Abstract: Compression index Cc and swelling index Cs are two important deformation parameters in soil mechanics which can be obtained by oedometer tests. However, due to time-consuming of the test, several empirical correlations between compression index and some basic physical parameters (especially liquid limit wL, natural water content wn, initial void ratio e0 and plastic index Ip) have been proposed by many researchers. The empirical relationships of compression index all over the world have been compared and it is found that relationships between compression index and natural water content and void ratio are less discrete. Consequently, the unified correlation equations are given respectively. The oedometer tests have been conducted on specimens from 2nd to 6th soil layers in Shanghai. Samples were retrieved by the thin wall sampler. Consolidation test data available in literatures and geotechnical investigation data from 69 sites in Shanghai were collected and analyzed. Empirical relationships between compression index Cc and wL, wn, e0, Ip of Shanghai clay were given. Meanwhile, it was noted that there were highly linear relationships between Cc /n0 and Cc, Cs /n0 and Cs (n0 is initial porosity). Therefore, empirical formulas for predicting compression index Cc and swelling index Cs of Shanghai clay based on n0 were given. The relationship between compression index and swelling index was also analyzed. The results show that the value of Cc/Cs of Shanghai normally consolidated clay ranges from 4.8 to 6.9, with an average value of 5.8. While the value of Cc /Cs for over-consolidated clay ranges from 3.3 to 5.2, with an average value of 4.3.

Key words: compression index, swelling index, Shanghai clay, initial porosity, empirical relationship