DISCUSSIONS ON INTERRELATION BETWEEN INITIAL STATE OF NATURAL SOIL STRATA AND THE COMPRESSIBILITY

The analysis of some in-situ test means, such as self-boring pressure meter has revealed a phenomenon that the coefficient of lateral earth pressure at rest in natural soil strata is commonly on the high side. One of the reasons of the phenomenon is that the vertical stress estimated with the traditional theory is on the low side. For undisturbed sample had gone through the process of unloading and expanding, the gravity density of the soil tested in lab is no longer equal to that at the initial state in buried conditions before exploration and excavation. Influenced by the overburden pressure in initial state, the physical properties of soil should not be deviated from the compressible nature. So it is improper that the natural soil is identified in the idea of homogenization assumption. This paper takes technical measures, for example, adding 100kPa to the consolidation pressure in order to reform the analyzing model for compression test. It tries to build the mathematical model of the initial state of the soil with the conditions associated with the virgin compression, recompression and stress history of the soil body. Combined with case analysis, the recompression index proposed in experimental observation is not enough to reflect the expansion of samples. The physical meanings of minimum dry density and limit of liquidity may be the virgin compression of soil's characteristics of void ratio in loosest state. The compression index cannot give expression to the compressibility principle satisfactorily.