seismic intensity is 7 and the designed ground motion parameter is prescribed by the new generation of zoning map. Comparison of liquefaction sites caused by Tangshan Earthquake and sites predicted by the method descried in this thesis, liquefaction has been carried out to analyze the difference and the causes.