A DISCUSSION ON THE DEPTHS OF LIQUEFIED SANDY SOILS IN BEIJING AND ADJACENT REGIONS DURING THE 1976 TANGSHAN EARTHQUAKE

The determination of the depth of liquefied sandy soil is an all concerned problem in earthquake engineering. Previous studies of the depth of liquefied sandy soil have been done with indirect or macroscopic methods, giving quite varied results. In this paper, we propose a mineralogical method for study of liquefaction, basing on the direct correlation of ejected sands with subsurface sand layers.After the 1976 Tangshan Earthquake, the present authors collected samples of sands in five drill holes and of ejected sands on the surface in the areas of Xiji and Wangzhuan of the Tongxian County with seismic intensity Ⅷ, and areas of Luosi-wang, Qukou and Xianghe, Hebei Province with seismic intensity Ⅶ. The results of investigation by mineralogical and granulometric analysis indicate that the ejected sands are similar to the sands from a layer at depth of 12.26 m in the area of Xiji, to the sands from depth of 11.02 m in Wangzhuang area, to the sands from depth of 12.3 m in Luoziwang area and to the sands from depth of 9.2 m in the area of Xianghe and the sands from depth 11.28 in Qukou area.According to these data we can conclude that the maximum depth of liquefaction of sandy soils does not exceed 12.30 m in areas with seismic intensity of Ⅶ and Ⅷ for the Tongxian and Xianghe Counties during the Tangshan Earthquake of 1976 and varies in the range from 9.2 to 12.30 m and is probably shallower in areas with inten-sitv Ⅶ.